Common path point diffraction interferometer using liquid crystal phase shifting
AssigneeThe United States of America as represented by the Administrator of the National Aeronautics and Space Administration
InventorCarolyn R. Mercer
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Abstract
A common path point diffraction interferometer uses dyed, parallel nematic liquid crystals which surround an optically transparent microsphere. Coherent, collimated and polarized light is focused on the microsphere at a diameter larger than that of the microsphere. A portion of the focused light passes through the microsphere to form a spherical wavefront reference beam and the rest of the light is attenuated by the dyed liquid crystals to form an object beam. The two beams form an interferogram which is imaged by a lens onto an electronic array sensor and into a computer which determines the wavefront of the object beam. The computer phase shifts the interferogram by stepping up an AC voltage applied across the liquid crystals without affecting the reference beam.
Claims16
A common path, point diffraction interferometer for forming interferograms from simultaneously produced object and reference beams derived from a single incident light beam which comprises a liquid crystal cell having a pair of transparent, parallel and opposing substrates and enclosing within a liquid crystal layer containing at least one microsphere whose diameter is equal to the distance between said substrates, each said substrate having a transparent electrode adjacent an opposing surface.
A method for forming an interferogram which comprises focusing a coherent, polarized incident light beam proximate a transparent microsphere surrounded by a layer of liquid crystal so that a portion of said incident light is diffracted by said microsphere to form a reference beam, with the remainder of said incident light traveling through said liquid crystal layer to form an object beam simultaneously with said reference beam and wherein said object and reference beams are coherent and produce said interferogram.
A method for forming an interferogram which comprises focusing a coherent, polarized incident light beam proximate a transparent microsphere surrounded by a layer of uniaxial nematic liquid crystal so that a portion of said incident light is diffracted by said microsphere to form a reference beam, with the remainder of said incident light traveling through said liquid crystal layer to form an object beam simultaneously with said reference beam, wherein said object and reference beams are coherent and produce an interferogram which is phase shifted by applying an AC voltage across said liquid crystal layer to phase-shift said object beam, but not said reference beam, wherein said nematic liquid crystals are oriented parallel to each other and the plane of said polarized incident light is parallel to the orientation plane of said nematic liquid crystals in their relaxed state, and wherein said crystal layer contains a dye to attenuate the intensity of said object beam.
Dependencies are inferred from the claim text.