Spectral resolution improvement in laser-induced breakdown spectroscopy through the generation of high-temperature and low-density plasmas

Abstract

Spectral resolution improvement was achieved in laser-induced breakdown spectroscopy (LIBS) through generating high-temperature and low-density plasmas. The first pulse from a KrF excimer laser was used to produce particles by perpendicularly irradiating targets in open air. The second pulse from a 532 nm Nd:YAG laser was introduced parallel with the sample surface to reablate the particles. Optical scattering from the first-pulse plasmas was imaged to elucidate particle formation in the plasmas. Narrower line widths (full width at half maximums: FWHMs) and weaker self-absorption were observed from time-integrated LIBS spectra. Numerical calculation of plasma temperatures and densities indicates that high temperature and low density can be achieved simultaneously in plasmas to improve LIBS resolutions. From the calculation, the temperature of the laser-induced plasmas from the reablation with the second pulse was as high as that of the first-pulse plasma. The temperature of the first-pulse plasma is ∼6400 K with a plasma density of ∼1.2×1018 cm−3. The temperature of the reablation plasma, for instance, with an interpulse delay (the delay between the two pulses in dual-pulse LIBS (DP-LIBS)) of 100 µs, was ∼6200 K. However, the plasma density was ∼3.3×1017 cm−3, much lower than that of the first-pulse plasma.Spectral resolution improvement was achieved in laser-induced breakdown spectroscopy (LIBS) through generating high-temperature and low-density plasmas. The first pulse from a KrF excimer laser was used to produce particles by perpendicularly irradiating targets in open air. The second pulse from a 532 nm Nd:YAG laser was introduced parallel with the sample surface to reablate the particles. Optical scattering from the first-pulse plasmas was imaged to elucidate particle formation in the plasmas. Narrower line widths (full width at half maximums: FWHMs) and weaker self-absorption were observed from time-integrated LIBS spectra. Numerical calculation of plasma temperatures and densities indicates that high temperature and low density can be achieved simultaneously in plasmas to improve LIBS resolutions. From the calculation, the temperature of the laser-induced plasmas from the reablation with the second pulse was as high as that of the first-pulse plasma. The temperature of the first-pulse plasma is ∼6400...