Interferometric measurements of displacement on a diffusing target by a speckle tracking technique

Operation of a laser interferometer with a noncooperative target surface, and on a substantial span of displacement (1 m), is reported for the first time to our knowledge In the paper, we first analyze the errors of an interferometer operating in the speckle pattern regime, then propose the technique of tracking the speckle relative maximum amplitude as a solution far problems so far preventing interferometric measurements of large displacements. Examples of the speckle-statistics improvements are reported. Residual errors are of the order of few wavelengths on a I-m displacement, indicating that a 10(-6)-class instrument can be developed. The proposed approach has been implemented with an injection interferometer.