Unobtainium

FilmStar calculates and optimizes multiple films on multiple massive layers. It is therefore the program of choice for designing bandpass filters as well as active devices.

Imagine a film which is 1 QWOT at all wavelengths and has index equal to the square root of the index of  the layer onto which it is deposited. This film of unobtainium acts as an ideal antireflector at normal incidence. As illustrated the (pink) layer of unobtainium enables FilmStar to simulate a slightly absorbing massive layer as entrance medium. This is useful for calculations involving active devices.

Mixed Material Dialog

The first task is to set up a square root index function or dispersive table for unobtainium. There are several ways to do this. Perhaps the most elegant is to utilize FilmStar's Mixed index capability as shown here.

Film Indices Dialog

Function name TIO2_AR is then specified in the Film Indices editor. But how do we tell FilmStar to automatically convert unobtainium layers to 1 QWOT at each evaluation wavelength? This is accomplished by including string QWOT  in the material's Description column as illustrated here. 

Unobtainium on TiO2

To test that this works as expected, we try a design with unobtainium on both sides of a slab of dispersive TiO2 (.25M 2H .25M). 

Note that it is not necessary to use a dispersive index function or table. If the massive layer can be approximated by a constant, one need only enter its square root for the unobtainium index.