Ptychographic coherent x-ray diffractive imaging in the water window

Abstract

Coherent x-ray diffractive microscopy enables full reconstruction of the complex transmission function of an isolated object to diffraction-limited resolution without relying on any optical elements between the sample and detector. In combination with ptychography, also specimens of unlimited lateral extension can be imaged. Here we report on an application of ptychographic coherent diffractive imaging (PCDI) in the soft x-ray regime, more precisely in the so-called water window of photon energies where the high scattering contrast between carbon and oxygen is well-suited to image biological samples. In particular, we have reconstructed the complex sample transmission function of a fossil diatom at a photon energy of 517 eV. In imaging a lithographically fabricated test sample a resolution on the order of 50 nm (half-period length) has been achieved. Along with this proof-of-principle for PCDI at soft x-ray wavelengths, we discuss the experimental and technical challenges which can occur especially for soft x-ray PCDI.

Soft X-ray spectromicroscopy using ptychography with randomly phased illumination

“…4b: the shape of the pinhole is well defined, with a diameter B5 mm, and the structure of the wavefront within it demonstrates the effectiveness of the random hole array as a diffusing mask. One issue with our method is the difficulty of sufficiently localizing the probe at the plane of the sample, a problem also noted by Giewekemeyer et al 9 . This was exacerbated in our case by the requirement to bin the diffraction data (see Methods section).…”

“…At X-ray wavelengths, ptychography has been used to characterize the focusing properties of X-ray optics [4][5][6] , to image interconnects within microchips 7 and to image yeast cells 8 . X-ray ptychography has recently been demonstrated using soft X-rays 9,10 , and has been used with polarized illumination to generate dichroic image contrast from magnetic thin films 11 . It can also be combined with tomography to produce three-dimensional reconstructions [12][13][14] .…”

A study on new approaches in coherent x-ray microscopy of biological specimens

“…6.10B unphysical phase discontinuities in horizontal direction have been removed using the Matlab-built-in one-dimensional phase unwrapping routine unwrap.m. The function recognizes phase jumps larger than a pre-defined tolerance value ∆ϕ along the vertical [55].…”

“…6.10D). This superiority of the phase versus the amplitude [55]. reconstruction has very advantageously been utilized before [33] and can be considered as a remarkable prospect of coherent imaging methods which enable simultaneous reconstruction of the phase and amplitude.…”

“…Ptychographic soft x-ray microscopy The illuminating wave field is confined by a small pinhole with a diameter on the order of 2 µm, before it impinges onto the sample after propagating over a distance z 1 [55].…”