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Proceedings Paper

Surface topometry by multiwavelength technique and temporal Fourier transformation
Author(s): Hans J. Tiziani; Bernhard Franze; Pascal Haible; Charles Joenathan
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Paper Abstract

Absolute interferometry can be a powerful tool for distance and shape measurement. Two and more wavelengths can be used to increase the range of unambiguity in interferometry. Furthermore it leads to the possibility to apply interferometric methods to measure optical rough surfaces. A continuously tunable laser in a two beam unequal path interferometer is used to overcome the ambiguity problem of classical interferometric methods. While the laser wavelength is tuned continuously, the variation of the interference intensity is recorded sequentially. At each image pixel the frequency of the signal modulation is analyzed, giving the absolute depth information for the corresponding object point. The wavelength tuning step governs the depth of measurement whereas the tuning range determines the depth resolution to be obtained. The method can be applied for optical as well as for technical surfaces. In the latter case, the intensity variation is observed independently in each speckle. However, the resolution of the measurement of optically rough surfaces is limited by the surface roughness. The continuous tuning of the wavelengths is performed with a diode laser with external cavity where a frequency variation of 30 nm can be obtained without mode hops within one second. Furthermore a novel method to measure the shape and steps heights by rotating the object and using temporal evaluation of the speckles' modulation is presented. Currently a temporal Fourier- transformation is used, similar to the evaluation method used in wavelength scanning interferometry.

Paper Details

Date Published: 29 September 1998
PDF: 8 pages
Proc. SPIE 3407, International Conference on Applied Optical Metrology, (29 September 1998); doi: 10.1117/12.323299
Show Author Affiliations
Hans J. Tiziani, Univ. of Stuttgart (Germany)
Bernhard Franze, Univ. of Stuttgart (Switzerland)
Pascal Haible, Univ. of Stuttgart (Germany)
Charles Joenathan, Univ. of Stuttgart (United States)

Published in SPIE Proceedings Vol. 3407:
International Conference on Applied Optical Metrology
Pramod Kumar Rastogi; Ferenc Gyimesi, Editor(s)

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