Enhancement of UV Second-Harmonic Radiation at Nonlinear Interfaces with   Discontinuous Second-order Susceptibilities
  We investigate the generation of ultraviolet (UV) second-harmonic radiation on the boundary of a UV transparent crystal, which is derived from the automatic partial phase matching of the incident wave and the total internal reflection. By adhering to another UV non-transparency crystal with larger second-order nonlinear coefficient \chi^{(2)}, an nonlinear interface with large disparity in \chi^{(2)} is formed and the enhancement of UV second-harmonic radiation is observed experimentally. The intensity of enhanced second harmonic wave generated at the nonlinear interface was up to 11.6 times at the crystal boundary. As a tunable phase-matching method, it may suggest potential applications in the UV, even vacuum-UV, spectral region. 
Xiaohui Zhao, Yuanlin Zheng, Huaijin Ren, Ning An, Xuewei Deng, and   Xianfeng Chen
physics.optics