Influence of vibrational kinetics of HCI on the growth of microinstabilities and the characteristics of an electric-discharge XeCI laser under inhomogeneous preionisation conditions

A one-dimensional model of an electric-discharge XeCl laser was used in an investigation of the growth of microinstabilities induced by perturbations both of the initial electron density and of the electric field under homogeneous field and inhomogeneous preionisation conditions. A mechanism of attachment–vibrational stabilisation of a discharge in mixtures containing HCl molecules was proposed and investigated. It was found that dissociative attachment to vibrationally excited HCl molecules delays considerably the growth of microinstabilities and contraction in a selfsustained discharge. This accounts for the well-known experimental observation that a discharge in a mixture containing HCl is more stable than a discharge in a mixture containing F₂. A full description of this effect could be given in the one-dimensional approximation only when one effective level was replaced by four vibrational levels (υ = 0–3). A study was made of the influence of microinstabilities on the energy characteristics of the laser. Critical perturbations of the electric field, which suppressed lasing, amounted to ~0.15% and ~1% for the KrF and XeCl laser models. These values were nearly two orders of magnitude less than the critical microperturbations of the electron density (~5% and ~100%, respectively). In the case of mixtures containing HCl there were ranges of perturbations of the initial electron density and of the electric field (up to 20% and 0.2%, respectively) in which the discharge was stable. However, there were in practice no such ranges for mixtures containing F₂. The experimental results obtained for a 10-litre XeCl laser were explained when the influence of microinstabilities and contraction of the discharge current on the operational characteristics of the laser was taken into account.