Obtaining molecular information deeper within optically turbid samples is valuable in many applications. However, in many cases this is challenging, in particular when the sample elicits strong laser-induced fluorescence emission. Here, we investigated the use of time-gated and micro-spatially offset Raman spectroscopy (micro-SORS) based on spectral multiplexing detection to obtain sub-surface molecular analysis and imaging for both fluorescing and non-fluorescing samples. The multiplexed spectral detection achieved with a digital micromirror device (DMD) allowed fast acquisition of the time-gated signals to enable three-dimensional Raman mapping (raster scanning in the lateral x,y plane and using time-of-flight calibration for the axial z-direction). Sub-millimeter resolution molecular depth mapping was achieved with dwell times on the order of seconds per pixel. To suppress fluorescence backgrounds and enhance Raman bands, time-gated Raman spectroscopy was combined with micro-SORS to recover Raman signals of red pigments placed behind a layer of optically turbid material. Using a defocusing micro-SORS approach, both fluorescence and Raman signals from the surface layers were further suppressed, which enhanced the Raman signals from the deeper sublayers containing the pigment. These results demonstrate that time-gated Raman spectroscopy based on spectral multiplexed detection, and in combination with micro-SORS, is a powerful technique for sub-surface molecular analysis and imaging, which may find practical applications in medical imaging, cultural heritage, forensics, and industry.

中文翻译：

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EXPRESS：使用时间门控拉曼光谱复用技术在混浊介质中进行亚表面分子分析和成像

在光学混浊样品中更深入地获取分子信息在许多应用中都很有价值。然而，在许多情况下，这是具有挑战性的，特别是当样品引起强烈的激光诱导荧光发射时。在这里，我们研究了基于光谱复用检测的时间选通和微空间偏移拉曼光谱 (micro-SORS) 的使用，以获得荧光和非荧光样品的亚表面分子分析和成像。使用数字微镜设备 (DMD) 实现的多路复用光谱检测允许快速采集时间选通信号，以实现三维拉曼映射（横向 x、y 平面中的光栅扫描并使用飞行时间校准轴向） z 方向）。亚毫米分辨率的分子深度映射是通过每像素秒级的驻留时间实现的。为了抑制荧光背景并增强拉曼谱带，将时间门控拉曼光谱与微 SORS 相结合，以恢复放置在光学混浊材料层后面的红色颜料的拉曼信号。使用散焦微 SORS 方法，来自表层的荧光和拉曼信号都被进一步抑制，从而增强了来自含有颜料的更深亚层的拉曼信号。这些结果表明，基于光谱复用检测的时间门控拉曼光谱与微 SORS 相结合，是一种强大的亚表面分子分析和成像技术，可在医学成像、文化遗产、法医学、和工业。