Minoshima K, Matsumoto H
National Research Laboratory of Metrology, 1-1-4 Umezono, Tsukuba, Ibaraki 305-8563, Japan.
Appl Opt. 2000 Oct 20;39(30):5512-7. doi: 10.1364/ao.39.005512.
A high-accuracy optical distance meter with a mode-locked femtosecond laser is proposed for distance measurements in a 310-m-long optical tunnel. We measured the phase shift of the optical beat component between longitudinal modes of a mode-locked laser. A high resolution of 50 microm at 240-m distance was obtained without cyclic error correction. The group refractive index of air is automatically extracted to an accuracy of 6 parts per million (ppm) by two-color measurement with the pulses of fundamental and second-harmonic wavelengths. Finally, an absolute mechanical distance of 240 m was obtained to within 8-ppm accuracy by use of a series of beat frequencies with the advantage of a wide range of intermode frequency, together with the results of the two-color measurement.
