Master model objects are dielectric function models with the additional feature that you can compute the values of selected susceptibility parameters from user-defined parameters by user-defined formulas. This provides a very high modelling flexibility.

There are two types of situations where master models are useful. In the first one the parameters that you want to obtain from the optical analysis are not those that appear in the susceptibility types that the program provides. A typical example is the determination of carrier concentrations by infrared spectroscopy: This quantity is proportional to the square of the Drude parameter plasma frequency which is the fit parameter to be used here. In master model objects you can define a fit parameter called 'Carrier concentration' and compute from its value the plasma frequency of the Drude model which is then used in the calculation of the optical spectra. The user-defined fit parameters are called master parameters whereas the model parameters computed from the master parameters are called slave parameters.

In the second case of problems you want to control many model parameters by only a few master parameters. A good example is the description of amorphous oxides for various oxygen contents. If you use the OJL model for the interband transition and you investigated already how the OJL parameters like gap energy, mass and gamma depend on the oxygen concentration in the oxide, you may want to describe the oxide by only one parameter, namely the oxygen content. Applying a master model object you can define the fit parameter 'Oxygen content' and specify for all model parameters that vary with the oxygen content how they depend on the master parameter by suitable expressions. This way a complex optical constant model can be completely controlled by only one parameter.