Spatial and polarization characteristics of radiation from a cw neodymium-doped garnet laser with a nonplanar ring resonator

A theoretical analysis is made of the normal polarization modes and of the effect of field rotation outside and inside the resonator of a cw neodymium-doped garnet laser with a nonplanar ring resonator. It is found that, as a result of induced birefringence in the active element, the polarization of the radiation is generally elliptic and only tends to circular when the degree of nonplaneness of the resonator is fairly high. The radiation field is rotated both outside and inside the resonator and the angle of rotation is the sum of two angles defined by the degree of nonplaneness of the resonator and the focal length of a thermal lens in the active element. The transverse modes have a degree of axial symmetry which is a multiple of the total angle of rotation of the field in the resonator. Experimental results confirm these effects.