气体对介质阻挡放电激发XeCl*辐射的影响

在气体配比和气压易控制的小尺寸气体混合腔中．通过对混合气体Cl2／Xe进行参量(配比、气压)范围调节．研究了不同气体配比、气压下介质阻挡放电激发准分子XeCl*的辐射特性。结果表明．在一定放电功率下．合适的气体配比和气压能产生峰值辐射。对于放电管在气体比例pc12／p1在I．5％-4％范围内，放电形貌及准分子XeCl*辐射的强度和光谱特征表现出明显的差异。同比条件下．混合气体He／Cl2／Xe中放电产生的准分子辐射强度弱于混合气体Cl2／Xc。     

Experimental verification of a zero-dimensional model of the kinetics of XeCl* discharges by XeCl*(B)-, XeCl*(C)-, and Xe2Cl*-density measurements

Absolutely calibrated emission spectroscopy has been used to determine the particle number densities of XeCl^*(B), XeCl^*(C), and Xe₂Cl^* in a small scale Ne/Xe/HCl discharge with well-defined current and voltage pulses for a wide range of parameters. The measured particle number densities could be reproduced quite well by numerical model calculations using the rate-coefficient values of Quiñones et al. [1] for the quenching of XeCl^*(B,C) by Ne, Xe, and 2Xe, but 3.0 × 10^–31 cm⁶/s for the formation of Xe₂Cl^* by (Ne + Xe)-quenching. For the electron quenching, we recommend a rate coefficient value of 3.2 × 10^–8 cm³/s. From the equilibrium ratio of the particle number densities of XeCl^*(C) and XeCl^*(B), the energy separation between these states has been estimated to be 72 ± 33 cm^–1 with the B state placed above the C state.     

Variable reflectivity unstable resonators for a long pulse XeCl excimer laser

The divergence of a long pulse, low gain XeCl excimer laser has been improved using confocal positive branch unstable resonators with variable reflectivity mirrors as outcouplers. With variable reflectivity unstable resonators, nearly diffraction limited beams are obtained. Variable reflectivity resonators lead to high brightness beams (9.1 10 W/(cm sr)). Different reflection profiles were studied with respect to their influence on the beam quality and the energy extraction.     

Spectroscopic investigation of the ionization kinetics in XeCl laser discharges by Xe* density measurements

Time and spatially resolved absorption measurements of Xe^* particle number densities performed at an X-ray preionized self-sustained XeCl^*-laser discharge were used to investigate the reaction kinetics of such discharges and to test the validity of the commonly-made assumption that they are fit well by spatially homogeneous numerical models. It turned out that the Xe^* density distribution over the discharge cross section remains homogeneous for less than 100 ns only. Comparing the experimental results of the homogeneous discharge phase with zero-dimensional model calculations, we conclude that induced emission modeled using two excited xenon levels must be taken into account for the quantitative interpretation of the absorption measurements. For the interpretation of the Xe 6s-6p absorption measurements even a multilevel model will be necessary. Further we conclude from the relative courses and the absolute values of the Xe^* particle number densities that realistic HCl kinetics should contain three vibrationally excited levels and stepwise excitation processes as proposed by Dem'yanov et al. [8].     

C-C转移放电泵浦XeCl准分子激光器能量沉积特性的分析

本文报道了一台使用UV自动预电离,C-C转移放电泵浦的XeCl准分子激光器,并且以激光器放电信号和输出激光信号的同时测量结果为依据,分析了激光器放电的能量沉积过程.可为设计同类型准分子激光器提供一些参考数据.     

Experimental verification of a zero-dimensional model of the kinetics of XeCl* discharges by Xe*-, Cl*-, Ne*-, and H*-density measurements

Absorption spectroscopic measurements of effective particle number densities of excited Xe, Ne, Cl, and H performed on a small scale discharge with well-defined current and voltage pulses are compared with the results of model calculations over a wide range of discharge parameters. The reaction kinetic pathways determining the ionization and dissociative attachment rates have been verified by the good agreement obtained during the quasi-steady-state phase of the discharge for Xe and H. To reproduce the rise times of the excited Xe particle number densities during the ignition phase, the electron collision excitation cross sections of ground state Xe published by Puech and Mizzi [1] had to be enhanced by about 25%. From the Ne measurements it is concluded that the electron collision excitation cross sections of ground state Ne published by Puech and Mizzi [1] may be too large near the threshold. Measurements of excited Cl particle number densities are unsuitable to check the attachment kinetics of HCl, because these densities are mainly determined by reactions not involving the formation of Cl^– ions.     

Development of a nanosecond oscillator–four pass amplifier XeCl laser system

This paper describes the development of a nanosecond oscillator–four pass amplifier XeCl laser system. A two times increase of the pulse peak power of the free running amplifier module has been experimentally demonstrated. The comparison with numerical results issued from a code describing the amplification of the oscillator beam in the active amplifier medium suggests further experimental improvements to optimize the energy extraction from the amplifier.     

308nmXeCl准分子激光泵浦猝灭式可调谐染料激光器研究

描述了获得准分子激光超脉冲的一种方法，理论上扼要地介绍了淬来式染料激光器产生超短脉冲激光的机理。实验上以香豆素４９８染料得到波长为４９６ｎｍ，脉宽１ｎｓ，能量１．１ｍＪ的染料激光。     

Vibrational relaxation of KrF* and XeCl* by rare gases

A steady-state, chemiluminescence technique has been used to measure effective rate constants for vibrational relaxation as a function of vibrational level for KrF^* in collisions with He, Ne, and Ar and XeCl^* with Ar. The effective rate constants reported include contributions to relaxation due to intersystem crossing between theB andC states, in addition to direct relaxation within theB state. The relevance of these results to the understanding of previous measurements in KrF and XeCl lasers is discussed.     

UV Radiation of Low Pressure XeCl* and KrCl* Glow Discharges

The positive column of low pressure DC glow discharges in Xe/Cl₂ and Kr/Cl₂ gas mixtures has been investigated with respect to its UV radiation power and radiative efficiency for a wide range of parameters (total gas pressure: 1–30 mbar, current 10–30 mA, partial pressure of Cl₂: 1–33%). Also the radial distribution of the particle number densities of XeCl* (B) and KrCl* (B) has been determined by absolutely calibrated emission spectroscopy. Optimum UV (190–350 nm) output and efficiency has been found in gas mixtures with a relative Cl₂ partial pressure of 2–3% and total gas pressure of 12–18 mbar. At these parameters, the UV radiation power per column length is greater than 40 Watt/m with a radiative efficiency of 15–18%. These discharges could be used for UV induced photochemical processes.     

Optimization of a Dielectric Barrier Discharge for Pulsed UV Emission of XeCl at 308 nm

A pulsed dielectric barrier discharge (DBD) has been investigated in a wide range of experimental conditions with the purpose of optimization for XeCl excimer radiation. For that the following operation parameters had been considered: four different lamps of coaxial geometry with gas gaps in the range of 1.3 ‐ 6.5 mm; gas mixtures of xenon and chlorine containing admixtures of 1%, 2% and 4% Cl₂ at total filling pressures between 5 mbar and 600 mbar; voltage rise times of 20 ‐ 50 ns and voltage amplitudes of up to 12 kV. A maximum radiation pulse energy of 1.8 µ J has been detected at 310 ± 10 nm with an estimated radiation decay by three orders of magnitude within about 5 µ s. It was shown that the minimization of the voltage rise time is essential for enhancing the radiation pulse energy. Furthermore a correlation between the discharge geometry and the optimum pressure for maximum radiation output was observed. The decay characteristics of the excimer emission provides evidence of the harpoon reaction being the main channel of XeCl formation under our operation conditions (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Experimental verification of a zero-dimensional model of the ionization kinetics of XeCl discharges

An improved 0-dimensional model for XeCl high-pressure glow discharges is presented. Calculated discharge voltages are compared with precise measurements at a small, very homogeneous discharge. Excellent agreement in a wide parameter field demonstrates that this model may serve as a reference for simpler models describing the ionization kinetics.     

Interferometric measurement of two-dimensional Xe and electron density distributions in XeCl laser discharges

A near-infrared, interferometric measurement of the density distribution of the electrons and excited xenon atoms has been performed at two discharge pumped, X-ray preionized XeCl lasers. The experimental results of one of these lasers are in good agreement with model calculations for the homogeneous phase. The electrons and excited states of xenon show a different behaviour in their spatial distributions at both lasers. In addition a region of inhomogeneities, which is identified as the hot-spot region, is been found near the cathode. Filamentation of the discharge can occur after a short time. The dimension of the hot-spot region depends on the preionization delay time. The same holds for the filamentation process, which in addition depends on the HCl partial pressure.     

A Miniaturized XeCl Dielectric Barrier Discharge as a Source of Short Lived,Fast Decaying UV Radiation

A dielectric barrier discharge (DBD) of coaxial geometry has been examined as source of intensive, short‐lived UV radiation. A binary gas mixture consisting of 98% Xe + 2% Cl₂ and a ternary composition of 96% Ne + 6% Xe + 0.2% HCl were investigated in the pressure range between 10 and 750 mbar. The discharge was excited by unipolar high voltage square pulses with amplitudes of 3 to 7 kV at a repetition rate of 100 Hz. UV radiation intensity is increased by combining 5 square pulses with a period of 1 μs each in one train (burst). Radiation decay on three orders of magnitude within 10 μs was obtained for both gas mixtures in burst mode. Maximum energy of the light pulse was the same for both gas mixtures and estimated as 40 nJ. It is shown that the optimum gas pressure for highest radiation intensity depends not only on gas composition but also on applied voltage and number of pulses in the train. A variation of the spectral band shape of XeCl emission during the pulse is detected (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Non-equilibrium vibrational,attachment and dissociation kinetics of HCl in XeCl selfsustained laser discharges

The vibrational kinetics of HCl in a Ne-buffered XeCl selfsustained laser discharge is self-consistently calculated by coupling the vibrational master equation with the chemical one, the Boltzmann equation for electron transport and the circuit equations. The results show the limits of the classical simplified schemes of HCl vibrational kinetics used in the literature. Problems connected with the neglection of HCl depletion instabilities in the calculations are discussed using a parallel resistor network model.     

Spatially Homogeneous Modelling of a Stabilized XeCl* Laser Discharge

Recently an improved technique to create a stable and homogeneous discharge for pumping excimer laser plasmas has been proposed in [1]. This technique is based on the additional use of a stabilizing low-current preliminary discharge. For the study of such laser discharges a self-consistent spatially homogeneous model with the inclusion of the time-dependent Boltzmann equation for the electrons, of the rate equation system arising from the heavy particle and photon kinetics and of the electrical circuit equations has been employed. A brief presentation of important features of the comprehensive model is given. An iterative procedure to solve self-consistently the system of kinetic, rate and circuit equations has been generalized and applied to discharge conditions where a dominant electron-electron interaction occurs. Model calculations have been performed for typical XeCl* laser plasmas which operate according to the improved discharge technique. On this basis a detailed analysis of main features of this laser discharge is given and the impact of various parameters on significant characteristics of the discharge is calculated and discussed.     

The homogeneity of a stabilized discharge-pumped XeCl* laser

* laser arrangement. The special pumping technique of this laser discharge is based on the additional use of a stabilizing low-current preliminary discharge. The model takes into account the time-dependent electron Boltzmann equation including electron–electron interaction for the determination of the electron kinetics, an extensive reaction kinetics involving various heavy particles and photons, and the relevant electrical circuit equations. The study has shown that density perturbations of preionization electrons lead to the inhomogeneity of the discharge plasma and the laser output. Furthermore, the impact of the spatial distribution of preionization electrons, of the HCl portion of the gas mixture, and of a low-current preliminary discharge for the discharge operation is discussed. Received: 10 September 1996/Revised version: 21 July 1997     

Evaluation of probe lasers employed in optical diagnostics for phase transformation of thin films during excimer laser crystallization

The stability and reliability of probe laser is an important factor affecting the inspection of the phase transformation process of Si thin films during excimer laser crystallization using in-situ time-resolved optical measurements. The changes in 2D intensity profile, peak power density, and beam wander of the commonly used helium–neon (He–Ne) and diode laser are investigated experimentally. It is found that the peak power density of He–Ne laser is higher than that of diode laser, while the total power of He–Ne laser is lower than that of diode laser. Although the instability in the peak power density of He–Ne laser will increase with increasing the operation time, the beam stability of He–Ne laser is better than that of diode laser. For long-time operation (>24 h) of optical measurements, the diode laser is a good candidate of probe laser. Conversely, the diode laser is suitable for the short-time operation (<24 h) of optical measurements because the beam-wander is higher than that of He–Ne laser.     

Comparison of characteristics of an x-ray preionized XeCl laser, pumped by water transmission line and low inductance capacitor bank

With a high uniformity of x-ray preionization, a long pulse duration and a high specific energy (9 J l^-1), an XeCl excimer laser output has been obtained by using a compact low inductance capacitor bank as the laser excitation circuit. The superior features of the low inductance capacitor bank (LICB) compared to the water transmission line (WTL) are attractive for repetitively pulsed XeCl excimer lasers.     

Verification of a XeCl* laser model by measurement of the plasma conductivity

Measurements of current, voltage, and laser emission of an X-ray preionized selfsustained XeCl^* laser discharge using Ne:Xe:HCl gas mixtures are compared with predictions of spatially homogeneous model calculations. As a prerequisite an accurate and detailed model of the electrical circuit is developed. For current and voltage measurements electro-optical methods are used. Corrections to the measurements and the reliability of the final data are discussed in detail. Using collision cross sections from the recent literature and stepwise vibrational excitation of HCl up tov=3 reproduces the electrical conductivities measured in a large field of parameters. The reliability and numerical stability of the model calculations depend on the way in which the e-HCl collision terms of the Boltzmann equation and the e-HCl collision rates are evaluated. The predicted total laser pulse energies are too small, but the shape and timing of the pulse correspond to the experimental values.