Design of Imaging Spectrometer Based on Czerny-Turner in FUV

It is the astigmatism that leads the traditional imaging spectrometer based on Czerny-Turner to have low spatial resolution. And it is discovered that when the distance between concave mirror and grating, x, is equal to the twice of focal length, f, of the mirror, S-II = S-III = 0 and the aberration is the least as well as the astigmatism is eliminated greatly. Meanwhile the toroidal mirror is presented to correct the astigmatism, and as well the aberration caused by the large FOV is corrected by optimizing the surface tilt. Then both of the spatial and spectral resolutions are improved. Finally a Czerny-Turner imaging spectrometer working in FUV (120 nm similar to 180 nm) with 2.5 FOV is designed, and its focal length is 147.61 mm, its F number is 3.93. MTF of this imaging spectrometer is more than 0.39 at 20 lp/mm in the total wavelength band of FOV, which satisfied the requirements of imaging spectrometer working on satellite in FUV.