Comparison of Lateral Resolutions Obtained by Different Methods for Confocal Raman Microscopes

Confocal Raman microscopes are widely used in various applications because they provide physical and chemical information at a submicron scale. A high lateral resolution in the confocal Raman microscope is essential for obtaining high-quality images. Although several methods have been proposed to evaluate the lateral resolution of Raman microscopes, it is unclear how comparable or different the evaluated results are depending on the methods and samples used. In this study, we examined the grating method using a chromium-coated patterned three-bar sample, the straight edge method using the edge of silicon and tungsten in NMIJ CRM 5207-a, and the narrow line method using carbon nanotubes and fluorescent particles. The lateral resolution evaluated by the patterned three-bar sample according to ISO 18516:2019 was ~0.7 μm and much worse than that obtained by the other methods (0.30 to 0.41 μm), which was mainly attributed to both the inherent property and structure of the patterned sample used in this study. Although the lateral resolution obtained by the other methods did not show a large difference, each method had advantages and disadvantages including the inherent properties and structures of the samples as well as optical effects. Thus, it is important to decide on the methods and samples depending on the purpose, and the selected methods and samples should include the results and measurement conditions.