High-resolution confocal Raman microscopy spectrometer design based on echelle gratings

To address the inherent challenge of balancing broad spectral coverage with high resolution in conventional Raman spectrometers, this paper presents a cross-dispersed confocal Raman spectrometer based on an echelle grating. First, a compound aberration correction module comprising cylindrical and spherical lenses is introduced into the traditional echelle grating spectrometer. Compared with traditional echelle grating spectrometers, this design improves resolution by approximately a factor of two without sacrificing light throughput. Second, a custom confocal Raman collection module enables microscale spot focusing on samples, effectively enhancing Raman signal collection efficiency and improving the signal-to-noise ratio. The designed echelle grating spectrometer and confocal Raman collection module are connected via optical fibers, enabling portability and modularity of the entire system. An echelle grating with a groove density of 52.67 grooves/mm is employed as the main dispersive element, achieving high-resolution detection of 1 cm^-1 and a broad wavenumber range of 70-4130 cm^-1. Simulation results demonstrate that the aberration correction system reduces the RMS spot radius to below 25 μm, more than doubling the performance compared with conventional designs. Experimental validation confirms the high performance; through calibration with standard light sources and reference materials, high-precision calibration results were obtained. Testing with an Hg lamp demonstrated a full width at half maximum of 1.02 cm^-1, closely achieving the design target of 1 cm^-1 resolution. Measurements of the test substances revealed that the characteristic peak positions and signal-to-noise ratios align with design specifications. This study provides a high-resolution solution for material analysis, biomedical research, and environmental monitoring in laboratory and field settings.