非线性光子晶体中的非线性衍射高阶次谐波

High-Order Nonlinear Diffraction Harmonics in Nonlinear Photonic Crystals

提出一种在非线性光子晶体中实现非线性衍射高阶次谐波的方案。基于观察到的多个锥形四次谐波,理论分析了实现五次谐波和六次谐波的可行性。当仅有一种激光光束入射到非线性光子晶体中时,可观察到红、绿和蓝锥形光的同时输出,这可为环形三基色、连续环形谐波以及环形白色光源的实现提供参考。其中,蓝色锥形光波可能源于有倒易矢量参与的级联五次非线性衍射谐波过程。同一基频波长下非线性切伦科夫五次谐波的辐射锥角均大于低阶次谐波的辐射角,且不同基频波长下的非线性切伦科夫五次谐波存在最小的辐射锥角。当入射基频波长为3319.5 nm时,五次谐波中e光的形成过程为非线性布拉格衍射,这可为六次非线性衍射谐波的产生提供有利条件。

A scheme for realizing high-order nonlinear diffraction harmonics in a nonlinear photonic crystal is described. Based on the multiple conical fourth-order harmonics observed, the feasibility of realizing the fifth-order and sixth-order harmonics via nonlinear diffraction is theoretically analyzed. The simultaneous generation of red, green, and blue conical harmonics is observed under only one input laser beam, which is beneficial to the realization of three primary colors, continuous harmonics and even ring white light sources. The blue conical output harmonics may be attributed to the cascaded nonlinear diffraction process of fifth-order harmonic involving the reciprocal vectors. Under the same fundamental wavelength, the conical angle of the fifth-order nonlinear ?erenkov harmonic is always larger than those of the other lower-order harmonics. Moreover, there always exists a minimum conical angle for the fifth-order nonlinear ?erenkov harmonics under different input wavelengths. When the input fundamental wavelength is 3319.5 nm, the generation process for the fifth-order harmonic e light is corresponding to nonlinear Bragg diffraction, which is helpful for the effective generation of a sixth-order nonlinear diffraction harmonic.