Thermally-induced-birefringence effects of highly Nd3+-doped Y3Al5O12 ceramic lasers

Thermally-induced-birefringence effects of Nd:YAG ceramic lasers are accurately measured. Depolarization for the ceramics is found to be nearly the same with that for (1 1 1)-cut single crystals if Nd3+ concentration is the same. Under non-lasing condition, the thermally-induced birefringence becomes larger as Nd3+ concentration increases due to severer quenching. Under lasing, however, depolarization is measured to be one-third of that under non-lasing because the stimulated emission reduces the nonradiative process, which decreases the thermal load. Moreover, direct pumping into the emitting level by use of a 885 nm pump source intrinsically reduces the heat generation compared with the conventional 808 nm pumping; we have experimentally verified that the depolarization and the thermal load are reduced by 30% by the direct pumping.