Spatial Heterodyne Raman Spectrometer (SHRS) for In Situ Chemical Sensing Using Sapphire and Silica Optical Fiber Raman Probes
Spatial Heterodyne Raman Spectrometer (SHRS) for In Situ Chemical Sensing Using Sapphire and Silica Optical Fiber Raman Probes
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DOI：
10.1177/0003702819868237
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发表时间：
2019-10-01
影响因子：
3.5
通讯作者：
Carter, J. Chance
中科院分区：
文献类型：
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作者：
Ottaway, Joshua M.;Allen, Ashley;Carter, J. Chance
介绍了一种空间外差拉曼光谱仪(SHRS)，该光谱仪采用模块化光笼和透镜管系统，与商用二氧化硅和定制的单晶(SC)蓝宝石光纤拉曼探头一起使用。这些光纤耦合的SHRS化学传感器使用532 nm激光激励，用于获取固体(硫)和液体(环己烷)拉曼标准的拉曼测量，以及实际世界中由1，3，5-三氨基-2，4，6-三硝基苯(TATB)和octahydro-1，3，5，7-tetranitro-1，3，5，7-tetrazocine(HMX)含能材料组成的塑料粘结炸药的拉曼测量。SHRS是一种基于固定光栅的色散干涉仪，配备了一个阵列探测器。使用傅里叶变换方法从其对应的条纹图像(即干涉图)中提取每个拉曼光谱。拉曼测量是用SHRS Littrow波长设置在激光激发波长上，光谱范围类似于1750 cm(-1)，光谱分辨率类似于8 cm(-1)蓝宝石，类似于10 cm(-1)的石英光纤探针。SHRS的大口径允许在不降低光谱分辨率的情况下使用更大的光纤直径，正如蓝宝石收集光纤直径(330微米)比石英光纤(100微米)所展示的那样。与双石英光纤拉曼探头不同，双蓝宝石光纤拉曼探头不包括在距离样品最近的光纤探头尖端进行过滤。即便如此，SC蓝宝石光纤探头测量产生的背景比石英光纤少，从而使拉曼测量接近激发激光的85厘米(-1)。尽管用于构建蓝宝石探针的蓝宝石光纤较短，但在环己烷和高荧光的HMX基PBX的SHRS光谱中观察到了清晰的420、580和750 cm(-1)的蓝宝石拉曼光谱。后者的SRS测量在提取的拉曼光谱中产生的背景干扰很小，因为宽带荧光(即直流分量)对干涉图强度(即交流分量)没有贡献。文中还讨论了SRS的光谱分辨率、吞吐量和信噪比，以及在拉曼测量中使用蓝宝石拉曼光谱作为内部性能参考和内部波长校准标准的优点。
A spatial heterodyne Raman spectrometer (SHRS), constructed using a modular optical cage and lens tube system, is described for use with a commercial silica and a custom single-crystal (SC) sapphire fiber Raman probe. The utility of these fiber-coupled SHRS chemical sensors is demonstrated using 532 nm laser excitation for acquiring Raman measurements of solid (sulfur) and liquid (cyclohexane) Raman standards as well as real-world, plastic-bonded explosives (PBX) comprising 1,3,5- triamino- 2,4,6- trinitrobenzene (TATB) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) energetic materials. The SHRS is a fixed grating-based dispersive interferometer equipped with an array detector. Each Raman spectrum was extracted from its corresponding fringe image (i.e., interferogram) using a Fourier transform method. Raman measurements were acquired with the SHRS Littrow wavelength set at the laser excitation wavelength over a spectral range of similar to 1750 cm(-1) with a spectral resolution of similar to 8 cm(-1) for sapphire and similar to 10 cm(-1) for silica fiber probes. The large aperture of the SHRS allows much larger fiber diameters to be used without degrading spectral resolution as demonstrated with the larger sapphire collection fiber diameter (330 mu m) compared to the silica fiber (100 mu m). Unlike the dual silica fiber Raman probe, the dual sapphire fiber Raman probe did not include filtering at the fiber probe tip nearest the sample. Even so, SC sapphire fiber probe measurements produced less background than silica fibers allowing Raman measurements as close as similar to 85 cm(-1) to the excitation laser. Despite the short lengths of sapphire fiber used to construct the sapphire probe, well-defined, sharp sapphire Raman bands at 420, 580, and 750 cm(-1) were observed in the SHRS spectra of cyclohexane and the highly fluorescent HMX-based PBX. SHRS measurements of the latter produced low background interference in the extracted Raman spectrum because the broad band fluorescence (i.e., a direct current, or DC, component) does not contribute to the interferogram intensity (i.e., the alternating current, or AC, component). SHRS spectral resolution, throughput, and signal-to-noise ratio are also discussed along with the merits of using sapphire Raman bands as internal performance references and as internal wavelength calibration standards in Raman measurements.