Terahertz single-photon detection and imaging have attracted full attention recently. Nonlinear optical frequency up-conversion is a promising technique that can be expected to satisfy this demand thanks to its high sensitivity and fast response. In this paper, theoretical analysis and numerical calculations based on the organic salt 4′-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal were performed to show that the optimization of the detection of terahertz is different from that of the generation of terahertz, including the use of difference-frequency generation (DFG) technique, the larger thickness of the crystal, and especially the selection of the polarization direction of the pumping laser. For two different polarization configurations, the photons of the up-converted signal light both can be amplified compared with the number of incident terahertz photons under some optimal designs of the nonlinear frequency conversion process. Therefore, terahertz single-photon detection can be realized with single-photon detectors (SPDs) or even possibly with ordinary avalanche photodiodes (APDs). Furthermore, for terahertz single-photon imaging, the frequency up-conversion with the pumping laser polarized along b-axis of DAST crystal has a better performance, which is rarely used in terahertz generation.

太赫兹单光子检测和成像最近引起了人们的广泛关注。非线性光学频率上变频是一种很有前途的技术，由于其高灵敏度和快速响应，可以满足这种需求。本文基于有机盐4'-二甲氨基-N-甲基-4-stilbazolium tosylate（DAST）晶体进行了理论分析和数值计算，表明太赫兹检测的优化方法与世代不同。太赫兹，包括使用差频生成（DFG）技术，更大的晶体厚度，尤其是泵浦激光器的偏振方向选择。对于两种不同的极化配置，在非线性频率转换过程的某些最佳设计下，与入射太赫兹光子的数量相比，上转换后的信号光的光子都可以被放大。因此，太赫兹单光子检测可以用单光子检测器（SPD）甚至可能用普通的雪崩光电二极管（APD）来实现。此外，对于太赫兹单光子成像，泵浦激光沿DAST晶体的b轴偏振的频率上转换具有更好的性能，很少用于太赫兹生成。