Features of Second Harmonic Generation of Intense Short Laser Pulses in Crystals with a Regular Domain Structure Under Conditions of Self-Action, Nonstationarity, and Synchronism of Group Velocities

Abstract

The process of frequency doubling of the first type of interaction (oo-e) of intense short laser pulses in crystals with a regular domain structure has been studied by a numerically. The influences of the dispersion of the group velocity of the medium up to the third order and cubic nonlinearity of the Kerr type on the formation of the second harmonic pulse are analyzed. The case is considered when both the conditions of quasi-phase matching and the synchronism of group velocities are simultaneously satisfied. It is shown that, in this case, an insignificant change in the domain size from the exact value providing the condition of quasiphase matching leads to a significant increase in the efficiency (almost twofold) of second harmonic generation. Calculations show that the latter is due to the mutual compensation of phase shifts caused by the Kerr-type cubic nonlinearity, the dispersion of the medium and the additional value of the wave number of the nonlinear grating. Lithium niobate with a 5% addition of magnesium oxide (5 % MgO:LiNbO₃) was chosen as a periodically polarized crystal, in which it is possible to create the conditions of quasi-phase matching and synchronism of group velocities at a certain wavelength of the main radiation (~1560 nm)