No Abstract Available.

Max Born started studying astronomy, mathematics, and physics in 1901 at the University of Wroclaw the town where he was born on December 11th, 1882. In my talk I would like to follow his reminiscences (Max Born: My Life. London 1978) and to illustrate them with pictures and documents from his time at the university. We will start with a view of the main building of the university where the lectures in mathematics were given. Then we find the astronomical observatory located at the top of the mathematical tower of the university building. The situation there at the time of Max Born will be illustrated by historical photographs. Finally we will follow the way the students took in those days to the physical institute. Pictures of the building and the great auditorium will end the presentation of the historical sites. Parallel to this I would like to tell you how Max Born judges his first years studying in Wroclaw and what the reasons were for him to go to Goettingen.

No Abstract Available.

No Abstract Available.

The paper is an attempt at reconstructing the academic life in Wroclaw (Breslau) before the Second World War. Included are fourteen Nobel Prize Winners whose life was connected in different way with the city. The scientists are divided into three groups - born in Wroclaw (Breslau), studying in the city, and working at the Wroclaw (Breslau) University.

We review progress in the development of a novel mode of operation of the planar waveguide carbon dioxide laser (referred to as the ultra-super-pulse or USP mode), which is capable of delivering, at high efficiency, up to ten times higher peak power and up to ten times shorter pulse duration than the 'conventional' planar waveguide laser. These enhanced bream properties extend the range of applications to the micro-processing of materials with higher machining threshold and/or low absorption coefficients and with the added advantage of producing reduced heat affected zone.

The copper vapor laser (CVL) is the most powerful and efficient laser in the visible spectrum. Four stages in its development are described in the current paper.

A technique for eliminating electrical standing waves from the electrodes of a large area CO₂ Slab laser is described. This method is general and may be used to smooth the electric field distribution over planar electrodes of arbitrary dimensions and coaxial electrodes.

Laser power capability, pulsing issues and beam quality issues associated with multi-line operation have been investigated for a carbon monoxide planar waveguide laser with a negative branch unstable resonator operating at room temperature, and producing output laser power of 300W.

In this study, power deposition characteristics of the 40MHz slab excitation carbon dioxide laser has been carefully investigated in which the relationship between the filled gas pressures and input power densities have been obtained so as to sustain stable α discharges. As a result, a laser output power of 60-90W was obtained with a corresponding conversion efficiency as high as 9.5-10% under the condition of 0.6 -1 kW discharge input into Xe-added 1:1:8 Helium-rich gas filling which corresponds to 22-37 W/cc of the input power density. The obtained characteristics in this work shows that relatively high conversion efficiency can be realized with stable α discharge by choosing the optimum operational gas pressures and power input densities under the use of the Xe(2.5%)-added, Helium-rich gas mixture(1:1:8).

The problem of line-hoppng in a short cavity, slab waveguide CO₂ laser is studied by modeling of the laser signature and the experimental determination of laser spectra. It is shown that small increments of resonator length, less than 100 µm, significantly change the number of lines in the spectra and at a specific resonator length near 408.7 mm there is the possibility of single line operation. To reduce line-hopping and lock the laser to the 10P20 line, a 10th order, 2 dimensional grating has been laser engraved on one surface of the planar waveguide.

In the paper, we show the present state of the art of high pulse repetition frequency (PRF) metal vapor lasers (MVL’s) and metal halide vapor lasers (MHVL’s) development. We also analyze underlying physical features, which limit optimum and maximum PRF of the above lasers and mention the results of the experimental study of high PRF CuBr and PbBr₂ vapor lasers. By use of a powerful tasitron as a switch and a small hydrogen additive to the buffer gas Ne we obtained the output power of a practical use with PRF more than 200 kHz. Given PRF 250 kHz and a laser tube of diameter 2.5 cm and length 76 cm, we have got the output power 1.5 W. For PRF 200 kHz and 100 kHz, the output power 3 W and 10.5 W has been got respectively without gas flow across the discharge tube. Experimental and numerical modeling data evidence that the small H₂ (or Cs) additives improve the frequency and output features of MVL’s and MHVL’s.

An e-beam pumped Xe-laser is experimentally investigated with additions of molecular gases. For a pump pulse duration from hundreds of nanosecond to 1 μs, the highest laser energies are reached without molecular additions at a comparatively low e-beam current density (~ 10 kW cm^-3 atm^-1). However, in setups with specific pump powers above 40 kW cm^-3 atm^-1 and a working mixture pressure limited by strength of the laser chamber, molecular additions result in an increase in the radiation energy and efficiency. In wide-aperture facilities with high pump powers, molecular additions improve the distribution of the radiation power density over the laser-beam cross section.

A new mechanism of pulsed laser using ion-ion recombination is considered. Advantages of using ion-ion recombination in pulsed operation are considered and estimates of possible characteristics of the lasers are presented.

Pulse repetitive generators with inductive energy storage unit and semiconductor opening switch were developed and used for pumping lasers on CO₂, N₂, Cu vapor laser and VUV Xe excilamp. For the first time, operation of the generators at pulse repetition rate up to 100 kHz has been realized. Improvement of the laser and excilamp output parameters were achieved.

The degenerate intra-cavity four-wave mixing on nonlinearity of gain of active medium of cw CO₂ laser was used for determination of turbulent parameter of active medium flow.

The paper presents the new concept for radiation mode selection, based on the spatial filter system, which disposed on the electrode surface of slab CO₂ laser. The results of the computer simulation and the experiment are discussed.

Theoretical propositions of powerful technological CO₂-laser operation with selection and correction phase of high order cross modes have been experimentally studied. The effective transformation of the high order mode oscillations field into the narrow directed beam with cophased light oscillations at the level of output power up to 1kW with help of phase corrector is reported for the first time. The physical nature intracavity aberrations with negatively influence on the beam quality is analyzed. It is shown that the most significant aberration such as optical wedge arising when we use the cross pumping of active medium and the cross discharge. The prospect of use of the considered method to receive narrow directed radiation is considered at high power values.

High gain for supersonic CO₂ laser excited by RF discharge in closed-cycle has been achieved. The relationship between output power and the relaxation time of carbon dioxide is also disclosed in this paper.

Influences of shock waves with Mach number of 1.1-1.35 on excitation discharge in transversely excited atmospheric gas laser have been investigated eliminating the other factors. The shock waves are produced by using a shock tube with the gas mixture of helium and argon. The schlieren photographs of shock wave and direct images of light emitted from the discharge are recorded simultaneously by a streak camera. It is found that the discharge does not collapse with the shock wave of 1.1 in Mach number. The shock waves at Mach number above 1.2 tend to collapse the glow discharge in spite of no halogen gas. If the shock wave does not reach to the center of the electrode, glow discharge occurs only in front of the shock wave. Even if the shock wave passes through the center of the electrode, the glow discharge occurs, however, the discharge concentrates in the tight space between the shock front and the edge of the electrode. A streamer exists in the shock front when the shock wave just reaches the edge of electrode. It becomes clear that the discharge characteristics depend on the Mach number of shock wave and the position of shock wave.

Four-channel structures in form of the second rank 2x2 matrix were investigated. For CO₂ lasers we applied phase-locking techniques. He-Ne and He-Xe lasers were built as independent four-channels and optimized for their output power.

No Abstract Available.

We have investigated the power scaling behavior of a kinetically enhanced copper vapor laser as a function of the plasma tube thermal insulation. By reducing the insulation to levels much lower than typically used for conventional copper vapor lasers we obtained increases in the specific output power of a small-to-medium scale device (0.8L) up to 130W/litre (i.e., total output power 104W). The laser wall-plug efficiency remains approximately constant (~1.4%) when the supplied power is increased from 5.9kW to 7.4kW. Radially-resolved Cu density measurements show that the depletion of Cu atoms is similar to other devices having much lower specific input power. The results show that kinetic enhancement reduces the depletion of atoms from the axial region by ion-pumping due to reduced fractional ionization and rapid charge recombination during the interpulse period.

The main processes during initial stage of pulsed discharge in copper vapor lasers including the operation of a cathode and discharge development in cold end zones of a discharge tube are considered. The importance of fast voltage rise, proper operation of the cathode and recombination processes in the cold zones is emphasized.

Dynamic properties of the output intensity profiles of the CO₂ laser beam are studied under conditions of the loss modulation caused by a freely expanding stream of an absorber gas injected into the laser cavity. The temporal and spatial output beam characteristics are measured under various experimental conditions specified by the operational parameters of gas-dynamic modulator.

The investigations and constructions of compact RF-excitation CO₂ lasers with slab discharge channel geometry and unstable-waveguide resonators are described. The output average power scale up to 260 W from electrode area of 198 cm² have been obtained in sealed-off mode because use a catalyst effect in discharge volume.

Compact programs have been implemented to the information devices of PDA, personal digital assistants, in order to analyze the power distribution of discharge excited gaseous media. The simulation codes are cross-developed between Macintosh computers and PDA.

New simulation code has been developed for gas flow CO lasers by the combined computing technique of server-side and client-side processing. The input and output interfaces are processed on the client-side and numerical calculations are processed on the server-side.

A CO₂ laser with the nitrogen selective excitation in barrier discharge and afterglow gas-mixing is presented. One of the main advantages of barrier discharge is connected with the possibility to operate at atmospheric pressure with rather high energy density. The laser is very sensitive to the gas mixture composition and mixing conditions.

We have studied two different optical schemes, namely, a stable multipass resonator and a hybrid stable-unstable resonator, using the same Radio-Frequency excited slab geometry. The experimental results show that the stable multipass resonator allows extraction of a good quality output beam, together with improved power stability.

We introduce a new optical system that is able to simultaneously make homogeneous the spatial energy distribution and vary the spot size of any light beam, including beams having strong local intensity fluctuations, without replacement of lenses and without changing the total length of the optical system. This homogeniser technology includes a software to design the optimum optical system to achieve the wished output beam performance, as well as to know how the beam shape changes when changing the position of each optical element. In this paper, we present the design software and the experimental results achieved with our technology applied to a large volume excimer laser.

This paper presents the novel optical closed-loop adaptive system (CLAS) for compensation of the laser beam aberrations and results of its application in high power lasers. A closed-loop adaptive algorithm is developed to control for a continuous-surface deformable bimorph mirror. The control voltages applied to the electrodes reduce the wavefront distortions measured by a Shack-Hartmann wavefront sensor (SHWS). Adaptive system can correct the low-order aberrations with the frequency is about 25 Hz. The amplitude of corrected aberrations is about 10 microns and sensitivity is about 0.08 microns. The examples of the use of such systems to control for radiation of TW Ti:Sa lasers are presented.

Two models of gain and thermal guiding effects were derived. In the first one the complex ABCD matrix for a crystal under gain and thermal guiding was applied to describe the operation of microchip near threshold. In the second one, the simple iterative procedure was proposed to calculate effective fundamental mode parameters of a cavity under thermal and gain guiding for given bare cavity ABCD matrix and pumping parameters, including gain saturation, passive cavity losses and reabsorption ones. The influence of gain guiding effects causes changes of waist width in the range up to 50% comparing to expectations derived from thermal guiding theory. Application of such method for resonators of passively Q-switched lasers was developed. Results of calculations for microchips were verified with experiment.

We demonstrate wide-range wavelength tunability of high-power laser diodes emitting at 660 nm, 808 nm, and 980 nm. Pressure shifts of the emission wavelength are due to the increase of bandgaps of III-V semiconductors under pressure with the rate of about 10 meV per kbar. For the 980 nm InGaAs/GaAs laser the threshold currents and the quantum efficiencies remain constant with pressure which allows for the constant operating current and the emitted power in the full tuning range. For 808 nm GaAs/AlGaAs and 660 nm InGaP/AlGaInP lasers there is an increase of threshold currents with pressure related to the direct-indirect crossover in the conduction band of AlGaAs and AlGaInP. This limits the tuning range unless we operate the laser at lower temperature. We designed the pressure cell with Peltier cooling allowing for independent control of temperature down to 0 Celsius and pressure up to 20 kbar. This device allows for the tuning of 980 nm laser down to 840 nm, 808 nm laser down to 720 nm, 660 nm laser down to 620 nm.

A low-cost system for quick measurements of laser diodes far-field characteristics is demonstrated. The measurement results of various types of laser diodes are presented. The usefulness of the system for high-power laser diode testing is proven.

It is shown theoretically, that observed in experiments the strong low threshold feedback in the resonator with a high pressure gas (Xe) cell of the CO₂ laser, in which the frequency interval between axial modes is equal to frequency Stokes shift at Stimulated Brillouin Scattering (SBS) in Xe, can arise owing to nondegenerate four-wave mixing in a gas cell on generated as at SBS running phase gratings.

Reflectivity and fidelity of phase conjugation by stimulated Brillouin scattering (SBS) is studied in CS₂. Experimental results are presented for TEM₀₀ and TEM₀₁ mode pumping, at 1.06 μm. SBS reflectivity has been analytically calculated and compared with experimental data. Good healing of phase distortions was demonstrated.

The experimental preliminary results concerning the operation conditions of a cw CO₂ laser with a variable focus, concave mirror are presented in the paper. The mirror is introduced as a rear mirror into a stable cavity of the laser. The contour of the mirror is changed by adjusting the pressure of the cooling medium. The laser output properties are investigated versus the parameters describing the deformable mirror shape.

It has been shown, that a single line operation of the CO₂ laser can be easier sustained by careful choosing the laser resonator length. Selection of the right resonator length allows obtaining very sophisticated signatures.

In this paper the approximate analysis of the nonlinear operation of the open resonator laser with Gaussian reflectivity profile output mirror which allows to optimize power efficiency for different wavelengths is presented.

The roadmap of semiconductor fabrication predicts that the semiconductor market will demand 65 nm node devices from 2004/2005. Therefore, an Ultra-Line-Narrowed F₂ laser for dioptric projection systems has been developed under the ASET project of “The F₂ Laser Lithography Development Project”. The target of this project is to achieve a F₂ laser spectral bandwidth below 0.2 pm (FWHM) and an average power of 25 W at a repetition rate of 5 kHz. The energy stability (3-sigma) target is less than 10%. Simultaneously, it is also required to establish the technology of evaluating the optical performance. An Oscillator-Amplifier arrangement at 2 kHz was developed as a first step of an Ultra-Line-Narrowed F₂ laser system. With this laser system, we achieved the basic study of the synchronization technology for line narrowing operation using two system arrangements: MOPA (Master Oscillator/Power Amplifier) and Injection Locking. Based on this experience we have developed the 5 kHz system. With the 5 kHz Line-Narrowed Injection Locking system, we have achieved a spectral bandwidth of <0.2 pm with an output energy of >5 mJ and a pulse to pulse energy stability of <10%. The feasibility of a 5 kHz Ultra-Line-Narrowed F₂ Laser for Dioptric Projection Systems has been demonstrated.

We have observed Ar₂* emission at 126 nm by use of a high intensity laser pulse as an excitation source. Kinetic analysis revealed that high-intensity laser-produced electrons via optical field induced ionization (OFI) process initiated the Ar₂* production kinetics. Ar₂* production kinetics initiated by OFI electrons was mainly governed by the three-body association process, which was analogous to the case of electron beam excitation. The use of a hollow fiber controlled propagation characteristics of a high intensity laser pulse in a high-pressure gas, leading to the increase of the excimer emission intensity

Time-resolved scintillation technique and absolutely calibrated thermo-luminescence dosimeters have been applied to characterize bremsstrahlung x-ray emission from a large-aperture GARPUN KrF laser module pumped in a transverse geometry by double-sided e-beams stabilized by pulsed magnetic field of 0.1 T. It was produced by electrons with ~300 keV kinetic energy, 50 A/cm² current density, and 100 ns pulse duration when they passed from vacuum diodes through foil windows into laser chamber and were decelerated in a working gas. Regularization algorithm was developed to reconstruct the bremsstrahlung spectra using experimental data on x-ray transmission through different absorbers. The energy fluence of ionizing radiation escaped onto laser windows has been measured. It was shown that a long-term degradation of optical transmission due to bremsstrahlung x-ray irradiation should be taken into account for KrF laser application in Inertial Fusion Energy.

We have used a pair of newly constructed electrodes to improve the discharge stability and electrical input power. The electrode shape was designed so that the discharge width became narrower, which lead to the increase of the input power density by 22%. As a result, the maximum output energy increased from 150 to 200 μJ at 147.8 nm. The pulse duration of 250 ns (FWHM) became shorter compared to the previous result (400 ns). This long pulse operation indicated the laser oscillation in an afterglow mode. The laser beam shape was circular with a beam divergence of 2.5 mrad. Because of the long pulse duration, this beam shape reflected on a cavity mode (multi-mode) as a result of the optical feedback. A small signal gain coefficient increased almost linearly with the increase of the discharge voltage. The maximum gain coefficient at 147.8 nm was 3.5%cm^-1 at 31 kV.

The results of experimental investigations of the pumping conditions and radiation parameters of the KrF excimer laser for achieving the output radiation energy up to 1,0 J with maximal efficiency are presented. The high voltage excitation circuit on the basis of a LC-inverter type circuit including the peaking capacitors and automatic UV preionisation (API) has been developed. For the KrF laser with the active volume of 175 cm³ in He:Kr:F₂ -89,8:10:0,2% gas mixture at the total pressure of 2,7 atm the overall efficiency up to 2,2% with the output radiation energy of 0,84 J was achieved. The maximum output energy of the KrF laser was of 1,0 J with the overall efficiency of 2,0%. The pulse duration (FWHM) was 24±1 ns. The addition of up to 50% of Ne as a buffer gas to He at the pressure of 2,9 atm increases the maximal output energy up to 1,3 J with efficiency of 2,5% and the maximal efficiency up to 2,9% with output energy of 0,95 J.

Today the molecular fluorine (F₂) laser emitting at a wavelength of 157 nm represents the strongest commercially available coherent light source in the vacuum-ultraviolet spectral range. Lambda Physik produces a broad variety of F₂-Lasers which cover a wide range of output power (from less than 1 W to more than 20 W), repetition rate (from less than 100 Hz to more than 4 kHz) and single pulse energy (from less than 1 mJ to more than 30 mJ). The parameters of each of these kinds of F₂-lasers are designed and suitable for specific fields of application. In the paper we will review the main parameters of these different types of F₂-lasers, compare their special features and discuss the principle applications they are used for. The low energy, medium repetition rate is basically used for metrology and calibration tasks, the high energy or high repetition rate and high power F₂-laser systems are mainly used for material investigations and in a growing extent for 157 nm-micromachining. Lithography tools use the high repetition rate, high power single-line F₂-laser systems. All of these scientific or industrial applications take advantage of the unique properties of the 157 nm radiation, i.e. the ultra-short wavelength of emission and the very high photon energy of nearly 8 eV. Thus, very precise and fine microstructuring in the micrometer range is possible and the 157 nm optical lithography is on target for critical dimensions of integrated circuits below 70 nm. The short pulse duration and high photon energy also enables efficient and exactly located icroscopic ablation of most critical materials without thermal impact on the surrounding area. In the last part of the paper some recent results on F₂-laser development and an outlook on future products will be given.

A mini-excimer laser with a specially designed laser tube was operated at a constant energy of 8 mJ and a constant repetition rate of 500 Hz at 193 nm. A long-term test of this laser system was done. The output energy was constant over the test interval of 1.5 billion pulses. The pulse-to-pulse stability was constant over the total test period. The test was done without changing or cleaning the resonator optics.

Formation of high quality laser beam and the reasons of wave front distortion in electric discharge XeCl laser had been investigated. The influence of macro and micro-inhomogeneities in active volume on radiation divergence is discussed. Possibility of amplification of diffraction limited laser beam practically without distortion is shown.

For discharge pumped F₂ lasers, the uniformity of the laser medium is important for the laser quality. So that, we developed a one-dimensional simulation code to investigate the effect of the inhomogeneity of the initial electron density. Only a few percent initial fluctuations affected the main-discharge electron number density largely.

Visible light optical interferometer was used to observe the flow patterns of a F₂ laser. The particle density distribution before and after the discharge under high repetition rate operation was shown with different values of clearance ratio. It was found out that the value more than 2 was necessary to obtain suitable gas condition for the normal laser operation.

An X-ray preionized XeCl laser with a large aperture (9x7 cm) is described. Laser operates at Ne-Xe-HCl mixture with pressure up to 4 atm. Paper-oil pulse forming lines and rail-gap switch for discharge pump was used. 10 J output with optical pulse duration up to 300 ns (FWHM) have been extracted from active volume 5.4 l with an electric efficiency 1.2%.

A discharge in high-pressure xenon excilamps is studied experimentally and theoretically. In the absence of an additional source of xenon preionization, the volume discharge is produced in the form of a diffuse cloud or diffuse cones at pressures of several hundreds of torrs. Under these conditions, radiation is emitted with a high efficiency within the VUV spectral range. The results of simulations have shown that, at the pressure on the order of 100 Torr and the field voltage on the order of 10 kV/cm, the established near-cathode layer is on the order of several tens of microns, which is much less than the wire radius. The cathode layer, the potential drop in the near-cathode area is much lower than the voltage applied to the discharge gap. We put forward a hypothesis that the formation of the volume discharge is due to the presence of dense plasma in the near-cathode area, and this plasma plays the role of a plasma cathode.

Extreme Ultraviolet (XUV) sources based on femtosecond laser - high order harmonic generation (HHG) in atomic gases are presently in a period of rapid development. The HHG sources offer the additional advantage of delivering much shorter pulses compared to those of plasma generation or synchrotron sources. Furthermore, because they are coherent sources with high photon energy, they support attosecond pulse (10^-18 s) generation, pushing the frontiers in both science and technology. These pulses open up research on unprecedented time scales, characteristic of bound electron motion. Issues related to the production and characterization of such pulses are presented.

Precise phase matching and energy scaling of high-order harmonic generation enables us to obtain sub-microjoule up to microjoule optical energy in the XUV and soft-x-ray regions. Because of its good spatial profile and coherence, we can expect to achieve a focused intensity of 10¹³-10¹⁴ W/cm², which will be used to explore the ultrafast nonlinear optics and ultrashort pulse generation in the attosecond regime.

Pulse energies of 4.5 mJ (1 kHz) and 1 mJ (10 kHz) at a pulse length of 4.5 ps have been demonstrated with an Yb:YAG thin disk regenerative amplifier. Possibilities and current limitations of power scaling are discussed. The occurrence of bifurcation and deterministic chaos in the pulse energy has been studied.

A 24-mJ diode-pumped chirped-pulse regenerative amplifier with a cooled Yb:LiYF₄ crystal has been developed. A 10-mJ pulse energy with sub-ps pulse duration was obtained with a 660 fs pulse duration after compression.

Current status of CO₂ laser system “Picasso-2” intended to generate 10 μm pulse train with tunable pulses duration 2÷100 ps, interpulse separation ≈ 10 ns and train’s peak power over 1 TW is reported.

The pulsed barrier discharge for molecular (CO₂) laser excitation is presented and its superior characteristics are discussed. The volume-uniform barrier discharge in nitrogen and N₂:CO₂He mixture at 500 hPa is confirmed for nanosecond pulse generator. The spatially homogeneous discharge in whole working-gas volume, which is of key-importance for laser technology, was generated. In all considered cases the values of maximal energy deposition for pulse generator exceed 50-100% these obtained using AC sinus-like power-source. Moreover, the electrical efficiency of a pulsed generator was close to that of AC power-supply.

In the 25 years since its invention the first generation COIL technology has matured to an extent which is demonstrated by large scale high power laser projects. It is the intention of this paper to address the worldwide effort in COIL technology with special emphasis on new developments and alternative approaches. Singlet oxygen generator concepts and iodine mixing techniques are reviewed and evaluated as well as different optical resonator designs. A road map for future research and development work will address the issues of power scaling, pumping and ejector requirements, and beam quality. Finally, prospects for an all electric COIL technology will be given.

Spatial distributions of the gain, temperature and I₂ across the flow were studied for transonic and supersonic schemes of the iodine injection in a slit nozzle supersonic chemical oxygen-iodine laser (COIL) as a function of the iodine and secondary nitrogen flow rate and jet penetration parameter. The mixing efficiency for supersonic injection of iodine (~ 0.85) is found to be much larger than for transonic injection (~ 0.5), the maximum values of the gain being ~ 0.65%/cm for both injection schemes. Spatial distributions of the gain corresponding to the maximum power are found. A simple one-dimensional model is developed for the fluid dynamics and chemical kinetics in the COIL. Two different I₂ dissociation mechanisms are tested against the performance of a COIL device in our laboratory. The two mechanisms chosen are the celebrated mechanism of Heidner and the newly suggested mechanism of Heaven. The gain calculated using Heaven’s dissociation mechanism is much lower than the measured one. Employing Heidner’s mechanism, a surprisingly good agreement is obtained between the measured and calculated gain and temperature over a wide range of flow parameters.

Theoretical studies have indicated that sufficient fractions of O₂ (¹Δ) may be produced in an electrical discharge that will permit lasing of an electric discharge oxygen-iodine laser (ElectriCOIL) system in conjunction with injection of pre-dissociated iodine. Results of those studies along with more recent experimental results show that electric excitation is a very complicated process that must be investigated with advanced diagnostics along with modeling to better understand this highly complex system. In this paper, recent work in the development of the ElectriCOIL system is discussed. A kinetic package appropriate for the ElectriCOIL system is presented and implemented in the detailed electrodynamic GlobalKin model and the Blaze II laser modeling code. A parametric study with the Blaze II model establishes that it should be possible to attain positive gain in the ElectriCOIL system, even with subsonic flow. The Blaze II model is in reasonable agreement with early gain data. Temperature is a critical flow variable, especially in the subsonic cases. Simulations of a supersonic ElectriCOIL system indicate that significant performance levels can be attained, even at low yield levels of 20% or less. In addition, pre-dissociation of the iodine is also shown to be very important for the supersonic flow situation. Given the critical nature of the temperature issue, it appears that supersonic flow will be required for the ElectriCOIL system to achieve significant performance levels, but these simulations also indicate that it should be possible to demonstrate a subsonic system.

The paper presents experimental studies of supersonic oxygen-iodine laser (OIL) using twisted-flow singlet oxygen generator (SOG) over a wide range of the singlet oxygen pressures and the buffer gas flow rates. The experiments used different designs of the nozzle unit and mixing system for singlet oxygen and iodine gas with the carrier gas (such as nitrogen or helium). For a wide range of the key parameters, the study looked at the efficiency of supersonic OIL with variation of the singlet oxygen pressure. The measurements were made for different positions of the iodine injection plane with respect to the critical cross-section (both in the subsonic part of the nozzle and in the supersonic flow). The gas pressure at the nozzle unit entry was varied from 50 to 250 Torr. The total pressure loss have been found for different mixing designs. Experimental curves are given for energy performance and chemical efficiency of the supersonic OIL as a function of the key parameters. Comparison is made between the calculated and experimental data. For the optimum conditions of OIL operation, chemical efficiency of 25-30% has been achieved.

We present the experimental results on singlet oxygen generation via interaction of pumping photons (laser or lamp light), fullerenes (or fullerene-like nanoparticles - astralens) and oxygen in solid-state structures, in solutions and in suspensions. It was shown that the singlet oxygen is adsorbed by the solid-state fullerene coating and by powder-like astralen. It was shown that in course of evaporation of the solution (due to the pump action) is observed the singlet oxygen extraction to the gaseous phase, and the lifetime of ¹ΔO₂ grows significantly.

Ten kilowatt CW COIL with originally designed jet-type SOG has been developed and tested. Experimental and numerical methods used for diagnostics and simulation of laser operation are presented, as well as results of experiments and numerical simulation

The 10kW-class Chemical Oxygen-Iodine Laser (COIL) device of DLR¹ was used for demonstration of efficient power coupling into a commercial fiber optic system (HIGHYAG, Berlin) modified for 1.315 μm radiation. Transmission investigations were performed with different intra-cavity apertures of the stable COIL resonator to match the out-coupled laser beam to the fiber optic system. The transmitted power through the 20 m long fiber with core diameter of 1000 μm exceeded 6 kW during a typical 8 s test run of the laser. The highest transmitted power amounts to 11 kW, the highest value reported in literature. The transmission ratio was above 90%. Samples of metal and non-metal materials were cut by using nitrogen as processing gas. The materials were selected with regard to their application in the contaminated area of nuclear power plants. The results of the cutting experiments were used in theoretical models^2,3 for extrapolation of the cutting data. Scaling studies were performed to estimate achievable cutting depth with COIL systems of higher laser power.

An alternative chemical way of atomic iodine generation for the chemical oxygen-iodine laser (COIL) was studied. This development was aimed at the laser power increase and simplification of the laser operation control. The method is based on the fast reaction of hydrogen iodide with chemically produced chlorine atoms. Kinetics of the process was studied in two types of the small-scale reactor and verified in the cavity of the supersonic COIL. The optimum yield of atomic iodine formation in the nitrogen atmosphere was very high (up to 100%) even in the COIL cavity and declined slightly with the distance from the supersonic nozzle throat. In the first experiments of atomic iodine generation in the flow of singlet oxygen in COIL, the gain of 0.18%.cm^-1 was attained at rather low flow rate of atomic iodine (0.9 mmol.s^-1). In earlier investigation of COIL in the conventional arrangement with molecular iodine, no gain was achieved at the corresponding I₂ flow rate (0.45 mmol.s^-1). In the COIL with the new method of chemical generation of atomic iodine, a nearly constant gain along the flow axis was measured. It gives evidence that there is no strong quencher of excited atomic iodine in the reaction mixture. The published data represent the first results on gain measurement in the COIL with chemically generated atomic iodine. They promise an improvement of the COIL operation using the chemically generated atomic iodine.

Several kinds of high reflection thin films are prepared by electron beam gun with different designs and coating materials. The reflectivity, transmission, absorption and scattering of these thin films are measured and calculated, the loss of absorption and scattering of the thin films are mainly discussed. Furthermore, the absorption of films are also analyzed under different annealing temperature, it is found that the absorption loss can be dramatically reduced after annealing. At the same time, the compositions of thin films are tested by AES (Auger electron spectroscopy) to detect whether there is impurity or contamination.

Theoretical models for the chemical oxygen-iodine laser (COIL) depend on a variety of assumptions and empirical data to provide closure and simplify solution of the governing equations. Among the various assumptions and empirical data built into models for COIL are assumptions regarding steadiness in the time domain and which kinetic processes are significant in addition to the measured values for the rates at which the kinetic processes occur. The work discussed here is directed toward elucidating and increasing the understanding of the assumptions underlying COIL models and the implications for the modeled physical processes underlying the COIL, driven by current directions in the development of this technology. This is directly linked to efforts to achieve improved COIL efficiencies and performance, since excursions well outside traditional operational parameter space are necessary. As such excursions are made, the distance from the traditional parameter space where COIL models have been baselined and validated becomes much greater, increasing the importance for understanding the factors that influence the accuracy of the simulations. In this role of increasing the level of understanding regarding the limits to the accuracy of COIL models, these simulations provide information important to current work investigating configurations and operating conditions well outside of the traditional parameter space.

A modified simplified rate equation (RE) model of flowing chemical oxygen-iodine laser (COIL), which is adapted to both the condition of homogeneous broadening and inhomogeneous broadening being of importance and the condition of inhomogeneous broadening being predominant, is presented for performance analyses of a COIL. By using the Voigt profile function and the gain-equal-loss approximation, a gain expression has been deduced from the rate equations of upper and lower level laser species. This gain expression is adapted to the conditions of very low gas pressure up to quite high pressure and can deal with the condition of lasing frequency being not equal to the central one of spectral profile. The expressions of output power and extraction efficiency in a flowing COIL can be obtained by solving the coupling equations of the deduced gain expression and the energy equation which expresses the complete transformation of the energy stored in singlet delta state oxygen into laser energy. By using these expressions, the RotoCOIL experiment is simulated, and obtained results agree well with experiment data. Effects of various adjustable parameters on the performances of COIL are also presented.

A one-dimensional kinetic computer model of the subsonic Chemical Oxygen-Iodine Laser (COIL) is discussed. The computational results are used for a re-interpretation of data published earlier on the performance of a subsonic COIL experimental device in the Institute of Physics, Prague.

This paper reports on investigating self-sustained volume discharge (SSVD) characteristics in CH₃I, C₃H₇I, C₄H₉I, CF₃I and their mixtures with SF₆ and N₂, employed as buffer gases, and with O₂. The investigations performed in the plane-plane electrode system displaying high electric field edge enhancement have shown that in C₃H₇I, C₄H₉I and their mixtures with SF₆, N₂ and O₂ SSVD is realized in the form of a self-initiated volume discharge (SIVD)- SSVD with no any preionization. Addition of SF₆ or N₂ in C₃H₇I, C₄H₉I leads to increasing the discharge stability, the latter being not adversely affected by addition of O₂ in amounts of up to 300% of the iodide partial pressure. The fact that SSVD in C₃H₇I and C₄H₉I develops in the form of SIVD is indicative of these discharges to be promising for creation of high power pulsed and pulsed-periodic COIL. SIVD has been performed at total mixture pressures of up to 72 Torr and energy depositions of up to 130J/l in a volume of 1.5 l. The performed experimental modeling involving laser geometry of the discharge gap gives firm evidence that SIVD is promise for being used in creation of pulse and pulse-periodic COIL.

Pulsed oscillation of chemical oxygen-iodine laser, which is comprised of a pulsed singlet oxygen generator (SOG) and a photolytic iodine laser, is studied. This scheme allows one to produce a large aperture and high-pressure laser medium while maintaining a minimum degradation of stored energy by water vapor. The experimental apparatus consists of a porous pipe SOG, an iodine donor (CH₃I) injector, a flash lamp and an optical resonator. Laser oscillation experiments are conducted and the operational characteristics of the apparatus are investigated. Pulse duration is inversely proportional to the iodine donor concentration as expected. The oscillation capability for different iodine donors is studied and it is concluded that the iodine donors containing fluorine are not suitable for the proposed scheme. Unfavorable chemical dissociation of iodate, which was observed in the previous study, is avoided by the optimization of the iodine donor injection and flash exposure timings. Maximum output energy of 730mJ with pulse duration of 65μm is obtained.

Regeneration of Basic Hydrogen Peroxide (BHP) for Chemical Oxygen Iodine Laser (COIL) has been studied. The apparatus is an electrolyte H₂O₂ generator, which is composed of anode chamber, cathode chamber with gas diffusion electrode and cation exchange membrane. BHP containing 5 to 10 weight percent (wt%) of H₂O₂ is supplied to the apparatus and the change in the H₂O₂ concentration is measured for various operational conditions. A 5.11wt% BHP is regenerated with current efficiency of 92% and a 10.4wt% BHP is regenerated with current efficiency of 73%. It is found that the BHP flow rate and temperature of the BHP are critical to obtain high current efficiency.

Mixing enhancement technique of supersonic chemical oxygen-iodine laser (COIL) is studied. The difficulty of supersonic mixing due to the compressibility of the fluid has been overcome by the introduction of streamwise vortex into the flow. The developed nozzle is a staggered array of wedges, looks like “X” letter from the side of the flow duct. Computational fluid dynamics (CFD) is employed for the design optimization of the proposed mixing nozzle. A remarkable mixing condition is found when iodine injector is located at the exit plane of the mixing nozzle. Experiments are conducted and good agreement with calculation is obtained in terms of iodine molecule distribution. A 266W of output power with chemical efficiency of 14.6% is obtained and good mixing capability of the proposed nozzle design is confirmed.

Two-dimensional CFD model was applied for the study of mixing and reaction between gaseous chlorine dioxide and nitrogen monoxide diluted with nitrogen during atomic iodine generation. The influence of molecular diffusion on the production of atomic chlorine as a precursor of atomic iodine was predominantly studied. The results were compared with one-dimensional modeling of the system.

The paper presents data from experimental study and optimization of the iodine gas and singlet oxygen mixing process in a supersonic chemical oxygen- iodine laser (COIL) with a two- dimensional or honeycomb nozzle unit. The iodine concentration and the lasant gain fields inside supersonic flow have been found for a wide range of key parameters.

Mist singlet oxygen generator (Mist-SOG) has been developed in order to increase the BHP utilization. On the other hand, Mist-SOG generates much more water vapor than conventional SOG because the heat capacity of the BHP is small. It is well known that the water vapor deactivates the excited iodine. In order to remove the water vapor, we developed a jet-cold trap. In this method, a nozzle sprayed a chilled H₂O₂ at 238K with a thin layer form to the gas flow directly in order to get the large specific surface for the water vapor. As a result of experiment, Water vapor partial pressure reduced from 3.3 Torr at the BHP flow rate of 2.2 ml/s and Cl₂ flow rate of 3.5 mmol/s for the 65µm BHP droplets.

The work cites the experimental data on a small-scale Microwave Discharge Singlet Oxygen Generator. It was shown that a steady-state moving microwave discharge in the plasmatrone with a coaxial cavity resonator allows obtaining of the (¹Δ_g) singlet oxygen yield of 20-23% at 1-2 Torr pure oxygen.

A test facility was designed to operate a disk type singlet delta oxygen generator in a closed loop for the flow of basic hydrogen peroxide (BHP). The facility allows the investigations of the influence of operating conditions like BHP flow, gas flow, disk rotation speed, and system components like disk package parameters and type of liquid separator on the generator performance and the ascertainment of the facilities capability for long term COIL operation. The dimension of the generator in the closed flow loop is chosen in accordance with the 10 kW-DLR-COIL.

The gain optical guide effects in a COIL are found and studied for the first time. The non-uniform distribution of gain in one transverse direction is assumed to be caused by non-uniform injection of the secondary flow. Our calculations who that the gain and optical guide effects have an important influence on the transverse shape of the optical field, which results in some effects such as the reduce of the output power and the offset of the optical beam, which have been observed in the experiments made in China Academy of Engineering Physics.

Optimization of iodine injection scheme was conducted in Miki Pulley Co., Ltd. using CFD approach. Variation of the mixing speed as a function of an I₂ jet penetration depth, nozzle expansion ratio, and I₂ injection point are analyzed. It was found that the inherent geometry of our nozzle and I₂ injector affects the I₂ mixing process. Influence of a backpressure to the cavity flow condition was also investigated in order to estimate the pressure recovery capability of our diffuser. The normal shock based diffuser efficiency for Mach=2.7 flow was 54.5%.

Quality and power of the extracted beam from a Q-switched supersonic-flow chemical oxygen-iodine laser has been investigated by numerical simulation. The flow system adopted in this study is a throat mixing system proposed in the previous paper. The calculation code consists of two parts: one is a code for the gas flow and chemical reactions, and the other is that for the optics. Because of the difference of characteristic times between the phenomena in these two parts, every 300-time-steps of the latter calculation is coupled with one-time-step of the former. Both geometric and wave optics are calculated in order to assess the effects of diffraction. The wave optics is calculated with a paraxial wave equation derived in this study. The results indicate that the time dependence of the beam power is qualitatively similar between the wave and geometric optics. The peak power reaches to the maximum value at 90 ns after the initiation of oscillation. The peak value for the wave optics is 9% less than that for the geometric optics. The calculated spreading angle of the beam shows that the laser quality at the maximum power is slightly worse compared to that of continuous extraction.

Miki Pulley has pursued the development of a prototype COIL module for field and industrial applications since its transfer from Tokai University in 2000. The test module has already been constructed in our laboratory. The current status of the development is presented. The achieved chemical efficiency was 17.5% at the chlorine flow rate of 13.2mol/min. The corresponding laser power was 3.5kW.

The effect of the translational nonequilibrium on performance modeling of flowing chemical oxygen-iodine lasers (COIL) is emphasized in this paper. The spectral line broadening (SLB) model is a basic factor for predicting the performances of flowing COIL. The Voigt profile function is a well-known SLB model and is usually utilized. In the case of gas pressure in laser cavity less than 5 torr, a low pressure limit expression of the Voigt profile function is used. These two SLB models imply that all lasing particles can interact with monochromatic laser radiation. Basically, the inhomogeneous broadening effects are not considered in these two SLB models and they cannot predict the spectral content. The latter requires consideration of finite translational relaxation rate. Unfortunately, it is rather difficult to solve simultaneously the Navier-Stokes (NS) equations and the conservation equations of the number of lasing particles per unit volume and per unit frequency interval. In the operating condition of flowing COIL, it is possible to obtain a perturbational solution of the conservational equations for lasing particles and deduce a new relation between the gain and the optical intensity, i.e., a new gain-saturation relation. By coupling the gain-saturation relation with other governing equations (such as the NS equations, chemical reaction equations and the optical model of gain-equal-loss), we have numerically calculated the performances of flowing COIL. The present results are compared with those obtained by the common rate-equation (RE) model, in which the Voigt profile function and its low pressure limit expression are used. The difference of different model’s results is great. For instance, in the case of lasing frequency coinciding with the central frequency of line profile and very low gas pressure, the gain saturation relation of the present model is quite different with that of the RE model.

A new RF plasma jet generator (DSOG-4) of singlet delta oxygen has been developed for use in an oxygen-iodine laser. Two different modes of operation were studied: (1) chilling of the plasma jet by a neutral gas stream and (2) an energy transfer from plasma jet to a neutral gas stream. The plasma jet was produced in an Al cylindrical nozzle, having the cross section of 3 mm². The chilling mode used mixtures O₂:NO to produce the plasma jet, which was subsequently chilled by He, injected at the nozzle exit. The energy transfer mode used mixtures He:NO to produce the plasma jet, which was mixed with a neutral stream of O₂, allowing thus energy transfer to oxygen molecules with enhanced selectivity. The RF frequency was 99.9 MHz and the RF power was up to 200 W. Both the modes of operation were tested in a transverse flow Discharge Oxygen-Iodine Laser (DOIL). The singlet delta oxygen yield and the atomic iodine luminescence at the wavelength 1315 nm were measured. The energy transfer mode proved to be an effective alternative of the classic chilling mode. It enables new generating schemes, which may bypass some of the classic limitations in oxygen discharges.

The Japanese national R&D project “Advanced Photon Processing and Measurement Technology” started at the end of August, 1997 within the framework of the Industrial Science and Technology Frontier Program of MITI (now METI, Ministry of Economy, Trade and Industry) terminated its 5 year duration at the end of March, 2002, and has entered the stage of final evaluation. R&D activities of the project were promoted energetically by the 14 RIPE members and a national institute, and various excellent results of world top level were obtained. This paper summarizes the outline of the latest results obtained in the development of high-power, high-efficiency diode-pumped solid-state lasers within the project.

A double-clad thulium-doped silica fibre laser, pumped by two beam-shaped diode-bars operating at 787-790nm, has yielded 14W of single-mode output at ~2µm, with a slope efficiency with respect to launched power of 46%. Using a tunable laser configuration, comprising an external cavity with a diffraction grating, a maximum output power of 10.5W at 1921nm has been obtained, and wavelength tuning at multi-watt power levels over 215nm from 1855 to 2070nm has been demonstrated. The prospects for further improvement in performance will be discussed. In addition, a simple approach for further scaling of power levels from fibre lasers in the two-micron regime, based on intracavity wavelength combining of multiple fibre lasers is described. In a preliminary demonstration, four cladding-pumped thulium-doped silica fibre lasers are wavelength-combined yielding an output power >14W. The prospects for further increase in output power via this approach will be discussed.

Scaling studies of a Cr:LiSAF power oscillator are being performed and 80W average output power has been achieved at 10Hz repetition rate using a newly designed transverse flow cell. An SBS phase conjugate system using Fluorinert FC-75 has been set up and reflectivity measurements indicate very good fidelity with reflectivities >60%, at pulse energies of less than 1J.

Solid-state laser sources are required for numerous applications in industry and science. High output power while preserving a diffraction limited beam quality results in high brightness operation. However, conventional laser systems suffer from thermally induced phase distortions in the active medium, which considerably reduce the beam quality. Proper cooling, diode pumping, as well as active media with high quantum efficiency reduce the thermal load. But the still remaining phase distortions result in a reduction of beam quality. Phase conjugate mirrors are suitable to compensate for phase distortions in master oscillator power amplifier systems (MOPA). Stimulated Brillouin scattering (SBS) in commercial multimode silica fibers leads to reliable and stable phase conjugation. A further advantage is, that the fiber core diameter can be select in respect of the systems pulse energy to obtain the necessary intensity for high reflectivity SBS. Three systems with phase conjugators have been investigated. A pulse pumped, passively q-switched Nd:YAP System which delivers an average output power of 315 W with M² = 2.6. The pulse energy is about 160 mJ with a pulse width of 140 ns at 2 kHz repetition rate. Another pulse pumped MOPA system based on Nd:YAG with depolarization compensation delivers an average output power up to 124 W with M² = 2.2. Due to active q-switching the pulse repetition rate and peak power of this system are variable in a wide range. Furthermore a continuously pumped amplifier arrangement with nearly diffraction limited output of 120 W average power has been achieved at 10 kHz repetition rate.

The planar waveguide solid-state laser, using a large core neodymium doped YAG waveguide and face-pumping by diode bar arrays, is currently producing a multi-mode-mode power up to 160 W, and high beam quality operation at 100 W. The large core waveguide has been shown to be capable of scaling to higher powers. In this paper, experimental developments in multi-pass face-pumping are presented, using double-sided pumping of the waveguide section, and ray tracing techniques are presented which provide an assessment of the pumping efficiency.

We report on the development of passively Q-switched Nd:YAG and Nd:YAP lasers with solid-state stimulated Raman scattering (SRS) frequency conversion to 1.2-μm. A new barium tungstate (BaWO₄) crystal was investigated as nonlinear converter. Diode pumped Nd:YAG quasi-continuous-wave slab laser, operated at 14-Hz repetition rate, was passively Q-switched by a Cr⁴⁺:YAG crystal. A three-mirror linear laser cavity with BaWO₄ crystal produced the maximal Raman-shifted output pulse energy of 2.3 mJ. The first Stokes output energy was 1.5 mJ corresponding to 0.4 MW peak power. The SRS conversion efficiency with respect to laser operation at the fundamental wavelength was estimated to 55%. Flashlamp-pumped Nd:YAP laser was passively Q-switched by a BDN II thin film and the repetition rate was 2 Hz. The maximal first Stokes output energy was 12 mJ and the pulse peak power was 1.7 MW. Solid state Raman laser technology can therefore be employed to reach new laser output wavelengths using simple, reliable, and compact arrangements with a use of well-developed Nd-doped host lasers.

A scalable design for diode-pumped 10 kW solid-state laser systems is presented. The system is composed of 10 Nd: YAG discs arranged along a folded unstable resonator axis. The laser efficiency, required pumping power, output laser power are estimated.

A general review of high power solid-state laser research with diode laser pumping in some universities and institutes of China is given. Four research directions are indicated.

This work presents a comparative study of gain media for diode-pumped, high-average power solid-state disk lasers. Relative performance of Nd and Yb doped into several host media is evaluated under several pump and lasing conditions.

Recently, some noticeable effort as been realized in order to improve characteristics of HF/DF pulsed lasers. A few years ago it was supposed that the realization of a high energy HF/DF pulsed laser was only possible by using E-beam excitation, either for a non chain HF/DF gas mixture, or for a chain reaction mixture i.e. H₂/F₂ mixture. Flash lamp initiation of a high-energy chain reaction HF/DF laser was also demonstrated. However every one who wanted to make such a laser working repetitively was convinced of the difficulty of operating an E-beam system or high energy flash for large volume due to the strong electronegative character of the used gases. First attempts to realize large volume discharges have shown that this last idea was not true and that it was relatively easy to obtain homogeneous discharges in SF6 based mixture when the hydrogen donor was a hydrocarbon such as C₂H₄ or C₆H₁₂. This paper will present recent developments directed towards a better understanding of the discharge mechanisms and to an increase of the efficiency and of the specific output energy of HF/DF pulsed lasers by using chain reaction in discharge initiated repetitive and non-repetitive experiments.

This paper reports on the physics of a self-sustained volume discharge without preionization, self-initiated volume discharge (SIVD), in working mixtures of nonchain HF(DF) lasers. Dynamics of SIVD in discharge gaps of different geometry is thoroughly described. The mechanisms of restricting current density in a diffuse channel in electric discharges in SF₆ and SF₆ based mixtures determining the possibility of the existence of SIVD were suggested and analyzed using simple models. It is shown that the most probable mechanisms are the electron impact dissociation of SF₆ and other mixture components, electron-ion recombination and electron attachment to vibrationally excited SF₆ molecules. Starting from a comparison analysis of the rate coefficients of these processes, it was found that the electron-ion recombination is capable of compensating for electron detachment from negative ions by electron impact. It is established that SIVD can be observed not only in SF₆, but in other strongly electronegative gases, e.g., in C₃F₈ and C₃HC_l3. Analysis is given of the factors determining uniformity of active medium in nonchain HF(DF) lasers. Some special features of operating nonchain HF(DF) lasers with small, 2÷6cm, apertures are carefully examined and the results of measuring the nonchain HF(DF) laser divergence are presented. Consideration is given to the problem increasing the aperture and discharge volume of nonchain HF(DF) lasers and, based from the experimental results, the possibility is shown of increasing their energy to a level of ~ 1kJ and above.

Laser action and discharge in gas mixtures of SF6 with hydrogen, deuterium and hydrocarbons are studied. Non-chain HF lasers with specific output energy of 8,8 J/1×atm (140 J/ 1×atm) and DF-laser with output of about 1 J pumped by LC-generators were developed. HF laser efficiency with respect to deposited energy of 10 % was obtained for the first time using inductive and LC-generators.

The theoretical and experimental study of the spectral and energy characteristics of radiation of the pulsed photoinitiated HF/DF-laser operating on the chain chemical process in the gas mixture F₂(H₂+D₂):O₂:He=3:1:0.3:6.7 of atmospheric pressure depending on the relation between the initial concentrations H₂ and D₂ and the oscillation threshold is carried out. The optimum requirements for a simultaneous oscillation on molecules HF and DF in a wide spectral range from 2.7 up to 4.8 µm are determined in experiment and also by numerical modeling.

The problem of the increase of the energy conversion efficiency of a broadband CO2 laser amplifier with optical pumping by the multi-frequency HF-laser radiation is considered. To improve the utilization of the pumping radiation and to broaden the amplifier bandwidth the use of a buffered with Xe mixture of the isotopomers of carbon dioxide and nitrous oxide as active medium is proposed. Experimentally and by calculation the coefficients of an unsaturated absorption of ¹⁴N¹⁶O, ¹²C¹⁶O₂ and ¹³C¹⁶O₂ were determined on 19 lines of the pulsed chemical HF-laser which concentrate up to 60% of its total output energy. The estimations show that the application of a three-component mixture of these molecular gases enables to increase up to 30% the coefficient of the utilization of the pumping radiation at aperture about 10 cm.

A role of UV preionization in non-chain HF(DF) lasers has been investigated. The influence of preionization on the discharge uniformity and on the duration of stable burning of a self-sustained volume discharge (SSVD) in working mixtures of non-chain HF lasers as a function of the energy stored in capacitors are comprehensively studied. Also presented are discharge photographs taken under identical conditions with and without preionization. It is shown that SSVD characteristics and laser energy are scarcely affected by preionization if the discharge lasts more than 150ns and the cathode surface area is in excess of 300 cm². In HF lasers with the cathode surface area and discharge duration of less than 300cm² and 150ns, respectively, preionization is essential for nothing but stabilization of the discharge voltage and breakdown delay and for improving discharge uniformity. If the opposite takes place preionization has no influence on the laser characteristics.

The field of laser treatment on semiconductor materials is still displaying new important developments. Driven by the application to flat panel displays, excimer laser sources are being widely employed for the crystallization of silicon thin films. They are integrated with mass-production equipments and with techniques that control the location and orientation of the micro-grains, and this method allows to obtain thin film large-grain polycrystalline silicon whose carrier mobility is approaching silicon-on-insulator at a laboratory scale. Nowadays there is an increasing development of methods for improving the crystal fraction, the surface flatness, the grain arrangement on small and large areas. The method seems to be the only lasting approach to obtain high performance on flexible plastic substrates, unrivaled by devices based exclusively on organic materials. Here, the progress of recrystallized silicon obtained by excimer laser irradiation is reviewed, and its evolution is linked with the past decades of laser treatment of semiconductor materials. The advanced results obtained on glass are extrapolated to the case of polymer substrates.

Aluminum alloys are interesting in many and many industrial applications, from the classical aircraft industry to rail and road vehicles manufacturing (High Speed Train, Car Structure and Body). Recently much more attention for Aluminum Alloys, 5000 and 6000 Series, has been carried out by Shipbuilding Industry, especially for using in the H.S.L.C. (High Speed Light Craft). Therefore the aim of this experimental work has been to study, develop and test a reproducible CO₂ laser welding procedure and technique of four specific alloys, that is AA 5083, AA 5383, AA 5059 (Al-Mg Alloys), and AA 6082 (Al-Mg-Si Alloy). Different techniques, methodologies, covering gases, nozzles, focusing lenses and mirrors, welding speed range, laser power range (1000 and 2500 W) have been carefully experimented. The melted zones properties have been evaluated by cross sections, and some visual inspections by a NIKON LUCIA Imaging System correlating each experimental test, results and evaluations to the adopted process parameters and to the thermo-physical properties of the tested alloys.

We report on rapid in-situ analysis of liquid and solid steel samples under reduced ambient pressure by laser-induced breakdown spectroscopy (LIBS) using a transportable system. LIBS denotes a technique where a pulsed laser beam is used to ablate small amounts of the target material. The characteristic optical emission line intensities of the excited species in the laser-generated plasma plume allow a quantitative chemical analysis of the target material. Over a wide range of parameters the expansion of the plume can be described by a generalized shock wave model. LIBS is a fast, non-contact method, which can be carried out under various atmospheric conditions allowing large working distances between the sample under investigation and the detection system. These properties make LIBS applicable to process control especially for vacuum devices used in metallurgy.

The use of electromagnetic body forces in laser beam welding of aluminum alloys is a new method to shape the geometry and to enhance the quality of the weld seams. In this new approach, electromagnetic volume forces are utilized by applying magnetic fields and electric currents of various origins. Acting in the liquid metal, they directly affect the flow field and can lead to favourable conditions for the melt dynamics and energy coupling. Numerous welds with full and partial penetration using both CO₂ and Nd:YAG lasers demonstrate that this method directly influences the seam geometry and top-bead topography as well as the penetration depth and the evolution of pores and cracks. In the case of full penetration, it is also possible to lift or to lower the weld pool. The method, therefore, can be used to shape the geometry and to enhance the quality of the weld seam. Depending on the orientation of an external magnetic field, significant impacts are achieved in CO₂ welding, even without an external current: the shape of the cross-sectional area can be increased of up to 50% and also the seam width is changed. Whereas for such conditions with Nd:YAG lasers no significant effect could be observed, it turned out that, when an external electric current is applied, similar effects are present with both wavelengths. In further investigations, the effect of electromagnetic body forces resulting from the interaction of an external current and its self-induced magnetic field was studied. Hereby, the current was fed into the workpiece via a tungsten electrode or a filler wire. The resulting phenomena are the same independent from wavelength and means of current feed.

We have constructed a laser welding system, which enabled high-power laser welding by combining three laser beams of 1 µm wavelength. Its wavelength enables optical silica fibers transmission and the flexible system. The heart of this system consists of a 4 kW and a 6 kW Nd:YAG lasers and a 10 kW class Chemical Oxygen-Iodine Laser (COIL) beams of 6 kW Nd:YAG laser and COIL are combined in a coaxial beam and its maximum average power is 19 kW. The third laser beam, 4 kW Nd:YAG laser beam, is added obliquely from the same side of workpiece or oppositely from the reverse one. The effects of various welding parameters were investigated, such as the laser power, pulse modulation, and so on. As a result of the welding test with the 6 kW Nd:YAG laser, it was clarified that the pulse wave (PW) has good efficiency of deeper penetration at low welding speed. When the combined beam with CW COIL and PW Nd:YAG laser was used, 20 mm penetration on the stainless steel could be achieved at a welding speed of 1 m/min. By adding the third laser beam, the both side welding on 30mm thickness plate could be achieved.

A segmented pixel drawing (SPD) method has been proposed in our laboratory in order to create not only an accurate tone expression but also an artistic tasteful expression which has been expressed by peculiar visual effects and tones from a digital image. The visual effects and tones can be expressed by various surface structures in each segmented pixel. The segmented pixel consists of a dot-matrix arrangement with a controllable dot size. In this SPD method, a slab, RF excited CO₂ laser developed in our laboratory has been used. A transparent acrylic board was used for the processed material because of its high absorptivity to a CO₂ laser. In this study, random dot arrangement has been introduced to the SPD method in order to create a natural and smooth artistic work. By introducing the random dot arrangement, inconspicuous boundary of each pixel and fluent tone change have been realized. Fluent tone was expressed by number of dots in a pixel which is calculated from a logarithm function. Changing the exposed energy for each dot, a size of dot can be flexibly controlled to create various visual effects. From digital image, a tasteful artistic work which has a smooth boundary and fluent changing tone has been successfully obtained by using random dot arrangement.

The most important and experimentally established results of unusual solitary waves (pulses) are summarized, which taking place specifically in processes of laser-matter interactions and could be important also for active condense matter media of laser systems itself. This work was sponsored as project 00-02-17249 by RFBR (Russia).

Pulsed laser propulsion may turn out as a low cost alternative for the transportation of small payloads in the mass range of 1 to 10 kg to high altitudes and low Earth orbits (LEO). Using a pulsed, electron beam-sustained multi-wavelength laser with pulse energies as high as 410 J in CO₂ laser gas and possible repetition rates up to 100 Hz the launch of a “Lightcraft” has been demonstrated in the laboratory. A series of single pulse impulse measurements with a pendulum has been performed to derived the impulse coupling coefficient under various conditions. Simple plasma diagnostic and fluid dynamic investigations have been carried out as well.

Investigations on soft x-ray emission from a gas puff target irradiated with high-power laser pulses are presented. The aim of the studies is to develop a laser plasma x-ray source based on a double-stream puff target irradiated with nanosecond laser pulses and a compact, table-top soft x-ray laser using an elongated gas puff target irradiated with picosecond laser pulses.

AVLIS process for Yb has been studied theoretically and experimentally. Installations to produce highly enriched ¹⁶⁸Yb in industrial scales were created. The contents of ¹⁶⁸Yb in the laser produced plasma was reached 90 - 95 %, in the material deposited on the ions collector - up to 62 % and in the washing liquid - up to 45 %. The rate of the enriched yterrbium production was up to 5-10 mg/hour (over 1 g per month). For the first time a profitable commodity was produced by the AVLIS method. Using the selective two-stage ionization and Zeeman effect the essential enrichment of various isotopes of a palladium is reached: ¹⁰²Pd - up to 18 % (on a comparison with the natural contents 1 %), ¹⁰⁴Pd - up to 70 % (on a comparison - 11.4%), ¹⁰⁵Pd - up to 60 % (on a comparison - 22.33%).

The feasibility of producing continuous laser sparks (CLSs) with a resistance per unit length of 100-400 Ω/cm by focusing radiation from CO₂ laser with a conical mirror is demonstrated. The laser energy input per unit length required for this is experimentally found to be equal to ~200 J/m. The possibility to efficiently control the trajectory of an electric discharge by means of a CLS is demonstrated. A CLS is found to be an analogue of a high-conductivity metal rod during the electric breakdown and electric potential transfer. The effect of polarity in the electric breakdown of air gaps between the CLS plasma channel and a metal rod is discovered and interpreted. The transverse structure of the CLS conductivity is investigated. Most likely the CLS conductivity at the initial state is due to the photoionization of air by the radiation of primary nuclei of the optical breakdown.

This paper reports the findings of a research Design of Experiment (DOE) based to assess the impact of changes in a set of technological parameters on the morphological characteristics - in particular the microhardness of the welded section - of laser welded stainless steel (AISI 304 and AISI 430) lap joints. The Authors also highlight future research directions.

This experimental research work presents for the first time the results obtained by using a new non-conventional process, that is a cold and hot laser surface tratment on steels. The aim is to obtain Surface Hardening Structure by a sharp change in temperature obtained by employing a laser beam that passes on steel surfaces , having many tenths degrees below zero (≈ -196°C). The materials experimented have been some different Carbon Steels as Constructional ones (Fe 510 - Fe 360 B) and Medium and High Carbon content Steels ( C40-C70 ). The innovation of this new process consists havig to use a powerfull cooling medium - the liquid Nitrogen - into a Dewar recipient in which the steel has immersed for some minutes. The preliminary researches and tests have shown that, also on steels having a low content of Carbon, the Surface Hardness has significantly increased, so to reach values up to an increase of about 50% respect to the relate value measured on the base material.

An influence of laser beam surface alloying of such substrates as Armco iron as well as the structural carbon steel (45) and the corrosion resistant chromium steel (2Cr13) on their performance under the cavitation erosion conditions was investigated. The powders of various additives were melted and alloyed by means of CO₂ laser beam, and subsequently subjected to cavitation loading at the rotating disc facility. As a result of assays carried out four coatings of high (Co) or contributing to the increase in the impact toughness (Ni, Mn) were indicated as the responsible for the substantial improvement of the material wear properties.