How to return the index of refraction at a specific wavelength

There are a number of different ways in which OpticStudio 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.

Authored By Dan Hill


OpticStudio has several ways to analyze the index of refraction of material at a particular wavelength. These methods include:

  • The Dispersion Diagram
  • Reports
  • The Merit Function
  • ZPL

While the Dispersion Diagram reports the index of refraction of a given material over a number of wavelengths, it is not specific to any particular system. Should you want to analyze the index of refraction at a given surface in your system - with respect to the wavelengths used in that setup - then there are index reports and operands that may be utilized. 

The Dispersion Diagram

The Dispersion Diagram will plot the index of refraction of a selected material as a function of the wavelength in microns. To open the diagram, navigate to the Libraries tab and select Materials Analyses...Dispersion Diagram

The scaling of both the x and y axes are user definable under Settings:

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

The text version of the Dispersion Diagram reports the numerical data for the selected material in a two column format. It 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.  

Index reports and the INDX operand

The Reports menu in OpticStudio provides two different reports which may be used to return detailed index data. Specifically, the Surface Data report (Analyze...Reports...Surface Data) lists the index of refraction data for each design wavelength at the selected surface number. In the case below, Surface 1 has a material type of SK2, and the index for each of the design wavelengths is reported:

The Prescription Data Report (Analyze...Reports...Prescription Data), on the other hand, will display index data at each wavelength for every surface in your design.

In addition to the reports, the index of refraction can be returned in the Merit Function Editor via the INDX operand.

The only input values for this operand are the surface number and wavelength, and as is the case for any optimization operand, this data is also then accessible with the Zemax Programming Language through the OPEV() or OPER() functions.


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