Wavefront-enhanced laser-induced breakdown spectroscopy (WELIBS) utilizing a crystalline silicon wafer for a flat-top IR laser beam

Abstract

It has been found that transmission of the infrared (IR) laser beam through a thin crystalline silicon wafer induces changes in the laser wavefront profile from quasi-Gaussian to flat-top. This change in the laser wavefront profile was proven on a CW 1064 nm laser passing through a silicon wafer. The resultant wavefront was then evaluated using a Shack–Hartmann wavefront sensor (SHWFS). In this work, we present a novel approach to enhance the performance of the laser-induced breakdown spectroscopy technique utilizing a laser beam of a flat-top wavefront profile. The aim was to improve the LIBS sensitivity and limit of detection. Conventional LIBS and wavefront-enhanced LIBS (WELIBS) measurements were conducted on three pure metallic targets: aluminum, magnesium, and zinc. A two to threefold enhancement in the intensity of spectral lines was achieved in the case of WELIBS. Furthermore, seven standard bronze alloy samples were used to study the analytical performance of WELIBS. Calibration curves were plotted for Pb, Zn, and Sn to estimate the limit of detection (LOD) in LIBS and WELIBS, where the latter provided twice the improvement. Moreover, the statistical analysis of the obtained LIBS and WELIBS emission spectra via the partial least squares regression (PLSR) method yielded a superior coefficient of determination (R²) for WELIBS measurements (0.99) than for the LIBS (0.87). Finally, WELIBS as a novel, simple, and cost-effective approach can be applied for remote analysis and in hostile environments with improved analytical performance compared to traditional LIBS using IR laser light.