Optical design of micro-focus X-ray photon correlation spectroscopy beamline at Shenzhen Light Source

An optical design study of a beamline proposed for the 3 GeV synchrotron radiation facility, the Shenzhen Light Source, is described. The beamline was designed to cover an energy range from 2.0 to 20 keV with two experimental station, one for X-ray absorption spectroscopy (XAS) experiments and the other for X-ray photon correlation spectroscopy (XPCS) experiments. A 4 m planar undulator with a relatively short magnetic period (20 mm) was used as the radiation source. Horizontally and vertically focusing mirrors separately focus the source along the horizontal and vertical directions, respectively, thus enhancing the flexibility of the beamline. The focus point was employed as the secondary source, and a pair of KB mirrors were used to achieve a near-circular focus spot of about 4.5 mu m x 4.5 mu m. A Si(111) DCM was selected to produce the monochromatic light that covers the 2.0-20 keV energy range. When the photon energy is lower than 10 keV, the energy resolution can be better than 1.47 x 10-4 and the total flux is larger than 1 x 1014 photons/s. The longitudinal coherence length is in a few mu m range. With aperture size adjustment, the transverse coherence length at the sample position is approximately 3 mu m and the coherent flux is up to 1012 phs/s for the photon energy around 2.5 keV. This excellent coherence performance can be applied for the purpose of X-ray photon correlation spectroscopy related experiments.