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Proceedings Paper

An approach to combined multispectral reflectorless distance measurement and material probing
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Paper Abstract

Measuring the propagation delay of optical signals reflected by the illuminated surfaces is an established approach to non-mechanical distance estimation and the basis for 3d laser scanning. We have in the past extended a technique using the intermode beat notes obtained from a femtosecond laser to a coherent ultra-broadband source. Using cooperative targets, we have shown that this may enable inline correction of atmospheric delays by using a multispectral configuration and exploiting atmospheric dispersion. In this work, we enhance the scope by providing a first demonstration of successful application to reflectorless measurements on natural targets. This extension is relevant because of two aspects: (i) the field of applications of reflectorless distance measurement is much wider (in particular through laser scanning) than for highly accurate measurements to prisms, and (ii) the approach offers the opportunity to simultaneously acquire delay and spectral signatures of both delay and power thus allowing to combine distance measurement with material probing. We present a table-top experimental set-up that uses a coherent femtosecond laser supercontinuum to probe the displacement and multispectral relative distance of various material samples on 5 spectral bands of 50 nm in the visible and near-infrared regions. Using integration times of about 30 ms, we have achieved a distance measurement accuracy of better than 50 μm with promising perspectives regarding scalability to practical distances. Comparative measurements on 5 different materials additionally yielded repeatable material-dependent profiles in the multispectral relative distances, whose combination with reflectance estimations may allow mitigating surface related uncertainties and remotely identifying materials.

Paper Details

Date Published: 21 June 2019
PDF: 9 pages
Proc. SPIE 11056, Optical Measurement Systems for Industrial Inspection XI, 110561Q (21 June 2019); doi: 10.1117/12.2525841
Show Author Affiliations
David Salido-Monzú, ETH Zurich (Switzerland)
Andreas Wieser, ETH Zurich (Switzerland)

Published in SPIE Proceedings Vol. 11056:
Optical Measurement Systems for Industrial Inspection XI
Peter Lehmann; Wolfgang Osten; Armando Albertazzi Gonçalves Jr., Editor(s)

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