Research on synchronous radiation scanning transmission X-ray microscopy system closed-loop control method

BackgroundThe Scanning Transmission X-ray Microscopy (STXM) endstation, located at the Shanghai Synchrotron Radiation Facility (SSRF), stands as China's sole STXM device. It boasts the capability for high spatial resolution imaging down to a 15 nm scale. Utilizing the scanning coherent diffraction imaging method (i.e. ptychography), this station achieves an optimal resolution of 7.32 nm, necessitating utmost system stability. However, the STXM system operates within a complex environment where the impact of external vibrations on imaging quality is increasingly problematic.PurposeThis study aims to develop a closed loop control method for the vibration of STXM system to improve imaging quality.MethodsFirst of all, system vibration between the Fresnel zone plate (FZP) and the sample was analyzed in detail, so did the vibration suppression methods. Then, a software-driven closed-loop control system was developed on Field Programmable Gate Array (FPGA) platform by leveraging these insights, and a Fast Fourier Transform (FFT) based approach was implemented to process precise (picometer-scale) and rapid (1 kHz) positional data captured by a laser interferometer. Finally, the internal sensor of motor controller was replaced by laser interferometer to realize the closed-loop control to suppress vertical vibration, and vibration data were applied to a piezo motor for effectively replacing its internal sensors to suppress system vibrations.ResultsThe optimal performance achieved by the closed-loop control scheme shows that the root mean square (RMS) value of the vibration is reduced to 4.833 nm, which is around one third of the value before.ConclusionsThe successful implementation of this closed-loop control scheme has furnished robust technical foundations for further enhancements in the imaging resolution of the STXM system.