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 (LN2). 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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