Patent ID: 8253943
Filing Date: 2012-08-28
Classification: G01B

Abstract:
1. An interferometer comprising: a source of a light beam; a first beam splitter for splitting the light beam from the source into at least first and second beams; a first reflector positioned in the path of the first light beam; a second reflector, comprising a convergent lens and a mirror, positioned in the path of the second light beam following reflection from a target; and at least one detector for detecting fringes formed by interference of the first and second light beams following reflection from the first and second reflectors respectively; characterised in that the mirror of the second reflector has a radius of curvature R within 10% of the value determined using the formula: and the focal length f of the convergent lens is within 10% of the value determined using the formula: where i are the segments of optical path, each of length l, and having 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.