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.     

CW laser action in atomic fluorine

We have obtained CW laser action on four transitions in the doublet system of atomic fluorine for the first time. All previously reported laser action was on a pulsed basis only. CW laser radiation was obtained when F2or AgF was used as a fluorine donor in an electron beam pumped helium plasma. A multiline output power of 200 mW was obtained.     

Comparison of two new microwave plasma sources for HF chemical lasers

The performances of two microwave sources used to produce fluorine atoms by dissociation of SF6for a CW hydrogen fluoride chemical laser are compared. The first device, large microwave plasma (LMP), is a slow-wave structure while, the other (surfatron) excites a plasma surface wave. Their performances, as far as electrical and chemical efficiencies are concerned, are quite similar when operated at the same microwave power level. However, the slow-wave structure can sustain higher microwave power, providing larger laser output power, while the surfatron has much smaller dimensions, allowing for a more compact laser system.     

Excited-state absorption of SF6at 936.8 cm-1

An effect that is opposite to saturable absorption in the infrared was observed when a CO2laser beam was passed through SF6. An increase of absorption occurred when the radiant flux of the laser was increased to 10 W/cm². The effect was observed for the P(28) line of the00deg1-10deg0band of the CO2laser, and was attributed to absorption from excited vibrational states of SF6.     

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.     

Influence of the active zone diameter, on the UV-ion Ne-CuBr laserperformance

An active-zone-diameter scanning of an ultraviolet (UV) Cu⁺ laser excited in a nanosecond, pulsed longitudinal Ne-CuBr discharge with an excitation pulse repetition frequency of 19.5-25 kHz is carried out. The discharge conditions for achieving a maximum average output power on the UV lines-248.6, 252.9, 260.0, and 270.3 nm are found for each active zone diameter. A record average output power of 1.3 W is obtained for multiline operation. The specific average output power is 57 mW/cm³ at an active volume of 23 cm³. The highest peak pulse power and average laser power on the 248.6-nm laser line for the UV Cu⁺ lasers are also measured-3.25 and 0.85 W, respectively. A simplified kinetic model, which describes the discharge afterglow processes, is made     

Improved Ti:sapphire laser performance with new high figure ofmerit crystals

The continuous-wave (CW) laser performance of Ti:Al₂O ₃ crystals with high figure of merit is described. Using a 0.1% Ti:Al₂O₃ crystal (FOM=1000), output powers of 3.5 W at 800 nm are obtained, pumping with a 9.6 W argon ion laser operating multiline. Continuous tunability of the CW Ti:Al₂O ₃ laser extending from 665 to 1070 nm is also demonstrated for a 5 W pump power     

A double-discharge-initiated HF laser

A double-discharge hydrogen fluoride chemical laser using SF6+ C4H10and SF6+ H2is described. A maximum pulse energy of 102.5 mJ is reported, with a peak power of about 400 kW. The energy density is 300 mJ/l, and the electrical efficiency is 0.6 percent.     

Performance and diagnostics of lasers initiated by the reaction of NO with ClO2

A purely chemical HCl laser employing transverse flow was operated with a maximum multiline output power of 13 W which represents a chemical efficiency of 8.6 percent based on the total exothermicity of the pumping reaction. The required nonequilibrium concentration of Cl atoms was generated by the branched chain reaction of NO with ClO2. Mass spectrometric and absorption spectroscopic measurements of species concentrations in the NO/ClO2reaction system showed that the effectiveness of production of the branched chain decreased with inereasing total pressure.     

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.     

Br, C, Cl, S, and Si laser action using a pulsed microwave discharge

Low power Br, C, Cl, S, and Si infrared laser action has been obtained using 2.45 GHz pulsed microwave discharges of molecular source gases and helium. The atomic laser molecular source gases were Br2, CO2, CO, CF4, Cl2, CH3Cl, CH2Cl2, CCl4, SF6, CS2, and SiH4.     

Intense electron-beam initiation of a high-energy hydrogen fluoride (HF) laser

A superradiant hydrogen fluoride (HF) laser is described in which an intense electron beam, propagating in a SF6and C2H6mixture, is used to initiate chemical reactions that produce vibrationally excited HF molecules. The variation of laser energy as a function of SF6pressure for fixed composition and as a function of composition at a fixed SF6pressure has been investigated. These experimental parametric curves are discussed in terms of the relevant physics. The maximum laser energy of 228 J in a 55- ns full-width-at-half-maximum (FWHM) pulse was obtained with a mixture of400-torr SF6and 40-torr C2H6. Measured efficiency for converting deposited beam energy to laser energy propagating in the forward direction was as large as 8 percent.     

Experimental investigation of the atomic fluorine laser

The atomic fluorine laser, as produced by a fast pulsed discharge in He-NF3mixtures, is investigated experimentally. Total collisional quenching rates of He 2³S on NF3, BF3, CBrF3, CCIF3, CHF3, CF4, C2F6, CO2, SF6, and N2are reported. Upper limits for collisional quenching rates of He 2¹S, 2³P, and 2¹P atoms on NF3are determined. We conclude that energy transfer from excited neutral He to NF3is not the primary pumping mechanism in the He-NF3atomic fluorine laser.     

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.     

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.     

Optimization of a UV Cu+ laser excited bypulse-longitudinal Ne-CuBr discharge

The discharge conditions for high average output power on four UV Cu⁺ lines at 248.6 252.9, 260.0, and 270.3 nm, in a nanosecond pulse-longitudinal Ne-CuBr discharge, have been investigated in two discharge tubes of different designs. A record average output power of 210 mW (and a peak pulse power of 1.7 W) on the 238.6-nm laser line, and of 270 mW for multiline operation has been obtained. An optical effect enhancing the 248.6-nm laser line power has been observed as the intensity of two Cu atom laser lines (510.6 and 578.2 nm) increases. It has been shown that the presence of Br atoms in the discharge leads to a fall of the Ne metastable density via Penning ionization and, hence, to a decrease of the Cu⁺ metastable density and an increase of the laser output     

A purely chemical HCl laser employing transverse flow

A purely chemical continuous wave HCl laser has been developed. The purely chemical production of nonequilibrium concentrations of Cl atoms is achieved by a branched chain reaction between NO and ClO2. Three modes of accomplishing the prepumping chemistry are discussed and their effects on HCl laser performance are evaluated. A transverse flow laser was operated having a maximum HCl multiline output power of 4 W and a chemical efficiency of 6.6 percent based on the total exothermicity of the pumping reaction.     

A laser augmented reaction: SF6+ SiH4→S*2+ SiF4+ HF + H2· retention of isotopic selectivity during detonation

A single unfocused pulse of a free running CO2laser, area ∼ 8 cm², initiates an explosive reaction between SF6and SiH4. This occurs at a minimum energy of 4 J [full width at half maximum (FWHM)sim 1.5 /mus] of which about one half is absorbed in an 8 cm long cell; total pressure 12 torr; 0.65 <p(SiH4)/p(SF6) < 1.8. The spectral and temporal distributions of the emitted chemiluminescence depend sensitively on the fuel to oxidizer ratio, and on the pulse energy; we investigated the range 4 → 20 J. The principal emission is due to S2(B^{3}Sigma-_{u} rightarrow X^{3}Sigma-_{g}). Transitionsupsilon' (0-4) rightarrow upsilon" (2-15)were recorded. In the³Sigma-_{u}state, vibrational temperatures range from 3000-13000 K. The luminosity peaks sharply at (SiH4)/(SF6) = 1.0 ± 0.05. On each side of the maximum of the emission versus composition curve [at (SiH4)/(SF6) ≈ 0.95 and 1.22, for a 12 J pulse] the residual SF6(0.2-0.5 percent of initial amount) is enriched in³⁴SF6; the observed fractionation factors at these two compositions are 8 ± 2. The separation between the two sharply peaked optimum compositions appears to increase with increasing pulse energy. Preliminary results with other fuels suggest that the concurrent absorption of CO2laser radiation by the fuel, as well as a highly exothermic reaction, are pre-requisite for fine tuning of composition, injected power, and total pressure for optimum isotope fractionation.     

Efficient V-V energy transfer in a multiphoton excited mixture of SF6and CF4

Spectral and temporal measurements of infrared fluorescence (IRF) in SF6, CF4, and mixtures of SF6and CF4gases excited by a pulsed CO2laser are reported. Using the 944.2 cm^-1[P(20)] laser line for excitation and measuring the IRF spectra between 700 and 1500 cm^-1, a strong red shifted IRF peak of the ν3mode in pure SF6was found. No IRF was observed under these conditions in pure CF4. In a 13:10 mixture of SF6and CF4, two strong IRF peaks of the ν3modes, shifted to the red relative to the room-temperature fundamentals at 948 cm^-1and 1283.2 cm^-1, were observed. The peaks are almost equal in height and since both molecules have almost the same ν3band intensity, the present result suggests that efficient intermolecularV-Venergy transfer occurs from excited SF6to cold CF4molecules. The temporal behavior of the IRF signals under high excitation (langlenrangle approx 6) in pure SF6exhibits two relaxation times, one of bulk cooling withtau_{1} approx 1ms and the other of aV-Tnature withPtau_{2} approx 20 mus . torr. In the mixture, an additional relaxation of the intermolecularV-Venergy transfer process is observed withPtau_{3} approx 10 mus . torr. The red shift dependence of the IRF peaks on the degree of excitation was also measured and used to examine population distributions, specific IRF transitions, and anharmonicity parameters.     

Efficient operation of a low-impedance Blumlein discharge initiated HF/DF chemical laser

A study is described on the efficient operation of an HF/DF chemical laser initiated by a low-impedance Blumlein discharge. Some combinations of 0.33 and 0.66-Ω flat-plate Blumlein lines with simple discharge chambers of various active volumes were investigated. For an SF6/H2mixture, an HF laser gave a maximum efficiency of 6.3 percent, and 5 J/1 was extracted. Substitution of D2for H2gave a DF laser output energy as high as 80 percent of the HF chemical laser output.