Shortening of the femtosecond pulse duration during second harmonic generation

The results of theoretical and experimental studies aimed at studying the possibility of reducing the second harmonic (SH) pulse duration during its generation under conditions of phase matching violation are presented in this paper. Generation is studied in a nonlinear KDP crystal pumped by transform-limited radiation pulse with a duration of 50 fs at a central wavelength of 950 nm. The efficiency of SH generation and the broadening of its spectrum as a function of the pump pulse energy and phase-matching angle detuning in different regions of the beam cross section are studied. The behavior dynamics of SH spectrum with a change in the phase-matching angle is shown, the optimal detuning angle corresponding to the maximum broadening of SH spectrum is determined. A nonlinear phase shift over SH beam cross section is noted, the sign of which depends on the sign of phase mismatch. The possibility of reducing femtosecond pulse duration by 1.5–1.7 times is shown.