Nonlinear thermal and stress effects and scaling behavior of YAG slab amplifiers

Yttrium aluminum garnet (YAG) has thermal and mechanical properties that vary strongly with temperature. In the paper, we extend previously reported rod amplifier nonlinear average power scaling relationships to slab amplifiers. As found previously with rod amplifiers, we show that, at room temperature and below, temperature profiles obtained are nonquadratic and that the magnitude of the stresses are seriously underestimated if variations in YAG properties with temperature are ignored. Our results are applied to Nd:YAG and Yb:YAG lasers operating with coolant temperatures at room temperature and 77 K. As found previously with rod lasers, significant increases in average power can be obtained by operating Nd:YAG and Yb:YAG lasers at 77 K. In addition, we compare the nonlinear average power scaling behavior of rod and slab amplifiers using both linear and nonlinear approaches.