Investigation on the coherence of undulator source and soft X-ray interference lithography beamline in SSRF

Background:Synchrotron radiation(SR) has some unique features such as higher brightness and continuously adjustable wavelength.Sometimes SR source will be a unique choice in some experiments.And with the development of the SR facility,especially the appearance of various low emittance undulators,the experiments such as coherent diffraction imaging(CDI) that needs high brightness coherence source can be conducted.The traditional ray trace software,such as Shadow,using the geometrical optics methods,could not be applied for the coherent beamlines.Purpose:We want to provide a basis for the beamline design and the X-ray coherent experiments,the effective evaluation of the spatial coherence in beamlines is needed.Undulator source,which can be calculated precisely,will become a plane source with some features.As the source of the beamline,undulator was calculated.And the spatial coherence of the exit slit can be calculated too.So we can analyze the coherence of the beamline.Methods:Firstly,we used BPM to measure the intensity of the diffraction of the slit,and simulated the intensity distribution of the slit diffraction using the MCI(a software written by ourselves) to confirm the coherent length of the secondary source at slit.Secondly,we calculated the undulator supposed as a plane source,and used the MCI to numerically calculate the propagation of partially coherent X-ray in the soft X-ray interference lithography beamline from the undulator to the exit slit.Finally,we compared the difference of the coherent length at the slit by the above two methods.Results:We calculated the coherent length at the different place in the beamline,such as mirrors and slits.The most important thing was that we could not only know the coherent length with different size of the slits,but also control the spatial coherence quantitatively.When the slit size was 40 m×40 m,the spatial coherence was almost fully coherent.And we used the method to do some simulation about the coherent experiments and the coherent beamline design.Conclusions:The new method was available for the coherence analysis of the beamline.The calculation of the undulator was proper.And the quantitative analysis and control of spatial coherence could provide a basis for the X-ray coherent experiments and the coherent beamline design.