Johannes Lettner, Bernhard Zagar,
"An Application of Laser Speckle-Based Coating Thickness Measurement"
, in TM - Technisches Messen, Vol. 78, Nummer 11, Oldenbourg Wissenschaftsverlag, Seite(n) 534-539, 11-2011, ISSN: 0171-8096
An Application of Laser Speckle-Based Coating Thickness Measurement
Sprache des Titels:
A non-contacting method based on laser speckles
for determining thin liquid layers on optically rough surfaces
is presented. The optical system allows large stand-off distances
between the specimen and the sensor so the system
can also be used in harsh environments and industrial applications.
The thickness of organic residues or polar liquids
to be measured can be in the typical range of about the
same as the roughness of the surface. The distribution of
the oil on the rough surface is dependent on the adhesion
and cohesion forces, the temperature and mainly of the surface
topography itself. The speckle generating effect is thus
dependent on the surface roughness as well as the film thickness
(and also its optical properties).These two effects change
the structure of the so-called laser speckles due to laser
light illumination on any dielectric coating on metallic surfaces.
The speckle patterns viewed at by a video camera are
evaluated and their rather strong dependence on liquid film
properties are presented in this paper.