Optical profilometry

rapid, non-contact, standardized roughness determination

Optical profilometry is an analytical method for the non-contact characterization of surface topography. Newer devices achieve depth resolutions of approx. 1 nm. Various measurement modes are available for the analytical work, which allow a determination of sample roughness in accordance with DIN EN ISO 4287. Such analyses can be performed even on transparent media (e.g., glasses, optical fibers, ...) after appropriate sample preparation.

Optische Profilometrie Profil Bild Topographie

Details on optical profilometry

Physical priciple - information gained - analytical possibilities

With optical profilometry, the topography of a surface can be investigated without contact with a vertical resolution of up to one nm. The measuring device used by tascon GmbH allows both confocal and interferometric analyses.

In confocal microscopy, a monochromatic light beam is focused on a sample surface. The use of suitable diaphragms ensures that only the light reflected in the focal plane reaches the imaging CCD sensor. Thus, only the area that is illuminated in focus of the incident light is imaged. By a computer-controlled, continuous variation of the distance between the sample surface and the optical system, corresponding individual images of the sample surface are obtained. These images are used to calculate a three-dimensional model of the sample surface.

In the interferometric analysis, the sample surface is irradiated with monochromatic light. During the measurement, the distance between the sample and the lens of the interferometer is increased in small increments. Due to the topography, for each point at the surface, different transit time differences between the reflected light beam and a reference light beam occur. The superposition of both light beams results in an interference pattern that moves across the surface during the fine step change in vertical distance to the sample. These sequences of interference images result in interferograms for each object point, from which the sample topography can be calculated.

The decision which of the measuring methods is used depends on the analytical question and the sample properties. All samples with reflective surfaces with height differences of max. 2 cm are suitable. Analyses of optically transparent sample systems (for example, mirrors, glasses, etc.) are only possible to a limited extent. For an accurate determination of topographic information, it is recommended to deposit a thin, reflective metal film on the surface of these systems.

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