Suppression of amplified spontaneous emission from a four-pass dye laser amplifier

We demonstrate a new design for a four-pass dye laser amplifier that can be used to reduce amplified spontaneous emission (ASE) in the amplifier output beam. Compared with the results obtained from normal operation of the four-pass dye laser amplifier without a frequency-selective device, by using a diffraction grating in the amplifier we can reduce the ASE ratio by a factor in excess of 10 and increase output energy by ~4%. The obtained ASE ratio of the four-pass amplifier system is <1.5%.