Influence of birefringence-induced bifocusing on optical beams

We studied the influence of thermal birefringence-induced bifocusing on optical beams. An analytical model was developed to describe the bifocusing aberration. With this model we determined the circle-of-least-confusion location and the amount of beam quality degradation expected. A numerical model was developed to describe wave-front deformation by a bifocal lens and the intensity distribution at the foci of the polarization components-radial and tangential as well as at the circle of least confusion. Model predictions for beam quality degradation and intensity distributions along the focal range were confirmed experimentally using a strongly pumped Nd:YAG rod as a bifocal lens. It is shown that bifocusing is an important aberration in high-power rod-based lasers that must (and can) be corrected to achieve high beam quality. (C) 2005 Optical Society of America.