Department of Biomedical Engineering, Stony Brook University, 100 Nicolls Rd, Stony Brook, NY, 11794, USA.
Sci Rep. 2021 Nov 23;11(1):22804. doi: 10.1038/s41598-021-02068-7.
Current terahertz (THz) spectroscopy techniques only use the coherent light beam for spectral imaging. In the presence of electromagnetic scattering, however, the scattering-mitigated incoherent beams allow for flexible emitter-detector geometries, which enable applications such as seeing through turbid media. Despite this potential, THz spectroscopy using diffuse waves has not been demonstrated. The main obstacles are the very poor signal to noise ratios of the diffused fields and the resonance-like spectral artifacts due to multiple Mie scattering events that obscure the material absorption signatures. In this work, we demonstrate diffuse THz spectroscopy of a heterogeneous sample through turbid media using a novel technique based on the wavelet multiresolution analysis and the bimodality coefficient spectrum, which we define here for the first time using the skewness and kurtosis of the spectral images. The proposed method yields broadband and simultaneous material characterization at detection angles as high as 90° with respect to the incident beam. We determined the accuracy of the wavelet-based diffuse spectroscopy at oblique detection angles, by evaluating the area under the receiver operating characteristic curves, to be higher than 95%. This technique is agnostic to any a priori information on the spectral signatures of the sample materials or the characteristics of the scattering medium, and can be expanded for other broadband spectroscopic modalities.
目前，太赫兹（THz）光谱技术仅使用相干光束进行光谱成象。然而，在存在电磁散射的情况下，散射缓解的非相干光束允许灵活的发射器-探测器几何形状，从而能够实现诸如穿透混浊介质等应用。尽管有这种潜力，但使用漫射波的太赫兹光谱技术尚未得到证明。主要障碍是漫射场的信噪比非常低，并且由于多次米氏散射事件引起的类似于共振的光谱伪影，这些伪影掩盖了材料吸收特征。在这项工作中，我们通过使用基于小波多分辨率分析和双模态系数谱的新技术，展示了混浊介质中异质样品的漫射太赫兹光谱，我们在这里首次定义了双模态系数谱，使用光谱图像的偏度和峰度来定义。所提出的方法在与入射光束成 90°的检测角处产生宽带和同时的材料特性，我们通过评估接收者操作特性曲线下的面积，确定了在倾斜检测角下基于小波的漫射光谱的准确性，该准确性高于 95%。该技术对样品材料的光谱特征或散射介质的特性没有任何先验信息的要求，并且可以扩展到其他宽带光谱模式。
