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Measurements with Laser Ablation Molecular Isotopic Spectrometry (LAMIS) are usually performed in atmosphere for rapid isotope analysis, and an understanding of molecule formation via plasma–air chemical reactions is important for quantitative analysis by LAMIS. In this work, the expansion of a plasma plume from ablation of pure aluminum in air is studied with time- and space-resolved monochromatic imaging and emission spectroscopy. The distributions of neutral Al and O atoms and AlO radicals formed through plasma chemical reactions are characterized. The emission spectra of the AlO bands of a B2Σ+–X2Σ+ system are recorded and the rotational–vibrational temperature was obtained through fitting experimental spectra. Inter-molecular vibrational band interference is well re-constructed, and self-absorption of bandheads, especially for the (0–0) band, is corrected. Interpretation of the spatial–temporal evolutions of plasma species and plasma temperature provides insights into the formation mechanism of AlO radicals in laser-induced plasma.

We investigate experimentally spatiotemporal characteristics of fluorescence emission from fs-laser-induced filaments in air. Emissions accompanying the transitions of N

Laser ablation molecular isotopic spectrometry (LAMIS) was recently reported for isotope analysis of samples and for molecules formation mechanism investigation by analyzing the isotopologues in laser induced plasma. LAMIS was utilized to quantify the OD and OH molecules in fs-laser ablated plasma from moist water samples carried by pure Ar gas at ambient environment. A theoretical spectral fitting model for OD and OH molecules was developed and was used to extract the isotopic ratio OD/OH by fitting of experimental spectra. Time-resolved spectra were measured and the influences of spectrum intensity and signal to noise ratio (SNR) on isotopic quantitative analysis performance were evaluated. The relative concentration of OD and OH molecules in laser induced plasma from a set of water samples with D2O concentrations in the range of 0% to 99.8% are quantified, and a very good linear relationship between D concentration and D2O concentration was obtained. The linear curve exhibited R2 exceeding 0.9997 and a slope of 1.006. In addition, no standard sample is necessary for quantitative analysis, demonstrating the advantages of spectral fitting LAMIS.

© 2018 Optical Society of America. We report the influence of femtosecond (fs) laser weakly ionized air channel on characteristics of plasma induced from fs-laser ablation of solid Zr metal target. A novel method to create high temperature, low electron density plasma with intense elemental emission and weak bremsstrahlung emission was demonstrated. Weakly ionized air channel was generated as a result of a non-linear phenomenon. Two-dimensional time-resolved optical-emission images of plasma plumes were taken for plume dynamics analysis. Dynamic physical properties of filament channels were simulated. In particular, we investigated the influence of weakly ionized air channel on the evolution of solid plasma plume. Plasma plume splitting was observed whilst longer weakly ionized air channel formed above the ablation spot. The domination mechanism for splitting is attributed to the long-lived underdense channel created by fs-laser induced weakly ionization of air. The evolutions of atomic/molecular emission intensity, peak broadening, and plasma temperature were analyzed, and the results show that the part of plasma entering weakly ionized air channel features higher initial temperature, lower electron density and faster decay.

We investigate experimentally spatiotemporal characteristics of fluorescence emission from fs-laser-induced filaments in air. Emissions accompanying the transitions of N2 (C3Πu−B3Πg) and N 2+ (B2Σu+−X2Σg+) are dominant. The decay dynamics of fluorescence from different radial positions and longitudinal sections of a filament column are obtained along with high resolution spectra. A decay curve contains two exponential components: a fast one (with a decay time constant ∼10s ps), and a slow one (∼sub-ns). The lifetime of the N 2 fluorescence is about three orders shorter than its spontaneous emission lifetime, indicating that most of the N 2 molecules in the excited state (C3Πu) are de-excited through collision. Different de-excitation mechanisms of N 2 (C3Πu) molecules contributing to fluorescence decay constants, e.g., the e −−N2, N 2−N2, and O 2−N2 collisions, are elucidated. We analyze the variations of decay constants together with corresponding fluorescence intensities, and obtain temperature distributions by fitting band spectra of N 2 molecules and N 2+ ions with a synthetic spectral model. Our results suggest that the fast and slow decay processes originate from the e −−N2 and O 2−N2 collisions, respectively.