Laser-induced optical breakdown spectroscopy of polymer materials based on evaluation of molecular emission bands

New challenges and insights in the detection and spectral identification of organic explosives by laser induced breakdown spectroscopy

Femtosecond laser induced breakdown spectroscopy (LIBS) has been shown to be sensitive to a variety of ERC's (explosive-related compounds) deposited on substrates. In LIBS, surface material is excited by a high-powered laser pulse forming a plasma. The optical emission from this plasma is collected and spectrally analyzed to determine the surface species entrained in the excitation event. The detection of explosive related compounds in the field presents many challenges, one of these being the wide variety of materials surfaces that might be covered with ERC's. Results from femtosecond and nanosecond LIBS of ERC's of metal, glass, and polymer substrates show that the optical properties of the substrate play a large role in the observed emission. Results indicate that nanosecond LIBS of ERC's on metal surfaces yield strong atomic emission while nanosecond LIBS of ERC's on glass results in some molecular emission. Molecular emission is also present in femtosecond LIBS spectra of ERC's on all surfaces but is particularly strong for metal substrates. In particular emission from the CN molecular fragment could provide a means to understand the effect of the substrate on the excitation event in nitroaromatic compounds since it is present in both nanosecond LIBS spectra of the TNT/glass system and femtosecond LIBS spectra of the TNT/Al system. The origins of this CN molecular fragment are currently being studied since fragmentation and reaction processes in LIBS events are not fully understood at this time.

Laser-induced breakdown spectroscopy (LIBS) technique was utilized to investigate the green mineral fluorite (CaF2) samples. The LIBS experiment was implemented by using Nd: YAG Laser system and a linear array CCD detector coupled with an Avantes spectrometer in an air atmosphere. The emission spectra of ten various fluorite samples were studied. The molecular bands correspond to the green B2Σ+-X2Σ+ and orange A2Π-X2Σ systems of diatomic CaF-molecule, specifically at Δν = -1, 0, +1 sequences and the CaO diatomic molecule between 618 nm and 630 nm were detected. It was observed that the CaF-diatomic molecular emission bands exhibited stronger optical emission compared to the fluorine (F) atomic lines. Chemical composition (wt.%) analysis was acquired using CF-LIBS methodology under optically thin and local thermodynamic equilibrium (LTE) conditions. Our CF-LIBS studies revealed that Ca (50–60%) and F (30–40%) were the major elements, while C (3–5%) and O (2–5%) were minor elements present in all samples. For comparison, we employed energy-dispersive X-ray (EDX) technique to study the essential elemental composition (wt.%). The results achieved from CF-LIBS were found to be in good agreement to that obtained from the EDX technique. To validate CF-LIBS results, the calibration curve method was employed using the validated samples (S3, S5, and S7). Furthermore, we utilized a principal component analysis (PCA) technique on the LIBS spectral data to classify the fluorite samples.

This work introduces laser induced breakdown spectroscopy (LIBS) as a novel, cheap and non‐destructive method to study the changes of mechanical properties of plastic bonded explosives (PBX) during their aging. Accelerated aging was used in three different temperatures 60, 70, and 80 °C to obtain different aged samples. The measurements of mechanical properties analysis were also done on the aged samples to validate the resulted data from LIBS spectroscopy. LIBS tests were done in both air and argon atmosphere, in which molecular bands such as CN and C2 radiation were compared for all aged samples. In order to more accurate discrimination between spectra of different samples, principal component analysis (PCA) was used as a suitable chemometric method. All these results represent the changes in the chemical structure of specimens, which are due to increasing time and temperature during their aging processes.

Laser-induced breakdown spectroscopy (LIBS) is an emerging atomic spectroscopy detection technology in recent years. It provides a convenient and accurate new method for qualitative and quantitative analysis in explosive trace detection. Explosives detection includes two types of indoor and outdoor scenes. In the current applications in the field of anti-terrorism and security, crowded indoors are important detection scenarios, and indoor attachments and indoor gas are important samples. The current main LIBS systems for indoor dangerous goods detection can be divided into two types: indoor surface attachment detection system; and indoor deep embedded object detection system. In the exploration of application, many studies have revealed the formation mechanism of LIBS atomic lines and molecular band, and explored the influence of substrate, environment, and other factors on LIBS spectrum, which provides a theory for the large-scale application of LIBS technology in the field of security support.

Early screening and staging of melanoma using blood based on laser-induced breakdown spectroscopy

Investigation of the CN and C2 emission characteristics and microstructural evolution of coal to char using laser-induced breakdown spectroscopy and Raman spectroscopy

In minimal invasive laser osteotomy precise information about the ablation process can be obtained with LIBS in order to avoid carbonization, or cutting of wrong types of tissue. Therefore, the collecting fiber for LIBS needs to be optimally placed in narrow cavities in the endoscope. To determine this optimal placement, the plasma plume expansion dynamics in ablation of bone tissue by the second harmonic of a nanosecond Nd:YAG laser at 532 nm has been studied. The laserinduced plasma plume was monitored in different time delays, from one nanosecond up to one hundred microseconds. Measurements were performed using high-speed gated illumination imaging. The expansion features were studied using illumination of the overall visible emission by using a gated intensified charged coupled device (ICCD). The camera was capable of having a minimum gate width (Optical FWHM) of 3 ns and the timing resolution (minimum temporal shift of the gate) of 10 ps. The imaging data were used to generate position-time data of the luminous plasma-front. Moreover, the velocity of the plasma plume expansion was studied based on the time-resolved intensity data. By knowing the plasma plume profile over time, the optimum position (axial distance from the laser spot) of the collecting fiber and optimal time delay (to have the best signal to noise ratio) in spatial-resolved and time-resolved laser-induced breakdown spectroscopy (LIBS) can be determined. Additionally, the function of plasma plume expansion could be used to study the shock wave of the plasma plume.

Identification and discrimination of Pseudomonas aeruginosa bacteria grown in blood and bile by laser-induced breakdown spectroscopy

Conditions for the simultaneous production of argon and xenon chlorides and excited nitrogen molecules in a longitudinal dc glow discharge in Ar/Cl2/air, Xe/Cl2/air, and Ar/Xe/Cl2/air mixtures are studied. The electrical parameters of the plasma and its optical characteristics in the 130-to 350-nm wavelength range are investigated. It is shown that a small admixture of air added to argon or xenon leads to the production of excited nitrogen molecules, whose decay is accompanied by the molecular band emission in the range Δλ=176–271 nm. The conditions for simultaneous emission of the ArCl(B-X), XeCl(B-X), and nitrogen molecular bands are determined.

Synthesis of carbon nitride films by high-density helicon wave-excited plasma sputtering

Recently, a mercury-cadmium-telluride (MCT) linear array detection system that is capable of rapidly capturing (~1-5 second) a broad spectrum of atomic and molecular laser-induced breakdown spectroscopy (LIBS) emissions in the longwave infrarμed region (LWIR, ~5.6 to 10 μm) has been developed. Similar to the conventional Ultraviolet (UV)-Visible (Vis) LIBS, a broad band emission spectrum of condensed phase samples covering the entire 5.6 to 10 μm region can be acquired from just a single laser-induced micro-plasma or averaging a few single laser-induced micro-plasmas. This setup has enabled probing samples “as is” without the need for extensive sample preparation and also offers the possibility of a simultaneous UV-Vis and LWIR LIBS measurement. A Martian regolith simulant (JSC Mars-1A) was studied with this novel Vis + LWIR LIBS array system. A broad SiO2 vibrational emission feature around 9.5 μm and multiple strong emission features between 6.5 to 8 μm can be clearly identified. The 6.5 to 8 μm features are possibly from biological impurities of the simulant. JSC Mars-1A samples with organic methyl salicylate (MeS, wintergreen oil) and Dimethyl methyl-phosphonate (DMMP) residues were also probed using the LWIR LIBS array system. Both molecular spectral signature around 6.5 μm and 9.5 μm of Martian regolith simulant and MeS and DMMP molecular signature emissions, such as Aromatic CC stretching band at 7.5 μm, C-CH3O asymmetric deformation at 7.6 μm, and P=O stretching band at 7.9 μm, are clearly observed from the LIBS emission spectra in the LWIR region.

Chemiluminescent emission spectra of lead, chromium, ruthenium, iron, manganese, rhenium, osmium and tungsten in the reactive flow detector

Laser ablation - spark discharge - optical emission spectroscopy (LA-SD-OES) and Laser-induced breakdown spectroscopy (LIBS) are applied for the analysis of minor elements Manganese (Mn) and Chromium (Cr) in steel and for the chemical imaging of micro-patterned photoresist layers. In LA-SD-OES a weak laser pulse (typical energy 50 μJ to 5 mJ) triggers an electric discharge between a high voltage electrode and the laser ablated spot on the sample surface. Intense emission lines of neutral and singly-ionized atoms are observed with both spectroscopic techniques. However, lines of doubly-ionized atoms are detected with LA-SD-OES only. The line intensities of C III and Al III increase with decreasing laser pulse energy, surprisingly. The appearance of intense doubly-ionized lines indicates that the mechanisms of plasma excitation are different in LA-SD-OES compared to LIBS and that the combined plasma is not in local thermodynamic equilibrium at low laser energy. The calibration curves of Mn and Cr in industrial steel reveal steeper slope (higher sensitivity) for the Mn II and Cr II lines measured with LA-SD-OES and for the Mn I and Cr I lines measured with LIBS. Chemical imaging of the photoresist layer with LA-SD-OES at the atomic lines of C I and C III and the molecular band of CN reveals all details of the sample. Similar images are obtained for C I and CN using LIBS, however, no image contrast is obtained at the C III line. The very low pulse energy in LA-SD-OES enables soft sampling and may be beneficial also for the analysis and imaging of sensitive material.

Rhythmic calcium ion activity related to glioma growth reveals the mechanism of ion transmission