Characteristics investigation of Yb3+:YAG crystals for optical refrigeration

Yb3+:YAG crystal is one excellent material for developing high-power radiation-balanced lasers (RBLs). An experimental study of the laser cooling performances of YAG crystals with various doping Yb3+ concentrations, especially for application of RBLs, is reported here. With improved Yb3+ doping concentration in YAG crystal, though the resonance absorption coefficient increases, the corresponding external quantum efficiency has been found to decrease with the average fluorescence wavelength being red shifted, which is detrimental to anti-Stokes fluorescence (ASF) cooling. The decrease of the external quantum efficiency can cause the first zero crossing wavelength to red shift, which is not conducive to RBLs. Based on the comprehensive study of the cooling characteristics of the series of Yb3+-doped YAG crystals, the optimal Yb3+ doping concentration for ASF cooling has been suggested.