ZEMAX is supplied with the glass catalogs of the major manufacturers (which are built-in to ZEMAX), but there are times when you still need to add your own glass data. There are several methods to do this in ZEMAX.
 
Sometimes, you may have refractive index data at only a single wavelength, and other times you may have only two or three data points available to you.  In these cases, the table glass may be the best way to enter the data into ZEMAX.  Table glasses are defined by data stored in an ASCII file.  Within the ASCII file, you can specify the refractive index and transmission of the glass at specified wavelengths, and then ZEMAX uses these exact values at the specified wavelengths.  If refractive index values are needed at intermediate wavelengths, ZEMAX automatically fits the data to a smooth spline curve to model the dispersion of your glass. 

The table glass is ideal in cases where certain wavelengths must have specific corresponding indices of refraction.  One or more data points are required, and the spline-fitting performed by ZEMAX is simply used to create a smooth transition from one data point to the next.  In any case, using the table glass you can be assured that the index of refraction for a given wavelength will be exactly as you define in the table glass; there is no fitting function which may deviate from the data being fitted by the data points.

The table glass file is a simple ASCII list, and includes the density of the glass (optional), wavelength-index pairs, and transmission data.  The file format is as follows:



The ASCII table glass file must end in the extension “.ZTG” (for ZEMAX Table Glass) and must be placed in the “Glass Path” subdirectory as defined in File > Preferences dialog (by default the directory is /{ZEMAXRoot}/Glasscat).  The name of the file, including the extension, must not exceed 20 characters in length.

Please aslo note the following (this is also covered in Chapter 18 of the ZEMAX User’s Guide):

• For the table glass, any blank line or a line starting with the “!” symbol is assumed to be a comment and is ignored by ZEMAX.
• The DENSITY data line refers to the density of the glass in grams per cubic centimeter.  If this line is omitted, then the density is assumed to be zero.
• The wavelength values must always be in units of micrometers, and should be listed in ascending order
• The index of refraction and transmission values must also be positive values.
• The thickness values of the glass are in millimeters (regardless of the system lens units) for the specified internal transmittance.
• Both the transmission and thickness values are used to determine the internal transmission per unit length.  If both of these values are excluded from the table glass file, then the material is assumed to be 100% transmitting.
• Up to 1200 lines of wavelength data may be defined per file.  At least 5 data points should be defined to provide a reasonable spline fit.