The new class of diode-pumped alkali vapor lasers (DPALs) offers high efficiency cw laser radiation at near-infrared wavelengths: cesium 895 nm, rubidium 795 nm, and potassium 770 nm. The working physical principles of DPALs will be presented. Initial 795 nm Rb and 895 nm Cs laser experiments performed using a titanium sapphire laser as a surrogate pump source demonstrated DPAL slope power conversion efficiencies in the 50-70% range, in excellent agreement with device models utilizing only literature spectroscopic and kinetic data. Using these benchmarked models for Rb and Cs, optimized DPALs with optical-optical efficiencies >60%, and electrical efficiencies of 25-30% are projected. DPAL device architectures for near-diffraction-limited power scaling into the high kilowatt power regime from a single aperture will be described. DPAL wavelengths of operation offer ideal matches to silicon and gallium arsenide based photovoltaic power conversion cells for efficient power beaming.

This paper reviews the basic concepts of laser propulsion and summarizes work done to date using a 10 kW device. The paper describes a candidate megawatt class CO₂ laser system which can be scaled relatively near-term to multi-megawatt power levels using demonstrated technology. Such a system would potentially be capable of launching micro-satellites into low earth orbits (LEO) at relatively low cost. Our projections indicate that payloads of about 1kg/megawatt are achievable. The long wavelength of a CO₂ laser will require the use of a large aperture telescope and/or large effective beam capture area for the lift vehicle. We believe that these limitations, not withstanding, rep-pulsed CO₂ in a blow-down configuration lasting 200-300 seconds could achieve the desired propulsion objectives. The laser would use a helium-free, nitrogen/carbon dioxide mixture to provide a very cost effective fuel.

Short pulse laser breakdown in a non-uniform vapor cloud is considered as an instant local energy release (point explosion). The breakdown generates a strong shock wave propagating over the cloud. Propagation of the shock is described using an approach developed by A. S. Kompaneets. This approach is generalized to the case of arbitrary density and pressure profiles in the vapor cloud. For this case, the equation for shock wave shape is reduced to the eiconal equation in optics. Exact solutions are obtained for particular density distributions.

We start with a short introduction of some newer thermodynamical approaches to the description of nonequilibrium processes related to the interaction of short laser pulses with matter. Then we shall use the example of electronic thermal conductivity to show why the equations usually derived in standard solid state theory have to be reconsidered. This is mandated by the loss of local thermal equilibrium, the nonstationarity, and the enhanced contribution from electron-electron scattering. Based on Boltzmann’s equation we derive an expression for the thermal conductivity with new qualitative and quantitative properties. These results are supported by comparison with experiments.

The expansion of a plasma plume in a background gas is a key problem for film deposition and laser ablation studies. Combined diagnostic measurements of deposition rates and ion time-of-flight (TOF) signals have been used to study the dynamics of a laser ablation plume in an oxygen gas. This study is similar to our previous work on an argon background gas and shows essentially the same trend. At an enhanced gas pressure, the angular distribution of collected ablated atoms becomes comparatively broad, while the total collected yield decreases strongly. The total collected yield exhibits three separate regimes with increasing pressure, a vacuum-like regime, a transition regime with increasing plume broadening and splitting of the ion signal, and at the highest pressures a diffusion-like regime with a broad angular distribution. In the high pressure regime, the expansion can be described by a simple model based on diffusion from a confined plume.

We present a continuum model, based on a drift-diffusion approach, aimed to describe the dynamics of electronic excitation, heating and charge-carrier transport in different materials (metals, semiconductors, and dielectrics) under femtosecond and nanosecond pulsed laser irradiation. The laser-induced charging of the targets is investigated at laser intensities above the material removal threshold. It is demonstrated that, under near-infrared femtosecond irradiation regimes, charging of dielectric surfaces causes a sub-picosecond electrostatic rupture of the superficial layers, alternatively called Coulomb explosion (CE), while this effect is strongly inhibited for metals and semiconductors as a consequence of superior carrier transport properties. On the other hand, simulations of UV nanosecond pulsed laser interaction with bulk silicon have pointed out the possibility of Coulomb explosion in semiconductors. For such regimes a simple analytical theory for the threshold laser fluence of CE has been developed, showing results in agreement with the experimental observations. Various related aspects concerning the possibility of CE depending on different irradiation parameters (fluence, wavelength and pulse duration) are discussed. This includes the temporal and spatial dynamics of charge-carrier generation in non-metallic targets and evolution of the reflection and absorption characteristics.

The modifications of microstructure and of physical properties induced by the use of an additional radiofrequency beam discharge during the pulsed laser deposition (PLD) process has been investigated for different classes of materials. The materials concerned are piezoelectric oxides (ZnO), gate dielectric oxides (ZrO₂), ferroelectric oxides (BaTiO₃), ferroelectric relaxors (Pb_1-xLa_x)(Zr_0.65Ti_0.33)O₃ (PLZT) with variable La contents, respectively. Using a special configuration of the radio frequency discharge, a beam of excited and/or ionized oxygen species was produced and directed towards the substrate. RF plasma excited species identified in the spectra and impinging the substrate surface are very reactive at the surface with metals ions, neutral and sub-oxides which arrive from the laser plasma, with respect to discharge-off conditions. Thus, the RF plasma contribution is very important between the laser pulses, especially in the early after-pulse stages, when the surface of the fresh deposited film is not completely stabilized. A parametric study has been performed to evidence the corroborative effects induced by RF beam and other parameters as laser wavelength (265 nm, 355 nm, 530 nm and 1060 nm), laser fluence (2 - 25 J/cm²), oxygen pressure (0.2 - 0.8 mbar), substrate temperaeture (RT-650°C) on the composition and crystallinity and on dielectric and ferroelectric properties.

One of the critical elements in the manufacture of long lengths of high temperature superconducting wires is the development of deposition diagnostics correlated with the quality of deposited material for process control. Fast imagery, emission spectroscopy, and time-of-flight spectroscopy of the very energetic plumes resulting from the pulsed laser deposition of YBa₂Cu₃O_7-x have been recorded for a wide range of deposition conditions at four military, DoE, and industrial facilities. Several optical signatures that are strongly correlated with the deposited critical currents have been identified with strong potential for process control. In addition, the partioning of energy among translation, electronic and ro-vibrational degrees of freedom as a function of laser fluence, chamber pressure, and position in the plume have been characterized.

Shaped femtosecond laser driven shock waves fulfill the requisite time resolution required for following shock induced chemical kinetics, and enable very small scale shock physics experimentation. However, comparison to large scale experiments requires detailed characterization of the generated pressure profile. Spectroscopic studies at pressure and temperature are hindered by fluctuations in shock strength as functions of space and time. Representative time resolved broadband infrared absorption data on shocked polyvinylnitrate thin films are presented, followed by current efforts to alleviate spatial shock strength variations with spatial pulse shaping, and calculations of the interferometric phase shifts expected at long times, during the rarefaction.

We report on the development of a suite of novel techniques to measure important characteristics in intense ultrashort laser solid target experiments such as critical surface displacement, ablation depth, and plasma characteristics. Measurement of these important characteristics on an ultrafast (~50 fs) time scale is important in understanding the primary event mechanisms in laser ablation of metal targets. Unlike traditional methods that infer these characteristics from spectral power shifts, phase shifts in frequency domain interferometry (FDI) or laser breakthrough studies of multiple shots on bulk materials, these techniques directly measure these characteristics from a single ultrafast heating pulse. These techniques are based on absolute displacement interferometry and nanotopographic applications of wavefront sensors. By applying all these femtosecond time-resolved techniques to a range of materials (Al, Au, and Au on plastic) over a range of pulse energies (10¹¹ to 10¹⁶ W/cm²) and pulse durations (50 to 700 fs), greater insight into the ablation mechanism and its pulse parameter dependencies can be determined. Comparison of these results with hydrocode software programs also reveals the applicability of hydrocode models.

We have used two-dimensional ultrafast microscopic interferometry to observe the hydrodynamic motion and the time dependent changes in the optical properties of two metals (6061-T6 aluminum and ASTM 336 1018 steel) illuminated with 130 fs 800 nm laser pulses. We hve also observed the electron dynamics in optically excited aluminum, gallium, and gold at a metal-glass interface using the same technique. The interferometric technique allows construction of the two-dimensional spatial profile for laser pumped materials with a temporal resolution of < 300 fs and out-of-plane spatial resolution of 0.5 nm using 130 fs probe pulses. Best fits to the diamond turned aluminum data were obtained by assuming physically motivated functional forms for the expected hydrodynamic motion and the time-dependent complex index of refraction. Extraction of changes in the index of refraction provides evidence for melting in the gold targets. These experiments offer a new path for the observation of phase changes and/or for temperature measurements in shocked or laser excited materials, by allowing a determination of the complex index under dynamic conditions and comparing the measured values to those obtained under static conditions.

Analysis of the trapped and untrapped motion of particles, combined with direct numerical simulation of the 1D non-stationary Boltzmann equation, demonstrates that atoms and molecules initially at room temperature can be accelerated to velocities in the 10 to 100 km/s range over distances of 100's microns using an optical lattice. The quantity, final velocity, and velocity/energy spread of the accelerated distribution controlled by tailoring the fluence, duration and frequency chirp of the laser beam that make the lattice, indicating the potential for a compact, versatile, and configurable hyper-thermal accelerator/decelerator. Using similar lattice potentials, differential transport of atomic and molecular species with different polarizability/mass ratios leads towards the possibility of gas mixture separation in short pulses or in hollow fibers. A bulk drift can be induced in a gas by the lattice forces, even when the mean kinetic energy is much greater that the maximum dipole potential of the optical field. In this process the transfer of energy from the slowly traveling optical lattice to the gas is analogous to Landau damping of a plasma wave by charged particles.

The authors' research on the laser interaction with semiconductors, high-performance ceramics, oxides, and glasses with pulse durations of 30 fs and 130 fs is reviewed. Near-ablation threshold investigations were concerned with the generation of periodic nanostructures and their correlation with physico-chemical properties of the solid phase such as e.g. the material-dependent surface energy. Molecular dynamic modeling in the sub-picosecond time domain considered ultrafast opto-electronic processes triggering surface reorganization reactions. Fluid containment of solid interfaces showed strong influence on the resulting micro- and nanostructures due to its drastic reduction of the surface energy. The phenomena are discussed in respect to the minimization of the surface free energy in dependence of material composition and interfacial structure.

Femtosecond lasers show much promise as potential sources of choice in a number of laser micromachining applications, including semiconductors, photonics and biomedicine. Their ability for minimal damage and precise processing has been thoroughly researched for the past few years. One of the requirements for precise processing is high precision beam steering. Acousto-optic devices (AODs) are commonly used in laser direct writing systems to steer the beam with high precision and speed. However AODs cannot be applied for steering femtosecond laser beams, because, dispersion associated with acousto-optic interaction will cause serious spatial deformation on the writing spot. A detailed study of the AOD dispersion and the method to compensate this dispersion have been discussed in this paper.

Although the laser was not yet invented Eugen Saenger, one of the most prominent German personalities in the early development of rocket science and technology suggested to use photons for the propulsion of spacecrafts in the fifties. In contrast to current schemes which are basically aimed at laser induced ablation processes, Eugen Saenger started with the idea of using the radiation pressure itself for propulsion purposes. A review of his pioneering work in that area will be supported by numerous historical documents and personal remembrance showing his effort to promote unconventional ideas. The paper also emphasizes how some of the original concepts are being revisited and partly implemented by using today’s laser technology.

A novel approach is outlined for a singlet oxygen generator (SOG), a laser minimum length nozzle (MLN), and an iodine injector system for a chemical oxygen-iodine laser (COIL). A unified approach, referred to as a SOG/MLN/I₂ system, is partly based on past experimental work. For instance, the SOG concept stems from sparger technology and a KSY fesibility experiment. A MLN with a curved sonic line is used for the laser nozzle, and slender struts are used for the injection, in the downstream direction, of iodine/helium vapor. The heated struts are located downstream of the nozzle's throat. The engineering logic behind the approach is discussed; it has a diversity of potential system benefits relative to current technology. These include a compact, scalable laser that can operate in space. The SOG operates at a significantly higher pressure with a high O₂(¹Δ) yield. In addition, basic hydrogen peroxide reconditioning is not required, a water vapor removal system is not required, and diluent may be unnecessary, although useful for pressure recovery. The impact on a COIL system in terms of power, efficiency, and pressure recovery is briefly assessed.

The uncertainty in both the fluorine atom concentration and the gain length has inhibited the development of accurate and device independent models of HF overtone lasers. Furthermore, previous methods of measuring the small signal gain were cumbersome and could not easily generate spatial maps of the gain in the cavity. Experimental techniques have been developed to directly measure the concentration of fluorine atoms, the gain length and the small signal gain in a hydrogen fluoride 5 cm slit nozzle laser. A gas phase titration technique was utilized to measure the fluorine atom concentration using HCl as the titrant. The gain length was measured using a pitot probe to locate the interface of the primary flow with the high Mach number shroud flows. A tunable diode laser was utilized to perform small signal gain measurements on HF overtone (ν=2→0) transitions.

The demonstration and characterization of a multiwatt All Gas-phase Iodine Laser (AGIL) are described. A 20-cm subsonic reactor was used to produce NCl(a¹Δ) for a series parametric studies of the I*(²P_1/2) - I(²P_3/2) small signal gain and extracted power dependence on reactant flow rates and reaction time. A reduction in the flow channel height led to improved performance. The highest measured gain was 4.2 x 10^-4 cm^-1 and the highest power observed was 31 W.

Progress toward developing a "controlled avalanche"-based, electric oxygen singlet delta generator module will be reported. Problems that previously limited pressure scalability using this approach are addressed. A new computer model has been developed and used to calculate real-time oxygen singlet delta (O₂¹Δ) evolution along with all other known related chemical species -- beginning with the onset of the process and ending as the flow stream exits the generator. The calculations indicate that a demonstrator module can now be constructed that is capable of producing O₂¹Δ fractional yields in excess of 35% at 50 torr total pressure, while developing 0.05 to 0.1 moles/second 0₂¹Δ. A more detailed and accurate understanding of process dynamics has emerged, which has been incorporated into the excitation methodology and generator design. Fabrication of this generator should begin shortly. The next step will be to characterize its fractional O₂¹Δ yield using spectroscopic techniques. The generator should be capable of driving a supersonic-flow, transverse oxygen iodine laser aimed toward developing 3 - 6 KW continuous power in blown-down configuration. Tentative design details and characteristics for the integrated generator-laser system are be presented.

The problem of development of a singlet delta oxygen O₂(¹Δ_g) (SDO) generators alternative to chemical one needs application of the accurate methods of measuring the SDO concentration. A chemical SDO generator providing efficient operation of a chemical oxygen-iodine laser (COIL) is proposed to be used as a reference source for absolute calibration of the system measuring the SDO concentration. The principle of the COIL operation results in the threshold and output COIL parameters make it possible to evaluate the SDO yield with a satisfactory accuracy. A convenient sparger chemical SDO generator was applied as a reference source for absolute calibration of detectors of dimole (λ=634nm) and b→X (λ=762 nm) radiations. The values of b-state concentration formed in a longitudinal electric discharge were evaluated. The intracavity laser spectroscopy (ICLS) was absolutely calibrated for measuring the SDO concentration. ICLS method has a very high sensitivity and makes it possible to monitor the absorption corresponding to the O₂(¹Δ_g)→O₂(¹Σ_g⁺) (λ = 1.91 μm) transition. The cross-sections of lines of the Q - branch of the vibrational 0-0 band of the a¹Δ_g → b¹Σ_g⁺ transition of molecular oxygen were measured. The method developed was applied to measure the concentration of singlet oxygen produced in the microwave discharge. He - Ne laser (λ = 633 nm) was used for absolute calibration of a system monitoring the dimole radiation. The rate constant of the process responsible for dimole emission was measured. The value obtained k_d=7.34•10^-23 cm³/s is in agreement with literature.

An idea to replace singlet delta oxygen (SDO) generator working with wet chemistry by electric discharge generator has got much attention last years. Different kinds of discharge were examined for this purpose, but without a great success. The existing theoretical models are not validated by well-characterized experimental data. To describe complicated kinetics in gas discharge with oxygen one needs to know in detail processes involving numerous electronic excited oxygen molecules and atoms. To gain new knowledge about these processes experimental studies were made on electric discharge properties in gas mixture flow with independent control of inlet SDO concentration. The theoretical model extended to include minor additives like oxygen atoms, water molecules, ozone was developed. Comparison with careful experimental measurements of electric characteristics along with gas composition allows us to verify the model and make theoretical predictions more reliable. Results of numerical simulations using this model for an electron-beam sustained discharge are reported and compared with the experimental data.

Electric properties and spectroscopy of an e-beam sustained discharge (EBSD) in oxygen and oxygen gas mixtures at gas pressure up to 100 Torr were experimentally studied. The pulsed discharge in pure oxygen and its mixtures with noble gases was shown to be very unstable and characterized by low input energy. When adding small amount of carbon monoxide or hydrogen, the electric stability of the discharge increases, specific input energy (SIE) per molecular component being more than order of magnitude higher and coming up to 6.5 kJ/(l atm) for gas mixture O₂:Ar:CO = 1:1:0.1. The results of experiments on spectroscopy of the singlet delta oxygen O₂(a¹Δ_g)(SDO) and O₂(b¹Σ_g⁺) states in the EBSD are presented. The calibration of the optical scheme for measuring the SDO absolute concentration and yield using the detection of luminescence of the SDO going from a chemical SDO generator was done. The preliminary measurement of the SDO yield demonstrated that it was ~3% for the SIE of ~1 kJ/(l atm), which is close to the results of theoretical calculations for such a SIE. Theoretical calculations demonstrated that for the SIE of 6.5 kJ/(l atm) the SDO yield may reach ~20% exceeding its threshold value needed for oxygen-iodine laser operation at room temperature, although a part of the energy loaded into the EBSD goes into the vibrational energy of the molecular admixture, (which was experimentally demonstrated by launching a CO laser operating on an oxygen-rich mixture O₂:Ar:CO = 1:1:0.1 and measuring its small-signal gain).

The kinetic modeling and design of a carbon monoxide (CO) gas laser is presented. In contrast to the more widely known fundamental band CO laser, this laser is designed to operate on the first overtone bands, the Δν = 2 vibrational quantum transitions. Lasing on these bands is known to produce multi-line output at wavelengths from 2.5 microns to beyond 4.0 microns in the infrared. The present study is to develop a compact, wall-cooled CO overtone laser, that can develop average powers O[100 W]. A kinetic modeling code has been developed to guide the design, and to calculate both continuous wave (c.w.) and Q-switched performance. There are distinct advantages in Q-switched operation of this laser, which is potentially one of the few truly efficient lasers scalable to very high average powers.

The paper considers the physical principles of developing the fullerene-oxygen-iodine laser (FOIL) with optical (sunlight in particular) pumping. Kinetic scheme of such a laser is considered. It is shown that the utmost efficiency of FOIL may exceed 40% of the energy, absorbed by fullerenes. Presented are the experimental results of singlet oxygen generation in liquid media (solutions and suspensions) and in solid-state structures, containing either fullerenes or fullerene-like nanoparticles (FNP). In experiment was shown the possibility of the singlet oxygen transfer to the gaseous phase by means of organizing of the solution (suspension) the boiling as well as of the gasodynamic wave of desorption from the solid-state structures, containing fullerenes or FNP. We present the preliminary experimental results of pulsed generation in optically pumped FOIL with the use of primary photodissociation of iodide for preparation of the atomic iodine in the generation zone. In the experiments on FOIL generation was implemented the principle of spectral separation of optical pumping.

A concept combining the advantages of solid-state and gas-laser technologies is being developed to realize a scalable, efficient 4-micron laser. A Nd:YAG laser is tuned to 1.3391 microns by temperature-tuning and cavity selection. The addition of diode seeding permits excitation of a specific v = 3 rotational state of HBr. Lasing can potentially occur in three subsequent steps to the ground state, emitting numerous lines in the 4-micron region, which enhances efficiency and spectral coverage. Using up to 25-mJ pump energy, two elements of the possible three-level cascade have been observed. We have observed emission selectivity due to intracavity carbon dioxide and inferred the presence and contributory influence of pure-rotational stimulated emission, which may have importance to the overall behavior of other similar molecular pulsed lasers (and even continuous-wave HX lasers). We present theoretical and experimental results demonstrating the operational principle and utility of this laser system.

Discharge and laser parameters in mixtures of SF₆ with H₂ and D₂ are studied using inductive and LC-generators. Excitation pulse parameters providing ultimate performance of discharge non-chain HF- and DF-lasers are determined. Processes affecting efficiency of the lasers are discussed. Ultimate intrinsic efficiency η_int of the HF and DF lasers up to 10% and 7%, respectively, was realized in the SF₆-H₂ (D₂) mixtures. Electrical efficiency of the lasers up to η₀ = 5-6% with the output over 1 J was demonstrated for the first time.

The phototriggering has been proposed many years ago as a way to improve the reliability of excimer lasers. It is now a mature technique that is used in conjunction with the most recent solid-state devices to make an industrial high average power excimer laser. After a brief historical introduction we here analyze the main features and scientific aspects of this discharge technique and give very recent results.

A new concept of the direct amplification of femtosecond optical pulses in photochemically driven active media, such as Xe₂Cl, XeF(C–A) and Kr₂F, is discussed with the main emphasis on the XeF(C–A) active medium as one of the most widely studied system. The main advantage of these systems is that they are characterized by a broad gain bandwidths (60–100 nm) which allow to support 10 fsec pulses and are centered in the blue-green region (490, 480 and 420 nm, respectively) spectrally matching to the second harmonic of a Ti:Sa laser. The last circumstance is important from the viewpoint of considerable increasing temporal contrast ratio of ultrahigh peak-power fsec systems.

The carbon dioxide laser uses as the light amplifying medium a weakly ionized mixture of carbon dioxide, nitrogen and helium (glow discharge). Pumping is performed automatically by interparticle collisions and light output per unit volume is considerably high up to several watt per cubic centimeter. Thus carbon dioxide lasers were most successful in generating high powers, where several construction schemes have been developed during the last twenty years as for instance slim cylindrical plasmas (gas transport lasers) and thin slabs (diffusion cooled lasers). A third geometry has been developed by the author showing an annular cross section of the light emitting plasma with coaxial electrodes for the supply with electrical power. The latter geometry together with RF excitation and a very fast gas flow for heat dissipation shows an unbeaten beam power capability. The concept of the coaxial laser has been realised at the University of Technology in Vienna and proved to be excellently suited for technological purpose. Moreover a theoretical estimation showed that the latter concept can be extended to a feasible construction of a 100 kW cw laser consisting of 4 plasma modules, each having a diameter of 25 cm and a length of 75 cm. The excitation must be carried out with a 1 Megawatt RF transmitter as it is used in broadcasting. For cooling extra strong blowers are necessary. In the bulk of the paper first the already existing 6 kW coaxial laser will be presented and then the concept for a 100 kW cw carbon dioxide laser will be discussed.

Large area, narrow discharge gap, diffusion cooled gas lasers are nowadays a well established technology for the construction of industrial laser sources. Successful examples exist both with the slab (Rofin-Sinar) or coaxial (Trumpf) geometry. The main physical properties and the associated technical problems of the transverse large area RF discharge, adopted for the excitation of high power diffusion cooled gas lasers, are reviewed here. The main problems of this technology are related to the maintenance of a uniform and stable plasma excitation between closely spaced large-area electrodes at high power-density loading. Some practical solutions such as distributed resonance of the discharge channel proved successful in the case of square or rectangular cross-sections but hardly applicable to geometries such as that of coaxial electrodes. In this paper we present some solutions, adopted by our group, for the development of slab and annular CO₂ lasers and for CO₂ laser arrays with linear or circular symmetry. We will also briefly mention the difficulties encountered in the extraction of a good quality beam from an active medium with such a cross section. A problem that has also seen some interesting solutions.

The micro laser plasma thruster (μLPT) is a micropropulsion device, designed for the steering and propelling of small satellites (10 to 100 kg). A diode laser is focused on a two-layer polymer tape, where it forms a plasma. The thrust produced by this plasma is used to control the satellite motion. Three different polymers (GAP, PVN and PVC) doped with carbon and/or IR-dye were investigated for their performance as fuel polymer. The different dopants for GAP seem to have only little influence in the ablation properties. The most pronounced differences are observed in the fragment ejection detected in the shadowgraphy measurements and the crater appearance. For all carbon doped polymers, the ablation spots have a similar rough morphology. The shadowgraphy measurements of PVN reveal, that the shockwave and particle plume propagates faster as in the case of the other polymers. The particle plumes showed a very different expansion behavior for all polymers, whereas the plasma temperature and electron density measurements showed no significant difference. Only PVC displayed a slower almost linear drop of the plasma temperature over time. The thrust measurements showed the best results for GAP.

Active galactic nuclei, supernovae and some massive luminous stars are sources of intense radiation at all wavelengths. η Carinae is an unusual radiation source producing UV laser-like radiation. Estimates of the intensity of these sources indicate that interstellar dust clouds produced during the star's penultimate period of stability, will be strongly affected, with the possibility of some dust particles being accelerated to near relativistic velocities. Theoretical work by Bingham, Marx, McInnes, Spitzer, Tsytovich is reviewed and its applicability to photon propulsion is discussed. Photon propulsion will be the ideal propellant for nanoscale satellites.

Impulse generation using laser energy has advantages for aerospace propulsion; energy can be supplied from a remote device, thereby reducing a necessary mass on board and accompanied cost; the specific input energy is not limited by inherent energy of working fluid. After Kantrowitz proposed the concept of laser propulsion in 1972, impulse generation and launch performance either with single or multiple laser pulses has been experimentally studied. Possible application of this technique ranges even to space debris de-orbiting. As the example which actually launched a projectile, Yabe conducted an experiment that 0.1-gram paper airplane with an acryl overlay was launched at about 1.4 m/s using 0.6-J-class Nd:YAG laser. In Tanaka et al.'s experiment, 7 -microgram multi-layered flyer was accelerated to about 13 km/s using 20-J-class Nd:glass laser. Myrabo, using a 10-kW-class repetitive-pulse carbon dioxide laser, successfully launched a 51-gram 'lightcraft' at about 15 m/s up to altitude of 71 m. In these experiments, the values of impulse (i.e., momentum) and momentum coupling coefficient were estimated about 0.14 x 10^-3 kg-m/s, 91x10^-3 kg-m/s and 765x10^-3 kg-m/s and about 240 N/MW, 4 N/MW and 50 N/MW, respectively. The objective of this study is to enhance a laser-driven impulse using a 300-J-class single pulsed laser owing to fluid-dynamic process. In this paper, we discuss a high-speed launch performance of a 1-gram projectile by enhanced impulse and achieved momentum coupling coefficient which are significantly improved using fluid-dynamic effect.

High average power (10-50W) slow mode-locked lasers operating with repetition rates of a few MHz provide a unique combination of high peak power, short pulse duration, and high brightness that makes them ideal for applications in pulsed laser ablation and nonlinear optics. With peak powers in the MW range and near diffraction-limited output beams, focussed intensities can exceed 10¹²W/cm²: sufficient for ablation of most solid materials or to saturate nonlinear optical interactions.

Space debris constitutes a significant hazard to low earth orbit satellites and particularly to manned spacecraft. A quite small velocity decrease from vaporization impulses is enough to lower the perigee of the debris sufficiently for atmospheric drag to de-orbit the debris. A short pulse (picosecond) laser version of the Orion concept can accomplish this task in several years of operation. The "Mercury" short pulse Yb:S-FAP laser being developed at LLNL for laser fusion is appropriate for this task.

The paper presents pulsed laser propulsion performance data for three 11-cm diameter aluminum parabolic (or "bell-shaped") engines, tested with the 10-kW PLVTS pulsed CO2 laser at White Sands Missile Range, NM. The single-pulse and multiple-pulse tests were conducted on two campaigns, Sept. 2000 and Sept. 2001, using a ballistic pendulum apparatus. The results from two different sets of PLVTS resonator optics were gathered (both 2X and 3X magnification). Assuming the vertex is set at the parabola's focus (i.e., and viewing outward towards the 11-cm exit plane), the bell engines had three different total included angles of 60, 87.2, and 120 degrees. As expected, the impulse and coupling coefficient performance of the 60 deg. bell generally exceeded that of the 87.2 deg. engine, which in turn outperformed the 120 deg. bell. The maximum single-pulse coupling coefficients varied from 275 to 375 N-sec/MJ. Multiple-pulse engine performance data was also gathered with the same ballistic pendulum in the first campaign. A sequence of from 2 to 8 pulses was transmitted into each bell at a pulse repetition frequency of 25 HZ -- all delivered within the first 1/8^th cycle of the pendulum's swing. In general, only small variations in the coupling coefficient were observed throughout the string of pulses.

This work summarizes the combination of experimental and digital image processing technique developed for determination of plasma expansion velocity angular profiles. Such profiles were used further for assessment of specific impulses for ablative laser propulsion. The technique uses time-resolved intensified charge-coupled device (ICCD) camera with 18 ns minimum time delay, 100 μm spatial resolution, and 5 ns gating speed. The plasma was formed in vacuum (~ 3x10^-3 Torr) by focusing output pulses of a laser system (100-ps pulsewidth at 532 nm wavelength and ~35 mJ energy) on surfaces of C (graphite), Al, Si, Fe, Cu, Zn, Sn, and Pb targets. Plasma expansion velocity profiles were derived from plume edge contours. Specific impulse (I_sp) was then deduced from the profiles. New I_sp data appeared in excellent agreement with specific impulses derived from force measurements, conducted earlier. Observed angular profiles of plasma edge velocity and integral intensity are reported and discussed.

Laser-powered lightcraft systems that deliver microsatellites to low earth orbit have been studied for the Air Force Research Laboratory. One result of this study has been discovery of the significant influence of laser wavelength on the power lost during laser beam propagation through Earth’s atmosphere and in space. Here, energy and power losses in the laser beam are extremely sensitive to wavelength for earth-to-orbit missions. And this significantly affects the amount of mass that can be placed into orbit for a given maximum amount of radiated power from a ground-based laser.

The picosecond barrier to high brightness electron pulses has been broken. Electron diffraction harbors great potential for providing atomic resolution to structural changes at critical points — a real-time view of atomic motions during structural transitions. Femtosecond electron pulses of sufficient number density to execute nearly single-shot structure determinations are needed. This requirement places severe constraints on the electron pulse propagation. A new photoactivated electron gun design has been developed based on an N-body numerical simulation and mean-field calculation of the electron wavepacket propagation that is capable of less than 600 femtosecond electron pulses with high enough brightness to provide structural details in the small shot number limit. Time-resolved diffraction studies with this new instrument have focused on strongly driven solid-liquid phase transitions of aluminum as a model problem of a structural transition. The signal to noise and available diffraction orders were sufficiently high to give direct access to fluctuations leading to the disordering or melting process and the associated radial distribution function. This work gives atomic level details of a solid-liquid phase transition, i.e., we can literally watch the atoms move during melting. The promise of atomically resolving transition state processes is at hand and applications along this line will be discussed.

Coherent THz radiation was produced from relativistic electron bunches of subpicosecond duration. The electron beam was produced by strongly focused (≈ 6 μm), high peak power (up to 10 TW), ultra-short (≥50 fs) laser pulses of a 10 Hz repetition rate Ti:sapphire chirped pulse amplification (CPA) laser system via self-modulated laser wakefield acceleration (SM-LWFA) in a high density (> 10¹⁹ cm^-3) pulsed gas jet. As the electrons exit the plasma, coherent transition radiation is generated at the plasma-vacuum boundary for wavelengths long compared to the bunch length. Radiation yield in the 0.3 to 19 THz range and at 94 GHz has been measured and found to depend quadratically on the bunch charge. The measured total radiated energy in the THz range for two different collection angles is in good agreement with theory. Modeling indicates that optimization of this table-top source could provide more than 100 μJ/pulse. Together with intrinsic synchronization to the laser pulse, this will enable numerous applications requiring intense terahertz radiation. This radiation can also be applied as a useful tool for measuring the properties of laser accelerated bunches at the exit of the plasma accelerator.

The mechanisms of melting and photomechanical damage/spallation occurring under extreme superheating/deformation rate conditions realized in short pulse laser processing are investigated in a computational study performed with a hybrid atomistic-continuum model. The model combines classical molecular dynamics method for simulation of non-equilibrium processes of lattice superheating and fast phase transformations with a continuum description of the laser excitation and subsequent relaxation of the conduction band electrons. The kinetics and microscopic mechanisms of melting are investigated in simulations of laser interaction with free-standing Ni films and bulk targets. A significant reduction of the overheating required for the initiation of homogeneous melting is observed and attributed to the relaxation of laser-induced stresses, which leads to the uniaxial expansion and associated anisotropic lattice distortions. The evolution of photomechanical damage is investigated in a large-scale simulation of laser spallation of a 100 nm Ni film. The evolution of photomechanical damage is observed to take place in two stages, the initial stage of void nucleation and growth, when both the number of voids and the range of void sizes are increasing, followed by the void coarsening, coalescence and percolation, when large voids grow at the expense of the decreasing population of small voids. In both regimes the size distributions of voids are found to be well described by the power law with an exponent gradually increasing with time. A good agreement of the results obtained for the evolution of photomechanical damage in a metal film with earlier results reported for laser spallation of molecular systems and shock-induced back spallation in metals suggests that the observed processes of void nucleation, growth and coalescence may reflect general characteristics of the dynamic fracture at high deformation rates.

The fundamental mechanisms of matter removal involved in the interaction of short laser pulses with absorbing solids have been investigated using molecular-dynamics/Monte~Carlo simulations. This is accomplished under the two following assumptions: (i) the elementary thermodynamic properties of targets (metals and semiconductors) are adequately described by empirical potentials; (ii) in the regime where ablation is thermal, the complete time evolution of the system can be followed in p-T-P space and the result mapped onto the equilibrium phase diagram of the material. We find remarkable similarities in the physical pathways to ablation in metals and semiconductors for pulse durations ranging from 200 fs to 400 ps: (i) under conditions of isochoric heating and rapid adiabatic cooling with femtosecond pulses, several mechanisms can simultaneously account for matter removal in the target: spallation, phase explosion, vaporization, and fragmentation; the latter is identified for the first time in the context of laser ablation. (ii) Under nonadiabatic cooling with picosecond pulses, ablation is driven by a "trivial" fragmentation process in the metallic, supercritical fluid; this suggests a pulse duration upper limit for phase explosion of ~ 10^-11 s.

The positive ion yield as a function of delay between ultraviolet femtosecond pulse pairs for four alkali halide single crystals has been measured. Two-pulse correlation allows direct observation of solid state and surface dynamics on an ultrafast timescale. The ion yield from 265 nm irradiated NaBr, KCl, KBr, and KI depends critically on the time delay between the two sub-threshold pulses. Following irradiation of single crystal NaBr and KCl, the positive ion desorption yield displays three distinct features; a coherence peak, followed by rise, and decay features. In contrast, the yield of K⁺ from KBr displays only the coherence peak and picosecond decay features while the yield from KI shows only the coherence feature. The data suggest that although the nanosecond ion desorption mechanism may be dominated by defect photoabsorption, significant electron-hole pair production may contribute to the desorption mechanism following femtosecond excitation.

We review recent developments in the generation and metrology of XUV-attosecond (as) pulses. The review includes an extended report on the recently achieved 2^nd-order autocorrelation measurement of a sub-femtosecond (sub-fs) pulse train.

In this paper, we summarize the performance of a diamond cooled diode pumped solid state (DPSS) Nd:YAG laser developed by Textron Systems Corporation (TCS). Over 50% intrinsic extraction efficiency at 50-Watts average power, equivalent to volumetric power extraction of 2000 W/cc, has been experimentally demonstrated. Beam quality (BQ) of less than 1.1 XDL has been measured in an oscillator configuration with the laser operating in TEM₀₀ mode. With a simple passive thermal lens correction, BQ of less than 1.5 XDL was obtained from an oscillator amplifier arrangement at specific pump rates up to 1600 W/cc and 600 W/cc, respectively. By using an intra-cavity acousto-optic modulator, Q-switched laser pulses as short as 6 ns were obtained from the oscillator. This concept is amenable to scaling up to very high power levels. A conceptual design, using our validated database, for a 100-kW class laser is also presented.

We report on the effectiveness of bend-loss mode filtering for power scaling of large-core, rare-earth-doped fibers. The technique affords a diffraction-limited beam quality from multimode fibers, which is crucial for practical applications of fiber sources. We demonstrate the technique in a >300-kW-peak-power, <1-ns-pulse-duration Yb-doped fiber amplifier, which we used for multiple harmonic generation.

Laser ablation of polyimide (PI) and polymethyl-methacrylate (PMMA) at 248 nm with pulse lengths τ ranging from 200 fs to 200 ns was investigated. The measured ablation rates increase towards long and very short pulses and show minima for pulse lengths of about 5 ps (PMMA) or 50 ps (PI). Measurements of the reflected and transmitted portion of the ablating laser pulse give additional information about the factors influencing the ablation rates. The minimum of the ablation rate coinciding with a maximum of the reflectance of the ablating pulse can be explained by a dynamic plasma reflection model: A fast build up of a dense plasma is followed by high obscuration for a brief transition time and self-regulating opacity for the rest of the pulse. This model of plasma mediated ablation leads to a τ^1/4-dependence of the ablation rate at fixed fluence, which fits very well to the measured data in the range above 50 ps. In the long pulse regime (20 ns to 200 ns), the attenuation of the ablating laser pulse by the expanding ablation plume was investigated by using a small sensing hole in the sample within the ablation spot. In combination with ablation rate measurements with varying laser spot size, these results lead to the conclusion, that the three dimensional plume expansion determines the fraction of the laser pulse actually reaching the sample. Concerning plasma and plume effects at high fluence irradiation, three effects influence the ablation behavior on different time scales: The time constant for plasma formation is important on the fs-ps time scale, self regulating plasma on the ps-ns time scale, three dimensional plume expansion on the ns-µs time scale.

We performed 1.5-dimensional simulation of the Fokker-Planck equation using the CIP method to investigate femto-second-laser heating processes. We found that the heat flux in the solid part approaches the classical thermal conduction theory like Spitzer-Harm theory in quite a short time scale ω_pt<100, while the heat flux on the vacuum side becomes free streams which don’t depend on temperature gradient. On the basis of this result, we performed hydrodynamic simulation using the CIP method with classical thermal conduction and the experimental ablation depth was replicated very well showing that even fs pulse laser processing can be satisfactorily described by the classical heat conduction. As an application to nanosecond laser, we tried to drill a crack-free high-aspect-ratio hole through glass by YAG laser of 1μm wavelength, 5ns pulse width and 30-630mJ/pulse. The hole is 25.5mm long with 500 μm radius and no crack is observed even in atmospheric condition. This success is due to translucent adhesive tape pasted on glass surface in which the temperature is controlled and thermal stress is reduced.

CFD simulations on effects of a focused laser pulse for combustion enhancement characteristics were conducted for supersonic airstreams with a transverse hydrogen-fuel injection. In order to estimate behaviors of a laser-induced plasma, temporal variations of its emission, and laser absorption processes were measured with photodiodes. From these measurements, characteristic time scales of the absorption process of an incident laser pulse and a plasma formation process were estimated. Numerical simulations using a time-dependent Navier-Stokes equation with finite-rate chemistry were also conducted to elucidate laser-induced ignition and mixing enhancement characteristics in supersonic airstreams with a transverse hydrogen injection. From the results, it was confirmed that, depending on the laser energy density and focal points, radicals, a shock wave, and shock-induced local turbulences were being formed through the laser irradiaton. Then recirculation zones with flamelets were induced. Moreover it was shown that these flamelets were growing in moving upstream and downstream from the focal point up to 1 msec. Consequently, it was shown that laser-induced plasmas could be effective in both combustion reaction and mixing enhancements for the supersonic combustion.

The paper addresses different aspects of the numerical modeling of laser ablation. In particular, the advantages of microscopic and macroscopic numerical approaches are underlined for specific parts of the complex laser ablation process. Multi-scale, or hybrid models combining different methods are shown to provide most promising results. These models permit not only to diminish considerably the calculation time, but also to perform more realistic calculations facilitating the interpretation of experimental results. Numerical results are presented for the cases of both nanosecond and femtosecond laser pulses under conditions typical for such applications as reactive laser ablation and laser-induced plasma spectroscopy. Several experimentally observed physical phenomena taking place during laser plume formation and expansion are visualized and are explained by using the proposed combined models.

Pulsed-laser deposition is a unique technique that has been employed for thin film growth of a broad variety of materials. We report on the deposition and characterization of advanced piezoelectric thin films and ceramic/polymer composite layers. Pulsed-laser ablation and micro-patterning of piezoelectric GaPO₄ is presented.

Mechanisms responsible for the limitation of the aspect ratio obtained by deep drilling of hard metals are investigated in the present work. Cemented carbide targets have been irradiated with laser pulses of 100 fs duration and 100 μJ maximum energy delivered by a Ti:sapphire laser system. The experiments are carried out in different gas environments (vacuum, air, helium up to atmospheric pressure) with incident laser fluences ranging from 1 to 20 Jcm^-2. During deep drilling, the laser-induced ablation plume is characterized by means of in-situ plasma diagnostics. Fast imaging is used to observe the expansion behavior of the plasma plume whereas time- and space-resolved emission spectroscopy is employed to analyze the plasma composition. After irradiation, the laser-produced craters were examined by optical microscopy. A correlation between the ablation plume characteristics and the morphological changes of the mciro-holes is established. The results indicate that nanoclusters, that present a significant part of the ablated material, are responsbile for the alteration of the crater shape in the high laser fluence regime.

Laser milling of a variety of substrates is investigated with the intention of achieving high quality material removal to create three-dimensional shapes in the material. A high power Q-switched Diode Pumped Solid State Nd:YAG Laser at 1064nm is used in all cases. Materials investigated include Nickel Superalloys, Thermal Barrier Coatings, Steels, Tungsten Carbide and Polycrystalline Diamond. Multi-layer substrates are also considered. The effects of laser intensity, plasma formation, pulse duration, material properties, and resulting removal rate, recast and surface finish are explored for this process. This paper defines the findings of this study within the context of commercial imperatives.

Hydrodynamic instabilities are key issues of the physics of inertial confinement fusion (ICF) targets. Among the instabilities, Rayleigh-Taylor (RT) instability is the most important because it gives the largest growth factor in the ICF targets. Perturbations on the laser irradiated surface grow exponentially, but the growth rate is reduced by ablation flow. The growth rate γ is written as Takabe-Betti formula: γ = [kg/(1+kL)]^1/2–βkm/p_a, where k is wave number of the perturbation, g is acceleration, L is density scale-length, β is a coefficient, m is mass ablation rate per unit surface, and ρ_a is density at the ablation front. We experimentally measured all the parameters in the formula for polystyrene (CH) targets. Experiments were done on the HIPER laser facility at Institute of Laser Engineering, Osaka University. We found that the β value in the formula is ~ 1.7, which is in good agreements with the theoretical prediction, whereas the β for certain perturbation wavelengths are larger than the prediction. This disagreement between the experiment and the theory is mainly due to the deformation of the cutoff surface, which is created by non-uniform ablation flow from the ablation surface. We also found that high-Z doped plastic targets have multiablation structure, which can reduce the RT growth rate. When a low-Z target with high-Z dopant is irradiated by laser, radiation due to the high-Z dopant creates secondary ablation front deep inside the target. Since, the secondary ablation front is ablated by x-rays, the mass ablation rate is larger than the laser-irradiated ablation surface, that is, further reduction of the RT growth is expected. We measured the RT growth rate of Br-doped polystyrene targets. The experimental results indicate that of the CHBr targets show significantly small growth rate, which is very good news for the design of the ICF targets.

Ultrafast lasers promise to become attractive and reliable tools for material processing on micro- and nanoscale. The additional possibility to temporally tailor ultrashort laser pulses by Fourier synthesis of spectral components enables extended opportunities for optimal processing of materials. An experimental demonstration of the technique showing the possibility to design particular excitation sequences tailored with respect to the individual material response will be described, laying the groundwork for adaptive optimization in materials structuring. We report recent results related to the implementation of self-learning, adaptive loops based on temporal shaping of the ultrafast laser pulses to control laser-induced phenomena for practical applications. Besides the fundamental interest, it is shown that under particular excitation conditions involving modulated excitation, the energy flow can be controlled and the material response can be guided to improve processing results. Examples are given illuminating the possibility to control and manipulate the kinetic properties of ions emitted from laser irradiated semiconductor samples using excitation sequences synchronized with the phase transformation characteristic times.

Although valuable experimental work has been performed in order to explore the optimum conditions of application of the treatments and to assess their capability to provide enhanced mechanical properties, there is little work done on the theoretical prediction of these optimum parameters. In the present paper, a model is presented to provide an estimation of the residual stresses and surface deformation in order to see the influence of the different parameters in the process. The influence of pulse duration, pulse pressure peak, spot radius, number of shots, overlapped shots and material properties are studied. The great influence of 3D deformation effects in the process is clearly shown as one of the most important limiting factors of the process traditionally neglected in previous literature. Additionally, from the experimental point of view, in the present paper a summary is provided of different results obtained from the most recent LSP experiments carried out by the authors along with some conclusions for the assessment of LSP technology as a profitable method for the extension of fatigue life in critical heavy duty components.

Hydrodynamic regimes of KrF laser interaction with solid and thin-film targets in atmospheric and reduced pressure air were investigated at high-energy GARPUN installation. These experiments were performed with 100-J, 100-ns laser pulses in planar focusing geometry and compared with numerical simulations with ATLANT code to verify the concept of laser-driven shock tube (LST), which could accelerate a gas to hypersonic velocity and produce strong shock waves (SW). Laser beam was focused by a prism raster optical system that provided very uniform intensity distribution at moderate laser intensities q ≤ 1 GW/cm² over a square spot of ~ 1-cm size. Dynamics of laser-produced plasma and SW in a surrounding gas were investigated by means of high-speed photo-chronograph and streak camera in combination with shadow or schlieren techniques, time and space resolved spectroscopy in a visible spectral range. Both experiments and simulations confirmed that target evaporation and blow-up of expanding plasma are the main mechanisms of UV laser-target interaction in a surrounding gas. Planar shock waves with velocities up to 7 km/s towards the laser beam were observed in a normal density air and up to 30 km/s in a rarefied air. Acceleration of thin CH films of 1 to 50-μm thickness was investigated both in a free-expansion and plasma-confined regimes with the highest achieved velocities up to 4 km/s. The SW damping law in a free space independently on laser intensity and air pressure could be approximated by a power law x ~ tⁿ with a power indexes n₁ = 0.85 - 0.95 at the initial stage and n₂ = 0.5 - 0.6 later, when a distance of the SW front from a target became comparable with a size of the irradiated spot. Instability growth at contact interfaces between ablative plasma and accelerated film, as well as between plasma and compressed air were observed and compared for various initial irradiation non-uniformities. They were introduced by a grid, which was set in front of the film target.

The future CMOS generations for microelectronics will require advanced doping techniques capable to realize ultra-shallow, highly-doped junctions with abrupt profiles. Recent experiments have shown the potential capabilities of laser processing of Ultra Shallow Junctions (USJ). According to the International Technology Roadmap for Semiconductors, two laser processes are able to reach ultimate predictions: laser thermal processing or annealing (LTP or LTA) and Gas Immersion Laser Doping (GILD). Both processes are based on rapid melting/solidification of the substrate. During solidification, the liquid silicon, which contains the dopants, is formed epitaxially from the underlying crystalline silicon. In the case of laser thermal annealing dopants are implanted before laser processing. GILD skips the ion-implantation step: in this case dopants are chemisorbed on the Si surface before the laser shot. The dopants are then incorporated and activated during the laser process. Activation is limited to the liquid layer and this chemisorption/laser shot cycle can be repeated until the desired concentration is reached. In this paper, we investigate the possibilities and limitations of the GILD technique for two different substrates: silicon bulk and SOI. We also show some laser doping applications for the fabrication of micro and nanoresonators, widely used in the MEMS Industry.

Key features are presented of the Exitech MS-13 EUV Microstepper tool developed for EUV resist testing & technology evaluation at the 32nm node and beyond. Details of the tool design architecture, module layout, vacuum chamber, major subsystems including source, optics and performance specifications are given.

A compact electron-based extreme ultraviolet (EUV) source for at-wavelength metrology is developed. The source concept is based on the transfer of advanced microfocus x-ray tube technology into the EUV spectral range. This allows the realization of a flexible, debris-free, and long-term stable EUV source. In the EUV tube, silicon targets are used to generate radiation at 13.5 nm. Detailed characteristics of the source performance are reported and different applications of the EUV tube in the field of at-wavelength metrology are presented.

The main technological challenge of a future extreme ultraviolet (EUV) light source is the required average power of 115 W at the intermediate focus. High repetition rate laser produced plasma (LPP) sources are very promising to face this challenge. We report the current status of the laser produced light source system we started to develop in 2002. The system consists of the following main components: The plasma target is a liquid xenon jet wih a maximum diameter of 50 micrometer and a velocity of more than 30 m/s. A Nd:YAG laser oscillating at 1064 nm produces the plasma. The laser is a master oscillator power amplifier (MOPA) configuration with a maximum repetition rate of 10 kHz and an average power of 1 kW. The EUV system currently delivers an average EUV in-band power of 4 W (2% bandwidth, 2π sr) having a stability of 0.54% (1σ, 50-pulse moving average). Related to future collector mirror lifetime considerations, a magnetic confinement scheme is evaluated for fast ions mitigation.

Powerlase has made significant advances towards making the LPP EUV source the most likely choice for a full production EUV lithography machine. Our main achievement was enhancing the performance of the LPP driver and particularly increasing the average power per laser module. This was achieved by increasing the electrical to optical conversion efficiency of our gain modules. In order to increase the conversion efficiency of the in-band EUV, we are currently using cryogenic solid xenon, as well as other target materials. The combination of an efficient and cost effective laser driver with appropriate choice of target material significantly lowers the Cost of Ownership (CoO) of the LPP EUV source, including day to day running, making it comparable to the cost of Discharge Produced Plasma (DPP) sources.

The availability of extreme ultraviolet (EUV) light sources, measurement tools and integrated test systems is of major importance for the development of EUV lithography for use in high volume chip manufacturing which is expected to start in 2009. The estimates of cost of an EUV exposure tool in combination with sophisticated throughput models leads to a throughput of 120 wafers per hour necessary for economic use of EUV lithography. Concluding from that light sources are necessary which deliver an EUV output power of 115 W at 13.5 nm at the entrance of the illuminator system. The power requirement in combination with the required lifetimes of source components and collector optics make the source technology the most critical issue to be solved when developing EUV lithography. The present paper gives an update of the development status of EUV light sources at XTREME technologies, a joint venture of Lambda Physik AG, Goettingen, and Jenoptik LOS GmbH, Jena, Germany. Results on both laser produced plasma (LPP) and gas discharge produced plasma (GDPP), the two major technologies in EUV sources, are given. The LPP EUV sources use xenon-jet target systems and pulsed lasers with 500 W average power at up to 10 kHz developed at XTREME technologies. The maximum conversion efficiency from laser power into EUV in-band power is 1.0% into 2π solid angle. 2.0 W EUV radiation is generated at 13.5 nm in 2π sr solid angle. The small source volume of < 0.3 mm diameter will allow large collection angles of 5 sr. The intermediate focus power is estimated to 1 W. Collector mirror lifetime tests showed 5 million pulses lifetime without debris mitigation. With debris mitigation in place lifetimes of more than 1 billion pulses are estimated. For the next generation of higher power EUV LPP sources a laser driver has been tested at 1.3 kW average laser power. This will lead to 5 W EUV power in intermediate focus. The GDPP EUV sources use the Z-pinch principle with efficient sliding discharge pre-ionization. Prototype commercial gas discharge sources with an EUV power of 35W in 2π sr were already delivered for integration into EUV microsteppers. These sources are equipped with a debris-filter which results in an optics lifetime exceeding 100 million discharges at 1 kHz repetition frequency. The same lifetime was achieved for the components of the discharge system itself. The progress in the development of high-power discharge sources resulted in an EUV power of 150 W in continuous operation at 4.5 kHz repetition rate by implementation of porous metal cooling technology. The EUV plasma has a FWHM-diameter of 0.5 mm and a FWHM-length of 1.5 mm. The intermediate focus power is calculated to be in the range of 15 W - 20 W, depending somewhat on the transmission of the optical path to the intermediate focus and on the etendue specification. The typical fluctuations of the EUV energy are standard deviation σ<5% without any active stabilization. Discharge sources with Sn as emitter were investigated as more efficient alternative to Xenon. Estimates regarding Sn sources reveal the potential of achieving 65 W intermediate focus power by using developed porous metal cooling technology. Improvement of cooling could open the path to 115 W of power for high volume manufacturing using EUV lithography. However, Sn-sources are technologically risky und much less advanced than Xe sources, since fuel-handling and debris mitigation is much more challenging in comparison to Xe-sources. GDPP and LPP sources still compete for the technology of high volume manufacturing sources for EUV lithography. Optimization potential of the etendue of the optical system of EUV scanners will certainly influence any technology decision for HVM sources.

We propose CO₂ laser-produced plasma as the extreme ultraviolet (EUV) light source for future optical lithography. The laser beam from a transversely-excited atmospheric (TEA) CO₂ laser (4 J, 50 ns FWHM) was focused on a Xe gas target, a Xe cryogenic target and a nano-structured tin-based target to generate EUV radiation around 13.5 nm. The EUV pulse of about 100 ns in FWHM was measured 50 ns after the CO₂ laser irradiation. The EUV spectra were measured by an X-ray CCD camera with a transmission grating spectrograph (TGS). A characteristic EUV spectrum was observed from CO₂ laser produced Xe plasma. The EUV energy was measured by a Flying Circus II detecting system and an output energy of 3 mJ/pulse and a conversion efficiency of 0.2% per 2π sr at 13.5 nm (2% B.W.) were obtained with Xe targets. These values are comparable to those of YAG laser-produced Xe plasma, indicating the potential scalability of the EUV light source using a CO₂ laser produced plasma.

As is known in literature are discussed the number of methods of high power EUV sources creation for EUV lithography including laser application, micro pinch, plasma focus, capillary discharge etc. The aim of this paper is to find the optimal physical conditions in plasma as EUV source taking into account, before all, the kinetics an transfer of light quantum. It is shown that the efficiency of plasma EUV source depends, in the main, on material of target, density of electrons and their temperature. In conclusion a variant of creating an alternative ("linear") EUV source on the basis of self-compression of plasma shells in the regime of slow energy input is considered.

Investigations of possibilities for nanostructuring with femtosecond laser pulses of different materials are reported. The aim is to develop a simple laser-based technology for the fabrication of two- and three-dimensional nanostructures with structure sizes on the order of several hundred nanometers. This is required for many applications in photonics, for the fabrication of photonic crystals and microoptical devices, for data storage, displays, etc. Sub-wavelength structuring of metals by direct femtosecond laser ablation is performed. The band gap dependence of the minimum structure size for transparent materials is identified.

Surface morphology and structural changes upon femtosecond laser ablation from crystalline silicon (001) were examined ex-situ by optical, scanning electron, and atomic force microscopy, as well as Raman spectroscopy. After repetitive illumination with several thousand laser pulses at an intensities below or near the single shot damage threshold (2x10¹² W/cm²), self-assembled periodic nanostructures with periods of 200 nm resp. 600-700 nm develop at the crater bottom. Micro-Raman spectroscopy reveals phase transformations inside the crater from Si-I to the polymorphs Si-III, Si-XII, hexagonal Si-wurtzite (Si-IV), and amorphous silicon, pointing to substantial pressure and volume changes during the interaction. The ablation dynamics was monitored by time-of-flight mass spectroscopy, showing the emission of superthermal positive ions with a kinetic energy of several eV as well as significant contributions at lower kinetic energies. The results suggest that the ablation is associated with considerable recoil pressure and leaves behind a severely perturbed crystal surface. The resulting instability relaxes by a self-organization, independent of the initial, and surrounding, crystal structure.

We will report on nanostructure fabrication on silicon (Si) substrate by 800 nm femtosecond laser pulses. Spherical alumina particles were placed on the substrate surface. After femtosecond laser irradiation at below-ablation-threshold fluences, we have successfully observed the nanoholes formation with around 100 nm in diameter using scanning electron microscope (SEM) and atomic force microscope (AFM). The dependence of nanohole formation on the laser fluence and laser pulse number was investigated. The mechanism for the nanohole drilling is the near-field optical enhancement effect induced by interaction between local surface plasmon on the particles surface and surface plasmon polariton on the Si substrate surface.

Permanent refractive index change in bulk glasses induced by femtosecond laser has opened up new ways for photonic devices fabrication. In this technique, temporal profile of femtosecond laser is found to be important because it is a nonlinear material processing. In this paper we investigate temporal profile dependence on the optical waveguides properties written by tightly focused femtosecond laser and loosely focused femtosecond laser. With tight focus writing, optimization of pulse interval of pulse train with a few ps decreased the optical loss of the fabricated waveguides. With loose focus writing, longer femtosecond laser increased the length of the induced refractive index change. 2-D Bragg diffraction gratings were well fabricated using this loose focus method.

Laser direct writing (LDW) process is developed using 3-rd harmonic Diode Pumped Solid State Laser (DPSSL) with the near UV wavelength of 355 nm. Photo-sensitive curable polymer is irradiated by UV laser and developed using polymer solvent to obtain quasi-3D patterns. We performed basic experiments for the various process conditions such as laser power, writing speed, laser focus, and optical polymer property to get the optimal conditions. This process could be applied to fabricate a single-mode waveguide without expensive mask projection method. Experimentally, the patterns of trapezoidal shape were manufactured into dimension of 8.4μm width and 7.5μm height. Propagation loss of planar waveguide was 1.42 dB/cm at wavelength of 1,550 nm.

This work presents our attempts to grow thin films of the ferromagnetic half-Heusler alloy NiMnSb and also a bi-layered structure MnSb/NiMnSb onto (100) semiconductor substrates using Single Beam and respectively Double Beam Pulsed Laser Deposition. We investigated the samples by XRD, scanning electron microscopy (SEM), Energy Dispersive X ray (EDX) analysis and SQUID magnetometry. The thin films obtained in both configurations are crystalline, single phase with stoichiometry corresponding to the bulk material. The out of plane magnetisation of the bi-layered structure reaches the saturation value more rapidly than the NiMnSb/Si film.

The aim of this work was to check if the development of laser cleaning could be suitable for complementary surface modifications of aluminium alloys before bonding. Therefore, the effects of laser treatment parameters on the induced changes of the surface composition of aluminium alloys were studied. A Q-switched Nd:YAG laser with pulse duration 10 ns, 1064 nm wavelength and 8 ns, 355 nm was used. For the in-depth surface analysis of the treated specimens, X-Ray Photoelectron Spectroscopy (XPS) in combination with Argon ion sputtering as was used. It was demonstrated by the surface analysis measurements that the remaining lubricants as well as the native oxide were removed by the applied laser treatments. This removal was resulted even though at the lowest examined laser fluence (0.8 J cm^-2). It was also clear that thermal oxidation took place, which caused a significant increase of the oxide thickness and a magnesium enrichment at the outer part of the oxide. In the range of laser fluences which was examined (0.8 – 1.4 J cm^-2), the thickness of the oxide and the magnesium enrichment were increasing by the increase of the laser energy. Nevertheless, the magnesium enrichment does not lead to a continuous and brittle layer of MgO but to a "micrograin" texture of the surface which is probably not detrimental to adhesion.

We report on a detailed parametric study of an extremely efficient supersonic chemical oxygen-iodine laser (COIL) with supersonic mixing of iodine and oxygen. Output power exceeding 0.5 kW with chemical efficiency of ~33% was obtained in a 5 cm gain length for Cl₂ flow rate of 17 mmole/s. 33% efficiency is the highest reported chemical efficiency of any supersonic COIL. Comparison between different mixing schemes shows that for supersonic mixing the output power and chemical efficiency are about 20% higher than for transonic mixing scheme. The optimal conditions for the efficient operation are investigated. Diagnostic measurements of the small-signal gain shows that the value of the gain for the supersonic mixing scheme corresponding to the maximum efficiency is about 0.75%/cm, about 1.5 times larger than for transonic mixing scheme. Studies of different supersonic mixing schemes show that to achieve further power increase the injection location should be moved downstream.

This study provides experimental results in investigating the use of a 5.34 kW ytterbium-doped multiclad fiber laser with an emission wavelength of 1.07 microns for creating deep hole configurations in different types of rock for production applications in oil and gas wells. Recent developments in high power fiber lasers offer technical advantages when compared to other industrial lasers that may now allow economic subsurface applications to rock formations, delivering the beam through optical fiber from the surface via the wellbore. Successful applications in this manner would provide an alternative to conventional methods that employ rotary drilling and shaped charge explosives. Various parameters affecting laser penetration into samples of sandstone and limestone were studied and optimized. A maximum penetration depth of 30 cm for 8.9-mm hole diameter was achieved in limestone, while 15 cm penetration depth was achieved in sandstone with the same hole diameter. In all cases, the hole diameter was no greater than the beam diameter applied.

Ablation thresholds, etch rates, and quality of ablated structures often differ dramatically if a conventional, UV-Vis-IR laser delivers radiation energy onto a material surface in a short (nanosecond) or ultra-short (picosecond/femtosecond) pulses. Various short-wavelength (λ < 100 nm) lasers emitting pulses with durations ranging from ~ 10 fs to ~ 1 ns have recently been put into a routine operation. This makes possible to investigate how the ablation characteristics depends on the pulse duration in the XUV spectral region. 1.2-ns pulses of 46.9-nm radiation delivered from a capillary-discharge Ne-like Ar laser, focused by a spherical Sc/Si multilayer-coated mirror were used for an ablation of organic polymers and silicon. Various materials were irradiated with an ellipsoidal-mirror-focused XUV radiation (λ = 86 nm, τ = 30-100 fs) generated by the free-electron laser (FEL) operated at the TESLA Test Facility (TTF1 FEL) in Hamburg. The beam of the Ne-like Zn XUV laser (λ = 21.2 nm, τ < 100 ps) driven by the Prague Asterix Laser System (PALS) was also successfully focused by a spherical Si/Mo multilayer-coated mirror to ablate various materials. Based on the results of the experiment the etch rates for three different pulse durations are compared using the XUV-ABLATOR code to compensate for the wavelength difference. Comparing the values of etch rates calculated for short pulses with the measured ones for ultrashort pulses we may study the influence of pulse duration on the XUV ablation efficiency.

Laser processing which used in the 3C industry is the new technology. The PCB (printed circuit board) Laser drilling is the new manufacturing process for the PCB industry. In this paper we report the results of an investigation exploring the feasibility of laser drilling microvias. The process relies on the use of pulses from a CO₂ laser to drilling small holes in the panels of acrylic. There are two part of this paper, first we will drilling the small holes of the acrylic by the different parameter of the laser (pulse width, repetitive frequency, mask size and etc.). There are two result of this paper; first we find the repetitive frequency and mask size will be change the holes diameter and depth, and the pulse width will affect the quality of the drilling holes. In Addition we can find the optimal process parameter by this paper.

Under high-intensity laser pulses the morphology and size of a crater created in biotissue depends both on biotissue properties and on irradiation mode. Wounds have been investigated formed in biotargets under single as well as repetitive laser pulses of nanosecond duration of visible and near IR-range. The analysis of the produced damage has demonstrated that its morphology and size depends on ablation mechanism. The latter in its turn depends on irradiation temporal characteristics for a given specimen and wavelength.

In the range of intensity 10¹³-10¹⁴ W/cm², material processing with ultrashort laser pulses is characterized by the absence of a plasma shielding effect and a small heat affected zone. The understanding of sub-picosecond laser pulse effects involves detailed study of laser-solid interaction processes. The dependence on fluence and pulse duration of the ablation rate can be studied experimentally. To analyse the laser-metal ablation mechanisms, we have inserted an electron-ion decoupling into a hydrodynamic code. The hydrodynamic simulations reveal many details of the processes yielding ablation.

In this paper we discuss the application of sensitive, non-intrusive diagnostic techniques to characterize species in the flow that are critical for chemical oxygen iodine laser (COIL) devices and the electric discharge oxygen iodine laser (DOIL) concept. The key diagnostics include chemiluminescence to detect O₂(a,b) and I(²P_1/2) and tunable diode laser absorption measurements of I* and temperature. We have characterized variations in O and O₂(a) yields with discharge power and oxygen mole fraction. We observe O₂(a) yields to increase dramatically with decreasing oxygen mole fraction. We also discuss the application of a novel imaging diagnostic to obtain 2-D images of species concentrations and temperature.

A decade has passed, since Discharge Oxygen Iodine Laser (DOIL) research started in our laboratory. Singlet delta oxygen production tests were carried out using RF discharge singlet oxygen generator of the first version (DSOG-1) in 1993. The maximum yield of 4.2% was achieved by DSOG-1. Efforts for improving RF-DSOG have been continuously carrying on and DSOG-5 is now under operation. The DSOG-5 consists of a jet nozzle having a diameter of 3 mm, an injector quarts nozzle of 2 mm diameter set inside the jet nozzle at coaxial position and a mixing slit nozzle with the height of 0.2 mm set surrounding the jet nozzle exit. High electric field is laid on inside surface of the jet nozzle by 200 W RF power source. The singlet delta oxygen is produced by energy transfer from Argon plasma which is produced in the jet nozzle. It is important for achieving high yield to have a good mixing of oxygen, blown from the slit nozzle and the quarts nozzle, with the Argon plasma. The yield of 24% was recorded when oxygen gas 110 sccm was mixed with 700 sccm Argon gas at the pressure 0.6 torr and the RF power 196 W. With a new laser system reinforced by a discharge iodine dissociation and a laser gas cooling device, oscillation tests were carried out in conjunction with the DSOG-5. Performance of the system was confirmed by an emission from excited iodine atoms which energy was transferred from the singlet delta oxygen. It is obvious that the new system gives a progress for the DOIL oscillation.

Integrated laser ablation simulation code includes phase transition from liquid to neutral gas to partially ionized plasma, detail laser absorption processes, equation of state, hydrodynamics, and radiation transport, is developed to describe ablation phenomena with phase transition and properties of emission plasmas. For an application of this simulation code, we perform simulations on optimization of laser produced plasmas for extreme ultra violet (EUV) light sources. Because of very low laser intensities (from 10¹⁰ W/cm² to 10¹¹ W/cm²) compared with that in laser fusion cases, it is necessary to include phase transition effects into ablation radiation hydrodynamics code.

With interest growing in the earth engineering industries for practical laser applications, research in using lasers for rock destruction progresses every year. This research yields tremendous amounts of data that must be properly documented and analyzed. However, with nearly 20 laser parameters and rock properties to consider, the analysis requires powerful analytical tools as well as proper selection of influential parameters. In an effort to understand laser-rock interaction, this paper presents analysis of several years of data and yields new understanding of the results. Attempts are made to reduce the number of variables used in experiments by performing data analysis with commercial statistical software tools. By using these tools, trends and correlations of variables identified the significant variables that control rock removal by laser. The significant variables that govern the success of rock removal are: the time the rock is exposed to the laser energy and the laser power settings. Furture experiments will be tailored to optimize these variables. Likewise, the variables such as bulk density, which introduce little or no error in resulting calculations, can be eliminated from consideration and can save valuable testing time. From the analyses performed we found that rock density can be ignored in mineralogically simple rock, although further tests must be done on complex rocks in order substantiate its omission in such cases. The observations presented in the paper should aid in developing future rock destruction experiments.

Singlet oxygen generators for COIL devices that utilize electrical or microwave discharge excitation are currently being investigated. A unique characteristic of these types of generators is that they deliver relatively high yields of O atoms. Dissociation of I₂ will be facilitated by reaction with O atoms. However, a potential complication is that quenching of I* by O may be rapid. In recent studies using discharged oxygen to excite I* it was found that addition of NO₂ to the output of the generator improved the yield of I*. In an attempt to understand the mechanism of the enhancement we have investigated the quenching of I* by O(³P) and NO₂.

We show that it is possible to improve the efficiency of a laser system by adding a classical heat engine cycle to the laser gas that can remove both thermal and vibrational energy from the gas. A rapid pulsed CO₂ laser/gas expansion cycle engine and a continuous CO₂ laser, Stirling or Brayton cycle engine are analyzed. We derive a theoretical total energy recovery efficiency for a CO₂ laser combined with a classical heat engine of 89%. Then, several distinctly different functional laser-coupled heat engine designs will be evaluated to determine the viability of these concepts in practice. Ultimate practical device efficiencies are projected to reach 75% efficiency.

In 1995 Professor Anatoly Napartovich of the Triniti Institute in Troisk, Russia developed a powerful computer code specifically tailored to study the electric, controlled-avalanche, ionized, refrigerated O₂¹Δ generator developed by Plasmatronics. An enormous kinetics rate equation solver was coupled to a Boltzmann electron-energy solver. Both regimes of the process -- the over-volted E/N ionization pulses and the continuous, low E/N excitation field -- were analyzed, but were not time-integrated over a string of successive controlled avalanche pulses. Professor Lowell Morgan of Kinema Research Corporation has prepared a very similar code, except that it tracks the development of O₂¹Δ continuously over time, starting with the first controlled avalanche pulse, then through the DC excitation phase, and continuing unitl the gas exits from the generator. Both ionization and excitation phases are separately programmed to track E/N and current density in an alternating fashion, where each new segment begins with the initial conditions established by the earlier segment. So now it is possible to test any combination of specified parameters and track all processes over time, wherein a fully developed solution for all gas-species emerges as these exit the generator. This latest Morgan Code has significantly contributed to the development of an electric O₂¹Δ generator. A number of calculations that address specific issues of particular interest will be presented. Finally, similarities and differences between the Napartovich and Morgan codes will be identified.

IR-IR double resonance experiments were used to study the state-to-state rotational relaxation of CO with CO, He, and Ne as collision partners. Individual rotational lines of the (2 - 0) vibrational overtone band were pumped by a pulsed IR laser and the subsequent rotational relaxation was monitored using a cw source. The resulting data sets were analyzed by fitting to numerical solutions of the master equation. State-to-state rate constant matrices were generated using fitting law functions. Fitting laws based on the modified exponential gap (MEG) and statistical power exponential gap (SPEG) and energy corrected sudden with exponential power (ECS-EP) models were used. Rate constant matrices for CO+He and CO+Ne were generated from scattering calculations that employed the appropriate ab initio potential energy surfaces. These theoretical rate constant matrices yielded kinetic simulations that agreed with the data nearly as well as the fitted MEG model and were unique in their ability to reproduce both the rotational energy transfer and pressure broadening data for CO+He and CO+Ne.

An assessment of a novel laser-electric hybrid propulsion system was conducted, in which a laser-induced plasma was induced through laser beam irradiation onto a solid target and accelerated by electrical means instead of direct acceleration only by using a laser beam. A fundamental study of newly developed rectangular laser-assisted pulsed-plasma thruster (PPT) was conducted on discharge characteristics and thrust performances with increased peak current compared to our previous study to increase effects of electromagnetic forces on plasma acceleration. At 8.65 J discharge energy, the maximum current reached about 8000 A. With a newly developed torsion-balance type thrust stand, thrust performances of laser assisted PPT could be estimated. It was shown that the impulse bit and specific impulse linearly increased. On the other hand, coupling coefficient and the thrust efficiency did not increase linearly. The coupling coefficient decreased with energy showing maximum value (20.8 μNsec/J) at 0 J, or in a pure laser ablation case. Thrust efficiency first decreased with energy from 0 to 1.4 J and then increased linearly with energy from 1.4 J to 8.6 J. At 8.65 J operation, impulse bit of 38.1 μNsec, specific impulse of 3791 sec, thrust efficiency of 8%, and coupling coefficient of 4.3 μNsec/J were obtained.

We begin with a brief critical discussion of the existing definitions of melting and damage thresholds and the different kinds of experimental determinations of the thresholds. Then we investigate the thermal and athermal melting of a wide-band gap semiconductor (SiO₂) and of silicon by two different methods consisting of a rate equation for the excited electrons and of a complete self-consistent solution of a coupled system of differential equations for the electron density and for the electron and phonon temperatures. In particular, we focus on the role of the critical electron density in the case of athermal melting. Our calculations suggest that this is determined by the critical plasma density. Finally, we conclude with a discussion of the benefits and drawbacks of the two approaches.

A new laser-assisted process called "Laser Die Transfer" is developed for high speed assembling of miniature electronic components. Silicon dies, fabricated on an optically transparent carrier are released using a laser pulse. This process has the potential to offer major advantages compared to existing transfer processes for future needs: high manufacturing speeds, contact-free, ability to handle very small and thin components. In this paper we present a thermal model, which describes the nonlinear behavior of silicon and carrier material under the influence of 1064 nm laser irradiation. The threshold intensities for die release and silicon damage will be explored as a function of operating laser beam characteristics. Experimental verification is presented to compare the simulated predictions and experimental results for the die release process.

A few years ago, it has been demonstrated that the use of hydrocarbons such as C₂H₄ or C₆H₁₂ as hydrogen donor allows realizing high-volume discharges in SF₆ based non-chain HF/DF gas mixture. However, for some uses, the specific output energy, the efficiency and, to a less extent, the optical quality of all these lasers remain insufficient. It appears now that the only way to increase these values is to use chain reaction. But chain reaction is known to be delicate to control, especially when working at high repetition rate. This paper will describe recent work directed towards a better understanding of the discharge mechanisms and an increase of the efficiency and of the specific output energy of HF/DF pulsed lasers by using chain reaction in discharge initiated repetitive and non-repetitive experiments. High volume discharge cells compatible with repetition rate have been realized. Discharge initiated repetitive chain reaction has been studied up to 10Hz with large gap. Efficiencies as high as 70% have been obtained in single pulse experiments. Computer modeling allows now predicting satisfactorily the performances of discharge-initiated chain reaction HF/DF lasers as a function of electric circuit characteristics and gas composition.

For high power laser applications like the "Laser Megajoule" facility under construction in France, laser-induced damage threshold (LIDT) in fused silica is a limitation. CEA has made efforts to improve LIDT at the wavelength of 351 nm. Polishing and post polishing processes have been optimized. Laser damage sites density was decreased by several orders of magnitude by combining different fabrication steps. In order to further enhance optical laser resistance and to remove damaged sites on full-size optics, several small-beam raster scanning techniques have been studied and developed to condition fused silica optics. To stop the growth of damage sites, a continuous CO₂ laser was used to re-melt them. Laser induced damage tests, performed on instrumented and automated facilities, are reported in order to check and illustrate the effectiveness of these treatments. Damage initiation studies as well as damage growth measurements are presented.

The aim of the current work is two-fold: First, the aim is to investigate the transition, for a number of metals, from a smooth ablation process to an explosive one. Secondly we aim to study the dependence of the ablation threshold in metals on the applied laser shot number. Ablation of polycrystalline metal samples was performed with multiple pulses from a femtosecond laser (Clark MXR, CPA2001). Morphological investigations of the laser processed areas were recorded using optical and scanning electron microscopies (SEM) and white light interferometry. The investigations have been carried out on sample matrices which were processed for a range of laser fluences and applied laser shots for four metals. Data obtained on ablation rates, ejected particle sizes and crater morphologies prove that ablation changes from a smooth to an explosive process at high fluences, as identified with changes in the material removal mechanisms. Threshold fluences were measured for both the smooth and explosive ablation processes. The ablation threshold fluence depends on the number of pulses applied to the same spot. It was found that the build up of laser induced mechanical stresses, due to the heating and cooling cycles of the samples between consecutive laser shots, plays an important role in the material modification process. It leads to the observed dependence of ablation threshold on shot number, which is described by a power law based on a mechanical fatigue model. The strength of the dependence is governed by the incubation coefficient, S, which has been measured for all materials studied. It is expected that the build up of laser energy or incubation leads to the accumulation of material defects and residual stresses which has the effect of lowering the energy required to cause ablation using a large number of incident laser shots.

Plasma emission or ablation from laser-irradiated targets shows very complicated properties. One novelty was observed at irradiation of neodymium glass laser pulses of ps duration and TW power if there was a very strong suppression of prepulses by a contrast ratio of about 10⁸ until 100 ps before the main pulse arrived. The emitted ion maximum energy was more than 50 times below the values observed in all the comparable numerous experiments. The other anomaly is that the number of the fast ions did not change when the laser intensity varied by a factor 30. This permitted a separation of the usual effects of self-focusing and permitted an analysis fully based on simplified plane geometry as a skin layer interaction mechanism. The consequence is that plasma blocks are accelerated by the nonlinear (ponderomotive) force with ion current densities above 10¹⁰ A/cm². This provides basically new aspects for laser fusion using uncompressed solid DT fuel and a new kind of x-ray laser process may be possible.

The laser ablation of fused and crystal silica and natural silicates induced by pulsed CO₂ laser irradiation (total pulse time of 35 μs, pulse increase time of 0,1 μs, pulse energy of 10 J) has been studied. By action of focused laser radiation at the surface of samples the appearance of erosion plume at the irradiated surface take place. For study of ablation regimes the frame image of laser induced plume by use of high speed photography method with 2 microsecond expose of each frame have been made. It has been observed the formation of two different type of laser plume during laser pulse action. First type plume represents a long narrow plume with the onset close to start of laser pulse. The maximal length of this plume is about of 20 millimeter. The second type of plume represents a conical plume with the onset, which is late from laser pulse start for a few microsecond. The first type plume expands in to laser beam direction. The second type plume expands normal to the surface. The velocity of laser plume particles by means of measurements of moment transferred into samples during laser pulse action has been measured. It has been obtained, that value of this velocity varies in region of 1-3•10³ m/s in dependence of laser fluency value. The appearance of first time plume have a threshold which equal to 0,15 kJ/cm² whereas the appearance of second type plume have not a such threshold and may take place at low laser fluency. We believe, that the first type plume connects with the selective ablation of Si_mO_n complexes whereas second type plume connects with the thermal heating caused by dissipation of laser energy in to system of low frequency acoustics phonons.

One of the technical issues of waveguide fabrication technique inside transparent materials using femtosecond laser has been an optical loss which may be caused by a nonuniformity of the modified volume. In this paper we report on the optical waveguides fabrication inside fused silica glasses using double pulse femtosecond lasers to solve this issue. We investigate writing conditions of optical waveguides with adjusting pulse intervals and relative fluence of the double pulses. The pulse separation time of the double pulses is varied from 500 fs to 200 ps. The better optical property of the optical waveguides under the conditions that the first pulse energy and the second subsequent pulse energy of the double pulse mode are 30 nJ and 160 nJ, respectively and pulse separation time is 3 ps. This optical loss is smaller than that of the waveguides fabricated using a single pulse femtosecond laser.

As distinct from numerous papers where the problem of the electron thermal conductivity limitation is considered to be a consequence of arising plasma turbulence this paper deals with a "classic mechanism" of limitations. It has been shown that the above-mentioned limitation follows from the condition of the plasma quasi neutrality conservation on the absorption area near the surface of a target irradiated by a laser pulse, where the electron density is critical for the given laser wave length. The thermal conductivity limitation which is discussed below complies with experimental data.

In the experiments on the CO₂-laser facility TIR with output pulse duration ~15 ns and pulse energy ~100 J high-current beams of ions with charge Z~20 ÷ 30 and energy up to ~1 MeV were obtained. High quality of spatial and temporal light beam characteristics as well as possibility to vary its parameters in accordance with required target irradiation conditions provide an opportunity for generation of ion beams with high charge and large number of particles. Results of measurements of ion energy spectra and ion fluxes for different expansion angles are presented. Technological and medical applications of such beams are discussed.

Silicon substrate is very important for integrated opto-electronic devices applications; because it is widely used the ULSI industries and allowing technically matured processing. However, the large refractive index of Si does not allow for an optical waveguide structure on it by direct growth. Nd:KGW waveguide laser is also a very promising device, which has not only a high stimulated emission cross-section as the laser crystal, but also a high 3rd nonlinear susceptibility. Here we will present our recent results of pulsed laser deposition (PLD) of Nd:KGW thin films on (100) Si substrate by introducing (100) CeO₂ buffer layer. The waveguide structure is achieved by the lower refractive index of CeO₂. It is well known that films containing alkali metal fabricated with single crystal targets have lower alkali metal concentrations than the stoichiometric target. One solution is the use of K-rich ceramic targets instead to prevent lack of the K during deposition. In this paper, we demonstrate the K compensation and high quality films growth from the viewpoints of crystallinity and optical properties by use of K-rich target. Moreover, we will investigate the required thickness of CeO₂ buffer layer and prove the validity of results using a numerical analysis.

This paper describes a new growth method of ZnO nano-rods. Firstly ZnO nanoparticles were synthesized in an oxygen and He background gas by laser ablation. These nanoparticles were used to deposit nano-structured-ZnO thin films. Under an optimized deposition conditions, ZnO nano-roods with a diameter of about 300 nm and 6 μm in length have been synthesized without any catalyst by nanoparticle assisted laser ablation deposition. The laser action was observed in the nano-rods under an optical excitation at 355 nm, indicating a high quality of the crystal.

The assessment of energy partition between air and solid propellant has been conducted using a TEA CO₂ laser. The experiments were performed by focusing output pulses of the laser (200 ns pulsewidth at 10.6 μm wavelength and ~10.6 J pulse energy) on aluminum targets mounted on a ballistic pendulum. Coupling coefficients and mass removal rates were determined as functions of air pressure, which varied from 1 atm to 3.5 mTorr. The data from both coupling coefficients and mass removal rates show that there is a sharp transition region ranging between 1.0 and 10 Torr. In this region the momentum imparted to the target via air breakdown appears comparable and, at higher pressures, dominating the momentum due to the breakdown on the target surface.

This paper presents the results of an experimental study to establish process parameters for repeatable, high quality ablated features in ferrous substrates using a Ti:sapphire femtosecond laser system. Initial trials with stainless steel substrates were conducted in ambient atmospheric conditions. Laser power and exposure parameters were varied, in addition to the angle of the substrate relative to the beam. Ablated holes were sectioned, and examined. Data was reduced according to the Taguchi/ANOVA method. The optimal process parameter set minimized the figures of merit for quality or accuracy of the ablated hole. In trials using pulsed ablations, high accuracy holes were associated with laser power greater than 600 mW, substrate angles of 30-45 degrees, and 1000 pulses. In the dwell experiments, high accuracy holes were achieved with a similar power level, and a 1-second dwell time. In contrast to the pulse results, a shallow substrate angle (30 degrees or less) yielded favorable results. In subsequent trials, kovar substrates were processed in a vacuum at constant fluence with a 1-second dwell time. A localized flow of nitrogen removed ablation products. Results were compared to those of the initial trial, leading to significant observations regarding the use of vacuum and secondary process gas.

Chemical lasers offer the highest powers necessary for many weapons applications, but require significant logistical support in the delivery of specialized fuels to the battlefield. In the Chemical Oxygen-Iodine Laser (COIL), which is the weapon aboard the Airborne Laser (ABL), gaseous chlorine and liquid basic hydrogen peroxide are used to generate the singlet oxygen energy reservoir. The goal of the current multi-university research program is to demonstrate an oxygen-iodine laser with electrical discharge production of singlet oxygen. Typically, oxygen discharges are limited to about 15% yield for singlet oxygen. The electron excitation cross-sections as a function of E/N are well established. However, the kinetics for electron and singlet oxygen interactions is considerably more difficult to study. Optical diagnostics for O₂(a, b), and O, have been applied to a double microwave discharge flow tube. By examining the difference in singlet oxygen kinetics between the two discharges in series, considerable information regarding the excited-state, excited-state interactions is obtained. Under certain discharge conditions, the O₂(a) concentration significantly increases outside of the discharge, even after thermal effects are accounted.

Femtosecond laser ablation occurs on timescales faster than the thermalization of the excited electrons and the lattice in solid materials. The ultrafast deposition of energy competes with the slower electron-phonon energy redistribution, raising the question of what is the optimal pulse duration for efficient deposition of energy while minimizing peripheral damage, and whether the shortest pulse is always the most efficient. We studied femtosecond laser ablation of silicon and several metals, varied the pulse duration while keeping all other parameters equal, and looked for optimal conditions. The main findings in our study are that at low fluences, not too high above the ablation threshold, the shortest pulses are the most efficient, whereas under high fluence conditions, well above the ablation threshold, longer pulses ablate more efficiently. In order to facilitate eventual direct, real time optimization, we developed a diagnostics tool for the monitoring of the ablation efficiency over a wide range of pulse durations. The intensity of the emission at atomic lines (i.e. the 289 nm line in Silicon, calibrated by plasma emission at other wavelengths) provides such information, while optical and AFM microscopy provide reliable information about the quality of ablated structures.

Energy requirements for near-Earth object (NEO) threat mitigation are addressed. Due to a large NEO mass range and the possibility of limited available time for orbit change, energy requirements can be large (~petajoules). To quantitatively determine energy requirements for a given momentum change use is made of the momentum coupling coefficient, C_M, that depends on the type of energy transfer, energy density, interaction time scale, and target material properties. Inhomogeneous and flawed NEO materials are empirically confronted through experimental methodologies that generate parameters on high energy density mechanical and radiative induced momentum coupling to (primarily) meteorite targets serving as near-Earth asteroid surrogates. Interactants include high speed (> 8 km/s) mechanical projectiles, high intensity (~ GW/cm²) infra-red laser radiation, and (~200 GW/cm²) soft X-ray radiation. Issues exists and are addressed regarding momentum coupling scaling from coupon sized (~mm²) to much larger (~m²) targets. Applications include high energy planetary and astrophysical momentum coupling dynamics.

When a femtosecond laser pulse is moderately focused inside a glass using an objective lens, the density of the irradiated region increases. Although this phenomena has become one of the key technique to fabricate various three dimensional devices, the mechanism has not been well understood. In this study, the initial step of refractive index change of the irradiated region was investigated using the time-resolved transient lens method with a time resolution of sub-picosecond. The oscillating signal intensity with several GHz was observed, and it was interpreted in terms of the density change due to the thermoelastic relaxation after the photoexcitation. The calculation of the thermoelastic relaxation of the ultrafast heated material surrounded by the solid material indicates that the density at the center of the heated region is reduced, and the acoustic wave is generated and propagated. The oscillation in the transient lens signal can be almost perfectly simulated using the density change from the thermoelastic calculation. The temporal profile of the transient lens signal will be a good method to monitor the time dependence of the refractive index change at the laser light focal region.

A low density medium like a gas is attractive for laser amplification due to its high breakdown threshold and scalability to very large volumes. Moreover, the non-linear index of refraction of a gas is of three orders of magnitude lower than for a solid medium that is particularly suitable for direct amplification, without pulse stretching, of high-power ultrashort pulses. Among all gas laser media, application of the photolytical XeF(C-A) laser for high energy amplification is very attractive for the development of ultra-high power laser systems up to the petawatt power level due to the XeF(C-A) broad amplification bandwidth (80 nm FWHM centered near 475 nm) and a rather high saturation fluence (~0.05 J.cm^-2), as well as a very low level of Amplified Spontaneous Emission. The paper presents the strategy of the LP3 laboratory to develop a high-contrast multiterawatt femtosecond laser chain based on a hybrid (solid/gas) technology, including a Ti:Sapphire oscillator generating 50 fs pulses at 950 nm, an Optical Parametric Chirped Pulse Amplification stage, a frequency converter, and a final high-energy amplification in the photolytical XeF(C-A) amplifier. Our approach is supported by first pilot experiments of femtosecond pulse amplification in a compact photolytical XeF(C-A) amplifier.

The collector mirror lifetime of a future extreme ultraviolet lithography light source system is an important development issue. Beside vacuum cleanliness and heat load, fast ions are especially critical in case of laser-produced plasmas causing quick degradation of the multilayer structure of near normal incidence collector mirrors. We are currently developing a light source system based on a laser-produced plasma for next generation lithography. The plasma target is a liquid xenon jet. Energy distributions of fast xenon ions from the laser-produced plasma have been measured by time-of-flight (TOF) experiments. Two low repetition rate Nd:YAG lasers at 1064 nm with pulse lengths of 8 ns and 150 ps have been used for plasma generation and mean ion energies of 3 keV and 7 keV have been measured, respectively. In addition, the effects of fast ions on Mo/Si multilayer mirrors have been studied using a Xe ion gun. Ion sputtering of the multilayer structure is the main damage mechanism but boundary layer mixing and increased surface roughness are also observed.

Chemical generation of atomic iodine for a Chemical Oxygen-Iodine Laser (COIL) was investigated experimentally. This all-gas process includes atomic fluorine as an intermediate species. In the two-step reaction mechanism, F atoms are produced in reaction of molecular fluorine with NO and react further with hydrogen iodide to iodine atoms. The efficiency of this process was studied in dependence on mixing conditions, flow rate of reacting gases and pressure in the reactor. The maximum concentration of atomic iodine was obtained at approximately equimolar ratio of reacting gases (F₂, NO and HI), which agrees with the stoichiometry of the production reactions. A shortage of any of the reacting gases limits the rate of atomic iodine formation. A considerable excess of F₂ against NO at a simultaneous deficit of HI had a most detrimental effect on atomic iodine production. Sufficiently high concentrations of atomic iodine (5 to 8 x 10¹⁵ cm^-3) can be achieved by this method even at pressure 4 - 9 kPa that enable to inject the gas with iodine atoms into the singlet oxygen flow upstream the nozzle throat in the chemical oxygen-iodine laser.

It has been shown that the use of gas diodes with cathode electric field enhancement and voltage pulses having a short leading edge allow to form high-current subnanosecond electron beams. An electron beam appears at voltage pulse leading edge with duration at FWHM not more than 0.3 ns. On the beam current termination the discharge is usually continued in a quasi-stationary mode having a volume character. With a diode filled in with air under atmospheric pressure, beam current amplitude over ~240 A at a pulse duration at FWHM of ~0.2 ns and current density of ~40 A/cm² was obtained. It has been also shown that at a small gas diode inductance the subnanosecond electron beams are formed in various gases in a wide pressure range (up to 6 atm in helium, and up to 4 atm in nitrogen). It has been established that with the new method an electron beam is formed due to critical field reached between an anode and plasma propagating from a cathode.

The experimental results of the studies on process of radiation interaction of the pulsed CO₂ - laser with polytetrafluoroethylene (PTFE) are presented. A dependence of PTFE transmission factor at λ = 10.6 μm versus temperature in the range -90 - 300°C has been obtained.

In order to investigate the ultrafast dynamics of free carriers generated in bulk dielectrics by intense femtosecond laser pulses we have designed a setup for ultrafast time-resolved imaging Mach-Zehnder interferometry. The application of the 2D-Fourier-transform technique allows us to accurately reconstruct the actual laser-induced phase shifts and transmission changes for the probe pulses, which provide the properties of free carriers. Interferometric measurements in high-purity fused silica clearly demonstrate that the dominant ionization mechanism for intensities below 10 TW/cm² is multiphoton ionization.

The small signal gain of a small-scale HF overtone laser was measured using a sub-Doppler tunable diode laser system. The spatially resolved, two-dimensional small signal gain maps that were generated show a highly inhomogeneous gain medium indicating the dominant role played by mixing of the H₂ and F streams in HF laser performance. The measured gain data were analyzed with the aid of a two-dimensional computational fluid dynamics model. The results show that reactant mixing mechanisms have a large effect on the gain averaged over a vertical profile while kinetic rate mechanisms, including reaction rate constants and reactant concentration, have a greater effect on the maximum system gain.

The activity of development a COIL with high potential recovered pressure, high gain and efficiency is described. Two nozzle banks with conical supersonic nozzles for the driver nitrogen but with different nozzle arrangements have been developed for generation of the gain flow of chemical oxygen-iodine laser. The nozzle banks were supplied by oxygen flow from the cross-flow singlet oxygen generator with filament-guided jets. Results of aerodynamic tests, visualization of flows by laser induced fluorescence, scanning of the excited iodine atoms distribution and laser power extraction are presented. The efficient penetration of the driver buffer flow into the gain flow was observed at distances less than 100 mm from the nozzle banks. The total power exceeding 1 kW with chemical efficiency more than 24% was obtained in 5 cm gain length COIL without helium dilution. The lasing was observed for both nozzle banks at total mirror transmission more than 10%.

Femtosecond laser ablation of silicon in air was studied and compared with nanosecond laser ablation at ultraviolet wavelength (266 nm). Laser ablation efficiency was studied by measuring crater depth as a function of pulse number. For the same number of laser pulses, the fs-ablated crater was about two times deeper than the ns-crater. The temperature and electron number density of the pulsed laser-induced plasma were determined from spectroscopic measurements. The electron number density and temperature of fs-pulse plasmas decreased faster than ns-pulse plasmas due to different energy deposition mechanisms. Images of the laser-induced plasma were obtained with femtosecond time-resolved laser shadowgraph imaging. Plasma expansion in both the perpendicular and the lateral directions to the laser beam were compared for femtosecond and nanosecond laser ablation.

We propose an automobile driven by piston motion, which is driven by water-laser coupling. The automobile can load a solar-pumped fiber laser or can be driven by ground-based lasers. The vehicle is much useful for the use in other planet in which usual combustion engine cannot be used. The piston is in a closed system and then the water will not be exhausted into vacuum. In the preliminary experiment, we succeeded to drive the cylindrical piston of 0.2g (6mm in diameter) on top of water placed inside the acrylic pipe of 8 mm in inner diameter and the laser is incident from the bottom and focused onto the upper part of water by the lens (f=8mm) attached to the bottom edge.

Extreme ultraviolet (EUV) emission from laser produced tin plasma was investigated for 1064, 532 and 266 nm laser wavelengths. The EUV conversion with tin target tends to be high for shorter laser wavelength and is optimized at 4-5x10¹⁰ W/cm² for 1064 and 532 nm. The EUV emission exhibits laser wavelength dependence in terms of angular distribution and structures of emission spectra. It is found that spectra for 532 nm and 266 nm showed spectral dips at around 13.5 nm and these dips are well replicated in computer simulations. Both the angular distribution together with the spectral dips may suggest existence of opaque plasmas surrounding the EUV emission region.

We have investigated the energy and mass distribution of particles ejected from metals and semiconductors after irradiation with intense ultra-short laser radiation. Neutral atoms and clusters have been investigated. In many cases, clearly fast particles in the eV range and slow thermal particles can be identified. The influence of the laser pulse width on the energy distribution as well as the ion to neutral ratio have been investigated.

Analysis of processes affecting transient optical absorption and photogeneration of electron-hole plasma in silicon pumped by an intense NIR or visible femtosecond laser pulse has been performed taking into account the most important electron-photon, electron-electron and electron-phonon interactions and, as a result, two main regimes of such laser-matter interaction have been revealed. The first regime is concerned with indirect interband optical absorption in Si, enhanced by a coherent shrinkage of its smallest indirect bandgap due to dynamic Franz-Keldysh effect (DFKE). The second regime takes place due to the critical renormalization of the Si direct bandgap along Λ-axis of its first Brillouin zone because of DFKE and the deformation potential electron-phonon interaction and occurs as intense direct single-photon excitation of electrons into one of the quadruplet of equivalent Λ-valleys in the lowest conduction band, which is split down due to the electron-phonon interaction.

A model experimental "thin variable thickness transparent liquid layer on opaque (absorbing) solid substrate" geometry has been chosen to study explosive boiling and lift-off of a pre-deposited 2-propanol (isopropanol, IPA) layer on a crystalline Si substrate heated by a nanosecond KrF excimer laser using contact photoacoustic and optical plume transmission techniques. The threshold-like transition from the low-amplitude (sub-MPa) bipolar to the intense (near GPa) unipolar temporal shape of acoustic transients has been observed above the ablation threshold of 0.17 J/cm² ("universal" for micron-thick IPA layers used) due to sub-nanosecond explosive near-critical expansion and boiling in the nanometer-thick liquid IPA sub-layer near the film/substrate interface heated by conduction from the Si substrate. This pressure build-up exceeding many times the critical pressure of 2-propanol (4.8 MPa) exerted a reactive force on the cooler liquid overlay of the IPA layer and accelerated it to lift-off (ablative plume) velocities from several m/s to several tens m/s depending on the film thickness, while the initial expansion velocity of the superheated IPA sub-layer was about 1 km/s. In a good agreement with experimental data, calculations of the IPA/substrate interface temperatures versus laser fluence have shown near-critical state of the IPA sub-layer near the ablation threshold. These data allow testing the general sub-surface explosive boiling mechanism, characteristic for pulsed laser ablation of both opaque and weakly-absorbing materials.

In all excimer laser irradiation data, the induced laser ablation process is constantly referred to an energy density (fluence) and, eventually, to a fluence threshold that sets the onset of matter emission. In the work presented here, ablation experiments have been performed on a specific class of ceramic (sialon) with two excimer sources A and B that differ in their respective time-profiles, with a full pulse width of either (A) 23 or (B) 44 ns. Working with these sources at identical fluences and number of pulses, products of irradiation may differ drastically. In particular, it is observed that an irreversible surface decomposition may be achieved with laser A at a given threshold fluence, not with laser B that requires a higher fluence. Results are analyzed and interpreted taking into account the time dependence of the laser emission and its consequences in terms of photon-electron interactions at the material surface. Differing strongly from existing moels of ablation, a two-step model is presented that incorporates (1) creation of a free-electron gas at the material surface and (2) its subsequent photoemission giving rise to surface ionization and structural instability. Results are discussed in the light of that model. In particular, a distinct advantage is given to short pulse excimer sources in their ability to modify surface properties at lesser fluences and with reduced heat generation, as compared to longer pulse sources.

The studies of laser ablation have lead to a new theory of nuclei, endothermic nuclei generation and quark-gluon plasmas. The surface of ablated plasma expanding into vacuum after high power laser irradiation of targets, contains an electric double layer having the thickness of the Debye length. This led to the discovery of surface tension of plasmas and to the internal dynamic electric fields in all inhomogeneous plasmas. The surface causes stabilization by short length surface waves smoothing the expanding plasma plume. Generalizing this to the degenerate electrons in a metal with the Fermi energy instead of the temperature, resulted in the surface tension of metals in agreement with measurements. Taking then the Fermi energy in the Debye length for nucleons results in a theory of nuclei with stable confinement of protons and neutrons just at the well known nuclear density, and in the Debye length equal to Hofstadter's decay of the nuclear surface. Increasing the nuclear density by a factor of 6 leads to the change of the Fermi energy into its relativistic branch where no surface energy is possible and the particle mass is not defined, permitting the quark-gluon plasma. Expansion of this higher density at the big band or in a supernova results in nucleation and element generation. The Boltzmann equilibrium permits the synthesis of nuclei even in the endothermic range limited to about uranium.

Radio frequency (RF)-excitation of carbon monoxide (CO) in a supersonic cavity with only a 10 cm gain length has yielded an observed fundamental band (Δv=1) multi-line lasing output power of 2.1 kW utilizing a one-pass resonator, with an electrical efficiency of 21%. More importantly, this work generated 50 W of overtone multi-line lasing around 2.7 micron. This was the first time lasing on CO overtone bands (Δv=2) had been demonstrated with a RF-pumped supersonic system.

For the first time, we have measured the momentum coupling coefficient and plasma expansion velocity (specific impulse) in the femtosecond region, over a laser intensity range from ablation threshold to thirty times threshold. These measurements extend the laser pulsewidth three orders of magnitude relative to previous reports. We studied several pure metals and three organic compounds as targets. The organic compounds were exothermic polymers specifically developed for the micro-laser plasma thruster, and two of these used "tuned absorbers" rather than carbon particles for the laser absorption function. The metals ranged from Li to W in atomic weight. We measured time of flight profiles for ions and found dramatic two-temperature distributions for some conditions. Specific impulse reached record values for this type of measurement and ablation efficiency was near 100%.

The scaling of the laser fluence for dielectric breakdown with respect to pulse duration and material bandgap was investigated in the sub-ps regime using various oxide films (TiO₂, Ta₂O₅, HfO₂, Al₂O₃, and SiO₂). A phenomenological model attributes the pulse duration dependence to the interplay of multiphoton ionization, impact ionization, and sub-ps electron decay out of the conduction band. The observed linear scaling of the breakdown fluence with bandgap, which is nearly independent of the pulse duration, can be explained within the framework of our model by invoking the bandgap dependence of the multi-photon absorption coefficient from Keldysh photoionization theory.

A spherical particle can be used as a lens for focusing laser radiation. It has potential applications in high-density data storage and high-resolution optical lithography for nano-device fabrication.