Water window ptychographic imaging with characterized coherent X-rays

Abstract

A ptychographical coherent diffractive imaging experiment in the water window with focused soft X-rays at 500 eV is reported. An X-ray beam with high degree of coherence was selected for ptychography at the P04 beamline of PETRA III synchrotron radiation source. The beam coherence was measured with the newly developed non-redundant array method, and a coherence length of 4.1 mm and global degree of coherence of 35% at 100 mm exit slit opening in the vertical direction were determined. A pinhole, 2.6 mm in size, selected the coherent part of the beam that was used to obtain ptychographic reconstruction results of a lithographically manufactured test sample and a fossil diatom. The achieved resolution was 53 nm for the test sample and was only limited by the size of the detector. The diatom was imaged at a resolution better than 90 nm.

Data compression strategies for ptychographic diffraction imaging

“…The photon flux behind the pinhole was about 700 photons/s. Compared to a previous experiment with a twice smaller pinhole diameter [36], a similar photon flux at three times smaller X-ray bandwidth was obtained due to a newly added horizontal focusing mirror. The measurements were performed in the HORST (holographic roentgen scattering) vacuum chamber in the PCDI mode [37].…”

Spatial coherence determination from the Fourier analysis of a resonant soft X-ray magnetic speckle pattern

“…γ τ r r 1 2 varies from zero for a fully incoherent beam to one for a fully coherent beam In our XRMS experiment, the largest path-length difference given by the dimension of the illuminated area is 0.87 µm l Δ = which is considerably smaller than the temporal (longitudinal) coherence length 4.8 µm L ξ ≈ determined by the resolving power of the monochromator (see above) [13,22]. Hence, in the so-called quasi-monochromatic approximation, meaning a narrow spectral bandwidth of the X-ray…”

“…Within the framework of the Gaussian Schell model (GSM), which is widely used to describe synchrotron radiation from an undulator, the CDC and the intensity distribution of the X-ray beam are assumed to be Gaussian functions. In this case, a global degree of coherence can be introduced, which characterizes the transverse coherence properties of the beam by one number [13,21,22] ( ) ( )…”

“…There are several powerful X-ray techniques emerging along with the development of X-ray sources that require coherent X-ray radiation. These are, e.g., coherent diffractive imaging (CDI) [3][4][5][6][7], X-ray holographic microscopy (XHM) [8], Fourier transform holography (FTH) [9][10][11], X-ray ptychography [12][13][14] and X-ray photon correlation spectroscopy (XPCS) [15][16][17]. Consequently, the determination of the coherence properties of X-ray sources is of high interest since they are the essential prerequisites for these experiments.…”

High-dynamic-range water window ptychography

“…Due to the integrating nature of the detector and electronic imperfections, noise and dark-current and the maximum photon number per pixel (898 photons/pixel) the effective dynamic range (DR) of the detector is limited. This is a severe limitation for CDI and water window ptychography of weakly scattering samples due to the large DR of diffraction patterns [7]. Different approaches exist to circumvent this problem.…”