Radially Polarized and Passively Q-Switched Nd:YAG Laser Under Annular-Shaped Pumping

We reported, for the first time, a radially polarized and passively Q-switched Nd:YAG laser with annular-shaped pumping. The annular intensity profile of the pump light was originated from the mode conversion in a conventional multi-mode fiber under off-focus coupling. Radially polarized pulse from this laser had 3.3 kW peak power, 39 ns duration at 2.5-kHz repetition rate with ~90% degree of polarization. When the laser crystal was slightly tilted, the polarization state of laser beam was switched to azimuthal polarization at high pump power, while remained radial polarization at lower pump power.