Spatially offset Raman spectroscopy (SORS) is a proven technique for sub-surface detection. SORS is able to separate Raman signals from a container and its contents, thereby demonstrating application to through-barrier detection for defence and security. Whilst SORS has been demonstrated to reduce fluorescence from the barrier (or surface), fluorescence from the sample (or sub-surface) can still be problematic for some materials when using Raman excitation wavelengths typical in commercially available instrumentation (e.g. 785 nm). Previous work has demonstrated that short-wave infrared (SWIR) excited SORS (e.g. 1064 nm) can reduce fluorescence from the sample and barrier, thereby providing the potential to detect a wider range of materials through a wider range of barriers. In this paper we highlight an additional challenge for detection through some plastic container materials (e.g. high density polyethylene (HDPE) and other opaque plastics) that absorb and scatter both incident and Raman scattered photons in the SWIR band, leading to distortion of the resultant SORS spectrum. The existence of this effect and its impact is explored, along with a potential solution to overcome this challenge that uses multi-wavelength Raman excitation to avoid the detrimental HDPE absorption region.

中文翻译：

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校正短波红外空间偏移拉曼光谱测量中的传输损耗，以减少荧光穿透屏障的检测

空间偏移拉曼光谱法（SORS）是用于地下检测的一种成熟技术。SORS能够将拉曼信号从容器及其内容物中分离出来，从而证明了其在通关检测中的应用，以实现防御和安全性。尽管已证明SORS可以减少来自势垒（或表面）的荧光，但是当使用市售仪器中通常使用的拉曼激发波长（例如785 nm）时，对于某些材料来说，来自样品（或子表面）的荧光仍然是有问题的。先前的研究表明，短波红外（SWIR）激发了SORS（例如1064 nm）可以减少来自样品和阻挡层的荧光，从而提供了通过更广泛的阻挡层来检测更广泛范围的材料的潜力。在本文中，我们着重介绍了通过一些塑料容器材料（例如高密度聚乙烯（HDPE）和其他不透明塑料）进行检测的另一挑战，这些材料会吸收和散射SWIR波段中的入射光和拉曼散射光子，从而导致所得SORS发生畸变光谱。探索了这种效应的存在及其影响，以及克服这一挑战的潜在解决方案，该解决方案使用多波长拉曼激发来避免有害的HDPE吸收区域。