We know how Zemax handles stack coatings when applied on a air to glass surface :
“
If the surface specified is a boundary going from air to glass, the coating layer order is interpreted exactly as specified in the coating file.
[...]
If the surface specified is a boundary going from glass to air, then the order of the layers is automatically reversed, so that the coating is the same as if it had been applied going from air to glass.
“
But whan happens for other coatings, for example an IDEAL coating with R and T value when going from air to glass ?
Are R and T reversed when going from glass to air ?
Based on the TABLE section : “Angles of incidence are assumed to be in the incident media, and for coatings placed on refractive surfaces, that the incident media has a lower index of refraction than the substrate. For coatings placed on surfaces where the rays go from high index to low index (such as glass to air), the refracted angle in the low index media is used as the angle of incidence.”, so that basicaly means that the transmission from 2 to 1 at refracted angle theta is the same as the transmission from 1 to 2 at incident angle theta. In other words, ignoring the angle consideration (imagine an angle-indepedant coating), the transmission from 1 to 2 is the same as the transmision from 2 to 1. Is that the case for other coatings as well ? (IDEAL, IDEAL2, etc)