In conclusion, we have observed power dependent temperature shifts in the phase-matching curves for femtosecond SHG in a thick KNbO{sub}3 crystal. We have found that the SHG efficiency is increased when the phase-matching temperature is reset ateach input power. In addition, the temperature dependent SHG efficiency and the input power dependent phase-matching temperature in our femtosecond experiments are significantly different from those in the cw case. It was found that the optimumphase-matching temperature significantly depends not only on the input power, but also on the focusing, which is attributed to the heating of the crystal resulting from the nonlinear absorption. Our results provide important information on optimizing theSHG efficiency in frequency doubling experiments using the intense and broad bandwidth femtosecond pulses.
展开▼
