ACTUATION MECHANISM, OPTICAL APPARATUS, LITHOGRAPHY APPARATUS AND METHOD OF MANUFACTURING DEVICES

摘要

An actuator (300) to displace, for example a mirror, provides movement with at least two degrees of freedom by varying the currents in two electromagnets (370, 372, 376, 378). A moving part includes a permanent magnet (362) with a magnetic face constrained to move over a working area lying substantially in a first plane perpendicular to a direction of magnetization of the magnet. The electromagnets have pole faces (380, 382) lying substantially in a second plane closely parallel to the first plane, each pole face substantially filling a quadrant of the area traversed by the face of the moving magnet. An optical position sensor (390) may direct a beam of radiation (398) at the moving magnet through a central space between the electromagnets. The sizes of facets in a pupil mirror device may be made smaller in a peripheral region, but larger in a central region, thereby relaxing focusing requirements.