Zhang Ming-Hao, Xiao Wen, Wang Wei-Min, Zhang Rui, Zhang Cun-Lin, Zhang Xi-Cheng, Zhang Liang-Liang
Opt Express. 2022 Oct 10;30(21):39142-39151. doi: 10.1364/OE.472753.
Water-based coherent detection of broadband terahertz (THz) wave has been recently proposed with superior performances, which can alleviate the limited detection bandwidth and high probe laser energy requirement in the solid- and air-based detection schemes, respectively. Here, we demonstrate that the water-based detection method can be extended to the aqueous salt solutions and the sensitivity can be significantly enhanced. The THz coherent detection signal intensity scales linearly with the third-order nonlinear susceptibility χ or quadratically with the linear refractive index η of the aqueous salt solutions, while the incoherent detection signal intensity scales quadratically with χ or quartically with η, proving the underlying mechanism is the four-wave mixing. Both the coherent and incoherent detection signal intensities appear positive correlation with the solution concentration. These results imply that the liquid-based THz detection scheme could provide a new technique to measure χ and further investigate the physicochemical properties in the THz band for various liquids.
最近有人提出了基于水的宽带太赫兹（THz）波相干探测方法，该方法具有卓越的性能，分别可以缓解基于固体和空气的探测方案中有限的探测带宽和对探测激光高能量的要求。在此，我们证明基于水的探测方法可以扩展到盐水溶液，并且灵敏度可以显著提高。太赫兹相干探测信号强度与盐水溶液的三阶非线性极化率χ成线性比例关系，或者与线性折射率η成二次比例关系，而非相干探测信号强度与χ成二次比例关系，与η成四次比例关系，这证明其潜在机制是四波混频。相干和非相干探测信号强度均与溶液浓度呈正相关。这些结果表明，基于液体的太赫兹探测方案可以提供一种测量χ的新技术，并进一步研究各种液体在太赫兹波段的物理化学性质。
