Fluid Mechanics and Acoustics Laboratory - UMR 5509

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Home > Research Support > Scientific instrumentation > Techniques > Chromatic confocal measurement

Chromatic confocal measurement

The confocal measurement technique with a chromatic encoding is an optical measurement technique to measure a distance or a thickness of transparent materials.

The incident white light goes through lenses placed in order for a controled chromatic aberration to focus the light at different distances as a function of the wavelength. Therefore we obtain an encoding of the distance by the color. When an object is present in this color field, the only focused wavelength at its surface is reflected towards the optical system. The backscattered beam goes through a filtering pinhole and is acquired by a spectrometer. The specific wavelength of the beam is then calculated to determine with precision the distance from the surface to the probe. In the case of a transparent film, the probe detects two spikes which allows to measure the thickness of the film.