Thermal and spectroscopic characterization and evaluation of thermal effects for cryogenic cooled Yb:LuAG

Temperature dependent thermal and spectroscopic properties of Yb:LuAG crystal were presented in detail at temperature ranging from 298 to 77 K. We measured the thermal expansion coefficient, thermal conductivity and specific heat as functions of temperatures. Then, the thermal shock resistance parameters were evaluated, which were significantly increased from 0.75×10 6 to 10.19×10 6 W/m as temperature varies from 298 to 77 K. Moreover, the spectroscopic parameters, such as absorption and emission cross-sections and fluorescence lifetime were also determined. In order to evaluate Yb:LuAG’s potential to generate high power laser output, a numerical model was employed by finite element method and ray tracing method. We simulated the temperature distribution in Yb:LuAG crystal slab when temperature reduces from 298 to 77 K. The maximum principal stress in slab decreases from 74.8 to 29.4 MPa and the maximum principal strain decreases from 23.76×10 -5 to 7.63×10 -5 for a given heat power of 1500 W with the temperature dropping from 298 to 77 K. The simulated near-field and far-field profiles of probe beam demonstrated a better beam quality at low temperature. These results indicate that cryogenically cooled Yb:LuAG is a promising laser medium for high power output while maintaining good beam quality