Three mirror off-axis optical system with an obscuration hole as a fore optics of the hyperspectral imager

摘要

A three-mirror off-axis optical system was designed as a fore optics of a hyperspectral imager. The secondary mirror (M2) has an obscuration hole in the middle for the slit assembly. Despite of the disadvantages of having a slit hole in the mirror surface such as stray light defect and mirror surface fabrication difficulty, the configuration has great advantages of maximizing telecentricity while maintaining the wide field of view (FOV). [1] To evaluate the integrity of the optical system design, the stray light effect was analyzed including the spectrometer channel and confirmed that it has little effect on the image performance. Also, the RMS wave front error (WFE) of M2 is measured to be 20.12 nm exceeding our expectation including the edge of the hole. As a result, the optical system is aligned to have WFE less than 90 nm RMS in all fields. [1]