Absolute distance measurements based on the frequency comb of a femtosecond pulse laser

We describe absolute distance measurements performed by exploiting the frequency comb of a femtosecond laser as a precision wavelength ruler. The frequency comb is first stabilized to a Rb atomic clock of time standard. Then multi-wavelength interferometry integrated with a wavelength-scanning scheme is implemented by tuning an external cavity diode laser to the pre-selected frequency modes of the optical comb. The achieved wavelength uncertainty is 5.9 parts in 10 12 , which enables absolute distance measurements up to ~1 meter with overall uncertainty less than 20 nm.