Laser-induced thermal blooming in rectangular waveguides

Steady-state thermal blooming in perfectly conductive rectangular waveguides is described by the coupling between the Helmholtz equation and the diffusion equation without convection. The fields are pinned at the walls by Dirichlet and Neumann conditions and the temperature by Dirichlet conditions. The equations are solved by Green's functions in a perturbation scheme employing the Born approximation. The first-order solutions indicate that only about 4 percent of the energy is transferred from the unperturbed mode, as defined by a constant index of refraction, to all the higher-order modes for moderate absorption.