Applications
Film Thickness Measurement
Method Principles
Schematic Gauge Setup
Example: Lacquer Coatings
Example: Vapor Deposition
Example: Webcoater
A commonly well-known
effect, which occurs for example with soap bubbles or on a thin oil film on water, is used
here for the determination of the film thickness. You can see many colors which change
according to the layer thickness, e.g. when a soap bubble is blown up. Also check out this Soap Bubble
website for some really nice pictures and detailed explanation of this effect!
These "colors at thin layers" are based on the interference phenomenon, i.e. on
the superposition of light waves, which have been reflected at the front and back side of
the layer (at two boundaries with different optical densities):
The undisturbed superposition of the two reflected light rays 1 and 2 leads to periodical
amplifications and extinction in the spectrum of a white continuum light source (such as a
halogen spectral lamp as a pseudo white-light source). Since the superposition
of the two light rays is not purely additive, a so-called interference occurs. The figure
righ beside shows the interference spectrum of a 1 micron and 2 micron thick
layer.
