Device for measuring angular deviation of a light beam by use of gratings

Claim 1

An instrument for measurement of angular deviations comprising a luminous source for projecting a luminous beam along an optical axis, means for angularly displacing the beam with respect to the optical axis as a function of the angular deviation to be measured, a transmitting diffraction grating interposed between said source and said beam displacing means and having tracks of recurrent transparent areas for producing an image with a given transverse field, a receiving diffraction grating disposed downstream of the beam displacing means for receiving said image of the transmitting diffraction grating thereon, and means for detecting displacement of the image of the transmitting grating on the receiving grating, said image covering substantially the entire extent of the receiving grating, said gratings being centered on said optical axis and each being constituted by a plurality of engraved track arrangements, the image of each track arrangement of the transmitting grating being projected onto a corresponding track arrangement of the receiver grating, the corresponding track arrangements having tracks with corresponding spacing, the track arrangements of each grating having stepwise successively increasing spacing between tracks, said gratings extending over the width of the field such that each track is illuminated over the entire length thereof, the width of each track being greater than the displacement corresponding to the maximum angular deviation to be measured.