Generation of actively Q-switched pulses with radial polarization using a laser-written S-waveplate in a Ho:YAG laser

The development of a 20.6 W radially polarized Ho:YAG laser is reported, which has been actively Q-switched in order to generate 0.52 mJ pulses with a 210 ns full-width half-maximum duration. By utilizing a laser-written spatially-variant birefringent waveplate (S-waveplate) with ultra-low scattering losses inside the cavity, the linearly polarized beam exiting the acousto-optic modulator is transformed into radial polarization with very high conversion efficiency. The excellent radial polarization purity (49:1) and beam quality (M2 of 2.14) highlight this approach as a very suitable platform for high power operation, assisted by the large damage threshold and customizability of the S-waveplate.