It is possible to define an auxiliary dependent variable for the optical path length by selecting the Compute optical path length check box in the Additional Variables section of the physics interface node’s Settings window. Initially the optical path length is set to 0 for all released rays. It is possible to reset the optical path length to 0 when the rays interact with boundaries.

The phase of a ray is necessary for some applications that require information about the instantaneous electric fields of multiple rays, such as interferometers. To define an auxiliary dependent variable for phase, select the Compute phase check box in the Intensity Computation section of the physics interface node’s Settings window. This check box is only available if the ray intensity is computed.

The instantaneous phase can be used to visualize interference patterns where the rays intersect a surface. See the Results Analysis and Visualization section.