Concept of a broadband Hettrick–Underwood monochromator for an X-ray reflectometer for the 6–27 nm wavelength range

The paper describes the design of a broadband VLS monochromator based on the Hettrick–Underwood scheme as part of a reflectometer intended for use with a laser-plasma soft X-ray source. The design is supplemented with a crossed mirror to increase the monochromator throughput. A reference measurement channel, along with an X-ray beam splitter located at the monochromator output, is used to ensure absolute reflection/transmission coefficient measurements. The optical layout of the device, its parameters, the parameters of the VLS grating, and the optical layout for fabricating the VLS grating by 532 nm interference lithography are calculated. The resolution, throughput, and accuracy of the lithographic design are verified using numerical ray tracing.