Discharge XeCl Laser Research Articles

High-power gas-discharge excimer ArF, KrCl, KrF, and XeCl lasers on buffer-gas free gas mixtures

Results of experimental studies of the gas mixture (laser active medium) effect on the lasing energy and overall efficiency of excimer discharge ArF (193 nm), KrCl (222 nm) KrF (248 nm), and XeCl (308 nm) lasers operating in buffer-free gas mixtures are presented. The optimal (in terms of maximum radiation energy) ratios of the gas components of the excimer laser active media are found, at which efficient operation is achieved with a sufficiently high power of the laser radiation. It is confirmed experimentally that for the rare gas halide discharge pumped excimer lasers the presence of a buffer gas in the active medium is not required for efficient laser operation. For example, in two-component excimer laser gas mixtures, containing working rare and halogen-containing gases, laser pulse energy of up to 170 mJ and high pulsed power of laser radiation of up to 24 MW have been attained for the first time for pulsed gas-discharge excimer lasers operating on electronic transitions at excimer ArF*, KrCl*, KrF*, and XeCl* molecules pumped by a transverse electric volume discharge of a low-pressure buffer-free gas mixture. A overall efficiency maximum of up to 0.8% was experimentally attained for binary gas mixture of KrF and XeCl lasers.

Positive streamer formation in cathode region of pulsed high-pressure discharges for transversely excited atmosphere laser applications

A two-dimensional model of a high-pressure cathode region with nonuniform secondary electron emission has been used for conditions close to those used in pulsed discharge XeCl lasers. To simulate processes leading to a cathode spot formation, an inhomogeneity in the cathode electron emission was introduced by varying the electron emission in a 100 μm-radius cathode surface region. The results obtained indicate that the inhomogeneous cathode emission can induce an instability in the cathode-faced surface of the bulk discharge plasma leading to the development of a cathode-directed streamer inside of the cathode region.

Spontaneous and stimulated emission spectra for 124Xe35Cl molecules

Abstract. The influence of the isotopic composition of active medium on a lasing spectrum of a XeCl laser has been investigated. Spectra of spontaneous and stimulated emissions for monoisotopic 124 Xe 35 Cl molecules were measured. The frequencies in lasing spectrum were determined. The frequencies of vibrational edging in the luminescence spectra of the molecule 124 Xe 35 Cl were also measured. We showed that varying the isotopic composition of the active medium one can get the lasing on frequencies different from the lasing ones in the natural XeCl laser. Keywords: excimer laser, isotopic composition, emission spectra, fine structure. Manuscript received 17.03.05; accepted for publication 18.05.05. 1. Introduction The electric discharge XeCl laser is one of the most powerful sources of coherent UV radiation now. This laser has wide applications for different scientific and technological branches. Many applications need for a narrow spectrum, whereas the XeCl laser spectrum is quite wide. It is well known that, under common lasing conditions and if there are no additional selecting elements, there are four electron-vibrational transitions: 0-0, 0-1, 0-2, and 0-3 in the vicinity of 308 nm. Different schemes were used for narrowing the lasing spectrum. Some papers reported that, under the low pressure of a working medium (0.3–0.5 atm), there is a line structure caused by rotation of molecules [1, 2]. While the frequency is tuned in a laser with the selective resonator, this structure becomes apparent at the high pressure (2-3 atm) [3], which makes the tuning discrete in the tuning range. The identification of the rotational spectrum of the XeCl laser has to be performed with taking into account the great number of overlapping lines from different rotational branches. One of the ways for simplification of the spectrum structure for its study is usage of mixtures enriched with isotopes [4]. Furthermore, usage of a mixture enriched by isotope, the concentration of which in the natural mixture is low, makes it possible to obtain new lasing lines. This paper shows spectra of luminescence and lasing for molecules

Effect of the degree of preionisation of a gas on the homogeneity of a volume discharge and generation of radiation in a wide-aperture XeCl-laser

The results of investigation of an electric discharge XeCl laser with active region apertures 8 × 11, 10 × 15, and 15 × 15 cm are presented. The preionisation of the Ne — Xe — HCl working mixture was performed by soft X-rays and a low-current electron beam, which provided the initial concentration n0 of electrons in the gas from 106 to 2 × 1013 cm-3. For n0 < 1012 cm-3, the homogeneity of the initial electron concentration and of an electric field in the discharge gap have a considerable effect on the homogeneity of the volume discharge and output characteristics of the laser. For n0 ≥ 1012 cm-3, a homogeneous volume discharge is ignited and is stable if the inhomogeneity of the electric field in the discharge gap does not exceed 10%. A storage capacitor charged to double the voltage of the quasi-stationary discharge operation is sufficient for discharge formation. It is shown that an improvement of the volume discharge homogeneity and a decrease in the size of the discharge chamber make it possible to increase the efficiency of a wide-aperture XeCl laser.

Chemical instabilities in the XeCl laser discharge: a stochastic approach

A simple stochastic model for the electron kinetics in Ne/Xe/HCl discharges for XeCl lasers is proposed in order to investigate the non-equilibrium fluctuations of the electron density. Critical fluctuations are observed for a discharge which is controlled by electron attachment to molecules, but not for a recombination-controlled discharge. A connection is proposed between this mechanism and the observed rapid spoiling of the optical quality of the XeCl laser plasma on increasing the HCl mole fraction in the discharge mixture.

Theoretical studies on microscopic and macroscopic nonuniformities in electric-discharge-excited XeCl lasers

The satbilit r of the pumping discharge for XeCI (Ne/Xe/HCI) lasers is investigated by using different one-dimensional models, considering both bulk discharge instabilities and filamentary ones. It is found that the bulk stability in a XeCl laser discharge can he improved, under certain conditions, due to the vihrational excitation of HCl molecules: this effect is studied by using different models for the HCl vihrational kinetics. It is established that the very short instability time found in experiments cannot he explained as a result of hulk instability of the discharge. On the other hand, a satisfactory comparison with experiments can he obtained by adding to the model a simplified microinstability which develops in the discharge.

Effect of electrode processes on the spatial uniformity of the XeCl laser discharge

The effect of electrode processes on the spatial uniformity of a self-sustained XeCl laser discharge has been experimentally studied. It has been shown that the longitudinal discharge structure, much as the classical one, is formed towards the end of the pre-breakdown stage. The primary disturbances of the uniform discharge structure have been observed during the formation stage at a current density of about 1-10 A cm-2. It was supposed that non-local effects play a part in discharge filamentation. The effect of the rate of increase of current on the development of the discharge instabilities has been revealed.

A new mode to excite a gas-discharge XeCl laser

The charge mode is a new mode to excite a discharge XeCl laser based on the dynamics of a spiker-sustainer circuit with a magnetic pulse compressor. The breakdown voltage is higher than in any other mode, due to a very fast rise time. The higher breakdown voltage provides a wider discharge and we found that more energy can be deposited before discharge instabilities terminate the optical output.

Simplified and complex modeling of self-sustained discharge-pumped, Ne-buffered XeCl laser kinetics

Two simple kinetic models of a Ne-buffered XeCl laser discharge are presented based on different simplifications of the chemical kinetics of a complex model that recently appeared in the literature. When applied to the study of a small-volume XeCl laser, the results of both simple and complex models are in satisfactory agreement with the experiments. Shifting to a larger-volume laser, both models show problems due to loss of stability of the discharge. A one-dimensional modelling is performed, and it is found that different assumptions on the kinetics of the NeXe+ ion in the discharge lead to completely different results as regards the effect of a preionization-triggered instability.

Compact discharge XeCl laser with an output energy ∼ 1 J and a pulse length of 100–300 ns

The LIDA-D compact discharge XeCl laser is described. The length of output pulse is shown to be determined by the capacitance of the intermediate energy storage bank. Pulses 100–300 ns long have been produced at an output energy above 1 J.

Self-consistent modelling of X-ray preionized XeCl-laser discharges

In this theoretical work a 0-D model for a self-sustained X-ray preionized XeCl-laser discharge is presented. The model is self-consistent in the sense that it simultaneously solves, contrarily to the usual decoupling procedure, the Boltzmann equation for electrons, the kinetic equations for excited and ionic species, the equations for the electrical circuit and the laser photon density. It includes a rather complete kinetics of HCl(v) vibrational excitation, dissociation and dissociative attachment. The influence of electron collisions with excited species and of e-e Coulomb collisions on the plasma parameters and transport coefficients is discussed. Some evidence of the non-stationary equilibrium between the electron distribution and the reduced electric field E/N is given. Results of the model are compared with experimental ones corresponding to a XeCl-laser discharge driven by a L-C inversion circuit. The model predicts well the main trends for the variation of the laser energy in a large range of experimental conditions. The discrepancy between experiment and model for absolute values of the laser energy is discussed.

Active-medium inhomogeneity and beam divergence of the electric discharge XeCl laser

Active-medium inhomogeneity and beam divergence of the electric discharge XeCl laser

Simulation studies of the prepulse-main-pulse XeCl discharge lasers with magnetic switching

A self-consistent model of a self-sustained discharge XeCl laser (Ne/Xe/HCl mixture) with prepulse-mainpulse excitation and magnetic switching which leads to high efficiency operation is described. The validity of the model is confirmed by comparing the results of the calculations with the measured time dependences of discharge voltage, current and lasing pulse for different operation modes as well as by comparing the results with the dependences of the laser output energy and efficiency on the charging voltage and capacitance of the pulse forming network for two different laser heads. The numerical evaluation has shown that our developed laser system operates under optimum conditions.

Space and time resolved discharge evolution of a large volume X-ray triggered XeCl laser system

The spatial distribution and the temporal development of the net gain have been measured in a ten liter active volume switchless discharge XeCl laser. The experimental results are compared with both zero-dimensional and two-dimensional kinetic code predictions. The comparison between the results of the kinetic codes and of some measurements relevant to the time-dependent discharge homogeneity allows a deeper insight into the influence of the streamer evolution on the discharge characteristics.

Some design limitations for large-aperture high-energy per pulse excimer lasers

Some limitation problems for gas discharge excimer lasers, when scaled to a high pulsed energy output with high repetition rate are discussed. As an example, we present some experimental results obtained with an X-ray preionized (10×10×100) cm3 active volume, low-repetition-rate-operated gas discharge XeCl laser system.

Small volume long pulse X-ray preionized XeCl laser with double discharge and fast ferrite magnetic switch

A long pulse, high efficiency X-ray preionized discharge XeCl laser has been obtained with a Ne/Xe/HCl mixture at 2.3 atm pressure in a 50 cm 3 active volume, for a 25 cm gain length, by combining double discharge technique (spiker/sustainer) with a new fast ferrite magnetic switch. An efficiency of 3%, with 120mJ extracted optical energy in a 140 ns (fwhm) laser pulse length, has been demonstrated.

Optical cavity design for long pulse excimer lasers

The design and performance of various optical resonator cavities are described for a 1-J XeCl discharge laser with a 200-ns FWHM optical pulse. Advantages inherent in many cavity round trips for efficiently controlling linewidth, spatial coherence, and polarization are indicated.

Theoretical simulation of spatial-time characteristics of a discharge XeCl excimer laser active medium

A model of a discharge XeCl laser with one-dimensional spatial discharge description is considered. The densities of the components of the laser active medium and the lasing pulse are modelled in time and space in the direction transverse to the electric force lines. The results of the calculations of the laser plasma components and the lasing pulse spatial-time dynamics, as well as of discharge current and voltage, are compared with the measured ones. The influence of the electric field and pre-ionisation inhomogeneity on the spatial distributions of the components of the XeCl laser active medium is considered.

High-efficiency operation of a gas discharge XeCl laser using a magnetically induced resonant voltage overshoot circuit

An electrical to optical efficiency of 5% has been demonstrated in an x-ray preionized XeCl discharge laser using an improved prepulse-mainpulse circuit, based on resonant charging of the peaking capacitor. In contrast to known prepulse-mainpulse circuits, the new scheme has no time delay between prepulse and mainpulse nor a voltage reversal on the electrodes. We present three possible configurations of the scheme and one of them has been realized for demonstrating its high-efficiency capabilities.

Time-dependent Boltzmann equation in a self-sustained discharge XeCl laser: Influence of electron-electron and superelastic collisions

Electron energy distribution functions (EEDF) in a XeCl laser have been obtained by solving the time-dependent Boltzmann equation coupled to the circuit equations, plasmachemistry, and photon kinetics. The results show that in some zones of temporal evolution, EEDF does not instantaneously follow the alteration of electric field. Moreover, electron-electron and superelastic collisions play a non-negligible role in affecting EEDF and related quantities.