Study of the XeCl laser pumped by a high-intensity electron beam

We present the results of a detailed experimental study of the XeCl laser pumped by a high-intensity electron beam. The laser system was optimized as an oscillator for mixtures of Xe and HCl with Ne, Ar, and Kr diluents. The peak intrinsic efficiency (laser energy out/electron-beam energy deposited) was near 4.5 percent for each of these diluents. Small-signal gain and background absorption were measured as a function of electron-beam deposition rate from 0.4 to 6 MW/ cm³. The ratio of small-signal gain to absorption was found to be constant over this range with a value of ∼5. Measurements of absorption in the presence of a large photon flux indicated that there was no appreciable saturable contribution to the absorption. Measurements of fluorescence from theBandCstates indicate that collisional mixing between these states is very rapid. The formation efficiencies of theBandCstates are estimated to be 0.15 and 0.05, respectively. A vibrational relaxation rate of between 1 and1.5 times 10^{-10}cm³. s^-1was determined. The effect of this finite relaxation rate is to reduce the energy available to the stimulated process by a factor of 0.67-0.75. Estimates of the XeCl* deactivation rates by HCl and electrons were also obtained. A value of1.7 times 10^{-9}cm³. s^-1was obtained for quenching by HCl, and a value ofsim 1 times 10^{-7}cm³. s^-1was estimated for electron deactivation.     

Measurement of lasing performance and efficiency of e-beam pumped xenon chloride

Ane-beam pumped XeCl laser has been operated in mixtures of Ne/Xe/HCl and Ar/Xe/HCl. Careful measurement of energy deposited by thee-beam was made to allow accurate determination of intrinsic medium efficiency. Laser output in neon was found to agree well with the predictions of a kinetics model, and yielded efficiency of 5-6 percent. In an argon diluent, we have found efficiency as high as 8.0 percent.     

Formation dynamics of excited components in discharge XeCl laser plasma from the data of dye laser absorption probing

The absorption spectra in the 335-610 nm spectral range and the time dependences of the concentrations of Xe^*, He^*, Ne^*, Ar^*, Xe+*, Cl-, and XeCl* were measured by the pulse dye laser absorption (gain) probing of the active medium of a XeCl discharge laser for different buffer gas mixtures. The formation dynamics of excited atoms, ions, and excimer molecules is discussed. It is shown that at the initial stage of discharge the dominant process in the formation of XeCl* molecules is the "harpooning" reaction, whereas at the following stages the ion-ion recombination gains predominance. The rate constants of the ionic XeCl* formation reaction are determined for He, Ne, and Ar buffer gases.     

Theoretical high-efficiency extraction study of a short-pulseelectron-beam-pumped ArF laser amplifier with atmospheric pressureAr-rich mixtures

The single-pass (50 cm) amplifier performance of an atmospheric-pressure ArF laser pumped by a 65-ns full-width-at-half-maximum short-pulse electron beam was investigated theoretically for a wide range of excitation rates (0.1-2.0 MW/cm³ ). Atmospheric mixtures of Ne, Ar, and F₂ (three mixtures of Ar=40%, 70%, and Ne-free) were studied. A kinetic numerical model of the ArF amplifier with a Ne buffer system was constructed. A one-dimensional propagation treatment considered the gain depletion and saturation absorption spatially and temporally along the optical axis. In this model the rate constants for electron quenching of ArF* of 1.6×10^-7, 1.9×10^-7, and 2.4×10 ^-7 cm³/s were used for Ar concentration of 40, 70 percent, and Ar/F₂ mixture, respectively     

Maximum performance of discharge-pumped exciplex laser atλ=222 nm

The results of an experimental investigation into lasing and spontaneous emission from Ne(He, Ar)-Kr-HCl are presented. Evidence has been gathered of the effect of the pumping power, preionization rate, pumping pulse duration, and composition and pressure of the gas mixture on the lasing characteristics under discharge pumping. KrCl* formation efficiency is shown to be nearly half as much as for XeCl*. The output energy was 0.65 J for ~60 ns laser pulse duration (FWHM), 2.5% efficiency based on the pumping power, and 0.65% efficiency based on the stored energy while for the 10 ns pulse duration, 2.7% efficiency based on the pumping power and 0.8% efficiency based on the stored energy the output energy was 0.15 J. Recommendations are made for development of KrCl lasers with maximum output parameters     

Efficient XeF(C→A) laser excited by acoaxial electron beam at intermediate pumping rates

Experiments carried out with an electron-beam apparatus that produced pump pulses with an intermediate pulse length of about 174 ns (FWHM) and a power-deposition rate on the order of 1 MW/cm³ are described. The authors present initial measurements with gas mixtures in which part of the Ar is replaced by Ne as a buffer gas. The lower stopping power of Ne can be compensated for by using a higher gas pressure because the system presented can be pressurized to a total gas pressure of 10 bar. It was found in earlier experiments with other excimers (ArF,KrF) that the variation of the buffer gas may have important effects on the optimum pressure regime total output energy, and kinetics. Useful information can be gained for discharge-excited systems, although the ionic channel dominates the electron-beam excitation kinetics     

Efficient E-beam excitation of XeCl

Efficient laser output at 308 nm has been obtained from XeCl in an Ne/Xe/HCl mixture at a pressure of 4 atm bye-beam excitation and bye-beam controlled discharge pumping. Maximum energy extraction is 7 J/1 fore-beam excitation and 9 J/1 for thee-beam controlled discharge. Efficiencies based on total energy deposited in the gas are approximately 4 percent. Similar results were obtained with KrF in the same device, indicating that undere-beam ore-beam controlled discharge excitation, XeCl may be as efficient as KrF.     

The importance of three-body processes to reaction kinetics atatmospheric pressures. III. Reactions of He2+ withselected atomic and molecular reactants

For pt.II see ibid., vol.22, p.47-50 (1986). Results are presented from studies of the reactions He₂⁺ with five species displaying a wide variation of molecular structures and polarizabilities: Ar, Xe, Ne, O₂, and CO₂. Measurements were made in the afterglows of preionized discharges into the reactant gas mixtures diluted in 1-6-atm pressures of helium. Effective rates of reaction were obtained that could be separated into contributions from bimolecular and termolecular channels. The latter generally dominated, showing no evidence of saturation up to 6 atm pressure of diluent. These results continue to confirm earlier reports that the initial capture step in the reaction is not limited by the Langevin rate as usually applied. Such super-Langevin rates appear to be a general phenomenon at high pressures, at least for the reactions of He ₂⁺. In the most extreme case examined, He₂ ⁺+CO₂, the effective rate of reaction contributed by all channels was found to exceed Langevin by a factor of five at 6-atm pressure of diluent     

Density measurements of excited components in a longitudinaldischarge excimer laser

Time-dependent particle number densities of the excited components (Xe^+*, He^*) in a longitudinal-discharge XeCl excimer laser have been measured by laser absorption probing with a CW dye laser. The densities are compared with those in transversal-discharge XeCl excimer lasers. The formation dynamics of the XeCl excimer molecules, excited atoms, and excited ions are discussed. The dependence of the particle number densities of the Xe^+* ions on the buffer gas pressure, the Xe gas pressure, and the HCl gas pressure is investigated     

Long-pulse N2UV lasers at 357.7, 380.5, and 405.9 nm in N2/Ar/Ne/He mixture

Using long-pulse electron-beam pumping, long-pulse laser emissions at 357.7, 380.5, and 405.9 nm have been observed in the second positive system of nitrogen with pulse durations of 150, 400, and 400 ns, respectively. Substantial improvements in laser performance were observed by adding excess Ne and He into N2+ Ar mixtures. Peak powers of 56, 44, and 66 kW/cm²have been obtained for the three wavelengths, respectively.     

Oscillator performance and energy extraction from a KrF laser pumped by a high-intensity relativistic electron beam

A laser cell with 21 of excitation volume was used to study the electron-beam pumped KrF laser system at excitation rates of 1.8- 7.0 MW/cm³. The system was optimized as an oscillator for various mixtures of Ar, Kr, and F2at total pressures of 1000 and 2500 torr. The resulting optimum conditions gave an intrinsic efficiency (laser energy out/electron-beam energy deposited) of 12 percent for the 1000 torr total pressure mixture with an output energy of 11 J/1. An efficiency of 10 percent with an output of 40 J/1 was obtained for the 2500 torr mixture. The system was then used as an amplifier to measure the extracted power as a function of input power for the two mixtures. The small-signal gain go, the nonsaturable absorption α, and the saturation intensity Iswere determined for the two mixtures. Analysis of the data gave g0= 16-18 percent/cm,alpha = 0.75-1.25percent/cm, and Is= 2 MW/cm²for the 1000 torr mixture and g0= 17-19 percent/cm,alpha = 1.0-1.5percent/cm, andI_{s} = 9MW/cm²for the 2500 torr mix.     

1.27μm atomic argon laser parameters in fission-fragment excitedHe/Ar and He/Ne/Ar gas mixtures

The authors examine the power efficiency of the fission-fragment-excited atomic argon laser operating on the 1.27-μm (3d'[3/2]₁-4'_p[3/2]₁) argon transition as a function of pump power, gas mixture, and pressure. The maximum measured power efficiency was 1.1±0.3% for a gas pressure of 1300 torr and a He/Ar ratio of 99.88/0.12. Neon addition to the He/Ar gas mixture increased both the energy deposited in the gas and the energy output without decreasing efficiency for a neon gas fraction of less than 0.5. Small-signal gain and saturation intensity are between 0.15-0.27%/cm and 25-200 W/cm² for pump rates of 7.5-30 W/cm ³ in He/Ar and He/Ne/Ar gas mixtures. The laser threshold as a function of total pressure and argon concentration is presented     

XeF laser performance for F2and NF3fuels

XeF laser performance has been investigated for F2versus NF3as the halogen donor (fuel). The experiments were all performed in 3 AMAGAT Ne/Xe/fuel mixtures at ambient temperature and a pump rate of 132 KW/cm³on a 1 me-beam pumped laser. The F2-based laser mixture has been shown to be recyclable, with no loss in laser output, while laser performance steadily degrades for NF2-fueled mixtures under repetitively pulsed conditions. Despite the fact that F3absorbs at the XeF wavelength, it has been demonstrated that under appropriately chosen conditions the XeF intrinsic efficiency is essentially the same (2.2 percent) for both F2and NF3fuels for deposited energy loadings up to at least 150 j/l. Absorption, gain, fuel burn-up, and fluorescence were also measured in order to better characterize the laser medium and to determine the major factors contributing to the efficiency.     

High average and high peak brightness slab laser

A high average and high peak brightness Nd:YAG MOPA laser system composed of a laser-diode-pumped Nd:YAG master oscillator, flash-lamp-pumped slab power amplifiers and a phase conjugated mirror was developed. The system demonstrates an average output power of 235 W at a repetition rate of 320 Hz and a peak power of 30 MW at a pulse duration of 24 ns with M²=1.5. Both an average brightness of 7×10⁹ W/cm²·sr and a peak brightness of 1×10¹⁵ W/cm2·sr are achieved simultaneously. The system design rules that we confirmed suggest that by replacing lamp pumping in the amplifier with laser-diode pumping, an average output power of ~1 kW can be obtained at ~1 kHz with a higher average brightness of ~3×10¹⁰ W/cm²·sr and a higher peak brightness of ~3×10¹⁵ W/cm²·sr     

Electrical characteristics of an E-beam controlled KrF*discharge

Plasma electrical characteristics have been measured as a function ofe-beam current density (JB) and fluorine concentration for Ar, Kr, and F2gas mixtures in order to identify the stable operating regime of KrF* laser interest. The data were obtained from a 120 cm³active volumee-beam controlled discharge laser. The optimum F2concentration was found to be 0.17 percent at JB= 17.9 A/cm². This mixture also gave the best laser extraction efficiency and consequently produced the highest laser output energy. The dissociative electron attachment rate constant in the laser mixture was determined from the discharge voltage and current measurements.     

Gain studies of electron beam excited XeF laser mixtures

Detailed optical gain measurements of electron beam pumped Ar/Xe/NF3and Ne/Xe/NF3laser mixtures for theB rightarrow Xand theC rightarrow Atransitions of XeF at 351 and 488 nm are reported using a direct laser probe and two different fluorescence techniques.     

Electron-beam pumped KrF laser extraction measurements for high Kr concentration gas mixtures

Energy extraction measurements are obtained with a 350 ns electron-beam pumped KrF laser (Ar diluent) at Kr concentrations from 4-99.6 percent. During the measurements, the F2number density is held constant at8.9 times 10^{16}cm^-3, and the average pump rate is maintained at ≈120 kW/cm³by adjusting the total pressure of the gas mixtures in order to compensate for the different electron stopping powers of Ar and Kr. For the 4, 10, and 99.6 percent Kr cases, total pressures are 1040, 1004, and 665 torr, respectively. Average output efficiencies in percent of 9.3 at 4 percent Kr, 11.2 at 10 percent Kr, and 9.2 at 99.6 percent Kr are obtained. Peak power efficiencies in percent of 9.6 at 4 percent Kr, 12.5 at 10 percent Kr, and 11.6 at 99.6 percent Kr are derived from the data. Our computer model predictions agree with the results.     

Experimental and modeling studies of a Brillouin amplifier

KrF laser-pumped backward Brillouin amplification of nanosecond pulses at 248 nm is investigated both experimentally and numerically. Gain and saturation of the amplifier system are studied for an SF₆ Brillouin medium at pressures of 5 to 15 atm and 24 ns pump pulses at an intensity of ≈9 MW/cm². The input Stokes intensity is varied from 0.001 to 1.0 MW/cm². Power gains of 20 are achieved at energy extraction efficiencies of 40%. Experimental results are compared to a time dependent numerical model of pulse amplification which incorporates arbitrary pump and Stokes pulse shapes and intensities. The effect of laser bandwidth is investigated in the model calculations in order to assess its influence on Brillouin amplification     

XeBr XeCl激光同时振荡的研究

本文报道了由ＨＣｌ／ＨＢｒ／Ｘｅ／Ｎｅ体系获得的ＸｅＢｒ与ＸｅＣｌ两种激光（２８２ｎｍ，３０８ｎｍ）同时振荡。对同时振荡的过程作了初步的分析，并在单独振荡的情况下研究了ＨＣｌ对ＸｅＢｒ激光能量及寿命的影响与ＨＢｒ对ＸｅＣｌ激光能量及寿命的影响。     

Efficiency characterization of vacuum ultraviolet molecularfluorine (F2) laser (157 nm) excited by an intense electricdischarge

Detailed experimental results of a discharge-excited high-pressure F₂ laser are compared with a model prediction. Special emphasis is placed on the output performance of the discharge-pumped F ₂ laser at extremely high excitation rates (10~35 MW/cm³ ) by using high-pressure laser mixtures up to 8 atm. The kinetics model predicts fractional contributions of excited F₂ formation channels, relaxation channels, and absorption channels together with the formation and extraction efficiencies at the experimental conditions. Although the only experimental quantity compared with the model prediction is laser output energy, it is enough to obtain a better understanding of major F₂ laser kinetics and key issues for improving the efficiency