Enhanced LIBS detection of atomic oxygen via two-photon LIF

Laser-induced breakdown spectroscopy (LIBS) is a versatile analytical technique with applications in several fields of science and technology. It requires minimal or no sample preparation and can provide information about the composition of the analyte, with limits of detection typically at the ppm level. There is growing interest in the scientific community in improving the sensitivity and specificity of LIBS. In this work, we explore the combination of LIBS with two-photon laser-induced fluorescence (TALIF) for the enhancement of atomic oxygen spectra signatures originating from a nanosecond laser-produced plasma on a solid target. The line intensity of the O I transition at 844.67 nm was enhanced up to 29.3 times by exciting an oxygen atomic resonance using a second UV nanosecond pulse at 225.59 nm, with a focused intensity of ∼2.4×107 W/cm2, produced with an optical parametric oscillator. The enhancement did not significantly increase the background, leading to a comparable increase in the signal-to-noise ratio. The dependence of the enhancement on the UV excitation wavelength and on the inter-pulse delay is presented. The demonstrated LIBS-TALIF combination permits the exploration of high-lying gaseous transitions not accessible with classical laser-induced fluorescence and unlocks the pathway to applications where increased sensitivity and specificity are imperative.