OpticalFit Manual 18.06	Table of contents	Peak fitting	« Last page	Next page »

Peak fitting

Opening the peak table

To begin peak deconvolution, select the ‘Peak fitting→Peak table’ menu option, as below:

The peak fitting menu option.

This will open the ‘Peak table’ window, shown below:

The peak table window (empty).

Note peak fitting should be performed with the spectrum plotted in energy or wavenumber, but not wavelength. Plotting a spectrum in terms of wavelength will distort the profile of energy-symmetric peaks, resulting in a poor fit or the need for a larger number of physically meaningless peaks to adequately fit the spectrum (see Peak fit in energy, not wavelength! section).

Adding peaks to the peak table

To add a peak to the peak table, double click the left mouse button over the point in the spectrum at which you would like the peak to be added. This will show the inspection marker.

Adding a peak using the inspection marker.

Once the marker is in the correct position for the peak, press the ‘Add peak’ button in the peak table window. OpticalFit will place the peak at the position of the inspection marker, and automatically determine the peak height and full width at half maximum (FWHM) by fitting the peak against the current residual spectrum.

The peak table, with one peak added.

With the peak added to the table, the spectrum plot will refresh to show the peak profile (as below).

The spectrum display, showing the new peak.

When you add a new peak, the peak height and width are determined by fitting the peak against the residual spectrum. However, the peak position is fixed at the selected energy/wavelength, as set by the user via the inspection marker. Often, it is a good idea after adding a peak to fit all the peak parameters, including the position. To do this, press the ‘Fit!’ button in the peak table window. The adjusted peak will be moved and scaled to minimise the fit error, as shown below:

The spectrum display, showing the new peak with a fitted position.

You may repeat the above process to add as many peaks as are required to adequately fit the spectrum. In the case of the boron nitride example shown above, three peaks were required to adequately fit the spectrum, as shown below:

The spectrum display, showing three peaks.

The peak table lists the positions, heights and width of the three peaks, and also lists several fit metrics at the bottom of the table area:

The peak table, with three entries.

The 'Fit!' button

To optimise the peak fit using a nonlinear least-squares fitting algorithm, press the ‘Fit!’ button. This will optimise the fit quality by varying the peak height, width and FWHM of all peaks in the peak table, except those explicitly locked in the peak table (i.e. ‘Fit’ = ‘No’).

Editing the peak table

To edit any of the entries in the peak table, double-click the left mouse button on the entry.

The meanings of the various entries are described below:

Label	The text used to label the peak in the spectrum view. If not set explicitly by the user, the default label will be the peak position.
Colour	The colour used to display the spectrum profile in the spectrum view.
Fit All	This button determines whether all parameters for the selected peak (position, height, FWHM, G/L) are free to be modified by the fitting algorithm (fit all = yes) or will be locked and not modified by the fitting algorithm (fit all = no).
Position	The position of the peak centre along the x-axis, measured in the current x-axis units.
Fit	This button determines whether the position parameter will be free to be modified by the fitting algorithm (fit = yes) or will be locked and not modified by the fitting algorithm (fit = no).
Height	The height of the peak, measured in the same units as the spectrum y-axis.
Fit	This button determines whether the height parameter will be free to be modified by the fitting algorithm (fit = yes) or will be locked and not modified by the fitting algorithm (fit = no).
FWHM	The full width at half maximum of the peak, measured in the current x-axis units.
Fit	This button determines whether the FWHM parameter will be free to be modified by the fitting algorithm (fit = yes) or will be locked and not modified by the fitting algorithm (fit = no).
G/L	The ratio of Gaussian to Lorentzian peak profile, ranging from 0 (Lorentzian only) to 1 (Gaussian only).
Fit	This button determines whether the G/L parameter will be free to be modified by the fitting algorithm (fit = yes) or will be locked and not modified by the fitting algorithm (fit = no).

Deleting peaks from the peak table

To delete a peak from the peak table, select it from the peak table using a single click of the left mouse button, then press the ‘Delete peak’ button.

Loading and saving the peak table

Please refer to the loading and saving peak tables page.

The ‘OK’ and ‘Cancel’ buttons

Pressing the ‘OK’ button will apply your changes and close the window.
Pressing the ‘Cancel’ button will close the window and restore the entries in the peak table to those which were present before the peak table window was last opened.