Use of partial coherence in coherent X-ray diffraction imaging experiments

Coherent X-ray diffraction imaging is a promising new technique to observe samples in material science and biology with a spatial resolution of around 10 nm. However, the range of applications is still not very wide, because the method requires that the X-ray source be highly coherent both laterally and longitudinally. Thus, one of the most important questions for users is the feasibility of the technique when only a partially coherent source is available. A research group led by Professor K. Nugent (University of Melbourne, Australia) has recently reported some quite good news on this issue. So far, it has been often said that the lateral coherence length should be at least twice the greatest spatial extent of the object. The longitudinal coherence length is determined by the bandwidth of the monochromatic X-ray beam. According to the present study, one could relax the minimal criteria by a factor of 2 for both lateral coherence length and longitudinal coherence length, if the coherence properties are known either a priori or through experiment. In other words, more flux could be made available at the sample position for the coherent X-ray diffraction imaging experiments with the use of a partially coherent X-ray source. For more information, see the paper, "Diffraction imaging: The limits of partial coherence", B. Chen et al., Phys. Rev. B86, 235401 (2012).