In addition to fitting index data, it is also important to define the transmission properties of the glass in ZEMAX, if any exist. ZEMAX models the transmitted intensity user Beer’s Law:

                                                  T = e^-at

where a is the absorption coefficient and t is the path length through the glass. The parameter a generally depends upon wavelength and has units of inverse length.

To modify or set the transmission data for a glass, select the “Transmission” button near the bottom right hand corner of the Glass Catalog dialog:



Selecting the “Transmission” button invokes the Transmission Data dialog, which includes a spreadsheet of 3 different columns:  Wavelength, Transmission, and Thickness. Wavelengths are always entered in micrometers, and thicknesses are entered in millimeters, regardless of the system Lens Units.



Multiple data points may be defined in the transmission data editor. Internally, ZEMAX converts the data to transmission “per mm,” and interpolates between the defined wavelengths. If a ray is being traced at a wavelength outside of the wavelengths defined in the Transmission Data editor, then the data for the closest wavelength is used. Otherwise, ZEMAX performs a linear interpolation between data points defined.

Note that if transmission data has been omitted, then ZEMAX assumes the internal transmission for a material is 1.0 at all wavelengths. It is very important to verify the transmission data to ensure the most accurate results.