Vers une exactitude sub-micronique dans la mesure des distances kilométriques sans interférométrie

A laser ranging method is described that uses the phase of an amplitude-modulated laser beam: the frequency of the modulation is permanently adjusted to maintain a constant dephasing, and the distance is deduced from its measurement. We show that phase drifts and cyclic errors are suppressed using a fast polarization switch that interchanges the roles of the reference and measurement paths. Preliminary measurements are obtained using this novel design, showing a measurement stability better than 10 nanometres. The comparison of a displacement with an interferometric system shows an agreement of the order of one micron. An analysis of the source of the systematic errors suggests that an accuracy better than one micron can be expected with this very simple set-up.