Control of ghost reflections in interferometer based measurement systems using curved optical elements

摘要

The present disclosure relates to high-stability plane-mirror interferometers which are e.g.. used to accurately measure the position of a mirror that is connected to an object such as a stage. Interferometer technology is e.g. described in US 7,652,771 B2. Interferometers or interferometer measurement systems may be affected by undesired residual reflections that are caused by optical elements such as windows or quarter wave plates that are arranged in an optical path of the interferometer beam. Such reflections can be referred to as ghost reflections. Such ghost reflections can cause errors in the interferometer signal in the order of several pm to a nm, when these ghost reflections end up on the detector of the interferometer. Several strategies are known to control such ghost reflections, such as tilting the interferometer or the optical element that causes these ghost reflections. These strategies often cause new issues, like large Wulk-Off. Such new issues can in turn be fixed, e.g. by a Double Polarizing Beam Splitter or DPBS.