Oblique light incidence on a diffuse transmission plate significantly impacts the results in the spectral calibration process. Analysis of the spectrometer's diffraction grating reveals that oblique angles cause uneven energy distribution at the entrance pupil, leading to spectral shifts. This study uses Mie scattering theory to model the diffuse transmission plate and explains the spectral shift, particularly in the infrared region where the plate's micron-scale particles have a pronounced effect. For a 1064nm laser incident at 45° on a 50-micron particle plate, the calculated spectral shifts at 45°, 55°, and 65° are 0.077nm, 0.108nm, and 0.139nm, respectively. Experimental Gaussian-fitted results show actual shifts of 0.044nm, 0.052nm, and 0.085nm. The paper concludes with an analysis of the differences between experimental and theoretical results.

Spectral calibration, Mie scattering, Grating system