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A genetic algorithm technique was implemented to determine a set of unknown parameters that best matched the Blaze II chemical laser model predictions with experimental data. This is the first known application of the genetic algorithm technique for modeling lasers, chemically reacting flows, and chemical lasers. Overall, the genetic algorithm technique worked exceptionally well for this chemical laser modeling problem in a cost effective and time efficient manner. Blaze II was baselined to existing chemical oxygen-iodine laser data taken with the research assessment and device improvement chemical laser device with very good agreement. Mixing calculations for the research assessment and device improvement chemical laser nozzle indicate that higher iodine flow rates are necessary to maintain a significant fraction of the nominal performance as the total pressure is increased by the addition of helium ; this agrees with research assessment and device improvement chemical laser experimental data. It may be possible to implement this genetic algorithm technique to optimize the performance of any chemical laser as a function of any of the flow rates, mirror location, mirror size, nozzle configuration, injector sizes, and other factors. This modeling procedure can be used as a method to guide experiments to improve chemical laser performance.

2Broadwell, J. E., “Effect of Mixing Rate on HF Chemical Laser Performance,” Applied Optics, Vol. 13, No. 4, 1974, pp. 962–967. 3Mirels, H., Ho and, R., and King, W. S., “SimpliŽ ed Model of Continuous-WaveDiffusion-Type Chemical Laser,” AIAA Journal, Vol. 11, No. 2, 1973, pp. 156–164. 4Gross, R. F. W., and Bott, J. F. (eds.), Handbook of Chemical Lasers, Wiley, New York, 1976. 5Driscoll, R. J., “Effect ofReactant-Surface StretchingonChemical Laser Performance,” AIAA Journal, Vol. 22, No. 1, 1984, pp. 65–74. 6Acebal, R., “Hydrogen Fluoride vs Deuterium Fluoride Space-Based Laser Performance Comparison,” AIAA Journal, Vol. 36, No. 3, 1998, pp. 416–419. 7Rose, P.H., “AdvancedLaser TechnologyDevelopment in ShockTubes,” Shock Tube and Shock Wave Research, edited by B. Ahlborn, A. Hertzberg, and D. Russell, Univ. ofWashington Press, Seattle, WA, 1978, pp. 508–518. 8Bott, J. F., and Cohen, N., “A Shock Tube Study of the Reaction of Methyl Radicals with Hydroxyl Radicals,” International Journal of Chemical Kinetics,” Vol. 23, No. 11, 1991, pp. 1017–1033.

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

Performance data for a continuous-wave hydrogen fluoride (cw HF) chemical laser master oscillator/power amplifier showed that, regardless of the oscillator or resonator used to generate the input beam, the amplification ratio is an inverse function of the input power (intensity) and, for maximum amplification, the peak of the input intensity distribution must be matched to the peak of the zero power gain distribution in the amplifier. The matc/mismatch of the oscillator/amplifier flowfields has a second-order effect on amplifier performance

The Hydrogen Fluoride Overtone Chemical Laser Technology Program has exploited the technology base developed over the last two decades For hydrogen fluoride lasers and successfully demonstrated a short wavelength chemical laser. This technology development centers on overtone lasing of the hydrogen fluoride molecule to produce laser radiation at 1.33 μm rather than the conventional fundamental lasing at 2.8 μm. The overtone wavelength can lead to significant improvements in brightness potential as well as atmospheric propagation properties

A method is presented for passively containing reacting gas within the cavity of a chemical laser using a combination of cavity wall displacement and jet curtains. Suggesting several advantages over the matched pressure approach, the concept was evaluated in an application to a DF laser using the hydraulic analogy. Analyses were made to determine the flow characteristics of the confined and unconfined laser gas, the jet curtain requirements, and basic information for the design of the test hardware (water table). Experiments were conducted on the water table with the jet nozzle size, jet exit Froude number, and wall displacement as the variables. The results of these experiments qualitatively demonstrated the feasibility of the containment concept and demonstrated that for a given nozzle size, the ideal wall displacement is that which requires the minimum jet Froude number for containment. N a chemical laser, the power is extracted from the cavity in a transverse direction to the gas flow. This means that the optical system requires apertures in the cavity walls and that these be located downstream of the entrance to the cavity and sized to approximately span the iasing zone. The heat release within the Iasing zone will generate a static pressure rise which, when combined with the aspirating effect of the flow across the apertures, will result in a transverse pressure gradient and a lateral expansion of the laser gas. Some of this gas will enter the tunnels leading to the mirror cavities and may reach and contaminate the mirror surfaces unless measures are taken to prevent it. Reference 1 describes a method of preventing the laser gas from entering the tunnel by injecting a noncontaminating gas into the mirror cavity and thereby increasing the flow static pressure there to a point where it matches the laser gas static pressure at the aperture. This is referred to as "matched pressure'* injection. This paper discusses a recently completed study of a more passive method of gas containment in which an aerodynamic barrier is used much in the same manner as described in Ref. 2. In this concept, the gas is permitted to expand freely in the lateral direction, and its capture is achieved by a lateral displacement of the cavity sidewalls. In addition, a constant Mach number inert gas jet located at each aperture and flowing across it in the direction of the laser gas serves as a barrier or curtain to prevent the latter's entrance into the mirror cavities. When wall displacement is sufficient to capture the laser gas plus a major portion of the flow from the jets, while diverting the remainder into the mirror cavity, then this containment concept exhibits the following desirable features: 1) Capturing the expanded gas rather than forcibly con- taining the unexpanded gas eliminates the introduction of shock disturbances in the Iasing zone. 2) The placement of the coflowing jet adjacent to the laser gas when coupled with an adequate wall displacement will prevent the formation of a large zone of recirculating laser gas at the tunnel entrance as a result of the latter's partial en- trance into the tunnel. Such a recirculation can bring harmful deactivants back to the start of the Iasing zone. 3) The coflowing nature of the jet minimizes its distur- bance impact upon the laser gas compared with jets used to replenish the mirror cavities for matched pressure injection.

This paper presents a means by which the chemical laser device weight can be minimized with respect to its performance and the device power minimized with respect to the target range. Chemical laser performance parameters such as the specific power and nozzle power flux are then used in conjunction with weight and propagation models to determine system effectiveness. A measure of merit is given by which systems can be contrasted. An illustrative example is included in which DF and Iodine laser systems are compared for an airborne scenario. 14 references.

The analytical and experimental studies aimed at developing an acoustic attenuator for a high-energy pulsed chemical laser are described. A numerical finite-difference code was developed to analyze the attenuation of strong pressure waves (shocks) in ducts. The attenuation concepts analyzed include variable flow area, vented walls, porous flow-through absorbers, and combinations of these. Experimental results were obtained for a vented duct attenuator on a shock tube. The code was used to design the acoustic attenuator of a 50-pulse/s D2 /F2 laser module. Code predictions for the laser device were compared with experimental data.

The temperature of a SF6-He gas mixture in the plenum of a supersonic diffusion laser was measured by observing spectra of the HF(v) molecules when trace amounts of H2 were injected into the hot plenum gas. Because the plenum pressures were relatively high and the mean free path very short, rotational equilibrium was expected to be obtained. Thus, the rotational temperature obtained from the observed spectra was expected to equal the gas translational temperature. Precision of the temperature was + or - 10% largely because of the limited precision involved in the measurement of the slope of the intensity data. The observed values are about 10 to 36% higher than temperatures obtained from a pressure ratio method. This difference is probably because of the wall heat loss that occurs between plenum and throat, which was not taken into account in the pressure ratio method.

This study investigates choking in the optical cavity of a CW HF or DF chemically-pumped laser. Choking can occur because of the large heat release when the flow in the cavity is constrained by plume shrouds. An analysis procedure is described that starts in the oxidizer and fuel plenums, follows both gases through the nozzles where the flow is viscous, and into a constant area laser cavity where mixing and heat addition occur. A parametric investigation is performed that centers around a He diluent case and an N/sub 2/ diluent case. The parameters that are varied include plenum conditions, composition, nozzle geometry, etc. The most important results are (1) a He diluent flow is more likely to choke than one with N/sub 2/, (2) the oxidizer stagnation temperature and oxidizer diluent ratio are the dominant choking parameters, (3) shifting diluent from the oxidizer to the fuel flow can lead to choking, (4) nozzle geometry has a minor effect on choking, and (5) Reynolds number scaling for choking is demonstrated.

The simplified two-vibrational-level model of a cw diffusion-type chemical laser presented by Mirels, Holfland, and King is extended to include multiple vibrational levels. Both laminar and turbulent diffusion are considered. Expressions for axial gain distribution and net output power from a Fabry-Perot optical resonator are deduced. For a given lasing species, the resulting cw chemical laser scaling laws are the same as those previously deduced by Mirels, Hofland, and King, except for the dependence of certain coefficients on rotational quantum number J and temperature T. Broadwell previously presented a multiple-vibrational-level model for a cw chemical laser that was limited, however, to turbulent diffusion. The flame-sheet-mixing model used in the present study is shown to give results that are identical with those from the scheduled-mixing model of Broadwell when mean chemical rates are used.

Knowledge of local fluid dynamic properties in the flowfield of a continuous supersonic diffusion HF chemical laser is required to characterize its performance. The application of techniques for measuring local pressure and pitot pressure is described with modifications required for the hostile fluorine environment. Spectroscopic measurements of static temperature and relative concentration of HF(1) and HF(2) in the reacting fluorine-hydrogen flow then permit the deduction of crucial local flow properties in the laser medium, such as the mass density. In this report, measurements of the distribution of pitot and static pressure, static temperature, mass density, Mach number, and jet velocity are presented and the limitations in the measurements discussed. The measured concentration ratio [HF(2)]/[HF(1>] reflects the nature of the gain zone.

The multiline performance of a cw HF chemical laser was measured as a function of the SF6 and H2 flow rates, cavity losses, pressure and resonator type. The first data from a cw laser for a near-resonant energy transfer from v = 3, /=3,4 to v = 2, /=14 with a subsequent rotational cascade to v = 2, /=11 were obtained. The stable resonator data indicated that the polarization introduced by the Brewster windows affects the power spectral distribution. The amplitude, frequency, and Fresnel number dependence of the time-dependent oscillations which were predicted to occur on lines whose saturated gain does not fill the unstable resonator were measured. The data showed that the oscillations do not occur for Fresnel numbers below 1.5 and that their amplitudes increase as the fraction of the resonator filled by the oscillating lines decreased. The a priori prediction of these characteristics of the time-dependent oscillations by the MNORO3UR computer model was in agreement with the data.

A phenomenological model for reactant mixing in trip nozzle chemical lasers by means of a surface-stretching mechanism is used in conjunction with a two-level laser model to derive scaling laws for numerous features noted in the trip nozzle data. This mixing model is then employed with an aerokinetics code in order to obtain quantitative laser gain predictions. The results yielded by the code are in good agreement with small-signal data. It is determined that trip jet mixing will not increase laser efficiency at low cavity pressures, but will at high cavity pressures result in a doubling of laser power output. 12 references.

A cold flow laser Doppler velocimeter study was performed in the mixing region of supersonic mixing nozzles that employed gas-trips for enhanced mixing; the nozzles were operated with room-temperature nitrogen under simulated laser flow conditions. A determination was made of three mean and turbulent velocity components, in addition to two turbulent shear stress elements, under both trip-on and trip-off operation. To preclude velocity biasing, the primary, secondary, and trip streams were simultaneously seeded with 0.357-/*m-diam latex spheres. The objectives of this activity were to acquire basic cold flow information on trip nozzles in order to help develop some insight into the tripped mixing phenomenon and to acquire information that could be correlated with sophisticated computer models of the mixing process. The velocimeter results appear to support ob- servations that were made earlier during a related laser-induced fluorescence visualization study. N many combustion devices (e.g., chemical rocket and jet engines, lasers) unmixed reactants are independently fed via adjacent mixing nozzles into a reaction chamber, where mixing and chemical reactions occur. It has been found that the mixing phenomenon has a significant effect on the per- formance of the device. Gas-trips have recently been installed in various mixing nozzles in an attempt to enhance mixing and thereby improve device efficiency. With this approach, gas is injected through small orifices that are located in the nozzles near the exit plane in an attempt to "trip" the flow; that is, as one theory goes, trigger premature transition from laminar flow. The use of gas-trips in the cavity mixing nozzles of chemical lasers has resulted in more than a doubling of the laser power. Infrared radiometer scans of the mixing region have verified that the power increase was due to enhanced reactant mixing. * While a number of theories have been proposed to explain this enhanced mixing, evaluation of these theories has been frustrated by a lack of extensive experimental in- formation. Because of this, a cold flow experimental project was initiated on chemical laser nozzles that employ gas-trips. The primary objective of this activity was to acquire basic gasdynamic information on supersonic trip nozzles, under simulated laser flow conditions, to help develop some insight into the trip-enhanced mixing phenomenon. Earlier in this program, testing was conducted on four different supersonic slit nozzle arrays that utilized gas-trips. Included were extensive pitot probing and flow visualization studies using laser-induced fluorescence of selectivity seeded iodine vapor.2 In this phase of the program, the mixing region of a BCL- 10 trip nozzle array was probed with a laser Doppler velocimeter (LDV). In addition to satisfying the primary program objective, a secondary goal of the LDV phase was to acquire information that could be correlated with sophisticated computer models of the mixing process.3'5 Hence, measurements were made of three mean and turbulent velocity components, as well as two turbulent shear stress elements, under both trip-on and trip-off cold flow operation. A considerable amount of gasdynamic research has been

A third generation of supersonic diffusion chemical laser analysis is introduced, namely, the complete solution of the Navier-Stokes equations for the supersonic mixing flowfield, fully coupled with chemical kinetics for both the hot and cold reactions for HF. Results are obtained for laminar-flow conditions and show that such Navier-Stokes solutions are feasible for studying specific cases of interest. A comparison is made between cold flows (chemical kinetics switched off) and hot flows (with fully coupled chemical kinetics). The results show that temperature distributions are affected the most and velocity distributions the least by chemical energy heat release. The results have impact on the interpretation of cold-flow aerodynamic experiments in the laboratory, and their proper extrapolation to the real chemical-laser flows. Also, comparisons between the present Navier-Stokes results and other, more approximate, existing calculations, are made. Advantages of the Navier-Stokes solutions are delineated.

Nonreacting and reacting flow visualization experiments were used to demonstrate the ability of a new supersonic nozzle design (called the ramp nozzle) to accelerate mixing in a deuterium floride chemical laser via the reactant surface stretching mechanism. Unlike trip nozzles, which use inert gas injection to cause reactant surface stretching, the ramp nozzle causes a similar effect through its geometry without gas injection. The results from laser-induced fluorescence experiments indicate the ramp nozzle design produces a factor of two increase in the reactant interface length within about a centimeter of the nozzle exit. A side-by-side comparison in reacting flow of the ramp and gas trip nozzles suggest that both designs produce similar levels of mixing enhancement. These data are used to develop a phenomenological model for mixing enhancement in gas trip and ramp nozzles. This model describes a possible mechanism by which trip jets cause reactant surface stretching, indicates how the surface stretching rates can be calculated from the reactant nozzle geometry and flow conditions, and permits performance scaling laws consistent with the trip nozzle data to be derived. 13 references.

The essential fluid dynamic and kinetic phenomena required for a quantitative, computationally efficient, rotational nonequilibrium model of a cw HF chemical laser are identified. It is shown that, in addition to the pumping, collisional deactivation, and rotational relaxation reactions, F-atom wall recombination, the hot pumping reaction, and multiquantum deactivation reactions play a significant role in determining laser performance. Several problems with the HF kinetics package are identified. The effect of various parameters on run time is discussed.

A laser-induced iodine fluorescence visualization technique has been refined and used extensively to study supersonic cold-flow mixing. In particular, visualization studies were performed in the mixing region between supersonic slit nozzles that employed gas trips for enhanced mixing. The nozzles were operated with roomtemperature helium under simulated chemical laser flow conditions. The primary objective was to develop insight into the trip-enhanced mixing phenomenon. Three-dimensional information was therefore acquired on the size, shape, location, structure, and interaction of the primary, secondary, and trip jets under both trip-on and trip-off operation. This has led to postulations on the existence of three trip-induced convective mechanisms that appear to contribute to enhanced mixing. The active mechanisms, as well as the dominant mechanism, appear to depend upon: the type of trip configuration used, the nozzle width, and the flow field location since one mechanism appears to dominate in the primary nozzles and another in the secondary nozzles.

An analytical model for predicting optical performance of a cw chemical laser has been developed. The model is constructed in which mixing, kinetics, and stimulated emission are coupled with a half-symmetric-unstable resonator with intercavity axicon (HSURIA). The formulation has been tested by anchoring to experimental small signal gain and closed-cavity power. The mixing parameters established from the data anchoring are used to examine the role of the resonator magnification, medium gain length, lasing line selection, optical axis location, and mode width in predicting laser performance. The dependence of laser performance trends on resonator parameters is predicted by the numerical results of the present study. Other resonator parameters affecting the power extraction have also been identified.

The development of a thermochemical technique for generating large quantities of carbon monosulfide (CS) is reported. The CS is produced from the thermal dissociation of carbon disulfide (CS/sub 2/) in a cyanogen-oxygen-CS/sub 2/ combustor operating at 1 atm and temperatures in excess of 2500 K. The CS is extracted from the combustor through a Mach 4 supersonic nozzle. The supersonic flow stream was sampled and then analyzed with a quadrupole mass spectrometer, and the data were compared with the results of an equilibrium calculation. Ratios for CS/CS/sub 2/ greater than two were measured. Such ratios are sufficient to fuel a CO chemical laser directly with CS.

A one-dimensiona l flow model of the chemical laser, from combustor to subsonic diffuser, is developed for the study of laser pressure recovery. Combustor and flow chemistry effects, nozzle and cavity boundary-layer losses, laser cavity combustion, and nozzle, cavity, and diffuser geometry influences are included in the analysis. The results from experimental tests on a laser nozzle array with a constant area diffuser are presented. Diffuser exit pressures as high as 263 Torr were measured during these experiments. The one-dimensional flow model is shown to be in agreement with the measured diffuser exit pressures over the full range of test conditions.

The supersonic free jets of an arc-driven 10-kW cw HF chemical laser were studied for fixed-flow conditions with and without lasing. A spatially, spectrally, rapidly scanning spectrograph and a spatially scanning stagnation and static pressure probe were used in the diagnosis. The average static temperature and average HF(3) populations were deduced for a very large number of positions in the flow. Salient results include the capability of evaluating the uniformity of reaction in the jet, especially along the cavity axis near the nozzle exit plane, and a qualitative evaluation of the degree of consumption of lasant reactant in the cavity region. A significant local cooling effect resulting from power extraction was observed. Spatial scans of stagnation and static pressures were made for the zero-power case, and Mach numbers and local mass densities were deduced.

This paper discusses the adaptation of the detailed fluorine wall-recombination model into the fluid-dynamic equations governing the flow of dilute atomic fluorine in a tiny generic-type nozzle reminiscent to those found in HF (and DF) lasers. The wall-recombination model is briefly described, as are the fluid-dynamic equations making up the computational framework within which this study was made. Results are given for a range of nozzle wall temperatures form 450 to 650 K. These results are compared to those obtained when a noncatalytic wall and a fully catalytic wall are assumed.

High-pressure DF chemical lasers use gas trip jets to increase the laser cavity reactant mixing rate. The trip jets can improve the laser efficiency by about 100% when compared to the laminar mixing value. It is postulated that the trip jets create a secondary flow which increases the mixing rate by stretching the contact surface between the reactant streams. The surface stretching rate can be described in terms of a strain rate s0. A qualitative explanation for the performance characteristics of trip-nozzle lasers is provided herein by developing flow and laser models which can define the effect of strain on the reactant burning rate and laser efficiency. Strain affects laser performance via a single parameter 7 = 2s0/kc, where kc is a characteristic collisional deactivation rate for the lasing specie. Strain levels of 7 = 2-3 appear to be consistent with trip nozzle data. The model also indicates the efficiency of low-pressure laminar mixing (7 = 0) lasers could be increased significantly for strain rate levels in the 7 = 3-5 range. Nomenclature BJ,B2,B3 = constants, B1=(p2/p1)B2\ B3 defined by Eq. (19) Cj,C2,C3 = constants in gain equation, see Eq. (10) Dj,D2,D3 = constants, Dl =KI/K3,D2 =K2/K3 D = molecular dif fusivity fiJ2 ~ functions in amplifier solution, Eq. (22)

This paper deals with 2-D flow and acoustic analysis in a pulsed laser system. The analysis method utilizes numerical solutions of the 2-D Euler/Navier-Stokes equations in the laser flow channel and 1-D Euler equations in the sidewall muffler volume with closely spaced baffles. Several comparative studies with experiments have been performed to establish the validity of the approach. Idealized laser related problems have been computed to demonstrate the influence of sidewall muffler parameters on the transverse wave decay process in a laser cavity. An assessment of viscous effects on the cavity flow and acoustic clearing is also presented. 18 references.

Diagnostic experiments were conducted on a DF chemical laser to obtain data on the reaction zone structure for laminar mixing and when the mixing has been augmented by gas jet injection at the reactant interface. DF and HF emission from the reaction zones was recorded using infrared sensitive film and an IR scanner with an InSb detector; DF small-signal gain experiments were also conducted. The IR scanner and gain measurements were used to verify the photographic data which showed a decrease in the axial mixing length from 5 cm to 0.51.0 cm in going from the laminar to the augmented mixing mode.

The primary objective of the study was to determine the effect of the optical resonator magnification and centerline location on the near-field output power from a cw chemical laser. Geometric optics are used. The flowing gain medium is assumed to be adjacent to one of the resonator mirrors. Analytic solutions are obtained in the limits M $Yields$ 1 and M much greater than 1, where M is cavity magnification. Effects of resonator and laser medium parameters on laser output power are then discussed. Turbulent and laminar diffusion is considered. (TFD)

11 Moore, C. B., "Vibration-Rotation Energy Transfer," Journal of Chemical Physics, Vol. 43, No. 9, Nov. 1965, p. 2979. 12 Shin, H. K., "Deexcitation of Molecular Vibration on Collisions: Vibration-tp-Rotation Energy "transfer in Hydrogen Halides," Journal of Physical Chemistry, Vol. 75, No. 8, Aug. 1971, p. 1079. 12 Shin, H. K., "Vibration-Rotation-Translation Energy Transfer in HF-HF and DF-DF," Chemical Physics Letters, Vol. 10, No. 1, July 1971, p. 81; "Erratum", Vol. 11, No. 5, Nov. 1971, p. 628. 14 Schafer, T. P., Siska, P. E., Parson, J. M., Tully, F. P., Wong, Y. C., and Lee, Y. T., "Crossed Molecular Beam Study of F 4D2," Journal of Chemical Physics, Vol. 53, No. 8, Oct. 1970, p. 3385. 15 Parker, J. H. and Pimentel, G. J., "Vibrational Energy Distribution Through Chemical Laser Studies: I. Flourine Atoms Plus Hydrogen or Methane," Journal of Chemical Physics, Vol. 51, No. 1, July 1969, p. 91. 16 Stephens, R. R., and Cool, T. A., "Vibrational Energy Transfer and De-excitation in the HF, DF, HF-CO2, and DF-CO2 Systems," Journal of Chemical Physics. 17 Wilkins, R. L., "Monte Carlo Calculations of Reaction Rates, II. H + HF(u) = H2(t/) + F and H+FH(i?) = HF(i/) + H," Journal of Chemical Physics. 18 Mercer, P. D. and Pritchard, H. Q., "The Gas Phase Fluorination of Hydrogen Methane Mixtures," Journal of Physical Chemistry, * Vol. 63, No. 9, Sept. 1959, p. 1468. 19 Rapp, D. and Englander-Golden, P., "Resonant and NearResonant Vibrational-Vibrational Energy Transfer Between Molecules in Collisions," Journal of Chemical Physics, Vol. 40, No. 2, Jan. 1964, p. 573. 20 Rapp, D., "Interchange of Vibrational Energy Between Molecules in Collisions," Journal of Chemical Physics, Vol. 43, No. 1, July 1965, p. 316. 21 Rapp, D. and Kassal, T., "Theory of Vibrational Energy Transfer Between Simple Molecules in Nonreactive Collusions," Chemical Reviews, Vol. 69, No. 1, Feb. 1969, p. 61. 22 Bott, J. F. and Cohen, N., "Shock Tube Studies of HF Vibrational Relaxation," Journal of Chemical Physics, Vol. 55, No. 8, Oct. 1971, p. 3698. 23 Airey, J. R. and Fried, S. F., "Vibrational Relaxation of Hydrogen Fluoride," Chemical Physics Letters, Vol. 8, No. 1, Jan. 1971, p. 23. deVries, A. E. and Klein, F. S., "Ultraviolet-Induced Isotope Exchanges in Gaseous Mixtures of HC1 and D2 and of DC1 and H2," Journal of Chemical Physics, Vol. 41, No. 11, Dec. 1964, p. 3428. 25 Ridley, B. A. and Smith, I. W., "The Vibrational Relaxation of HC1 (v = 3, 2, and 1) by Cl Atoms," Chemical Physics Letters, Vol. 9, No. 5, June 1971,0.457.

The theoretical performance of an HF diffusion-type chemical laser is investigated by means of exact numerical solutions for the laminar diffusion of a finite stream of H2 into a semi-infinite stream containing F and a diluent in the presence of an incident coherent radiation field. This flow model corresponds to flow in a single semichannel of a diffusion-type chemical laser. The initial flow velocity, temperature, and hydrogen stream thickness is held constant, and the effect of pressure level, initial fluorine partial pressure, and incident radiation intensity on peak integrated gain, axial extent of the lasing region, laser output power, and chemical efficiency is investigated.

A simplified analytical model of a diffusion-type HF chemical laser is presented. In this device, H2 is diffused into a supersonic stream to react with F atoms and form vibrationally excited HF that is made to lase. The reaction between H2 and F is assumed to commence at a flame sheet. A two-vibrational level model for the HF molecule is adopted. The dependence of laser amplifier and oscillator performance on diffusion rate, forward reaction rate, collisional deactivation rate, and radiative deactivation rate is determined. (Author)

Experimental results on the operation of HF chemical lasers on the v = 2 to v = 0 overtone transitions are presented. Two separate CW laser devices with gain lengths of 15 and 30 cm produced 21 and 56 W of overtone power. The comparable power on fundamental transitions of the same lasers was 97 and 180 W. Thus, these overtone HF lasers produce 22 and 31 percent of the available fundamental power, much higher percentages than previous overtone chemical lasers. The implications of this new short wavelength chemical laser for high power lasers are discussed briefly. 17 references.

A laser-induced fluorescence experiment is described which was performed in the flow field of a 1-kW supersonic chemical laser. In the experiment molecular iodine vapor was injected into the chemical-laser cavity and made to fluoresce by Ar(+) laser excitation. The results obtained demonstrate that laser-induced fluorescence can be applied successfully to study mixing zones in chemical-laser cavities. The following potential seeding candidates for studying hot flows in chemical lasers are suggested, in addition to I2: popop dye vapor, SiH4, and H2S.

The use of pressure-geometry scaling allows a tradeoff to be made between power flux and lasing mode length in chemical lasers, while the desired specific power is maintained. This significantly simplifies experimental and theoretical performance evaluation tasks, by reducing a three-parameter family of variables to a two-parameter one. The scaling analysis is conducted through the application of the flowfield aerokinetics-radiation conservation equations and constitutive relations; the results obtained are then verified by means of the numerical solution of the governing equations. 5 references.

Introduction V effective means of generating population inversion for flow systems have been studied in recent years. New results as well as rather up-to-date reviews of the subject are found in Refs. 1-8. Extensive studies ~ 8 have been carried out on the chemical lasers wherein the population inversion is created through the combustion of initially unmixed reactants. Most of the analyses" are based on laminar flow and mixing. The laminar analysis was modified for turbulent lasers by employing the conventional gross mixing concept of turbulent flow. This standard method of modifying the laminar analysis for chemically reacting turbulent flow includes a rather fundamental assumption which could lead to substantially inaccurate results. It is the implicit assumption that the eddy mixing immediately allows the commencing of chemical reaction in the manner analogous to the laminar mixing. The general relationship between the turbulent mixing and the chemical reaction has been studied for various systems in the past." 17 Particularly, the importance of correctly describing the turbulent mixing in the analysis of the combustion of initially unmixed reactants was elucidated in Refs. 13-17. In the present Note, the order of error that can result in the predicted power output of a turbulent chemical laser from employing the conventional mixing concept is investigated. This investigation is carried out within the context of the simplified approach of Ref. 4.