Once the fit is performed, the resulting dispersion and thermal coefficients can be used to define a new glass. For example, for the case described in the previous section the glass SI_THERMAL was added to the glass catalog SG_MISC.AGF. Using the Glass Catalog tool, we see that all of the coefficient and wavelength information has been transferred to this glass, as has data for the reference temperature and the valid wavelength range:



As indicated in the previous section, all data in the glass catalogs are referenced to atmospheric pressure (P₀ = 1 atm). Thus, the minimum and maximum wavelengths represent values for the relative wavelengths rather than the inputted wavelengths.

This glass may now be used in any ZEMAX lens design of interest. We can verify that the coefficients specified for the glass are correct by setting up a simple system which uses this glass at a pressure, temperature and wavelength corresponding to one of the input data values. For example, image a simple system with three surfaces in which the glass is placed on surface 1:



For this system, the wavelength is set to 1.1 microns:



and the system temperature and pressure are set to -243.15 degrees C and 0 atmospheres, respectively:



The “Adjust Index Data To Environment” button must be checked if the system pressure and temperature are to be used in calculating the index of refraction. We can determine the index at this surface using the Prescription Data Report:



The reported value for the index is 3.51104019:



This value is within 9.0E-05 of the inputted index value (3.51113) for this temperature and wavelength. This temperature and wavelength represent the data point with the maximum fit error – as we can see in the fitting text output file ZEMAX_fit_Si_data.txt – so we would expect the difference between the ZEMAX result and the inputted data point to equal the maximum fit error, as it does. If we were to change the temperature and/or wavelength, we would find in all cases that the ZEMAX result would differ from the corresponding input value by an amount equal to the Delta value provided in the fitting text output file.

To test the calculations at a system pressure other than vacuum (e.g. at a pressure of 1 atmospheres), a bit more setup is required. When calculating the index values in vacuum, it does not matter what the surface temperature is relative to the system temperature – the data are always absolute. However, if the system pressure is non-zero, the surface and system temperatures need to be carefully specified, to ensure that the correct values for the relative index are calculated. This can be done using the Multi-Configuration Editor. For our simple system, we add 3 lines to the editor, as shown here:



The first line sets the temperature to -243.15 degrees C for all operands which follow this line in the editor. In this case only one GLSS operand follows this line, and it corresponds to the surface on which the glass has been placed. Therefore, this surface will have a temperature of -243.15 degrees C. All other surfaces in the system will be at the system temperature, which is set to be 21.85 degrees C (i.e. the reference temperature of the glass) in the third line of the editor (in general, the last TEMP operand in the Multi-Configuration Editor will always set the system temperature).

To calculate the index in this case, the system wavelength also needs to be converted from absolute to relative. Based on the formulas provided earlier in this article, we find that the relative wavelength at 1 atmosphere – the system pressure we will use for this test – corresponding to a vacuum wavelength of 1.1 microns is 1.09970583 microns. The value of the index at this wavelength and a temperature of -243.15 degrees C, for a system temperature of 21.85 degrees, may again be found in the Prescription Data Report:



The value reported by ZEMAX agrees with the value provided under the Fit column in the fitting text output file to within round-off error (4.0E-09 in this case). This is found to be the case for all values of temperature and wavelength provided in the input data file.

The results generated at system pressures of 0 and 1 atmosphere confirm that the dispersion and thermal coefficients obtained from the Glass Fitting Tool can be used to accurately model the glass in ZEMAX.