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A high-power sub-50 fs diode-pumped Yb:CALGO laser oscillator is demonstrated. The peak power achieved for 45 fs pulses directly from the oscillator was 1.7 MW. To the best of our knowledge, this is the highest peak power in the sub-50 fs pulse regime that has ever been produced directly from any diode-pumped Yb-ion-doped laser oscillator to date. The shortest generated pulses were 38 fs long with 187 kW of peak power.

Thermal lensing was studied in an N g -cut monoclinic Yb:KY(WO 4 ) 2 (Yb:KYW) laser crystal under high-power diode pumping at ∼980  nm, for the two principal light polarizations, E||N m and E||N p . For both polarizations, the thermal lens (TL) was positive. It was found that operation of an Yb:KYW laser with the E||N p polarization corresponds to a weaker TL that results in a better quality of the laser beam and superior power scaling capabilities. The sensitivity factors of the TL in this case were M=0.37 and 0.57  m -1 /W for the mg and pg principal meridional planes, respectively, and the astigmatism degree was as low as S/M=35% (for a pump beam radius of w p =175  μm). The photoelastic terms, fractional heat loading, and generalized thermo-optic coefficients were evaluated.