Cryogenic Yb:YAG thin-disk laser

Abstract

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.

High‐Power Laser Systems

“…For the active medium of Yb:YAG, as the temperature decreases from room temperature to 80 K, the laser material changes from a quasi‐three‐level system into a four‐level system, reducing the reabsorption of the laser. [ 65 ] When cooled to a low temperature, the thermal conductivity of undoped YAG increased by nearly nine times relative to that at room temperature. Although this advantage is weakened when a moderate level of doping is introduced, there is still a significant improvement of three to five times.…”

“…Auxiliary heat dissipation methods such as pulsed diode laser (PDL) pumping, [ 57–61 ] zero‐phonon‐line (ZPL) pumping, [ 54,62,63 ] cryogenic cooling, [ 61,64,65 ] or gas cooling [ 50,66 ] are required in addition to the basic configuration's heat dissipation benefits. Furthermore, large‐aperture crystals' amplified spontaneous emission (ASE) must be reduced by eliminating the edge oscillation conditions.…”