Laser and thermal characteristics of Yb : YAG crystals in the 80 — 300 K temperature range

The spectral and thermooptical characteristics of an Yb : YAG crystal were measured in the 80 — 300 K temperature range. On cooling the crystal, the amplification cross section increases fivefold, the peak of the cross section spectrum shifts from 1030.1 to 1029.3 nm, and its width lowers from ≈10 to 1.3 nm. These effects must be taken into account when operating with cryogenic amplifiers. Also measured were thermooptical constants P and Q as well as the photoelastic anisotropy parameter. These material constants completely determine the thermal and phase polarisation distortions in an active element when the heat release and the thermal conductivity coefficient are known. The thermoinduced depolarisation was shown to lower by a factor of 1000 and the optical strength by a factor of 50 on cooling the Yb : YAG crystal to a temperature of 78 K.