Method and apparatus for sensing surface displacement orthogonal to the line of sight

Claim 3

The method of claim 1 having in addition thereto the steps of: a. recording said superimposed images on a transparency, b. illuminating said transparency by a narrow band point source of light, and c. spatially filtering said illuminated transparency to remove low spatial frequency components at near zero frequency due to the spacing between individual speckles, but passing the first and higher order frequency due to said speckled gratings.

Claim 4

The method of claim 1 wherein superimposition of said grated speckle images is performed by obtaining a photograph of said object in a first surface position and viewing said object through said photograph in a different surface position.

Claim 5

The method of claim 1 wherein said superimposition is performed by doubly exposing a photographic film in said viewing plane at instants that said object is in two different surface positions.

Claim 6

The method of claim 1 wherein said object is in vibratory motion and wherein said superimposition is provided by taking a time exposure of said object through a plurality of cycles of vibration.

Claim 7

Apparatus for sensing surface displacement of an object orthogonal to the line of sight comprising: a. a single source of coherent light for illuminating said object so that when said object is imaged a speckled image of said surface is produced, b. a lens for imaging said illuminated surface in a viewing plane, c. a mask restricting the imaging of said surface by said lens, said mask having two spaced parallel slits permitting the superposition of the speckles imaged by two regions of said lens in said viewing plane to create interference gratings having a predetermined spatial frequency within individual speckles and forming a grated speckle image in the viewing plane, and d. means to superimpose two grated speckle images in said viewing plane at different instants corresponding to two different surface positions with the gratings in identical speckles overlapping, said superposition forming moire'' bands whose spacing and orientation indicate the magnitude and direction of in-plane displacement of said surface, said bands occurring at integral multiples of said grating intervals.

Claim 8

Apparatus for sensing surface displacement of an object orthogonal to the line of sight comprising: a. a single source of coherent light for illuminating said object so that when said object is imaged a speckled image of said surface is produced, b. a lens for imaging said illuminated surface in a viewing plane, c. a mask restricting the imaging of said surface by said lens, said mask having two spaced parallel slits permitting the superposition of the speckles imaged by two regions of said lens in said viewing plane to create interference gratings having a predetermined spatial frequency within individual speckles and forming a grated speckle image in the viewing plane, and d. means to superimpose two grated speckle images in said viewing plane at different instants corresponding to two different surface positions with the gratings in identical speckles overlapping, said superposition forming moire'' bands whose spacing and orientation indicate the magnitude and direction of in-plane displacement of said surface, said bands occurring at integral multiples of said grating intervals.

Claim 9

An apparatus as in claim 6 wherein said lens is an element of a camera, said camera including means for supporting film in said viewing plane, and a barrel for supporting said lens aNd said slitted mask in front of said lens.

Claim 10

An apparatus as in claim 7 wherein said means to superimpose two images comprises a shutter permitting double exposure of said film.

Claim 11

Apparatus as set forth in claim 8 having in combination therewith a viewer comprising: a. a holder for a transparency obtained from said camera, b. condensing optics for illuminating said transparency, c. means for directing light from said coherent source into said condensing optics, and d. means for imaging said illuminated transparency, including means for reducing low frequency information including the zero order of said grating image.

Claim 12

Apparatus as in claim 9 wherein said imaging means for said transparency comprises a viewing screen, a lens for imaging said transparency on said viewing screen, and a stop in the plane in which said laser source is imaged by said condensing optics for blocking the zero order of said grating image.