Halides formation dynamics in nanosecond and femtosecond laser-induced breakdown spectroscopy

Abstract

LIBS is an analytical technique based on the measurement of the emitted radiation coming from a laser-induced plasma (LIP) created after irradiation of a sample by a short duration laser pulse. Research about molecular presence in LIPs has increased because the use of molecular emission has proven an encouraging way to improve LIBS abilities. LIPs are dynamic plasmas with fast time and spatial evolutions, in which atoms and molecules can follow different paths in their evolution and distribution. Molecular creation mechanisms within LIPs are still a challenging issue under investigation and the prevalence of some specific mechanisms are dependant on experimental conditions (sample nature, laser parameters, surrounding atmosphere…). In this work, different time and spatially solved experiments were carried out in ns- and fs-LIBS to investigate the dynamics of alkaline-earth (Ca) halide (F) diatomic molecule formation. Experiments were carried out on powdered CaF2 samples for both ns- and fs-LIBS. The effects of a gas flow (air, He, Ar) over the plume are investigated for ns-LIBS. Nebulization-modified ns-LIBS experiments in which the alkaline-earth element is externally added to the plasma plume as an aerosol were carried out on (C2F4)n samples. The spatial separation between atomic and molecular emission distribution was found to take place with and without external modifications over the ns-LIP. Behaviour in fs-LIPS was determined to differ significantly from analogous experiments with nanosecond lasers, but temporal optimization remains the optimum method for molecular detection as spatial separation was not found to provide any remarkable advantage.

Quantitative fluoride imaging of teeth using CaF emission by laser induced breakdown spectroscopy

“…51,74 The plasma condition and its evolution in time has been studied under different gas ows; as helium, argon or air; and using different substrates. [75][76][77] The CaF molecular formation has also been studied under helium, 40,73,78 argon 78 and air gas ows. 51,74,78 However, the effect of using 266 nm laser and different gas ows on the CaF LIBS molecular signal from a tooth substrate has not been studied.…”

“…[75][76][77] The CaF molecular formation has also been studied under helium, 40,73,78 argon 78 and air gas ows. 51,74,78 However, the effect of using 266 nm laser and different gas ows on the CaF LIBS molecular signal from a tooth substrate has not been studied. For all LIBS optimization experiments, the laser spot size and energy were constant at 100 mm and 8 mJ.…”

Improving Cl determination in cements by molecular LIBS using noble gas-enriched atmospheres and new approaches for interference removal

“…This conventional LIBS configuration was already used in previous studies and a scheme can be found in ref. 43.…”

“…This conventional LIBS conguration was already used in previous studies and a scheme can be found in ref. 43. Each sample spectrum is the result of the in-soware accumulation of 20 spectra from consecutive laser shots, all of them acquired using a grating of 1200 lines per mm positioned to collect light wavelengths between 577 and 610 nm.…”

“…Specically, Ar is a promising buffer gas candidate since it was already used for atomic, [40][41][42] and also for molecular CaF signal enhancement. 43 Another substantial improvement in the accuracy of Cl determination involves the proper processing of the spectral interferences within the spectral CaCl bands, which are strongly interfered with by several emission signals from CaO, Ca and Na. A common alternative to overcome this problem is to apply polynomial functions to t the background and then remove it.…”