High efficient cryogenically-cooled Yb:YAG Active-Mirror laser using Total-Reflection geometry

we proposed a novel oscillator configuration called "TRAM" (Total-Reflection Active-Mirror) laser with a cryogenically cooled (under 100 K) Yb:YAG. We reported on TRAM laser experiments using a composite all-ceramics Yb:YAG, with no high-reflection coating and was directly cooled with liquid nitrogen. The obtained output power was 273 W with a slope efficiency of 72%, which to the best of our knowledge is the highest slope efficiency reported for high power laser systems from a 400 mum-thick Yb:YAG ceramic. For a laser diode spot size of 6 mm, the output power increased linearly over the whole diode pump power range. In this work, we investigated the limitation of the pump density for 180 mum, 400 mum, and 600 mum-thick Yb:YAG samples.