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 rate. The amplifier has a unique design consisting of a three-mirror multipass ring configuration with a highly doped Ti:sapphire crystal as the 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 106. The amplifier is more than 10% efficient, and the shot-to-shot energy fluctuation of the output is less than 2%. The output beam focuses to 1.8 times the diffraction limit.
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