Displacement metrology with sub-pm resolution in air based on a fs-comb wavelength synthesizer

We report on a displacement metrology setup that provides sub-pm resolution in air. The setup is based on a Fabry-Perot cavity. However, unlike current Fabry-Perot cavity based displacement setups we incorporate a novel fs-laser based arbitrary wavelength synthesizer that provides efficient suppression of atmospheric disturbances while providing very wide and precise tuning of the output wavelength. The wavelength synthesizer provides sub-10 attometer wavelength resolution. The setup provides subpm length stability for integration times of up to one minute and sub-10 pm for up to half an hour without airtight enclosure of the Fabry-Perot cavities.