The strength of empires and civilizations has often depended on novel forms of transportation: the Viking long boat, the Roman road, Iberian galleons, French and British steam ships, Indian trains, the car of the early twentieth century, the plane of the middle and the rocket of late. But Space has now come up against a barrier: the enormous and barely affordable expense of putting things into orbit and the unaffordable energy required to travel to the stars. The recent advent of very energetic lasers may reduce the cost. The pioneering ideas of the mid sixties appear less fanciful. Laser space propulsion is about to become such an important topic that its scientific origin and engineering roots need to be investigated. This is by no means an exhaustive survey. We review here the laser propulsion work of four eminent experts: Eugen Saenger, George Marx, Wolfgang Moeckel and Arthur Kantrowitz.

Laser-induced material processing is reviewed with special emphasis on recent achievements mainly obtained by the Linz group. Among those are investigations using optical fiber tips for nanoscale photophysical etching, laser-induced ablation using self-assembled microspheres, the pulse-laser deposition of thin films of high-temperature superconductors (HTS) and polytetrafluoroethylene (PTFE), and the modification and cleaning of surfaces.

At the Laser Zentrum Hannover investigations of possibilities to use femtosecond laser pulses for direct ablative writing and microstructuring of solid materials have been started in 1995. Since then considerable progress in understanding and in the application of different femtosecond technologies has been obtained. At present, we are able to produce high quality microstructuring and large area patterning of solids with structure sizes between one and ten micrometers. By using tightly focused femtosecond pulses it is possible to produce even sub-micrometer structures. In this paper we pursue the goal to find and characterize the limits of femtosecond laser micromachining. Detailed investigations of possibilities to use femtosecond lasers for the sub-wavelength microstructuring of metals and for fabrication of periodic structures in transparent materials with the scale length of the order of several hundreds nanometers are reported.

The US Air Force Airborne Laser (ABL) is an airborne, megawatt-class laser system with a state-of-the-art atmospheric compensation system to destroy enemy ballistic missiles at long ranges. This system will provide both deterrence and defense against the use of such weapons during conflicts. This paper provides an overview of the ABL weapon system including: the notional operational concept, the development approach and schedule, the overall aircraft configuration, the technologies being incorporated in the ABL, and the risk reduction approach being utilized to ensure program success.

Excimer laser polymer ablation has been an active field of research and development for some twenty years now. We briefly review basic mechanistic aspects of the interaction, practical considerations related to polymer processing by ablation and applications in micromachining.

The electric-discharge-excited carbon monoxide laser is one of the most efficient laser sources known that is scalable to very high continuous wave powers. We review work at Ohio State where such lasers are used to excite flowing molecular gas plasmas, in mixtures of CO and other diatomic gases, including air. These plasmas are stable, diffuse, and can be operated at high gas pressures and low gas kinetic temperature. They are being employed for various plasma chemistry applications. Recent results are presented in which such an optically pumped plasma reactor is used to synthesize single-walled carbon nanotubes, which show surprising order and alignment.

Time resolved studies using femtosecond laser pulses at 800 nm illuminate the distinctions in the dynamics of ultrafast processing of dielectrics compared to semi-conductors and metals. Dielectric materials are strongly charged at the surface on the sub-ps time scale and undergo an impulsive Coulomb explosion prior to thermal ablation. Provided the laser pulse width remains in the ps or sub-ps time domain this effect can be exploited for processing. Otherwise, the high localization of energy accompanied by ultrafast laser micro structuring is of great advantage also for high quality processing of thin metallic or semi-conductive layers, where the surface charge is effectively quenched.

The ablation characteristics of various polymers were studied at low and high fluences. The polymers can be divided into three groups, i.e. polymers containing triazene groups, designed ester groups, and reference polymers, such as polyimide. The polymers containing the photochemically most active group (triazene) exhibit the lowest threshold of ablation (as low as 25 mJ cm^-2) and the highest etch rates (e.g. 250 nm/pulse at 100 mJ cm^-2), followed by the designed polyesters and then polyimide. Neither the linear nor the effective absorption coefficients reveal a clear influence on the ablation characteristics. The different behavior of polyimide might be explained by a pronounced thermal part in the ablation mechanism. The laser-induced decomposition of the designed polymers was studied by nanosecond interferometry and shadowgraphy. The etching of the triazene polymer starts and ends with a laser pulse, clearly indicating photochemical etching. Shadowgraphy reveals mainly gaseous products and a pronounced shockwave in air. The designed polymers were tested for applications ranging from microoptical elements to polymer fuel for laser plasma thrusters.

Ultrafast time resolved microscopy of femtosecond laser irradiated surfaces reveals a universal feature of the ablating surface on nanosecond time scale. All investigated materials show rings in the ablation zone, which were identified as an interference pattern (Newton fringes). Optically sharp surfaces occur during expansion of the heated material as a result of anomalous hydrodynamic expansion effects. Experimentally, the rings are observed within a certain fluence range which strongly depends on material parameters. The lower limit of this fluence range is the ablation threshold. We predict a fluence ratio between the upper and the lower fluence limit approximately equal to the ratio of critical temperature to boiling temperature at normal pressure. This estimate is experimentally confirmed on different materials (Si, graphite, Au, Al).

High quality thin films (100nm to several 1000nm) of many complex material systems such as the high temperature superconductor YBCO, have been deposited using pulsed laser ablation. Long lengths of high quality YBCO on metallic conductors are needed to meet industrial and government requirements. Although, pulsed laser deposition (PLD) grows the best YBCO films on meter lengths of metallic conductors, it has not been proven to be a consistent manufacturing process. PLD is simple in concept but has quite complicated plume and growth dynamics which are not well understood. In this study we use in-situ time-resolved mesurements of collision-driven plume emissions to characterize critical deposition parameters and to develop a computational model which includes these dynamics in a reacting PLD plume.

Presently, from the world data available on interaction of laser radiation with metal and dielectric surfaces and development of experimental diagnostic techniques by itself it is possible to raise a reverse question, namely, restoration of laser radiation energy spatial distribution through surface imprint. With this in mind, we have made the detailed morphology of imprint of a pulse HF-laser interaction with carbon steel surface through atomic force microscope. Interaction of the radiation of a relatively short pulse of ArXe-laser ((tau) _½equals400 ns, (lambda) equals1,73 micrometers , Q ~ 20 J/cm+2)) with carbon steel surface of 40X (4140 (USA)) type besides the surface layer hardening leaded to decrease of steel hardness at below original value on depth of about 10 - 12 micrometers . This effect can be related to occurrence of deformation and thermal residual stresses in the subsurface layer. At multiple-pulse interaction (~500 pulses) of UV-laser focused radiation ((lambda) equals0,222 or 0,308 micrometers , (tau) _½equals 12 or 20 ns) with the steel 40X (4140 (USA)) surface a distinct interference imprint of laser beam is formed after diffraction at outer diaphragm being determined by its form.

The present paper deals with the impact of pulsed laser radiation on dielectric and semi-conducting materials. Energy trans-fer leads to fast heating and thermal ablation. Mechanical stresses additionally cause deteriorations, cracks, fragmentation or perforation. These processes develop quasi-explosively even at low energy levels. Laser effects are discussed using microsecond(s) - to ps- pulses, acting both on optically passive and active materials (optical sensors). Evaluations of plasma-sustained en-ergy transfer by the impact of ns-pulses in comparison to ps-pulses are included as well. In the medium energy range by contrast, target effects are considered which require three to four orders of magnitude higher energies per pulse and corre-spondingly higher average powers which in the burst mode are determined by the repetition rate. The repetitively pulsed CO₂-laser at ISL provides energies up to 150 J, repetition rates up to100 pps, an average power of 15 kW corresponding to peak power values of 75 MW for 2 microsecond(s) pulses. This laser provides a valuable tool, particularly suited for large area out-of-band target studies. Thermo-mechanical processes, as experimentally observed are discussed and compared with results of numerical simulation. Transparency changes of optics due to ablation as quantitatively measured by the modulation trans-fer function are further included in the discussions.

Laser ablation of transparent materials is induced by non- linear absorption and some laser-induced damages are introduced in the bulk as well as on the surface. This process is used in laser marking and other applications such as refractive index modification of optical materials and 3- D data storage. We have observed the laser ablation dynamics in inside of bulk transparent materials by nanosecond time- resolved imaging technique. Output of fundamental radiation (1064nm) from a Q-switched Nd:YAG laser was focused at the inside of bulk PMMA and soda glass. Second harmonic radiation (532nm) from the same laser was used as illuminating light and images were taken by a CCD camera with a band-pass filter at 532 nm. Series of images were taken at different intervals between the fundamental and the second harmonic light, which was controlled by the optical delay line. In observation at longer intervals than 50ns, another laser was used as illuminating source. When the laser was focused at inside of the bulk PMMA, damages occurred simultaneously at several independent points without the ablation at the surface. They located along laser incident axis. Propagation of shock waves, which started from these points, was clearly observed in the bulk. In the glass, absorbing point in the bulk formed a continuous line and its end-point moved from inside outward to the surface along the laser beam. Laser induced damages (cracks) continued to develop until some microseconds after laser pulse in PMMA.

The excimer laser nitriding and carburizing process reported is developed to enhance the mechanical and chemical properties of aluminum alloys. An excimer laser beam is focused onto the alloy surface in a cell containing 1 bar nitrogen or propylene gas. Vapor plasma expands from the surface then dissociates and ionizes ambient gas. Nitrogen or carbon atoms from plasma in contact with the surface penetrate in depth due to plasma recoil action onto the target surface heated by the plasma. It is thus necessary to work with a sufficient laser fluence to create the plasma, but this fluence must be limited to prevent laser-induced surface roughness. The nitrogen or carbon concentration profiles are determined from nuclear analysis. Crystalline quality is evidenced by X Ray Diffraction (XRD) technique. Transmission Electron Microscopy (TEM) gives the in-depth microstructure. Fretting coefficient measurements exhibit a satisfying behavior for some experimental conditions. The polycrystalline nitride or carbide layer obtained is several micrometers thick and composed of pure A1N or Al₄C₃ (columnar microstructure) top layer standing on a diffusion layer.

A significant improvement in the quality of ultrafast laser micromachining of brittle dielectrics is demonstrated by using temporally shaped pulse trains with sub-ps separation, synchronized with the material specific relaxation times. The individual material response to laser radiation depends on the efficiency of electron generation and on the ability to release the energy into the lattice. Loss mechanisms in the electron population, surface charging, as well as the strength of the electron-phonon interactions control the effectiveness of the energy deposition into the lattice. Knowledge of the response times of materials establishes a guideline for using temporally shaped pulses or pulse trains in order to optimize the structuring process with respect to the efficiency of material removal and reduction of the residual damage. The sequential energy delivery induces a material softening during the initial steps of excitation changing the energy coupling for the subsequent steps. This leads to lower stress, cleaner structures, and provides a material-dependent optimization process.

Laser annealing, laser surface processing and laser lift-off procedure are reviewed as applied to semiconductor nitride- based structures (GaN films and InGaN/GaN optoelectronic device structures grown on sapphire substrates). Data on laser ablation of composite GaN/sapphire material are reviewed with more detailed consideration of the ablation rate under subpicosecond laser pulses and under long-pulse irradiation in the IR range (wavelengths of 5.0-5.8 and 9.6 micrometers ).

The CIP method is used to calculate macroscopic plume expansion combined with the Zeldovich-Raiser theory for cluster formation process such as nucleation and growth. The effect of background gas and latent heat is examined in one-dimensional case. The latent heats keep the plume temperature at 2500K for a long period and this explains the delayed photoluminescence. Two contradicting experiments on the size dependence on ambient pressure are clearly explained and are attributed to the difference of laser energy. In two dimensional simulation, mushroom-like plume shape is replicated consistent with experimental results.

Laser-induced surface structuring of silicon was studied using fluences close to the metering threshold and He gas background atmosphere. The effects of an initial surface microstructured region and of light polarization on the evolution of the surface topography were investigated. The microstructured surface topology consisted of an array of microholes surround by microcones of 2-3 micrometers tip-diameter and over 20 micrometers high. Pulsed laser irradiation of laser- microstructured silicon induces the formation of nanostructures. Nanocolumns having a diameter of 100 to 200 nm and reaching a height of up to 3 micrometers upon cumulative laser pulses grow on top of every microcone. The mechanisms of nanocolumn origin and growth are analyzed. Periodic undulations approximately 10 nm-high are formed when flat silicon substrates are irradiated with polarized laser light. These periodic structures have a wavelength that is a function of the light wavelength and the angle of incidence of the laser beam. At a slightly higher laser fluence, approximately 30 nm-diameter nanoparticles form on the surface of laser irradiated flat silicon specimens. Linear arrays of silicon nanoparticles with fairly uniform size that extend up to a millimeter are formed if the irradiation is performed using polarized light or the irradiated area contains a microstructured region. These nanostructures are analyzed within the frame of the theory of laser induced surface periodic structures.

We use short-pulse high-power lasers to selectively modify the structure of nanolaminates and nanocrystals. It is demonstrated that femtosecond pulses can achieve superior results for microscopic thin film removal. Laser pulses can also be used to modify the crystal structure of thin films. It is also demonstrated that coherent laser excitation promotes a selective modification of nanocrystals, resulting in the change of size, shape and crystal structure of nanocrystals.

We present studies of the consequences of simultaneous exposure of inorganic single crystals to radiation and water. The first case consists of a biomineral namely CaHPO ₄ 2H₂O (brushite) which is a wide band gap, hydrated inorganic single crystal. We examine the laser induced ion and neutral emissions accompanying 248-nm excimer laser radiation. Both types of emission are several orders of magnitude higher following exposure to 2 keV electrons at current densities of 200 μA/cm 2 and doses of 10²-10³ mC/cm². We show the that the enhancements in emission are strongly correlated with e-beam induced morphology changes (including recrystallization) on this unusual surface. We then examine similar effects on dry crystals such as NaCl and NaNO₃ which are exposed to 10^-5 Pa partial pressures of H₂O. Again dramatic enhancements in radiation induced emissions are exhibited along with the generation of unique morphological structures with nanometer scale dimensions.

For 10 previous years dry laser cleaning has been analyzed in the frame of 1D model with homogeneous surface heating. This model gave qualitative description of the process and was sufficient for initial studies. Nevertheless further examinations show that 1D model is in one-two order magnitudes discrepancy with experiment. The problem is that the particle on the surface produces non-homogeneous distribution of laser intensity. For example, a small transparent particle can work as a near-field lens. This produces nonstationary 3D distribution of temperature and nonstationary 3D thermal deformations of the surface. 3D model is qualitatively different from the 1D model (the latest does not permit the inward motion of the surface). In some region of parameters 3D model predicts a result close to the experimental one (for small particles, typically smaller than 1 micrometers ). With higher particle size intensity under the surface becomes so strong that the particle is removed by the flux of evaporated material.

Laser microprocessing has been extensively studies with applications in microelectronics, data storage and photonics. In addition to the fundamental aspects of laser materials interactions, we have investigated various applications of laser microprocessing in different areas. Laser cleaning has been studies systematically both theoretically and experimentally for dry surface cleaning and steam surface cleaning. This technology has been applied for cleaning magnetic head, magnetic sliders, suspension, laser mold cleaning and laser deflash for IC packages. Laser texturing and related processes such as laser bumping, laser tagging have been studied for magnetic recording applications. The other laser works include real-time monitoring of laser surface processing, laser-induced controllable periodic structures, laser nanopatterning by scanning probe microscope tip-enhanced laser irradiation. The further prospects of using laser microprocessing for applications in formation of ultrashallow (less than 50 nm) pn junction for next-generation MOS devices, laser generation of Si nanoparticles for quantum-dot flash memory and light emission devices are addressed.

In the present work, the laser ultrasonics technique has been applied as diagnostic of the laser induced decohesion of coating. A modeling system consisting in a 304 stainless steel coated by a plasma sprayed layer was used to describe the basic measurements. These acoustic measurements were performed using an interferometric probe. It is concluded that this contactless technique can be used to follow the cleaning of oxidized materials.

Hybrid laser processing for precision microfabrication of glass materials, in which the interaction of a conventional pulsed laser beam and another medium on the material surface leads to effective ablation and modification, is reviewed. The main role of the medium is to produce strong absorption of the nanosecond laser beam by the materials. Simultaneous irradiation of the vacuum ultraviolet (VUV)laser beam, which possesses extremely small laser fluence, with the ultraviolet (UV) laser greatly improves the ablation quality and modification efficiency for fused (VUV-UV multiwavelength excitation processing). Metal plasma generated by the laser beam effectively for assists high- quality ablation of transparent materials, resulting in microstructuring, cutting, color marking, printing and selective metallization of glass materials (laser-induced plasma-assisted ablation (LIPAA)). The detailed discussion described in this paper includes the ablation mechanism of hybrid laser processing.

Femtosecond and nanosecond laser ablation and delamination of anodic oxide layers on an aluminium alloy were investigated. Laser wavelengths of 800 nm (125 fs pulse duration) and 532 nm (7 ns), respectively, and two oxide layers with thicknesses of 70 micrometers (opaque) and 30 micrometers (transparent) were considered. Laser-induced shock waves measured by means of a microphone provided an in-situ diagnostic tool for the monitoring of the coating removal process. The transparent anodic oxides showed contrasting ablation mechanisms in the nanosecond and femtosecond pulse duration regime. Nanosecond pulses led to spallation, whereas femtosecond treatment resulted in ablation.

Pulsed laser deposition of complex, chemically sensitive polymers using tunable, picosecond infrared laser excitation has shown great promise for producing films of these materials appropriate for a wide variety of sensor and coating applications. Fourier-transform infrared spectra of the bulk starting polymers and those of the deposited thin films are nearly identical, verifying that the short-range order and chemical functionality of the polymers are preserved during the process. Gel permeation chromatography and mass spectrometry have been used to characterize the polydispersity of the mass distribution; here the results are mixed, with the mass distributions of some poly-mers being preserved while others show significant bond scission. Most recently, we have demonstrated that it is possible to coat cantilever structures with the polymer SFXA; the deposited polymer responds as desired when 'challenged' by appropriate chemicals.

Nanosecond-interferometry and shadowgraphy is used to observe the dynamic behavior of the etching process during and after the irradiation pulse. Commercially available polymers exhibit quite often poor laser ablation properties for irradiation wavelengths >=248nm. At these wavelengths the absorption is due to the quite photostable aromatic groups. A photolabile triazene polymer was selected to compare the influence of a photolabile group on the laser ablation process. The photochemical active triazene reveals a strong absorption band at 332 nm and is responsible for the observed high etch rates and the low threshold for 308 nm irradiation. The absorption coefficients at 193 nm and at 308 nm are comparable, allowing to study the influence of the different absorption sites by ns-interferometry and shadowgraphy measures. The etching of the triazene polymer starts and ends with the laser beam. No surface swelling, which is assigned to photothermal ablation, is detected for fluences above the threshold of the ablation. The expansion of the laser ablation induced shockwave was measured for the photolabile triazene polymer and the photostable polyimide. The speed of the shockwave increases with fluence and is higher for irradiation with 193 nm than for 308 nm. A shockwave with equal or higher velocity is observed for the triazene polymer than for the polyimide.

The technology of laser sintering is introduced. Based on the researching of laser heating property, power thermal physics parameters, as well as laser sintering process, a numerical model of the temperature field during length- alterable line-scanning laser sintering of polymer-coated metal powder has been constructed. The calculations of numerical model have been finished by the using of Finite Element Method (FEM). The temperature field during laser sintering was measured to verify the calculated results. Experimental results show well conformity between them.

The study examines chemical and structural modifications effected in the UV ablation of polymers. For the study of the chemical processes, aromatic photosensitive compounds with well-defined photochemistry are employed as dopants and their reactivity is examined as a function of laser parameters (fluence, wavelength and laser pulse width). A 'pump-probe' scheme based on laser-induced fluorescence is employed for monitoring photoproduct formation in the polymeric substrate following UV irradiation. Ablation is shown to result in a change of the photolysis degree of the dopant and in the efficient formation of bi-aryl compounds, indicative of a high species mobility. Furthermore, kinetics of photoproduct formation in the ablative regime is shown to differ distinctly from that in the irradiation at low laser fluences. However, the quantitative extent of these changes is critically affected by the absorptivity of the substrate at the irradiation wavelength. On the other hand, structural modifications induced in polymer films are probed via holographic interferometry. Deformations are shown to be induced at distances far away (approximately 2-3 cm) from the irradiation spot. The implications for UV laser material processing schemes are briefly discussed.

Two new laser mask projection techniques Synchronized Image Scanning (SIS) and Bow Tie Scanning (BTS) have been developed for the efficient fabrication of dense arrays of repeating 3D microstructures on large area substrates. Details of these techniques are given and examples of key industrial applications are shown.

Titanium carbide (TiC) thin films have very desirable properties that make them ideally suited for applications to MEMS devices. TiC has been one of the preferred coatings for improving the performance of macroscopic moving mechanical components due to its established wear-resistance. Pulsed laser deposition (PLD) has been an excellent method for the deposition of TiC because unlike any other deposition process for TiC, PLD offers the capability of producing high-quality films even at room-temperature. Using a patented PLD technique, especially designed and optimized for the deposition of high-hardness, particulate-free films, we have deposited TiC coatings on a variety of surfaces, including Si and several MEMS compatible film-layers. Our results have demonstrated that TiC coatings also offer a high wear-resistance to Si surfaces. This, together with the excellent chemical and mechanical properties, and thermal stability of our PLD TiC coatings, has led to our application of TiC to moving MEMS devices fabricated from Si. The fabrication of Si MEMS devices is quite well established, however, the reliability and performance of MEMS devices such as microgears, micromotors and microactuators, which involve sliding Si surfaces, remain an open question. The short functional life of these devices is attributed to the excessive wear rate of Si induced by high friction. The work presented here describes a hybrid process whereby PLD is used in conjunction with the Aerospace MEMS fabrication process (AIMMOS) for inserting TiC coatings into critical interfaces in MEMS devices that would involve sliding contact between two Si surfaces. The PLD of TiC, the spectroscopy of the plume, and the properties and applications of PLD-TiC for MEMS will be discussed.

Pulsed laser ablation is a well-known technique used for thin film deposition, extending from oxydes to hard and wear resistant Diamond-Line Carbon (DLC) films. Most of the previous studies devoted to DLC thin films elaboration have used pulsed duration in the nanosecond range. The present study concerns femtosecond (10^-15 s range) laser ablation of a graphite target for the elaboration of Diamond-Like Carbon. Compared to conventional nanosecond laser ablation, femtosecond laser pulses allow the production of high energy (up to a few keV) ions in the plasma, which may strongly affect the structure and properties of the deposited films. DLC films have been deposited under vacuum onto (100) p-type silicon substrates at room temperature, by ablating graphite targets with femtosecond laser pulses. The nature and properties of the film have been characterized by various techniques, including Raman, XPS and AFM. Discussion will be focused on the comparison between present results obtained using femtosecond laser pulses, with previously published results related to DLC films deposited using nanosecond laser pulses. Especially, Raman spectra of DLC films obtained by nanosecond laser ablation always show the two well-known D and G bands (located respectively at around 1350 cm^-1 and 1550 cm^-1), whereas some DLC films obtained when using femtosecond laser pulses exhibit an intense peak at 1140 cm^-1, which may be attributed to nanocrystalline diamond.

We have studied the shock induced pressures due to the interaction of soft X-ray thermal radiation with foam-layered metal targets. Thermal X-ray radiation was produced by focusing a high energy laser inside a small size hohlraum. Experiments were performed using a 3ω converted (λ=0.44 μm) Iodine laser of τ≈450 ps (FWHM) duration. An increase in shock pressure was observed with the foam layered targets as compared to bare metal targets. Results are analyzed on the basis of the role of foam density and thickness.

We have used femtosecond laser pulse pairs to measure the positive ion yield, from wide band-gap single crystals, as a function of time-delay between pulses. Two pulse correlation allows direct observation of solid state and surface dynamics on an ultrafast timescale. The ion yield, from 265 nm irradiated MgO and KBr, depends critically on the time delay between two sub- threshold pulses. For example, the Mg⁺ desorption yield displays three distinct features; a coherence peak, followed by rise, and decay features. In constrast, the yield of K⁺ from KBr displays only the coherence peak and picosecond decay features. The data suggest, that although the nanosecond ion desorption mechanism is dominated by defect photoabsorption, significant electron-hole pair production may contribute to the desportion mechanism following femtosecond excitation. Nanosecond photoexcitation of KBr near 64 eV leads to desorption of hyperthermal neutral bromine atoms without a significant thermal velocity component. Two-photon femtosecond excitation at 3.2 eV produces very similar results. Multiphoton femtosecond excitation provides an efficient excitation mechanism of the wide-gap material. There results are likely general for ionic crystals and are consistent with a recently described theoretical model.

Semiconductor materials are still the material of choice also in many microsystems applications. This is mainly justified by the availability of mature processes and equipment originally developed for microelectronics fabrication. However, for microsystems more flexible requirements have to be fulfilled and new tools have to be developed especially with regard to smaller part numbers than in microelectronics. But also in microelectronics, conventional machines have often reached their limits in semiconductor processing which leads to the requirement of new processes. Lasers are generally able to ablate semiconductor materials. Especially ultrafast lasers are able to perform processes with high efficiency and accuracy. One of the most challenging conditions is not to influence the bulk material. Within this paper, the general interaction of ultrafast lasers with semiconductors is investigated. The ablation process is outlined and beam parameters influencing the removal and especially the cutting process are described, and potential applications are shown.

These are discussed microscopic physical processes underlying early phases of femtosecond laser-induced damage and ablation of wide band-gap solid dielectrics. They can result in 1) variations of energy-level structure of electron subsystem (in particular band-gap), and 2) instability of crystal structure. Those two microscopic processes are local and can be detected through different effects (variations of linear and nonlinear optical response and x-ray diffraction) each having its own characteristic time. There is analysed and estimated possibility of developing of instability of crystal structure and structure of electron energy levels of the solids under action of positive feedbacks. The feedbacks results from laser-induced ionization, straight action of electric field of laser radiation on ions, both resulting in increasing of density of laser-induced point defects. Estimations are obtained on the basis of the simplest relations describing laser-induced microscopic processes. Obtained results are compared with experimental data and shown to be capable of explaining some features of femtosecond laser interaction with transparent media.

The advent of table top high repetition rate regeneratively amplified femtosecond lasers has opened the way to many recent and fast developments towards applications of economical interest. The most well known are microprocessing, thin film elaboration, waveguide photoinscription, surface treatment, dentistry, ophthalmology. Recent studies on microprocessing and laser-matter interaction using femtosecond lasers are reported. This is done using largely presently performed work in Saint-Etienne including investigations on Heat Affected Zone (HAZ), plume expansion characterization, and thin film elaboration. Indeed specific characters appear as compared to what is obtained using multipicosecond/nanosecond laser pulses : Typical submicronic HAZ lengths have been evidenced and particle energies of plasma plume ranging up to a few KeV (carbon target) using typical pulse energies of 1 mJ (150 fs, 800 nm, 1 KHz), creating specific conditions for deposition. The concept of the often vocabled 'athermal' interaction is discussed. Emphasis on actual microprocessing capability of the existing sources to approach industrial applications are questioned in terms of energy per pulse, timewidth, repetition rates and the need for further source development and control beam improvement stressed. A brief review of the progresses under way in these fields and their capability to answer to actual large scale commercial applications are given.

We have developed an automatic pulsewidth tunable femtosecond Ti:sapphire laser system that can generate an output of 50fs-1ps and sub-mJ/pulse at a repetition rate of 1 kpps. The automatic pulse compressor enables on to control the pulsewidth in the range of 50fs-1ps by the use of a personal computer (PC). We describe our recent results of tailored ablation processing of advanced functional materials such as GaN, BN, and hydroxyapatite. By use of the femtosecond laser pulse tailored for a specific material, we have demonstrated precise processing without chemical composition change and heat affected zone.

From both a theoretical and an experimental point of view, the properties of fs laser pulses are fascinating. For a deeper understanding and for the prediction of the experimental results, the knowledge is necessary of absorption and of the optical penetration depth on the fs scale. For the description of the interaction of a fs-laser pulse with a solid, the stan-dard values of the properties of a solid are not suited because they have been experimentally determined or theoretically derived under the assumptions of a steady state and local thermal equilibrium. Depending on the property considered and the laser pulse duration either one or both of these conditions may be violated. In this paper, we derive equations for the optical properties of metals in the case of local thermal nonequilibrium be-tween the electron and phonon system. For a given laser intensity, we calculate, as an example, the absorption and opti-cal penetration depth for gold. For this purpose, we need the time dependent temperatures of the electrons and phonons. They are evaluated by means of our extended two temperature model. Finally, we compare the results with the standard equilibrium behavior as well as with the experimental findings and close with a short discussion.

There is a need in many scientific and manufacturing processes to drill to small diameter holes with high aspect ratios in both brittle materials as well as metals. Femtosecond lasers operating at 795 nm or frequency doubled to 400 nm provide a unique tool for carrying out these processes. In this work, the femtosecond laser nanomachining facilities at the University of Nebraska is discussed to drill 1 micrometers holes in Si/SiO₂ with aspect rations > 8. The quality of the cut and the small nanoparticles are discussed.

Fabrication of deep high-quality holes in different materials is required for many industrial applications. In this presentation we provide results of detailed investigations on deep drilling of metals by femtosecond laser pulses. We identify most important parameters which should be fulfilled for the fabrication of high-quality holes and efficient femtosecond laser ablation, discuss the role played by the laser-induced optical breakdown, debris, and laser pulse repetition rate.

Damage experiments of absorbing filters (Schott BG18 and BG36) were performed with Ti:sapphire laser pulses with durations from 30 fs to 340 fs (800 nm, 1 kHz) in air. The direct focusing technique was employed under single- and multi-pulse irradiation conditions. Ablation threshold fluences were determined from a semi-logarithmic plot of the ablation crater diameter vs. laser fluence. The damage threshold fluence decreases for shorter pulse durations. In the investigated pulse duration range, the measured multi-pulse ablation threshold fluences are practically similar to those of undoped glass material (~1 Jcm^-2). That means that the multi-pulse ablation threshold is independent on the doping level of the filters. For more than 100 pulses per spot and all pulse durations applied, the threshold fluence saturates. This leads to technically relevant damage threshold values in the femtosecond laser pulse duration domain.

We describe several scenarios of basic femtosecond machining and materials processing that should lead to practical applications. Included are results on high through-put deep hole drilling in polymers and glasses in ambient air, and precision high speed micron-scale surface modification of materials.

Femtosecond laser ablation shows promise in machining energetic materials into desired shapes with minimal thermal and mechanical effects to the remaining material. We will discuss the physical effects associated with machining energetic materials and assemblies containing energetic materials, based on experimental results. Interaction of ultra-short laser pulses with matter will produce high temperature plasma at high-pressure which results in the ablation of material. In the case of energetic material, which includes high explosives, propellants and pyrotechnics, this ablation process must be accomplished without coupling energy into the energetic material. Experiments were conducted in order to characterize and better understand the phenomena of femtosecond laser pulse ablation on a variety of explosives and propellants. Experimental data will be presented for laser fluence thresholds, machining rates, cutting depths and surface quality of the cuts.

The results of theoretical studies are reported for threshold characteristics of a metal ablation by picosecond and femtosecond laser pulse. Two possible mechanisms of the laser ablation at laser fluence F ≤ F_th are considered: thermal mechanism of ablation connected with a kinetics of a metal-vacuum surface evaporation and the mechanism of ablation connected with a hydrodynamics of a dense matter. The analysis has been made within the framework of a two-temperature model of metals for femtosecond and picosecond region of laser pulse duration and the extended of a two-temperature model of the metal in the case when the surface temperature T_i more than the critical temperature of metals. Analytical expressions for the ablation-threshold fluency F_th as well as the threshold values of the lattice temperature and the characteristic time of lattice temperature decay t_d(F_th) are obtained. This analytical description is in satisfactory agreement with particular numerical calculations.

Laser ablation has proven to be an important technology in an increasing number of applications. The fundamental mechanisms underlying laser ablation processes are quite complicated, and include laser interactions with the target as well as plasma development off the target. While substantial progress has been achieved in understanding laser ablation on the nanosecond and picosecond time scales, it remains a considerable challenge to elucidate the underlying mechanisms during femtosecond laser ablation. We present experimental observations of plasma development inside silica glass during single femtosecond laser pulse (100 fs, 800 nm) irradiation. Using a femtosecond time-resolved imaging technique, we measured the evolution of a laser-induced plasma inside the glass that has an electron number density on the order of 10¹⁹ cm^-3. Additionally, we observed an air plasma outside the target which forms long before the explosion of a material vapor plume.

A series of experiments has been performed to investigate the interaction of intense laser pulses with cryogenic noble gas droplets. Understanding of the time scales for this interaction is important for optimization of extreme ultraviolet (EUV) sources for next-generation lithography that utilize laser-produced plasmas. The temporal character of the plasma formed by the irradiation of micron-sized argon and krypton droplets with intense 200-mJ, 100-ps laser pulses was investigated using a pump-probe scheme. The evolution of the droplet plasma was assessed by monitoring delay-dependent x-ray and EUV emission, and by imaging frequency-doubled probe light scattered from the interaction region. Depending on the spectral region of interest and the droplet characteristics, the effective plasma lifetime extends from a few hundred picoseconds to several nanoseconds. These results are explained in terms of the plasma expansion, excitation emission, and recombination emission time scales.

Within the PREUVE project, the GAP of CEA Saclay has developed an EUV source that should meet (alpha) -tool specifications by the end of this year. In particular, a laser-produced plasma source has been developed that uses a dense and confined xenon jet target. Our technical solution is based on a specific target injector design and the use of well adapted nozzle materials to avoid debris formation by plasma erosion. After injection, the xenon is recycled and highly purified to reach a low cost round- the-clock operation. This source provides both high conversion efficiency and low debris flux. These are necessary conditions for its industrial application in the future EUV microlithography. The conception of the so-called ELSA (EUV Lithography Source Apparatus) prototype allows in principal 2 years full operation on the French lithography test bench BEL (Banc d'essai pour la lithographie) that has been developed during PREUVE. In parallel, the EXULITE consortium that is coordinated by Alcatel Vacuum Technology France (AVTF) has started its activities in the frame of the European MEDEA+ initiative on EUV source development. In collaboration with Thales and the CEA, AVTF develops a prototype power source for EUV lithography production tools by the end of 2004. A low cost and modular high power laser system architecture has been chosen and is developed by Thales and the CEA to pump the laser plasma- produced EUV source.

As a mass limited target the water droplet laser plasma source has been shown to have many attractive features as a continuous, almost debris-free source for extreme ultraviolet (EUV) and X-ray applications. Through a dual experimental and theoretical study, we analyze the interaction physics between the laser light and the target. The hydrodynamic laser plasma simulation code, Medusa103 is used to model the electron density distribution for comparison to electron density distributions obtained through Abel inversion of plasma interferograms. In addition, flat field EUV spectra are compared to synthetic spectra calculated with the atomic physics code RATION.

This paper reviews the basic phenomena and technologies associated with design of repetitively pulsed CO₂ lasers operating at power levels of approximately 100 kW and pulse repetition rates of approximately 100 Hz. Such systems are of potential interest for ablative propulsion investigations and as potential drivers for higher power systems for launching of small payloads to space.

A modified electron beam controlled pulsed CO2 laser is used as a multi spectral multi purpose test bed in order to generate high power fundamental and first overtone laser transitions in CO. The revisited concept includes an all solid state power supply which provides a highly reproducible operation at pulse repetition frequencies of up to 100 Hz. The active gas mixture is recirculated in a closed loop and kept at near room temperature using conventional water cooling. Discrimination of the CO fundamental band is obtained by using specially coated dielectric mirrors and introducing additional intracavity diaphragms. Unprecedented laser pulse energies of 25 J are reported in the overtone transitions covering a spectral range between 2 micrometers and 3.5 micrometers . Further scaling of pulse energies is expected in the near future using larger diameter resonator mirrors.

This work presents an improved disk laser concept, where a diode- pumped disk is hydrostatically clamped to a rigid substrate and continuously cooled by a microchannel heat exchanger. Effective reduction of thermo-optical distortions makes this laser suitable for continuous operation at ultrahigh-average power.

Revision of theoretical model of CO laser kinetics was performed including new data on intra- and inter-molecular vibration exchange processes and vibration relaxation in highly excited CO molecules, spontaneous radiation Einstein coefficients for fundumental and overtone bands of CO molecules and cross sections for cascade excitation and de-excitation of CO molecules by electron impact.

Great success has been obtained in the R&D of a chemical oxygen-iodine laser (COIL) operating on the electronic transition of the iodine atom, which gets an excitation from the energy donor -singlet delta oxygen (SDO). The latter is normally produced in a chemical SDO generator using very toxic and dangerous chemicals, which puts a limit for civilian applications of COIL that is still a very unique apparatus. Totally new non-chemical SDO generator is needed to allow oxygen-iodine laser to achieve its full potential as a non-hazardous efficient source of high-power laser radiation. There was interest in producing SDO in electric discharge plasma since the 50's long before COIL appearing. The idea of using SDO as a donor for iodine laser was formulated in the 70's. However, the injection of iodine molecules into a low- pressure self-sustained discharge did not result in iodine lasing. One of the main factors that could prevent from lasing in many experiments is a rather high threshold yield ~15% at 300K, which is needed for obtaining an inversion population. An analysis of different attempts of producing SDO in different kinds of electric discharge plasma has been done which demonstrates that high yield at gas pressure of practical interest (p > 10 Torr) for modern COIL technology can be obtained only in non-self sustained electric discharge plasma. The reason is that the value of relatively low reduced electrical field strength E/N ~10^-16 V.cm², which is an order of magnitude less than that for the self-sustained discharge, is extremely important for the efficient SDO production. Although different kinds of non-self sustained discharges can be used for SDO production, we got started experiments with e-beam sustained discharge in gas mixtures containing oxygen. High specific input energy up to ~3 - 5 kJ/l. atm [O₂] has been experimentally obtained. Theoretical calculations have been done for different experimental conditions indicating a feasibility of reasonable SDO yield. Experimental and theoretical research of self-sustained electric discharge in SDO produced in a chemical generator, which is very important for getting plasma-chemical kinetic data needed for an estimation of SDO yield, is also discussed.

Chemical Oxygen-Iodine Laser operating in a pulsed mode makes it possible to generate pulses with power significantly exceeding the average laser power. Such a mode can find an application in processes in which the power is a crucial factor. They are ablation, cutting, frequency conversion due to nonlinear processes, etc. The different approaches can be used to obtain pulsed COIL operation. The Q-switch method, pulsed singlet oxygen generation and volume instantaneous generation of atomic iodine will be considered. The merits and demerits of every method are discussed below. The recent results on pulsed COIL are presented too.

A tunable diode laser was used to probe the overtone gain medium of a small-scale HF laser. Two-dimensional, spatially resolved small signal gain and temperature maps were generated for the P(3) ro-vibrational transition in the first HF overtone band.

A new Chemical Oxygen-Iodine Laser (COIL) has been developed and demonstrated at chlorine flow rates up to 1 gmol/s. The laser employs a cross flow jet oxygen generator operating with no diluent. The generator product flow enters the laser cavity at Mach 1 and is accelerated by mixing with 5 gmol/s, Mach 5 nitrogen diluent in an ejector nozzle array. The nitrogen also serves as the carrier for iodine. Vortex mixing is achieved through the use of mixing tabs at the nitrogen nozzle exit. Mixing approach design and analysis, including CFD analysis, led to the preferred nozzle configuration. The selected mixing enhancement design was tested in cold flow and the results are in good agreement with the CFD predictions. Good mixing was achieved within the desired cavity flow length of 20 cm and pressure recovery about 90 Torr was measured at the cavity exit. Finally, the design was incorporated into the laser and power extraction as high as 20 kw was measured at the best operating condition of 0.9 gmol/s. Stable resonator mode footprints showed desieable intensity profiles, which none of the sugar scoop profiles characteristic of the conventional COIL designs.

Experimental lasing results for the Chemical Oxygen Iodine Laser, (COIL), using four different ejector nozzle configurations are presented. These nozzle banks differed in the location of Iodine injection, the area of the oxygen nozzles, and the nozzle contour of the primary driver nitrogen. The aerodynamic choking of the oxygen jets caused by the under expanded primary driver nitrogen resulted in a reduction of the O₂ (¹(Delta) ) yield and chemical efficiency. Dilution of chlorine with helium in the ratio of 1:1 reduces the partial pressure of oxygen and increases the velocity resulting in a chemical efficiency of 25% at 250 mmoles/sec and 23% at 500mmoles/sec of driver nitrogen respectively. The corresponding Pitot pressures are 50 and 90 torr.

Efficient subsonic chemical oxygen iodine laser operating with small buffer gas flow rate at Mach number M<EQ1 is reported. The highest value of output power of 415 W with chemical efficiency 23% was obtained at Cl₂ flow rate of 20 mmole/s. It was found that the power does not almost depend on N₂ or CO₂ buffer gas flows up to two times higher than oxygen flow rate.

Electrical to EUV conversion efficiency is a key parameter for systems scaled to EUV emission in the 100W regime. Improvement in efficiency of conversion from laser radiation at the EUV source, reduces the required laser power and as such can lend itself to reduced heat load and debris emission. Also, improvement in the electrical to laser conversion efficiency results in a direct reduction in cost of ownership. Laser solutions optimised for efficient conversion to high M² CW laser radiation are not optimised in design for efficient short-pulsed operation; the mode of operation required for EUV generation. Aspects of both EUV source and laser design are discussed, with a view to optimising conversion efficiency for scalable EUV solutions.

Development of long-pulse discharge XeF- and KrF-lasers pumped by a generator with an inductive energy storage and semiconductor-opening switch is reported. It is shown that use of inductive storage element allows significantly improve discharge stability and expand laser pulse duration. Pulse duration (FWHM) of 60 ns was obtained both in Ne-Xe- NF₃ and Nr-Kr-F₂ gas mixtures. Laser specific output of 2,5 J/l and intrinsic efficiency over 1% have been obtained for KrF laser.

The overview of spectral properties of the CO₂ laser radiation in modern RF excited waveguide, multi-waveguide, and slab-waveguide laser structures is given. Spectral phenomena in lasers operated in a pulse regime are also demonstrated. The influence of specific spectral features of the CO₂ laser on designing the high-brightness and spectrally pure laser devices is shown.

Due to a narrow window of high atmospheric transmission near 4 microns, there is a great deal of interest for a scalable laser energy source in this spectral region. We propose a concept that combines the advantages of solid-state and gas laser technology. A Nd:YAG laser is tuned to 1.3391 microns by inserting an intracavity etalon and raising the operating temperature of the laser rod to 85 degree(s)C. This allows us to excite the v (0 →3), J (4 → 5) vibrational-rotational transition of HBr. To stabilize the frequency, a diode laser locked to this HBr transition seeds the Nd:YAG laser. Once excited, HBr can potentially lase in three subsequent steps to the ground state, emitting three photons in the 4-micron region. We present theoretical and experimental results demonstrating the operational principle of this laser system.

The paper discusses several approaches to record of so-called 'blazed' dynamic holograms (thin dynamic holograms with asymmetric fringe profile) in optically addressed spatial light modulators (OA SLMs). Such holograms have much higher (up to 100% in comparison with standard 30-40%) diffraction efficiency to the working order of diffraction, than the traditional dynamic holograms, recorded in OA SLMs, and can be thus used for holographic correction of distortions in laser systems of various kind.

On the basis of developed physical and mathematical model for thermal nonequilibrium chemical processes involving electronically excited molecules the analysis of the mechanisms resulting in initiation of combustion in closed reactor and detonation in supersonic flow behind inclined shock wave in H₂+O₂(air) mixtures at excitation of the (see paper for formula) states of oxygen molecules by resonant laser radiation with wavelengths (lambda) equals1.268 micrometers and 762 nm has been carried out. The numerical analysis has shown that induced by laser radiation excitation of O₂ molecules leads to significant decrease of the autoignition temperature and allows to initiate detonation at very low temperature (~500 K) behind shock wave at relatively small values of laser radiation intensity. Excitation of (see paper for formula) state by laser radiation is more effective to influence on combustion kinetics and initiation of detonation in supersonic flow.

High power lasers are currently employed in production technology for processes with material removal as in cutting and ablation and in processes with material joining as in welding, cladding or the generation of 3-dimensional parts, e.g. for rapid prototyping. Nevertheless, lasers are rarely used in forming technology, where bulk material, sheets and wires are shaped without changing their volume. The reason for this scenario is that for forming metals large forces are needed that cannot be generated by conversion of optical energy as delivered by lasers. Nevertheless, the permanent plastic deformation of metals can be facilitated by selective irradiation with lasers in those regions of the workpiece, where the strongest deformations take place, since then the material is softened in those regions, thus reducing the necessary mechanical forces. In addition to this benefit of reduced forces also brittle materials, that cannot be deformed at room temperature without cracks or rupture, can be processed with laser assistance without the necessity of heating the whole workpiece as in hot forming, as e.g. forging. Several processes of the latter kind have up to now been investigated and successfully operated at the authors department at Vienna University of Technology/Austria, as bending, deep drawing and also dieless calibration of wires. In the actual paper an overview over successfully finished studies and newly planned investigations on laser assisted forming is given

We will briefly summarize our experimental results obtained for 1 ps long filaments. Theoretical studies show that scaling those filaments to ns should enable us to trap up 1 J in a single channel. Applications for laser induced lightning and high aspect ratio hole drilling will be discussed.

Recent applications for laser-induced shock waves have been demonstrated in the aeronautical and nuclear industries, due to the development of new generations of lasers that enable high cadency rates with rather small designs. In this paper, we first aim at making an overview on basic physical processes involved in Laser Shock Processing, and a presentation of pressure loadings generated by different laser conditions. In a second part, a specific focus is given to new ranges of applications like wear resistance, uniform and localized corrosion or modeling of fatigue behaviour after LSP. For instance it is demonstrated that the pitting corrosion behaviour of 316L steel in saline medium can be improved by laser-induced pure mechanical effects surrounding inclusions. It is also shown that wear rates of a 100Cr6 tool steel can be reduced after LSP provided applied pressures are kept below a material deposit threshold. Last but not least, the fatigue cracking behaviour of 2024-T351 aluminum alloy after LSP was improved and calculated through a computed program taking into account work hardening together with residual stress effects.

Studies of the influence of pulse length on material processing with different lasers have shown that a long pulse is beneficial for processing speed. In this paper a technique of pulse length variation is used in which the pulse length is the only varied parameter. Pulses between 5 and 150 ns length are sliced out of the 175 ns pulse of a long pulse excimer laser. The beam quality for each sliced pulse length is similar. In this paper the results are shown of hole drilling experiments in 125 micron aluminium foil with pulses of 10 and 100 ns length. The influence of the pulse length on material processing is discussed in relationship with equal energy and equal power density of the pulses. This study shows that in both cases long pulses remove more material than short pulses.

This paper describes the experimental results of selective rock removal using different types of high power lasers. US military owned continuous wave laser systems such as MIRACL and COIL with maximum powers of 1.2 MW and 10 kW and wavelengths of 3.8 and 1.3 mm respectively, were first used on a series of rock types to demonstrate their capabilities as a drilling tool for petroleum exploitation purposes. It was found that the power deposited by such lasers was enough to drill at speeds much faster than conventional drilling. In order to sample the response of the rocks to the laser action at shorter wavelengths, another set of rock samples was exposed to the interaction of the more commercially available high power pulsed Nd:YAG laser. To isolate the effects of the laser discharge properties on the rock removal efficiency, a versatile 1.6 kW Nd:YAG laser capable of providing pulses between 0.1 millisec and 10 millisec in width, with a maximum peak power of 32 kW and a variable repetition rate between 25 and 800 pulses/sec was chosen. With this choice of parameters, rock vaporization and melting were emphasized while at the same time minimizing the effects of plasma shielding. Measurements were performed on samples of sandstone, shale, and limestone. It was found that each rock type requires a specific set of laser parameters to minimize the average laser energy required to remove a unit volume of rock. It was also found that the melted material is significantly reduced in water saturated rocks while the drilling speed is still kept higher than conventional drilling.

Two sets of experiments indicate a renewal of interest in South Africa in the topic of laser propulsion. Both sets were conducted under the auspices of the new National Laser Center. In the first set, a 1 kW, CO2 laser (1 kHz, 1 J, 100 ns) was used to propel small (ca 1 gram) targets through a vertical tube-launcher and the momentum-coupling coefficient for a variety of conditions was estimated. The somewhat disappointing results were accounted for in terms of the poor beam quality from a single oscillator and premature break-down of the exhaust vapor in the tube. These experiments were conducted with one module of the now dismantled 'MLIS' uranium isotope separation system. The second set of experiments being conducted in Durban with a small but more energetic 'marking' laser (CO2 20 Hz., 4 J, 100 ns). The chief purpose of this, was to better understand the discrepancies between the recent vertical propulsion experiment at Pelindaba and earlier propulsion attempts with the original MLIS chain. Preliminary pendulum experiments were carried out. Burning targets exhibited enhanced coupling for single pulses.

Experiments on pure and inhomogeneous materials (meteorite samples) have been performed at the Sandiad National Laboratory (SNL) using a hohlraum source of soft X-rays. It is of interest to deduce the scaling of the ablation pressure with the radiation temperature in this class of experiment. This paper uses similarity relations deduced from a radiation diffusion model together with several theoretical expressions for the Rosseland mean free path of the target material. The resulting scaling laws are compared. The momentum coupling coefficient scaling with input radiation temperature is also given. As an example of the methodology, scaling results are given for the types of meteorites used in these recent experiments as well as for a comet model based on opacities obtained from the LANL TOPS code. This work is part of an on-going program to model the dymanic properties and interactions of Near Earth Object (NEO) materials in the context of NEO hazard mitigation.

It is possible to quantify cutting of plant stems by a laser beam in contrast to mechanical cutting. The biomass of the plants after a certain period under standard green house conditions was used to measure the effect of partial or complete cutting with a laser. Continuous laser irradiation at 10.6 micrometers of the plant stem turned out to be very efficient at values of the energy per width unit above 6 J/mm. The effect of laser irradiation at 355 nm or 1064 nm is less pronounced, but also at these wavelengths the re- growth or continuous growth are reduced. A monocotyledon- type, winter what (Triticum vulgare L), is substantially more resistant than a dicotyledon-type, charlock (Chenopodium album L.) against radiation. The exposure limits for laser light in living plants have been explored as well. The limit in terms of re-growth of the irradiated plants exceeds the MPE (maximum permissible exposure) of human skin by several orders of magnitude. The consequence is that very powerful (unfocused) lasers can be used in any environment without significant impact on living plants.

An experiment has been conducted to compare the ignition energy of an existing digital thruster design between a pulsed electrical and laser excitations. A 355nm Nd-YAG pulsed laser is used to ignite the stored lead styphnate propellant charge. Given the device design, roughly 800 μJ is necessary to ignite a 180 μg charge volume with a 90% probability of ignition. This energy value is considered an upper limit. Under equivalent conditions, roughly 2.4mJ of electrical energy is required to ignite the same volume. The digital thruster concept is one approach to provide a valveless, slap-on propulsion capability for small (1kg mass class) and large satellites (1000kg mass class) to help maintain attitude or control the damping of low frequency oscillations in extended surfaces.

Small, lightweight, low power solid state and semiconductor lasers are enabling the development of a new class of thruster systems for micro- and nanosatellites. These devices generate thrust by laser ablation of a solid propellant using on-board lasers and permit small satellites to perform maneuvers such as orbit maintenance, precision pointing, and formation flying. In this work we present a concept for micropropulsion called the microchip laser thruster (MLT) that is based on laser ablation by a passively Q-switched Nd:YAG microchip laser. The microchip laser enables on-board ablation by sub-ns, high peak power, high repetition rate Gaussian pulses. A propellant feed concept is proposed that consists of a cylindrically shaped solid propellant and a single drive motor. Based on measurements of single pulse laser ablation in aluminum, copper and indium targets, we find that aluminum provides the best overall thrust and specific impulse (I_sp). Specifically, for a MLT system employing a 10 μJ/pulse, 10 kHz, 1064 nm microchip laser and Al propellant, we report the following system parameters: thrust range equals 0.5 μN - 5 μN, I_sp equals 4900 s, system mass equals 455 g, and maximum required power equals 6.5 W. Atomic force and scanning electron microscope images of craters formed by single and multi-pulse ablation are shown to provide insight into effective propellant feed mechanism designs.

Hybrid laser experiments have been conducted in a variety of high power/energy laser experiments: beat wave electron accelerators, rainbow and ignitor fusion, particle acceleration and double pulse laser propulsion schemes. Following our determination that the momentum coupling coefficient for burning targets is much higher than for cold targets, we propose using solar energy from a vast thin foil mirror, laid on a pre-prepared surface, to boost the satellite during its atmospheric trajectory. Solar power propels a lighter than air craft during the first part of the ascent and enhances the coupling to the pulse laser during the second. We present preliminary pendulum coupling results for burning targets and describe a solar and laser hybrid experiment.

Laser-boosted lightsail experiments were carried out on 4-8 December 2000 with the 150 kW LHMEL II carbon dioxide CW laser at Wright Patterson Air Force Base - in their 2.74 m long, 2.13-, diameter vacuum chamber. All 5-cm diameter sail specimens were fabricated by ESLI. The prior Dec. '99 pendulum tests used ultralight carbon microtruss discs, sputter-coated with molybdenum on the front face to improve reflectivity at 10.6 um - and are the first known measurements of high power laser photonic thrust with real candidate lightsail materials. The Dec. '00 vertical wire- guided tests employed an improved moly-coated carbon-foil material with the same basic microtruss substructure. The performance of this new carbon foil sail was superior to the earlier specimens.

In the paper, the problems of laser propulsion for space application is considered. To simulate the laser propulsion creation, the computer codes are developed. These codes allow us to simulate both gas-dynamics of the propulsion creation and processes of laser pulse interaction with propellants.

Laser propulsion has many advantages over other conventional methods of producing thrust in space applications. For example, laser energy can be delivered to a remote objects such as space debris which otherwise is impossible to make thrust on its surfaces to remove from the orbits. However, essential advantage of laser propulsion lies in the fact that the characteristics of laser propulsion can be controlled over wide range of parameters by changing laser irradiation conditions. This advantage is based on the capability of controlling specific energy carried by propellant. The specific energy is a key parameter of thrust performance since it determines the propellant temperature or expanding velocity and thus propulsion efficiency. A number of researches so far conducted have treated laser plasma interactions created on solid surfaces with laser parameters such as wavelength, pulse width, intensity, as well as ambient gas pressure. The present study will give a new insight to laser plasma interactions and/or new mechanism of laser thrust generation. Laser energy is deposited inside solid target and, as an initial condition, confined by solid material. Since the confinement time is an order of milli-second, both shock waves and thermal conduction can tale part in the energy transfer process and therefore, give more controllable parameters over the thrust characteristics. In this manner, specific energy carried by target material or propellant can be controlled by changing the depth of energy deposition region. This will give a new dimension of controlling laser plasma characteristics for laser propulsion. In this paper, experimental results and physical insights will be presented as to propelled mass and velocity dependence on laser energy and temporal behavior of impulse generation, as well as enhancement of impact generation over the conventional ablation scheme.

The Air Force Research Laboratory/Directed Energy Directorate (AFRL/DE) and NASA/Marshall Space Flight Center (MSFC) are looking at a series of joint laser space calibration experiments using the 12J 15Hz CO₂ HIgh Performance CO₂ Ladar Surveillance Sensor (HI-CLASS) system on the 3.67 meter aperture Advanced Electro-Optics System (AEOS). The objectives of these experiments are to provide accurate range and signature measurements of calibration spheres, demonstrate high resolution tracking capability of small objects, and precision dray determination for LEO. Ancillary benefits include calibrating radar and optical sites, completing satellite conjunction analyses, supporting orbital perturbations analyses, and comparing radar and optical signatures. In the first experiment, a Global Positioning System (GPS)/laser beacon instrumented micro-satellite about 25 cm in diameter will be deployed from a Space Shuttle Hitchhiker canister or other suitable launch means. Orbiting in low earth orbit, the micro-satellite will pass over AEOS on the average of two times per 24-hour period. An onboard orbit propagator will activate the GPS unit and a visible laser beacon at the appropriate times. The HI-CLASS/AEOS system will detect the micro-satellite as it rises above the horizon, using GPS-generated acquisition vectors. The visible laser beacon will be used to fine-tune the tracking parameters for continuous ladar data measurements throughout the pass. This operational approach should maximize visibility to the ground-based laser while allowing battery life to be conserved, thus extending the lifetime of the satellite. GPS data will be transmitted to the ground providing independent location information for the micro-satellite down to sub-meter accuracies.

We have developed a new type of miniature jet for pointing microsatellites. It is based on laser ablation produced by a multi-mode diode laser. The target is a specially prepared tape with a transparent layer through which the laser light passes and an absorbing layer which produces the thrust. We have achieved specific impulse up to 1000 seconds (greater than possible with chemistry), together with laser momentum coupling coefficients of order 6 dyne/W. The preprototype should achieve 100 dynes of thrust. We will discuss the target interaction physics, the materials science involved in creating the targets, and some of our measurements with the preprototype thruster.

The laser plasma thruster (LPT) is a new microthruster for small satellites. We report on development and testing of a prototype LPT. Some advantages of the LPT are: thruster voltage 4 V, mass less than 1 kg, power-to-thrust ratio 10 kW/newton and Isp up to 1000 seconds. Typical thrust level is 250 (mu) N with PVC fuel. Thrust of 1 mN is expected with energetic fuel. The pre-prototype continuous thrust experiment includes the laser mount and heat sink, lens mounts, and focusing mechanism, which are coupled to the target material transport mechanism. The target material is applied to a transparent plastic tape, and the laser is focused on a series of tracks on the tape. The tape drive hardware and laser drive electronics, are described, as well as the control and diagnostic software. Design, construction, and calibration of the thrust stand are described. During continuous operation, the exhaust plume is deflected in the direction of the moving tape. When the laser is operated in pulsed mode, the exhaust plume is perpendicular to the tape (parallel to the optical axis). This provides some thrust vector control.

An end-to-end model is presented of the transient plume created by a micro laser-ablation plasma thruster. The laser ablation and plasma formation processes are modeled using a semi-analytical approach. This procedure provides boundary conditions at the target surface for the plume model that is based on a particle computational approach. The present study considers a 2 W diode-based laser irradiating a poly- vinyl chloride target over a spot radius of 10 micrometers for a pulse of about 100 microsecond(s) ec. The plume simulations reveal many details of the multi-component plasma expansion. The results are used to predict plume induced contamination effects.

Laser supported propulsion of a micro-airplane with water-covered ablator is demonstrated. The repetitive use of overlay structure is experimentally demonstrated with specially-designed water supply. The various transparent overlay is investigated by the CIP-based hydrodynamic code and experiments by pendulum and semi-conductor load cell. The momentum coupling efficiency of 5000 N-sec/MJ has been achieved by ORION experiments that agree with the simulation code. With the maximum efficiency approximately 10⁵ N- sec/MJ predicted by the simulation, 30 pulses of MJ laser can give the sound speed to 10tons airplane. The concept can also be used for driving a micro-ship inside human body and a robot under the accidental circumstance of nuclear power reactor in which large amount of neutron source makes electronic device useless.

The laser-driven in-tube accelerator (LITA) is a unique concept of laser propulsion. It is characterized by accelerating an object in a tube. Owing to a confinement effect, the thrust performance can be improved. This device has other advantages over the existing technology on the simplicity and suitability to environment. Experiments on the thrust performance of LITA were conducted. The thrust was determined from the object hovering condition. The measured dimensionless momentum coupling coefficient agrees between xenon and argon as the working gas. This implies that in order to obtain a high impulse chemical species with a low speed of sound is useful.

Conversion of pulses of CO₂ laser energy (18 microsecond pulses) to propellant kinetic energy was studied in a Myrabo Laser Lightcraft (MLL) operating with laser heated STP air and laser ablated delrin propellants. The MLL incorporates an inverted parabolic reflector that focuses laser energy into a toroidal volume where it is absorbed by a unit of propellant mass that subsequently expands in the geometry of the plug nozzle aerospike. With Delrin propellant, measurements of the coupling coefficients and the ablated mass as a function of laser pulse energy showed that the efficiency of conversion of laser energy to propellant kinetic energy was approximately 54%. With STP air, direct experimental measurement efficiency was not possible because the propellant mass associated with measured coupling coefficients was not known. Thermodynamics predicted that the upper limit of the efficiency of conversion of the internal energy of laser heated air to jet kinetic energy, (alpha) , is approximately 0.30 for EQUILIBRIUM expansion to 1 bar pressure. For FROZEN expansion (alpha) approximately 0.27. These upper limit efficiencies are nearly independent of the initial specific energy from 1 to 110 MJ/kg. With heating of air at its Mach 5 stagnation density (5.9 kg/m³ as compared to STP air density of 1.18 kg/m³) these efficiencies increase to about 0.55 (equilibrium) and 0.45 (frozen). Optimum blowdown from 1.18 kg/m³ to 1 bar occurs with expansion ratios approximately 1.5 to 4 as internal energy increases from 1 to 100 MJ/kg. Optimum expansion from the higher density state requires larger expansion ratios, 8 to 32. Expansion of laser ablated Delrin propellant appears to convert the absorbed laser energy more efficiently to jet kinetic energy because the effective density of the ablated gaseous Delrin is significantly greater than that of STP air.

A brief analytical review of basic data obtained in theoretical and experiments into the process of acceleration of solid bodies by a laser pulse in a mode of laser ablation in presented. It is noted the possibilities of laser acceleration methods have not been exposed yet. This can be ascribed to a great variety of physical conditions of acceleration by use of laser ablation depending on the problem stated and approach to its realization including the choice of material for ablation, type of laser facility, laser beam intensity and so on. The paper deals with the following: data on flat foil acceleration by a nanosecond laser pulse; conditions of accelerating frozen hydrogen pellets by a CO₂-laser pulse in the regime of laser driven rocket thrust; and possibilities of launching satellites into low-altitude earth orbits by use of high- power lasers. Optimal physical conditions in a laser plasma corona (vapours near the surface irradiated) which enable the best results to be reached are discussed.

The impulse coupling coefficients of two radically different laser propulsion thruster concepts (lightcrafts), each 10 cm in diameter, have been measured under equal conditions using two different pendulum test stands. One test stand and one lightcraft of toroidal shape were provided by the U.S. Air Force Research Laboratory. The other test stand and a bell shaped (i.e. a paraboloid) lightcraft were those of the German Aerospace Center (DLR). All experiments employed the DLR electron-beam sustained, pulsed CO₂ laser with pulse energies up to 400 J. The laser was operated with two configurations: 1) a stable resonator (flat beam profile); and, 2) an unstable resonator (ring shaped beam profile). A first series of experiments was carried out in the open laboratory environment. Propellant, therefore, was either the surrounding air alone, or Delrin as an added solid propellant. The coupling coefficient was determined as a function of the laser pulse energy. In a second series, the same experiments were repeated at various reduced pressure levels with the German lightcraft suspended in a vacuum vessel. This simulates the conditions of a transitional flight from within the atmosphere to outer space. As an additional parameter the specific mass consumption of Delrin (gram/Joule) was measured for each parameter set, allowing the determination of the average exhaust velocity in vacuum.

Laser supported propulsion of multi-layered target is investigated by the CIP-CUP (Cubic-Interpolated Pseudoparticle Combined Unified Procedure) based hydrodynamic code PARCIPHAL and experiments by pendulum and semi-conductor load cell. The momentum coupling efficiency of 5000 [N.s/MJ] has been achieved by ORION experiments that agree with the simulation code. Time evolution of ablation process and subsequent acceleration is investigated by load cell experiment and simulation. The double-layered target that consists of transparent tamper (Exotic Target) shows higher acceleration rate even with small laser. A propulsion concept is proposed to drive and control a micro-airplane that can be used for observation of climate and volcanic eruption where no one can access directly. In this concept, it is necessary to irradiate a micro-airplane repetitively. Therefore the double-layered target attached a liquid overlay is useful because the device that supplies the surface with liquid can be simple and light. In this paper, the simple device using water as an overlay is presented. Furthermore, from the results of experiments and simulation, it is clear that the mechanism of ablation process differs between the target attached a water layer and the target attached a solid layer.

In this report the concept of vehicle-based reactor-laser engine for long time interplanetary and interorbital (LEO to GEO) flights is proposed. Reactor-pumped lasers offer the perspective way to create on the base of modern nuclear and lasers technologies the low mass and high energy density, repetitively pulsed vehicle-based laser of average power 100 kW. Nowadays the efficiency of nuclear-to-optical energy conversion reached the value of 2-3%. The demo model of reactor-pumped laser facility is under construction in Institute for Physics and Power Engineering (Obninsk, Russia). It enable us to hope that using high power laser on board of the vehicle could make the effective space laser engine possible. Such engine may provide the high specific impulse ~ 1000 - 2000 s with the thrust up to 10 - 100 n. Some calculation results of the characteristics of vehicle-based reactor-laser thermal engine concept are also presented.

Unusual solitonic-type excitations were found by our group in 1992. As it was shown since that time this waves travel trough different condensed matter with discrete velocities in the range of 9 orders of value (between km/s and less then μs). These waves can carry heat or cold as it can be seen from the sign of local parameters variation. Explanation to this facts one can find in suggestion that this waves could be as compression as expansion ones (the physical mechanism of all phenomenon not known yet). This work contains short review of experimental results, which show characteristically sign variation for different materials. This work was sponsored as projects 00-02-17249-(a) and 02-02-26611-(3) by RFBR, its presentation - by SPIE and KIE.

Although laser ablation of solid materials is finding applications in a growing number of fields, the basic mechanisms underlying laser ablation processes have not been fully understood. One fundamental parameter for high-power laser ablation applications is the ablation depth resulting from the interaction of individual laser pulses. The ablation depth for laser ablation of single-crystal silicon shows a dramatic increase at a laser intensity threshold of approximately 20 GW/cm². Above this threshold, micron-sized particulates have been observed to eject from the target surface. We present an analysis of this threshold phenomenon and demonstrate that thermal diffusion and subsequent explosive boiling after the completion of laser irradiation is a possible mechanism to describe the observed dramatic increase of the ablation depth. Calculations based on this delayed phase explosion model provide a satisfactory estimate of the measurements. In addition, we find that the shielding of an expanding mass plasma during laser irradiation plays an important role on this threshold phenomenon.

Laser directly writing of nanostructures on metal film surfaces with optical near field effects has been investigated. Spherical silica particles (500-1000 nm) were placed on metal films. After laser illumination with a pulsed ultraviolet laser, naoholes were obtained at the original position of the particles. The mechanism of the formation of nanostructure pattern was investigated and found to be the near-field optical resonance effect induced by particles on the surface. The size of the nanohole has been studied as a function of laser fluence and silica particle size. A comparison with relative theoretical calculations of near-field light intensity distribution showed good agreement with the experiment results. The method of particle enhanced laser irradiation allows the study of field enhancement effects as well as its potential applications for nanolithography.

The retrieval of the photoinduced changes in the dielectric function from time-resolved pump-probe spectroscopy of thin films is investigated. In addition to the Fabry-Perot effect on the probe beam, we consider modulated excitation across the sample thinkness due to interference effects on the pump. General expressions for calculating the standing wave intensity distribution for arbitrary pulse length to film thickness ratios are presented. Emphasis was put on films transparent at the pump wavelength where the excitation is through a nonlinear absorption process. A unique approach for the retrieval of the changes of the dielectric function from the measured changes of the probe reflection and transmission is discussed. The method is applicable to measurements with a white light continuum probe which is used to get spectral resolution in addition to time resolution. From the retrieved time evolution of the dielectric function one can indentify various relaxation processes; starting from hot electron thermalization to the dynamics of the formation of a new material state. The results help identify damage and incubation mechanisms.

Several works on laser-matter interaction has shown the differences in sizes for the Heat Affected Zone (HAZ) obtained with nanosecond and femtosecond regimes in laser cutting or drilling. To understand more clearly the basic phenomena that occur in femtosecond regime during the absorption of light by matter, and specially in the case of metals, we have developed both an experimental and a theoretical approach. We use a new method aimed at quantifying the dimensions of the HAZ, using thin-down samples which are micro-drilled and then observed by a transmission electronic microscopy (TEM) technique. The grain size in the samples is analysed near the micro-holes. According to theoretical studies, the thermal diffusion is due to the smaller value of the electron specific heat compared to the lattice one. The thermal diffusion length is found to be a few hundred of nanometers in the case of metals. We use a thermal model to describe the heat diffusion in the sample in order to obtain a theoretical estimation of the HAZ. Holes are drilled in Aluminum using nanosecond and femtosecond laser pulses and characterized by Transmission Electronic Microscopy (TEM). The method for quantifying the dimensions of the heat affected zone (HAZ) surrounding micro-holes is based on the analyze of the grain size evolution. The experiments are using the same Ti-Sapphire laser source (1 kHz, 800 nm). The regeneratively amplified ultra-short pulses (150 fs) are utilized at a low fluence regime (typically 0.01-0.5 mJ/pulse), while the longer pulses (ns) are obtained from the regenerative amplifier without oscillator seeding (0.5 mJ,τ approximately 7-8 ns). The main conclusion is that a 40 micrometers wide HAZ is induced by nanosecond pulses, whereas the femtosecond regime does not produce any TEM observable HAZ. It has to be noticed that the width of the femtosecond HAZ is roughly less than 2 micrometers , which is our observation limit. These results are in agreement with theoretical predictions.

The crater morphology in transparent insulators upon femtosecond laser ablation was investigated by ex-situ optical and electron microscopy. After multishot irradiation (several thousand shots), a superposition of up to three differently spaced ripple patterns developed at the crater bottom, the finest one running perpendicular and the next larger one parallel to the laser polarization. The ripples periods do not show any relation to the incident laser wavelength. On the contrary, they appear to be strongly influenced by the incident intensity, regardless of the wavelength. The coarsest structure exhibits features of plastic surface waves, reflected at the boundaries of the crater as well as at individual irregularities inside the crater. The finest ripples exhibit strong features of chaotic self-organization and percolation, such as bifurcations. Together with the fact, that ablation under the applied conditions is due to Coulomb explosion of the surface, our observations indicate that local thermal effects can be ruled out as the origin of the ripples formation, in contrast to the classical interference picture of ripples formation. This is further confirmed by two-pulse interference experiments.

The laser surface treatment is applied to a multilayer component (copper alloy plated with two thin coatings, nickel and gold). The aim of the study is to melt the whole gold layer (thick < micrometers ) without damaging the underlying layers. The gold melting must be homogeneous and the process must be fast to avoid heat diffusion in the depths. For these reasons, the laser has been chosen for surface treatment. The application of this laser surface treatment is to improve the corrosion of resistance of electrical contacts due to columnar microstructure of gold deposited by electrolytic process. Tests of corrosion are carried out in the humid synthetic air containing low contents of pollutants (NO₂, SO₂ and Cl₂). An numerical study has been realized to find the best laser conditions to melt the whole gold layer.

The ability of UV femtosecond laser pulse to fabricate the fine-pitched microgratings on fused silica or ZnO surfaces has been demonstrated through a two-beam laser interference technique. A pump and probe method has been developed to find the time coincidence of the two UV pulses through a laser-induced optical Kerr effect or transient transmission change. The UV pulses achieve to narrow the grating pitches as small as 290nm. The establishment of the technique provides a novel opportunity for the fabrication of periodic nanoscale structures in various materials.

The problem of producing fast ion plasma fluxes on laser irradiation of a target with atomic number Z₀>1 in a strong magnetic field is considered. It is shown that the energy of multiply charged ions in the plasma fluxes can achieve high values of the order of 1 MeV at relatively low temperatures of the order 3-5 keV in the plasma corona where the Pekle number Pe>>1. The flux intensity grows with rising a total radiation power, depends on the laser wavelength and attains values of the order of several mega amperes when the target irradiated with CO₂-laser pulse with a relatively moderate power of the order of 10 TW.

The surface modification of titanium based ceramics thin films, induced by pulsed laser beam, was investigated in this work. Thin films of titanium nitride (TiN) and titanium diboride (TiB₂) were deposited on austenitic stainless steel substrate by two Physical Vapor Deposition (PVD) techniques and exposed in air atmosphere to a focused Transversely Excited Atmosphere (TEA) CO₂ laser irradiation. In these experiments two types of laser pulses have been used. One pulse was composed of an initial spike (FWHM equals 120 ns) with a tail (duration of 2 microseconds) while the other contained only the initial spike (FWHM equals 80 ns). Morphological changes of deposited ceramics, induced by successive laser pulses, have shown a dependence on the laser beam parameters (pulse energy, laser pulse duration, peak power density, number of pulses, etc.) and thin films characteristics. Thin films, investigated in this work, possessed reflectivity above 90% at wavelength of about 10 microns. Pulse peak power densities of 100 and 170 MW/cm² were used in these experiments and have induced the surface modifications of TiN and TiB₂ thin films. Depending on laser beam parameters, a change of color, grain growth, hydrodynamic effects, in TiN thin film were registered while on TiB₂ we noticed a change in color of the thin film, cracking and exfoliation.

The feasibility of laser ablation in micro-machining of 3D structure of MEMS (Micro Electro Mechanical Systems) parts, specifically micro optics was studied in this paper. The micro-machining characteristics of polymer such as etching rate vs. energy fluence, number of pulse are investigated experimentally. The threshold energy density of polyurethane is about 30 mJ/cm² and ablated depth per pulse can be precisely controlled in the range of 0.1-0.8μm by the attenuation of energy fluence. By mask moving technique, the micro prism, cylindrical lens and inclined surface were fabricated. These 3D structures can be used as master in electro-plating mold. This paper also summarized the work on the development of a simulation program for modeling the process of machining quasi-three dimensional shapes with the excimer laser beam on a constant moving polymer. Relatively simple masks of rectangle, triangle and half circle shape are considered. The etching depth is calculated by considering the number of laser pulses and the wavelength of laser beam irradiated on the various specimen surface such as PMMA, polyurethane and PI. It was found that similar shapes as experimental results, mask shape was designed to gain-lens surface which we want. As another method to manufacture micro lens the mask is made circular type and rotated during laser beam illumination. Opened mask area and scanning speed determine the surface shape of lens. Precise control of various parameters is admitted to fabricate micro optics.

This paper describes the process of nanoparticle synthesis by laser ablation of consolidated microparticles, focusing on the dynamics of ablation plume. We have generated nanoparticles by high-power pulsed laser ablation of Al and Cu microparticles using a Q-switched Nd:YAG laser (wavelength 355 nm, FWHM 10 ns, fluence 0.8~2.0 J/cm²). Microparticles of mean diameter 18 ~ 80 micrometers are ablated in the ambient air. The generated nanoparticles are collected on a glass substrate and the scanning electron micrographs of the samples are examined for characterizing the particles. The effect of laser fluence and collector position on the distribution of particle size is investigated. Optical diagnostics and numerical simulations are conducted to study the flow field and plume dynamics. The dynamics of ablation plume and shock wave is analyzed by monitoring the photoacoustic probe-beam deflection signal. Nanosecond time-resolved images of the ablation process are also obtained by laser flash shadowgraphy. Based on the results of experiment and numerical simulation, discussions are made on the dynamics of ablation plume.

The formation of well-defined craters is a general feature of laser ablation with ultrashort laser pulses, indicative of a sharp ablation threshold. Results of a microscopic characterization of ablation craters on semiconductors after irradiation with single intense ultrashort laser pulses are presented.

Theoretical and experimental analysis of a possibility of creation of high-energy gasdynamic laser generating infrared radiation with wavelength (lambda) equals27.971 micrometers on the vibration-rotation transition 001(633) --> 020(5₅₀) of H₂O molecule is presented. It was shown that at expansion of preheated water vapour in a wedge-shaped supersonic nozzle with 30 degree(s) opening angle and critical section height h* less than or equal to mm the nonequilibrium population of vibrational levels 001 and 020 of H₂O molecules is realised for the pressures P₀equals0.2-0.5 MPa and the temperatures T₀equals1930-2580 K at the nozzle inlet. The numerical analysis has demonstrated that for a plate profiled nozzle whose supersonic section is designed to provide uninterrupted flow at initial parameters T₀equals2500 K, P₀equals0.3 MPa, h*equals0.1 mm and nozzle expansion ratio (epsilon) equals20 the amplification coefficient behind the nozzle may achieve 1 m^-1. In this case the specific radiation energy may be of about 20 J/g. The principal feature of H₂O-gasdynamic laser is necessity to use the nozzle with rapid expansion and small values of parameter P₀h*. The latter should be considerably less (in a factor of 50-100) than for traditional CO₂-gasdynamic lasers.

At present time, excilamps excited by a barrier discharge are the simplest and perspective as the sources of UV and VUV radiation. Much research is devoted to such excilamps. Traditionally, sinusoidal oscillators are used as excitation sources. The present work devoted to study the impact of excitation pulse form and other conditions on efficiency of a barrier KrCl and XeCl excilamps. The main results of the work performed are the following. The most high specific radiation power values were obtained at the excitation at the excilamp by voltage pulses of different polarity at maximum pulsed repetition rate (p.r.r) of 100 kHz, and made depending on operating conditions of excilamp, up to 120 mW/cm³. From the oscilloscope traces of voltage pulses, current and radiation it is seen that radiation is being registered within the whole current pulse duration. The most high values of average radiation power and efficiency were achieved, correspondingly, 100 W and 13%. Influence of pulse repetition rate of excitation of different temporal mode on the type of formed discharge, as well as efficiency and output parameters of Xe-Cl₂ barrier discharge excilamp were studied. It has been found that at pulsed repetition rate of about 1 kHz and higher there are brightly glowing microdischarges - filaments observed in the discharge plasma. With this, the efficiency of excilamp practically keeps unchanged in the frequency range <EQ 1 kHz and monotonously decays either at further increase of excitation p.r.r. or at excitation power increase for the fixed frequency of excitation pulses.

We report an experimental study on the X-ray emission from aluminum clusters (diameter approximately 0.4micrometers ), carbon (diameter approximately 0.5 micrometers ) and gold (diameter approximately 1.25 micrometers ). They were ingrained in a polymer and irradiated with 1.06 micrometers laser, 10 ns (FWHM) at an intensity approximately 10¹² W/cm². Aluminum and carbon clusters show a different spectra compared to their respective bulk material whereas gold clusters evolve towards bulk gold. Experimental data are analyzed on the basis of cluster dimension, laser wavelength and pulse duration. PIC simulations are performed to study the behavior of clusters at higher intensity I ≥ 10¹⁷ W/cm² for different size of the clusters irradiated at different laser wavelengths. Results indicate the dependence of cluster dynamics on cluster size and incident laser wavelength.

Through laser initiation of explosives offers many advantages like controlled threshold energy over wide range, replacement of complicated safety arming mechanisms to simple and better system, immunity to RF/EMI environment etc, but there is greater difficulty to build detonator for all purpose applications and regular field trials. The challenges are to understand the interaction of laser radiation or its induced plasma with explosives, launching and transmission of high power laser beam, coupling and focussing to desired target area. This paper looks into the details of those facts.

Temporal behavior of small signal gain (SSG) for a frequency tunable first-overtone CO laser has been studied both experimentally and theoretically. The laser operates on highly excited vibrational transitions from 20→18 up to 38→36 that correspond to laser wavelength range between ~3 and 4 microns coinciding to atmospheric 'transparency window'. Maximum SSG comes up to 0.4 m^-1. It is shown that multiquamtum and asymmetric VV exchange has to be taken into account when analyzing processes of population formation on high vibrational transition.

Simulations of laser-fused silica interactions at 0.351 μm are a key issue in predicting and quantifying laser damage in large laser systems such as LIL and LMJ. Validation of numerical simulations requires detailed knowledge of the different parameters involved in the interaction. To concentrate on a simple situation, we have made and tested a thin film system based on calibrated gold nanoparticles (0.2-0.8 μm diameter) inserted between two silica layers. The fused silica overcoat was either 2 or 10 microns thick. We have performed simulations of laser energy deposition in the engineered defect (i.e. nanoparticle) and the surrounding fused silica taking into account various laser/defect induced absorption mechanisms of SiO₂ (radiative ionization, avalanche and multiphotonic ionization). We have studied crater formation produced by the absorber explosion with a 2D Lagrange-Euler code taking into account crack formation and propagation in the brittle material. We discuss the influence of the defect depth (with respect to the surface) on the damage morphology. The simulations are compared with our experimental results.

The mathematical model of the optically pumped molecular laser has been built. The satisfactory fit of the computer simulation results with the experimental data has been established. The optimization of the CO laser with the optical pumping in (2,0) overtone was carried out by the numerical modeling methods.

The quantitative analysis of sensitivity and selectivity characteristics for spectroscopic gas detection with different mid-infrared molecular lasers was carried out. In particular, the partial and cross sensitivity, the partial selectivity and total parameter of selectivity and sensitivity for gas detection in gas mixture of seven components with HF, DF and first-overtone (FO) carbon monoxide lasers were calculated. The analysis demonstrated that FO CO laser due to its spectral properties is very perspective source of light for laser spectroscopy of multicomponent gas mixtures. The FO CO laser spectral range (2.5-4.2 microns) overlaps the 'transparency window' of the atmosphere in the wavelength range (~3 - 4 microns) and covers that of HF and DF lasers, with its ro-vibrational line spacing being several times less than that of those lasers. The FO CO laser spectral lines coincide with a large number of absorption lines belonging to numerous organic and non-organic substances which can be found in plasma induced by laser ablation. The linear and nonlinear absorption of the FO CO laser by different gaseous substances was calculated and compared with the experimental data.

The 157nm F₂ laser wavelength is strongly absorbed by glasses, even those with high silica content, making it potentially well suited for machining these materials by ablation. This is of interest for fabricating micro-optics and micro-devices in glass, provided crack-free surfaces with minimal laser-induced stress and surface roughness can be produced. Experimental studies are reported on the ablation threshold, ablation rate and surface quality of N-BK7 and soda lime glass for exposure with the VUV F₂ laser. Optical probe techniques and etching are employed to determine the ablation threshold and removal rate and scanning electron microscopy to assess the surface quality of the glass following laser exposure. The interaction is discussed within the framework of a thermal vaporization model and the surface thermal loading is used to make a preliminary assessment of resolution attainable in micro-feature definition.

Nonlinear plasma effects important for femtosecond-scale heating dynamics are considered. It is shown that heating of electrons due to the inverse bremsstrahlung absorption of high-power short-pulse laser radiation results in parametric generation of ion-acoustic waves. The range of wave numbers where the amplitude of the ion-acoustic oscillations in-creases by more than an order of magnitude is determined. A self-similar description of electron and phonon kinetics in metals with a sharp gradient of the electron temperature is developed. It is shown that the Cherenkov generation of nonequilibrium phonons results in suppression of the electron heat flux and rapid disintegration of the metal lattice.

The results of theoretical and experimental investigation of gas phase chemical generation of atomic iodine, I(²P_3/2), for stimulated emission in chemical oxygen-iodine laser (COIL) are presented. The method of I atoms generation employs a principal reaction X+HI implies I(²P_3/2)+HX, where X equals F or Cl. A computational modeling was based on the 1D flow development exploring the chemical processes within the reaction systems, and was aimed at the theoretical understanding of the two complex reaction systems and finding out which is better applicable for conditions in COIL. The results of modeling were further used for a design of the device and conditions during the experimental investigation, and for an interpretation of the experimental results. The experimental work has been done, for the present, on the atomic iodine generation via Cl atoms. A high yield of atomic iodine of 70% to 100% (related to the initial HI flow rate) was attained in a flow of nitrogen. Gain was observed in preliminary experiments on the chemical generation of atomic iodine in a flow of singlet oxygen.

The efficiency and threshold of ablation of polymethylmethacrylate (PMMA), polytetrafluoroethylene (PTFE), and monocrystalline silicon by single pulses of soft x-rays emitted from Z-pinch, plasma-focus, and laser-produced plasmas were investigated. The Z-pinch was driven by the S-300 pulsed-power machine (Kurchatov Institute, Moscow) and the plasma focus was realized in the PF-1000 machine (Institute of Plasma Physics and Laser Microfusion, Warsaw). Higher temperature plasma than with the discharge plasmas was obtained by focusing the near-infrared beam from the PALS high-power iodine laser system (Czech Academy of Sciences, Prague) on the surface of a metallic slab target. The role of nonthermal processes in x-ray ablation was evaluated. Possible ways to use x-ray ablation for micromachining are discussed.