Rolf W. F. Gross

ISOTOPE SEPARATION WITH THE cw HYDROGEN FLUORIDE LASER

A cw hydrogen fluoride laser has been used successfully to separate deuterium from hydrogen by specific photocatalysis of the reaction of methanol with bromine. The strong absorption of H/sub 3/COH was demonstrated for the HF laser lines P1(5), P1(6), and P1(7). No absorption of the HF beam by deutero-methanol was observed. Excitation of H/sub 2/COH by the absorbed beam increased the rate of H/sub 3/COH removal by reaction with bromine. Irradiation of a 1:1 H/sub 3/COH:D/sub 3/COD gas mixture in the presence of bromine for a period of 1 min with the 90-W cw hydrogen fluoride laser beam produced isotope enrichment to greater than 95 percent D/sub 3/COD.

Temperature Dependence of Chemiluminescent Reactions. II. Nitric Oxide Afterglow

Using the glow discharge shock tube developed in this laboratory, we measured the temperature and density dependence of the β, γ, and δ bands for the NO recombination afterglow. We also determined the absolute rate constants for each of the vibrational transitions of the three bands at room temperature. Our results for the total band intensities are Iβ = 3.09 × 10−34(T / 300)−1.40[N][O][N2] photons / cm3·sec, Iγ = 1.18 × 10−17(T / 300)−0.35[N][O] + 2.12 × 10−34(T / 300)−1.24[N][O][N2] photons / cm3·sec, Iδ = 6.75 × 10−18(T / 300)−0.35[N][O] photons / cm3·sec. The results are critically reviewed and compared with previous experiments in the final part of the paper.

PRELIMINARY PERFORMANCE OF A cw CHEMICAL LASER

Preliminary performance of a cw chemical laser is presented. Hydrogen is diffused into a supersonic stream containing F atoms. Population inversion is due to the reaction H2+F→ HF(v)+H, ΔH=−31.7 kcal/mole, v=1, 2. An atomic F flow rate of 0.030 moles/sec has produced 475 W of laser power in the 3‐μ region. This represents 12% of the chemical energy involved in the above reaction. Zero power gain is 8%/cm. Spectroscopic observations of laser transitions are included.

Time-Resolved Spectroscopy of a Flash Initiated H2-F2 Laser

The time‐dependent output spectrum of a helium‐diluted H2–F2 chain‐reaction chemical laser has been observed. Reaction of a 50‐Torr mixture with mole ratio H2 : F2 : He = 1 : 1 : 60 was initiated by flash photolysis of the F2. Strong lasing was found from P‐branch vibration‐rotation transitions of the v = 1 → 0, 2 → 1, 3 → 2, and 4 → 3 bands of HF. Within some bands, the time sequence of transitions suggests non‐Boltzmann distributions of rotational states. No lasing from vibrational levels higher than 4 could be detected.

COMPARISON OF HF AND DF CONTINUOUS CHEMICAL LASERS: II. SPECTROSCOPY

Continuous laser action has been observed on several HF and DF vibrational‐rotational transitions. The HF lases between 2.6 and 2.9μ and DF lases between 3.6 and 4.1μ. The lines are identified and the relative intensities are shown.

XeF laser pumped by high-power sliding discharges

We have developed a high‐power XeF laser photolytically pumped by two surface discharges. The discharges slide along 760‐mm‐long by 12‐mm‐wide ferrite rods. They were energized by a single 6 μF capacitor at 50 kV in a fast discharge circuit. Each emitted up to 38 kW nm−1 cm−2 at 140 nm in 3‐μs‐long pulses. This powerful radiation source was used to photolyze mixtures of 450 Torr argon, 50 Torr nitrogen, and up to 12 Torr XeF2 in an active volume of about 1 l. We extracted a maximum specific laser output energy density of 8 J/l at 351 nm from the B–X transition of XeF.

Temperature Dependence of Chemiluminescent Reactions. I. Nitrogen Afterglow

Using the glow discharge shock tube recently developed in this laboratory, we measured the temperature and density dependence of the Lewis–Rayleigh afterglow between 300° and 2400°K. We also determined the absolute efficiency, i.e., the rate constant of this chemiluminescent reaction. Our results can be represented by the following expression: I = 0.60 × 10−17 (T / 300)−0.90[N]2photons / cm3·sec. The value of the integrated rate constant given includes all radiation between 500 and 700 nm.

Experiments with active phase matching of parallel-amplified Multiline HF laser beams by a phase-locked Mach-Zehnder interferometer

Active phase matching of multiline HF laser beams by means of a phase-locked Mach-Zehnder interferometer was demonstrated by locking the interferometer to the central interference fringe at zero optical path length difference. The central fringe could be found by varying the spectral content of the input beam. Laser amplification in one leg of the interferometer decreased fringe visibility without adversely affecting locking. Single-line fringe patterns produced by an array spectrometer (while the interferometer was operated in its scanning mode) were analyzed to show that no significant dispersion occurred in the amplifier. The techniques developed have potential for measuring dispersion mismatch between larger parallel amplifiers. These experiments demonstrated in principle that a number of multiline HF amplified beams can be recombined and phase-matched to produce a high beam quality output beam.

Measurements of the anomalous dispersion of HF in absorption

We report quantitative measurements of the anomalous refractive index of the P_{1}(6),P_{1}(7) , and P_{1}(8) vibration-rotational transitions of hydrogen fluoride in absorption. The experimental technique uses the displacement of spatial fringes produced by a Mach-Zehnder interferometer containing the absorption cell. A frequency scanned, CW HF probe laser served as the light source and the spectrally selective element. In addition, we measured the absorption coefficient of the three transitions. The experimental results are in good agreement with calculated values derived from the transition-matrix theory of HF.

Stimulated-Brillouin-scattering properties of SnCl 4

Common liquid Brillouin media have poor optical and physical stability when they are pumped at high average powers. We demonstrate that tin tetrachloride, SnCl4, is stable and shows no thermal defocusing at 1064 nm for 20-ns pulses at fluences of 3 J/cm2 and a pulse-repetition frequency of 10 Hz. To characterize this new stimulated-Brillouin-scattering medium we measured the following stimulated Brillouin parameters: Brillouin shift at 35°C, νB = (2.21 ± 0.02) GHz or ωB = 7.37 × 10−2 cm−1; temperature dependence of the Brillouin shift, dνB/dT = −8.95 MHz/°C; small-signal gain coefficient at line center, g0 = (11.2 ± 0.5) cm/GW; Brillouin-gain linewidth, ΔνB = (182 ± 12) MHz, which corresponds to a phonon relaxation time τB = 1.75 ns; and refractive index n = 1.36 at 1.064 μm and 25°C.