Reflectometer ETA-ARC-AT

Optical lens elements are coated with highly efficient anti-reflectance coatings nowadays in order to minimize light losses at interfaces between glass and air and to avoid ghost images. A fundamental problem for quality assurance is the fact that because of the disturbing influence of the rear side surface reflection spectral reflectance of AR coated lenses often can not be measured without destroying the lens under test. This is why most of the time witness samples from the same coating job will be measured instead with their rear surface roughened and blackened.

AudioDev’s reflectometer model ETA-ARC-AT – which is exclusively marketed in Europe by Schneider Kreuznach – avoids this problem by using a unique and proprietary sensor head. It provides non-destructive and highly accurate 100% quality control on actual, curved lens surfaces. Suppression of the rear surface reflection works reliably and without any problem if the minimum lens thickness exceeds 2 mm. On the detector side a diode array is used, thus enabling typical measurement times of less than a second.

Result of reflection measurement with the Reflectometer ETA-ARC-AT

Since the probing light spot is pretty small and since it is possible to measure anywhere on the lens surface, the ETA-ARC-AT allows also studying the homogeneity of the AR coating. A perfect colour matching of tested lenses can be achieved from colorimetric data that the software calculated from the measured spectral reflectance data in accordance with standard CIE colour spaces. Moreover, the software can calculate the actual thickness of single hard coatings or cement layers if material data is available for these layers.

Please have a look at our technical article in the professional journal PHOTONIK, issue 1/2010 (German):
„ Zerstörungsfreie Vermessung von Antireflexbeschichtungen auf gekrümmten Oberflächen" from L. Völker, M. Schulz-Grosser, R. Kubitzek, (website of the publisher: www.photonik.de)

Abstract:
In order to minimize disturbing losses by reflection, optical components such as precision optical lenses or ophthalmic lenses are supplied with highly efficient anti-reflective coatings in these days. Measuring methods by means of scanning spectral photometers which are applied in quality assurance are in practice often either destructive or they can not be applied on any user-defined spot on a curved surface. A special measuring head design in conjunction with a diode array spectrometer are putting things right.

pdf (270 B)

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