Abstract
Optical frequency combs have developed into powerful tools for distance metrology. In this paper we demonstrate absolute long distance measurement using a single femtosecond frequency comb laser as a multi-wavelength source. By applying a high-resolution spectrometer based on a virtually imaged phased array, the frequency comb modes are resolved spectrally to the level of an individual mode. Having the frequency comb stabilized against an atomic clock, thousands of accurately known wavelengths are available for interferometry. From the spectrally resolved output of a Michelson interferometer a distance is derived. The presented measurement method combines spectral interferometry, white light interferometry and multi-wavelength interferometry in a single scheme. Comparison with a fringe counting laser interferometer shows an agreement within <10−8 for a distance of 50 m.
Highlights
Been shown using spectral interferometry[12,13], multi-heterodyne interferometry[14] and time-of-flight measurement[15]
A huge step is taken by demonstrating the power of mode-resolved comb interferometry for long range applications, up to 50 m in air, which is promising for a wealth of applications requiring high-accuracy and absolute long distance measurement
A femtosecond frequency comb is the spectrum of a laser that is stabilized against a time standard like a cesium atomic clock, by phase-locking both the repetition rate frep and the offset frequency f0
Summary
Been shown using spectral interferometry[12,13], multi-heterodyne interferometry[14] and time-of-flight measurement[15]. A huge advantage of frequency comb interferometry compared to conventional interferometry with a single wavelength is that the range of non-ambiguity is determined by the pulse-to-pulse distance, which is typically tens of cm to meters. For a conventional single-wavelength interferometer the range of non-ambiguity is half of the optical wavelength As a result these interferometer systems are usually used in fringe-counting mode, i.e. a displacement is measured instead of an absolute distance. A huge step is taken by demonstrating the power of mode-resolved comb interferometry for long range applications, up to 50 m in air, which is promising for a wealth of applications requiring high-accuracy and absolute long distance measurement. As a result the spectrum of the comb consists of thousands of optical modes, with a fixed mutual frequency difference of neighboring modes equal to frep These frequencies have a stability comparable to the stability of the reference clock.
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