12 MW peak power from a two-crystal Yb:KYW chirped-pulse oscillator with cavity-dumping.

We report on substantial pulse energy increase in Yb:KYW femtosecond laser oscillators by utilizing multiple laser crystals for an enhanced net-gain at higher pump power. The two-crystal oscillator generates pulse energies of 7 µJ at 1 MHz repetition rate which is, to our knowledge the highest energy ever reported from an Yb-doped tungstate fs-laser oscillator. The external pulse compression yields a pulse duration of 416 fs with a peak power of 12 MW being enough for stable white light generation in YAG.