Simultaneous distance measurement at multiple wavelengths using the intermode beats from a coherent supercontinuum

Abstract

Advances in ultrashort pulse lasers and spectral manipulation enable new approaches to metrological problems in various fields. Dimensional metrology may benefit particularly from this progress, including applications like long distance measurement and 3D laser scanning. Using the intermode beat notes obtained by direct photodetection of a mode-locked femtosecond laser has been demonstrated as a promising alternative to solutions based on actively modulated signals. In this work, we extend the approach to ultra-broadband sources derived from femtosecond lasers, aiming at investigating their potential as a technological basis for multiwavelength distance metrology. We have developed a short-distance experimental set-up for displacement measurement operating simultaneously at two wavelength ranges on both extremes of a 500 nm coherent supercontinuum. The results derived from the phases of the 1 GHz intermode beat notes show that the internal coherence of the source is sufficient to derive distances with an accuracy better than 50 μm. This is a promising first step for the prospective application of this method to develop spectrally-versatile solutions, which is of interest to provide surface material probing capabilities in laser scanning and to increase the accuracy of long distance measurement though dispersion-based refractivity compensation.