Dependence of Excimer Laser Energy on Gas Flow Velocity in High Repetition Rate Operations

Abstract

To investigate the dependence of laser energy on a gas flow velocity in high repetition rate operations, the excimer laser energy was measured by varying the gas flow velocity up to a repetition rate of 3kHz. The laser energy decreased at a clearance ratio of around 2 and 4 in our apparatus. When the upstream pin electrodes for preionization were removed, these decreases were not observed. This suggests that the preionization discharge products flow into the main discharge region at an onset of the following discharge and decrease the laser energy.
In order to show the influence of the preionization discharge products, we have defined the avoidance ratio AR (=d*f/v, d: distance between pin electrodes and a center of main electrode, f: repetition rate, v: gas flow velocity). If AR becomes an integral number, the filamentation is occured in following main discharges, resulting in laser energy reductions.