Absolute distance measurement system using a femtosecond laser as a modulator

Abstract

The generation of broadband microwave frequency comb from a femtosecond pulse train by direct photodetection opens the possibility for high-accuracy length measurements of long distances. We demonstrate a relatively simple realization of this measurement principle: an electronic distance measurement system based on a time-of-flight approach, driven by a femtosecond fibre laser source as a modulator. By the evaluation of the phase shifts of two distinct comb frequencies, a coarse and a fine measurement of the absolute distance can be performed. The range of the measurement system is demonstrated up to a length of 100 m. The experimental comparison of the femtosecond laser system with a conventional reference counting interferometer shows a precision better than ±10 μm at 100 m, corresponding to a relative measurement uncertainty of 1 × 10 −7 L. The limiting factors for the measurement uncertainty of the system are theoretically investigated and shown to be of the same order of magnitude.

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“…In recent years, in order to meet evergrowing industrial demands on the measurement precision and functionality, quit a few attempts have been made worldwide. Examples include synthetic wavelength interferometry [43][44][45], multi-wavelength interferometry [46][47][48][49][50], spectrally resolved interferometry [51][52][53][54], timeof-flight measurement [55][56][57][58][59] and dual-comb interferometry [60][61][62][63][64].…”