Glass data in ZEMAX is managed within catalogs, which are ASCII text files with the extension .agf. The glass catalog contains refractive, thermal, transmission and other data on each glass inside the catalog. Many glass catalogs are supplied with ZEMAX (schott.agf, ohara.agf, infrared.agf etc).

Important: you should never edit or change the glass catalogs supplied with ZEMAX. When you update ZEMAX at its next release, all files included with the installation (including glass catalogs) are overwritten with the versions supplied with that release. For this reason, when you want to add your own glass, the first step is to create your own catalog. Then add as many glasses as you want to your catalog. Your private catalogs will not be affected by updates to ZEMAX.

Also Important: never delete a glass from a catalog once it has been used. If you delete a glass from the catalog, any file that used the now-deleted glass will fail to trace, and will be useless. The correct approach is to mark the glass as 'Obsolete', and to use the comment field to explain why the glass should not be used. Both of these are discussed later in this article. The System Check utility will detect and warn the user if an obsolete glass is used, but the file will still ray-trace correctly. 

Chapter 18 of the User's Guide (entitled Using Glass Catalogs) should be read in conjunction with this article.

All glass catalogs are maintained in the Glass Path folder, which is defined under File...Preferences...Directories. By default, English-language versions of Windows will use

C:\Program Files\ZEMAX\GLASSCAT

and any other folder can be specified if desired, of course. Catalog files are text files with the extension .agf (ASCII glass file). Note that for every .agf there may be a .bgf (binary glass file) file also. The .bfg files are created by ZEMAX when the .agf is used, and these files should not be edited or used by the user in any way. These files can be ignored: only the .agf file is important.

To create a new glass catalog -we will call it MyCatalog.agf- there are two methods:

1. Just use Windows Explorer to navigate to the Glass Path folder, then right-mouse click in the folder and choose New...Text Document. Then rename this .txt file to MyCatalog.agf. This will produce an empty catalog

2. Within ZEMAX, click on Tools...Catalogs...Glass Catalogs, select a supplied catalog and then press the 'Save Catalog As' button to save the catalog with a new name. This will save the catalog and all glasses inside it, which can then be deleted, edited or left alone.

In the following pages, I have created MyCatalog.agf using method 1 above.

Run ZEMAX, and click on Tools...Catalogs...Glass Catalog and select MyCatalog.agf:



This window shows the data for the currently selected glass (there is no glass inside the catalog yet). The data can be separated into useful sections:

1. Refractive Index Data. Dispersion data is entered via dispersion formulae (Schott, Sellmeier, Conrady etc). If you have raw index data, ZEMAX can fit this to the various formulae for you. Just press the Fit Index Data button to enter index versus wavelength data and have ZEMAX fit it, or use the Glass Fitting tool. See the separate article Fitting Index Data for full details. If you do not use the fitting tools, you must enter the minimum and maximum wavelengths of operation of the glass by hand.

2. Thermal Variation data. ZEMAX can compute the refractive index at temperatures different to the reference temperature. The data values D0, D1, D2, E0, E1, Ltk and TCE are used by the thermal model. The glass fitting tool will take data at multiple temperatures and produce not only a fit to the refractive datya but also a fit to the thermal data. See the article How ZEMAX Calculates Refractive Index At Arbitrary Temperatures and Pressures, and the Users Guide for full details.

3. Transmission data. Press the Transmission button to enter the internal transmission of the glass. This data should ignore surface reflections, and represents the absorption of the bulk material. (Surface reflections depend only on the index of the glasses, the angle and wavelength of the incoming ray, and the ray's polarization state, and are not affected by bulk absorption losses.)

4. Other data. You can tell ZEMAX 'non-optical' data, like relative cost, stain resistance, climate resistance etc. In addition you can also provide a comment for the glass itself. The 'Status' entry is usually Standard or Preferred for easily available materials. 'Special' is available to describe unusual materials, and 'Obsolete' should be used to represent glasses that are no longer available (glasses should never be deleted once entered, as this would render designs that use that data useless). The status flag 'Melt' should normally only be used by ZEMAX's Melt Data fitting tool, although it can be used by hand if desired.

After entry, the glass catalog window will look like so:



There may be multiple glasses inside the catalog, and the data displayed represents whatever glass is highlighted in the Glass control below the catalog name. It is a good idea to give the catalog itself a descriptive comment, and a date or version number.

After you have entered the data, test it before use. ZEMAX provides multiple tools for this:

1. Within the Glass Catalog dialog, press the Glass Report and/or Catalog Report to get comprehensive listings of all the data entered.

2. Add your catalog to an existing design, under General...Glass Catalogs:



and then use Analysis...Glass and Gradient Index...Dispersion diagram to check the index versus wavelength values:



and Analysis...Glass and Gradient Index...Internal Transmission versus Wavelength to check this data also.