Nuclear Techniques ›› 2020, Vol. 43 ›› Issue (6): 60101-060101.doi: 10.11889/j.0253-3219.2020.hjs.43.060101


Research on the influence of slope error on free-electron laser focusing spot

Ximing ZHANG1,2,Zhi GUO2,3(),Xiangyu MENG2,3,Xiangzhi ZHANG2,3,Zuanming JIN1,Yong WANG2,3   

  1. 1.Shanghai University, Shanghai 200444, China
    2.Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China
    3.Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210, China
  • Received:2020-02-29 Revised:2020-04-04 Online:2020-06-15 Published:2020-06-12
  • Contact: Zhi GUO
  • About author:ZHANG Ximing, male, born in 1991, graduated from Tianjin University in 2014, master student, focusing on optical engineering
  • Supported by:
    the Key Projects of the Joint Fund for Scientific Research of Large Scientific Installations(U1732268);National Natural Science Foundation of China(11575284);National Key R&D Program(2016YFB0700404)

Abstract: Background

The self-amplified spontaneous emission (SASE) free-electron laser beamline, dedicated for live-cell imaging, is under construction in the Shanghai soft X-ray free-electron facility. The energy range of the beamline is from 100 eV to 1 000 eV and the beamline covers two branch lines, including frontend, attenuator, plane mirror PM1, variable-line-spacing grating PM2, monochromator, bendable mirror, Kirkpatrick-Baez (KB) mirrors and ellipsoidal mirror etc. The Kirkpatrick-Baez mirrors of the north branch line consisting of a plane mirror and two elliptical cylinder mirrors are used for biological-cell imaging. The surface of mirrors should be highly reliable and precise in the system of the free-electron laser beamline. Slope error of optical elements during the production processing is an important criterion for measuring the surface quality of optical elements. The slope error of mirror is associated with the height error, and affects the coherent and wavefront of the beam, and further affects the final light spot.


This study aims to explore the variation of the slope error on X-ray coherent and wavefront after propagating in the beamline, and choose appropriate mirror whose slope error has little influence on the beam.


The software SHADOW and SRW were employed for the simulation to trace the X-ray propagation in the KB mirror and the whole beamline.


When the slope error of plane mirrors is controlled between 0.1 μrad and 0.2 μrad, the slope error of elliptical cylinder mirrors is less than 0.4 μrad, and the height error is approximately 3 nm, the high-quality image with spot size less than 4 μm is obtained, satisfying the imaging needs of biological imaging experimental station.


Results of this study provide comprehensive detailed data for the optimal design of soft X-ray free-electron laser beamline.

Key words: Soft X-ray, Free-electron laser, Kirkpatrick-Baez mirror, Slope error

CLC Number: 

  • O434.1,O434