arXiv subjects

Jean-Pierre Guigay

Publications and source records attributed to Jean-Pierre Guigay.

4 recordsLinked to original sources

arXiv2024

Formulation of perfect-crystal diffraction from Takagi-Taupin equations. Numerical implementation in the crystalpy library

The Takagi-Taupin equations are solved in their simplest form (zero deformation) to obtain the Bragg-diffracted and transmitted complex amplitudes. The case of plane-parallel crystal plates is discussed using a matrix model. The equations are implemented in an open-source python library crystalpy adapted for numerical applications such as crystal reflectivity calculations and ray tracing.

physics.comp-ph↗

arXiv2021

X-ray focusing by bent crystals: focal positions as predicted by the crystal lens equation and the dynamical diffraction theory

The location of the beam focus when monochromatic x-ray radiation is diffracted by a thin bent crystal is predicted by "crystal lens equation". We derive this equation in a general form valid for Bragg and Laue geometries. This equation has little utility for diffraction in Laue geometry. The focusing effect in the Laue symmetrical case is discussed using concepts of dynamical theory and an extension of the lens equation is proposed. The existence of polychromatic focusing is considered and the feasibility of matching the polychromatic and monochromatic focal positions is discussed.

physics.optics↗

arXiv2019

Translative lens-based full field coherent X-ray imaging

We describe a full-field coherent imaging approach suitable for hard X-rays based on a classical (i.e. Galilean) X-ray microscope. The method combines a series of low-resolution images acquired at different transverse lens positions into a single high-resolution image, overcoming the spatial resolution limit set by the numerical aperture of the objective lens. We describe the optical principles of the approach, demonstrate the successful reconstruction of simulated phantom data, and discuss aspects of the reconstruction. We believe this approach offers some potential benefits over conventional scanning X-ray ptychography in terms of acquisition speed, spatial bandwidth and radiation dose rate.

physics.optics↗

arXiv2017

A finite element approach to dynamical diffraction problems

A finite element approach to solve numerically the Takagi-Taupin equations expressed in a weak form is presented and applied to simulate X-ray reflectivity curves, spatial intensity distributions and focusing properties of bent perfect crystals in symmetric reflection geometry. The proposed framework encompasses a new formulation of the Takagi-Taupin equations, which appears to be promising in terms of robustness and stability and supports the Fresnel propagation of the diffracted waves. The presented method is very flexible and has the potential of dealing with dynamical X-ray or neutron diffraction problems related to crystals of arbitrary shapes and deformations. The reference implementation based on the commercial COMSOL Multiphysics software package is available to the relevant user community.

physics.optics↗