Investigation of the factors affecting the limit of detection of laser-induced breakdown spectroscopy for surface inspection

Abstract

Laser-induced breakdown spectroscopy (LIBS) was examined to detect a trace substance adhered onto Al alloys for the surface inspection of materials to be adhesively bonded. As an example of Si contamination, silicone oil was employed and sprayed onto substrates with a controlled surface concentration. LIBS measurements employing nanosecond UV pulses (λ=266 nm) and an off-axis emission collection system with different detecting heights were performed. Because surface contaminants are involved in the plasma formed by laser ablation of the substrates, the relative contribution of the surface contaminants and the substrates to the plasma emission could be changed depending on the conditions for plasma formation. The limit of detection (LOD) was evaluated under several detecting conditions for investigating the factors that affected the LOD. A significant factor was the standard deviation values of signal intensities obtained for the clean substrates. This value varied depending on the measurement conditions. For the Al alloy (A6061), the smallest LOD obtained was 0.529 μg•cm −2 . Furthermore, an improved LOD (0.299 μg•cm −2 ) was obtained for the Al alloy with a lower Si content.

Bayesian optimization of the conditions for highly sensitive detection of surface contamination by laser-induced breakdown spectroscopy

“…In the previous work, smaller LODs were obtained under defocused conditions. 10 Fig. 6(c) shows a maximum around the center, although one result that shows an exceptionally large value was observed at dZ = +1.5 mm (grid index: 61).…”

“…The experimental setup was similar to that reported previously. 10 Fourth-harmonic pulses ( λ = 266 nm, τ = 8 ns) of a Nd:YAG laser (Quantel, Q-smart100 with harmonic modules: QSM100-SHG-KTP and QSM100-FHG) were focused onto the samples with a plano-convex lens of focal length, f = 50 mm. A lens with a focal length smaller than that used previously ( f = 100 mm) 10 was employed to explore more defocused conditions.…”

“…7 Subsequently, the conditions for sensitive detection were explored, and the LOD value was improved to 0.529 μg cm −2 . 10 In this exploration, optimization of conditions of laser ablation was found to be effective as well as the conditions of LIBS signal detection. Since a surface contaminant forms a thin layer on a substrate, probing the spot size becomes an important factor separately from laser fluence which affects laser ablation and consequent plasma formation.…”

Detection of Al, Mg, Ca, and Zn in copper slag by LIBS combined with calibration curve and PLSR methods

“…The full channel spectrum of the slag sample and the characteristic spectral lines of the target element in different channels are shown in figure 2. All emission lines were identified based on a representative spectrum utilizing the NIST LIBS database [25].…”

From big to strong: growth of the Asian laser-induced breakdown spectroscopy community

“…Still, important work on fundamental LIBS such as femtosecond dual-pulse LIBS on the signal enhancement [8], pressure effects on underwater LIBS in ocean environment [9], accuracy improvement on CF-LIBS [10], self-absorption effect at ungated scheme [11] as well as a review on the mechanism and elimination of self-absorption effect [12] was included in this special issue. Several works on the experimental point of view to optimize the LIBS performance were also included, such as a method of laser focusing control in micro LIBS [13], the effect on lens-to-sample distance [14], experimental parameter settings on the matrix effect [15] and experimental factors affecting the limit of detection [16] etc. From the practical point of view, the end users market of LIBS is huge in Asia, leading to a significant focus on the research of applications on LIBS, with a special focus on the data processing methods.…”