IEEE JOURNAL O F QUANTUM ELECTRONICS, JANUARY 1973 202

rates of HF(v) by a variety of gases (He, Ar, Nz, Hz, OZ, COZ, NFs, and CH4). Laser operation from MoFG-HJIe mixtures could be attained at total pressures up to 2 a tm with a reduction of output energy by a factor of 2 compared to the optimum pressure; at 1-atm pressure the reduction factor is only 1.1. All of the gases studied were found to be considerably more deleteri- ous to HF laser performance than helium.

WCS. A TEMoo Short Pulse H F Oscillator, K. J. Pettipiece, Lawrence Livermore Laboratory, Livermore, Calif. 94550.

A single mode HF chemical laser oscillator with a pulse of less than 5 ns FWHM and a peak output of greater than 0.1 MW has been built and evaluated. A flowing mixture of SFG/CH( was used in our helical TEA laser. The output mirror had a 2-m concave surface with a 50-percent reflective coating. The rear mirror was a gold coating on a flat substrate or a 625 line grating which could be adjusted for a single line. There was an adjustable aperture inside the cavity for transverse mode control. The cavity was stabilized with 4 super Invar rods and was less than 40 cm long to control longitudinal modes. A Field Emissions Corporation Model 231 pulser, with an output of 6 J in less than 50 ns, was used to supply the electrical input pulse.

The profile of the laser output was scanned in both the near and the far field revealing a pulse with a divergence of 1.4 times diffraction limit and a TEMoo mode. A time resolution of the pulse was displayed on a 519 scope using a liquid helium cooled Ge-Cu detector, revealing a pulse less than 5 ns FWHM and a TEMooo mode. The preceding was done with a Pz(5) line at a pressure of 190 torr. Using a monochromator we found almost all of the output of this oscillator on the four lines P2(4)-P2(7).

This oscillator pulse has been amplified using a single stage pin amplifier resulting in a rhorting of the pulse.

WC6. HF Laser Action Above the Second Explosion Limit,' J. Wilson, D. Northam, and P. Lewis, Avco Everett Research Laboratory, Everett, Mass. 02149.

Experiments are described in which pulsed laser action was obtained from mixtures of fluorine, hydrogen or deuterium, and a diluent a t pressures above the second explosion limit. The gases were mixed at atmospheric pressure in a rapid flow system and did not react until reaction was triggered by photolyt,ic dissociation of the fluorine. The laser pulse duration for a high output coupling mirror (50 percent) was about 10 ps, which is longer than the flash duration of approximately 1 ps. This result indicates that the chain reaction betareen hydrogen and fluorine is proceed- ing.

The laser energies obtained are compared with values calculated using a theoretical model of the reaction. The model includes ten vibrational levels, each with its own production rate (chemical production plus cascading from the level above) and deple-

1 This research was supported by the Air Force Weapons Laboratory, Air Force Systems Command'

Advanced Research Projects Agency, under ARPA U. S. Kirtland Air Force Base, N. Mex., and the

Order 0870 and Contract F29601-72-C-0017.

tion rate (vibrational relaxation and stimu- lated emission). The agreement between theory and experiment is reasonable provi- ded the H F vibrational relaxation rate is assumed to increase rapidly with increasing vibrational quantum number v.

WC7. Pressure Dependency of the NF,- HZ Transverse Pulse-Initiated H F Chemical Laser,l R. K. Pearson, J. 0. Cowles, G. L. Hermann, K. J. Pettipiece, and D. W. Gregg, Lawrence Livermore Laboratory, Livermore, Calif.

We found that the energy output of several pulsed NFI-Hz chemical lasers, with various NF3-I-Iz compositions, was a maximum at pressures from 10 to 100 torr. The pressure of maximum lase energy was higher for lasers with shorter initiation pulses. At the chemical composition producing maximum energy (NFJHz E 5), both the maximum chemical efficiency (-1 percent) and the maximum overall electrical efficiency (-1 percent) of t.he laser occurred at pressures below the pressure of maximum energy. At low pressures, the VZ-' transitions lase first and comprise more t,han 70 percent of the energy of lasing followed by about 20 percent of the total lase energy in Vi-0

and 10 percent in A plot of the lase pulsewidth at half maximum versus inverse pressure gave a straight line, indicating the termination of the lase may be due to collisional relaxat,ion phenomena. We de- tected no change in the slope of the lase energy-pressure curve in going from a non- exploding to an exploding regime. The addition of helium to NF3-H2 mixtures increased lase energy at low reactant pressures and decreased lase energy a t high reactant pressures. At low pressures, lase energy was proportional to P N F 3 a t low P X F I and to P H , a t low PR,. The preceding data imply that 1) lasing €IF molecules are produced from species generated in the electric discharge rather than by chain reactions and 2) decreases in efficiency and total lase energy at higher pressures are due to radical recombination processes.

Energy Commission. 'This work was supported by the U. S. Atomic

WC9. Chemical Efficiency in a Pulsed HF Laser,' W . H. Beattie, G. P. Arnold, and R. G. Wenzel, Los Alamos Scientific Laboratory, Los Alamos, Ai. Mex. 875.44.

Quantitative analysis for I-IF production in the product gases of an electrically initiated H2:SFG laser has been performed by aqueous titration. Measurements were taken at an IIF laser output of approxi- mately 1 J/pulse. Gas chromatographic analysis has revealed the presence of SF,. A likely mechanism to describe the decom- position of SF6 in a n electric discharge and mechanisms to account for H F production in the laser and t.itrimeter are given. Based upon total HF production in the laser, 7.2 percent of the chemical energy available from the reaction F + Hz 3 HF* + H appears as laser light output. As the atomic ratio of F to H in the SF8 + Hz mix is increased from 3 to 65, the chemical effi-

1 This work was supported by the auspices of the U. S. Atomic Energy Commission.

ciency is increased and the HF production is decreased, suggesting that collisional deactivation of I3F* by HZ limits the laser efficiency.

WClO. HF-DF CW Combustion/Mixing Chemical Laser, R. A. Meinzer, United Aircraft Research Laboratories, East Hartford, Conn. 06108.

A CW combustion/mixing laser has been constructed which does not require the use of any electrical power for its operation. Chemical energy is used for the production of F atoms via the hypergolic reaction of a fluorine-rich Fz/Hz mixture in a combustor. As much as 50 mole percent of the combus- tion products of this reaction is atomic fluorine. Most of this F-atom concentration is frozen via a n aerodynamic expansion which is rapid with respect to atom- recombination kinetics. The injection of Dz into this expanded flow produces a popula- tion inversion in the newly formed D F molecules. The vibrational energy in these molecules is converted into laser power by means of an ordinary optical cavity. This laser operates in the 24-p wavelength region and watts of CW laser power have been extracted on a continuous bases for periods of time in excess of 10 min. The laser itself will be described and the results of some spectroscopic measurements of the optical power and gain will be discussed. The results of the gain measurements were utilized t,o make quantitative estimates of both the rotational and vibrational tempera- tures.

WC11. HF CW Laser Performance: The Chain Versus Cold Reaction, G. Emanuel and N. Cohen, Aerospace Corporation, Los Angeles, Calif. 90045, and T. A. Jacobs, TRW Systems Group, Redondo Beach, Calif. 90278.

Analytic and experimental study of €IF CW laser performance is presented. I n partic- ular, operation in the chain reaction regime is compared with operation in the cold reaction regime. These two regimes are defined by consideration of the reactions

F 4- H, + HF" + H (1)

H + F, f HF" + F (2) where the asterisk (*) indicates a vibra- tionally active molecule. When both reactions (1) and (2) contribute to t.he lasing process, the chain is defining one regime. In the absence of Fz, only reaction (I), the cold reaction, suppovts lasing, defining the second regime.

The presentation centers on performance parameters generated by numerical solution of the coupled nonlinear equations that govern the interaction of fluid mechanics, chemical kinetics, and stimulated emission in a chemical laser medium. We will point out the pertinent factors such as V-R rates, that contribute to degradation of perform- ance in the chain reaction regime.

Some experimental results, obtained with an HF CW chemical laser operated in a purely chemical mode, will be presented t o show confirmation of theoretical expecta- tions. Areas for further reaction growing from the theoretical and experimental studies will be suggested.