Method for material identification with laser induced breakdown spectroscopy (LIBS)
This invention discloses a method for material identification by analyzing the LIBS spectrum of the sample. The LIBS spectrum is pre-processed to equalize the contribution of elements with strong and weak emission lines. In the meantime, the number of spectral variables is reduced to enhance the specificity and minimize the influence of instrument noise. Commonly used spectrum identification and library search algorithms are then applied to the pre-processed LIBS spectrum for material identification.
1. A method for material identification with laser induced breakdown spectroscopy (LIBS), the method comprising the steps of:
collecting the LIBS spectra of a plurality of library samples;
calculating an equalized LIBS spectrum for each library sample, wherein the spectral response of each element of interest is equalized;
collecting the LIBS spectrum of an unknown sample;
calculating an equalized LIBS spectrum for the unknown sample, wherein the spectral response of each element of interest is equalized; and
comparing the equalized LIBS spectrum of the unknown sample with the equalized LIBS spectra of the library samples to identify the material of the unknown sample.
2. The method of claim 1 , further comprising the step of selecting one or more spectral regions for each element of interest and performing principal component analysis (PCA) for a selected number of library samples at the selected spectral regions to extract principal components for the element.
3. The method of claim 2 , wherein the equalized LIBS spectra of the library samples and the unknown sample are calculated by calculating the PCA score of each element of interest for the corresponding LIBS spectra using the extracted principal components and normalizing the PCA score in reference to the maximum PCA score of the element among the selected number of library samples.
4. The method of claim 1 , further comprising the step of normalizing the intensity of atomic (ionic) emission in reference to the intensity of continuum radiation of the LIBS spectra of the library samples and the unknown sample to obtain normalized LIBS spectra of the library samples and the unknown sample.
5. The method of claim 1 , further comprising the step of calculating derivative of the LIBS spectra of the library samples and the unknown sample.
6. The method of claim 1 , wherein the LIBS spectra of the library samples and the unknown sample are measured with a LIBS apparatus comprising a high repetition rate pulsed laser, wherein the high repetition rate pulsed laser produces a train of laser pulses at a high repetition rate in the kHz or even higher range.
7. The method of claim 6 , wherein the LIBS apparatus comprises a non-gated spectrometer.
8. The method of claim 7 , wherein the integration time of the non-gated spectrometer is adjusted to cover a plurality of periods of the laser pulse train.