INFLUENCE OF VIBRATIONAL KINETICS OF HCL ON THE GROWTH OF MICROINSTABILITIES AND THE CHARACTERISTICS OF AN ELECTRIC-DISCHARGE XECL LASER UNDER INHOMOGENEOUS PREIONISATION CONDITIONS

A one-dimensional model of an electric-discharge XeCl laser was used i n an investigation of the growth of microinstabilities induced by pert urbations both of the initial electron density and of the electric fie ld under homogeneous field and inhomogeneous preionisation conditions. A mechanism of attachment - vibrational stability of a discharge in m ixtures containing HCl molecules was proposed and investigated. Ie was found that dissociative attachment to vibrationally excited HCl molec ules delays considerably the growth of microinstabilities and contract ion in a self-sustained discharge. This accounts for the well-known ex perimental observation that a discharge in a mixture containing HCl is more stable than a discharge in a mixture containing F-2. A full desc ription of this effect could be given in the one-dimensional approxima tion only when one effective level was replaced by four vibrational le vels (v = 0-3). A study was made of the influence of microinstabilitie s on the energy characteristics of the laser. Critical perturbations o f the electric field, which suppressed lasing, amounted to similar to 0.15% and, similar to 1% for the KrF and XeCl laser models. These valu es were nearly two orders of magnitude less than the critical microper turbations of the electron density (similar to 5% and similar to 100%, respectively). In the case of mixtures containing HCl there were rang es of perturbations of the initial electron density and of the electri c field (up to 20% and 0.2%, respectively) in which the discharge was stable. However, there were in practice no such ranges for mixtures co ntaining F-2. The experimental results obtained for a 10-litre XeCl la ser were explained when the influence of microinstabilities and contra ction of the discharge current on the operational characteristics of t he laser was taken into account.