Starting with object generation 5.05 the list of spectra offers a new object type called ‘Function fit’. It allows the user to define a function which may contain terms that retrieve optical functions, fit parameters and integral quantities (the latter in CODE only, but not in SCOUT). The function value is computed based on the current model and compared to a user-defined target value, or an interval of allowed target values. The fit deviation of the object is the absolute difference between current value and target value (or closest limit of the target range), taken to a user-defined power. If the function value stays within the target interval the deviation is zero.
Objects of this type can be used to impose restrictions to the model. If, for example, an optical function returns the real part n of the refractive index at a certain wavelength, you can define a target interval for n and generate a large deviation outside the target interval. This forces the fit to look for solutions that are compatible with the given range of refractive index values.
Times change, and the way we handle software licenses is changing, too. The info page has been updated recently (=today) – we are sure that for most users nothing will change in the way SCOUT and CODE are used.
We have included a new fit option which helps to increase the speed of analysis in time critical applications: In methods which use pre-fit sets in the list of fit parameters you can now include the current fit parameter values in the pre-fit search. This eventually avoids many fit iterations if differences between consecutive measurements are small.
The new feature can be turned on or off in the dialog of fit options.
Starting with object generation 4.77 you can generate low and high limits for fit parameters automatically when you generate them – at least for thickness values. In the fit options dialog (File/Options/Fit) you can set a percentage (lower right corner) which is used to compute the low and high limit of the available thickness range. The reference value is the thickness value at the time the new fit parameter is generated.
Note that the automatically generated range is also the range of parameter sliders that are based on fit parameters.
Note also that you can automatically generate thin film thickness values as fit parameters by drag&drop of a layer stack to the list of fit parameters in the treeview. If the list of fit parameters is shown in a view this is certainly the fastest way of generating thickness sliders.
Here is an example showing sliders with limits of +/-5% that have been generated automatically:
How can I display the difference of simulated and measured spectra?
Sometimes it is advantageous to inspect the difference of simulated and measured spectra in order to find out about appropriate model extensions. Please read the instructions below to activate the drawing of difference spectra.
Open the spectrum for which you want to see the difference with a right-click in the treeview. Select the local menu command File/Options/Difference/Show to turn on the difference display. This menu item is a checked property: Clicking on it changes its status from checked to unchecked or vice-versa.
The additional menu commands File/Options/Difference/Pen and File/Options/Difference/Line mode are used to control the appearance of the difference curve. Use these settings to clearly separate the difference curve from the simulated and measured spectra. You can use, for example, pen 3 (green by default) and line mode 3 (dashed).
