title: Extension of the time-dependent dynamical diffraction theory to 'optical phonon'-type distortions: application to diffraction from coherent acoustic and optical phonons.
abstract: An extension of the time-dependent Takagi-Taupin theory to 'optical phonon'-type distortions is presented. By splitting the susceptibility into the contributions from each atom in a unit cell, modifications to the structure factor as well as lattice parameter are taken into account. The result is a compact, surprisingly simple, equation with a strong formal similarity to the classical Takagi-Taupin equation, with the latter included as a special case. Time dependence is explicitly retained and thus the analysis is applicable to situations where the crystal is modified on time scales comparable with that for the X-rays to traverse an extinction depth. A comparison is made between the influence of coherent acoustic and optical phonons on the diffraction of X-rays. Numerical and perturbative analytical solutions of the generalized Takagi-Taupin equation are presented in the presence of such phonons.
authors.affiliation: Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, England. p.sondhauss1@physics.ox.ac.uk
authors.forename: Peter
authors.initials: P
authors.lastname: Sondhauss
authors.forename: Justin S
authors.initials: JS
authors.lastname: Wark