There are really a number of different ways in which ZEMAX can be used to return the index of refraction of a particular material at a given wavelength.  The different methods are outlined in this article.

Under Analysis > Glass and Gradient Index is the Dispersion Diagram.

The dispersion diagram will plot the index of refraction of a selected glass as a function of the wavelength in microns.  The scaling of both the x and y axes are user definable:

The glass may be chosen from the pull down menu in the settings of this feature.  Only the glasses from the catalogs listed under the System > General dialog are included in the pull down list.  So, if you wish to plot the index of refraction as a function of wavelength for a glass, first make sure that the catalog which contains that glass is listed under the Glass Catalogs tab of the System > General dialog:

The text version of the Dispersion Diagram reports the numerical data in a two column format, and also lists the Temperature and Pressure for which the data is being reported:

The Dispersion Diagram is often useful, but if you would like to obtain the index data for your specific design wavelengths, there are other ways of achieving this.  Please advance to the next page to find out more.