WP3: Femtosecond laser-based long distance metrology

Femtosecond laser-based distance measurement schemes have been intensively studied for the last years. A number of different approaches have been studied with performances justifying further effort in the field (a selection of papers can be found, e.g., Opens internal link in current windowhere). 

The aim of this workpackage is to investigate new measurement schemes for distance determination with femtosecond frequency combs, acting as multi-wavelength sources, and to pave the way for field applications of these advanced sources.

Mode filtered spectrum with a spacing of 41 GHz ((c) by ISI Brno and VSL)

 

 

1. Cavity‑based mode filtering of optical frequency combs (equivalent to repetition rate multiplication) was successfully demonstrated by ISI Brno and VSL. This is a key technology for many activities in WP3. It is one way to make use of robust fibre-based frequency comb sources in length metrogy.

Multiple parallel phase detection by heterodyne signal analysis of frequency comb interferometers ((c) by PTB)

 

 

2. PTB develops a novel approach to use parallel phase detection of multiple  comb modes in order to combine a macroscopic range of non-ambiguity with inteferometric resolution. Opens external link in new windowA preliminary study with the limited bandwidth of electro-optic comb pairs showed a highly promising uncertainty scaling of the overall measurement result.

Many-wavelength inteferometer at the VSL 50m interference comparator. ((c) by VSL)

 

3. VSL and TU Delft have performed distance measurements of up to 50 m with their many-wavelength interferometer based on spectral interferometry. Under these test conditions, the relative agreement with the HeNe reference interferometer was better than 10-8. This is the first that this technology was applied to such a macroscopic distance.