The sensitivity advantage of waveguide-enhanced Raman spectroscopy (WERS) over free-space Raman, measured by the signal-to-noise ratio, is well established for thin molecular layer sensing, which traditionally relies on confocal Raman setups. However, for bulk liquid or gas samples, WERS must be benchmarked against nonconfocal Raman configurations. We use ray tracing to calculate the power collection efficiency of several model free-space systems, such as microscopes and probes, encompassing both single-objective and dual-lens systems. It is shown that considering only the focal volume of the source beam or the confocal volume of the microscope significantly underestimates the collected power from free-space Raman systems. We show that waveguide-based systems can still outperform high signal collection free-space systems in terms of both the signal collection efficiency and signal-to-noise ratio.

中文翻译：

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自由空间和波导拉曼对大体积感测的灵敏度比较

通过信噪比测量的波导增强拉曼光谱（WERS）相对于自由空间拉曼的灵敏度优势在薄分子层传感方面已得到充分确立，该技术传统上依赖于共聚焦拉曼设置。但是，对于散装液体或气体样品，必须将WERS对照非共聚焦拉曼配置进行基准测试。我们使用光线跟踪来计算包括单物镜和双镜头系统在内的几种模型自由空间系统（例如显微镜和探头）的功率收集效率。结果表明，仅考虑源光束的聚焦体积或显微镜的共聚焦体积会大大低估从自由空间拉曼系统收集的功率。