We demonstrate for the first time to our knowledge the use of mismatch
ed grating pairs between the stretching and compression systems in a c
hirped-pulse amplification laser. Pulses as short as 57 fs are generat
ed with 2000-lines/mm gratings in the compressor and 1200-lines/mm gra
tings in the stretcher. (C) 1998 Optical Society of America.