LIBS Calibration

To calibrate our LIBS spectrometer measurements to correspond to real peak wavenumbers and intensities we can use the following methods:

Wavelength calibration

To calibrate a spectrometer resulting wavelengths we use the following method. We plot a theoretically calculated(see: Artificial references) element LIBS spectrum and a measured element spectrum in the same figure. We adjust the fitting function, a second degree polynomial, parameters A, B and C until the plots match each other and save the resulting funtion as a lookup-table from pixel to wavelength.

For a calibration target we use peaks of elements O and N which are always present in the air.

Note that in our example results we use combined measurements from two different spectrometers and so this calibration is done separately to each spectrometer. For some instruments a 2-degree polynomial fitting might not make a good match. Some other function fit or lookup-table might be necessary.

Intensity calibration

The light intensity for each wavelength of light is different for differing optical setups and spectrometers. Therefore a calibration curve to bring your device signal levels to a "standard" is a good idea.

Note that this kind of calibration only fixes the averages. Often the varying focus distance and LIBS intensity changes the relative intensities of different peaks thus complicating the issue.

Element concentration calibration

Methods for this are presented in the section for quantitative elemental analysis.