High Accuracy Surface Metrology Of X-ray Mirrors Research

Advanced X-ray source(synchrotron radiation / X-ray free electron laser)plays an important role in cutting-edge scientific research and industrial core technology development.It can study the atomic and molecular structure of materials,and become One of the most advanced and irreplaceable tools for research the foundation and application of material science,life science,environmental science,physics,chemistry,medicine,geology and other disciplines.China's advanced X-ray sources have been started to build,and a large number of high-precision optical elements are urgently needed.However,at present,almost all related components are imported,which has become a "neck sticking" problem in the construction of large scientific devices such as advanced X-ray sources in China.Metrology technology plays a vital role in the manufacture of Xray mirrors.The subject focuses on the surface measurement technology of X-ray mirror,and Xray mirror was measured by the stitching interferometry.The process and technical difficulties of stitching interferometry for X-ray mirror are introduced in detail.There are two main technical difficulties.One is the registration algorithm.Because the surface features of the mirror are not obvious and it is not suitable to mark points on the surface of X-ray mirror,the traditional registration algorithm is not applicable,and the cost of using high-precision positioning device is too high.Another technical difficulty is the error accumulation.In the process of stitching interferometry for X-ray mirrors,it is necessary to stitch multiple sub apertures,and the error of each stitching will accumulate after multiple stitching,resulting in inaccurate measure results.A new one-dimensional registration algorithm based on the consistency of surface shape have be proposed to solve the problem of registration in stitching interferometry for X-ray mirror.The algorithm enumerates all registration cases within the error range,calculates the residual of overlapping area in all cases,and judges the optimal registration situation by the flatness of the residual.The noise sensitivity of the algorithm and the position error in the measure process have been analyzed through simulation,which proves that the algorithm can achieve good registration effect when the random noise is small.The feasibility of the algorithm have been verified by the experiment of comparing the marked points with the one-dimensional registration algorithm.In order to solve the problem of error accumulation in the stitching process,the hardware and algorithm of stitching interferometry were studied.A stander plane mirror was used to calibrate the stitching angle of X-ray mirror to obtain a more accurate stitching angle.The platform of stitching interferometry was built,and the experiments was carried out.And The stability of the platform required for this experiment was evaluated.The global stitching algorithm based on the least square was applied to the stitching interferometry for X-ray mirror.The global stitching algorithm avoids the accumulation of stitching errors by directly calculating the least square solution of all the overlapping region of all sub apertures.Experimental results showed that the global stitching algorithm can solve the problem of error accumulation.Finally,a plane mirror was measured by stitching interferometry,The high measurement accuracy of approximately 0.15nm(root-mean-square)was achieved.