Allen Ashley, Waldron Abigail, Ottaway Joshua M, Chance Carter J, Michael Angel S
Department of Chemistry and Biochemistry, University of South Carolina, Columbia, USA.
Appl Spectrosc. 2020 Aug;74(8):921-931. doi: 10.1177/0003702820906222.
A new hyperspectral Raman imaging technique is described using a spatial heterodyne Raman spectrometer (SHRS) and a microlens array (MLA). The new technique enables the simultaneous acquisition of Raman spectra over a wide spectral range at spatially isolated locations within two spatial dimensions (, ) using a single exposure on a charge-coupled device (CCD) or other detector types such as a complementary metal-oxide semiconductor (CMOS) detector. In the SHRS system described here, a 4 × 4 mm MLA with 1600, 100 µm diameter lenslets is used to image the sample, with each lenslet illuminating a different region of the SHRS diffraction gratings and forming independent fringe images on the CCD. The fringe images from each lenslet contain the fully encoded Raman spectrum of the region of the sample "seen" by the lenslet. Since the SHRS requires no moving parts, all fringe images can be measured simultaneously with a single detector exposure, and in principle using a single laser shot, in the case of a pulsed laser. In this proof of concept paper, hyperspectral Raman spectra of a wide variety of heterogeneous samples are used to characterize the technique in terms of spatial and spectral resolution tradeoffs. It is shown that the spatial resolution is a function of the diameter of the MLA lenslets, while the number of spatial elements that can be resolved is equal to the number of MLA lenslets that can be imaged onto the SHRS detector. The spectral resolution depends on the spatial resolution desired, and the number of grooves illuminated on both diffraction gratings by each lenslet, or combination of lenslets in cases where they are grouped.
本文描述了一种使用空间外差拉曼光谱仪（SHRS）和微透镜阵列（MLA）的新型高光谱拉曼成像技术。这项新技术能够在电荷耦合器件（CCD）或其他探测器类型（如互补金属氧化物半导体（CMOS）探测器）上单次曝光，在二维空间（x，y）内空间隔离的位置上同时获取宽光谱范围内的拉曼光谱。在此处描述的SHRS系统中，使用了一个4×4毫米的MLA，其包含1600个直径为100微米的小透镜来对样品成像，每个小透镜照亮SHRS衍射光栅的不同区域，并在CCD上形成独立的条纹图像。每个小透镜的条纹图像包含该小透镜“看到”的样品区域的完整编码拉曼光谱。由于SHRS不需要移动部件，所有条纹图像可以通过单次探测器曝光同时测量，在脉冲激光的情况下原则上使用单次激光脉冲即可。在这篇概念验证论文中，使用各种异质样品的高光谱拉曼光谱来根据空间和光谱分辨率的权衡来表征该技术。结果表明，空间分辨率是MLA小透镜直径的函数，而可分辨的空间元素数量等于可成像到SHRS探测器上的MLA小透镜数量。光谱分辨率取决于所需的空间分辨率以及每个小透镜在两个衍射光栅上照亮的刻槽数量，或者在小透镜分组的情况下小透镜组合照亮的刻槽数量。
