Yin Xiaoqin, Fan Shuzhen, Zhang Xingyu, Li Yongfu, Liu Zhaojun, Zhao Xian, Fang Jiaxiong
Opt Express. 2022 Jun 6;30(12):21797-21807. doi: 10.1364/OE.460988.
Frequency upconversion technology with good performance including high sensitivity, fast response, and room-temperature operation is a promising method for terahertz-wave detection. The sum-frequency conversion and difference-frequency conversion jointly affect the detection ability for upconversion detection using organic crystals as nonlinear media. The concurrence of both processes has been ignored in past studies, which results in discrepancies between theoretical simulations and experimental results. In this paper, four-wave interaction equations involving two nonlinear conversion processes are proposed, and the effect of the sum-frequency process is analyzed in upconversion terahertz-wave detection via a 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal. The ratio of the sum-frequency signal to the difference-frequency signal varies for different terahertz frequencies and crystal thicknesses. Experiments suggest that theoretical simulations are good at predicting physical processes. Under certain conditions, the detection efficiency can be improved by simultaneously utilizing the two signals. The total signal photon number is not sensitive to the crystal thickness. Furthermore, the theoretical exploration of terahertz single-photon detection provides a noteworthy reference for future experiments.
具有高灵敏度、快速响应和室温操作等良好性能的频率上转换技术是一种很有前景的太赫兹波检测方法。和频转换和差频转换共同影响以有机晶体作为非线性介质的上转换检测的检测能力。在过去的研究中，这两个过程的同时存在被忽视了，这导致了理论模拟和实验结果之间的差异。本文提出了涉及两个非线性转换过程的四波相互作用方程，并通过4-二甲氨基-N-甲基-4-苯乙烯基吡啶对甲苯磺酸盐（DAST）晶体分析了和频过程在太赫兹波上转换检测中的作用。和频信号与差频信号的比值随太赫兹频率和晶体厚度的不同而变化。实验表明理论模拟能够很好地预测物理过程。在一定条件下，同时利用这两个信号可以提高检测效率。总信号光子数对晶体厚度不敏感。此外，太赫兹单光子检测的理论探索为未来的实验提供了值得注意的参考。
