Printer-friendly versionOptical models for surfaces and layers
The combination of our advanced measurement technology and our knowledge about the physical properties of optical interfaces allows us to extract various characteristics, such as film thickness, chemical composition, index of refraction, etc. In the following, the methodology for obtaining information from our optical measurements is presented.
A measurement of a thin film deposited on a substrate shows a reflectance variation with wavelength. Knowing the exact type of the materials involved or at least the material category the belong to, it is possible to construct a physical model, that can describe the expected reflectivity. In such a model the layer thickness and the optical parameters of the materials determine the exact shape of the reflectivity curve. Using a computer program to vary one or more of these parameters until the best fit between the measured and calculated curve is reached, it is possible to determine layer thicknesses and optical constants. omt engineers have successfully adapted this concept to many systems to the demands in industries like semiconductor, glass coating, surface treatment, etc...
Color measurement
Color is everywhere. Having an exact measure for color is important not only for the manufacturers of paints but also for many people in printing industry and wherever exact color rendition is a key for consistent product quality. Color is measured in the same way as other spectral properties. However the spectrum is then compared with the properties of specific reference light sources and models describing the sensitivity of the human eye.
Moisture and chemical composition
In the infrared range of the wavelength spectrum it is often the case, that light is absorbed at specific wavelengths. This absorption process results from direct interaction of the light with certain chemical groups inside molecules. If it is known how the observed absorption at a given wavelength or in a certain wavelength range is related to the molecules, the number of molecules or their concentration can be retrieved from the optical spectrum.
The adjoining figure shows the measured transmission spectrum of a plastic foil which is used in security glass for windshields in cars. The simultaneous detection of a CH2 peak and a water band can be used to calculate the thickness of the foil, the amount of water in the foil and as a result the moisture content.