Accurate drift calibration of soft X-ray microspectroscopy images at SSRF

The BL08U soft X-ray microspectroscopy station of Shanghai Synchrotron Radiation Facility has been built and open to users successfully.The spatial resolution is about 30 nm.Due to limitation of mechanical precision and errors in repeatability,the drift of scanned images is inevitable at different scan energies.This gives rise to serious errors and data analysis inaccuracy.Therefore,the images scanned by X-rays at different-energies should be registered before data analysis.For solving the problem,efforts have been made in both hardware and software.A laser interferometer is used to precisely detect the sample position and measure its position drift,and the drift rates can be calculated with a standard sample(pattern) using the slope function.The drift rates are used for dynamic calibration of the sample stage position,which is initiated automatically once there is a sample moving.To a large extent,this eliminates the position drifts.On the other hand,a multi-window cross correlation technique to automatically register the scanned images has been developed.The result shows that the technique can reach a precision of 1 pixel.