Soft X-ray spectromicroscopy using ptychography with randomly phased illumination

Abstract

Ptychography is a form of scanning diffractive imaging that can successfully retrieve the modulus and phase of both the sample transmission function and the illuminating probe. An experimental difficulty commonly encountered in diffractive imaging is the large dynamic range of the diffraction data. Here we report a novel ptychographic experiment using a randomly phased X-ray probe to considerably reduce the dynamic range of the recorded diffraction patterns. Images can be reconstructed reliably and robustly from this setup, even when scatter from the specimen is weak. A series of ptychographic reconstructions at X-ray energies around the L absorption edge of iron demonstrates the advantages of this method for soft X-ray spectromicroscopy, which can readily provide chemical sensitivity without the need for optical refocusing. In particular, the phase signal is in perfect registration with the modulus signal and provides complementary information that can be more sensitive to changes in the local chemical environment.

Measuring spectroscopy and magnetism of extracted and intracellular magnetosomes using soft X-ray ptychography

“…3B and Movie S2. Maiden et al (29) reported the ptychography phase spectrum of CoFe 2 O 4 in the Fe 2p region and found the minimum phase around the same energy, whereas Shapiro et al (32) found the minimum in the ptychography phase spectrum at 708.0 eV in LiFePO 4 and 708.5 eV in FePO 4 . The ptychography absorption spectrum of magnetosome chains tracks the X-ray absorption spectrum.…”

“…The significant change in the contrast and morphology in the phase signal several electronvolts below the absorption maximum means that the phase signal might offer advantages in terms of chemical differentiation and mapping. Often, the changes in phase signal across an edge provide more detail, and clearer features than the absorption signal (29,32), at energies where the X-ray absorption is smaller, which gives advantages with respect to reducing radiation damage. In addition, analysis of the combined phase and absorption signals provides improved chemical contrast, as shown by Shapiro et al (32).…”

“…This procedure allowed measurement of the full Fe L-edge ptychographic absorption and phase spectra of magnetosomes in whole cells. Previously, other studies showed that chemical differentiation can be achieved through the phase signal derived from ptychographic measurements (29,50,51). However, the ptychographic data in those prior studies were only collected at a few discrete energy points so that the full ptychography spectra were missing.…”

“…Unlike conventional lens-based microscopic imaging techniques, such as STXM, ptychography is not limited by the properties of the X-ray optics used, has the potential to reach near atomic-scale spatial resolution with very short-wavelength X-rays (27), and can image with Rayleigh wavelength-limited resolution in the soft X-ray region (at the Fe L 3 edge, the wavelength is 1.8 nm). Ptychography has been used to image biological cells (28,29), labyrinthine domains in magnetic multilayers (30), and 3D structure with 16-nm spatial resolution (31). Recently, soft X-ray spectro-ptychography was developed at the Advanced Light Source (32)(33)(34)(35), which opens up the possibility of chemical speciation via X-ray spectroscopy with spatial resolution of a few nanometers.…”

Coherent diffractive imaging using randomly coded masks

“…It is an extension to CDI that utilizes a series of known, randomly coded masks to encode additional information into the measured diffraction patterns to guarantee uniqueness of the retrieved image, 16 and that builds on recent ptychography work which showed that randomized illumination improves reconstruction quality. [17][18][19] Related numerical work has also been done with phase-only masks in the field of optical cryptography. 20,21 We expect that this technique will be particularly effective for data with a low signal to noise ratio, helping in cases of weak contrast such as soft X-ray diffraction from orbital domains, 22 and with further development may even provide the potential to become a single-shot method for use at X-ray free electron laser sources.…”