Measurement of water film thickness by laser-induced fluorescence and Raman imaging

In: Applied Physics B: Lasers and Optics, Jg. 102 (2011) ; Nr. 1, S. 123 - 132
ISSN: 0946-2171, 1432-0649
Zeitschriftenaufsatz / Fach: Maschinenbau
We present two non-intrusive, laser-based imaging
techniques for the quantitative measurement of water
fluid film thickness. The diagnostics methods are based on
laser-induced fluorescence (LIF) of the organic tracer ethyl
acetoacetate added to the liquid in sub-percent (by mass)
concentration levels, and on spontaneous Raman scattering
of liquid water, respectively, both with excitation at 266 nm.
Signal intensities were calibrated with measurements on liquid
layers of known thickness in a range between 0 and
500 μm. Detection via an image doubler and appropriate filtering
in both light paths enabled the simultaneous detection
of two-dimensional liquid film thickness information
from both methods. The thickness of water films on transparent
quartz glass plates was determined with an accuracy
of 9% for the tracer LIF and 15% for the Raman scattering
technique, respectively. The combined LIF/Raman measurements
also revealed a preferential evaporation of the current
tracer during the time-resolved recording of film evaporation