Initial performance of an electric-discharge-initiated chemical laser pumped by the H2-F2 chain reaction is presented. Uniform microsecond-scale discharges in atmospheric-pressure laser mixtures have been obtained after a short-duration ionizing pulse of high-energy electrons. Care in discharge pulse shaping is required to avoid late-time arcs. Informaiton is presented on the effects of several parameters on laser performance. With a 3 H2 : 6 F2 : 54 He : 37 Ar mixture as much as 28 J/liter of discharge energy could be deposited in the mixture, and laser energies up to 42 J/liter were obtained. This corresponds to a chemical efficiency of 6.3%, based on the H2 content, and an electrical ’’efficiency’’ of 148%, based on the available lasing volume and total energy input to the medium.
Time-resolved uv absorption measurements of the rate of F2 disappearance have been compared with a theoretical pulsed chemical laser code to infer electrical dissociation efficiencies of electron-beam-irradiated discharges. The results indicate that a 400-keV 50-nsec e-beam of ~ 10 A/em' dissociates approximately 0.3% of the reactants initially present in dilute F,/H, mixtures, producing four chain carriers per ionizing collision. With the addition of a discharge field at 80% of the self-breakdown limit, initial reactant dissociation increases to approximately 1.1 %, corresponding to 15 chain carriers per ionizing event and a dissociation efficiency of 7.5%. An earlier analytical plasma model of reactant dissociation that has been generalized to account for the presence of Ar and H2 suggests that heating of the negative ions of fluorine, leading to electron detachment in heavy-particle collisions and direct electron-impact dissociation of reagents by slow electrons become dominant mechanisms with the application of a strong undervolted field. In general, the approximate plasma analysis is shown to yield results that are in qualitative agreement with the experimental data.
Output pulse observations are presented for a helium-diluted CO2 laser pumped by VV (vibration-vibration) energy transfer from vibrationally excited DF produced by the D2–F2 chain reaction. Flash photolysis of the F2 served to initiate the reaction. A 290-cm3 reaction chamber containing a 0.5-atm mixture with mole ratio D2:F2:CO2:He = 0.33:1:8:10 gave a single-pulse output energy of 2.8 J. Relative to the amount of D2 present in the reaction chamber, this corresponds to a chemical efficiency greater than 5%.
Volumetric irradiation by a short-pulse electron beam has been used to trigger long-duration spatially uniform electric discharges in gas mixtures of He and F2 or SF6. Uniform energy deposition to 300 J/liter has been observed for atmospheric F2–He mixtures at nominal electron-beam currents of 3 A/cm2 and discharge currents up to 20 A/cm2. Operation suitable for efficient initiation of pulsed HF/DF chain lasers appears possible over a wide range of E/N and mixture ratios, limited by breakdown at large E/N and negligible field enhancement at low E/N. Approximate analytical plasma models are presented and used in conjunction with time-resolved afterglow current measurements to obtain rate constants for F−-ion F2+−ion recombination and F2+−ion electron recombination. Estimates of F2 dissociation fractions achieved in the experiments imply the possibility of scalable and efficient initiation of pulsed chemical lasers with such discharges.
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