Abstract
We investigate the generation of ultraviolet (UV) second-harmonic radiation at 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-transparent crystal with a larger second-order nonlinear coefficient χ(2), a nonlinear interface with large disparity in χ(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 is up to 11.6 times that at the crystal boundary. As a tunable phase-matching method, it may suggest potential applications in the UV, and even vacuum-UV region.
Highlights
To overcome these difficulties, other efficient frequency conversion processes taking advantage of tunable and flexible phase matching methods can find a way out[20,21]
We propose an automatic non-collinear phase matching method, which exploits the internal total reflection with no restrictions on wavelength
The second harmonic (SH) radiation is enhanced at the nonlinear interface with large disparity in χ(2), which is formed by adhering another UV non-transparent crystal with higher χ(2)
Summary
Xiaohui Zhao[1,2,3], Yuanlin Zheng[1,2], Ning An2,3, Huaijin Ren[4], Xuewei Deng5 & Xianfeng Chen[1,2]. The nonlinear coefficients of these two VUV-transparent crystals (d11 = 0.49 pm/V for KBBF and d32 = 0.039 pm/V for BMF) are significantly smaller than that of the nonlinear crystals commonly employed in the visible to infrared region, for example LiNbO3 (LN) (d3L3N = 34.45 pm/V) To overcome these difficulties, other efficient frequency conversion processes taking advantage of tunable and flexible phase matching methods can find a way out[20,21]. When the wave vector of nonlinear polarization smaller than that of harmonic, SH wave emits at a specific angle θ which is regarded as the nonlinear Cherenkov radiation satisfying the longitudinal phase-matching condition[24,25,26]: k2sinθ = 2k1sinα Since this is an automatic and tunable phase-matching process, one can always find suitable incident angles for SHG without wavelength limitation. It indicates that one can employ a medium with a larger nonlinear coefficient to enhance the SH generated in UV-/VUV-transparent crystals no matter the medium itself is transparent or not
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