Simple model of halogen depletion in XeCl discharge pumped lasers

Abstract

The aim of this work is to study the development of the macroscopic non-uniformity of the electron density of high pressure discharge for excimer lasers and eventually its propagation because of the medium kinetics phenomena. This study is executed using a transverse mono-dimensional model, in which the plasma is represented by a set of resistances in parallel. The time variations of the electron density in each plasma element are obtained by solving a set of ordinary differential equations describing the plasma kinetics and external circuit. The use of the present model allows a good comprehension of the halogen depletion phenomena, which is the principal cause of laser operation premature termination and allows a simple study of a large-scale non-uniformity in preionization density and its effects on plasma electrical and chemical properties. The results obtained indicate clearly that about 50% of halogen is consumed at the end of the pulse.

Theoretical investigation of streamer characteristics in Ne–Xe–HCl pulsed high-pressure discharges

“…The balance of electron production and loss, in preionized discharges for excimer lamps and lasers, is strongly influenced by the halogen concentration in the mixture due to the dominant electron loss process, which is the dissociative attachment of electrons to halogen molecule [5,10,14,15,18,[30][31][32][33][34]. To know the effect of the gas mixture composition on the streamer's characteristics, we performed calculations for five concentrations of halogen HCl: 0.044, 0.13, 0.26, 0.36, and 0.5%.…”

“…Despite these remarkable proprieties, XeCl laser suffers from some limitations; when sustained by highpressure discharges, it is subject to instabilities. The instability mechanism is assumed to result from the following circumstances: (a) streamers can appear near each electrode and lead to arcing during the formation of the plasma [14]; (b) once the plasma is formed, chemical kinetic instabilities can lead to plasma filamentation due to volume instability known as halogen depletion instability [15][16][17][18]. Experimental investigations of XeCl lasers have proved that the instabilities occur before the end of laser emission [19][20][21].…”

Theoretical study of the pre-ionized XeCl laser

“…In this section, we present some general results for the case of a uniform plasma. The scheme of the discharge model and external circuit are also shown in [6,7].…”

“…Laser output energies of greater than 10 J were obtained in largeaperture systems using this discharge scheme [4,5]. The present work is, therefore, a logical extension of our previous works [6,7]. Here, we focus on the computation of the electron reaction rate coefficients, breakdown delay time and impulse duration, NeXe + species concentration, and discharge current.…”

“…The solution of the KE leads to the determination of the electron density also required for the resistance calculation. The set of reactions and their rate coefficients used in the present calculations of the characteristics of the Ne-Xe-HCl mixture for laser discharge are reported in our previous works [6,7].…”