Picosecond gain and saturation measurements in a KrF laser amplifier depumped by amplified spontaneous emission

The input/output characteristic of a large aperture (270-mm diam) electron-beam-pumped KrF laser amplifier is obtained for pulses of 6- and 40-ps duration. The off-resonance absorption coefficient is estimated by measurement of loss at 268 nm. The gain-to-loss ratio is found to decrease from 8 to 6 as the specific pump rate is increased from 0.3 to 0.65 MW cm−3. Gain depumping due to amplified spontaneous emission (ASE) is treated by a simple 1D code and found to give good agreement with experiment. A 3D code incorporating wall reflections gives even better agreement. The spatial distribution of gain and ASE is recorded using visible and ultraviolet imaging.