Efficient frequency conversion for cubic harmonic generation at 266 nm in centrosymmetric α-BBO crystal

Direct third-harmonic generation (THG) is a third-order nonlinear process without the restriction to the symmetric characteristic of crystals. It is of great interest for setting up a (chi)(3) optical parametric oscillator which can be used in multiphoton quantum correlation. To obtain pure and strong THG, we proposed to elect the centrosymmetric crystal with delocalized pi bond as the nonlinear media during the frequency conversion process. An unprecedented cubic harmonic energy 37.6 mu J (average power similar to 37.6 mW, conversion efficiency similar to 2.5%) at 266 nm was generated in alpha-BBO crystal (not the beta-BBO), indicating direct THG in practical application. These results also demonstrated a succinct and efficient way to generate deep-UV laser and another development direction of nonlinear crystals in UV region. (C) 2018 Optical Society of America