IMPROVED INTERFEROMETER

摘要

An interferometer comprises a source of a light beam, and a beam splitter for splitting the light beam from the source into at least first and second beams. A first (reference) reflector is positioned in the path of the first light beam. A second reflector, comprising a convergent lens and a mirror, is positioned in the path of the second light beam following reflection from a target. At least one detector is provided for detecting fringes formed by interference of the first and second light beams following reflection from the first and second reflectors respectively. The mirror of the second reflector has a radius of curvature within 10% of the value determined using the formula (I): and the focal length f of the convergent lens is within 10% of the value determined using the formula (II): where i are the segments of optical path, each of length l i , and having a refractive index n i, between the convergent lens and the mirror, and k are the segments of the intended optical path, each of length l k and having refractive index n k between the convergent lens and the target, in use.