Cultural relics are a symbol of various times. The protection and restoration of cultural relics is a multidisciplinary work covering archaeology, physics, chemistry, and biology, etc. Exploring scientific means of nondestructive testing has always been the development direction of cultural relic protection workers. Terahertz has been widely used in various fields as an emerging discipline in the past 20 years. Utilizing the terahertz technology to the cultural relic has also been a research hotspot in recent years. This paper mainly describes the application of terahertz reflection imaging to a lacquer box. The experimental results show that the lacquer box sample has a double-layer structure. The bottom layer is a wooden basis, however, the upper surface is painted with lacquer and painted on it in order to achieve the purpose of decoration. The results demonstrate that the potential of terahertz reflection imaging can carry out non-destructive testing of samples with layer structure to study whether there is damage inside.
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.
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