41A consists of two experimental branches, RIXS and coherent scattering, specializing resonant inelastic X-ray scattering and coherent scattering, the latter including coherent diffraction imaging (CDI) and ptychography. Both branches share the same focusing optics and monochromator grating.
The RIXS branch provides high photon flux and a small beam size at the sample. The key optical components are active grating monochromator (AGM) and active grating spectrometer (AGS) which include their namesake bendable gratings. The AGM-AGS configuration is based on the energy compensation principle of grating dispersion to improve the efficiency of RIXS measurements significantly and without any resolution degraded. Our simulations show that the expected energy resolving power will be better than 60,000 for photon energies from 500 eV to 1000 eV. The refocusing optics, AGS and its two-dimensional detector are mounted a rotational platform with a wide range of scattering angle, from 17° to 163°. The detection system includes a multilayer polarimeter and is equipped with CCDs of single-photon sensitivity.
The coherent scattering branch incorporates a an in-vacuum diffractometer with two principal rotation axes for resonnat soft X-ray absorption. A soft X-ray spectro-microscope system using the Kirkpatrick-Baez (KB) focusing optics is attached to the diffractometer. The system operates in the transmission or the Bragg refection geometry for ptychography and Bragg CDI, respectively. Through the resonance of soft X-ray scattering, a 2D area detector in the reflection geometry is used to image a superstructure diffraction to obtain the spatial information of spin, charge and orbital ordering. For ptychography, the probe is defined by a 1-μm pinhole placed 1.5 mm upstream the object.