Abstract

We have demonstrated temperature rises that result from nonlinear absorption in single-pass frequency-doubling experiments using femtosecond pulses and a 3-mm-thick ${\mathrm{KNbO}}_3$ crystal. These temperature changes shift the phase-matching curve and must be accounted for to optimize the conversion efficiency. We obtained a maximum second-harmonic generation (SHG) efficiency of 66% at an input power of 107 mW and a slope efficiency of ∼1.5%/mW at low input powers. We have investigated, for the first time to our knowledge, the focusing dependence of the phase-matching temperature. We have also found that the temperature-dependent SHG efficiency in femtosecond SHG experiments is significantly different from that obtained for frequency doubling of continuous-wave light.

© 1999 Optical Society of America

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