Ciaffoni Luca, Matousek Pavel, Parker William, McCormack Elin A, Mortimer Hugh
RAL Space, UKRI STFC Rutherford Appleton Laboratory, Didcot, UK.
Central Laser Facility, Research Complex at Harwell, UKRI STFC Rutherford Appleton Laboratory, Didcot, UK.
Appl Spectrosc. 2021 Mar;75(3):241-249. doi: 10.1177/0003702820957311. Epub 2020 Oct 12.
The desire for portable Raman spectrometers is continuously driving the development of novel spectrometer architectures where miniaturisation can be achieved without the penalty of a poorer detection performance. Spatial heterodyne spectrometers are emerging as potential candidates for challenging the dominance of traditional grating spectrometers, thanks to their larger etendue and greater potential for miniaturisation. This paper provides a generic analytical model for estimating and comparing the detection performance of Raman spectrometers based on grating spectrometer and spatial heterodyne spectrometer designs by deriving the analytical expressions for the performance estimator (signal-to-noise ratio, SNR) for both types of spectrometers. The analysis shows that, depending on the spectral characteristics of the Raman light and on the values of some instrument-specific parameters, the ratio of the SNR estimates for the two spectrometers () can vary as much as by two orders of magnitude. Limit cases of these equations are presented for a subset of spectral regimes which are of practical importance in real-life applications of Raman spectroscopy. In particular, under the experimental conditions where the background signal is comparable or larger than the target Raman line and shot noise is the dominant noise contribution, the value of is, to a first order of approximation, dependent solely on the relative values of each spectrometer's etendue and on the number of row pixels in the detector array. For typical values of the key instrument-specific parameters (e.g., etendue, number of pixels, spectral bandwidth), the analysis shows that spatial heterodyne spectrometer-based Raman spectrometers have the potential to compete with compact grating spectrometer designs for delivering in a much smaller footprint (10-30 times) levels of detection performance that are approximately only five to ten times poorer.
对便携式拉曼光谱仪的需求不断推动着新型光谱仪架构的发展，在这种架构中可以实现小型化，而不会牺牲较差的检测性能。空间外差光谱仪因其更大的 étendue 和更大的小型化潜力，正成为挑战传统光栅光谱仪主导地位的潜在候选者。本文通过推导两种光谱仪性能估计器（信噪比，SNR）的解析表达式，提供了一个通用分析模型，用于估计和比较基于光栅光谱仪和空间外差光谱仪设计的拉曼光谱仪的检测性能。分析表明，根据拉曼光的光谱特性和一些仪器特定参数的值，两种光谱仪的 SNR 估计值之比（）可能相差多达两个数量级。针对拉曼光谱实际应用中具有实际重要性的一部分光谱区域，给出了这些方程的极限情况。特别是，在背景信号与目标拉曼线相当或大于目标拉曼线且散粒噪声是主要噪声贡献的实验条件下，一阶近似下，的值仅取决于每个光谱仪的 étendue 的相对值以及探测器阵列中的行像素数量。对于关键仪器特定参数的典型值（例如，étendue、像素数量、光谱带宽），分析表明，基于空间外差光谱仪的拉曼光谱仪有潜力与紧凑型光栅光谱仪设计竞争，以小得多的占地面积（10 - 30 倍）提供检测性能水平，而检测性能仅约低五到十倍。
