Sub-mJ., Sub-20-fs Pulses from Ti:sapphire without Using a Pulse Stretcher

Snb-10O-fs klla-repetitioii-rate ainpliliers combine the benefits of high peak powers with the possibility of using sensitive signal-averaging tecliniques. The technique of chirped pulsc aniplification (CPA) led to significarit progress i n the amplification of femtosecond pulses. llecent advances resulted i n the generation of optical pulses of 30 Is duration a t the TW level a t a repetition rate of 10 I I z . ' . ~ A t klIz repetition rates pJ-energy 304s (Ref. 131) and 0.9-mJ 214s pulses4 have recently been reported. Uoth results have been achieved by using complex and lossy grating-based pulse stretching systems. In this contribution we report for what we believe is the first time on the generation of sub-mJ-energy femtosecond pulses without using a pulse stretcher. We have developed a compact eight-pass Ti:S amplifer, which is seeded with -10 Is, 100nm-bandwidth pulses (@ 800nm) from a mirror-dispersion-controlled Ti:S oscillator. The system can be safely operated without an additional stretcher because the pulse broadening introduced by the pulse slicing and isolation components is sufficient to prevent nonlinear effects and damage in the amplifier crystal. In contrast with the conventional approach, pulse selection by a Pockels cell is performed only after the full 8O-MHz pulse train passed through the amplifier crystal four times. In this manner, ASE could be dramatically suppressed as compared to previously reported results.' Carefully placed apertures prevent the high-gain amplifier setup from lasing. After amplification the chirped pulses are recompressed in a setup consisting of dispersive mirrors and a low-dispersion FK5 (Schott) prism pair, resulting i n a quartic-phase-limited amplifier system.