High-flux, high-resolution compact Offner imaging spectrometer for hyperspectral applications.

A high-flux, high-resolution Offner imaging spectrometer with a compact configuration is proposed and demonstrated. By introducing a custom-designed lens group between the entrance slit and the primary concave mirror, the effective slit is optically transformed into a virtual slit with extended divergence and path length. This design fundamentally alleviates astigmatism and enables a larger numerical aperture (NA = 0.3), while preserving the intrinsic aberration-free benefits of the Offner configuration. Theoretical modeling and optical analysis were conducted to derive aplanatic conditions and optimize focal power distribution. A three-lens assembly, including a toroidal surface, was employed to decouple meridional and sagittal focal lengths and correct residual aberrations. The optimized system covers the 400-1000 nm spectral range with a measured spectral resolution of 1.35 nm and maintains an MTF>0.7 at 28 lp/mm across the full field of view. Compared to a conventional Offner spectrometer of equal resolution, the proposed design improves optical throughput by a factor of 2.25 and reduces system volume by 14.5%. Laboratory calibration using a mercury-argon lamp confirmed its high-resolution capabilities, and field experiments demonstrated excellent spectral and spatial imaging performance. The improved Offner spectrometer offers a compact, aberration-free, and high-resolution solution for applications requiring high-precision spectral imaging.