Three different diagnostic techniques are investigated for measurement of the thickness of liquid water films deposited on a transparent quartz plate. The methods are based on laser-induced fluorescence (LIF) from low concentrations of a dissolved tracer substance and spontaneous Raman scattering of liquid water, respectively, both excited with
of radiation, and diode laser absorption spectroscopy (DLAS) in the near-infrared spectral region. Signal intensities are calibrated using liquid layers of known thickness between 0 and
. When applied to evaporating liquid water films, the thickness values derived from the direct DLAS and Raman scattering measurements correlate well with each other as a function of time after the start of data recording, while the LIF signal derived thickness values decrease faster with time due to selective tracer evaporation from the liquid. The simultaneous application of the LIF with a tracer-free detection technique can serve as an in situ reference for quantitative film thickness measurements.
© 2011 Optical Society of America
(300.2530) Spectroscopy : Fluorescence, laser-induced
(300.6260) Spectroscopy : Spectroscopy, diode lasers
(300.6450) Spectroscopy : Spectroscopy, Raman
(310.6870) Thin films : Thin films, other properties
LASER APPLICATIONS TO CHEMICAL, SECURITY, AND ENVIRONMENTAL ANALYSIS
Original Manuscript: July 12, 2010
Revised Manuscript: October 27, 2010
Manuscript Accepted: October 29, 2010
Published: December 3, 2010
Vol. 6, Iss. 3 Virtual Journal for Biomedical Optics
Daniel Greszik, Huinan Yang, Thomas Dreier, and Christof Schulz, "Laser-based diagnostics for the measurement of liquid water film thickness," Appl. Opt. 50, A60-A67 (2011)
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