High average power picosecond lasers require special approach since such lasers must withstand both the high peak power of ultrashort pulses and at the same time the high heat load caused by the demand for high repetition rate of a pulse train. Thin-disk laser architecture adopted by HiLASE proved to be ideal solution of this issue. Several thin-disk laser systems based on Yb:YAG gain medium have been developed in-house at HiLASE providing nearly diffraction-limited beams at the average output power exceeding 500 W.