Lithographic apparatus, device manufacturing method and angular encoder

摘要

In a lithographic projection apparatus, a measuring system for measuring the position of the projection system PL relative to a reference frame RF includes sensors rigidly mounted in relation to counterpart sensors of a measuring system measuring the substrate table WT position. An angular encoder which sends light from a target 41 down two optical paths having opposite sensitivities to tilt is used to measure rotation of the projection system PL about its optical axis. <IMAGE>