We have developed a Ti:sapphire amplifier system capable of producing
pulses of 1 mJ, with 20-22-fs pulse duration, at a 1-kHz repetition ra
te. The amplifier has a unique design consisting of a three-mirror mul
tipass ring configuration with a highly doped Ti:sapphire crystal as t
he gain medium. Pulses of 15-fs duration from a Ti:sapphire oscillator
are temporally stretched and injected into the amplifier, which is an
eight-pass system with a total gain of 10(6). The amplifier is more t
han 10% efficient, and the shot-to-shot energy fluctuation of the outp
ut is less than 2%. The output beam focuses to 1.8 times the diffracti
on limit. (C) 1995 Optical Society of America