Redstone™ Optical Spectrum Analyzer Chapter 8: Operation
Rev C, January 21, 2022 Page 50
displays the values of the fit parameters. The mathematical function used in the curve fit is a sum of different
components. The following components can be used as terms in this function:
• Polynomials with an order from 0 to 9
• Gaussian
• Lorentzian
Please note that curve fitting is a computationally heavy process. It is not advisable to fit Gaussian or Lorentzian
functions to an entire interferogram, since the data set can be very large, resulting in an unresponsive program
for a large period of time. In general, we recommend only using polynomials to fit interferograms.
Defining the Function to Fit to the Trace
The fitting function is defined using the “Function Builder” dialog box (see Figure 5150), which can be opened
by clicking on the “Edit Function” button in the Curve Fit tool window (see Figure 5251).
This dialog box is composed of three parts. The top contains two buttons that adds, modifies, or deletes function
terms, the middle section displays the function used to fit the trace (labeled as the “Final Function”), and the
bottom part displays the parameters of the currently selected function term. The currently selected term is
outlined in black.
To add a new term to the Final Function, click on the “Add” button at the top of the dialog box, and a list of the
available components will appear. To remove a term from the Final Function, click on the term, then click on the
“Delete” button at the top of the dialog box.
By default, all parameters in each term of the Final Function are scaled in order to best fit the analyzed trace.
To reduce computational time, parameters can be set to fixed values, thereby preventing them from being
scaled. To do this, select the term, check the “Fixed” check box for the parameter you wish to fix, and type the
desired fixed value into the “Value” column.
Please note that it is not possible to fit multiple polynomials simultaneously; the Final Function may only contain
one polynomial term (which may have order up to 9).
Figure 51. The fitting function is defined using the Function Builder dialog box.
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