Design of a prism–prism–grating Raman imaging spectrometer

This study introduces a Raman imaging spectrometer utilizing a prism–prism–grating (PPG) dispersive module. The dispersion characteristics of the compound prism and the transmission grating are analyzed independently, and a mathematical model for the PPG combined dispersive element is established to determine structural parameters achieving low spectral smile and high dispersion uniformity. System simulation according to design specifications yields a spectral smile below 4 µm, dispersion linearity below 0.005, and an operational Raman shift range of 100−4100cm −1 , thereby satisfying the required low spectral smile and high dispersion uniformity. Further research on the influence of prism materials indicates that a greater refractive index difference between the two prisms in the composite prism improves the dispersion uniformity of the system. A performance comparison between PPG and prism–grating (PG) dispersion modules shows that for the same grating groove density, the PPG module has more uniform dispersion, while the grating groove density corrected by the double prism in the PPG module is much higher than that corrected by the single prism in the PG module, thus achieving higher resolution.