Patent ID: 6483593
Filing Date: 2002-11-19
Classification: G01B

Abstract:
A heterodyne interferometer comprising:a beamsplitter for splitting each of a first beam and a coherent second beam into at least two partial beams, said first beam and said partial first beams including signals having a first frequency, said second beam and said partial second beams including signals having a second frequency; a reference arm, downstream of said beamsplitter, for receiving a partial first beam and a partial second beam; and a measurement arm, downstream of said beamsplitter, for receiving another partial first beam and another partial second beam, wherein the length of a signal path defined by said measurement arm is at least partially defined by the position of a target; wherein the first beam and the partial first beams created by said beamsplitter propagate in a first plane, and wherein the second beam and the partial second beams created by said beamsplitter propagate in a second plane, offset from the first plane, such that the first beam and the partial first beams propagate in a downstream direction without spatially overlapping with the second beam and the partial second beams at any point upstream of respective ends of said reference and measurement arms; wherein one of said reference arm and said measurement arm is configured to receive a partial beam propagating in one of the first and second planes and to reflect the partial beam in the other of the first and second planes; and wherein the other of said reference arm and said measurement arm is configured to receive a partial beam propagating in one of the first and second planes and to reflect the partial beam in the same plane.