Generally, the efficiency of nonlinear Cherenkov radiation (NCR) is dramatically affected by the abrupt change of the second-order nonlinearity, which contains not only the -1 to 1 modulation corresponding to the domain wall but also the 0 to 1 modulation corresponding to the crystal surface. By using sum-frequency polarization wave generated by incident and internal total reflected waves, previous studies have achieved enhanced NCR on the crystal surface. Such NCR can provide good light quality and relatively high efficiency, which allows for further practical applications, such as nondestructive diagnostics, harmonic conversion and ultra-short pulse characterization.

Using the coupled wave equation, we demonstrate the effect of reciprocal vectors of photonic crystals to the radiation angles of NCR. Experimentally, we analyzed the properties of NCR generated at the surface of one-dimensional nonlinear photonic crystals. When the internal reflection inside the crystal boundary is utilized, the sum-frequency polarization of the incidences assisted with different orders of reciprocal vectors can emit multiple NCRs which exhibits second-order nonlinearity spatially modulated pattern. Particularly, at specific incident angles, we have observed degenerated NCR which leads to remarkable enhancement on the intensity.

Refer to: OPTICS EXPRESS 25,12, 13897-13902 (2017)