Glasses

Glasses are entered by name in the glass column. Available glasses may be reviewed, and new ones entered using the glass catalog tool. See the Chapter Using Material Catalogs for details.

Blanks are treated as air, with unity index. Mirrors can be specified by entering "MIRROR" for the glass type, although this name will not appear in the glass catalog. The index of refraction of the mirror space is always equal to the index of refraction of the media before the mirror.

If a surface or object has the material type MIRROR, light will only be reflected. The transmitted part will be ignored. The behavior is different depending on whether a coating has been specified:

• If no coating is specified, the surface is assumed to be coated with a thick layer of aluminum, with an index of refraction 0.7 - 7.0i. The aluminum layer is assumed to be thick enough that no light propagates past the layer. This means that an uncoated mirror surface has a reflectivity of less than 1 although the exact value will depend on the polarization of the rays.

• If a coating is specified, the reflectivity will be that of the coating.

For information on the effect of temperature and pressure on index of refraction data, see Defining Temperature and Pressure.