Radially polarized 33  W emission from a double-pass Ho:YAG thin-slab amplifier

The generation of a 33.7 W radially polarized output is demonstrated by way of double-pass amplification in a Ho:YAG thin-slab crystal. The amplifier system was seeded with the radially polarized output beam from a continuous-wave 13.2 W, 2.1 µm Ho:YAG rod laser, which exploited gain medium bifocusing and a ring-shaped pump spot to promote preferential lasing on the radially polarized Laguerre–Gaussian mode. By compensating for both the thermally induced stress birefringence in the thin-slab crystal and the Gouy phase shift resulting from astigmatic focusing of the 13.2 W seed, only marginal beam degradation was observed across the 95 W range of pump power into the amplifier.