Absolute distance measurement by dual-comb interferometry with adjustable synthetic wavelength

TLDR

Absolute distances were measured using two femtosecond lasers with different pulse repetition rates, revisiting the dual‑comb interferometric method of Coddington et al. (2009 Nature Photonics). The authors propose a hardware design that extends the non‑ambiguity range, enabling dual‑comb interferometry for diverse terrestrial applications. The apparatus eliminates dead zones by separating measurement and reference pulses with orthogonal polarization, and tunes the signal laser’s repetition rate to adaptively adjust the synthetic wavelength based on air‑stability considerations. Open‑air tests show a 69.3 m target distance can be measured continuously at a 200 µs update rate despite a ~170 µm optical‑path drift from refractive‑index fluctuations.

Abstract

Absolute distances were measured using two femtosecond lasers of different pulse repetition rates by revisiting the dual-comb interferometric method proposed by Coddington et al (2009 Nature Photon. 3 351–6). The apparatus built for experiments was designed to eliminate the dead zones in the measurement range by separating the measurement pulses from the reference pulses using orthogonal polarization. In addition, the pulse repetition rate of the signal laser was made tunable in order to extend the non-ambiguity range (NAR) by adaptively adjusting the synthetic wavelength in consideration of the de facto measurement stability in the air. Actual tests performed in the open air proved that a target distance of 69.3 m is measured without interruptions at a 200 µs update rate in the presence of a ~170 µm drift of the optical path length caused by the fluctuation of the refractive index of air. The proposed hardware system design for effective NAR extension will facilitate the use of dual-comb interferometry for various terrestrial applications.