Nonlinear Raman–Nath diffraction of inclined femtosecond laser by periodically poled lithium niobate nonlinear grating

When a pump laser beam strikes the surface of a nonlinear crystal with modulated second-order nonlinearity, various nonlinear diffraction phenomena occur, with nonlinear Raman–Nath diffraction (NRND) being a prominent example. In this study, we use an 800-nm Ti:sapphire femtosecond laser beam to pump the surface of a periodically poled lithium niobate (PPLN) crystal thin-plate nonlinear grating. By rotating the crystal, we change the incidence angle and observe and measure the exit angle, polarization, and power of NRND spots on the other side of the crystal. The experiment shows that NRND characteristics are highly sensitive to the incidence angle of the pump laser beam, which are consistent with the theoretical prediction. We expect that this research will advance the understanding of nonlinear diffraction and provide valuable insights for nonlinear optical interaction in complicated geometric and physical configurations.