Patent ID: 7253875

Claim:
A lithographic apparatus, comprising: (i) a reference frame; (ii) a measurement system configured to measure at least one of a position and a movement of a component of the lithographic apparatus relative to said reference frame, the measurement system comprising: (a) a target mounted to one of said component and reference frame; (b) a radiation source mounted to the other one of the component and the reference frame, and configured to project a beam of radiation to said target; and (c) a sensor configured to detect a pattern of radiation propagating from the target, said pattern being indicative of said at least one of the position and the movement of the component relative to the reference frame; wherein the component comprises one or more gas outlets configured such that, when a gas supply is provided to said gas outlets, a volume of a space through which said beam of radiation propagates to said target is substantially encapsulated by a flow of gas from said one or more gas outlets.