Design of a high-resolution VLS monochromator for synchrotron radiation

A high-resolution monochromator with a broad spectral range of 125 – 4200 $\mathring{\mathrm{A}}$ is designed for the measuring beamline for the projected synchrotron radiation source “SKIF” (Novosibirsk). The optical configuration of the monochromator comprises a grazing-incidence concave mirror, a plane VLS grating, and an exit slit. It is planned to use two replaceable VLS gratings with central line frequencies of 600 mm$^{-1}$ and 150 mm$^{-1}$ intended for subranges of 125 – 1000 $\mathring{\mathrm{A}}$ and 900 – 4200 $\mathring{\mathrm{A}}$, respectively. Wavelength tuning in each of the two subranges is effected by only the rotation of the VLS-gratings. Due to the proper choice of $p_1$ VLS-grating coefficients, the focal distance varies only slightly over the entire spectral range, and the $p_2$ VLS-grating coefficients are used to suppress the aberrations of the mirror and the gratings. The resolving power of the configuration obtained by numerical ray tracing exceeds 1000 in the 125 – 1000 $\mathring{\mathrm{A}}$ range and 2000 in the 900 – 4200 $\mathring{\mathrm{A}}$ range.