Real-time fingerprinting of structural isomers using laser induced breakdown spectroscopy

Standoff Identification of Plastic Waste Using a Low-Cost Compact Laser-Induced Breakdown Spectroscopy (LIBS) Detection System

We report the standoff/remote identification of post-consumer plastic waste by utilizing a low-cost and compact standoff laser-induced breakdown spectroscopy (ST-LIBS) detection system. A single plano-convex lens is used for collecting the optical emissions from the plasma at a standoff distance of 6.5 m. A compact non-gated Czerny-Turner charge-coupled device (CCD) spectrometer (CT-CCD) is utilized to analyze the optical response. The single lens and CT-CCD combination not only reduces the cost of the detection system by tenfold, but also decreases the collection system size and weight compared to heavy telescopic-based intensified CCD systems. All the samples investigated in this study were collected from a local recycling plant. All the measurements were performed with only a single laser shot which enables rapid identification while probing a large number of samples in real time. Furthermore, principal component analysis has shown excellent separation among the samples and an artificial neural network analysis has revealed that plastic waste can be identified within ∼10 ms only (testing time) with accuracies up to ∼99%. Finally, these results have the potential to build a compact and low-cost ST-LIBS detection system for the rapid identification of plastic waste for real-time waste management applications.

Time-Dependent Intensity Ratio-Based Approach for Estimating the Temperature of Laser Produced Plasma

Reported here is a rapid and simplified approach for modeling the temporal evolution of the plasma temperature. The use of only two emission lines makes this technique simple, accurate, and fast. Usually, multiple emission lines are required for estimating plasma temperature using Boltzmann/Saha-Boltzmann plots. But, in several cases, either multiple emission lines are not available for every element and/or sufficient lines are not free from self-absorption effect. The proposed method greatly increases the possibility of plasma temperature estimation as it requires only two lines. A brass target was used to generate the plasma, using a conventional single-pulse nanosecond laser of ∼7 ns pulse duration at an excitation wavelength of 532 nm. The initial temperature of plasma and the radiation decay constant were estimated using a proposed intensity ratio model. The results were estimated using various combinations of emission lines, which show an excellent agreement with the values obtained using the previously reported method.

Identifying C2H4N4 structural isomers using fs-laser induced breakdown spectroscopy

Four C2H4N4 structural isomers are investigated with fs laser-induced breakdown spectroscopy. Plasma emissions, C I, Hα, the CN violet system (B2Σ+-X2Σ+, Δν = 0 sequence) and C2 swan system (d3Πg-a3Πu, Δν = 0 sequence) are measured. The temporal evolution of the characteristic emission intensity is obtained for each emission and their lifetimes are calculated. The lifetimes of the molecular emissions are much longer than those of the atomic emissions. Characteristic emission intensities and lifetime are correlated with the molecular structures of the four isomers to a certain extent. Plasma temperature is extracted by fitting the spectrum of the CN violet system, B2Σ+-X2Σ+; Δν = 0 sequence, and is weakly correlated with the molecular structures of the four isomers. Using the characteristic emission intensities as input, principal component analysis (PCA) and artificial neural network (ANN) analysis are performed and the individual isomers can be well identified with PCA or ANN.

A low-cost LIBS detection system combined with chemometrics for rapid identification of plastic waste

We present, rapid and efficient identification of ten different types of post-consumer plastics obtained from a local recycling unit by deploying a low cost, compact CCD spectrometer in laser-induced breakdown spectroscopy (LIBS) technique. For this investigation, spectral emissions were collected by an Echelle spectrograph equipped with an intensified charge-coupled device (ES-ICCD) as well as a non-gated Czerny Turner CCD spectrometer (NCT-CCD). The performance is evaluated by interrogating the samples in a single-shot as well as accumulation mode (ten consecutive laser shots). The results from principal component analysis (PCA) have shown excellent discrimination. Further, the artificial neural network (ANN) analysis has demonstrated that individual identification accuracies/rates up to ~99 % can be achieved. The data acquired with ES-ICCD in the accumulation of ten shots have shown average identification accuracies ~97 %. Nevertheless, similar performance is achieved with the NCT-CCD spectrometer even in a single shot acquisition which reduces the overall analysis time by a factor of ~15 times compared to the ES-ICCD. Furthermore, the detector/collection system size, weight, and cost also can be reduced by ~10 times by employing a NCT-CCD spectrometer. The results have the potential in realizing a compact and low-cost LIBS system for the rapid identification of plastics with higher accuracies for the real-time application.

Femtosecond laser induced breakdown spectroscopy based standoff detection of explosives and discrimination using principal component analysis

We report the standoff (up to ~2 m) and remote (~8.5 m) detection of novel high energy materials/explosive molecules (Nitroimidazoles and Nitropyrazoles) using the technique of femtosecond laser induced breakdown spectroscopy (LIBS). We utilized two different collection systems (a) ME-OCT-0007 (commercially available) and (b) Schmidt-Cassegrain telescope for these experiments. In conjunction with LIBS data, principal component analysis was employed to discriminate/classify the explosives and the obtained results in both configurations are compared. Different aspects influencing the LIBS signal strength at far distances such as fluence at target, efficiency of collection system etc. are discussed.

In situ analytical characterization and chemical imaging of tablet coatings using laser induced breakdown spectroscopy (LIBS)

The first report that describes direct visualization and quantitative evaluation of the coating uniformity using the LIBS-based 3D chemical imaging technique.