The Average Power Laser Experiment program has a goal of demonstrating a fully operational RF driven FEL by 1996. When commissioned, this laser will produce 10 micron radiation at power levels greater than 100 kW for at least three minutes. The device will operate in the single accelerator, master-oscillator, power amplifier mode, with the oscillator providing a seed laser of about 75 watts to drive the amplifier. A preliminary design of the APLE was reported elsewhere. In this paper we report further progress in the design definition.

A compact 20 MeV linac with an RF laser-driven electron gun will drive a high-gain (10 cm gain length), 10.6 micrometers wavelength FEL amplifier, operating in the SASE mode. FEL physics in the high-gain regime will be studied, including start-up from noise, optical guiding, sidebands, saturation, and superradiance, with emphasis on the effects important for future short wavelength operation of FEL's. The hybrid undulator, designed and built at the Kurchatov Institute of Atomic Energy in the U.S.S.R., has forty periods, each 1.5 cm long. The magnetic material is a hybrid combination of SmCo5 blocks and Nd-Fe-B blocks, with vanadium-permendur yokes. The gap distance between pole-tips is fixed at 5 mm. On axis the peak value of the completed undulator's magnetic field was measured to be 7.3 kGauss (+/- 0.25%). Measurements during the conditioning phase of the RF gun for the electron beam's peak dark-current show 6 mA without the longitudinal magnetic focusing field in the gun and 34 mA with the focusing field active. The peak current from photoemission is calculated to be 200 A.

New methods of copper excitation are currently being studied for use as a copper vapor laser. The most promising technique thus far is the use of pulsed and continuous wave (CW) microwaves in a resonant cavity to both vaporize and dissociate copper chloride. The microwave experiment combines CW microwaves at 2.45 GHz, the resonant frequency of the cavity, and pulsed microwaves using a hybrid junction. The combined signal is then introduced into an Asmussen resonant cavity. CW powers of approximately 100 watts both vaporize and dissociate copper chloride, producing neutral copper atoms. The pulsed microwaves of approximately 1,000 watts then further excite the copper atoms, increasing the light output of the discharge. Variations in the pulsed microwave frequency, as well as the pulse repetition frequency and pulse width, optimize the absorption of the pulsed microwaves by the discharge and are also used as a diagnostic of the discharge.

Lasing characteristics of an 80 mm-bore copper vapor laser (CVL) are investigated experimentally to increase the laser output power and efficiency. The experiment is carried out at a constant temperature of the CVL discharge tube. It is found that the laser output power increases proportionally to the discharge voltage across the plasma in the CVL discharge tube and that the discharge voltage is more important for the increase of laser output power than the population density of the metastable lower laser level. Higher discharge voltage is obtained with a buffer gas of neon and hydrogen mixture rather than with neon gas only. This suggests that hydrogen is effective to increase the recombination rate of the charged particles. A laser output power of 210 W is obtained with the mixed buffer gas by applying the excitation pulses of 5 kHz to 80 mm-bore discharge tube of 2.1 m discharge length.

The ground state and the lower laser level copper densities were measured in a large-bore copper vapor laser (CVL). The beam diameter was 80 mm, the discharge length 1500 mm, and the output power about 100 W at an operation of a repetition frequency 5 kHz. A new laser-absorption method has been developed to measure the copper ground state density. The measured copper density of the ground state was 1 to approximately 5 X 1021 m-3 and the radial profile was hollow. The profile can be explained from the radial gas temperature profile. The lower laser level (metastable state) densities were measured by the ordinary laser-absorption method. The density of the lower laser level for green emission was about 1 X 1018 m-3 and that for yellow emission was about 3 X 1017 m-3 at the center. The lower laser level densities were higher at the center than near the wall in contrast with the ground state density.

Using the newly developed 1 kHz closed-cycle TEA CO2 laser with the efficient CO2 regenerator including the Pt/Al2O3 solid catalyst, we experimentally determined the minimum operational performance of the CO2 regenerator which is required for the stable and long-life operation of the closed-cycle TEA CO2 laser. The operational performance of the CO2 regenerator was evaluated by the fractional conversion (eta) from CO to CO2, which is defined as the ratio of the differential CO2 concentration increased by the CO2 regenerator to the total CO concentration introduced into the CO2 regenerator. The minimum eta of 0.07 was at least required to keep the laser output power at 95 percent of the initial laser output for the laser gas mixture of CO2/N2/He = 15/15/70 (percent) and at an input energy density and a clearing ratio of 150 J/l and 6.0, respectively. When operating the CO2 regenerator at eta of 0.10, no appreciable reduction of the initial laser output of 570 W due to CO2 decomposition was observed up to 1.8 x 10 exp 7 shots (5 hrs). At this time, gas analysis showed that the CO and O2 concentration in the laser gas mixture was maintained about at 0.17 percent and 0.055 percent, respectively.

A high power CO2 laser using a new negative-branch unstable resonator (M equals -1.5) is proposed and investigated both theoretically and experimentally. The resonator consists of a stepwise variable reflecting output coupler termed phase-unifying output coupler and a total reflector. A 5 kW CW laser beam with diffraction limited quality (2(theta) equals 0.45 mrad) is obtained, not affected by the focal point in the resonator. The misalignment angle to reduce the laser power to 95% is improved by a factor of 19 compared with a positive-branch unstable resonator (M equals 1.5) with a phase-unifying output coupler at the same resonator length.

In this paper, a united energy model of the free-electron laser with different magnetic structures has been established to calculate the energy transfer rate of the free-electron laser under the condition of weak signal. This model is simple in its calculations and clear in physical meaning. It should be used to deal with problems such as harmonic radiation, parameter variations, etc.. The model is also suitable for three-dimensional problems.

In the present work, we studied theoretically and experimentally the dynamics of a double mode CO₂/SF₆-He laser with a phaseanysotropic Fabri-Perot cavity with varying mode interaction and absorber pressure. We have revealed the domains of quasiperiodic and stochastic pulsing of the laser intensity and pointed out the regularities of the transition from quasiperiodic to stochastic behavior.

The paper presents experimental results of operating an iodine laser with an SBS mirror. We have investigated generation dynamics, optical phase conjugation quality, and optimal conditions for achieving the high brightness of output radiation.

The performance of a repetitively pulsed, high energy, closed cycle photolytic atomic iodine lasers at 1.315 microns is presented. Using an I₂ removal system for the photolyzed C₃F₇I laser fuel, more than 70 joules/pulse was acquired in the fundamental mode from a M equals 3 confocal unstable resonator at a 0.5 Hz repetition rate. The closed cycle chemical scrubber system consisted of a condensative-evaporative section, two Cu wool I₂ reactor sections, and an internal turbo-blower. This closed cycle system provided C₂F₇I gas at 10 - 60 torr absent of I₂. The turbo-blower produced longitudinal flow velocities greater than 10 m/s through the 150 cm long by 7.5 X 7.5 cm² cross sectional photolytic iodine gain region. In addition to the high energy output, the resulting 10 - 12 microsecond(s) ec laser had a beam quality of less than 1.5 times diffraction limited with a coherence length greater than 45 meters, and a polarization extinction ratio better than 100:1. Projections from this pulsed photolytic atomic iodine laser technology to larger energies, high repetition rates, and variable pulsewidths are discussed. In addition, the performance of cw photolytically excited atomic iodine laser at 1.315 micrometers is reported which has excellent scaling potential. Volumetric extractable cw powers of 55 watts/liter are reported with a small signal gain coefficient of 2%/cm. The potential of enhancing the cw powers to kilowatt levels plus producing variable pulsewidth, repetition rate iodine laser using an internal electro-optical modulator are also discussed.

Bismuth fluoride, BiF, a possible energy acceptor molecule in a chemically-pumped donor- acceptor electronic transition laser has been produced in a flow tube reactor. A high voltage discharge was used to produce bismuth and fluorine atoms which combined to form ground state BiF(X). Laser induced fluorescence studies confirmed that BiF was formed following the discharge. A vibrational temperature of 581 +/- 35 K was measured.

Characterization of atmospheric turbulence and thermal blooming for high energy laser propagation has been conducted for the Scaled Atmospheric Blooming Experiment (SABLE) under controlled experimental conditions. To enhance thermal blooming with a high brightness, moderate power laser beam, a hydrogen fluoride (HF) chemical laser, producing six major lines, P1(7), P1(8), P1(9), P2(7), P2(8), and P2(9), was utilized. This paper summarizes design options and the design and operation of an X-folding scheme and the resulting quad-pass resonator (QPR), which produced a spectrum shift of 2 J-lines, a near-field irradiance distribution that was more uniform along the flow direction, had less line-to-line variation in near-field irradiance distribution, and produced twice the far-field power after atmospheric propagation, when compared to a more conventional double-pass resonator (DPR).

In this study geometric and physical optics analyses were used to examine an HF overtone/UR90 design (OTR90). The geometric analyses were primarily used to calculate the physical optics parameters and to understand the misalignment sensitivities of the resonator. The physical optics calculations then provided information regarding output power, phase and intensity distributions, and mode control. The physical parameters used in the optical analyses were based on a rectangular resonator designed around the NACL, two-bank gain generator and facility; a likely candidate for a near-term HF overtone experiment. Also, the gain model was anchored to the small-signal gain (SSG) and spectrum of this device. These analyses show that indeed high power within a good mode can be extracted using this resonator and that the impact of mirror misalignment is greatly reduced.

The SABLE experiment investigated the ability of phase-conjugate adaptive-optics to compensate strong thermal blooming and turbulence encountered during atmospheric propagation of a high-power laser beam. The experiments utilized a 10 kW hydrogen fluoride laser, selected because its spectrum is strongly absorbed by the atmosphere. Characteristics of the beam at both the transmitter and receiver, of the atmosphere along the propagation path, and of the adaptive optics were measured and recorded during the tests and used to test the accuracy of a time-dependent computer propagation code. Wind variations along the propagation path were shown to significantly improve system performance and to suppress the phase conjugate instability.

From the solution for the linear theory of thermal blooming, the propagator is a 2 X 2 matrix that satisfies an integral equation of Fredholm type. We develop a generalized Fredholm series solution to this integral equation. Since the Kernel is a matrix, the usual determinants in the Fredholm series contain ordering ambiguities. We resolve all ordering ambiguities using the standard diagrammatic representation of the series. The Fredholm denominator is computed for the case of uncompensated and compensated propagation in a uniform atmosphere with uniform wind. When the Fredholm denominator vanishes, the propagator contains poles. In the compensated case, the denominator does develop zeros. The single mode phase compensation instability gains computed from the zeros agrees with results obtained from other methods.

The discovery of phase compensation instabilities has made conjugate field compensation an important research topic of high energy laser atmospheric propagation. Mr. Karr presented a scheme to produce conjugate field using two deformable mirrors, and gave an algorithm for uniform intensity source. In this paper, for nonuniform intensity source we present an algorithm composed of a linearized algorithm and a perturbation approximation algorithm. The algorithm is demonstrated effective by simulations using a Gaussian beam source. The simulations show that the smooth surface of deformable mirror eliminates the local phase fluctuations on the first mirror, evidently improving the intensity pattern on the second mirror, and that for the Gaussian beam, the needed phase is easily constructed by deformable mirrors. The effect of the distance between the mirrors on the requirement for phase performance range is also discussed, with some suggestions to reduce the performance range requirement.

Using near-axis approximation and quadratic approximation of average intensity, we develop a general formula of AOA fluctuation variance applied to the whole region and an analytic expression of the variance for a special condition of spheric wave propagation. Calculations indicate that the variance is related to the fresnel length of the receiving field as well as turbulent intensity, propagating distance, and receiving aperture.

Phase correction using deformable mirrors is being applied to improve the performance of optical imaging and laser systems. Karr derived a small signal algorithm for amplitude (or intensity) correction from a linear approximation of Rytov's equation. The idea developed a new application of deformable mirrors. In this paper, we describe another amplitude correction theory based on the paraxial wave equation. The results show an improvement over Karr's in some respects. We think the amplitude correction may be used in high power propagation in the atmosphere and laser inertial confinement fusion in the future.

We consider the compensation for thermal distortions of laser beams propagated through the atmosphere on horizontal and vertical paths. It is found that the critical power of the source can be increased about ten times when going from horizontal to vertical paths. The efficiency of different adaptive correction algorithms--namely, program correction, phase-conjugate, and amplitude-phase control--are studied.

Compensation for light beam distortions in the atmosphere using the phase-conjugate mirror based on stimulated Brillouin scattering is investigated both experimentally and theoretically. Correction of beam distortions caused by turbulent medium, atmospheric aerosol, and thermal self-action is considered. It is shown that as the structural characteristic of fluctuations in turbulent medium permittivity and the length of the medium increase, the correction accuracy parameter decreases. This parameter reduction follows the decrease in typical thermal self- action length of repetitive pulse radiation in the moving atmosphere. The correction accuracy parameter value decreases down to 0.5 only, as the optical depth of aerosol medium increases up to 3.0.

NASA's current research activities to evaluate laser power beaming systems are summarized with regard to their applications of greatest interest. Key technical certainties and uncertainties pertaining to laser power beaming systems appropriate for space applications are quantified. A path of development is presented that includes maturation of key technology components for reliable laser and millimeter wave power beaming systems during the 1990s.

The major technology options for high-energy FELs and adaptive optics available to the Space Laser Energy (SELENE) program are reviewed. Initial system evaluations of these options are described. A feasibility assessment of laser power beaming is given.

We examine the requirements placed on an adaptive-optics system used to compensate atmospheric effects in propagating high-power lasers from ground to space. The particular application involves energy transfer from a ground station to a satellite. Our analysis explores performance associated with various beacon configurations, including satellite-based beacons, beacons in the lead-ahead direction, and synthetic beacons. Other system parameters are adjusted as well, including number of actuators in the deformable mirror and bandwidth of the servo system. We show that with an optimized system design it is possible to achieve collection efficiencies of 10-50 percent over zenith angles as great as 70 deg.

Technical and architectural issues facing a laser power beaming system are discussed. Issues regarding the laser device, optics, beam control, propagation, and lunar site are examined. Environmental and health physics aspects are considered.

The anthropogenic emission of CFCs into the atmosphere over the past few decades has led to a reduction in the concentration of ozone in the stratosphere. Serious environmental damage may result. Even if the emission is stopped as proposed, the long lifetimes of the CFCs in the atmosphere will result in a deleterious loss of ozone for up to a century. A means for removing these in a shorter time is explored. The method used is induced dissociation by lasers of the CFCs in the troposphere, which prevents them from reaching the stratosphere.

The modern state and perspectives of development of high power multibeam CO₂ lasers are described. The problems of phase locking of laser arrays and main lobe energy maintenance increase are discussed also.

A comparative investigation of the amplitude stability of the power output from sealed-off CO and CO₂ lasers emitting the fundamental spatial mode has been made. It is shown that the use of a CW molecular CO laser emitting simultaneously due to a great number of cascade- coupled vibration-rotational transitions as the coherent radiation source makes it possible to achieve relatively high stability of the output power under conditions of emission of a single main mode without frequency-control facilities.

Optical components which highly reflect the hydrogen fluoride (HF) overtone wavelengths (near 1.3 micrometers ) and transmit or absorb the HF fundamental wavelengths (2.6 to 3.1 micrometers ) can be used to obtain high intensity 1.3 micrometers radiation with HF chemical laser technology. Initial efforts in overtone laser development centered around absorbing the fundamental wavelengths. More recently, coatings have been developed which transmit the fundamental through a silicon substrate. This paper describes the deposition of a series of such coatings made by the Plasma Plating deposition process. Also presented are the improved optical performance results for the coatings. Plasma Plating uses a low voltage, high current ion gun to produce a plasma in which the depositing species are highly ionized. The self- potential sheath around the substrate accelerates the ionized coating species into the substrate, producing dense, low-absorption coatings which have demonstrated a high laser damage threshold.

The results of research and development projects on XeCl lasers at the Institute of High Current Electronics (Tomsk) are presented. In terms of radiation energy, XeCl lasers compare unfavorably with KrF lasers. However, XeCl lasers have an advantage in that their active medium is less corrosive, so they are more useful in laboratory conditions.

Results are presented of studies into possible improvement of the efficiency of sealed-off CO water-cooled lasers due to reduction of the total optical cavity losses. The experimentally achieved laser efficiency amounted to 18 - 20%, the output power being about 32 W. The maximum laser power was as high as 38.5 W. An effect has been studied of the temperature of the discharge tube walls on the efficiency and power per unit length. With the change in temperature from 40 to 1 degree(s)C, the laser emitter efficiency increased from 8.5 to 18% and the power per unit length rose from 13 to 31 W/m. The feasibility of further improvement in the efficiency of the sealed-off CO-lasers is briefly discussed.

The generation of O₂(¹(Delta) _g) using the chlorine--basic hydrogen peroxide reaction is the heart of the chemical oxygen iodine laser. When O₂(¹(Delta) _g) is generated, almost two-thirds of the exothermicity of the reaction is dissipated as heat within the liquid solution. The impact of this heat release on the generation and transport of O₂(¹(Delta) _g) is the subject of this study.

A model for the loaded gain of a flowing chemical oxygen-iodine laser is described. The model, a generalization of that of Zagidullin et al., includes pumping of the upper laser level by O₂(¹(Delta) ), deactivation by water and energy pooling with O₂(¹(Delta) ). stimulated emission, and hyperfine and velocity cross-relaxation of the iodine atoms. The dependence of the optical saturation of the medium on Doppler- and collision-broadening, pumping, quenching, and hyperfine and velocity cross-relaxation is discussed. A simple, single-mode optical extraction model, in which the average flux loading the medium is assumed constant and the mode-averaged loaded gain is saturated to the threshold gain of the resonator, is described. This extraction model, together with the gain model, is used to parametrically examine the dependence and efficiency of optical extraction upon COIL medium conditions. The sensitivity of the loaded gain and extraction efficiency to the uncertainty in the magnitude of the velocity cross-relaxation rates is examined and the implications when interpretating experimental data and scaling from low to high power operation are briefly discussed.

The copper vapor laser (CVL) can be a very suitable tool for cutting and drilling with minimum roughness and maximum accuracy. Visible range of irradiation, perfect quality of output beam, high pulse power, and pulse repetition frequency favor this application. However, there is no data on productivity of cutting, which defines the economic benefit of using CVL technology. In the present paper, the cutting productivity is estimated on the basis of efficiency of material removal from the processing zone: the ratio of evaporated mass (multiplied by vaporization heat) to laser energy within the processing time. Aluminum specimens with 0.02 (mu) thickness (thin film) and 100 (mu) thickness (foil) are cut with different output power and cutting velocity. Use of specimens with these thicknesses allows the observation of two phenomena which define the cutting efficiency. One of them, evaporation from the free surface, is typical for thin (a few micron or less) materials. The second one, vapor flying and condensation, can only reduce initial efficiency when material thickness becomes more than cutwidth.

A solid-state excitation circuit is demonstrated without any compression circuits. The new circuit contains the dc pre-charging capacitors and pulsed charging capacitors. The applied voltage between the electrode is the sum of the pre-charging voltage and the pulsed charging voltage. Therefore, the switching voltage is lowered when increasing the pre-charging voltage. In TEA-CO₂ laser device, the stable discharge is excited by using only one thyristor device. In this circuit, the breakdown voltage is lower and output efficiency is higher than that obtained in the ordinary charge-transfer circuit. The high-repetition rate operation is tested up to 1 kpps. This circuit is also available for the excitation of KrF excimer laser.