Dong Jingtao, Yan Peizheng, Yang Lei, Zhang Yuzhong, Zhang Tengda, Zhang Lei, Zhou Sheng, Li Jingsong
Opt Express. 2020 Sep 28;28(20):29865-29875. doi: 10.1364/OE.404924.
Photothermal spectroscopy (PTS) working in the mid-infrared region is an effective technique for in-situ characterization of the chemical composition of surface contaminants. The sensitivity relies on the way that the laser-induced response of the sample is detected. We present a highly-sensitive PTS assisted with a dual-wavelength Mach-Zehnder interferometer (MZI), MZI-PST in short. The MZI aims to sense all the phase delays taking place at the sample and air when the heat produced by resonance absorption of the contaminant is transferred into its surroundings and further to amplify the total phase delay to a large intensity difference of a probe beam. To guarantee a stable quadrature phase bias of the MZI working in the balanced detection mode, we employ two separate wavelengths, one for sensing and the other for phase bias feedback, to lock the working point to the quadrature point in real time. The MZI is expected to have a 7.8-fold sensitivity enhancement compared with the conventional phase-sensitive PTS in theory. The results of the proof-of-concept experiment on the olive oil contaminated on a wafer surface verify the spectral fidelity and the sensitivity enhancement as well as the capability of photothermal spectral imaging of the MZI-PST.
工作在中红外区域的光热光谱法（PTS）是一种用于原位表征表面污染物化学成分的有效技术。其灵敏度取决于检测样品激光诱导响应的方式。我们提出了一种由双波长马赫 - 曾德尔干涉仪（MZI）辅助的高灵敏度PTS，简称为MZI - PST。当污染物的共振吸收产生的热量传递到其周围环境时，MZI旨在感知在样品和空气中发生的所有相位延迟，并进一步将总相位延迟放大到探测光束的大强度差。为了保证MZI在平衡检测模式下工作时具有稳定的正交相位偏置，我们采用两个单独的波长，一个用于传感，另一个用于相位偏置反馈，以实时将工作点锁定到正交点。理论上，预计MZI与传统的相敏PTS相比灵敏度提高7.8倍。在晶圆表面被橄榄油污染的概念验证实验结果验证了MZI - PST的光谱保真度、灵敏度增强以及光热光谱成像能力。
