Effect of photodetachment and e-beam uniformity on the stability of e-beam sustained discharge KrF lasers

Abstract

Electron-beam-sustained discharges (EBSDs) for rare gas-halide excimer lasers will operate stably for only a limited length of time (hundreds of nanoseconds to a few microseconds). An EBSD which makes a transition to an exponentially increasing electron and current density is said to have experienced an ionization instability. The instability is initiated by the sudden dominance of multistep ionization from excited states of the noble gas or by depletion of the halogen. The discharge can also become geometrically unstable by suddenly constricting. In this paper, results from a multidimensional time-dependent model for an EBSD KrF laser are used to study various aspects of discharge ionization and geometric stability and the relationship between the two. The onset of instabilities initiated by photodetachment of electrons from the halogen negative ion and the effect of circuit response on the onset of instabilities are examined, and the uniformity requirements for e-beam power deposition are discussed.