Mirrors of the optical system of crossed-dispersion spectrometers

The article considers variants of optical systems of a crossed-dispersion spectrometer using a prism to separate spectral orders, using different types of concave mirrors: two spherical mirrors, a collimating spherical and focusing toroidal mirrors, and two free-form mirrors. Using modeling in the Zemax program, the images of the spectrometer entrance slit (spectral lines) in the range of 167–810 nm were studied. It was shown that in the considered variants, the limitation on the entrance slit height due to astigmatism is the same for all schemes. The dependences of the spectral resolution on the wavelength are constructed for three spectral orders – the two extreme ones and the order containing the wavelength of 200 nm. The obtained graphs show that the best resolution is observed when using free-form mirrors. However, the resolution in the case of using spherical mirrors in the scheme deteriorates by no more than 10%, and at a wavelength of 200 nm is 7.8 pm.