Technical design of high-resolution monochromator in S³FEL

Abstract This paper presents the design and analysis of a high-resolution monochromator for the Shenzhen Superconducting Soft-X-ray Free Electron Laser (S 3 FEL), optimized for a working wavelength range of 1 to 3 nm. The monochromator’s physical parameters are determined through contour plots based on boundary requirements. To ensure high optical performance, the height error of the optical components needs to be less than 0.9 nm, and the slope error should not exceed 150 nrad. In the mechanical design, the required precise rotational resolution is achieved using a sine bar mechanism, where a linear motion motor drives the sine bar arm to facilitate the rotation. A 10-point support system is employed to mitigate gravity-induced deformations in the optics. For thermal management, top-side water cooling system combined with In-Ga wet contact technique is utilized. The vibration modes are optimized to be higher than 70 Hz, while flow-induced pitch vibrations are controlled to be below 30 nrad. The entire grating monochromator is expected to be operational by 2026.