Medium boundary effects

When a photon arrives at the boundary of a dielectric medium, its behaviour depends on the nature of the two materials which join at that boundary:

• Case dielectric $\to$ dielectric.
  The photon can be transmitted (refracted ray) or reflected (reflected ray). In case where the photon can only be reflected, total internal reflection takes place.
• Case dielectric $\to$ metal.
  The photon can be absorbed by the metal or reflected back into the dielectric. If the photon is absorbed it can be detected according to the photoelectron efficiency of the metal.
• Case dielectric $\to$ black material.
  A black material is a tracking medium for which the user has not defined any optical property. In this case the photon is immediately absorbed undetected.