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.
Highlights
With the advent of third-generation synchrotron radiation sources and free electron lasers coherent x-ray diffractive imaging (CDI or CXDI) has emerged as a new tool for structure analysis on the nanoscale [1, 2]
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 addition to slow convergence and uniqueness issues, this limitation has been a motivation for alternative approaches such as holography, based on deterministic single-step reconstruction [7,8,9,10]
Summary
With the advent of third-generation synchrotron radiation sources and free electron lasers coherent x-ray diffractive imaging (CDI or CXDI) has emerged as a new tool for structure analysis on the nanoscale [1, 2]. In an iterative process the object transmission function is recovered numerically from the measured intensity This conceptually rather simple experimental scheme has been applied very successfully (see [1, 2] and references therein) and has been proven to be extremely powerful in terms of resolution [4, 5]. Reconstruction is possible, if the diffraction pattern is band-limited and recorded on a fine enough grid to sample its smallest features [6]. This restricts the application of the method to isolated specimens of a lateral extent much smaller than the beam diameter. In addition to slow convergence and uniqueness issues, this limitation has been a motivation for alternative approaches such as holography, based on deterministic single-step reconstruction [7,8,9,10]
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