An Application on Laser Speckles for Coated Metallic Surfaces
Sprache des Vortragstitels:
20th IMEKO TC2 Symposium on Photonics in Measurement
Sprache des Tagungstitel:
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. Due to that fact the actual distribution of the liquid on rough surface is dependent on two effects, the adhesion and the cohesion, the output of the measurement is a function of the surface roughness, the adhesion of the liquid film to the rough surface and the cohesion within the film 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.