High-contrast detection of z-cut lithium niobate by using radially polarized light

Periodically poled lithium niobate (PPLN) is an optical crystal with excellent performance, featuring a large electro-optic coefficient and high nonlinear optical coefficient. Recently, several ultrahigh SHG and THG conversion efficiencies utilizing z-cut PPLN were demonstrated. To detect the domain structure of z-cut PPLN, the radially polarized light is used. This allows for enhanced domain wall detection signal in lithium niobate. We demonstrated that imaging using radially polarized light can achieve a contrast ratio of 0.83, which is only 0.71 for linearly polarized light. This technology is expected to pave the way for the promotion of integrated optical devices.