Animation Example
The phenomenon of total internal reflection (TIR) occurs when light travels from a high-index medium to a low-index medium and the incident angle is greater than the critical angle. The thin curves on the plot below show that TIR starts at about 41 degrees when the incident medium is glass (n=1.52) and the exit medium is air (n=1.0).
The phenomenon of FTR (or FTIR) occurs when light travels from a high-index medium, through a thin low-index layer, to a high-index medium. Below, the thick curves show the reflectance as the thickness of the low-index layer (air) changes from 10 to 900 nm. Note that as the layer thickness increases, the reflectance becomes closer to total at 41 degrees. That is, FTR gives way to TIR.
