Publications

A multistage cryogenic chirped pulse amplifier has been developed, utilizing two different Yb-doped gain materials in subsequent amplifier stages. A Yb:GSAG regenerative amplifier followed by a Yb:YAG power amplifier is able to deliver pulses with a broader bandwidth than a system using only one of these two gain media throughout. We demonstrate 90 mJ of pulse energy (113 W of average power) uncompressed and 67 mJ (84 W of average power) compressed at 1.25 kHz pulse repetition frequency, 3.0 ps FWHM Gaussian pulse width, and near-diffraction-limited (M^2 < 1.3) beam quality.

We review recent progress in pulsed lasers using cryogenically-cooled Yb3+ -doped gain media, with an emphasis on high average power. Recent measurements of thermo-optic properties for various host material at both room and cryogenic temperature are presented, including themral conductivity, coefficient of thermal expansion and refractive index. Host materials reviewed include Y2O3, Lu2O3, Sc2O3, YLF, YSO, GSAG, and YVO4. We report on performance of several cryogenic Yb lasers operating at 5-kHz pulse repetition frequency (PRF) a Q-switched Yb:YAG laser is shwon to operate at 114-W average power, with 16-ns pulse duration. A chirped pulse amplifier achieves 115-W output using a composite Yb:YAG/Yb:GSAG amplifier, with pulses that compress to 1.6 ps. Finally, a high-average-power femtosecond laser based on Yb:YLF is discussed, with results for a 10-W regenerative amplifier at 10-kHZ PRF.