Basic mechanisms of signal enhancement in ns double-pulse laser-induced breakdown spectroscopy in a gas environment

Abstract

Classifying ns double-pulse LIBS measurements according to the irradiation mode facilitates the interpretation of the mechanisms underlying intensity enhancement.

Optimal emission enhancement in orthogonal double-pulse laser-induced breakdown spectroscopy

“…By using a DP-LIBS approach, improvements on signal-to-noise ratio (SNR) [7], signal-to-background ratio (SBR) [8,9] and limits of detection (LOD) [10] have been reported. Overall results in the current literature suggest that mechanisms involving signal enhancement depend on many parameters such as material properties [5], laser pulse energies and power densities [11][12][13], laser pulse wavelengths [11,14,15], interpulse delay times (Δt) [9,[16][17][18] and geometrical configuration [5,6,19]. Despite efforts made to explain the signal enhancement mechanisms, these are not completely clear and optimal experimental conditions are yet to be determined.…”

“…Besides, for all shown PD, a SE larger than one was obtained for the lowest interpulse delay. At this Δt, the ablation plume has its largest particle density, thus increasing the absorption of the second pulse [19]. As Δt grows, the SE decreases since the second pulse finds a reduced density plume due to its expansion through the background atmosphere.…”

“…Results suggest that signal enhancement is related to an increase of ablated material and the plasma volume [19,[22][23][24]; as well as the energetic coupling between the plasma produced by the first pulse and the second pulse energy [19,22]. Although an optimal Δt value for maximum enhancement has been reported by several authors, in most cases, a plateau region of several microseconds can be considered with minimal effects on the maximum signal enhancement [11,12,14].…”

Signal enhancement in collinear double-pulse laser-induced breakdown spectroscopy applied to different soils

“…Among these the double-pulse (DP) laser has proven to be very effective in improving LIBS performance by offering a high flexibility in the choice of wavelength, pulse width and pulse sequence. This in order to better coupling laser energy to the target and ablated material, thus leading to a more efficient production of analyte atoms in the excited state [3,[11][12][13][14][15].…”

“…However, conventional LIBS shows specific drawbacks for many elements, which are related to sensitivity and precision that may not fulfill the analytical requirements requested. Anyway, in the last three decades various approaches have been proposed aiming to improve LIBS analytical capabilities [3][4][5][6][7][8][9][10][11]. Among these the double-pulse (DP) laser has proven to be very effective in improving LIBS performance by offering a high flexibility in the choice of wavelength, pulse width and pulse sequence.…”