Analysis of a spark-preionized large-volume XeF and KrF discharge laser

A uv-preionized discharge-excited XeF and KrF laser has been operated with various fluorine donors. Results of a parametric study of laser performance as a function of gas composition, total pressure, electrode voltage, and energy loading are presented. The effects of easily ionizable seed gases were also studied. Results include demonstration of highest energy per pulse (0.18 J for XeF and 0.30 J for KrF) and longest lasing pulse (70 ns) reported for any similar device. Ion recombination reactions are suggested as the major processes for XeF¹ and KrF¹ excimer formation.     

Influence of multi-photon ionization of Xe on a XeF discharge induced by KrF laser irradiation

Excimer laser preionization induced by an external laser was investigated for XeF excimer laser discharge induced by a KrF laser, paying attention to the ionized species in the gas. Enhancement of amplified spontaneous emission (ASE) was observed for XeF gas discharge preionized by a KrF laser with and without its irradiation. In contrast, no ASE enhancement was observed for KrF gas discharge with KrF laser preionization. ASE enhancement was larger for the longer wavelength, which was close to the two-photon resonance of the Xe atom, when tunable KrF laser irradiation was used. These results indicate that multi-photon ionization of Xe atoms supplied the initial electrons to the laser-induced preionization.     

Small signal gain measurement of KrF and XeF laser amplifiers

Effective amplification has been found in the double discharge TEA amplifier of KrF. The small signal gains measured in KrF and XeF are 2.3%/cm and 1.0%/cm respectively.     

Dynamic optical distortion in a KrF discharge amplifier

The dynamic optical distortion in a KrF amplifier was measured using a Sagnac interferometer. Maximum wavefront aberration at 249 nm was /3 using helium buffer gas, indicating the potential for transmitted beams very close to the diffraction limit.     

Compact and efficient kinetically enhanced copper-vapor lasers of high (100-W) average power

We report on severalfold increases in the output power of kinetically enhanced copper-vapor lasers operating in a regime of high specific input power and reduced tube insulation. Three laser tubes, of length 1 m and bore diameters 17.5, 25, and 32 mm, were investigated at constant input power. Output power of 104 W at 1.4% wall-plug efficiency was obtained for the largest tube. When the bore diameter was decreased to 17.5 mm, the output power and efficiency remained high (90 W at 1.0% efficiency), whereas the specific output power increased threefold. The output powers were as much as fivefold higher than those of previous small-scale (i.e., <25-mm-diameter) copper lasers of any type.     

N2 production in e-beam pumped XeF lasers containing NF3

The rate of build-up of N₂ was measured in electron-beam-irradiated Ne/Xe/NF₃ mixtures using mass spectroscopy. the amount of N₂ produced indicated that N₂ is the primary nitrogen bearing stable species created in these mixtures. The rate constant for dissociative electron attachment to the NF₂ fragments produced in electron attachment to NF₃ is estimated to be 5×10^–8 cm³/s in order to explain the amount of N₂ produced.This work was supported by DARPA under Contract No. DAA01-82-C-A125 and monitored by MICOM     

Measurements of some reaction rates of importance in KrF lasers

A flowing afterglow method has been used to study a number of reactions of importance in KrF lasers using NF₃ as the fluorine donor. Total rate constants are reported for Kr^*(³ P ₂)+NF₃ and Kr⁺+NF₃. The thermal energy attachment coefficient has been measured for NF₃ and the cross section for the electron excitation process Kr^*(³ P ₂) +e→Kr^*(³ P ₁)+e has been estimated. The relevance of these results to discharge pumped KrF lasers is discussed.     

Theoretical and experimental study of KrF fluorescence in amultimicrosecond longitudinal discharge

Multimicrosecond KrF (B→X) fluorescence characteristics were measured using KrF laser mixtures pumped by a low-pressure longitudinal stable discharge to make clear the mechanism of the premature termination of the KrF laser. Using the experimental setup with a seven-stage pulse-forming network (PFN), a KrF fluorescence pulse with a pulse duration of 2.0 μs was obtained at a total pressure of 75 torr, whose gas mixture was F₂/Kr/He=0.1/7.5/92.4(%). The pulse width (FWHM) of KrF fluorescence was decreased from 1400 ns to 500 ns with increasing F₂ concentration from 0.1 to 1.5%. The theoretical analysis made it clear that this termination mechanism was strongly due to the KrF fluorescence kinetics     

Space discharge and gas lasers

The main processes in TE lasers are analyzed. Significant attention is given to models for the formation of a homogeneous plasma column and space charge. The reasons for channel growth at the stage of increasing voltage are demonstrated. A method to increase the energy input to the gas using a cathode with high emission properties is proposed. It is demonstrated that, in TEA CO₂ lasers, the limiting deposited and radiated energy densities may amount to 1.35 and 0.085 J/cm³, respectively. Experimental results show that the duration of radiation can be increased using a variation in the composition and pressure of the active medium, the sectionalization of the active medium and the sequential excitation of the sections, and the excitation of the medium with a pulse train at a small (about 10⁷ s) pulse duration and an interpulse interval of about 10⁻⁵ s. Original Text ? Astro, Ltd., 2006.     

Efficient multi and single line atomic fluorine lasers

Intense multi- and single-line laser operation is reported from semiconductively preionised atomic fluorine lasers employing an optimised capacitor transfer excitation circuitry. The performance and spectral characteristics of these lasers are discussed and compared to the characteristics of previously described atomic fluorine lasers. The efficiency of one of these lasers described, at optimum conditions, is reaching a value as high as 0.14%. To the best of our knowledge, this is the highest efficiency reported up date, for an atomic fluorine laser.     

Operation of KrF and ArF tunable excimer lasers without Cassegrain optics

A commercial tunable excimer laser consists of an oscillator-amplifier combination. The oscillator produces high-quality light that is sent to the amplifier and is distributed throughout the amplifier cavity via Cassegrain optics. We describe here two alternative approaches, a single-pass configuration for use with KrF and a triple-pass configuration with ArF, both of which do away with the Cassegrain optics. In each approach, the beam energy is the same as with Cassegrain optics. For KrF, the changes provide better locking, a higher degree of linear polarization, and a better spatial beam homogeneity, but a poorer beam divergence. For ArF, there is also better beam homogeneity, but the locking efficiency and divergence are not as good as with Cassegrain optics.     

The bi-directional amplifier in the constant intensity approximation and its application to KrF lasers

Bi-directional and folded laser amplifiers are analysed in the constant intensity approximation. Simple analytical expressions are developed for gain, output intensity and extraction efficiency. The analysis is applied to electron-beam pumped KrF lasers and expressions for saturation intensity, small-signal gain coefficient and intrinsic efficiency in terms of gas composition and pump power per unit volume are given. The problem of fluorine burn-up in KrF lasers is discussed. Under certain conditions the analysis is shown to be equally applicable to oscillators and comparison is made with previous experimental results and computer code predictions.     

State of and prospects for XeF(C−A) optically pumped lasers

Experimental and theoretical results are presented on an XeF(C?A) blue-green laser driven by 5-kJ energy. The laser was pumped by a ferrite-induced discharge of 90 cm in length. The output energy of 0.22 J was obtained with a plane-parallel resonator. A program to simulate laser operation has been developed. Numerical results for a wide range of conditions are compared with experiments performed by us and by other authors. It is found that intracavity refractive losses limit laser operation for XeF pressures above 3 torr. The laser efficiency strongly depends on the discharge-to-cavity length ratio. Possible ways to increase the laser power and efficiency are discussed.     

Research on chemical and discharge oxygen-iodine lasers

Novel methods and device configurations for singlet oxygen and atomic iodine generation were proposed and investigated for operation of the chemical or discharge oxygen-iodine lasers (COIL/DOIL). A chemical centrifugal spray generator of singlet oxygen was developed, based on the conventional chlorine-basic hydrogen peroxide chemistry. Results of theoretical and experimental investigation of the generator parameters are presented and compared with parameters of other generator types. A design of experimental device for singlet oxygen generation by means of the hybrid DC arc and RF plasma jet is presented. An alternative method of atomic iodine generation by a radiofrequency discharge decomposition of iodine compounds like CH₃I or CF₃I is described employing advanced experimental configuration. Some representative experimental results of this investigation are presented.     

Excimer ArF/XeF lasers providing high-power stimulated radiation in Ar/Xe and F lines

Lasing in atomic lines of noble gases and fluorine, prior to excimer radiation, was observed in an electric discharge ArF/XeF excimer laser. Some Ar/Xe lines end at metastable levels, which are very important for the formation of ArF/XeF excimer molecules. Five new lasing lines of atomic fluorine have been obtained. Consideration is given to the use of lasing in atomic and molecular lines, that occurs in one burst, in investigations of the excitation kinetics of excimer states under the conditions of a high-pressure electric discharge.     

Compact, highly efficient ytterbium doped bismuthate glass waveguide laser

Laser slope efficiencies close to the quantum defect limit and in excess of 78% have been obtained from an ultrafast laser inscribed buried channel waveguide fabricated in a ytterbium-doped bismuthate glass. The simultaneous achievement of low propagation losses and preservation of the fluorescence properties of ytterbium ions is the basis of the outstanding laser performance.     

Compact, efficient 344-MHz repetition-rate femtosecond optical parametric oscillator

We describe configurations of a novel synchronously pumped femtosecond optical parametric oscillator based on the crystal RbTiOAsO(4) and operating with a signal-pulse-repetition frequency as high as 344 MHz. Average signal powers as high as 600 mW and pulse durations of 78 fs are demonstrated at a wavelength of 1.25 microm, and a characterization of the signal output using frequency-resolved optical gating implies asymmetric near-sech(2)(t) intensity-profile pulses with significant amounts of spectral cubic phase.     

毛细管放电Z箍缩等离子体X射线激光

毛细管放电Z箍缩等离子体软X射线激光器近几年发展非常迅速，已经获得了在46．9nm的波长上近毫焦量级的激光输出，重复频率达到了4Hz．利用这种软X射线激光在等离子诊断、物质烧熔等方面已开展了初步的应用实验研究．文章介绍了毛细管放电泵浦的两种物理机制，阐述了类氖氩离子2p^53p^1S0-2p^53s^1P1能级间粒子数反转的形成及毛细管放电等离子体柱的演变过程．深入理解这些物理过程，对发展毛细管放电软X射线激光将起到积极作用。     

DC discharge characteristics and fluorine atom yield in NF_3/He

DC discharge characteristics of NF3/He have been investigated experimentally under different experimental conditions, for example, different electrode materials, separations, flow rates of the gas NF3 or He, and series resistances. The optimum discharge parameters and the fluorine atom yield from the DC discharge of NF3 /He as function of load power are studied experimentally.