We demonstrate a new technique for absolute distance measurement with a femtosecond frequency comb laser, based on unraveling the output of an interferometer to distinct comb modes with 1 GHz spacing. From the fringe patterns that are captured with a camera, a distance is derived by combining spectral and homodyne interferometry, exploiting about 9000 continuous wave lasers. This results in a measurement accuracy far within an optical fringe ($\lambda /30$), combined with a large range of nonambiguity (15 cm). Our technique merges multiwavelength interferometry and spectral interferometry, within a single scheme.

• Received 6 December 2011

DOI:https://doi.org/10.1103/PhysRevLett.108.183901