Depolarization compensation with a spatially variable wave plate in a 116 W, 441 fs, 1 MHz Yb:YAG double-pass laser amplifier.

A subpicosecond laser system featuring a fiber chirped pulse amplification-based seed laser and a double-pass end-pumped Yb:YAG crystal power amplifier was investigated. The key novelty of the system was the application of depolarization compensation using a specially designed spatially variable wave plate. To the best of our knowledge, this method was applied for the first time. The presented laser system produced pulses of 441 fs duration, 116 µJ pulse energy at 116 W average power with a beam quality of M2∼2.1, featured optical-to-optical efficiency of 32% at room temperature (T=20∘C), and had residual depolarization level of 2.7%.