Investigation of parametric wave interaction processes under the conversion of radiation of femtosecond duration in nonlinear crystals

The efficiency of the second harmonic generation under conditions of a pulse pumping of femtosecond duration (150 fs) in nonlinear crystals, such as KTP, KDP, DKDP, BBO and LiIO$_3$, is investigated. The LiIO$_3$ crystal is found to be the most promising, in the case of type I synchronism the efficiency of conversion to the second harmonic is 25%. The spectra of parametric wave transformation both in collinear and noncollinear modes are analyzed. It is shown that the three-wave interaction is the most effective in the case of noncollinear optical parametric amplification, which is directly due to the coincidence of the group velocities of the waves participating in the process.