| Due to the advantages of high penetration,low damage,high sensitivity,and the combination of various experimental methods,the hard X-ray nanoprobe based on synchrotron radiation has attracted more and more attention from researchers in the fields of bioscience and materials.The hard X-ray nanoprobe beamline that is under construction in the beamline project of Shanghai Synchrotron Radiation Facility,based on the requirement of high flux,chose the multilayer K-B focusing mirrors combined with phase compensation technique to realize a focal spot size of 10 nm and meets the research needs in the field of frontier science.Current polishing techniques cannot process multilayer K-B mirrors with an ultrahigh precision figure to meet the requirement for nanometer diffraction-limited focusing.An in situ measurement method is used to acquire the wavefront phase error.Then a phase compensation technique by introducing an adaptive piezoelectric deformable mirror enables to compensate the wavefront phase error and effectively promotes the performance on the focusing system.However,there are also some problems,such as short duration of focusing optimization results and complex measurement of wavefront phase error.High-precision phase measurement and figure modification of piezoelectric optics are the two cores of phase compensation.In this paper,based on the construction requirements of the nanoprobe beamline,the innovative exploration was made on phase measurement and compensation.It lays a foundation for the realization of diffractionlimited focusing by hard X-ray nanoprobe beamline in the future.In terms of phase measurement,a simple and effective speckle-based measurement technique is selected,and the following research results are obtained:1.Based on the characteristics of X-ray near-field speckle formation and propagation,the models of diffuser and beam propagation were established based on speckle tracking technique,and the measurement accuracy was improved by theoretical research and exploration for high-precision wavefront detection.2.Based on the relevance theory of X-ray near-field speckle,the influence of the particle size of sandpaper,coherence of X-ray source,and sampling effect of the detector to the measurement accuracy of speckle-based technique was discussed and analyzed.The selection range of suitable particle sizes for the speckle-based technique is given and verified by simulation results of the simulator and measured results of the gold mesh sample.In addition,according to the analysis of cross-correlation map and power spectral density of the measured raw speckle patterns,it is found that there are two reasons for the higher calculation accuracy of the smaller particle size of the sandpaper in the appropriate range.(1)The small particles maintain sharper correlation peak in speckle processing which means higher computational resolution;(2)Small particles can retain more high-frequency information from an imaged sample.3.For the problem of subset size choice in the calculation of speckle-based technique,the relationship between subset size and sample components at different frequencies was discussed and analyzed.An adaptive subset size choice method is developed to select corresponding subset size according to the sample characteristics of different locations.The simulated and experimental results show that this method can avoid the experimental noises,background fluctuations,and false signals compared to the small subset choice and have the advantages of high resolution and time saving compared to the large subset choice.4.Based on the theory of speckle scanning technique,the influence of subset,calculation gap,and scanning step size on the measured curvature accuracy of onedimensional speckle self-scanning technique was discussed and analyzed.Some criterias on the selection of measurement parameters and calculation parameters are given.In addition,the vibration effects of different frequencies and amplitudes in the optical path were also studied,which lays a foundation for the stable and reliable practical application of phase compensation system.In the aspect of phase compensation,a prototype of piezoelectric deformable mirror is designed and manufactured in combination with the experimental conditions of hard X-ray microfocusing beamline station.The following research results are obtained.1.A piezoelectric deformable mirror prototype with both focusing and phase compensation functions was designed.Based on ANSYS simulation analysis,the piezoelectric response function of the deformable mirror was ex situ measured with the Fizeau interferometer and the hysteresis loop and piezoelectric stability were observed.2.A high-precision iterative global optimization algorithm for focusing state wavefront regulation is developed.The ex situ and in situ surface figure control test show that the global optimization surface figure control algorithm can realize the highprecision mirror figure control at the nanometer level.Based on the above-mentioned research results of phase measurement and compensation,the principle of the adaptive phase compensation system is explored according to the actual operation requirements of the hard X-ray nanoprobe beamline.Finally,by combining high-precision speckle scanning metrology with phase compensation technique,the phase compensation mirror prototype was installed at the hard X-ray microfocusing beamline.The focusing optimization performance of the compensation mirror was in situ tested,and the principle of the adaptive phase compensation system was verified.The experimental results showed that the focusing spot size was improved from 43.4 ?m to 12.9 ?m after three iterations.The results of this paper lay a foundation for the realization of stable nanometer diffraction-limited focusing based on adaptive phase compensation system in future hard X-ray nanoprobe beamline. |
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