this study explores the ability of a hard K α x-ray source (17.48 keV) produced by a 10 TW class laser system operated at high temporal contrast ratio and high repetition rate for phase contrast imaging. For demonstration, a parametric study based on a known object (PET films) shows clear evidence of feasibility of phase contrast imaging over a large range of laser intensity on target (from ~10 17 W/cm 2 to 7.0 × 10 18 W/cm 2). To highlight this result, a comparison of raw phase contrast and retrieved phase images of a biological object (a wasp) is done at different laser intensities below the relativistic intensity regime and up to 1.3 × 10 19 W/cm 2. this brings out attractive imaging strategies by selecting suitable laser intensity for optimizing either high spatial resolution and high quality of image or short acquisition time.
The purpose of this paper is to show that the Shack-Hartmann wavefront sensor (SHWFS) gives access to more derivatives than the two orthogonal derivatives classically extracted either by estimating the centroid or by taking into account the first two harmonics of the Fourier transform. The demonstration is based on a simple model of the SHWFS, taking into account the microlens array as a whole and linking the SHWFS to the multi-lateral shearing interferometry family. This allows for estimating the quality of these additional derivatives, paving the way to new reconstruction techniques involving more than two cross derivatives that should improve the signal-to-noise ratio.
We present a graphical tool that we call a "confidence map". It allows to evaluate locally the quality of a phase image retrieved from the measurement of its gradients. The tool is primarily used to alert the observer to the presence of artifacts that could affect his interpretation of the image. It can also be used to optimize a phase imager since it associates a cause with the creation of each artifact: dislocation, under-sampling and noise. An illustration of the use of the confidence map tool is presented, based on a microfocus X-ray tube using multilateral shearing interferometry, a gradient based phase contrast technique employing a single 2D-grating.
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