Patent ID: 7443511
Filing Date: 2008-10-28
Classification: G01B,G03F

Abstract:
1. An interferometer system for measuring displacement, along at least two directions within a three dimensional system of coordinates, of an object in a plane substantially parallel to a two dimensional plane, said interferometer system comprising: a plane mirror interferometer system; a differential plane mirror interferometer system; and a beam splitter configured to split a radiation beam associated with said plane mirror interferometer system and a radiation beam associated with said differential plane mirror interferometer system into respective measuring beams and respective reference beams; at least one measuring mirror fixedly connected to said object and comprising a plurality of measuring mirror areas; at least one reference mirror comprising one or more reference mirror areas, wherein, in use, a direction of propagation of the reference beam associated with the differential plane mirror interferometer system just before incidence on a reference mirror is in a direction substantially orthogonal to the direction of the reference beam associated with the plane mirror interferometer just before incidence on a reference mirror and away from the beam-splitter.