Enhancement of temporal contrast of high-power femtosecond laser pulses using two saturable absorbers in the picosecond regime

We characterized the transmission properties of a color-glass-filter (RG850) saturable absorber (SA) in a wide range of pulse durations (from 25 fs to 5 ps). The transmission properties were strongly related to the energy fluence, pulse duration, and chirp parameter. On the basis of these properties, the input pulse duration, chirp parameter, and energy fluence were optimized to maintain the width of the transmitted laser spectrum as much as possible with minimal energy loss. We demonstrated that, by transmitting a positively chirped 2.8-ps laser pulse to two identical SAs at an energy fluence of 15 mJ/cm², the temporal contrast ratio of the main pulse to the amplified spontaneous emission was enhanced by 4 orders of magnitude without any significant energy loss or strong spectral narrowing in a 10-Hz, 100-TW femtosecond laser system.