Fast alignment of an offner imaging spectrometer using a spherical autostigmatic method

Offner imaging spectrometers consist of a convex grating and two concave mirrors. The concentric characteristics of the optical structure allow it to have a large relative aperture, small distortion and a compact structure. In order to reduce the difficulty of aligning an Offner imaging spectrometer and improve its efficiency, this paper presents a fast alignment method for Offner imaging spectrometers based on the concentric characteristic and spherical autostigmatic method. Firstly, a spherical autostigmatic device is built, which can generate a point source. When the point source is located at the spherical mirror’s center of curvature (CoC), its reflection image point and the point source coincide. By measuring the distance between the reflection image point and the point source, the positional deviation of the spherical mirror’s CoC can be determined. The Offner imaging spectrometer is completed by locating the CoC of its primary mirror, convex grating and tertiary mirror. The results show that the location error of the two off-axis concave mirrors’ CoC can be controlled within 10 μm, and our imaging performance requirements for the imaging spectral system are satisfied. Compared with pre-existing methods, this method is easier to operate, lower in cost and has faster alignment capabilities.