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 found out three number parameters.

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 often 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. Spectrometer sensitivity curves are a good starting point but for accurate results you might need to tweak it.

Sensitivity curves for our spectrometers(Avantes and BWSpec)

Manufacturer provided

Experimental (Calculated to get best fit for our models)

Element concentration calibration

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