Patent ID: 7532330

Claim:
A method, comprising: directing a beam to reflect from an interface of a first optical element at a non-normal angle, the beam having an s-polarized component and a p-polarized component at the interface, wherein the non-normal reflection at the interface introduces a phase change upon reflection for the s-polarized component and a phase change upon reflection for the p-polarized component, where the phase changes upon reflection for the s-polarized and p-polarized components differ from one another by an amount that varies depending on the incident angle of the beam at the interface; detecting the beam after it has reflected from the interface; measuring an optical interference signal from the detected beam, wherein the optical interference signal comprises an interference phase related to the phase changes upon reflection between the s-polarized and p-polarized components of the beam; and determining information about the incident angle of the beam at the interface based on the measured optical interference signal.