Distance measurement by laser light

摘要

Method and apparatus for measuring a distance to an object includes directing first and second laser beams having frequencies omega 11 and omega 12 toward the object. A first reference signal is derived having a beat frequency omega 1= omega 11- omega 12. A first reflected light beam reflected from the object is detected and has the beat frequency omega 1 and a first phase difference with respect to the first reference signal. The first phase difference is then extracted from the first reference signal and the first reflected light beam and a first plurality of distance nodes is calculated from the first phase difference. Then, the frequency of the second laser beam is changed to omega 13. A second reference signal having a beat frequency of omega 2= omega 11- omega 13 is then derived. A second reflected light beam reflected from the target is detected and has the beat frequency of omega 2 and a second phase different with respect to the second reference signal. The second phase difference is then extracted from the second reference signal and the second reflected light beam and a second plurality of distance nodes is then calculated from the second phase difference. Finally, the minimum distance node coincident between the first and second pluralities of nodes is selected as the distance to the object.