The Radiative Beam in Absorbing Media (rbam) interface (), found under the Heat Transfer>Radiation branch (), is used to model the attenuation of an incident light within a semitransparent material due to absorption. The beam intensity is determined using the Beer-Lambert Law. As the beam is absorbed it deposits energy which acts as a heat source.

When the physics interface is added, these default nodes are added to the Model Builder: Absorbing Medium, Transparent Surface, and Initial Values. Right-click the main node to add boundary conditions or other features. Then, from the Physics toolbar, add other nodes that implement, for example, boundary conditions. You can also right-click Radiative Beam in Absorbing Media node to select physics features from the context menu.