42 W femtosecond Yb:Lu₂O₃ regenerative amplifier.

We report on a femtosecond high-power regenerative amplifier based on Yb:Lu₂O₃. Exploiting the excellent thermo-mechanical properties of this material, we were able to achieve up to 64.5 W in continuous-wave regime, limited only by the available pump power. In pulsed operation, 42 W of average output power at a repetition rate of 500 kHz with 780 fs long pulses could be demonstrated, resulting in a pulse peak power of ∼100  MW. The spectrum was centered at 1034 nm with an FWHM of 2.4 nm, potentially allowing for even shorter pulses. At the maximum output power the beam was nearly TEM₀₀, with an M² value of 1.2 in both axes.