Reduction of residual coma and astigmatism in a 1$middot$5 m Czerny-Turner spectrometer

Abstract

Ray tracing calculations have been performed in order to evaluate the geometrical aberrations of a high resolution 1·5 m in-plane Czerny-Turner spectrometer using spherical mirrors and a high blaze angle Echelle grating. Results show that for minimum instrumental broadening the focusing mirror off-axis angle must satisfy the Rosendahl cos3 relation, that the astigmatism can be reduced by using divergent grating illumination, and that circular slits can still be used to eliminate the inherent spectral line curvature.