Patent ID: 6744520
Filing Date: 2004-06-01
Classification: G01B,G01D

Abstract:
A method for measuring two-dimensional displacement using conjugate optics, comprising the following stepsâ€”emitting an incident beam from a light source; generating firstly diffracted beams by emitting the incident beam onto a diffraction element; selecting an axially symmetric pair of beams from the firstly diffracted beams, where the two beams are of the same order of diffraction; introducing corresponding sets of wavefront reconstruction optics so as to reflect the two selected firstly diffracted beams back along the same optical paths; generating secondly diffracted beams by emitting the two reflected beams back onto the same incident spot on the said diffraction element; selecting two axially symmetric pairs of beams from the secondly diffracted beams, where the two pairs amount to a total of four beams which are of the same order of diffraction and the set of which is axially symmetric; forming a first interference fringe by superposing the first pair of the selected secondly diffracted beams via mirrors and interferometric optics, and similarly, forming a second interference fringe by superposing the second pair of the selected secondly diffracted beams via other mirrors and interferometric optics; obtaining two linearly independent displacements of the diffraction element relative to the rest of the optics, mentioned in this claim, by decoding the two interference fringes.