Radially polarized emission with 635 W of average power and 2.1 mJ of pulse energy generated by an ultrafast thin-disk multipass amplifier.

We report on a thin-disk multipass amplifier delivering radially polarized laser pulses with an average power of 635 W and 2.1 mJ of pulse energy. To the best of our knowledge, this is the highest average output power and pulse energy reported so far for radially polarized ultrafast lasers. The amplifier is seeded by a TruMicro5050 with 115 W of average output power, 6.5 ps pulse duration, and a repetition rate of 300 kHz. A segmented half-waveplate was used for converting the linearly polarized beam into radial polarization in front of the amplifier. We present a scheme for direct amplification of such doughnut-shaped radially-polarized beams, the results obtained, and a solution to compensate for the depolarizing phase shift introduced by the tilted mirrors in the amplifier.