High-precision long-distance measurement using a frequency comb of a femtosecond mode-locked laser

High-accuracy long-distance measurement is performed using a broad and stable femtosecond frequency comb. Cyclic-error, which has been the main source of inaccuracy in conventional measurements, is reduced more than tenfold, directly achieving high accuracies of 50 mu m at 1-GHz frequency and 14 mu m at 10-GHz frequency in a 240-m distance measurement using the phase measurement of intermode beats of a femtosecond frequency comb. Traceability of distance meters is discussed.