If the medium properties are not temperature dependent and the domains do not undergo significant thermal expansion, then a unidirectional coupling is appropriate. The heat source generated by the attenuation of rays can be included in the heat transfer simulation by first computing the ray trajectories using a Ray Tracing study step, then computing the temperature using a Stationary study step. Both study steps are described in the COMSOL Multiphysics Reference Manual.

If the refractive index of the medium is temperature dependent, a more accurate approach is to set up a bidirectional coupling in which the attenuation of ray power affects the temperature distribution, which in turn affects the ray trajectories. The two physics can be solved for using an iterative solver loop consisting of a time-dependent solver for the ray trajectories and a stationary solver for the temperature. Such a solver sequence can be set up automatically using the Bidirectionally Coupled Ray Tracing study step, also described in the COMSOL Multiphysics Reference Manual.