Self-sustaining azimuthal polarization in a passively Q-switched Nd:GdVO₄ laser with a Cr₄+:YAG saturable absorber

An azimuthally polarized beam was generated in passively Q-switched Nd:GdVO₄ lasers with a Cr 4 :YAG saturable absorber. Based on the birefringence of the laser crystal inducing the different equivalent lengths for the ordinary and extraordinary rays, stable ordinary ray lasing can be achieved when the cavity configuration is operated around the edge of a stable cavity region. Because the laser is directly obtained from a general cavity without adding an intracavity element, the azimuthally polarized beam is the intrinsic lasing mode of the passively Q-switched laser system. The degree of polarization can be controlled up to 97.9%±0.7%, and the pulse width, repetition frequency, and peak power were 74.8 ns, 17.0 kHz, and 850 W at the pump power of 6.1 W, respectively.