Donald J. Spencer

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.

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.

Performance of cw HF Chemical Laser with N2 or He Diluent

Recent experimental results on the performance of a continuous HF (or DF) chemical laser are reported. In this device, an arc‐heated diluent is mixed in a plenum with SF6 to provide F atoms. The mixture is expanded to form a supersonic jet into which H2 (or D2) is diffused. Population inversion and lasing are due to the reaction H2+F=HF(v)+H; v≤3 and Δ H=−31.7 kcal. Power levels above 1 kW have been obtained in a N2 diluent gas flow, and levels above 1.7 kW have been obtained in a He diluent gas flow. Specific power yields are 43 and 108 kW sec/lb for the N2 and He systems, respectively. The variation of laser power and efficiency with cavity optical axis location and SF6 mass flow are reported for both N2 and He systems. A spectrum of the HF laser operating in a He flow is also presented that gives evidence of v=3 partial inversion.

COMPARISON OF HF AND DF CONTINUOUS CHEMICAL LASERS: I. POWER

Abstract : A continuous DF chemical laser radiating at approximately 4 microns is reported. Population inversion is obtained by diffusing D2 into a supersonic free jet containing F atoms. The performance of the DF laser is compared with a similar HF laser previously reported. The ratio of DF to HF laser output power is 0.7 for fixed supersonic jet conditions and the same molar flow of H2 and D2. The efficiency of conversion of chemical energy to laser energy is approximately 12% and 8% for the HF and DF lasers, respectively. (Author)

Power and efficiency of a continuous HF chemical laser

Experimental measurements of laser power output and chemical efficiency are reported for a continuous HF chemical laser. In this device, arc-heated N 2 is mixed in a plenum with SF 6 to provide F atoms. The mixture is expanded to form a supersonic jet into which H 2 is diffused. Population inversion and lasing are due to H 2 + F → HF(υ) + H, \upsilon \leq 3, \Delta H = -31.7 kcal. Power levels up to 1 kW have been obtained. The efficiency of conversion of chemical energy to laser power is 16 percent at low SF 6 flow rates and approximately 10 percent at peak power. For a fixed arc power, addition of O 2 into the plenum raises peak power by about 25 percent under present operating conditions and reduces sulphur deposition on mirror surfaces. The presence of HF and DF in the plenums of DF and HF lasers, respectively, did not appear to degrade laser performance. (HF and DF levels up to 10 percent of the local F concentration were studied.) However, the presence of HF and DF in the plenums of HF and DF lasers, respectively, did degrade laser output. For given flow conditions, peak net laser power was obtained when the optical cavity axis was about 2 cm downstream of the H 2 injection station. The net output power was reduced to zero when the cavity axis location was increased to 5 cm.

Small-Scale CW HF(DF) Chemical Laser

The construction and performance of a small‐scale cw HF(DF) chemical laser is described. A multiline output of about 15 W was achieved. During single‐line operation, 18 HF 2‐1 and 1‐0 transition lines, with powers from 0.1 to 2.4 W, and 24 DF 3‐2, 2‐1, and 1‐0 transition lines, with powers from 0.01 to 0.30 W, were observed. Amplitude stability varied from ±1.5 to ±5%, and free‐running short‐term frequency stability was about ±10 MHz.

Initial performance of a CW chemical laser

The performance of a continuous HF chemical laser is presented in this paper. Population inversion was obtained by diffusion of H2 into a supersonic jet containing F atoms [H2+F → HF(v)+H1 ΔH=−31.7 kcal/mole]. A peak power of 630 W was obtained with an F atom flow rate of 0.040 mole/sec, and the efficiency of conversion of chemical energy to laser energy was 12%. The performance of a corresponding DF laser is also given. Major laser output is from 2-1 and 1-0 transitions for both lasers. Radiation is at 2.6 to 2.9μm and 3.6 to 4.0μm for the HF and DF lasers, respectively. The ratio of DF to HF laser power is 0.7 under similar flow conditions.

Zero-power gain measurements in a CW HF laser using a pulsed-probe laser

Zero-power gain measurements in a supersonic diffusion-type CW HF laser have been made using a pulsed HF probe laser. A peak zero-power gain of 10 percent/cm was measured on a P_{2}(3) vibrational-rotational transition and 7 percent/cm on a P_{1}(6) transition for flow rates corresponding to 1.8 kW of closed-cavity power. The variation of zero-power gain with rotational quantum number J fits a simple rotational equilibrium model indicating increasing rotational temperatures with increasing distance x from the nozzle exit plane. The model also indicates a total inversion for x \leq 0.2 in for the P_{2}(J) transitions and a partial inversion further downstream.

Zero-power-gain measurements in CW HF(DF) laser by means of a fast scan technique

An improved technique for measuring zero power gain in a CW HF-DF chemical laser has been developed in which a CW HF(DF) single-line, frequency-stabilized TEM00mode probe laser is used. Through use of a flat rotating mirror and focusing elements, the streamwise distribution of zero-power gain was scanned at a rate of ∼1 mm/μs with a spatial resolution of ∼1 mm. The zero-power-gain profile was observed for two arc-driven chemical-laser nozzles with both HF and DF active species. The nozzles consisted of a 36-slit array with perforated tube H2injectors and a 55-slit array with uniform H2injection. Results are presented for the variation of zero power gain with axial distance, the magnitude and location of peak gain, and the gain cutoff location for a number of transitions. Peak gain values of 15 percent/cm and 5.5 percent/cm were measured with HF and DF active species, respectively, with the 55-slit nozzle array.

Scale‐up of NF(a1Δ) produced by the H+NF2 system in a subsonic cw laser device

A peak density of the electronically excited free‐radical species NF(a1Δ) of 2.4×10−9 mol cm3 has been chemically produced in a subsonic laser device. This high concentration confirms previous analyses and predictions of the chemical system. This is a concentration scale‐up of 104 from previous flow‐tube results.