HF and DF laser action by a pulsed microwave discharge

A pulsed electrodeless microwave discharge withE-field enhancement by a tapered waveguide has been employed to produce HF and DF laser radiation from premixtutes of SF6+ H6and SF6+ D2. The 720 patm (690 patm) HF (DF) laser had an average multiline output power of 6 mW (1 mW) for an efficiency of 0.1 percent (0.02 percent) while operating at 1 kHz (450 Hz) pulse-repetition frequency (PRF). The HF (DF) laser was operated at reduced output power and efficiency up to 4.2 kHz (2.5 kHz) PRF. Reduced HF laser efficiency was obtained when C3H8was substituted for H2.     

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 N2is mixed in a plenum with SF6to provide F atoms. The mixture is expanded to form a supersonic jet into which H2is diffused. Population inversion and lasing are due to H2+ F → HF(υ) + H,upsilon leq 3, DeltaH = -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 SF6flow rates and approximately 10 percent at peak power. For a fixed arc power, addition of O2into 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 H2injection station. The net output power was reduced to zero when the cavity axis location was increased to 5 cm.     

Stable discharges in an HF laser with large electrode seperation

The characteristics of a fast discharge HF chemical laser are described. A Blumlein pulse forming line is used with a resistive cathode (50 Ω . cm resistivity germanium). Uniform arc-free discharges have been obtained in gas mixtures of SF6/H2/Ar, SF6/C2H6/Ar, and SF6/C3H8/Ar with electrode separations up to 5.2 cm.     

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.     

Performance of an HF chain-reaction laser with high initiation efficiency

Output-pulse observations are presented for a tranverse electrically initiated, helium-diluted HF laser pumped by the H2+ F2chain reaction. Performance of this laser is studied over a wide range of the gas composition and for initial pressures between 0.1 and 0.5 atm. The gas mixture was stabilized by premixing O2, F2, and He and flowing this mixture into a cold trap (84 K) before mixing with H2. Optimum conversion of electrical-initiation energy into laser energy was found for a 240-torr mixture with a mole ratio 1 F2:0.23 H2:0.08 O2:12 He which, when initiated with a 25-kV, 333-pF discharge, gave a pulse energy of 0.150 J. This corresponds to a ratio of laser output energy to electrical input energy of 144 percent. After unnecessary losses are taken into account, this ratio becomes 160 percent.     

Parameter studies of pulsed HF lasers

The average output power of pulsed HF chemical lasers is found to depend strongly on the fluorine source used. The best performance was obtained from H2-C2F6-He mixes, which gave average powers of 850 mW and energies of 20 mJ/pulse. Peak gains of at least 0.036 cm^-1are observed. Average powers of 450 mW from DF and 70 mW from HCl are reported.     

Radio frequency pumped mid-infrared waveguide lasers

RF discharge waveguide laser technology has been extended from the 10.6 μm CO2laser to include 2.7 μm HF, 3.8 μm DF, and several rare gas mid-infrared lasers. The maximum achieved electrical efficiencies of 5.3 and 4.0 percent were demonstrated in pulsed HF and DF systems, respectively. These, as well as several low efficiency rare gas lasers were demonstrated in a 20 cm gain length device. The output power and spectral distribution were determined as a function of the gas composition, pressure, velocity, and the RF power, pulse length, and repetition rate.     

Submicrosecond pulses from a hydrogen-fluorine laser with high energy density and quantum efficiency

Submicrosecond pulses have been obtained from a photochemical H2-F2laser with a chemical efficiency of 0.5 percent. Energy densities of 6 J l^-1were obtained from 60 torr (at 213 K) of a stoichiometric H2-F2mixture stabilized with 5 mole-percent O2. Laser output energy and the reciprocal of the pulsewidth were both proportional to the gas pressure. Actinometry showed that the laser energy output was 16.6 times the energy necessary to provide F atoms for initiation. Time-resolved spectra revealed excitation up toupsilon' = 6.     

Gas additive effects in CO chemical lasers

The effects of gas additives on optical gain of the CO chemical laser (CL) have been measured for N2, SO2, H2, HF, CF4, CCl2F2, CO, OCS, N2O, and NO. One of the more unusual additives, NO, has been used to control the output spectrum of a laser oscillator by controlled sequential quenching of the high bands. The significance of these results for total power enhancement, output spectrum control, and alternate diluent use is discussed.     

Pressure dependency of the NF3-H2transverse-discharge pulse-initiated HF chemical laser

The pressure dependency of the performance of the NF3-H2chemical-laser system has been evaluated. The laser energies at various chemical compositions and initiation discharge energies are presented as functions of Pressure. Overall efficiency, laser pulsewidth, and effects of additive gases are also presented. For all compositions the laser energy maximized at a pressureP_{max}which was observed to be dependent on the pulsewidth of the initiation discharge. At pressures belowP_{max}the laser energy was proportional to the partial pressure of NF3or H2. No change in slope of the laser energy versus pressure curve was observed in going from low-pressure nonexploding regimes to high-pressure exploding regimes, implying that the reactions causing the explosion did not contribute to the lasing. Lasing usually occurred in two peaks, the first containingHF(V=2) rightarrow HF(V=1)lines and the second containingHF(V=3) rightarrow HF(V=2)andHF(V=1) rightarrow HF(V=0)lines. These data indicate that lasing is due to the reaction sequence: 1)NF_{3} + e^{-} = cdot NF_{2} + Fcdot + e^{-}; 2) Fcdot + H_{2} = HF+(V) + Hcdot; and 3)HF+(V) + hnu = HF+(V-1) + 2hnu.     

Vibrational energy transfer in CO2under laser conditions with and without water vapor

It is shown that in the case of a dry 1.5-torr CO2gas fill the upper laser level is indirectly excited by vibrationally excited CO produced during the discharge, whereas in the case of a 1.5-torr CO2and 0.2-torr H2O mixture the upper laser level is directly excited by the electrons in the discharge. The collision relaxation times measured under laser conditions for the symmetric valence vibration of CO2in a CO2-H2O mixture and in a CO2-CO mixture as produced during a discharge of an initially pure CO2fill were 19 and 73 μs, respectively. If the reasonable assumption was taken that half of the CO2was dissociated into CO then this result shows that H2O was 14 times more effective in depopulating the lower laser level than CO. The growth in laser intensity for the dry fill was shown to be due to the CO (nu = 1) transfer of energy to the asymmetric vibration of CO2(00°1) with a characteristic increase that was exponential strictly only for a time short compared with the relaxation time of the symmetric vibration. The characteristic transfer time for excitation of the asymmetric vibration was dependent upon the fraction of CO present. If we make the assumption of 50 percent dissociation, the intermolecular energy transfer time between CO and CO2was found to be 40 torr-μs. Results obtained with N2and He added to the laser mixture indicated that He was not more effective in relaxing the lower laser level than N2or CO and was less effective than H2O.     

用于大气吸收测量的小型电激励连续波DF/HF选线化学激光器

介绍了用于大气吸收测量的电激励双模块小型连续波DF/HF选线化学激光器,描述了其结构、运转方式和激光器的性能。在采用一级振荡、一级输出的利特罗(Littrow)自准直光栅色散腔结构的前提下,激光器目前共获得17支DF激光谱线,11支HF激光谱线,大部分单谱线基横模输出超过1 W,单次连续出光时间超过30 min,功率稳定性在±5%以内。将激光器激光光栅改装为球面腔镜后也可输出多谱线DF/HF激光,功率水平为20 W,选模后基横模输出6~8 W。     

A theoretical study of the atmospheric pulsed H2+ F2chemical laser including rotational nonequilibrium effects

An atmospheric pulsed F2/H2/He chemical laser is studied numerically by a model which incorporates rotational nonequilibrium effects. The results are compared with experimental results of Chen et al. The fit between the experimental and theoretical results was found to be reasonably good. The results were also compared with those obtained from a model with an equilibrated rotational distribution. It is found that inclusion of a rotational nonequilibrated distribution which decreases the output energy by 25 percent has a certain effect on the output energy distribution among the various vibrational states but is of little importance for the lasing duration.     

Time-resolved output spectrum from a hydrogen fluoride laser using mixtures of SF6and HI

The time-resolved spectrum from a transverse-discharge hydrogen fluoride (HF) laser using a mixture of SF6and HI is reported. Because this spectrum matches that from a high-pressure H2- F2laser, and because the SF2-HI mixture is chemically stable, this laser should be a suitable and convenient source for probing H2- F2amplifiers.     

Fuels for a premixed pulsed HCl laser

HCl pulsed chemical lasing was obtained from several premixed R-Cl/HI mixtures when initiated by a transverse pulsed discharge. The relative merits of these mixtures were compared to a premixed H2/Cl2mixture. For a constant stored electrical energy several mixtures have been found which give higher specific power than the H2/Cl2system. In addition, it has been possible to run some of these improved mixtures without diluent with no laser performance degradation.     

HCl chemical lasing with HI and chloro compounds

HCL chemical laser action has been obtained from chloro compounds when HI was used as the source of H atoms. Laser action was produced on severalupsilon = 3-2, 2-1, and 1-0 HCl transitions when initiated by transverse pulsed discharges in HI-He mixtures containing such chloro compounds as CCl4, CHCl3, and several Freons. Both HCl and HF lasing were observed when a Freon (C2Cl2F4) containing F as well as Cl was used. The measured wavelengths for these HCl lasers correspond to excellent atmospheric windows for transmission of infrared radiation. No HCl lasing was obtained when HBr, H2S, or H2were substituted for HI.     

CW DF/HF化学激光器性能与流场参数的相互关系

从增益系数、输出功率、激光效率的基本公式出发 ,得到了CWDF HF化学激光器性能对光腔中F和D2 H2反应区流场参数的依赖关系。利用数值模拟结果对该关系进行了验证。给出了提高CWDF HF化学激光器性能的F和D2 H2 反应区流场参数要求 ,为CWDF HF化学激光器喷管设计提供了依据     

The measurement of far-infrared laser gain and loss using a Michelson coupler

It is demonstrated that small values of small-signal gain and total internal losses in far-infrared lasers can, in principle, be determined by measuring the optimum and threshold output coupling coefficients with a Michelson coupler. Experimental results show that although accurate determination of the small-signal gain can be made, only a good approximation of the internal losses is obtained by this method. The gain of the 220-μm transition of H2O is shown to increase from 0.24 percent m^-1to 0.43 percent m^-1with the addition of helium to 0.25 tort H2O at a discharge current of 1.8 A.     

小功率连续波放电DF/HF化学激光器的功率

将SF6、O2、He3种可调气体预混合,喷入带有8个高压放电极的放电管,解离F离子,沿气流方向以亚音速喷入喉道,H2/D2由喉道上下喷入,光轴在H2/D2喷入下游1mm处。研究了连续波DF/HF激光器的多谱线输出功率与SF6、He和H2/D2的流量关系,以及混合气体中加入O2对激光器性能的影响。实现了HF最大输出功率12W,DF最大输出功率11W,连续可调,功率稳定,持续时间20min。     

Mass spectroscopic studies of the CO laser discharge

The effects of adding Xe, H2, and O2to the CO-He laser discharge are studied mass spectroscopically. Xe greatly reduces CO dissociation. H2does not react chemically but alters discharge kinetics. O2has little effect on the CO-Xe-He discharge but reduces CO dissociation in CO-He.