Broadband astigmatism-free Offner imaging spectrometer with high resolution.

An advanced optical design has been proposed for an astigmatism-free Offner imaging spectrometer with high resolution in the broadband spectrum. The anastigmatic theory is thoroughly analyzed. Astigmatism is corrected by two pairs of lens-mirror combinations. On the basis of the concentric structure, the lens is used to make the meridional image distance equal to sagittal image distance. An example of the design has been presented with f-number of 3 working in 400-1000 nm according to the optimized theory. By the ray-tracing results, the spectral sampling is 0.6nm/pixel, and the RMS spots radii in all fields of view are less than 5 µm. The spectral keystone distortion and smile distortion are less than 0.1%. The prototype is manufactured based on theory and tolerance analysis. The achieved prototype has advantages of high spectral resolution (3 nm) and compact configuration.