A 37% efficiency, kilohertz repetition rate cryogenically cooled Ti : Sapphire regenerative amplifier

We present a high-efficiency Ti:sapphire regenerative amplifier being developed as a pumping laser for a high-brilliance laser-plasma X-ray source operating at a multi-kHz repetition rate. A ring resonator is adopted for stable single transverse mode operation and a laser rod is cryogenically cooled to suppress the strong thermal lens effect. By reducing losses in the resonator and by matching the pumping mode volume with the resonator mode, the conversion efficiency is increased to 37%. The output power is 7.4 W when pumped by a 1 kHz 20W green laser.