Utilization of the Coherence Function with Welch's Method for Signal Analysis in Low Resolution Laser-Induced Breakdown Spectroscopy

Abstract

This work presents a technique by which a low resolution (≈1 nm) fiber-optic spectrometer may be used to definitively identify elements and molecular fragments in laser-induced breakdown spectroscopy. Commercial laser-induced breakdown spectroscopy (LIBS) spectrometers have high resolution in the area of spectral interest, and software is used to identify elements via a look-up table containing known spectral lines. When analyzing spectra from a lower resolution fiber-optic spectrometer, software based on look-up tables can produce erroneous results, reporting elements absent from the sample. As a solution to this problem, an analysis using the coherence function in conjunction with Welch's method is used to compare sample spectra with a library of reference spectra, which contain peaks primarily from a single element. The analysis has proved to be adept at identifying specific elemental signatures in multi-component samples. The technique leverages the increased information content of concomitant atomic emission lines, which are easily collected with a low resolution broadband (200–1100 nm) fiber-optic spectrometer. This technique alleviates the need for the user to visually verify the vicinity of individual peaks during testing. While Pearson's method is generally used for this type of analysis, we show that Welch's method has the advantage of being less susceptible to problems caused by continuum background.