上海光源硬X射线相干衍射成像实验方法初探

相干X射线衍射成像方法是一种先进的成像技术,分辨率可达纳米量级.国际上大多数的同步辐射装置和自由电子激光装置都建立了该成像方法,并有将其作为主要成像技术的趋势.上海光源作为目前国内唯一的一台第三代同步辐射光源,尚未建立基于硬X射线的相干衍射成像实验平台.随着一批以波荡器为光源的光束线站投入使用,使得该方法的建立成为了可能.本文基于上海光源BL19U2生物小角散射线站,通过有效的光路设计,搭建了相干衍射实验平台,在12 keV和13.5 keV能量点均获得了硬X射线相干光束,并基于小孔衍射测量了入射光束的空间相干长度.该平台支持常规和扫描相干衍射实验模式,对小孔衍射图样及波带片扫描衍射图样实现了正确的相位重建,证明了该平台初步具备开展硬X射线相干衍射成像实验的能力.硬X射线相干衍射成像实验平台为国内首次建立,将为国内该实验方法的发展和应用提供有效的软硬件支持.

Preliminary exploration of hard X-ray coherent diffraction imaging method at SSRF

Coherent X-ray diffraction imaging(CDI)method is a powerful X-ray imaging technique with high resolution up to nanometer scale.Most of the synchrotron radiation facilities and free electron laser facilities are equipped with this state-of-the-art imaging technique and have made many outstanding achievements in multiple scientific areas.Up to now,although scanning CDI(ptychography)method based on a soft X-ray source has been opened to users,the hard X-ray CDI experimental platform has not been built at Shanghai Synchrotron Radiation Facility(SSRF)which can research some relatively thick specimens and easily extend to three-dimensional imaging.As some new beamlines with undulator source were put into operation recently,it is possible and feasible to build up the CDI experimental platform with hard X-ray.In this article,we report the hard X-ray CDI experimental platform development process and preliminary experimental results of coherent diffraction pattern and image reconstruction at SSRF.Based on the operating BL19U2 biological small-angle Xray scattering(SAXS)beamline at SSRF,the hard X-ray coherent beam is obtained through effective optical path designation at 12 keV and 13.5 keV.The hard X-ray optimization includes tuning several slits,double crystal monochromator(DCM),horizontal deflection mirror,focusing mirror system and pinhole,etc.Furthermore,hard X-ray CDI experiments are conducted.The spatial coherent length of the incident beam is also measured from the pinhole diffraction pattern.This platform can provide both conventional mode and scanning mode(ptychography)for the coherent diffraction imaging method,and the correct image reconstruction from the experimental diffraction patterns proves that the platform has the experimental capability for hard X-ray CDI.In the conventional forward scattering CDI mode,coherent diffraction patterns of pinhole are collected and used to analyse the coherence property of the optimized X-ray beam.The structure of pinhole is also reconstructed from the diffraction pattern.In the scanning CDI mode,a zone plate is used as a sample.The central area of zone plate is reconstructed correctly.About 90 nm/pixel resolution of reconstruction is achieved which is extremely dependent on the X-ray flux density from the undulator source emission.Hard X-ray CDI experimental platform based on the synchrotron radiation facility is first built in China.It will provide effective software and hardware supporting for the development and application of hard X-ray CDI experiments in China in the future.