The design of astigmatism-free crossed Czerny-Turner spectrometer

The first-order astigmatism-free conditions in crossed Czerny-Turner (C-T) spectrometer are derived. To our best knowledge, there is no report about this kind of research. For the requirements of the optical parameters of the relative aperture of 8 and the working wavelength ranging from 780 nm to 1020 nm, according to the derived formula, the astigmatism-free crossed C-T spectrometer is built up with ZEMAX software. The correspondent coma-free crossed C-T spectrometer is also built up. The two initial structures of crossed C-T optical systems are then optimized, and the performance merits are compared. It is shown that, the astigmatism-free crossed C-T spectrometer has a superior optical performance, with the RMS of spot diagram only 12–52% that in the correspondent coma-free crossed C-T spectrometer. This indicates that the astigmatism-free crossed C-T spectrometer possesses not only a better energy concentration along the slit direction, which is beneficial to spectrometers requiring larger condenser capacity, but also a smaller spot diameter along the direction perpendicular to the slit, which implies a higher spectrum resolution achieved.