We derive equations for the ASE intensity, decay time, and heat load. The crux of our development is frequency integration over the gain lineshape followed by a spatial integration over the emitters. These integrations result in a gain length that is determined from experiment. We measure the gain as a function of incident pump power for a multi-pass pumped Yb:YAG disk doped at 9.8 at.% with an anti-ASE cap. The incident pump powers are up to 3kW. Our fit to the measured gain is within 10% of the measured gain up to pump powers where the gain starts to flatten out and roll over. In this comparison we extract the gain length that turns out to be 43% of the pump spot size of 7mm.

No abstract

Cryogenic solid-state laser materials offer many improvements in thermal, optical, structural, and lasing properties over their room temperature counterparts. As the temperature of Yb:YAG decreases from room to 80K it transitions from quasi-three-level lasing to a 4-level laser. In this study, we compare Yb:YAG thin-disk laser performance at room 293K and 80K. To achieve this direct comparison we have built two cooling systems based on R134A refrigerant and also on liquid nitrogen (LN 2 ). We have made an analytical calculation of the small signal laser gain that takes into account the spurious amplified spontaneous emission and photon re-absorption. The cold thin-disk laser clearly outperforms room temperature operation, and the theoretical results shows room temperature gain flattening.

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At cryogenic temperatures, Yb:YAG behaves as a 4-level laser. Its absorption and emission cross-sections increase, and its thermal conductivity improves. Yb:YAG thin disk laser performance at room and cryogenic (80°K) temperatures will be presented. The Yb:YAG gain media is cooled using either a pressurized R134A refrigerant system or by a two-phase liquid nitrogen spray boiler. Interchangeable mounting caps allow the same Yb:YAG media to be switched between the two systems. This allows direct comparison of lasing, amplified spontaneous emission, and temperature performance between 20°C and -200°C.