Reflection and Refraction
The default boundary condition is the Material Discontinuity condition on all interior and exterior boundaries. The Material Discontinuity causes rays to be reflected and refracted if the two adjacent domains have different refractive indices.
The direction of the refracted ray is based on Snell’s law. If the ray intensity or power is solved for, then they are reinitialized according to the Fresnel equations. You can modify the application of Fresnel equations by adding one or more thin dielectric layers to the surface.
Material Discontinuity Theory and Intensity, Wavefront Curvature, and Polarization in Theory for the Geometrical Optics Interface.
Suppressing the Release of Reflected Rays
The total number of released secondary rays in a model can sometimes grow rapidly and exhaust all of the preallocated secondary degrees of freedom. For example, a single ray reflecting back and forth between two Material Discontinuity boundaries can create an inordinately large number of rays, each with extremely low intensity.
It can be useful to constrain the release of secondary rays at boundaries so that only the most important rays are produced. If reflected rays are not of any interest at all, then in the Rays to Release section, select Never from the Release reflected rays list. If reflected rays are only relevant to the model under a certain condition, such as hitting a specific part of the surface or having a certain direction, instead select Based on logical expression and then enter a user-defined Evaluation expression that must be satisfied.
If ray intensity is solved for, you can also specify a Threshold intensity. If a reflected ray would have intensity below the threshold, it isn’t released at all. Similarly, if ray power is solved for, you can specify a Threshold power.