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What Limits Laser Probing?

Published online by Cambridge University Press:  22 February 2011

R. W. Dreyfus
R. W. Dreyfus*
Affiliation:
IBM Research Division T. J. Watson Research Center, Yorktown Heights, NY 10598
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Abstract

Laser-induced fluorescence, LIF, data provide a wide variety of detailed information about physical and chemical reactions and plasmas. In today's technological environment these areas commonly extend from nanosecond laser etching to ion etching (in the low gas density direction), or to combustion gases (near atmospheric pressure). In studying these dynamical processes, the laser probe is nearly ideal; note that one measures a specific species' density as a function of position, velocity, temperature and time within an unperturbed working environment (i.e. high vacuum not required). Examples are derived from our LIF probing of laser etch plumes; the surfaces included sapphire, polymers and benzene (both as a gas and frozen monolayer). LIF results distinguish between diatomic radicals due to thermal vaporization as compared to diatomics from a photochemical decomposition. Beyond the above LIF probing of a laser-etch plume, sophisticated diagnostic techniques such as CARS, multiphoton excitation and ionization, and dissociation immediately followed by optical excitation appear regularly. Enhanced information gathering by laser probing is also demonstrated by the fact that spectroscopic data can be recorded as a 2D picture of a reacting species.

With respect to limitations on laser probing, consider the following: Even though plasmas and etch plumes are luminous, the pulsed nature of laser experiments discriminates heavily against background light and dark current noise. While the various techniques measure relative densities at even very low densities, establishing accurate values for absolute densities is considerably more challenging. (Spectral-linewidth uncertainties are a common culprit.) Perhaps the main limitations on laser probing relate to the patience, dedication and budget of the experimenter.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 117: Symposium C – Process Diagnostics: Materials, Combustion, Fusion , 1988 , 11
Copyright
Copyright © Materials Research Society 1988

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References

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