Coherent Diffractive Imaging (CDI) uses a coherent X-ray beam to illuminate a sample and retrieve the phase information on the sample from phase-retrieval analysis of the far-field diffraction pattern. Of the many CDI variants developed ptychography has been shown to be the most robust and is a scanning technique where diffraction information is collected from overlapping regions and used to reconstruct the sample phase properties. The advantage of ptychography is that the spatial resolution achieved can be higher than that achieved with conventional optics.
Ptychography does not require sample isolation, and so represents an advance in CDI methods. In a ptychography experiment, the X-ray beam is focused onto a sample so that a small area is illuminated. The sample is then moved with respect to the beam to create a sequential array of overlapping illuminated areas. For each area, the light scattered by the sample is recorded as a diffraction pattern. The diffraction patterns are then processed with an iterative algorithm which retrieves the phase information. The output is a pair of images. One is a measure of the extent to which light has been absorbed by the sample. The other is a measure of the phase delay introduced to the beam as it passed through the sample.
Please note that Phase Focus Limited of Sheffield, UK has an international portfolio of patents and pending applications which relate to ptychography. A current list is available at www.phasefocus.com/patents.
Use of the patents and pending applications at Diamond is covered by an umbrella licence which Diamond has entered into with Phase Focus at no cost to Diamond’s users. Diamond users proposing to process datasets other than as part of Diamond activities are required to visit Phase Focus’ website in order to obtain a click-through licence from Phase Focus. Phase Focus grants non-commercial, royalty free licences of its patent rights for academic research use, for reconstruction of simulated data and for reconstruction of data obtained at synchrotrons at X-ray wavelengths. These licences can be applied for online by clicking on this link: www.phasefocus.com/licence