Quantitative determination of lateral spatial resolution in confocal Raman microscopy using graphene cross-edge scanning

Lateral spatial resolution (LSR) is a key parameter of confocal Raman microscopy, determining the system's ability to resolve fine structural and chemical details at micro- to nanoscales. This study introduces a quantitative method to determine the LSR of a confocal Raman microscope using cross-edge one-dimensional Raman scan measurements of the area-sensitive G mode and edge-length-sensitive D mode intensity profiles at graphene edges. The measured LSR values for an objective with numerical aperture (NA) of 0.90 approach diffraction-limited estimates when the pinhole size is close to zero; however, LSR measurements with large confocal apertures yield values significantly larger than diffraction-limited predictions, as confirmed by measurements across objectives with varying NAs (NA = 0.25-0.90). The results demonstrate that achieving optimal resolution requires precise laser focusing, appropriate pinhole size selection, and beam expansion matching the objective's entrance pupil, while defocusing or reduced beam diameter degrades performance. This method provides a practical and quantitative approach for LSR evaluation in confocal Raman microscopy, applicable to diverse experimental conditions.