Abstract
Transient laser plasma is generated in laser-induced optical breakdown (LIOB). Here we report experiments conducted with 10.6-micron CO2 laser radiation, and with 1.064-micron fundamental, 0.532-micron frequency-doubled, 0.355-micron frequency-tripled Nd:YAG laser radiation. Characterization of laser induced plasma utilizes laser-induced breakdown spectroscopy (LIBS) techniques. Atomic hydrogen Balmer series emissions show electron number density of 1017 cm−3 measured approximately 10 μs and 1 μs after optical breakdown for CO2 and Nd:YAG laser radiation, respectively. Recorded molecular recombination emission spectra of CN and C2 Swan bands indicate an equilibrium temperature in excess of 7000 Kelvin, inferred for these diatomic molecules. Reported are also graphite ablation experiments where we use unfocused laser radiation that is favorable for observation of neutral C3 emission due to reduced C3 cation formation. Our analysis is based on computation of diatomic molecular spectra that includes accurate determination of rotational line strengths, or Hönl-London factors.
Highlights
Laser-induced breakdown spectroscopy (LIBS) is a valuable technique for determining elemental composition with the ability to analyze solids, liquids, and gases with little or no sample preparation suitable for onsite analyses [1]
Transient laser plasma is generated in laser-induced optical breakdown (LIOB)
Several other laser sources have been historically applied for generation of microplasma with subsequent measurement methods based on use of atomic emission spectroscopy [2]
Summary
Laser-induced breakdown spectroscopy (LIBS) is a valuable technique for determining elemental composition with the ability to analyze solids, liquids, and gases with little or no sample preparation suitable for onsite analyses [1]. Several other laser sources have been historically applied for generation of microplasma with subsequent measurement methods based on use of atomic emission spectroscopy [2]. Recent interest includes applying dual- and multipulse excitation for the purpose of increasing sensitivity of LIBS. Examples of advantages of multipulse excitation include an increase of the plasma volume or plasma reheating by the second pulse, in turn, enhancement of detection limits for LIBS 10- to 100-fold and/or a decrease in relative standard deviation when comparing single- with double- pulse bursts [3]. Following short-pulse UV-excitation a CO2 laser may be used to enhance detection from a distance of atomic and molecular species [4,5,6]. Applications of CO2 lasers include aerosol measurements [9, 10]
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