A theoretical and experimental study of the polarization states of a Nd(3+):YAG laser

In this work, a model describing the polarization states of a Nd3+:YAG, single frequency laser is developed. Based on the symmetry of the Nd3+ site in the crystal, and the selection rules for electric dipole transitions in Kramers degenerate states, the phase relationships between the components of the electric dipole moment are found, without the use of the double group. Summing over the six sites of the crystal, the response of the gain material to an applied electric field is found, and the polarization behavior is determined to all orders in the electric field through a vector extension of the mean field model, similar to work done in gas lasers. The result is 16 coupled non-linear differential equations describing the polarization state of the laser. The predictions of the model are compared with results in the literature. While the model can explain most of these results, it is found that the effective output mirror model used to describe polarized feedback is inappropriate for a microchip laser with a long feedback path. New experiments are performed in the low birefringence regime, and for the case of elliptically polarized pump light. The predictions of the model are in semi-quantitative agreement with the low birefringence experiments, while for the case of circularly polarized pump fields, it is found that some of the approximations of the model become inappropriate. New experimental results on the bistability of the Nd:YAG microchip laser with polarized feedback are presented and briefly discussed. Suggestions for future experimental work and refinements to the model are presented.Ph.D