Abstract
In this study, we examine the atomic and molecular signatures in laser-induced plasma. Abel inversions of measured line-of-sight data reveal insight into the radial plasma distribution. Laser-plasma is generated with 6 ns, Q-switched Nd:YAG radiation with energies in the range of 100 to 800 mJ. Temporally- and spatially-resolved emission spectroscopy investigates expansion dynamics. Specific interests include atomic hydrogen (H) and cyanide (CN). Atomic hydrogen spectra indicate axisymmetric shell structures and isentropic expansion of the plasma kernel. The recombination radiation of CN emanates within the first 100 nanoseconds for laser-induced breakdown in a 1:1 mole ratio CO2:N2 gas mixture. CN excitation temperatures are determined from fitting recorded and computed spectra. Chemical equilibrium mole fractions of CN are computed for air and the CO2:N2 gas mixture. Measurements utilize a 0.64-m Czerny–Turner type spectrometer and an intensified charge-coupled device.
Highlights
Analysis of atomic species traditionally utilizes atomic emission spectroscopy of flames, plasmas, arcs, or sparks to quantify elements in the sample
Investigations of laser-induced hydrogen plasmas serve the purpose of addressing fundamental aspects of time-resolved emission spectroscopy and associated dynamic processes following optical breakdown
Electron density and excitation temperature are higher in the peripheral region than near the center due to expansion dynamics of the plasma kernel after optical breakdown
Summary
Analysis of atomic species traditionally utilizes atomic emission spectroscopy of flames, plasmas, arcs, or sparks to quantify elements in the sample. Investigations of laser-induced hydrogen plasmas serve the purpose of addressing fundamental aspects of time-resolved emission spectroscopy and associated dynamic processes following optical breakdown. Measurements of hydrogen plasmas allow one to determine important plasma parameters such as excitation electron density and temperature. One measures the width of Balmer series lines of hydrogen that occur in the visible spectrum for electron density determination, and one integrates the area of these lines with respect to the continuum and constructs Boltzmann plots for excitation temperature inferences. Optical emission spectroscopy (OES) indicates the presence of molecular species that can elucidate sample composition or interaction processes in the ambient atmosphere [3,4,5,6]. Atomic hydrogen lines, C2 Swan bands, and the cyanide (CN) violet system appear in various applications [6,7] of laser-induced OES such as in experiments with hydrocarbons [8]
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