The role of laser wavelength on plasma generation and expansion of ablation plumes in air

We investigated the role of excitation laser wavelength on plasma generation and the expansion and confinement of ablation plumes at early times (0–500 ns) in the presence of atmospheric pressure. Fundamental, second, and fourth harmonic radiation from Nd:YAG laser was focused on Al target to produc...

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Bibliographic Details
Published in:Journal of applied physics 2013-04, Vol.113 (14)
Main Authors: Hussein, A. E., Diwakar, P. K., Harilal, S. S., Hassanein, A.
Format: Article
Language:English
Subjects:
ABLATION
ABSORPTION
ALUMINIUM
ATMOSPHERIC PRESSURE
BREMSSTRAHLUNG
CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
COUPLING
ELECTRON DENSITY
EMISSION
EMISSION SPECTROSCOPY
EXCITATION
INTERFEROMETRY
LASER RADIATION
LASER TARGETS
LINE BROADENING
NEODYMIUM LASERS
PHOTOIONIZATION
PLASMA
PLASMA DENSITY
PLASMA PRODUCTION
WAVELENGTHS
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Summary:We investigated the role of excitation laser wavelength on plasma generation and the expansion and confinement of ablation plumes at early times (0–500 ns) in the presence of atmospheric pressure. Fundamental, second, and fourth harmonic radiation from Nd:YAG laser was focused on Al target to produce plasma. Shadowgraphy, fast photography, and optical emission spectroscopy were employed to analyze the plasma plumes, and white light interferometry was used to characterize the laser ablation craters. Our results indicated that excitation wavelength plays a crucial role in laser-target and laser-plasma coupling, which in turn affects plasma plume morphology and radiation emission. Fast photography and shadowgraphy images showed that plasmas generated by 1064 nm are more cylindrical compared to plasmas generated by shorter wavelengths, indicating the role of inverse bremsstrahlung absorption at longer laser wavelength excitation. Electron density estimates using Stark broadening showed higher densities for shorter wavelength laser generated plasmas, demonstrating the significance of absorption caused by photoionization. Crater depth analysis showed that ablated mass is significantly higher for UV wavelengths compared to IR laser radiation. In this experimental study, the use of multiple diagnostic tools provided a comprehensive picture of the differing roles of laser absorption mechanisms during ablation.
ISSN:0021-8979
1089-7550
DOI:10.1063/1.4800925