Oxford Centre for High Energy Density Science (OxCHEDS)

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.

Abstract:

We describe the first demonstration of a collisionally-excited optical field ionisation laser driven within a gas-filled capillary waveguide. Lasing on the 4d(9)5d-4d(9)5p transition at 41.8 nm in Xe8+ was observed to be closely-correlated to conditions under which the pump laser pulses were guided well by the waveguide. Simulations of the propagation of the pump laser radiation show that gain was achieved over essentially the whole 30 mm length of the waveguide.