Efficient generation of the second and third harmonics of high-power femtosecond Yb:KGW-laser radiation in nonlinear-optical BBO crystals

The frequency conversion of radiation into the second and third harmonics of a high-power femtosecond laser based on Yb:KGd(WO4)2 (Yb:KGW) crystals in BBO (β-BaB2O4) crystals has been experimentally and quantitatively investigated. Under the optimum compression conditions of femtosecond pulses of width 300 fs, the conversion efficiency into the second harmonic reached 50%, and that into the third harmonic reached 20%. The introduction of additional phase modulation reduced the generation efficiency of the second harmonic to an extent that is different for positive and negative signs of the phase modulation. The results of numerical calculations quantitatively agree with the experimental results.