MEASUREMENTS OF ULTRA-SMALL DISPLACEMENTS

Techniques for resolving small transverse distances are compared with those for resolving small longitudinal displacements. As the desired resolution becomes finer, there comes a point where both problems are best solved by switching to the transform domain. Techniques for measuring displacement can be divided into those used for nonoscillatory versus oscillatory motions. Examples are described for achieving lambda /10**5 for the former and lambda /10**9 for the latter. Fundamental limitations are discussed.