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In the last century the laser was invented in 1961 after that scientists aspired to produce a high-power laser (HPL) to be used in many fields as communications in a far-field, and for industrial purposes such as carving, cutting, and leveling, and in military applications, a super-powerful laser is used to destroy different enemy targets After several attempts and painstaking experiments, more than one conception was reached to reach a high-power laser, the first of which is the chemical laser, for example, the carbon dioxide laser, the carbon monoxide laser, the hydrogen and fluorine laser, the second type free-electron laser, and finally fiber laser. in this paper a chamber test of a high-power fiber laser beam (CTHPF) measures the absorption and scattering of the laser beam in a case almost real in the far-field, it simulates atmospheric aerosol and the effect of the laser beam after chamber on the piece of solid material like stainless steel and aluminum to measure heat capacities (HC) with a versus temperature (T), which its Produced by the laser beam.

Al is doped into 4H-SiC by irradiating pulsed KrF excimer laser to 4H-SiC immersed in AlCl3 aqueous solution. Impact on doping depth of the use of expanded laser-pulse width is investigated. Expanded laser pulse is produced by splitting and recombining the laser beam with mirrors. The laser pulse width was expanded from its original width of 55–100 ns, while the peak power of the expanded pulse is as half as that of the original pulse under the same laser fluence. Multiple shots of the expanded laser pulses increased the doping depth at the Al concentration of 1×1016 /cm3 to 100 nm from 30 nm of the single shot of the original short, high-peak power laser. The increased doping depth could be due to enhanced diffusion by extra vacancies generated by the repeated laser irradiations. Due to the smaller laser peak power, the expanded pulse laser can suppress damage generation under multiple laser shots and, as a result, leakage current of the pn junction diode is kept low.

The chemical oxygen–iodine laser (COIL) is the shortest-wavelength high-power chemical laser that has been demonstrated. The characteristics, such as good atmospheric propagation, short wavelength and excellent transmission through optical fibers, make the COIL a good candidate for high-power laser application. To model the complete COIL lasing interaction, a three-dimensional formulation of the fluid dynamics, species continuity and radiation transport equations is necessary. The computational effort to calculate the flow field over the entire nozzle bank with a grid fine enough to resolve the injection holes is so large as to preclude doing the calculation. The approach to modeling chemical lasers then has been to reduce the complexity of the model to correspond to the available computational capability, adding details as computing power increased. The modeling of lasing in the COIL medium is proposed, which is coupling with the effects induced by transverse injection of secondary gases, non-equilibrium chemical reactions, nozzle tail flow and boundary layer. The coupled steady solutions of the fluid dynamics and optics in a COIL complex three-dimensional cavity flow field are obtained following the proposal. The modeling results show that these effects have some influence on the lasing properties. A feasible methodology and a theoretical tool are offered to predict the beam quality for large-scale COIL devices.

Coherent beam combination can promote the emitting power of chemical laser in the extremely high power application. To achieve chemical laser coherent combining the optical paths of each channel should be adjusted to the same for the multi-line spectral characteristic and the combination effect is highly dependent on the optical path variance. The dependence of the combination effect on the optical path variance is calculated taking deuterium-fluoride (DF) laser for example. The feasibility and the validity of the multi-line chemical laser coherent combining are discussed with different optical path variances. The coherent combination of multi-line chemical laser is not totally unattainable as long as the precise optical path control measure is involved. To achieve excellent combination effect for chemical laser with ordinary optical path control measure, line-selecting technology is commonly needed.

The efficiencies of different fuel compositions used in the combustion chamber of an autonomous cw chemical HF—DF laser for obtaining high specific energy parameters during simultaneous lasing in HF and DF molecules in two spectral ranges are theoretically analysed. It is shown that mirrors with the reflectance above 99% in these spectral ranges can be manufactured in principle.

Nowadays, a chemical laser has been developed not only for a strategic military purpose, but also as a manufacturing tool in industrial usage due to its high power lasing characteristics. In order to increase the laser beam power in the chemical laser systems, the mixing efficiency of fuel and oxidant should be improved, since more excited molecules are followed by high mixing efficiency. Basically, the production of a lot of excited molecules in the laser cavity results from the high mass flow rates of fuel and oxidant based on efficient mixing and chemical reaction. Therefore, in order to supply higher mass flow to the chemical laser cavity, a radial-expansion nozzle array was used and examined here, not a planar nozzle array which has been widely employed until now. The laser beam generation in this system is achieved by mixing F atoms from supersonic nozzle with D2 molecules ejecting from holes of round-bended supply lines which are distributed in zigzag configuration, which would extend the reaction zone. Consequently, more excited molecules are expected to be produced, so the intensity of population inversion will be higher. Since the two-stream injection angle was considered to influence the performance of supersonic combustor, the effects of D2 injection angles against the main F flow on mixing enhancement, population inversion and gain characteristics were numerically investigated in this study. The results were discussed by comparison with three cases of D2 injection angles such as 10°, 20° and 40° against the main flow direction. As the injection angle increases, two counter-balancing effects were observed.

The energy and temporal parameters of radiation from a cw chemical medium-size HF/DF laser mechanically Q-switched by a mirror rotating at a frequency of up to 1 kHz are calculated and studied experimentally. The peak power of laser pulses in the repetitively pulsed regime exceeds the cw output power of the HF laser at least by a factor of four. The average power in the repetitively pulses regime is lower than that in the cw regime, but it increases (approximately doubles) with increasing modulation frequency. The time of the complete recovery of the gain profile in the active medium is measured to be 6–7 μs. Two numerical models are developed which describe the dynamics of Q-switched HF and DF lasers. Some specific features of the operation of these lasers are analysed with the help of these models.

This paper presents results from investigations of chemically reacting flowfields and optical gain profiles in HF chemical laser media by infrared hyperspectral imaging. Subsonic and supersonic chemiluminescent F+H2 reacting flowfields, produced in high-fluence microwave-driven reactors, were imaged at a series of wavelengths, 2.6-3.1 microm, by a low-order, spectrally scanning Fabry-Perot interferometer mated to an infrared camera. The resulting hyperspectral data cubes define the spectral and spatial distributions of the emission. Spectrally resolved images at high spatial resolution were processed to determine spatial distributions of the excited-state concentrations of the product HF(v, J) molecules, as well as spatial distributions of small-signal gain on specific laser transitions. Additional high-resolution Fourier transform spectroscopy and spectral fitting analysis determined detailed excited-state distributions in the reacting flowfields. The measurements showed that energetic HF(v, J) state distributions were generated by both the supersonic and fast-flow subsonic mixing schemes. In particular, the subsonic reactor produced a spatially distributed field of inverted, near-nascent state populations, with small-signal gains near 2-3%/cm.

A simple, low-cost light emitting diode-based quasi-real-time autocorrelator has been developed with two-fold enhancement in temporal scan range than conventional commercial autocorrelators. We use the technique of twin audio-speaker, but avoid the complex electronic circuitry to achieve two 180° out-of-phase ramp signals. Next, the use of pick-up coils, switching electronics and sum amplifier to generate a time marker signal for autocorrelation signal measurement is also dispensed with. The suitability of our setup is demonstrated by recording autocorrelation signals of ∼200 fs laser pulses from Nd:phosphate oscillator under different ramp signal voltages.

A mathematical model of a Q-switched cw chemical laser is developed. The model is based on a simplified description of the active medium and the exact wave description of the mode structure of radiation. The model is used to study numerically the spatial–angular parameters of the output beam of a HF laser. We considered an unstable cavity that provided a high stability of the axis of the laser-pulse radiation pattern upon Q-switching with the help of a rotating mirror. The results of numerical simulation showed that for typical dimensions of a plane or an unstable cavity of the positive branch in a cw chemical laser, the angular radiation divergence rapidly changes in time and on average exceeds the diffraction limit by an order of magnitude. The problem can be solved by replacing a rotating mirror Q switch by a fixed one with time-dependent transmission. We also considered a negative-branch unstable cavity which can provide a stable radiation divergence upon Q-switching produced by a rotating mirror.

Defense application for a chemical oxygen laser (COL) is explained. Although a COL has not yet been successful in lasing, the oscillator was estimated to produce a giant pulse with the full width at half maximum (FWHM) of ~0.05ms which makes the damage threshold for the mirrors several-order higher than that for a typical solid-state laser with a ~10ns pulse width. Therefore it has a potential to produce MJ class output considering the simple scalability of being a chemical laser. Since within 0.05ms a supersonic aircraft can move only a few centimeters which is roughly equal to the spot size of the focused beam at ~10km away using a large-diameter focusing mirror, a COL has a potential to make a damage to an enemy aircraft by a single shot without beam tracking. But since the extracted beam can propagate up to a few kilometers due to the absorption in the air, it may be suitable to use in space. While a chemical oxygen-iodine laser (COIL) can give a pulsed output with a width of ~2 ms using a high-pressure singlet oxygen generator (SOG). Therefore a pulsed COIL may also not require beam tracking if a target aircraft is approaching. Another advantage for these pulsed high-energy lasers (HELs) is that, in case of propagating in cloud or fog, much less energy is required for a laser for aerosol vaporization (LAV) than that of a LAV for a CW HEL. Considerations to use a COL as a directed energy weapon (DEW) in a point defense system are shown.

The performance parameters of reflecting mirrors such as absorption coefficient or thermal distortion determine the beam quality of the output laser, so the quality of mirrors is one of the most important factors affecting the capability of the whole laser system. At the present time, there was obviously insufficient in test methods for the mirrors performance. The reflection coefficient, absorption coefficient and scattering coefficient of mirrors could be measured by a lot of test methods such as cavity ring-down method, photothermal deflection method, surface thermal lens method and laser calorimetry. But these methods could not test under high power density radiation. So the test data and results could not indicate the real performance in a real laser system exactly. Testing in a real laser system would be expensive and time consuming. Therefore, the test sequence and data would not be sufficient to analyze and realize the performance of mirrors. To examine the performance of mirrors under high power density radiation, the working principle of intra-cavity was introduced in this paper. Utilizing an output mirror with a low output coupling ratio, an intra-cavity could produce high-power density laser in the resonant cavity on the basis of a relatively small scale of gain medium, and the consumption and cost were very low relatively. Based on a discharge-drived CW DF chemical laser, an intra-cavity device was established. A laser beam of 3kw/cm 2 was achieved in the resonant cavity. Two pieces of 22.5 degree mirrors and two pieces of 45 degree mirrors could be tested simultaneously. Absorption coefficient and thermal distortion were measured by calorimetry and Hartmann wavefront sensor respectively. This device was simple, convenient, low-maintenance, and could work for a long time. The test results would provide support for process improvement of mirrors.

There is always a challenge on large aperture medium power laser’s resonator design, stable resonator would supports significant higher order transverse modes, folded and telescope stable resonator are too complex and not preferred by engineers, unstable resonator need rather large round trip gain to compensate its high geometric out-coupling, which is difficult for this kind of laser since its gain length is limited due to the power level and large aperture. Partial feedback unstable resonator had been proposed to tackle this difficulty since the early days of laser development, however, the debates of its effect never stopped even with those distinguished optical resonator scientists such as Siegman, Anan’ev, and Weber. Recently integrated partial feedback unstable resonator design had been successfully demonstrated on a medium size chemical oxygen iodine laser. In this paper, we carry this resonator configuration on a small scale discharge driven supersonic nozzle array Hydrogen Fluoride chemical laser, a typical large aperture short gain length device. With magnification equals 4/3, we successfully get ten Watts level ring beam output.

An effective single line continuous wave HF chemical laser operation has been demonstrated using a Littrow-mounted diffractive grating cavity experimentally. Selection of spectral lines of the laser was investigated when the grating used as a reflector and an output mirror respectively. The feedback factor of the cavity is demonstrated important parameter of line selection. Output power of single line from grating cavity is obviously stronger than the same line within the full spectrum of the laser that operated without line selection.

A numerical simulation is presented for investigating the effects of pressure ratio of D 2 injector to supersonic nozzle on the population inversion in the DF chemical laser cavity, while a lasing concurrently takes place. The chemical laser is generally used for the industrial process and manufacturing as well as the military weapon system, which requires high power characteristic of laser system rather than the others. The population inversion is absolutely needed to generate the laser beam and is non-equilibrium process. The laser beam is generated between the mirrors in the cavity and it is important to obtain stronger population inversion and more uniform distribution of the excited molecules in the laser cavity in order to produce high-power laser beam with good quality. In this study, these phenomena are investigated by means of analyzing the distributions of the DF excited molecules and the F atom used as an oxidant, while simultaneously estimating the maximum small signal and saturated gains and power in the DF chemical laser cavity. For the numerical solution, a fully conservative implicit method and a second order total variation diminishing (TVD) scheme are used with the finite-volume method (FVM). An 11-species (including DF molecules in various excited states of energies), 32-step chemistry model is adopted for the chemical reaction of the DF chemical laser system. The results are discussed by comparison with two D 2 injector pressure cases; 192 and 388.64 torr. Major results reveal that in the resonator, stronger population inversions occur in the all transitions except DF(1)-DF(0), when the D 2 injection pressure is lower. But, the higher D 2 injection pressure provides a favorable condition for DF(1)-DF(0) transition to generate the higher power laser beam. In other words, as the pressure of D 2 injector increases, the maximum small signal gain in the v 1 - 0 transition, which is in charge of generating most of laser power, becomes higher. Therefore, the total laser beam power becomes higher.

In the chemical laser system with a radial expansion nozzle array, the laser beam generation is achieved by mixing F atom from supersonic nozzle and molecule from holes of round-bended supply line. Based on that the fuel injection angle with main stream has a great influence of performance on supersonic combustor, the effects of injection angles with the main F flow on mixing enhancement are numerically investigated. The results are discussed by comparison with three cases of injection angles; , and with the main flow direction. Major results reveal that as the injection angle increases, the maximum small signal gains and the static pressure in the laser cavity become higher. Consequently, the injection angle between and is recommended as an optimized geometric parameter in consideration of both of high gains and low cavity pressure.

A mathematical model for optimising the beam formation direction in an active medium with three-dimensional periodic perturbations is developed. This model is applicable to the refractive-index distributions that can be represented in a multiplicative form with separated variables. The analysis of the actual structure of perturbations that appear behind the original nozzle assembly of a cw chemical laser has shown that the optimal direction of the beam formation lies in the region of partial self-compensation for distortions, which ensures an acceptable wave-front quality of the formed radiation.

The operation on the first overtone transition of the HF(ν) molecule is demonstrated for a cw chemical laser with a three-jet nozzle unit using a nozzle — nozzle — nozzle reagent mixing scheme. The energy, spatial, and spectral characteristics of the laser, as well as the efficiency of conversion of the chemical energy of the pump reaction to the overtone radiation are experimentally estimated. Lasing with an output power of ~1.1 kW and a conversion efficiency of 18 % is obtained in the 1.321 — 1.34 μm wavelength range. The extent of the lasing region is 5.3 cm, which is several times longer than in a laser employing a two-jet nozzle unit with a radial expansion in a nozzle — injector scheme.

Cavity mirrors of high power lasers are easily damaged by heat absorption of laser beam, so there is an urgent need to detect the absorption coefficient of the coating layers on them. High power combustion drived lasers, which operate with large size cavity mirrors, high gas consumption and short running time, cannot offer a convenient source of radiation for studies of absorption coefficient. Other kinds of lasers cannot achieve the high power density required easily. To solve this problem, in this paper, a small-scale and cost-effective laser source is described to detect the absorption coefficient under high power density with a Quasi-Closed Cavity. This laser source is rebuilt on the basis of a 1000W-class Direct Current (DC)-discharge drived continuous-wave (CW) HF/DF chemical laser. At first, the structure of the laser source is introduced. Then, some performance parameters are measured and the experiment results are analyzed. The laser operated with a (He+NF 3 )+D 2 gas mixture, and output of about 126W with a transmission of 3% was achieved through the experiment, corresponding to an electrical efficiency of about 3%. Power density on the surfaces of mirrors under test reached 3.74 kW/cm 2 . It satisfies the requirement of the Quasi-Closed Cavity test well. Experimental results show that this improved DC-discharge drived CW HF/DF chemical laser is applicable as the laser source to detect the absorption coefficient under high power density.

Lasing on HF upon optical pumping by emission of an open discharge, using NF3 and ClF5 as donors of fluorine atoms, was obtained for the first time in a chemical laser and the bleaching-wave mode was realised in a chemical HF laser. An open surface discharge was used as a pump source. The velocity of the bleaching wave, which was formed under its action, reached ~8 km s-1. The formation of this wave leads to a rapid (with an ultrasonic velocity) replacement of the working medium in the lasing region, which provides a quantum laser efficiency close to unity. The optimum compo-sition of the working mixture was found to be NF3:H2:Kr =6:10:125 Torr. For this composition, the output laser energy in a 3.2-μs pulse reached ~0.4 J and the specific output energy was 3.5 J litre-1. Approximately the same output characteristics of laser emission (0.35 J in a 3.5-μs pulse in the ClF5:H2:Kr=3:20:50 Torr mixture) were obtained in the system using ClF5 as donors of fluorine atoms.

Spatial-energy, spectral, and optical characteristics of kilowatt supersonic cw HF chemical lasers of self-contained type with three-jet nozzle arrays using nozzle-nozzle-injector and nozzle-nozzle-nozzle configurations were experimentally studied. It was shown that such nozzle arrays enable one to form an active medium as long as 12.5 cm with a high optical quality. In a laser with a wide-aperture stable cavity, a laser beam with a nearly square cross section 11 × 10 cm in size was formed.

The wave approximation is used to analyse the energy parameters and the spatiotemporal behaviour of the electromagnetic field in a pulsed chemical laser based on a photon-branched chain reaction in an unstable telescopic cavity with an input coupling aperture through which the reaction is initiated by IR radiation in a gaseous disperse medium composed of H2 , F2 , O2 , He, and Al particles. It is shown that diffractive multifocal focusing of a plane input wave, ensuring minimisation of the initially excited volume and a correspondingly strong reduction (down to microjoules) of the required input pulse energy, occurs in the range of small input aperture diameters d0 = (3 — 30)λ. A giant energy gain of ~3×109 can be reached as a result of this optical effect and also because of auto-wave propagation of a photon-branched chain reaction throughout the whole volume of the laser. This giant gain makes it possible to construct a self-contained laser with a kilojoule output energy, which can be initiated by microjoule input pulses.

The flow field of a supersonic flow chemical oxygen-iodine laser is simulated by solving the three-dimensional full Navier-Stokes equations, and the dependence of the mixing/reacting zone structure and the resulting gain region on the penetration depth of I 2 jet into the primary flow of singlet delta oxygen O 2 ( 1 Δ) is investigated. The effects of wall catalysis are discussed by introducing the surface catalytic efficiency into the wall boundary condition. It is shown that an optimum condition for the secondary I 2 jet momentum exists, and that the jet that causes a high gain penetrates the primary flow up to an intermediate depth and does not collide with the counter one. It is also shown that the molar fractions of I( 2 P 1/2 ) and O 2 ( 1 Δ) are reduced markedly on the fully catalytic wall. The deactivated oxygen molecules are engulfed by the vortices generated behind the I 2 jet, leading to the presence of a large amount of unconsumed I 2 , the reduced formation of I( 2 P 1/2 ) and a large negative gain region in the center of the vortices even far downstream of the nozzle blades. The present study demonstrates the importance of the choice of wall material.

The flow and optical fields of a supersonic flow chemical oxygen-iodine laser are simulated by solving the three -dimensional Navier-Stokes equations as well as the paraxial wave equation, and the laser power extraction characteristics are studied. The present results show that considerable flow nonuniformity remains in the optical resonator. Therefore, the effects of refraction caused by flow nonuniformity on the near-field and far- field patterns of radiative flux, and the laser power are evaluated using an actual nonuniform flow and an equivalent uniform flow. The mixing between O 2 ( 1 Δ) and I 2 in the present condition is fairly satisfactory from the viewpoint of power extraction characteristics. It is also shown that the present simulation overestimates the small signal gain coefficient and the output laser power to some extent. It is thought, however, that the calculation predicts the extremely complicated phenomenon in S COIL fairly well in spite of the many assumptions used in the present study.

High‐power chemical lasers operating in high repetitive rate show a decrease of the output energy laser beam. In such lasers, the characteristic time which depends on the laser output is short in comparison with those related to the flow. Consequently, shock waves, acoustic waves and thermal perturbations, induced by the strong electric energy deposition and remaining in the laser cavity between two pulses, may explain the decrease of output energy of the laser beam. For a better understanding of the flowfields, a numerical approach is carried out using flux corrected transport algorithms (FCT methods) associated with a Riemann solver on the computational domain boundaries. Under two‐dimensional assumptions, the inviscid flow in the convergent‐divergent laser cavity is computed to describe the creation and propagation of the wave system and the hot gas column in both single and multidischarge operating modes. Distortions of the contact surfaces are put into evidence through the study of flowfield instabilities. Finally, the limitations of the two‐dimensional modelization become apparent. The numerical resolution is extended to a 3D case in order to take into account the optical direction. This allows to study the influence of shock waves travelling between optics and being generated by a side effect developing at the electrodes. These waves have an effect of long duration on the flowfield and lead to a high residual perturbation level.

The flow field of a supersonic flow chemical oxygen-iodine laser is simulated by solving three-dimensional Navier-Stokes equations and the effects of the mixing/ reacting zone structure on the resulting gain region are studied. It is assumed that the flow is laminar and the water vapor condensation due to the supersonic cooling is ignored. A chemical kinetic model encompassing 21 chemical reactions and 10 chemical species is used to determine the chemical composition of the gas mixture. The present results demonstrate that a pair of contrarotating vortices generated behind the I 2 jet greatly enhances the mixing and the simultaneous chemical reaction to produce the excited iodine atom with the singlet oxygen. In the present calculation, the small signal gain coefficient is overestimated to some extent as compared with the experimental one. It is thought that the overestimation is caused by the imperfect chemical kinetic model as well as by ignoring the water vapor condensation and the boundary layers on the upper and lower wall in the present calculation.

By establishing the model of chemical laser cavity, the eigen mode of laser and the phase distribution of output beam have been simulated numerically, and the influence of inhomogeneous gain on phase characteristics of output beam has been discussed detailedly by analyzing the power spectral density of wavefront phase. The results show that the inhomogeneous gain of chemical laser gives rise to the phase distortion of output wavefront and the obvious increase of high-frequency phase in distortion wavefront; in addition, the degree of high-frequency phase distortion is influenced by the ratio of each component in gain mediums. Therefor, the key factor that resulting in the distortion of high-frequency phase is the inhomogeneous gain.

An extended slit nozzle source, whose dimensions exceed previous designs by more than an order of magnitude and which maintains its structural integrity at temperatures in excess of 1100 K, has been designed to create an extended path length zone for the study of the interaction‐reaction of corrosive reactants at high concentration. We facilitate the interaction of an increased number density of reactants when an expanding sodium flux (Nax≥1021/cm2 s) sheath formed from the slit nozzle is intersected by comparable halogen atom fluxes. The construction of the large scale dual oven systems necessary to carry out such experiments using both pure and seeded alkali expansions is outlined with emphasis on the fabrication of the extended slit nozzle source. The operation of this alkali source is considered as it creates a long path length high concentration cooperative environment which might be used to monitor exciplex formation, to develop a visible chemical laser oscillator, or to study the long range interac...

We consider an approach to phase conjugation (PhC) of multifrequency radiation of a cw HF chemical laser (HF-CCL) using Bragg scattering in a resonantly absorbing medium. The choice of working components of this medium, HBr and Xe, is analyzed at length. Numerical calculations are performed employing a mathematical model presented in this paper; the reflectivity is plotted as a function of the component concentration ratio, the intensities of waves determining the volume hologram in a WFI cell, and the angle of their convergence. We consider the problem of cooling the medium by mixture circulation. The calculations show that the approach suggested is a candidate for implementing the PhC of a high-power multifrequency HF-CCL.

An investigation was made of the operation of a chemical laser based on a photoinitiated chain reaction of fluorine with hydrogen (deuterium) in a master oscillator—amplifier configuration. The experiments showed that it was possible to achieve an energy efficiency of ~100% in the amplifier. Studies were made of the spectral characteristics of the system and the divergence of the radiation was determined. Equations describing quasi-cw operation of a monochromatic laser were found to be capable of providing satisfactory quantitative estimates of the energy characteristics of the radiation from this chemical laser operating as an amplifier or in the free-running mode. The estimates agreed with the experimental results when the initiation power was varied.

The transmission and scattering coefficients of the cavity mirrors were determined at the wavelengths λ = 1.3–1.4 μm typical of the radiation emitted by an overtone cw chemical HF laser. The results obtained were used to formulate the requirements in respect of the quality of the optics (the reflection and scattering coefficients) and to propose optical cavity configurations for lasers with the active medium 40 and 70 cm long. These formulations and proposals were verified experimentally. The experimental small-signal gain was used in a numerical analysis of the influence of the mirror characteristics on the output power and the emission efficiency of overtone lasers of the investigated type. The optimal reflection coefficients of the output mirrors were determined.

Experimental study of a pulsed, electric-discharge-initiated, SF/sub 6/+H/sub 2/ pumped HF chemical laser is presented. The reactants were premixed and the laser medium was preionized by means of a plasma cathode. The laser pulse energy, as a function of the discharge voltage, was measured for various laser medium parameters. It was concluded that the ratio between the width and height of the active volume is an important issue in the laser performance.

This chapter reviews the updated status and applications of a defensive weapon based on high power lasers, in the battlefield. The laser weapon is a novel concept which utilizes a high power laser beam to traverse the distance to an incoming object at the speed of light, and then destroy or disable it. Various types of solid-state and fiber lasers and configurations will be discussed in this review. For reference we include in this review also gas lasers and free-electron lasers since they play a major role in any present or future high power laser applications. Although the emphasis of this chapter is on solid-state lasers, it includes discussions on various configurations such as airborne lasers (ABL), diode pumped crystals and disk lasers as well as heat-capacity lasers. Recent applications of ultrafast solid-state lasers for non-lethal or low collateral damage applications will be presented.

A study is made of the feasibility of constructing a driver for laser thermonuclear fusion in which the second harmonic of an oxygen—iodine chemical laser is used to pump solid-state lasers (for example, Cr3+-activated crystals). In contrast to the existing systems, a separate master oscillator is proposed for each channel of the driver. The proposal has the advantages of relative technological simplicity, high degree of uniformity of target irradiation, and providing optimal profile of a heating pulse at 0.8, 0.4, and 0.27 μm.

HF chemical laser with master oscillator power amplifier (MOPA) configuration is a good solution to achieve high output power with high reliability and good beam quality. Researches of spectrum on HF chemical lasers with MOPA configuration are important for both enhancing atmospheric transmission and ensuring high power extraction efficiency on multiple vibrational transitions. A HF chemical laser operated in the line-selected mode which makes the output frequencies located in the atmospheric transparency windows will allow low atmospheric absorption, which will reduce thermal blooming effects and increase the intensity on the target. This will make the CW HF chemical lasers a possible development for long-distance transmission within the atmosphere. In this paper, a HF chemical laser with MOPA configuration using two identical discharge-driven CW HF laser modules as the laser oscillator and amplifier is presented. A multiple-selected-line, confocal, unstable resonator is also introduced. Measurements of spectrum on the laser have been taken by varying the flow parameters of the discharge-driven HF laser. It is concluded from our experiments that, the spectrum keeps stable with fixed flow parameters, even though the relative power of different lines varies slightly, and the maximum power is on the direct cascade of P 2 (7) and P 1 (8) lines. It is also believed that control of the flow parameters may allow high J direct cascade levels transitions, which may ensure high power extraction efficiency from multiple vibrational transitions.

Chemical laser is one of the most widely used high power infrared sources. Thermal deformation of mirrors in a resonator is a key factor which hinders the improvement of the beam quality in high power chemical lasers, and it has been a matter of the utmost concern in the design of high power chemical laser systems. Water-cooled technique is one of the most widely methods employed in cooling mirrors in high power laser systems. Several kinds of water-cooled mirrors have been studied by researchers in the world. Research teams of the United States and Russia have done a lot of work and their water cooled mirrors behave very well. In China, the study of micro-channel water cooled silicon mirror has been carried out by Cheng Zuhai in detail and the research of water jet cooled mirror has been performed by Li Bin. Both the two types of water cooled mirrors show excellent capabilities in alleviating the thermal deformation of mirrors. However, the issues that how and to what extent the beam quality is improved when the water cooled mirrors are involved have not been analyzed so far. In this paper, through numerical simulations, the beam qualities of linear resonators with various types of water cooled mirrors are analyzed in detail, and the effects of the two types of water cooled mirrors are compared. The thermal distortion of uncooled Si mirrors is characterized by Zernike polynomials and the beam quality is characterized with Strehl ratio, β factor, and M 2 factor, which degenerates as the beam oscillates in the distorted resonator. The aberrance of mirrors non-uniformly heated by high energy laser mainly distributes on the low-even-order Zernike polynomials. When the uncooled Si mirrors are replaced by water cooled mirrors, the distortion decreases greatly and the beam quality is improved a lot. Although the performance of the water jet cooled mirror on mitigating distortion is better than the micro-channel water cooled mirror, the resonator made up of two water jet cooled mirror is not the best structure in improving beam quality. The resonator composed of an uncooled reflecting mirror and a micro-channel water cooled reflecting mirror has the most prominent capability in improving the beam quality. The research method of beam quality and some results in this paper are useful for the design of resonators with water cooled mirrors and the evaluation of beam quality in high power chemical laser systems.

An amplifier performance model that predicts a device's amplifier performance given the device's oscillator performance as a function of reflectivity was developed. Excellent agreement between single pass model predictions and single pass experimental data was obtained. The model was used to predict amplifier performance as the gain length was scaled from 0.3 to 4 m for three different lasers. When the amplifier performance curve is plotted in terms of nondimensiona l powers font vs ftn, gain length dependent, device independent curves result. The nondimensional amplifier performance curve showed that, with a single pass amplifier, one 0.3-m oscillator may be able to drive three amplifiers and one 4-m oscillator might be able to drive eight amplifiers. These results, which are independent of device, are sensitive to the oscillator power vs reflectivity performance curve in the 0-20% reflectivity range.

The overtone lasing performance of the supersonic continuous wave hydrogen-fluoride chemical laser at the University of Illinois at Urbana-Champaign was optimized by the same set of flow rates that optimized the fundamental performance. When the absorption/scattering losses of the mirrors were taken into account, an overtone efficiency (the ratio of overtone power to maximum fundamental power for the same flow conditions) of 70-90% was achieved. The overtone efficiency was a strong function of medium saturation. There was no significant change in overtone power and efficiency as the mode volume increased. However, there was an increase in the number of lasing lines and a shift to higher rotational (J) lines. Overtone performance was as sensitive to cavitypressure as fundamental performance was

A new approach to the design of laser drivers for laser inertial fusion is proposed. A visible-range oxygen-iodine chemical laser would be used to pump solid state lasers.

For pt.I, see ibid., vol.29, no.3, p.933-43 (1993). Results are presented from an experimental/theoretical investigation of the frequency shifting and tuning behavior of a chemical oxygen-iodine laser in the presence of an applied magnetic field. Frequency shifting measurements are presented for both P and S polarization over a range of magnetic field strength from 0 to 3000 G, in a pressure regime (3 torr) where the line shape is Doppler broadened. Theoretical predictions of the location and magnitude of the frequency shifts are shown to be in good agreement with both the present measurements and a previous investigation in the pressure broadened regime. >

For pt.II, see ibid., vol.29, no.3, p.944-53 (1993). The results from a combined experimental/theoretical investigation of the influence of a magnetic field on the gain and polarization in a supersonic chemical oxygen laser are described. Theoretical calculations are presented for the normalized gain as a function of magnetic field strength and are shown to be in good agreement with the experimental data. Experimental results are given for the gain suppression for P and S polarization over the range 0-1000 G. Without polarizing elements internal to the laser cavity the degree of P polarization was measured for field strength from 0 to 200 G, and a qualitative explanation is offered for the observed behavior. >

Pulsed HF chemical lasers oscillating in the midinfrared region of the spectrum where water can strongly absorb are suitable for the organic tissue ablation. For such a medical application, a flexible energy delivery system using an optical fiber is indispensable. The fluoride glass optical fiber may be used for low‐loss optical energy delivery of the pulsed HF laser. Using an intracavity CO2 absorption cell, we have optimized pulsed multiline HF chemical laser spectrum for low‐loss energy delivery through a fluoride glass optical fiber whose transmission loss is theoretically estimated to be minimum around 2.5 μm. The fractional output energy of P1‐0(3) and P1‐0(4) lines, which are sitting in the lowest loss spectral region of the practical fluoride glass fiber, exceeded half the multiline output energy using a line selective intracavity CO2 gas cell. The P1‐0(4) line extracted from the resonator with a diffraction grating was successfully delivered through a 3‐m‐long commercial fluoride glass fiber (cor...

A modified Rigrod theory that uses a nonhomogeneous gain saturation law is used to model outcoupled, total, and intracavity power from a high-gain and a low-gain cw HF chemical laser with good accuracy. The homogeneous gain saturation law is found to have significant limitations when used to model total power data over a wide range of threshold gain values. The use of a nonhomogeneous gain saturation law indicates that a gain saturation law parameter of m = 1.2 models University of Illinois at Urbana–Champaign supersonic cw HF fundamental laser data more accurately than a homogeneous gain saturation law (m = 1). A completely inhomogeneous saturation law (m = 2) models University of Illinois at Urbana-Champaign supersonic HF overtone laser data more accurately than a completely homogeneous gain saturation law.