On the performance of an ArF and a KrF laser as a function of the preionisation timing and the excitation mode

An X-ray preionised ArF and KrF excimer laser has been studied with three d ifferent spiker-sustainer excitation circuits. We observed large difference s in the laser performance, when the preionisation delay timing was varied on a nanosecond timescale. The behaviour of both lasers was found to be equ ivalent. The observations can be understood by considering the effect of th e discharge excitation technique on the preionisation process. An excitatio n mode with a prepulse well above the steady-state voltage Vss with a subse quent reversed overshoot voltage for initiating the discharge, in combinati on with a well-timed preionisation pulse is found to give the best results. Optimum output energies of 50 mJ with ArF and 175 mJ with KrF were obtaine d from an active volume of 60 x 1.5 x 1.2 cm in the so-called swing mode, w ith the preionisation applied 60 ns before the discharge breakdown.