This PDF file contains the front matter associated with SPIE Proceedings Volume 7131, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

High brilliance performance of chemical oxygen iodine lasers (COIL) requires resonator concepts that enable efficient power extraction from a low gain medium while the beam quality is close to the diffraction limit. Different resonator concepts are pre-evaluated by numerical methods and the promising candidates are adapted to a 10 kW-class COIL system. Theoretical predictions and experimental results are found to be in excellent agreement. The beam quality of different resonator architectures is evaluated by standards reported in literature. A further criterion for resonator assessment is introduced.

Supersonic chemical lasers, such as HF /DF and COIL, have always been in the focus of special interest as the most powerful sources of continuous wave generation. Presently, autonomous mobile laser complexes (both air- and landbased) are being developed on the basis of SCL [1-3]. It is commonly accepted that SCL appeared, conditionally speaking, at the crossroads of a number of sciences: of physics - quantum electronics and physical kinetics; chemistry - combustion theory and chemical kinetics; classic optics - theory of resonators, aero-optics, and gas dynamics (there is a supersonic flow in the SCL channel). Due to this fact, all tasks and problems which could be resolved in the course of SCL development have complex character and could be considered as the next stage of complexity in comparison with the well known similar tasks which had been considered earlier. This is why they should be resolved anew with consideration of the specific aspects of the SCL processes. This is true for the gas-dynamic problems: new parameter areas, non-traditional channel geometry, consideration of new phenomena, etc.Supersonic chemical lasers, such as HF /DF and COIL, have always been in the focus of special interest as the most powerful sources of continuous wave generation. Presently, autonomous mobile laser complexes (both air- and landbased) are being developed on the basis of SCL [1-3]. It is commonly accepted that SCL appeared, conditionally speaking, at the crossroads of a number of sciences: of physics - quantum electronics and physical kinetics; chemistry - combustion theory and chemical kinetics; classic optics - theory of resonators, aero-optics, and gas dynamics (there is a supersonic flow in the SCL channel). Due to this fact, all tasks and problems which could be resolved in the course of SCL development have complex character and could be considered as the next stage of complexity in comparison with the well known similar tasks which had been considered earlier. This is why they should be resolved anew with consideration of the specific aspects of the SCL processes. This is true for the gas-dynamic problems: new parameter areas, non-traditional channel geometry, consideration of new phenomena, etc.

1D subsonic COIL model with a mixing length was generalized to include the influence of a variable magnetic field on the stimulated emission cross-section. The results are compared with the measured pulse shape. Equations describing the chemical kinetics were solved taking into account together with the gas temperature also a simplified mixing model of oxygen and iodine molecules. A variable magnetic field transforms the CW regime in a pulsed operation. The advantage of the numerical procedure is a possibility to consider an arbitrary temporal dependence of the imposed magnetic field and to calculate directly the response of the laser output. The method was applied to model the experimental data measured with the subsonic version of the COIL device in the Institute of Physics, Prague, where the applied magnetic field had a saw-tooth dependence. Having achieved a reasonable agreement of our model for the CW regime with the measured dependence of the laser output, the purpose of this contribution is to confront the magnetically switched regime with the measured pulse shape.

An advanced kinetic package for COIL is proposed. The standard kinetic package was revised by adding processes describing the vibrational excitation and relaxation kinetics of I₂ and O₂. A multi-pathway I₂ dissociation mechanism and new kinetic data are key elements of the advanced kinetic package.

Overtone lasing and fundamental band tuning was for the first time obtained in a slab carbon monoxide laser. The compact slab CO laser with active volume 3×30×250 mm³ was excited by a repetitively pulsed capacitive RF discharge (81.36 MHz) with pulse repetition rate 100-500 Hz. The laser electrodes were cooled down to 120 K. Gas mixture CO:Air:He at gas pressures 15-22 Torr was used. An optical scheme "frequency selective master oscillator - laser amplifier" was applied for getting fundamental band tuning. Single line lasing with average power up to several tens of mW was observed on ~100 rotational-vibrational transitions of CO molecule within the spectral range ~5.0 - 6.5 micron. Multiline overtone lasing was observed on ~80 spectral lines within the spectral range ~2.5 -4.0 micron, with maximum single line average output power 12 mW. Total output power of the slab overtone CO laser came up to 0.3 W, with maximum laser efficiency 0.5%. Results of parametric studies of the overtone CO laser including complicated time behavior for laser pulses on different overtone vibrational-rotational transitions are discussed.

Experimental and theoretical study of influence of nitrogen oxides NO and NO₂ admixtures in oxygen containing gas mixture excited by pulsed electron-beam sustained discharge on input energy and time behavior of singlet delta oxygen (SDO) luminescence was carried out. Temperature dependence of the constant of SDO relaxation by unexcited molecular oxygen was estimated.

Numerical simulation and flow-tube experiments are conducted to understand the chemistry of an amine-based all gasphase iodine laser (AGIL). The numerical simulation code developed is a one-dimensional, multiple-leaky-stream-tubes kinetics code combined with all the known rate equations to date. Using this code, we find that the key reactions to achieve positive gain are the deactivation reaction of excited iodine atoms by chlorine atoms and the self annihilation reactions of NCl(¹Δ). The order of the injection nozzles is crucial to suppress these reactions. Flow reactor experiments are conducted based on these calculations, and small signal gain is measured. When NCl₃ is not supplied, absorption of the I(²P_1/2)-I(²P_3/2) transition is observed. When NCl₃ is supplied, the absorption is decreased and the dip occasionally turns to the hump, corresponding to a small signal gain of 5×10^-3 %/cm. To our knowledge, this is the first observation of positive small signal gain of the amine-based AGIL system.

An efficient and compact centrifugal bubbling SOG was employed as energy source in supersonic COIL. A centrifugal bubbling SOG generated gas at 100 torr of total pressure providing 90% of chlorine utilization and 60% of O₂(¹Δ) yield with efficient depletion of BHP chemicals in single pass through SOG. A 1 kW class ejector COIL powered by this SOG demonstrated a specific power of 12.5 W per 1cm³/s of BHP volumetric rate at chemical efficiency 22.7%.

Concentration of iodine molecules at the outlet of an electric discharge iodine atoms generator was measured using laser-induced fluorescence. Methyl iodine was used as an iodine atom precursor. Fraction of iodine extracted from CH₃I in the discharge generator was about 50%. Optimal mode of operation at which 80-90% of total extracted iodine was in the form of iodine atoms was found. Iodine atom content in the gas flow decreased during transportation down to 20-30% at the point of iodine injection into the oxygen flow. Fraction of power load spent on CH₃I dissociation amounted to ≈3%.

Systematic experiments have led to continued improvements in the hybrid Electric Oxygen-Iodine Laser (ElectricOIL) system that significantly increased the discharge performance, supersonic cavity gain, and laser power output. Experimental investigations of radio-frequency (rf) and pulser-sustainer (ps) discharges in O₂/He/NO mixtures in the pressure range of 10-50 Torr and power range of 0.1-2.0 kW have shown that O₂(a¹Δ) production is a strong function of geometry, pressure and diluent ratio. In our investigations, transverse rf discharges always resulted in higher performance (by all metrics) than did the ps discharges tested. Results with both molecular iodine injection and partially pre-dissociated iodine are presented. A gain of 0.17% cm^-1 was measured with a corresponding outcoupled power of 12.3 W (with a 5 cm cavity). Modeling with the BLAZE-V model is in good agreement with discharge and gain data, but significantly overpredicts laser power. This modeling result has led to an interesting investigation of power extraction questions for the ElectricOIL system; these studies include measurements of gain recovery downstream from the laser cavity and estimates of the role that diffractive losses play in our small cavity with high mirror reflectivities.

The active medium of a pulsed DOIL with volume generation of iodine atoms was experimentally simulated using the chemical generator of singlet oxygen and MW discharge to understand the feasibility of a pulsed oxygen-iodine laser with electrical generator of singlet oxygen.

Experimental and theoretical work in progress on supersonic COILs at Ben-Gurion University is reported. Following the achievement of a record value (40%) for the chemical efficiency of a supersonic 5-cm gain length COIL in our lab, a 10- cm gain length device was experimentally studied. Maximum output power exceeding 0.6 kW with chemical efficiency of 35% was obtained for 1% total mirror transmission in preliminary studies. Comparing the results of three-dimensional computational fluid dynamics model calculations to available experimental results [Nikolaev et al., IEEE J. Quantum Electron. 38, 421 (2002)], we show that the model is applicable to high pressure, ejector type chemical oxygen-iodine laser (COIL), reasonably reproducing the measured gain and temperature.

A cw/pulsed radiofrequency discharge coupled by electrodes in coaxial arrangement was used to dissociate iodine atoms from CH₃I or CF₃I molecules diluted in a carrier gas (a mixture of Ar and He). The discharge chamber was arranged directly inside an iodine injector (made of aluminum) to minimize the recombination of generated atomic iodine and enabling an increased assistance of UV light for a photo-dissociation enhancement of I atoms production. The effluent of the discharge chamber/iodine injector was injected into the flow of N₂ downstream the nozzle throat. Measurements of I atoms concentration distribution at different distances from the injection and in two directions across cavity were done by means of absorption measurements at the wavelength of 1315 nm. Dependences of atomic iodine concentration on main RF discharge parameters and flow mixing conditions were measured. This novel method could be an alternative to the chemical generation of atomic iodine and also an efficient alternative to other electric discharge methods of I atoms generation for chemical oxygen-iodine laser (COIL) and discharge oxygen-iodine laser (DOIL).

Based on the experiences made with a negative-branch hybrid resonator (NBHR) a double-pass configuration of the NBHR for a 10 kW class Chemical Oxygen Iodine Laser (COIL) is investigated. Measurements of the intensity distribution of the far field are performed, as well as measurements of the sensitivity against tilts of one of the resonator mirrors. The results are compared to calculations done with the help of the Fresnel-Kirchhoff theory. Enhanced results for divergence, power density in the far field and sensitivity are achieved.

High-power CO laser can be the effective tool in such applications as isotope separation using the free-jet CRISLA method. The way of transfer from CO small-scale experimental installation to industrial high-power CO lasers is proposed through the use of a low-current radio-frequency (RF) electric discharge in a supersonic stream without an electron gun. The calculation model of scaling CO laser with RF discharge in supersonic stream was developed. The developed model allows to calculate parameters of laser installation and optimize them with the purpose of reception of high efficiency and low cost of installation as a whole. The technical decision of industrial CO laser for isotope separation employing condensation repression is considered. The estimated cost of laser is some hundred thousand dollars USA and small sizes of laser head give possibility to install it in any place.

A new spray-type generator of singlet oxygen, O₂(¹Δ), with a following centrifugal separation of depleted liquid was studied. This generator was developed to fulfill following requirements suitable for an advanced Chemical Oxygen- Iodine Laser (COIL): (i) a high-pressure operation, (ii) a single pass of reaction liquid, (iii) an efficient disengagement of gas/liquid mixture, and (iv) a scalability for airborne and mobile application. The generator design takes advantage of very high g/l interfacial surface area of a fine spray produced by a two-phase nozzle and a very fast liquid separation by applying a high centrifugal force.

Since the initial demonstration of chemical oxygen iodine lasers in 1977, researchers have realized that the heart of the COIL system is the singlet oxygen generator. This drives the performance of the system in terms of output power, mass efficiency, engineering complexity, reliability and maintainability. For this reason the singlet oxygen generator has been the focus of intense research and development efforts over the last 30 years. This paper reports on the history of singlet oxygen generators - starting with the simple sparger design used in the initial COIL demonstration and ending with current jet or droplet generators used in laboratories around the world. The relative performance of the different generator types will naturally lead to performance goals for the research efforts of the future.

Singlet oxygen generators are multiphase flow chemical reactors that produce energetic oxygen to be used as a fuel for chemical oxygen iodine lasers. In this paper, a theoretical model of the generator is presented that consists of a twophase reacting flow model that treats both the gas phase and dispersed (liquid droplet) phase. The model includes the discretization over droplet size distribution as well. Algorithms for the robust solution of the large set of coupled, nonlinear, partial differential equations enable the investigation of a wide range of operating conditions and even geometric design choices.

The concept of a high-repetition-rate, high-average power γ-source is based on Compton backscattering from the relativistic electron beam inside a picosecond CO₂ laser cavity. Proof-of-principle experiments combined with comput

In this paper, a surface discharge optical pumping source module with high repetition mode is described. The electrical and radiative properties of the optical pumping source have been studied. The equivalent resistance and inductance, the maximum current and the deposition efficiency of the discharge circuit under various distances of electrodes have been compared. The framing photographs of XeF₂ photodissociation wave have been obtained which show the XeF laser can be formed under the experimental condition. The repetition characteristics of the optical pumping source have been experimentally studied. The maximum pulse repetition rate is up to 90 Hz. The ablation of the dielectric material surface is considered.

A generation of atomic iodine via F atoms with their immediate injection to the supersonic COIL nozzle has been studied. Very high concentrations of I atoms were obtained in the laser cavity in the absence of O₂(¹Δg). Low values of small signal gain measured in the O₂(¹Δg) flow did not correspond to high efficiency of I generation. This was ascribed to O₂(¹Δg) quenching by DO₂· radical.

The paper reports on a study of oxygen-iodine laser operating on active mixture formed by electric discharge in pulseperiodic mode. Experiments were performed with a laser cavity 5 m long. Laser pulses obtained for three various chlorine flow rates ((62 ± 2) mmol/s, (92 ± 2) mmol/s, (105 ± 2) mmol/s) have been manipulated by the statistic rules. The repetition rate of pulses was 12.5 Hz. The chlorine concentration in the laser cavity was varied in the experiments from 1.0·10¹⁵ to 1.0·1016 cm^-3.

Perturbation exchange processes in two-component active medium such as CO₂ : N₂ gas mixture were shown to be a significant factor determined the threshold of self-pulsing oscillations in FFL. Analytical expressions allowed to define increments and frequencies of the oscillations on the base of stationary lasing parameters were obtained

The energy parameters of an HF laser operating by using a new method for oxidising gas production, which is based on the principle of two-region mixing, are optimised. The total amount of the inert diluent (helium) supplied to the laser was varied during experiments by varying its relative fraction only in the second mixing region. For an optimal relative fraction of the diluent in the second mixing zone and for an optimal position of the optical axis of the cavity under a constant pressure in the gas generator, the laser radiation power and the specific power output could be increased by 50% and 60 %, respectively, compared to the laser operation regime realised in our previous experiments. In this case, the inert diluent amount decreased by 35% and the length of the lasing length increased by 20 %.

The results of three-dimensional computational fluid dynamics model calculations are reported in detail and compared to available experimental results [Nikolaev et al., IEEE J. Quantum Electron. 38, 421 (2002)]. It is shown that the model is applicable to high pressure, ejector type chemical oxygen-iodine laser (COIL), reasonably reproducing the measured gain, temperature, static pressure and gas velocity. A previous model which included I₂(A' ³Pi_2u), I₂(A ³Pi_1u) and O₂(a ¹Delta_g, v) as significant intermediates in the dissociation of I2 [Waichman et al., J. Appl. Phys. 102, 013108 (2007)] reproduced the measured gain and temperature of a low pressure supersonic COIL. The previous model is complemented here by adding the effects of turbulence, which play an important role in high pressure COILs.

A simple geometrical optics model is developed, describing the power extraction in chemical oxygen-iodine lasers with unstable resonators. The positive and negative branch unstable resonators with cylindrical mirrors that were recently used in the COIL are studied. The optical extraction efficiency and intensity spatial distributions in the flow direction for both kinds of resonators are calculated.

A double-pulse discharge method is used to simulate high-repetition-rate excitation discharge in TEA gas laser with supersonic gas flow. The supersonic gas flow is generated using a Ludwieg tube with a two-dimensional shock-free nozzle. A solid electrode with UV pins is used to generate the discharge. The test gas is a mixture of He and Ar (He:Ar = 9:1) with the density of 0.52 kg/m³ in a discharge cavity. In supersonic gas flow with the Mach number M = 2 (v = 860 m/s), not only gas density depression but also shock wave produced by the previous pulsed discharge has a key effect on stability of the subsequent discharge. For pulse repetition rate f = 60-25 kHz, the gas density depression has already been removed from the discharge cavity, whereas the traveling shock wave against the supersonic gas flow still remains. Hence the subsequent discharge becomes arc discharge. For f≤17 kHz, on the other hand, the subsequent discharge becomes glow discharge because both the shock waves and gas density depression have already been removed from the discharge cavity. A formula for estimating the maximum repetition rate of stable excitation discharge train in supersonic gas flow is proposed.

The initial stage in development of hybrid plasma jet generator of singlet oxygen O₂(¹Δ) for a discharge oxygen-iodine laser (DOIL) is presented. This novel type of generator is based on a fast mixing of hybrid argon plasma jet of DC electric arc and RF discharge with a neutral molecular oxygen stream. Arc plasma jets have a much higher density of electrons than RF plasma jets to compensate the electro-negativity of oxygen and they can be operated at a higher pressure for an efficient supersonic expansion cooling in DOIL. An RF discharge is applied to the DC arc plasma jet at the hollow anode of the plasmatron to switch it from a hot-spot mode to a diffusive mode. That is advantageous with the use of aluminum anode, which has a lower melting point and a significantly lower rate of O₂(¹Δ) quenching compared to a standard copper anode in a gas plasmatron. An enhanced non-equilibrium in the plasma jet caused by the RF discharge and neutral oxygen injection is desirable for an efficient O₂(¹Δ) generation. Preliminary calculations on the equilibrium composition of O₂-Ar mixture suggest keeping the arc temperature well down to prevent an excessive dissociation of the molecular oxygen.

The research activities in creation of atmospheric pressure laser with the output of ~ 33 W, pulse repetition rate up to 2200 Hz, efficiency of ~ 1.6% (DF-laser) and the output of ~ 40 W, pulse repetition rate up to 2000 Hz, efficiency of ~ 2% (HF-laser)

Actively mode-locked electron-beam-sustained-discharge CO-laser producing a train of ~5-15 ns (FWHM) spikes following with repetition rate 10 MHz for both single-line and multiline mode of operation in the mid-IR range of ~5 micron was experimentally studied. Total laser pulse duration was ~0.5 ms for both mode-locked and free running laser. Specific output energy in multiline CO-laser mode of operation was up to 20 J l^-1 Amagat^-1 and the laser efficiency up to 3.5%. The active mode-locking was achieved for single-line CO-laser mode of operation in spectral range 5.2-5.3 micron. This sort of radiation can be used for pumping an optical parametric amplifier for optical stochastic cooling in Relativistic Heavy Ion Collider, for laser ablation, and for studying vibrational and rotational relaxation of CO and NO molecules.

The factors of Chemical Oxygen-Iodine Laser (COIL) resonator expanding angle design are analyzed in this paper. It is shown that the primary factor is the rate of the releasing heat from the near resonant energy transfer reaction between O₂(¹Δ) and I at the resonator entrance with the laser extracting. It is a characteristic of COIL that the rate of the releasing heat with lasing is bigger than without lasing. A slightly bigger resonator expanding angle than that of constant pressure operating condition is sufficient to avoid the shock wave appearance.

Two approaches to two- and three-tone seeding of high power ytterbium-doped fiber amplifiers are investigated using a symbolic and numerical code that solves a two point boundary problem consisting of a 12×12 system of nonlinear differential equations. Optimization of amplifier action is considered in relation to the two most dominant nonlinear effects: stimulated Brillouin scattering and four-wave mixing. One approach uses a large wavelength separation among the input seed beams, while in the other approach the seeds are separated by precisely twice the Brillouin shift. It is found that for both techniques significant increase in amplifier output can be obtained, although for the latter case a substantial amount of power is generated in the four-wave mixing sidebands.

Stimulated Raman scattering (SRS) has been observed in more than 100 crystals generating about 2000 different wavelengths covering the ultraviolet, visible and infrared spectral regions with a mean spacing of 1 nm. Barium nitrate crystals have been used to demonstrate high Raman shifted output energy up to 156 mJ or high average power of 10 W at 1.197 μm, 1.369 μm and 1.599 μ;m wavelengths with quantum efficiencies of up to 66 %.

This paper will describe a comparative study on four different Yb-doped laser materials in a diode-pumped femtosecond chirped-pulse amplifier. Broadband multi-pass amplification using single crystalline Yb:CaF2, Yb:KGW, and Yb:YAG as well as Yb-doped fluoride phosphate glass was demonstrated. The seed pulses as short as 85 fs were generated in a Ti:Sapphire oscillator tuned to a center-wavelength of 1030nm and then boosted to the 100 μJ-level in a diode-pumped Yb:glass regenerative amplifier. Furthermore, the amplifier performance at nanosecond and microsecond time-scales was analyzed. With regard to the 10-nm line-width of the emission cross section the gain narrowing in Yb:YAG was investigated in particular. The pulse spectrum was narrowed to 1.9nm at a total gain of 103 in an Yb:YAG multi-pass amplifier. This corresponds to a compressed pulse duration of 0.85 ps. When seeding with nanosecond pulses of a Q-switched oscillator a maximum pulse energy of 220mJ at a repetition rate of 10Hz has been achieved.

A Nd:GSAG laser operated at the ⁴F_3/2 →⁴I_9/2 transition was tuned by a FPI-etalon achieving a tuning range of 1.5 nm with a center wavelength at 942.7 nm. Three water vapor absorption wavelengths with different absorption strength as suitable for a water vapor LIDAR are within this tuning range and lasing could be achieved at all three wavelength. Q-switched pulse energies up to 26mJ were obtained as required for long range detection.

We are currently developing a large aperture neodymium-glass based high-power solid state laser, Shenguang-III (SG-III), which will be used to provide extreme conditions for high-energy-density physical experiments in China. As a baseline design, SG-III will be composed of 48 beams arranged in 6 bundles with each beam aperture of 40cm×40cm. A prototype of SG-III (TIL-Technical Integration experimental Line) was developed from 2000, and completed in 2007. TIL is composed of 8 beams (four in vertical and two in horizontal), with each square aperture of 30cm×30cm. After frequency tripling, TIL has delivered about 10kJ in 0.351 μm at 1 ns pulsewidth. As an operational laser facility, TIL has a beam divergence of 70 μrad (focus length of 2.2m, i.e., 30DL) and pointing accuracy of 30 μm (RMS), and meets the requirements of physical experiments.

Thin disk laser is the most successful design to overcome the degradation of the beam quality caused by the gain medium's thermal effects and has many advantages in beam quality keeping and power scalability over the traditional rod and slab laser. In this paper a different type thin disk laser with the large-aperture Nd:YAG disk face-pumped by 2D-stack diode arrays was presented. Over 3kW average power with the beam quality less than 10 times diffraction limitation was achieved by optimizing the pumping optics designs and improving the gain medium mounting technique.

We developed several prototypes of ceramic Nd:YAG slab lasers pumped by different laser diode stacks. Compactness, efficiency and ruggedness have been the principal design drivers. Nevertheless beam quality and insensitivity to diodes temperature have also been pursued. An edge-pumped device with less than 12% power variation over a 20°C temperature range has been demonstrated.

We report a novel frequency tripler for efficient conversion of broadband high power laser pulses at 1 μ;m. The tripler is composed of several segmented partially deuterated KDP with discrete values of deuteration. Deuteration level can be used as a degree of freedom to alter the phase-matching wavelength of a partially deuterated KDP crystal. The segmented partially deuterated KDP crystal is made by thermal bonding method. It has been shown that this new tripler is capable of enhancing the acceptance bandwidth of frequency tripling. A two-segment design is presented, which is applicable to the efficient frequency tripling of chirped pulses with a bandwidth of ~1.2-nm.

Within a National Project on nanotechnologies, at the ENEA Research Centre in Frascati a micro-exposure tool for projection lithography at 14.4 nm has been developed. The laser-plasma soft X-ray source is equipped with a patented debris mitigation system developed in the frame of a European Integrated Project, in order to preserve the collecting optics. A 90-nm-resolution patterning has been achieved on resist by this laboratory-scale tool based on a Schwarzschildtype projection optics.

The aim of this work is the optimization of the resonator optics of excimer laser systems to achieve longer lifetimes and to reduce the cost of ownership. The degradation after long-term exposure to high photon fluxes (typically 80 mJ/cm² at the ArF laser wavelength of 193 nm was analyzed. Based on the investigations, a model describing the process of the deterioration of the out-coupling partial reflector was developed. It was found that contamination of the optics by the laser's discharge electrodes leads to absorption losses on the surface facing the inside of the resonator. As a consequence, the laser irradiation causes a temperature gradient in the CaF₂-substrates which leads to crystal cleavage and braking of the optics. Defects on the outward surface are the origin for the growth of Calcite crystals and organic compounds by photo induced chemical reactions of the substrate material and contaminations in the purge gas. It was demonstrated that the lifetime of the resonator optics can be substantially increased by adapted optical designs and coatings.

In vacuum ultraviolet (VUV) spectral region, coherent light sources are being thus in high demand for advanced precise and microscopic processing. A sub-picosecond VUV light source at 126 nm has been produced by the nonlinear wavelength up-conversion of a near infrared femtosecond Ti:Sapphire laser at 882 nm in rare gases. We obtained the maximum output of the 7th harmonic at 126 nm in Xe at the pressure of around 2 Torr. The 126 nm beam will be amplified by an optical-field-ionization produced Ar₂ medium and then high-power sub-picosecond VUV pulses will be obtained.

A creation of a laser with a wavelength in UV spectrum field, as an element of lidar systems, can be perspective for monitoring of the atmospheric impurities. A gas laser on electronic transition D'→A' (342 nm) with optical pumping (I₂- laser) is based on collisional transfer of electronic energy between terms 3Σ_u +(D) and ³Π_2g(D') of iodine molecules. The dependence of intensity of luminescence D'→A' on pressure of buffer gas for 25 substances was studied. Effective working mixtures of I₂-laser with optical pumping on a basis of perfluoroalkanes were found.

Fluorescence and transient absorption spectra of various rare gas mixtures with additions of fluorine-containing gases and nitrogen under e-beam pumping are investigated with the original time-gated probing technique. The obtained results allow us to specify KrF laser kinetics. Weak amplification of radiation at broadband trimer Kr₂F transition (4²Γ→1,2²Γ) is demonstrated.

The paper presents a review of the most recent achievements in the development of the industrial high power excimer lasers. The results of the development of a XeCl laser with the output energy above 900mJ and the pulse repetition frequency up to 600Hz will be demonstrated. The system performance such as energy, stability, spatial and temporal properties of the laser pulse as well as the extended maintenance cycles and finally low cost of operation in industrial applications will be discussed. Special emphasis will be placed on the design of the laser chamber and the pulsed power module, enabling the generation of a reproducible and homogeneous gas discharges which is indispensable for the required laser performance over the whole range of the laser output power.

We have demonstrated an OFI Ar₂^* excimer VUV amplifier at 126 nm pumped by a high-intensity laser in the table top size. We observed the Ar₂ ^* excimer emission centered at 126 nm with the spectral bandwidth of 10 nm (FWHM), which was produced in the OFI plasma. Significant amplification was observed inside the OFI Ar₂ ^* excimer as a result of the optical feedback provided by a VUV reflector. The gain-length product of 5.6 was observed at the Ar pressure of 11 atm. The population inversion density on the order of 10¹⁷ cm^-3 was evaluated inside the OFI plasma, which would be sufficient for the amplification of a subpicosecond VUV pulse at 126 nm produced by the harmonic generation.

An optical resonator for generating high-power, cylindrically polarized beams is demonstrated. The rear mirror of a commercial CO₂ laser is replaced by a novel triple-axicon retroreflector unit that is composed of a waxicon and an axicon accurately fitted together. Selection of the polarization is made by the reflectivity difference between p and s polarizations at the inclined surfaces. The resonator is designed for radially polarized oscillation, however, the output beam is azimuthally polarized because the oscillation occurs at unexpected 9.6 μm. A stable 1 kW output is generated, and the measured beam quality is M²=2.0.

In this paper we present the design of a CO₂ laser resonator that produces as the stable transverse mode a super-Gaussian laser beam. The resonator makes use of an intra-cavity diffractive mirror and a flat output coupler, generating the desired intensity profile at the output coupler with a flat wavefront. We consider the modal build-up in such a resonator and show that such a resonator mode has the ability to extract more energy from the cavity that a standard cavity single mode beam (e.g., Gaussian mode cavity). We demonstrate the design experimentally on a high average power TEA CO₂ laser for paint stripping applications.

The short overview is given of optical equipment developed within the ISTC activity for adaptive systems of new generation allowing for correction of high-power laser beams carrying optical vortices onto the phase surface. They are the kinoform many-level optical elements of new generation, namely, special spiral phase plates and ordered rasters of microlenses, i.e. lenslet arrays, as well as the wide-aperture Hartmann-Shack sensors and bimorph deformable piezoceramics- based mirrors with various grids of control elements.

The sensing of phase front of the vortex laser beams has been carried out with the help of a Hartmann-Shack sensor. The vortex beam is generated in the form of a Laguerre-Gaussian beam (LG0 1 mode) with the help of the special helicoidal phase plates manufactured by the kinoform technology. The measured shifts of focal spots on the hartmannogram are compared with the calculated shifts. From the measured wave front tilts the reconstruction of singular phase surface has been performed with using the novel reconstruction technique. The phase surface reconstruction is demonstrated in the case of distorted vortices as well. The correction of an optical vortex is undertaken in the close-loop adaptive system including the bimorph deformable piezoceramics-based mirror.

We present experimental results with a 10W-Nd:YVO₄-laser, which is Q-switched with a single crystal photo-elastic modulator made of LiTaO₃. This allows a simple setup driven by voltage amplitudes in the order of 10 V. We observed stable and unstable pulse sequences. In stable operation a 127 kHz - pulse sequence with 70ns pulse width and 1100 W peak power was achieved, while the average power remained constant at 10W.

In the recent years high-power laser beams with radial polarization have attracted an increasing interest because of their interesting properties in material processing. We present an overview of the current activities and different techniques to generate such beams in CO₂ and solid-state lasers. With a polarising end-mirror which comprises a resonant grating on a dielectric multilayer Bragg-structure we recently demonstrated a 3-kW radially polarised CO₂ laser. Current investigations are also focused especially on the application of this technology to thin-disk lasers. The specific requirements and the whole development from the design and fabrication to the characterization and test are illustrated with the example of a multilayer polarizing grating mirror developed to generate a radially polarised beam in an Yb:YAG thin-disc laser resonator. The potential of this kind of beams are discussed with a number of first application results, which largely confirm the predictions presented by Niziev et al1.

A new statistical approach to predict the possible increase of the laser generation in copper bromide lasers is presented. The results are based on a big amount of experimental data with wavelengths 510.6 nm and 578.2 nm, obtained in Georgi Nadjakov Institute of Solid State Physics, Bulgarian Academy of Sciences. The data are treated by statistical methods, such as multivariable factor analysis and linear regression modeling. The approximate increase of the output laser power up to 18% is obtained by using six input working parameters. The proposed methodology is applied for prognosticate the experiment and further design of the laser tube.

Mechanisms of nonlinear absorption and ionization of pure atomic argon and molecular nitrogen gases by UV femtosecond laser pulses were studied using photogalvanic and photoacoustic techniques. The effect of the intermediate Rydberg resonance, its dynamic Stark perturbation and ponderomotive upshift of the first ionization potential of argon atoms and nitrogen molecules by the intense laser pulses has been revealed by observing an increase of a power slope of ion yield from three to four at increasing laser intensity.

A comparative study of the ejection dynamic of organic materials by Laser-Induced Forward Transfer technique has been performed using nanosecond and picosecond pulses for applications in plastic micro-electronics. The ejection of organic materials has been carried out with various thicknesses and with and without a sacrificial metallic release layer inserted between the substrate and the organic donor film. The advantage of this technique is to preserve organic layers from being damaged by thermal and photochemical effects during the interaction. The dynamic of the process has been investigated by shadowgraphic imaging during 1.5 μs after the laser irradiation, under atmospheric conditions. We have determined the velocity of the transferred material and studied the influence of the metallic layer during the ejection using a wide range of fluencies. The high directivity of the ejected material offers the possibilities of high spatial resolution for the manufacture of micro-structures in non contact LIFT technique. The study of the influence of the distance between the donor and acceptor substrates on the deposit functionality is discussed.

The present paper summarizes the results of a study of the morphological, structural and compositional changes caused on dentin by processing with KrF excimer laser (λ= 248 nm). Different surface textures are achieved depending on the structure of the samples and on the processing parameters. Independently of the radiation fluence used, a significant reduction of the organic material content is observed in a surface layer a few nanometers thick, but no significant changes in the mineral phase occur.

Two integrating sphere system using the substitution method have been built to measure the reflectivity of 30CrMnSiA irradiated by Nd:YAG continuous wave laser with a wavelength of 1064nm.It can prevent the fluctuation of laser output energy. The back surface temperature was recorded using NiCr-NiAl thermocouples. Surface oxide film composition and thickness were studied by XPS and XRD. A one-dimensional heat conduction model implementing a parabolic oxide growth law was developed to obtain the temperature-dependent reflectivity. The computational and experimental results are well accordant with each other.

Characteristics of extreme ultraviolet (EUV) and debris emissions as well as debris reduction have been investigated for a laser-produced plasma (LPP) EUV source by using a colloidal/liquid jet target containing tin dioxide nanoparticles and tin chloride. The amount of deposited debris on a silicon witness plate was determined by a total laser energy irradiated onto a target. Double-pulse laser irradiation was effective for improving the EUV conversion efficiency as a result of plasma regulation. It was, however, not effective for reducing the deposited debris from a colloidal target with nanoparticles. In situ low-temperature heating of the witness plate was effective to reduce the amount of deposited debris. Room-temperature photon processing using an incoherent vacuum ultraviolet excimer lamp at 126 nm deoxidized a deposited tin oxide layer. In addition to these active debris reduction methods, the use of a tin chloride liquid target at a certain concentration passively reduced the amount of deposited debris as a result of production of chlorine atoms that sputtered and/or etched deposition. The EUV CE of more than 1% was observed from a tin chloride target by using double-pulse laser irradiation.

A high power repetition rate CO₂ laser with mechanical Q-factor modulation has been manufactured. Its generation characteristics have been studied. The structure of shock waves appearing at the interaction between a supersonic air jet and plasmoid formed by the optical breakdown, has been investigated.

The synthesis of bioactive glass from raw materials even during the laser deposition process, could provide formation of a biocompatible layer on the metallic prosthesis. During the laser irradiation melting and ultrarapid solidification of ceramic materials occur and glasses controlled by the process parameters (especially laser power and solidification rate) will be obtained. The aim of the present paper is to study the influence of the processing parameters on the laser synthesized glasses chemical composition, structure and bioactive behaviour.

The faint body image embedded into the Turin Shroud has not yet explained by traditional science. We present experimental results of excimer laser irradiation (wavelengths 308 nm and 193 nm) of a raw linen fabric and of a linen cloth, seeking for a possible mechanism of image formation. The permanent coloration of both linens is a threshold effect on the laser beam intensity and it can be achieved only in a surprisingly narrow range of irradiation parameters: the shorter the wavelength, the narrower the range. We also obtained the first direct evidence of latent images impressed on linen that appear in a relatively long period (one year) after a laser irradiation that at first did not generate a clear image. The results are compared to the characteristics of the Turin Shroud, commenting the possibility that a burst of directional ultraviolet radiation may have played a role in the formation of the Shroud image.

Inkjet direct writing of functional materials provides a promising pathway towards realization of ultra-low-cost, largearea printed electronics, albeit at the expense of lowered resolution (~20-50 μm). We demonstrate that selective laser sintering and ablation of inkjet-printed metal nanoparticles enables low-temperature metal deposition as well as highresolution patterning. Combined with an air-stable carboxylate-functionalized polythiophene, all-inkjet-printed and laser-processed organic field effect transistors with micron to submicron critical feature resolution were fabricated in a fully maskless sequence, eliminating the need for any lithographic processes. All processing and characterization steps were carried out at plastic-compatible low temperatures and in air under ambient pressure. The fundamental mechanisms of the nanoparticle sintering process have been investigated by both Molecular Dynamics (MD) simulations as well as in-situ probing.

This study is focused on laser structuring processes for producing secure tactile features on paper-based security documents. The feasibility of using the developed technique allows users and/or machines to discriminate among genuine and counterfeited security documents and/or facilitate the tactile detection by visually impaired people.

The interconnection complexity of the PCB (Printed Circuit Boards) is still growing and new technologies are introduced in the production of high density printed circuit boards. Recently the Laser Direct Imaging (LDI) technology is used for imaging electric circuits directly on PCB without the use of a phototool or mask. We presents our laboratory system for Laser Direct Imaging designed for tracks and spaces on PCB with minimum track/space widths distance of 50/50 μm. In comparison with conventional photolithography method, this technology is much better for 50/50 μm track and spaces. In our research we used photoresist with 50 μm resolution, but in case of using laser photoresists with better resolution (e.g. 25 μm) it is possible to image tracks in super-fine-line technology (25/25 μm). Our laboratory system for LDI consist of diode UV laser (λ=375 nm, P=9 mW), optical scanner head, telescope and XY planar table, which extends scanner head working area into 15 × 25 cm usable area. A sophisticated computer software was developed to control this system.

Systems for laser micromachining of the materials are very popular around the world. Unfortunately, this technology is not used widely in Poland. This is a result of very high prices of systems for laser micromachining, which Polish electronic manufacturers can not afford for. This article is focused on Polish proposition of the system for laser micromachining, which is adapted to producing metal stencils used in PCB manufacturing. Metal stencils are used during one of the PCB manufacturing steps. It allows to precisely position soldering paste on PCB laminate exactly on soldering places.

We combine laser processing and the technique of a scanning near-field optical microscope (SNOM) for realization of laser-patterning on a nanoscale, laser ablation near the fiber tip, and micro-analysis of solid surface samples by laserinduced breakdown spectroscopy (LIBS). We describe an universal SNOM-like setup allowing to produce near-field laser patterns by laser heating and laser ablation, laser-induced breakdown spectroscopy, and atomic force microscope (AFM) topography investigation with the same optical fiber tip, which is used as near-field emitter or as probe. With solid Si and Al samples, three laser processing regimes were observed with increasing laser pulse energy: (1) cone formation (only for Si, smallest features with 500 nm width and 100 nm height), (2) formation of small craters (smallest features with 450 nm width and 250 nm depth), and (3) crater formation with a width of more than 2 μm with emission of evaluable plasma emission line spectra.

Up-to-date fibre lasers produce multi-kw radiation with an excellent beam quality. Compared to CO₂-lasers, fibre lasers have relatively low operational costs and offer a very high flexibility in production due to the beam delivery with process fibres. As a consequence, fibre lasers have attracted more and more attention. On the other hand, their use in industrial applications especially in the automotive industry is still limited to a certain extent and fibre lasers haven't replaced all other laser sources till now as it could be expected. In laser cutting, the small kerf width produced by fibre lasers should be advantageous since the heated volume is smaller compared to CO₂-lasers. In fact, cutting velocities are usually much higher which is also caused by the higher absorption coefficient of most metals at the wavelength emitted by fibre lasers. Nevertheless, cutting with fibre lasers of some metals - e.g. stainless steels - is restricted to a small thicknesses of approx. 5mm. The reason for this is that the surface roughness of the edges increases dramatically with the thickness of the work piece. Applications of fibre lasers include e.g. remote welding or even remote cutting of a large variety of materials with usually excellent results. Due to the excellent beam quality the aspect ratio of the weld seam in relation to the penetration depth is quite good. In the case of thin sheet metal welding such a small beam waist is beneficial - but with thicker sheet metals it is very often disadvantageous since the preparation of samples is more complicated, costs increase and requirements on clamping devices rise. In this paper, advantages and disadvantages of fibre lasers are discussed briefly. Applications of a 1.5 kW fibre laser are presented and compared to classical laser systems.

A laser-based hybrid technique is shown to be effective for cutting concrete and drilling rock. Experimental conditions used included a laser power of 1-10 kW, 10 mm laser beam diameter and 1.25-50 mm/s scanning speed. The results of surface scanning tests and 100 mm deep cut tests indicated that the shortest operation time was about 3.5 hr/m² for plain concrete and 4.5 hr/m² for heavy concrete. The specific energy for the rocks (the amount of energy required to remove a unit volume of rock), which were granite and sandstone, was as same as that for heavy concrete. Thermal decomposition was observed for limestone. The specific energy of limestone was more than 1.5 times higher than that for granite and sandstone.

For mild steel of 5...25 mm thick, the parameters area of the maximum cutting quality has been determined experimentally. The conditions of cutting with minimum roughness are presented as a dependence of dimensionless values. It has been shown that the high-quality cutting features the specific volumetric input of laser energy, equal for any thickness. Normalized power W/λt(T_m-T₀), normalized velocity vb/γ (Peclet number) and kerf width have special optimum numbers.

A finite element model coupling heat transfer calculations, phase transformations kinetics and internal stresses calculations to simulate laser powder deposition of a titanium alloy is presented. The model was applied to the study of the influence of the deposition parameters on the microstructure, hardness and residual stresses in Ti-6Al-4V thin walls produced by this method.

High wear resistance Al-based composite coatings were prepared by laser cladding using powder mixtures of Al-12 wt. % Si+40 wt. % TiC and Al-40 wt. % Si+40 wt. % TiC. In the case of the coatings containing 12 % Si, the microstructure consists essentially of TiC particles dispersed in a matrix of primary α-Al dendrites and interdendritic α-Al+Si eutectic, whereas the Si rich coatings contain primary Si particles dispersed in the matrix. The low-Si coatings present an average hardness of 165 HV and an abrasive wear coefficient in a SiC-containing abrasive medium of 1.4×10^-3 mm³ (Nm)^-1, while the Si rich coatings present higher hardness of 220 HV but similar wear coefficient. The results show that increasing the Si content does not improve the abrasive wear resistance of the material, despite the 30% increase in hardness. This is explained by the fact that the hardness of Si (1200 HV) is much lower than that of the SiC abrasive particles (2800 HV), thus the primary Si particles do not contribute to reduce the grooving action of the abrasive.

This paper addresses the development of a laser metal deposition process which consists of a 2 kW Fibre Laser, a CNC table, a wire feeder and a temperature monitoring system. During its development, six infrared pyrometers were tried to compare their performance. The system utilizes two pyrometers to measure both the melt-pool and workpiece (upper layer) temperatures. Experiments have been performed to study the metal deposition parameters with stainless steel 308L wire deposited on stainless steel 304, and good quality metal deposition has been achieved. The results of the parameters study and the development of the temperature monitoring system are presented.

This study explores the potential ability of laser metal deposition (LMD) as metal foaming process, considering that its intrinsic high heating/cooling rates can avoid some of the common problems of gas leakage, in-homogeneity and anisotropy that arise when manufacturing metallic foams by conventional powder metallurgy (PM) methods. Highly porous coatings of aluminum and titanium alloys have been obtained by this PM-LMD metal foaming method.

The paper provides a thorough analysis of a surface layer prior to and after Laser Shock Processing under different parameter conditions. Optimum conditions were determined using a factorial design aided with an analysis of variance (ANOVA). As the first experimental factor, pulse density with 900 and 2500 pulse/cm² was chosen. The second factor was the type of material, i.e. aluminium alloys ENAW 6012 and ENAW 6082. Evaluation of different conditions of specimen treatment was made using three response variables, i.e. surface roughness, magnitude of residual stresses, and corrosion resistance given by pitting potential (Epitt). A thorough analysis of the modified surface layer was made with measurement of microhardness, and with images obtained in optical and electronic microscopy (SEM) and energy dispersion spectroscopy (EDS) to determine corrosion products around the pits formed after corrosion testing. The experiments confirmed characteristic influences of individual LSP parameters on properties of the treated material surfaces. ENAW 6012 aluminium alloy showed better corrosion resistance than ENAW 6082 alloy with lower pitting attack at its surface. Corrosion tests showed that a higher pulse density produces shifting of the pitting potential to more positive values, which ensures higher corrosion resistance from the viewpoint of preserving a passive protecting film on the surface layer.

This paper reports results from the theoretical and experimental study of the energy transfer during CO₂ laser beam welding of 10 mm low-alloyed steels square butt joints. The laser beam power and the welding speed are varied systematically from 9 kW to 32 kW and from 1 m/min to 5 m/min, respectively. The observed weld depth penetration is up to 10 mm and the width of weld seams is between 0.8 and 1.25 mm. The joining efficiency during the laser welding was in the range of 11.8 to 32 mm²/kJ. Melting efficiency is determined from the measured welding seams cross section for a specified laser power and travel speed. Theoretically, predicted values of melting efficiency are calculated using Rosenthal's and Rycalin moving heat sources equation in 2D (line source).

The kinetic time-dependent Fokker-Planck type equation for conduction electron energy distribution function is solved for bulk semiconductors and dielectrics in the presence of source terms such as laser field absorption, impact ionization and non-radiative recombination. The numerically calculated electron distribution function, time dependent electron number density and electron temperature are substituted into an equation for the lattice temperature evolution.

Experimental laser cleaning of black crusted calcareous stones, carried on to study the laser yellowing of petreous surfaces, showed different colour alterations on the exposed surface, after laser irradiation, depending not only on the incident fluence but also with the crust or stone irradiated layer.

This work intends to contribute towards the knowledge of AA6013 aluminum alloy weldability, autogenously welded with a high-power fiber laser. The quality and metallurgical characterization of the welds were done considering laser speed and power as process parameters. The present study shown that is possible to obtain welds with good macroscopic quality; i.e. with regular welds borders and without the presence of holes, cracks or porosities in speeds around 5 m/min using 1 kW laser power. Additionally, it had been verified that the liquation zone is well confined around 50 μm. The presence of porosities in longitudinal cuts was linked to keyhole instabilities, which could be appropriately controlled by the process parameters. Although this alloy is known for some propensity for solidification cracking, any cracking was verified. This could be linked to an appropriate thermal cycle during welding due to the high quality laser beam, which produces short solidification interval. The present results indicate that other difficult-to-weld Al-based alloys could be properly joined using the fiber laser.

Nowadays one the main problem of stone monuments conservation is not only the natural environment deterioration but the defaced, in particular esthetic, due to graffiti. This paper presents the different stages of the cleaning graffiti research: the laboratory study phase, in which the aims were to investigate the laser cleaning effect on substrate and testing user-friendly and efficient solutions for in situ application; the application phase in which the study results were applied in the restoration of Palazzo de Mattis facade. The graffiti cleaning were carried out by using a Q-Switch Nd:YAG laser source (λ=1064 nm with pulse duration, t=8 ns, f=2 to 20 Hz, energy per impulse up to 280 mJ) in dry, wet and Very wet modes adopting the Daurelio technique n.1 (blade spot laser). The Q-Switch Nd:Yag laser source has demonstrated to be the most suitable for a fully or, according to new restoring theory, "de veiling" graffiti ablation.

In this paper the microstructural changes and effects on corrosion resistance of duplex stainless steels UNS S32304 and UNS S32205, commonly used by the petroleum industry, were studied, following the execution of laser surface remelting (LSM) and post-thermal treatments (TT). In this way, data was obtained, which could then be compared with the starting condition of the alloys. In order to analyze the corrosion behaviour of the alloys in the as-received conditions, treated with laser and after post-thermal treatments, cyclic polarization tests were carried out. A solution of 3.5% NaCl (artificial sea water) was used, as duplex stainless steels are regularly used by the petroleum industry in offshore locations. The results obtained showed that when laser surface treated, due to rapid resolidification, the alloys became almost ferritic, and since the level of nitrogen in the composition of both alloys is superior to their solubility limit in ferrite, a precipitation of Cr2N (chromium nitrides) occurred in the ferritic matrix, causing loss of corrosion resistance, thus resulting in an increase in surface hardness. However, after the post-thermal treatment the alloys corrosion resistance was restored to values close to those of the as-received condition.

Results of experimental studies of the laser beam thermal blooming in the atmosphere are discussed. The influence both an atmospheric path and zone of stagnation between the laser source and the optical system on the beam defocusing are analyzed. The possibility of adaptive correction of distortions acquired by a beam on the initial section of a path between a laser and the transmitting aperture is analyzed in the paper as well.

We have developed hetero-core fiber techniques interrogated with a semiconductor diode laser based on single-mode transmission for wearable glove sensing applications. The hetero-core fiber sensor is suitable for the wearable sensing glove because of the advantages of the capable optical intensity-based measurement with the excellent stability of the usage of the single-mode transmission fiber and independence of temperature fluctuation. In order that the hetero-core sensor was unaffected to the random wrinkles at the position of joints in a glove garment, the hetero-core sensor elements were located in the back of hand. As a result, the hetero-core flexion sensor could detect the joint angle of fingers regardless of differences of their size of hands, and the hetero-core sensing technique enables the sensing glove to equip the minimum number of sensors. The optical loss performances of the hetero-core sensors have indicated monotonic characteristics with the flexion angle of joints. The optical loss change is 1.35 dB for the flexion angle of approximately 97.2 degrees with accuracy of detectable flexion angle of 0.84 degree. Real-time hand motion capturing was successfully demonstrated by means of the proposed wearable sensing glove with hetero-core fiber techniques without restricting human natural behaviors.

Possibility for visualization of 2D velocity fields in the atmosphere based on laser radiation scattered by the particles moving in a turbulent air flow is discussed. By numerical modeling it is demonstrated that visualization of the flow velocity field is possible based on displacements of large-scale intensity inhomogeneities in the speckle structure arising in the optical image of scattering layer of moving particles.

Present work is devoted to experimental study of reacting jet flow in a model open flame burner. The work was inspired by the problem of extension of the range for stable and effective combustion which basically determined by the turbulent flow structure in reaction zone. To approach this target spatial distributions of the mean velocity, turbulent kinetic energy were measured and the role of organized vortical structures have been studied.The main technique used is a laser based stereo Particle Image Velocimetry (PIV) system. The measurements were performed in a central section of the jet flame. Regular swirl parameter of the flow was varied from 0 to 1.0. Reynolds number was changed between 1000 and 8000. Equivalence ratio variation band was between 0.5 and 4. Effect of the nozzle geometry was studied by using nozzles with different exit diameters.

We set up an experimental apparatus to investigate the micro shock wave with high experimental efficiency. We have performed the micro shock wave visualization with schlieren method by using laser induced plasma, which generated by a focusing pulsed CO₂ laser. The propagation and reflection of the shock waves are investigated. Additionally, a numerical simulation for compressible and inviscid flow is also performed to understand the propagation characteristics. As a consequence, our experimental apparatus is very convenient to simulate the explosion phenomena. Moreover, the result from a numerical simulation shows an agreement with the experimental results.

Propagation of radiation of the photo-initiated chain HF-chemical laser (in a wavelengths range 2.6 - 3.4 μ) through a real atmosphere is studied experimentally. The coefficients of absorption by molecules CO₂ and CH₄ are measured for spectral lines of the photo-initiated chain and discharge-initiated non-chain DF- lasers (3.6 - 5 μ). Experimental and numerical dependences of a passing through an atmosphere of radiation integrated on spectrum of the HF- and DF-laser are determined on a trace length up to (240-500) m and 16 km, respectively.

Based on the fractal characteristics of turbulence-distorted wavefront, a new algorithm for generating a very long rectangular turbulent phase screen is proposed. The phase structure function of generated phase screens can be very well compared to the theoretical one. In comparison to existing approaches, the present algorithm shows obvious advantages.

The possibility of early forest fire detection within a range up to ~2 km using a portable eye-safe 1540 nm lidar is demonstrated in this paper, both on experimental and theoretical ground. An estimation of the detection efficiency using a mathematical model based on the 3D system of Navier-Stokes equations describing the smoke plume evolution in the presence of wind, agrees reasonably well with experimental results. Calculations made using the model show that a detection range up to ~5.5 km can be achieved by accumulating lidar return signals.

A simple and robust algorithm for lidar-signal classification based on the fast extraction of sufficiently pronounced peaks and their recognition with a perceptron, whose efficiency is enhanced by a fast nonlinear preprocessing that increases the signal dimension, is reported. The method allows smoke-plume recognition with an error rate as small as 0.31% (19 misdetections and 4 false alarms in analyzing a test set of 7409 peaks).

The singlet delta pooling rate has been measured in a chemical generator using gas phase laser Raman spectroscopy. The measured rate is four times the currently accepted pooling rate constant. Our measurement also agrees with recent ab initio rate calculations. This rate is one of the most important losses in the COIL laser and is believed responsible for the production of vibrationally excited singlet delta oxygen. The vibrationally excited oxygen is thought to play a role in the iodine dissociation process. A higher rate for this process will enhance dissociation at the cost of increased transport losses. The previous experimental measurement was reviewed and an over simplification of the data analysis identified.