Study on thermally induced depolarization of a probe beam by considering the thermal lens effect

In this paper, we present an accurate theoretical description of the birefringence characteristics in a Nd : YAG rod by taking the thermal lens effect into account. Considering that the birefringence is strongly dependent on the distance away from the centre of a birefringent rod, the convergent features of an incident probe beam were first evaluated for a side-pumped laser rod. A segmental accumulation method was then employed to calculate the total phase shift between the radial and the tangential components of polarization of a converged probe beam. The theoretical conclusions were compared with the measured results in both the degree of depolarization and the spatial birefringent distribution of a transmitted He-Ne laser beam. The experimental results are in good agreement with the theoretical ones so that we believe the algorithm given in this paper should be effective for the construction of a high-powered laser or amplifier system.