This PDF file contains the front matter associated with SPIE Proceedings Volume 7751, including the Title Page, Copyright information, Table of Contents, Introduction and the Conference Committee listing.

The present status of laser fusion researches in Japanis described. In the first, the fast ignition laser fusion is the high-light of high power laser applications. The recent progress of fast ignition research project at Osaka University: FIREX will be reported. As the industrial applications of laser produced neutron and X-ray, it is explored how they are used for diagnosing the chemical and physical processes in fuel cell and other chemical energyconverters. These applications are also important topics of this talk. As the laser fusion reactor technology, we will also present "UV Laser Ablations and Erosions to Investigate Fusion Reactor Surface Material Interactions, Hydrogen Storage Thin Layers Formations and the Related Subjects."

In this paper we describe several diagnostics that we have developed to assist the development of high power gas phase lasers including COIL, EOIL, and DPAL. For COIL we discuss systems that provide sensitive measurements of O₂(a), small signal gain, iodine dissociation, and temperature. These are key operational parameters within COIL, and these diagnostics have been used world-wide to gain a better understanding of this laser system. Recently, we have developed and integrated a similar suite of diagnostics for scaling the EOIL system and will provide examples of current studies. We are also developing diagnostics for the emerging DPAL laser. These include monitors for small signal gain that will provide both a more fundamental understanding of the kinetics of DPAL and valuable data for advanced resonator design. We will stress the application of these diagnostics to realistic laser systems.

Review on application of double-discharge circuits with inductive energy storage (IES) and semiconductor opening switch (SOS) for development of efficient gas lasers is presented. It was shown that the IES allows to form long-lived stable discharge in different gas mixtures. As a result, pulse duration, output energy and efficiency of the lasers under study were improved.

Experiments were carried out with a subsonic chemical oxygen-iodine laser (COIL), equipped with an electric discharge generator of iodine atoms. CH₃I entrained in a carrier flow of Ar was used as atomic iodine precursor. About 50% of iodine contained in CH₃I molecules was extracted in the generator. Up to 3.5% of electric power loaded into the discharge was spent on CH₃I dissociation. A straightforward comparison of COIL performance for two cases - conventional, when I₂ was injected in the singlet oxygen flow and when iodine atoms produced externally together with other discharge products were injected - was made. In the latter case nearly four times increase in output power was observed.

The kinetics of the chemical oxygen-iodine laser (COIL) has been studied alongside the technological efforts in COIL development. In particular, many efforts have been devoted to the study of the mechanism of I₂ dissociation in the COIL medium. Since O₂(a) is the energy reservoir of the COIL, it must be involved in the dissociation of I₂. Therefore, understanding the dissociation mechanism may help in finding ways of minimizing the O₂(a) consumption for dissociation and increasing the chemical efficiency of the laser. In the present paper previously suggested mechanisms of I₂ dissociation are briefly overviewed and recent measurements and modeling of the gain and the power in supersonic COILs carried out in our laboratory are presented. Our studies employ both an analytical model and numerical calculations which are outlined in the present paper, with more details on the models given in a following paper by Barmashenko et al. To unravel the I₂ dissociation mechanism we utilize kinetic-fluid dynamics three-dimensional modeling, where pathways involving the excited species I₂(X, 10 ≤ v < 25), I₂(X, 25 ≤ v ≤ 47), I₂(A, A'), O₂(X, v), O₂(a, v), O₂(b, v) and I(²P_1/2) as intermediate reactants are included. Both the gain and the power studies show good agreement between calculations and experiments. We believe that future modeling should include the above pathways and additional pathways should be considered when additional kinetic data is available.

Simple models are developed, describing the power extraction in chemical oxygen-iodine lasers (COILs) with stable and unstable resonators. For stable resonators the model is applied to the ejector high pressure COIL and the results are compared with the experimental data (see also a preceding paper by Rosenwaks et al.). The positive and negative branch unstable resonators with cylindrical mirrors that have been recently used in COILs are studied theoretically using a geometrical optics model. The optical extraction efficiency, spatial distributions of the intracavity radiation intensity in the flow direction and the intensity in the far field are calculated for both kinds of resonators as a function of both the resonator and COIL parameters. The optimal resonator magnifications corresponding to the maximum intensity in the far field are found.

Experiments and modeling have led to a continuing evolution of the Electric Oxygen-Iodine Laser (ElectricOIL) system. This continuous wave (cw) laser operating on the 1315 nm transition of atomic iodine is pumped by the production of O₂(a) in a radio-frequency (RF) discharge in an O₂/He/NO gas mixture. New discharge geometries have led to improvements in O₂(a) production and efficiency. Further, size scaling is presently showing a super-linear growth in performance; a 95% enhancement in cw laser power was achieved via a 50% increase in gain length, flow rates, and discharge power. New gain recovery measurements and modeling downstream of an operating laser cavity are presented in this work for a wider range of flow conditions to help identify previously unidentified kinetic processes. Larger volume resonators that extend further downstream in the flow direction were able to extract more of the excess energy being carried by the O₂(a) from the ElectricOIL gain medium; a further 87% increase in extracted laser power was obtained. As understanding of the ElectricOIL system continues to improve, the design of the laser systematically evolves. The gain has improved by more than 100-fold from the initial demonstration of 0.002% cm^-1 to 0.26% cm^-1, and similarly the outcoupled laser power has increased more than 600-fold from 0.16 W to 109 W.

Terawatt hybrid laser (THL-100) system on the basis of Ti:sapphire starting complex and final amplifier with gaseous optically driven active media on XeF(C-A) molecules is presented. Laser system is built at Institute of High Current Electronics SB RAS, Tomsk, Russia. It consists of Ti:sapphire starting complex and photochemical XeF(C-A) amplifier. The active media of amplifier pumped by VUV radiation has 24 cm aperture and 110 cm length. The results of numerical modeling of the output parameters and first experimental results are presented in this paper.

Breakdown of the gaps with a non-uniform electric field filled with nitrogen and air as well as with other gases under high-voltage nanosecond pulses was investigated. It is shown that conditions of obtaining a diffuse discharge without a source of additional ionization are extended at the voltage pulse duration decreasing. A volume discharge is formed due to the gap pre-ionization by runaway electrons and X-ray quanta. At a negative polarity of the electrode with a small radius of curvature, a volume (diffuse) discharge formation is determined by pre-ionization with runaway electrons which are generated due to the electric field amplification near the cathode and in the gap. At a positive polarity of the electrode with a small radius of curvature, the X-ray radiation, generated at the runaway electrons braking at the anode and in the gap, is of great importance in a volume discharge formation. A runaway electrons preionized diffuse discharge (REP DD) has two characteristic stages. In the first stage, the ionization wave overlaps the gap during a fraction of a second. The discharge current is determined by the conductivity current in the dense plasma of the ionization wave and the displacement current in the remaining part of the gap. The second stage of the discharge can be related to the anomalous glow discharge with a high specific input power. During the second stage, the gap voltage decreases and the cathode spots formed as a result of explosive electron emission can participate in the electron emission from the cathode. At the increase of the voltage pulse duration and specific input power, the REP DD transforms into a spark discharge form. A REP DD is easily realized in various gases and at different pressures; see [1] and references in [1]. At pressure decrease was obtained the anode electrons beam current to rise (up to ~2 kA/cm² in helium). At the REP DD, the anode is influenced by the plasma of a dense nanosecond discharge with the specific input power up to hundreds of megawatt per a cubic centimeter, by the electrons beam, shock wave and optical radiation from discharge plasma of various spectral ranges, including UV and VUV. This allows forecasting the REP DD application for modification and cleaning of metal and dielectric surfaces. The REP DD is promising as well for creation of the VUV-range excilamps with a high radiation power in a pulse. REP DD was use for pumping different gas lasers.

Recent advances in the RF atomic iodine generator for oxygen-iodine lasers are presented. The generator is based on the RF discharge dissociation of a suitable iodine donor immediately before its injection to the flow of singlet oxygen. The discharge is ignited directly in the iodine injector, and the configuration is ready for the laser operation. The dissociation fraction was derived from the atomic iodine number density measured at a presupposed position of laser resonator. The dissociation fraction and the fraction of RF power spent on the dissociation (discharge dissociation efficiency) were measured for the following donors: CH₃I, CF₃I and HI. A significant improvement of the discharge stability was achieved by increasing the cross-sectional area of the exit injection holes and employing a tangential inlet of working gas into the discharge chamber. The flow rates 0.15 mmol/s and 0.19 mmol/s of produced atomic iodine were achieved using the HI and CF₃I, respectively. The atomic iodine number density in the supersonic flow attained 4.22 × 10¹⁴ cm^-3. The dissociation efficiency was substantially better for HI than for studied organic iodides.

The present work is devoted to basic research of vapor-gas active media (SrI, SrII, Ne, and He) of lasers with nanosecond lasing pulses. Results of systematic investigations of a strontium vapor laser are presented for a wide range of conditions: pulse repetition frequency f = 1-100 kHz, buffer gas (neon or helium) pressure P = 30-400 Torr, volume of the active medium 200-600 cm³, etc. A number of record characteristics were achieved (average output power of 22 W, pulse repetition frequency of 100 kHz, and energy per lasing pulse of 2 mJ), lasing was simultaneously excited on the r-m and m-m transitions, and lasing in recombination and ionization modes was obtained in one active element. For the first time, lasing lines on many He and Ne atom transitions were obtained together with self-terminated Sr atom and ion lasing lines. Operation of a laser on self-terminated transitions of strontium atoms (6.45 μm) and singly charged ions (1.03 and 1.09 μm) in the modified mode (excitation of the active medium by pulse trains with high repetition frequency) was investigated. It was demonstrated that in this case, the strontium vapor laser pulse repetition frequency at wavelengths of 1.03 and 1.09 μm could reach ~1 MHz. In the present work, a number of advanced high-precision laser technologies based on application of the multiwavelength strontium vapor laser is considered, including precision controlled laser thermal cleavage of fragile nonmetallic materials, infrared laser resonant ablation, etc.

The characteristics of an all gas-phase iodine laser (AGIL) that uses molecular iodine as a source of iodine atoms is studied. The laser is based on the energy transfer reaction between metastable NCl(a¹Δ) and ground state I(²P_3/2) atoms, which are produced by the electric discharge of a mixture of I₂ and He. At fixed flow rates of the chemical species, the laser output powers are measured at three different positions in a flow reactor. The output power is characterized by a function of the optical axis position and is reasonably reproduced by the numerical calculation. A repetitive pulse of laser output at 50 Hz with a duty factor of 40% is observed. The highest output power is 40 mW at 210 mm downstream from the mixing point of I/H/He and NCl₃. This is 80% of the output power generated from the conventional system using HI as an iodine donor. The measured results of the time resolved laser output power suggest that the output power of the I₂- AGIL is more sensitive to the electric discharge plasma intensity as compared to that of the HI-AGIL. An AGIL operated using I₂ could potentially have the same output power as that of an AGIL operated using HI if a continuous-wave electric discharge generator is used.

The development of a discharge oxygen iodine laser (DOIL) requires efficient production of singlet delta oxygen (O₂(a)) in electric discharge. It is important to understand the mechanisms by which O₂(a) is quenched in these devices. To gain understanding of this mechanisms quenching of O₂(a) in O(³P)/O₂/O₃/CO₂/He/Ar mixtures has been investigated. Oxygen atoms and singlet oxygen molecules were produced by the 248 nm laser photolysis of ozone. The kinetics of O₂(a) quenching were followed by observing the 1268 nm fluorescence of the O₂ a → X transition. Fast quenching of O₂(a) in the presence of oxygen atoms and molecules was observed. The mechanism of the process has been examined using kinetic models, which indicate that quenching by vibrationally excited ozone is the dominant reaction.

The exciplex pumped alkali laser (XPAL) system has been demonstrated in mixtures of Cs vapor, Ar, with and without ethane, by pumping Cs-Ar atomic collision pairs and subsequent dissociation of diatomic, electronically-excited CsAr molecules (exciplexes or excimers). The blue satellites of the alkali D2 lines provide an advantageous pathway for optically pumping atomic alkali lasers on the principal series (resonance) transitions with broad linewidth (>2 nm) semiconductor diode lasers. Because of the addition of atomic collision pairs and exciplex states, modeling of the XPAL system is more complicated than classic diode pumped alkali laser (DPAL) modeling. Results from a time-dependent finite-volume model including transport, thermal, and kinetic effects appropriate for the simulation of a cylindrical closed cell XPAL system are presented. An initial kinetic set appropriate for modeling XPAL systems is presented. A two-dimensional, time-dependent baseline simulation of an operating XPAL cell is presented and compared to data. Good agreement is achieved on the time gap between pump and laser pulses, laser pulse full width at half maximum, laser pulse rise time, and output energy. A more detailed analysis of a similar case is presented in which good agreement is obtained between laser pulse energy as a function of pump pulse absorbed energy data and predictions. Higher XPAL efficiencies are predicted as temperature increases. Initial calculations of quasi-steady-state XPAL operation, a theoretical analysis of CW XPAL systems, along with advantages over the DPAL system are also presented.

Latest advances in development of a hybrid RF/DC plasma jet generator of O₂(¹Δ) for a discharge oxygen-iodine laser are presented. This novel apparatus is based on a fast mixing of hybrid Ar+He plasma jet of DC electric arc sustained by an RF discharge with an injected neutral O₂+He+NO stream. Calculations of singlet oxygen yield have shown that only non-equilibrium plasma with a high content of heated electrons (~3 eV) and a gas temperature of ~2500 K appears to be promising for an achievable yield of singlet oxygen up to ~42 %. A stable high-pressure hybrid RF/DC plasmatron with a diffusive arc mode near the anode side (assisted by a plasma anode) was demonstrated experimentally in the mixture Ar:He = ~9.84:5 mmol/s at a power level of 610 W (RF power 490 W and DC arc power 120 W) and at a pressure of 165 Torr. The specific energy of the plasma jet was 41 J/mmol. A generation of singlet oxygen was performed by a laterally symmetric injection of neutral mixture O₂:He:NO = 1.5:2.44:0.22 mmol/s into the plasma jet of the hybrid RF/DC plasmatron. The estimated yield of singlet oxygen O₂(¹Δ) was ~5 % at a pressure of 10.5 Torr.

A chemical oxygen-iodine laser driven by the centrifugal spray generator of singlet oxygen was developed and experimentally studied. Modeling and experimental studies showed that the designed generator can produce singlet oxygen, O₂(¹Δg), with a high efficiency (chlorine utilization 0.68 - 0.87 and O₂(¹Δg) yield 0.35 - 0.7) even at very high generator pressures (25 - 70 kPa), which cannot be attained by other O₂(¹Δg) generators. This high-pressure operation should be beneficial for a pressure recovery system of the laser. Another specific feature of the generator is a very high BHP utilization (0.24-0.6). The developed separator can effectively remove even small droplets (> 1 μm) from gas at the generator exit. Preliminary experiments on the COIL driven the centrifugal spray generator provided the small signal gain up to 0.5 % cm^-1.

The COIL operation using a new method of I₂ generation is demonstrated. The method is based on the gas-phase chemical reaction between Cl₂ and HI in a separate reactor. This process is easily scalable and can simplify the COIL operation by providing better control of I₂ flow rate. A yield of I₂ in the generation reaction up to 85% was achieved in a reasonable volume of the reactor. A small-signal gain up to 0.75 %-cm^-1 at temperature of 150 K in the center of supersonic cavity was measured. A comparison with the established evaporation way of I₂ delivery confirmed that the chemical method has little or no impact on the COIL kinetics. The COIL output power measured with the chemical and evaporation methods was nearly identical at comparable conditions.

Singlet oxygen generator is the key of chemical oxygen-iodine laser (COIL) which supplies energy for the system. However, the traditional generators have some drawbacks just as the bigger volume and the lower chemical efficiency. Specific surface area is the important factor restricting the development of singlet oxygen generator. Many researches on increasing specific surface area have been done to improve the performance of singlet oxygen generator. A new type eject singlet oxygen generator was introduced in this paper. Ejector was used in gas-liquid reaction. Liquid ejected through the nozzle with high velocity droved by high pressure, and gas ejected into mixing chamber along the tangent of nozzle. Gas and liquid were broken into many small droplets. Gas and liquid reacted in reaction chamber, then the mixture ejected into separator with very high speed. These droplets can produce mount of gas-liquid interface and increase the chemical efficiency of generator. Many numerical simulations have been done on the new type generator According to the simulations, eject singlet oxygen generator is feasible and has prospect. Therefore ejector may be a better type of singlet oxygen generator.

The paper describes the theoretical and experimental analysis of centrifugal flow singlet oxygen generator in order to identify the optimal conditions needed to satisfy the COIL requirement. The optimal conditions had been analyzed under Cl₂ flow rate, reaction length and generator pressure. The performance was achieved Cl₂ utilization of 94% and O₂(¹Δ) yield of 72%.

A variable magnetic field was incorporated into a 1D model of subsonic COIL model with a mixing length to include its influence on the stimulated emission cross-section and other lasing parameters. The model includes a fairly complete chemical kinetics of energy transfer from the excited molecular oxygen to the injected iodine, accounting also for the gas temperature effect and a simplified mixing description of oxygen and iodine molecules. The variable magnetic field transforms the CW regime in a pulsed operation. The numerical procedure gives a possibility to tackle an arbitrary temporal dependence of the imposed magnetic field and to calculate directly the response of the laser output. The calculation was focused on the experimental data measured with the subsonic version of the COIL device in the Institute of Physics, Prague, modulated by a saw-tooth magnetic pulses. Although the model gives a reasonable agreement for the CW regime it is difficult to match the exact shape of the measured magnetically switched laser pulses with the calculated one. In this contribution we shall demonstrate various additional refinements of the model to improve the agreement with the measured pulse shape.

A TEA-CO₂ laser with a supersonic gas flow has been developed, and the small-signal gain of a laser medium is measured. During the generation of the supersonic gas flow, the laser medium is cooled by the adiabatic expansion through a supersonic nozzle. Since excited CO₂ molecules in the cooled laser medium are concentrated within a specific range of the rotational quantum numbers J, the laser output and its wavelength should be changed by the cooling. An investigation is conducted with a single-pulse excitation discharge in the laser medium flowing at Mach number 2. The laser medium is cooled to 133 K under this condition. It is found that the breakdown voltage, the current, and the power density of the excitation discharge are estimated to be 22 kV, 3.8 kA, and 1.2 MW/cm³, respectively. The small-signal gain for this cooled laser medium is measured to be 2.2 %/cm, which is 1.3 times as high as that obtained for the laser medium at room temperature. It suggests that the TEA-CO2 laser with a supersonic gas flow has a potential for higher laser output. We also find that the wavelength for the maximum gain is 10.494 μm (J = 10) at 133 K, while is 10.551 μm (J = 16) at room temperature.

Measurements of the absolute spectral irradiance from O₂(a)-O₂-H₂O gas, produced by a chemical singlet oxygen generator, were performed. FWHM of singlet oxygen collision induced emission (CIE) at 634 and 703 nm have been measured in the temperature range 150-400 K. The measured rate constant of CIE at 634 nm - (6.72±0.8)×10^-23 cm³/s is in agreement with the value of the band intensity of the collision induced absorption. The rate constant of CIE at 703 nm relates to the rate constant of CIE at 634 nm as 1.06. The efficient rate constant of 8×10^-17cm³/s for the reaction O₂(a)+O₂(a)→"products" at about 360 K and the rate constant of (4.4±1)×10^-17 cm³/s for the reaction O₂(a)+O₂(a)→O2(b)+O₂ at about 330 K have been measured. These rates are larger than listed in the standard chemical oxygen-iodine laser (COIL) package. Nonequilibrium fraction of O₂(b,v=1) was measured against water fraction. It was deduced that the maximum number of oxygen vibrational quanta, generated in the sequences of the reactions O₂(a)+O₂(a)→O2(b)+O₂, O₂(b)+H₂O→O₂+H₂O, is less than 0.05. The analysis predicts that the fraction of vibrationally excited oxygen molecules at the exit of most-used chemical SOG most likely corresponds to the thermal equilibrium. Analysis of the data obtained from the tests of jet type SOG predicts O₂(a) nascent yield of about 90%.

The behavior of concentration of iodine atoms produced by a pulsed electric discharge in a mixture of iodide (CF₃I, CH₃I) with oxygen was investigated by using a method of absorption spectroscopy. The tunable diode laser was used as a source of a probe radiation. The significant difference between CF₃I, CH₃I was observed. The numerical modeling showed such a difference can be explained by an influence of a recombination process of iodine atom and radical RO₂.

Using a gas discharge tube typical for the middle infrared He-SrBr₂ laser, a study on gas and electron temperatures of nanosecond pulsed longitudinal discharge in pure He, as well as with Ne admixture, is carried out. Thermal conductivities of Ne-He binary gas systems are obtained on the base of experimental data fit, rigid sphere and 12-6 Lennard-Jones inter-atomic interaction approximations. Assuming that the gas temperature varies only in the radial direction and using the calculated thermal conductivities, analytical solution of the steady-state heat conduction equation is found for uniform power input. Measurement of the relative intensities of some He and Ne spectral lines, originating from different upper levels has enabled us to determine the average electron temperature.

Active diffuser- AD has been developed by blowing in the high pressure gas from small scale nozzles along the laser chamber walls. Blowing has stabilized boundary layers, decreased its thickness and prevented its separation. So AD operating has stabilized the gas flow parameters in resonator and localized the zone of slow down of laser flow - pseudoshock - after laser chamber. So regular shock - wave structures (X-type shocks) that could degrade the flow optical quality don't appear in resonator. The use of AD allows developing PRS on base of single-stage ejector with high ejection coefficient (usually ground -based COIL PRS consist from passive diffuser and two-stage ejector and has low ejection coefficient).

The method of the spectral narrowing of optically pumped XeF(C-A) laser is discussed. Two experimental schemes are used to narrow the spectrum of XeF(C-A) laser. Linewidth less than 1 nm can be obtained normally and the minimum linewidth is up to 0.2 nm with more than 2J output energy. Broadband tunability of the XeF(C-A) laser in the spectral range from 448 to 520nm is accomplished. The results of spectral narrowing of XeF(C-A) laser with different experimental schemes are compared and tunable spectra of the XeF(C-A) laser are given.

A computational model of the cross-flow type singlet oxygen generator (SOG) for chemical oxygen-iodine laser (COIL) is developed. The reaction zone, in which basic hydrogen peroxide (BHP) jets flow downwards and chlorine flows transversely, is discretized in two dimensions. Chemical and physical processes are calculated in each cell, the gas and liquid transport is modeled by a geometrical transfer rule. The processes involved in this SOG model are surface reaction between the gas-phase chlorine and the liquid-phase HO₂- ion, surface ion renewal by the diffusion process, heat release by the chemical reactions, heat exchange between gas and liquid phases, water evaporation and condensation, homogeneous deactivation of O₂(¹Δ), and heterogeneous deactivations of O₂(¹Δ) by the liquid column surfaces. We develop a 80 mmol/s-class SOG to validate the developed model. It is shown that the Cl₂-O₂ conversion efficiency (utilization) and O₂(¹Δ)/O₂ ratio (yield) are in good agreement with the theoretical model in a wide range of operational conditions. Heterogeneous deactivation probability affects the model prediction markedly, and 1×10^-3 yields the best agreement with the experimental results. This supports the values in previous publications.

Output power enhancement of an all gas-phase iodine laser (AGIL) by addition of hydrocarbon gases is studied. It is expected because hydrocarbon gases might scavenge Cl atoms, which are strong quencher of the upper state of the laser medium, I(²P_1/2). In AGILs, suppression of the Cl atom concentration is the key to improving the efficiency of laser operation because Cl atoms are inherently generated by the self-annihilation of the energy donor, NCl(a¹Δ). We found that the addition of CH₄ gave the best results because of its high scavenging rate constant and inertness to I(²P_1/2). An enhancement of 10% was observed in the output power when CH₄ was added at a flow rate twice that of NCl₃. On the other hand, when C₂H₄ or C₂H₂ were added at the same flow rate as that of CH₄, the output power reduced despite their fast removal rate of Cl atoms. The reason for the reduced output power was that the unsaturated bonds scavenged not only the Cl atoms but also the H atoms, resulting in a low density of H atoms, and this decelerated the production of NCl(a¹Δ). The observed laser characteristics could be reasonably explained by numerical model calculations.

The problem of obtaining high pulse repetition frequencies in metal vapor lasers is urgent from the viewpoint of laser application to various technologies, increase of productivity of industrial laser systems, study of transient processes, etc. In addition, the high pulse repetition frequency provides large average laser radiation power in spite of a rather low energy extracted from a single lasing pulse. In this work, the possibility of increasing the pulse repetition frequency of a laser on self-terminated strontium ion transitions was investigated. The double pulse method was used to demonstrate experimentally that a pulse repetition frequency of ~1 MHz could be achieved at wavelengths of 1.03 and 1.09 μm of the strontium vapor laser. To explain the results obtained, the kinetics of the active medium was modeled using the self-consistent mathematical model of a He- Sr⁺ laser.

The experimental setup and performance of a non-chain transverse excited HF laser with UV pre-ionization is described. Electric discharge characteristics in gas mixture of SF6 /C2H6 are investigated for various initial conditions by recording the discharge plasma fluorescence intensity and temporal evolution of discharge current and voltage. The laser pulse energy is studied in different charging voltage, gas mixture pressure and concentration. It is shown that the process of discharge in gas mixture has three phases: glow discharge, voltage plateau and arc discharge. The optimal energy deposition obtained at the critical point that the voltage plateau just disappears. Maximal output energy of 0.6J and electrical efficiency of 2.5% are obtained.

A novel concept of the chemical production of atomic iodine aimed for application in chemical oxygen-iodine laser was proposed. The method is based on nitrogen trichloride spraying auto-decomposition to generate chlorine atoms which subsequently react with iodine donors. Preliminary experimental and computational studies for the reaction system were explored. The experimental results show efficient generations of excited atomic iodine and computational results reveal that a large degree of atomic iodine can be generated via the reaction system including nitrogen trichloride combustion effluents and iodine donors.

Nowadays, the research and application of high-average-power diode-pumped solid-state lasers have attracted more and more attention and support in China. The output power of 5kW~10kW was obtained from different technological approaches. In the paper, the latest progress and development tendency of high power rod laser, thin slab laser, thin disk laser and fiber laser in China are introduced comprehensively. It also introduces the situation of the study on high power diode lasers and laser materials.

Stimulated Raman scattering (SRS) has been observed in various crystals generating a multitude of wavelengths covering the range from 280 nm to 3 μm with a mean spacing of 1 nm. Barium nitrate crystals pumped by two different pulsed Nd:YAG laser systems have been used to demonstrate Raman laser action achieving a high average power of 5 W or an output energy of up to 23 mJ with a quantum efficiency of 43% at 1.599 μm intended for CO₂ detection in longrange LIDAR systems. Spectral narrowing of the pump radiation reduced the Raman laser emission bandwidth to 0.08 cm^-1.

This paper is a survey of recent achievements at the College of Optics and Photonics/CREOL at the University of Central Florida in the use of newly developed diffractive optical elements which are volume Bragg gratings recorded in a photo-thermo-refractive (PTR) glass. Three levels of semiconductor laser design are proposed to achieve high-power low-divergence output. The first level is coherent coupling of emitters by means of PTR Bragg gratings which provide excitation of only one common mode in a multichannel resonator. This type of phase locking automatically leads to a narrow spectral width of emission usually not exceeding a few tens of picometers. The second level is a change of the mechanism of transverse mode selection from spatial selection by apertures to angular selection by PTR Bragg gratings. This approach allows increasing of the aperture size without increasing the length and selecting of arbitrary mode but not necessarily a fundamental one. The third level is spectral beam combining by PTR Bragg gratings which re-direct radiation from several high-power fiber lasers to co-propagate in the same direction with diffraction limited divergence. This approach allows simplification of the thermal management because only passive devices with low absorption (a PTR volume Bragg gratings) are placed in the path of high power laser beam.

In the framework of a national applied research project we have been designing and testing several different prototypes of ceramic slab Nd:YAG Lasers pumped by various laser diode arrays in vertical and horizontal stacks. We also investigated possible variations of the slab geometry. To reduce thermal effects, architecture with transverse (in the thinner cross-sectional dimension) or lateral (in the wider cross-sectional dimension) zig-zag propagation have been compared. Face- and edge-pumping have been tested with different diode stacks configurations. Finally the adoption of multipass-stable or hybrid stable-unstable resonators has been thoroughly investigated in CW and Pulsed operation. Compactness, efficiency and ruggedness have been the principal design drivers of our work. Nevertheless beam quality and insensitivity to diodes temperature have also been looked for. In this presentation the results of the whole research activity are summarized and explained.

Middle infrared and deep ultraviolet laser systems, which are based on high-power high-beam-quality stable-operating He-SrBr₂ and Cu⁺ Ne-CuBr lasers excited in nanosecond pulsed longitudinal discharge, are developed, patented and studied. Optimal discharge conditions, such as active zone diameter, vapor pressure, buffer-gas pressure, electrical excitation scheme parameters, average input power, pulse repetition frequency, are found. The highest output laser parameters are obtained for the Sr atom and Cu⁺ lasers, respectively. These lasers equipped with optical systems for control of laser radiation parameters, such as laser beam divergence, laser intensity distribution, etc. are used in a large variety of applications, such as precise material microprocessing, including biological tissues, determination of linear optical properties of different materials newly developed, laser-induced modification of conductive polymers, laserinduced fluorescence in wide-gap semiconductors, instead of free electron and excimer lasers, respectively.

The possibility of developing compact all solid-state lasers for short-wavelengths based on laser diode pumped single fluoride crystals is considered. The paper reviews our work and important data from the literature.

We have observed the optical amplification of the Ar₂^* excimer at 126 nm pumped by optical-field-induced ionization (OFI) caused by an infrared high-intensity laser. We have evaluated similar small signal gain coefficients of approximately 1.0 cm^-1 in two different experiments, where OFI Ar plasmas as gain media were produced in free space filled with Ar and inside an Ar-filled hollow fiber. This indicates that the function of a hollow fiber was to guide the infrared excitation laser and VUV Ar₂^* emissions, and not to regulate the OFI plasma. Despite the gain coefficient value at 126 nm, the laser oscillation has not been observed. This was limited by the optical quality of available state-of-the-art vacuum ultraviolet optics.

UV lasing is studied in nitrogen and the N2-SF6 mixture pumped by a volume discharge initiated by a runaway-electron preionised diffuse discharge (REP DD) produced in an inhomogeneous electric field. It is shown, that lasing at a wavelength of 337.1 nm is observed at pressures up to 2.5 atm without any preionisation source. At a pressure of 0.5 atm with the use of blade electrodes and the N₂ :SF₆ =10:1 active medium of length ~6 cm, the output laser energy of ~2 mJ was achieved for the pulse power of 0.55 MW. The REP DD pumping regime is compared with the regime of pumping by a volume discharge produced by a preionisation source.

For laser media with large cross-section and low small signal gain neither the stable nor the unstable conventional resonator is an applicable choice. Either the large Fresnel number leads to a multimode operation or the low output coupling ring results in large diffraction effects and therefore in a heavily structured far field. In order to reduce these diffraction effects a modified negative-branch unstable resonator (MNBUR) was introduced. In rotational symmetry the off-axis setup provides an output coupling in the shape of a half ring and is accomplished with the help of a scraper. The shape of this scraper can also be modified to adapt the MNBUR to a rectangular symmetry, whereas the spherical resonator mirrors are kept unchanged. The scraper either takes the shape of a rectangular bracket "[" or of the letter "L". The performance of both scrapers is tested using a chemical oxygen iodine laser (COIL) of the 10 kW class. The results are compared to numerical calculations.

We present a numerical analysis, modeling the behavior of a Hybrid Stable-Unstable Resonator (HSUR) in strongly non-confocal configurations. The simulation outputs enable us to attest the extracted beam properties observed in our experiments on a Diode Pumped Ceramic Nd:YAG laser equipped with a non-confocal HSUR. Beam structure and propagation factor M² are calculated and compared to the experimental measures. The parametric study of cavity losses and extracted beam properties also demonstrates that out-coupling coefficients compatible with design requirements and good quality extracted beams can be obtained also in this non-canonical cavity setup.

The phase-locked multichannel Nd:YAG laser systems with the long- and short-range coupling via the holographic gain gratings in the active elements are developed. The phase locking of various lamp- and diodepumped loop Nd:YAG lasers with an interference contrast of the laser channels of up to 0.87 and a singlemode lasing efficiency of up to 20% is experimentally demonstrated. The experimental results for the twoand three-channel laser systems are generalized on multichannel laser systems using the numerical simulation. It is demonstrated that the maximum number of the short-range-coupled laser channels can be increased owing to the leveling of the parameters of laser channels to a value that is greater than that the maximum number of the channels in the presence of the long-range coupling, which is limited by the damage threshold of the active element of the interchannel coupling. Use of the multi-loop configuration of the laser resonator allows compensating not only phase distortions but also a gradient of gain in the diode side-pumped active elements.

The goal of the project is to accomplish a circle of experimental, theoretical works on creation of super-long conductive canal technology for energy delivery from space. High repetition rate pulse-periodic laser system and the most important components for the project realization are presented. Optical system and dust plasma based conductive canal idea for long range energy delivery is discussed in details. Some experimental approaches for dust plasma conductivity tests and new data of measurements are discussed. New applications of "Impulsar" program suggested technology are highlighted.

The most recent fundamental research results to investigate surface erosions of nuclear fusion candidate chamber materials are described in short. We used a commercial surface profiler with a red semiconductor laser. Various material surfaces ablated and eroded by a rather short pulse electron beam and a short pulse ArF laser light were measured with this surface profiler and the associated three-dimensional analysis software. Threshold input levels for various sample surface erosions with electron and laser beams were clearly decided for the first time with our new method in this article. After the above fundamental results were gathered, the methods to inspect inner surface conditions of nuclear fusion reactor chambers were newly proposed with various kinds of laser displacement sensors. The first one is the erosion monitor with the above profiler, and the second one is the laser induced ultrasonic wave detection method to inspect deeper surface layers than the first one.

We report on the tuneabilities of Anderson localized light in random scattering systems and its lasing characteristics. By use of FDTD method, we investigated the impulse response of two-dimensional scattering systems consisting of closely packed dielectric particles, and analyzed the localized modes. We revealed the frequencies of the localized modes to be capable of being tuned by changing the structural parameters of the system: diameter, filling factor, and refractive index of the particles. It was also found to be able to tune the Q (quality) factors of the localized modes by changing the system size of the entire medium. Furthermore, by combining Maxwell's equations with rate equations for electron's system, we also theoretically demonstrate how the localized area serves as a laser "resonator" and random lasing is induced.

Laser processing of sheet metals are performed with a 2 kW cylindrically polarized CO₂ laser. Drilling and cutting capabilities are compared between conventional circular polarization and radial/azimuthal polarization beams of the same power. A 9 mm-thick mild steel is drilled with O₂ assist and azimuthal polarization shows a 15% faster drilling rate than circular polarization. A 4.5 mm-thick mild steel is cut with O₂ assist and radial polarization shows a 50% faster cutting speed than circular polarization. Smaller surface roughness of the cut is obtained by the radial polarization. A 2 mm-thick stainless steel is cut with high-pressure N2 assist. Although no difference of the maximum cut speed between radial and circular polarizations are seen, it is possible to reduce the assist gas pressure from 0.6 MPa to 0.3 MPa in the case of radial polarization.

Coherent Anti-Stokes Raman Spectroscopy (CARS) method is commonly used for measuring molecular structure or condition. In the aerospace technology, this method is applies to measure the temperature in thermic fluid with relatively long time duration of millisecond or sub millisecond. On the other hand, vibrational/rotational temperatures behind hypervelocity shock wave are important for heat-shield design in phase of reentry flight. The non-equilibrium flow with radiative heating from strongly shocked air ahead of the vehicles plays an important role on the heat flux to the wall surface structure as well as convective heating. In this paper CARS method is applied to measure the vibrational/rotational temperature of N₂ behind hypervelocity shock wave. The strong shock wave in front of the reentering space vehicles can be experimentally realigned by free-piston, double-diaphragm shock tube with low density test gas. However CARS measurement is difficult for our experiment. Our measurement needs very short pulse which order of nanosecond and high power laser for CARS method. It is due to our measurement object is the momentary phenomena which velocity is 7km/s. In addition the observation section is low density test gas, and there is the strong background light behind the shock wave. So we employ the CARS method with high power, order of 1J/pulse, and very short pulse (10ns) laser. By using this laser the CARS signal can be acquired even in the strong radiation area. Also we simultaneously try to use the CCD camera to obtain total radiation with CARS method.

We proposed and developed a novel surface analysis system using vacuum ultraviolet (VUV) photons. When the VUV photons were irradiated on the material surface, surface desorption was stimulated. The desorbed species were analyzed by the mass spectrometer. First, we studied the decomposition process induced by VUV photons from excimer lamps. We found that the different photon energy resulted in the different time dependence of the fragments signals even if the materials had similar chemical construction. It suggested that the identification of the materials should be possible by tracing the decomposition process. We developed an analyzing system, called "Photo-Stimulated Desorption (PSD) mass spectrometer" using a broadband VUV radiation from the Ar plasma excited by a Q-switched Nd:YAG laser. The desorbed species were analyzed by the quadrupole mass spectrometer. This PSD system was useful surface analysis tool not only for the semiconductor but also plastics, which is easily affected by heat.

The performance of high power gas laser has been analyzed. The numerical analysis has been executed not by a single computer but by the several Macintosh computers combined by Xgrid technology. The total computing power increases in proportion to the number of computers.

Photoluminescence and optical transmission spectra of several samples of natural and synthetic diamond and its imitators - fianite and corundum - are investigated. The band-A of luminescence at 440 nm, the vibronic N3 system of luminescence and absorption at 415.2 nm, the fundamental absorption edge at 225 nm, and the secondary absorption below 308 nm are the main identifying markers of natural diamonds. For synthetic diamonds, however, such identifying markers are the exciton luminescence at 235 nm, the band-A, and the fundamental absorption edge. Fianites can be identified by the structureless wide band at 500 nm and the wide transmission band in the entire visible range. Colored corundum samples with chrome impurities emit the narrow line at 693 nm and show the absorption band in the 500-600 nm spectral range. A new method for diamond express identification is developed on the basis of measurement of photoluminescence and optical transmission spectra of the samples. It is shown that a diamond tester can be designed combining a spectrometer and a KrCl-excilamp radiating at 222 nm.

The work covers a series of laser wakefield acceleration (LWFA) experiments carried out at the petawatt laser PEARL (PEtawatt pARametric Laser, Nizhny Novgorod, Russia). The use of different focusing angles and gas jets of various sizes is discussed. Modulation of the gas jet concentration profile for electron trapping improvement has been studied in experiments. Specific singe-shot laser-plasma interaction diagnostics adapted for low repetition rate systems with low output parameter stability, as well as a two-screen magnetic spectrometer with advanced accuracy of spectral measurements of electron bunches are considered.

For L.B.D. - Laser Beam Drilling (or Micro-Drilling) does not exist some measurement unit that carries out the efficiency of this process. All this for any type of laser used to produce micro-holes ("blind drills", "passing holes" as well "straight and tilted holes"). The usual parameters, measured on the micro-drill, such as Drill Height, Drill Diameter (on input and output), Aspect Ratio (height/diameter), Average Input and Output Diameters, Cylindrical shape (Average Input Diameter/Average Output Diameter), Ellipticity (on the input or output) furnish many information regarding the correct shape and geometry of the micro-drill obtained compared to one requested. In this experimental work and paper, some new quantitative parameters have been carried out to detect, evaluate as well as characterize the micro-drilling tests:
(1) P.D. / Pulse N. (μm / pulse) *
(2) Pulse N. x 150mJ / P.D. ( mJ / μm
(3) P.D. / Pulse N. × 150mJ ( μm / mJ )
(4) 1 Daud_E = μm / μ
(5) 1 Daud_V = μm 3/ m
where P.D. is the Penetration Depth for blind drills like to Drill Height for Passing Holes . So, a Laser Beam Drilling Efficiency unit, the Daud ( 1 Daud_E = μm / mJ or 1 Daud_V = μm³/ mJ ) could be adopted as a quantitative parameter to see how the process of micro-drilling, by that type of laser on that material, has been efficient. In this paper, for example, some results obtained on some different Metals and Alloys, by using a Nd- YAG Laser, λ2 ( 2^nd harm. ) 532 nm - Pulse Width 11ns - E 150 mJ / pulse, Focusing Lens in BK7 (borosilicate ) - 60mm F. L. and Optical Focused Spot on the surface of the target, are considered and evaluated. A laser percussion micro-drilling, fig.1, process has been tested on 11 different Aluminium and its alloys (Series 1000 - 2000 - 5000 and 6000; in particular AA1090 - AA2024 - AA5083 - AA5754 - AA6082 and AA 8090 ), on 7 different Cu and its alloys. The thicknesses tested for Al alloys ranging on 70 - 240 - 480 - 800 and 1000 μm as well as 50 - 100 - 180 - 280 and 500 μm for Cu and Alloys. A Nd-YAG Laser Source, (QUANTEL), YG 580 type, was used for the experiments. This laser , in Q-Switch Mode, has the following characteristics :
(1) Repetition Rates ( Single Shot, 2Hz and 10Hz ), Focusing Lens BK7 - 60 mm F.L.
(2) λ2 532 nm - Pulse Width 11ns - E 150 mJ/pulse.
The aim of this work was :
(1) the possibility to obtain micro-drills on the range from 500 to 25 μm diameters with some Aspect Ratio high values. At the same time the realization of some "blind drills", "passing holes" as well as "straight and tilted holes was proved;
(2) The possible adoption of a Laser Beam Drilling Efficiency (L.B.D.E.) unit, the Daud_E and / or Daud_V.

In this paper line x-ray emission from aluminum plasma at wavelength within range of 5 - 7 angstrom was studied numerically. The plasma was assumed to be produced by irradiating of aluminum target by long laser pulses (1000 ps ≥ τ_p ≥ 50 ps) at intensities up to I = 5×10¹⁶Wcm^-2. The plasma hydrodynamics was simulated by EHYBRID code. Using the data from this code and Saha-Boltzmann equation; the x-ray spectrum and total x-ray yield of the plasma were calculated within the time scale of irradiation. The influences of laser intensity as well as pulse duration on the total yield of x-ray line emission were investigated. The results show that, the emitted x-ray lines at the above wavelength range has duration similar to that of the laser pulse and the total x-ray yield can be increased by increasing laser intensity and pulse duration.

In this work femtosecond laser photo-excitation of GaAs is studied numerically. The transient plasma densities photogenerated during the pumping IR fs-laser pulses were evaluated having in mind experimental data of time-resolved reflectivity measurements of transient bandgap shifts. Theoretical modeling employing quantum kinetic formalism based on a generalized Boltzmann-type equation, including one/multi-photon photo-excitation, Joule heating and free-carrier absorption, interband excitation, impact ionization, Auger recombination of electron-hole plasma, thermal exchange with the lattice, etc. is performed. For the first time the effect of enhancement of ionization by transient bandgap renormalization (BGR) is considered both experimentally and theoretically. The energy spectra of the electron distribution function and the time dependence of the electron density are calculated and the key role of BGR in the transient electron-hole plasma dynamics is pointed out.

In this paper the dynamics of optical breakdown in dielectrics induced by femtosecond laser pulses was simulated numerically. Using rate equation and time and space dependent intensity for laser pulse the free electron density in focusing volume was calculated. In the calculations propagation of laser pulse through the focusing volume was considered. The temporal and spatial free electron density was used for simulating the footprint of the breakdown region in the focusing volume. In these calculations the influence of the laser power was investigated. The results and simulation show that lower laser power can generate asymmetric breakdown trace while the trace becomes more symmetric if the breakdown is generated by higher laser powers.

Experimental and theoretical studies on laser ablation of polymers (PMMA, polyimide) have been performed in a wide range of CO₂-laser fluences. Evolution of polymer laser plume in air has been investigated with simultaneous registration of radiation spectra of the ablation products, spatial dynamics of plasma flare, and temporal behavior of plasma emission on separate spectral lines. It has been found that spectral lines have intensity peak after laser pulse termination while plasma emission spectra are similar to those of organic material combusting. The results confirm that combustion of the laser-vaporized polymers occurs in the plasma plume. A thermo-chemical model of heating and ablation of organic polymers by CO₂ laser pulses has been developed which takes into account attenuation of radiation in laser plasmas and chemical processes leading to heating the plume of the ablation products. Temperature evolution in the irradiated sample, ablation dynamics, and laser beam attenuation are analyzed. The modeling results are compared with the experimental data on high-speed imaging of the plasma plume. The effect of the formation of a "plasma pipe" is revealed under polymer ablation in air under normal conditions.

Chemical etching is a non-traditional machining process where a chemical solution is used to remove unwanted material by dissolution. To shape the etched area, before the process, a chemical inert paint (maskant) is applied on the surface. Then the maskant is trimmed away and the uncovered area is subject to the etching. The maskant cut could be obtained mechanically or by laser ablation. In this work, the effect of process parameters, cutting speed and beam power, on interaction phenomena and defect formation in laser cutting of polymeric maskant is studied, using a 30W CO₂ laser source.

The opacity of some low Z plasmas that are in local thermodynamic equilibrium (LTE) was calculated numerically. In this study spectrally resolved opacities under different temperature and density plasma conditions was calculated. The calculation results show that by increasing of plasma density, the opacity can be significantly enhanced. It is also shown that the plasma opacity increase with rising the plasma temperature reaches to a maximum value and then decreases again with the plasma temperature.

This paper presents the experimental results of studying the distribution function of electrons plasma produced by irradiating aluminum target by nanosecond pulsed laser in vacuum. The laser beam was provided by second harmonic of a Q-switched Nd:YAG pulsed laser with ~10 nsec pulse duration and energy of 70 mJ. A home made Faraday cup was used for detecting the current signal. From analyzing the time of flight (TOF) experimental distribution function was determined. Comparing the experimental distribution function with Maxwell-Boltzamnn and effusion distribution functions, the electron temperature was estimated. From the experimental results, the velocity of maximum electron flux was determined. In this study the influence of the probe position and biasing voltage was investigated. The results show that the velocity of maximum electron flux and associated temperature rises with distance from the target surface. The results also show that effusion distribution function is more appropriate for modeling such plasma.

The dynamics of an aluminum plasma plume expanding in atmosphere air was studied experimentally. The plasma was produced by irradiating a thin film aluminum with a single pulse laser beam in ambient air. The laser pulse was provided by second harmonic of a Q-switched Nd:YAG laser with ~10 nsec pulse duration and ~ 50 mJ energy per pulse. A low power CW He-Ne laser beam was also used for probing the plasma. Both transmission and reflection of the probe were monitored temporally during the ablation time scale. For transmission three temporal stages can be distinguished and there is a substantial reduction in the reflection coefficient when laser ablation occurs.

In this paper, formation of microstructure on the surface of aluminum target is investigated. The target surface was irradiated by trains of nanosecond Nd:YAG laser in ambient air. The irradiation was performed at trains of 1 to 500 laser pulses with energies ranging from 0.1 to 0.4 mJ. Such laser pulse energies provided intensities at the order of 10⁷ W/cm²at the target surface. Using optical microscope, the irradiated region of the target surface was characterized by measuring of microstructures depth and length. In this study the effects of laser pulse energy and the number of pulses in microstructure formation was inspected. The results show quasi-Gaussian profile for the distributions of microstructure depth and length.

In this paper shock waves produced by nanosecond pulsed laser were characterized. The shock wave produced by focusing Q-switched Nd:YAG pulsed laser beam (with energy ~120 mJ, wavelength of λ=532 nm, and pulse duration of 10 ns) in ambient water. Using probe beam deflection technique, the shock velocity was measured around the breakdown region. The results show that the shock wave velocity near the breakdown region is at order of 7000 m/s, and slows down to ~1600m/s at further distances. Using the empirical relations the maximum shock pressure was also calculated. The results show that the shock pressure near the breakdown region is 2×10¹⁰ pa, and decreases with increasing distance from the center of the breakdown.

It is the oldest church in the city after the cathedral. It is among the purest examples of Romanesque. It was founded in 1074 and expenses for its construction helped the inhabitants of the agricultural hamlets of the Cirignano, Pacciano and Zappino. The church was dedicated to St. Adoeno Dado, bishop of Rouen, protector of Norman, because , according to tradition, the building also participated Norman soldiers. San Adoeno church has a façade at cusp with a truncated tympanum , crowned by an eagle. In the centre of the façade there is a rose ornament surrounded by four lions and a statue of St. Adoeno ( Figs. A to I ). On the outside walls of this Abbey many graffiti, produced by different coloured spray paints were found. After the usual photographical tests some Laser Paint Removal trials were executed to verify the damage threshold of the calcareous stony substrate as well as the possibility to ablate these paints by a Nd - YAG laser in Q-Switch mode. Even if all the classical four laser paint ablation techniques were employed some paints showed a great difficulty to be removed from the substrate. For these ones it was necessary to increase at maximum both the energy per pulse and the fluence value for obtaining some acceptable result but the substrate looked turned pale. It was decided to remove a small amount of these paints and subject to chemical analysis for determining whether they were acrylic based. At the same time it was investigated on the type of limestone substrate that appeared more porous and less hard on the surface than the common local limestone marble basin, that is, Trani or Bisceglie. So, on the light of these investigations, the possible solution for this hard laser ablation problem was carried out with an acceptable final result.

Some diverse spray paints, used for graffiti on the monuments and historical mansions, were selected and chosen. These paints are ones common used by some uncivil young peoples to produce graffiti on many monuments and historical mansions. These paints were sprayed on a stainless steel square plate substrate (30x30mm) and left to dry outdoors for 3 days. Then thickness measurements of each painting on these samples were carried out. Moreover each of the 18 paintings was subjected to reflectivity (absorption) measures by using a reflectance spectra in the range from 2500 to 300 nm. So many plots were recorded by an UV-VIS-NIR Cary 5 (Varian) spectrophotometer using a scanning rate of 600.00 nm / min, a data interval of 1,000 nm and average time of 0.1 s. By using the same technique the restricted range from 300 to 1200nm were investigated for a close, interesting and precise scanning. All this results much more useful and interesting as it can furnish many experimental information on the per cent absorption of a data laser wavelength for a specific spray paint , identified by a RAL (Reichsausschuss für Lieferbedingungen) Code for a normalized colour scales (RAL 840 HR for opaque colours and RAL 841 GL for brilliant colours). This information were not possible to obtain on the scientific literature as well as by some paint manufacturers, so it was necessary and useful to test for a better comprehension of the laser ablation process as well as for the possible chance of success. The works are still in progress.

The conventional industrial method for creating color transparent resin materials uses immersion of resin in heated dye diluted with water for a constant time. However, this method is not very efficient. Therefore, we developed a coloring method that uses a waveguide CO₂ laser for the effective coloring of transparent resin materials. Although it is possible to color with our new method, thermal deformation in the colored parts of the material was observed. Therefore, we have examined the optimum conditions required for using laser irradiation to color resins without thermal deformation artifacts. We performed thermal analysis on the resin surface during the laser irradiation process by thermography. In this paper, we describe the construction of a coloring system that uses a waveguide CO₂ laser which does not result in thermal deformation artifacts. We then employ this new system for a fundamental coloration experiment.

We present results on near-field ablation using Mie resonance high dielectric constant particles with small size parameter for establishing a new downsizing technique for nanopatterning. In this article, we first describe a comparative study of near-field properties on substrates using metallic and dielectric nanoparticle. The results indicate that combination of particle and substrate for efficient localized near-field nano-processing is important for selecting either metallic or dielectric particle. We then demonstrate nanoablation using a Mie resonance high dielectric constant small particle. Theoretical calculations clarified that the maximal enhancement factor and spot diameter close to the smallest size are obtainable on both low-refractive-index (SiO₂) and high-refractive-index (Si) substrates using a 200 nm Mie resonance dielectric particle (n~2.7) at magnetic quadrupole mode with 400 nm excitation wavelength. Experimental results with 200 nm amorphous TiO₂ particles (n=2.66+0.024i) by 400 nm femtosecond laser irradiation verified that clear circular nanoholes with about 100 nm in diameter were fabricated on both substrates even with laser fluence lower than a half ablation threshold of the bare substrates. As for nanopatterning with two-dimensionally arrayed 200 nm amorphous TiO₂particles, cohesion of nanoholes was observed in high laser fluence regime due to inter-particle near-field interaction.

We report a new phenomenon, formation of microstructures, observed at multipulsed nanosecond laser ablation of liquid metals (Ga, In, Sn-Pb alloy, Wood's metal). Laser irradiation of liquid metal targets was carried out in a gas chamber equipped with a heater. In contrast to vacuum conditions or an inert atmosphere when a crater is formed which is healed after termination of irradiation, ablation in a reactive ambient gas (air, nitrogen, sulfur hexafluoride, nitrogen trifluoride) leads to a horn-like structure growing on the irradiated surface with the rate of 3-20 μm per pulse depending on laser fluence and the types of metal and ambient gas. The interplay between different processes in a heat-affected zone of the irradiated samples is analyzed, including ablation, thermal expansion, temperature variations of viscosity, surface tension, thermal stresses, capillary and plasma effects, and surface chemistry. A clear picture of microstructure origin has been established and a qualitative modeling representation is given to explain the growth process of microstructures. The optimal conditions of microstructure growth have been determined and perspective applications of the discovered effect are discussed.

We present theoretical and experimental results of nanohole fabrication on a silicon substrate by plasmonic near field around multiple gold nanoparticles excited by oblique incidence of femtosecond laser. Using the enhanced near field around a gold nanoparticle, nanohole can be fabricated on the substrate surface even at the near-infrared laser excitation. The formation of nanoholes with the near-infrared incident wavelength will open up smart applications for new optical device fabrication in air. However, the plasmons inside gold nanoparticles are affected by the plasmons of neighboring gold particles, resulting in an alteration of near-field distribution and the shift of resonant wavelength of plasmons inside the gold particles. These cause inhomogeneous shape of nanoholes and decrease the near-field intensity on silicon substrate. Therefore it is necessary to control the direction of plasmon for precise nanohole fabrication. We propose a new method to reduce plasmon interaction between particles by using p-polarized irradiation at oblique incidence to the substrate surface. Experimental and theoretical study demonstrated that uniformed nanoholes can be achieved by restraining effects from neighboring plasmon when p-polarized beam is irradiated to gold nanoparticle arrays with optimal oblique incidence.

For plasmonic surface optical applications, localized optical field distribution properties in the vicinity of gold particles on a silicon substrate by backward and forward irradiation are presented. It is technically difficult to fabricate nanostructure on the surface by conventional forward laser incidence to the substrate because gold nanoparticles easily aggregate to form double-layered particle arrays. We calculated enhanced optical field properties in order to pattern the substrate surface only with a template of the bottom-layered particle arrays in case that the backward irradiation of femtosecond laser is used in the system of aggregated double-layered gold nanoparticle arrays. With the backward irradiation, the optical field intensity in the substrate for the double-layered hexagonal arrays is found to be only 30% lower than the mono-layered system. Moreover, near-field cannot be generated with the forward irradiation. As a result, only the backward irradiation scheme is found to be effective for uniform surface nanopatterning at enhanced plasmonic near-field zones.

High-precision processing and microfabrication has been realized with the use of a femtosecond laser which with an ultrahigh-peak power and an ultrashort pulse. Such processing of glass materials has never been accomplished through conventional methods, and has been realized only through nonlinear optical phenomena using femtosecond lasers. Moreover, photonic devices such as optical waveguides, photonic crystals and 3D-memory devices have been developed. In our laboratory, precise holes with high aspect ratios are created in micro-scale glass materials for the purpose of developing novel optical devices. This research is conducted by using a fundamental wave (800 nm) and a second harmonic generation (SHG: 400 nm) of a Ti-Sapphire laser with various irradiation conditions at each wavelength in order to find the optimal processing parameters. In addition, optical silica fibers have been used target objects. First, a calibration experiment was carried out by fixing the repetition frequency and the number of pulses and changing the irradiation fluence. Next, another calibration experiment was carried out by fixing the irradiation frequency and the number of pulses and changing the repetition frequency. Last, an experiment on changing the number of pulses was conducted by using the fundamental wave. In this paper, the results of these experiments and the processing parameters required for the development of novel optical devices are described.

In this work, we report the fabrication of silver (Ag) nanoparticles on silica substrate in vacuum by PLD using a third harmonic of Nd:YAG laser (λ = 355 nm). The existence of Ag nanoparticles was evidenced by transmission electron microscopy (TEM) and an analysis of the size of the nanoparticles as a function of the number of laser pulses was performed. The Ag nanoparticles produced had mean diameters in the range from 1 nm to 15 nm, with the size distribution centered near 5 nm. The presence of the Ag nanoparticles was also evidenced from the appearance of a strong optical absorption band into the measured UV-VIS spectra, associated with surface plasmon resonance. Broadening of the absorption peak and its shifting to the longer wavelengths was observed as the number of laser pulses increased. A theoretical study of the optical properties of Ag nanoparticles predicts the presence of a thin oxide shell covering the nanoparticles.

Pure commercial titanium is widely used because of its high corrosion resistance and lower cost compared with other titanium alloys, in particular when there is no high wear requirements. Nevertheless, the wear resistance is poor and surface damage occurs in areas under contact loadings. Laser melting deposition using a high power laser is a suitable technique for manufacturing precise and defect free coatings of a dissimilar material with higher wear and corrosion resistance. In this work a good understanding of laser metal deposition mechanisms allowed to obtain defect free coatings of Ti6Al4V and TiC metal matrix composite (MMC) using a flash lamp pumped Nd:YAG laser of 1 kW. A complete investigation of the process parameters is discussed and resultant wear and corrosion properties are shown. The results show the feasibility to apply the process for manufacturing, improving or repairing high added value components for a wide range of industrial sectors.

For bending of brittle materials it is necessary to heat up the forming zone. This can be done with a fiber coupled solid state laser, whose beam is evenly distributed on the bending line with a beam splitter installed in the lower tool (die) of a bending press. With polarization optics the laser beam is divided there into partial beams that are evenly distributed on the bending line with lenses and prisms. A setup for a bending length of 200mm heated by a fiber-coupled 3kW Nd:YAG-laser shows the feasibility of the concept. Successful operation was shown for the Mg-alloy AZ31, which breaks during forming at room temperature, but can be well formed at temperatures in the range of 200-300°C. Other materials benefiting from this method are Ti-alloys, high-strength-Al-alloys, and high-strength-steels. Typical heating times are in the range of up to 5s and much of the heat input is generated during the bending operation where the laser continues to work. Laser Assisted Bending with a fiber coupled solid state laser is a straightforward way to perform the bending of brittle materials in a process as simple as cold bending.

Laser metal deposition (LMD) with high power lasers consists of manufacturing precise layers of materials by fusing metal powder with a laser beam over a substrate. Typical dilution of 5% allows metallurgical adhesion of the coating. This technique provides a unique combination of high accuracy and low heat affecting zone which is attractive for processing high added value components such aeroengines. Nickel (Ni) base superalloys are widely used in aeroengines because of their high mechanical properties when working at high temperatures (creep). A repairing or manufacturing chain of these components by LMD requires a good understanding of many parameters; therefore process control plays an important role. This work is focused on the study of the LMD processing of a Ni base superalloy using two colour pyrometry for the process monitoring. Presented results show how temperature and cooling rates of the LMD tracks affect the shape, microstructure and corrosion of the LMD coatings.

The paper presents the results of the study of the CO₂ laser radiation absorption in the optical-breakdown plasma in a supersonic air stream. The experimental facility and procedures of the absorption coefficient measurement in plasma are described. Experimental dependencies of the radiation absorption have been obtained within the wide range of the gasdynamic parameters of the supersonic air stream (velocity, static pressure, density, Mach number). The results are helpful to choose the working modes of the wind tunnel to choose the influence of the energy supply into the supersonic stream on the sonic boom formation and its level.

A drill for concrete and rocks is being developed using a laser-based hybrid technique. The design locates the outlet hole of laser beam and drill blades on a common rotational axis. The laser beam weakens the concrete, and the blade breaks the weakened layer. The target performance is a drilling speed of 30 mm/min at a sound level less than 70 dB using 1-2 kW laser power to produce a φ20 mm × 300 mm hole.

In the Laboratory of Laser and Crystal Physics of Tomsk State University, the laboratory model of a multiplewavelength strontium vapor laser (SVL) with output power of 5-7 W was developed and manufactured, a number of investigations aimed at an increase in the output characteristics of this laser were performed, and a record energy characteristics were achieved, including total lasing power of 13.5 W, lasing power at two wavelengths in the region of 3 μm of 4.5 W, and lasing power at two wavelengths in the region of 1 μm of 1.9 W. A maximum total energy per lasing pulse reached 1.26 mJ for pulse repetition frequency of 8.6 kHz. Investigations were performed aimed at visualization of IR radiation of the strontium vapor laser by the violet recombination line of the strontium ion at λ = 0.4305 μm. These investigations indicated the possibility of developing a high-power strontium vapor laser with high lasing efficiency, wide range of variations of pulse repetition frequencies, and simultaneous multi-wavelength generation. In the present work, a number of applications of the multi-wavelength strontium vapor laser are considered in detail, including precision controlled laser thermal cleavage of fragile nonmetallic materials (glass thermo-optical space radiators, display screens, and chips on a sapphire substrate), and infrared laser resonant ablation (microsurgery and polymer treatment). In addition to the above-listed technologies, laser systems based on compact strontium vapor lasers can be used successfully for atmospheric sensing and gas analysis.

This paper will address long range laser propagation applications where power and, in particular beam quality issues play a major role. Hereby the power level is defined by the specific mission under consideration. I restrict myself to the following application areas: (1)Remote sensing/Space based LIDAR, (2) Space debris removal (3)Energy transmission, and (4)Directed energy weapons Typical examples for space based LIDARs are the ADM Aeolus ESA mission using the ALADIN Nd:YAG laser with its third harmonic at 355 nm and the NASA 2 μm Tm:Ho:LuLiF convectively cooled solid state laser. Space debris removal has attracted more attention in the last years due to the dangerous accumulation of debris in orbit which become a threat to the satellites and the ISS space station. High power high brightness lasers may contribute to this problem by partially ablating the debris material and hence generating an impulse which will eventually de-orbit the debris with their subsequent disintegration in the lower atmosphere. Energy transmission via laser beam from space to earth has long been discussed as a novel long term approach to solve the energy problem on earth. In addition orbital transfer and stationkeeping are among the more mid-term applications of high power laser beams. Finally, directed energy weapons are becoming closer to reality as corresponding laser sources have matured due to recent efforts in the JHPSSL program. All of this can only be realized if he laser sources fulfill the necessary power requirements while keeping the beam quality as close as possible to the diffraction limited value. And this is the rationale and motivation of this paper.

Up to now the long range filaments are considered as a balance between Kerr focusing and defocusing by plasma generation in the nonlinear focus. However, the above explanation of filamentation in far-away zone finds considerable difficulties. There are basically two main characteristic which remain the same at these distances - the super broad spectrum and the width of the core, while the power in a stable filament drops to the critical value for self-focusing. With such power the plasma and higher-order Kerr terms are too small to prevent selffocusing. We suggest here a new mechanism for stable soliton pulse propagation in far-away zone, where the power of the laser pulse is a little above critical, and the pulse admits super-broad spectra.

The purpose of this study is to fabricate an internal structure in a silica fiber using internal processing with a femtosecond laser to develop a novel optical fiber sensor. We have found that bending directions can be detected by measuring transmitted light that has been affected from non-axial symmetry-sensing region in our proposed optical fiber sensor. In this paper, an optical fiber-processing experiment is carried out with the intensity of light transmitted through the sensing region being measured so that light loss through internal processing is measured. In the processing experiment, it was confirmed that use of a Ti:sapphire laser results in a processed region inside the fiber. In the measurement experiment, light transmitted through the core of a processed fiber was measured when the fiber was bent toward the processed region and when the fiber was bent toward the other side. The intensity of transmitted light obtained was found to be dependent on the two bending directions. This indicates that detection of the bending direction is possible. Experimental results are presented for the optimum irradiation parameters for internal processing of optical fibers for the fabrication of various required dot structures in the vicinity of the fiber core surface. We also report measurement experiment for the processed fiber.