Patent ID: 9410796
Filing Date: 2016-08-09
CPC Classification: G01B,G03F

Claim Text:
1. A displacement measurement system, for measuring a displacement of a first beam of radiation, the displacement measurement system comprising: a two dimensional reflection grating configured to diffract the first beam of radiation a first time to form at least two diffracted beams; at least two retro reflectors configured to redirect the at least two diffracted beams to diffract a second time on the reflection grating; wherein the at least two retro reflectors are configured to redirect the at least two diffracted beams to diffract a third time on the reflection grating before the at least two diffracted beams are being recombined to form the second beam; wherein the at least two retro reflectors are arranged to redirect the at least two diffraction beams to diffract at least a fourth time on the reflection grating before the at least two diffracted beams are recombined to form the second beam, and a sensor configured to receive the second beam and determine the displacement from an intensity of the second beam, wherein reflectors of the at least two retro reflectors are positioned only between the reflection grating and the sensor, and wherein the at least two diffracted beams comprise information about the displacement in a first and a second direction, and wherein the first direction is different from the second direction.