Optical design and fabrication of the off-axis paraboloid and ellipsoidal mirrors of beamline for synchrotron radiation biological spectroscopic experiments

摘要

At present beamline 3B1 in Synchrotron Radiation Lab. of Beijing Electron Position Collider has been set up for soft X-ray photolithography experiment. 3B1B beamline branched from beamline 3B1 operates at VUV-VIS for biological spectroscopic experiment. This paper describes design and fabrication on optical system of 3B1B. The features of optical system design is to adopt an off-axis paraboloid mirror which focuses light beam from synchrotron radiation source on entrance slit of Vm-562 vacuum monochromator and homogeneously circular spot appears on focal plane. An ellipsoidal mirror is used to focus spot on exit slit onto sample. It is very difficult to fabrication two aspherical mirror, it is 600 mm from axis, focal length f $EQ 315.7, dimension 40 $MUL 100 mm$+2$/, length of long axis of the ellipsoidal mirror is 1200 mm and that of short axis is 848.52 mm. Al$PLU@MgF$-2$/ layer is coated on the surface mirror. We make use of special fabrication technology and testing method for mirrors and get satisfied with results. Figure error of two mirrors: diameter of circle of diffusion is less than 0.1 mm and surface roughness is less than 1 nm RMS. As it operates at 140 - 400 nm, incidence angle $theta $EQ 45$DGR@, reflectivity of the mirror is better than 75%. These conditions meet requirements for biological spectroscopic experiments in the beamline.