Interferometric tilt sensor

Claim 1

A method for remotely sensing the angular displacement of a test surface, comprising: a. producing two collimated light beams of substantially the same intensity which are coherent with respect to one another, one of said beams having a different frequency from the other beam, the frequency difference, Δf, being within the radio frequency (RF) range; b. directing each of said light beams toward separate optically reflective, good optical quality target areas on said test surface, said light beams being directed to reflect off of their respective target areas and to converge at a distance from said test surface thus forming a fringe pattern at said distance in an interference zone and producing an optical radiation field which is spatially and temporally modulated by the Δf, said fringe pattern continuously moving laterally along a direction perpendicular to the fringe planes of the interference zone at a rate equal to Δf; c. positioning a sampling means within the interference zone for sampling the laterally moving fringe pattern, said sampling means having at least one sampling aperture exposed to said interference zone, said at least one sampling aperture lying in a plane substantially perpendicular to a plane formed by the converging light beams, and having a width smaller than the effective spatial period of the fringe field, λ es , where λ es =λ s /cosφ, λ s being the spatial period of the fringe field and φ being the angular deviation of the plane of the sampling aperture from a plane which is perpendicular to said fringe planes; d. positioning a light detector to receive said modulated optical radiation which is sampled from the interference zone, said modulated optical radiation being converted into a sample electronic signal by associated electronic circuits; and e. sensing rotation of said test surface about the X-axis which is normal to the converging light beams by comparing the phase of said sample electronic signal to the phase of a reference electronic signal having a frequency equal to Δf.

Claim 2

A method for remotely sensing the angular displacement of a test surface, comprising: a. producing two collimated light beams of substantially the same intensity which are coherent with respect to one another, one of said beams having a different frequency from the other beam, the frequency difference, Δf, being within the radio frequency (RF) range; b. directing each of said light beams toward separate optically reflective, good optical quality target areas on said test surface, said light beams being directed to reflect off of their respective target areas and to converge at a distance from said test surface thus forming a fringe pattern at said distance in an interference zone and producing an optical radiation field which is spatially and temporally modulated by the Δf, said fringe pattern continuously moving laterally along a direction perpendicular to the fringe planes of the interference zone at a rate equal to Δf; c. positioning a sampling means within the interference zone for sampling the laterally moving fringe pattern, said sampling means having at least one sampling aperture exposed to said interference zone, said at least one sampling aperture lying in a plane substantially perpendicular to a plane formed by the converging light beams, and having a width smaller than the effective spatial period of the fringe field, λ es , where λ es =λ s /cosφ, λ s being the spatial period of the fringe field and φ being the angular deviation of the plane of the sampling aperture from a plane which is perpendicular to said fringe planes; d. positioning a light detector to receive said modulated optical radiation which is sampled from the interference zone, said modulated optical radiation being converted into a sample electronic signal by associated electronic circuits; and e. sensing rotation of said test surface about the X-axis which is normal to the converging light beams by comparing the phase of said sample electronic signal to the phase of a reference electronic signal having a frequency equal to Δf.

Claim 11

A method for measuring the angular displacement of a test surface, comprising: a. producing two collimated light beams of substantially the same intensity which are coherent with respect to one another, one of said beams having a different frequency from the other beam, the frequency difference, Δf, being within the radio frequency (RF) range; b. directing each of said light beams toward separate optically reflective, good optical quality target areas on said test surface, said light beams being directed to reflect off of their respective target areas and to converge at a distance from said test surface thus forming a fringe pattern at said distance in an interference zone and producing an optical radiation field which is spatially and temporally modulated by the Δf, said fringe pattern continuously moving laterally along a direction perpendicular to the fringe planes of the interference zone at a rate equal to Δf; c. positioning a slitted element within the interference zone for sampling the laterally moving fringe pattern, said slitted element having at least one slit formed therein which is exposed to said interference zone, said at least one slit lying in a plane substantially perpendicular to a plane formed by the converging light beams, and having a width smaller than the effective spatial period of the fringe field, λ es , where λ es is equal to λ s /cosφ, λ s being the spatial period of the fringe field and φ being the angular deviation of the plane of the slitted element from a plane which is perpendicular to said fringe planes; d. positioning a light detector to receive said modulated optical radiation which is sampled from the interference zone, said modulated optical radiation being converted into a sample electronic signal by associated electronic circuits; e. determining the extent and direction of the angular displacement of the test surface by measuring the magnitude and direction of the phase shift between said sample electronic signal and a reference electronic signal having a frequency equal to Δf.

Claim 12

A method for measuring the angular displacement of a test surface, comprising: a. producing two collimated light beams of substantially the same intensity which are coherent with respect to one another, one of said beams having a different frequency from the other beam, the frequency difference, Δf, being within the radio frequency (RF) range; b. directing each of said light beams toward separate optically reflective, good optical quality target areas on said test surface, said light beams being directed to reflect off of their respective target areas and to converge at a distance from said test surface thus forming a fringe pattern at said distance in an interference zone and producing an optical radiation field which is spatially and temporally modulated by the Δf, said fringe pattern continuously moving laterally along a direction perpendicular to the fringe planes of the interference zone at a rate equal to Δf; c. positioning a slitted element within the interference zone for sampling the laterally moving fringe pattern, said slitted element having at least one slit formed therein which is exposed to said interference zone, said at least one slit lying in a plane substantially perpendicular to a plane formed by the converging light beams, and having a width smaller than the effective spatial period of the fringe field, λ es , where λ es is equal to λ s /cosφ, λ s being the spatial period of the fringe field and φ being the angular deviation of the plane of the slitted element from a plane which is perpendicular to said fringe planes; d. positioning a light detector to receive said modulated optical radiation which is sampled from the interference zone, said modulated optical radiation being converted into a sample electronic signal by associated electronic circuits; e. determining the extent and direction of the angular displacement of the test surface by measuring the magnitude and direction of the phase shift between said sample electronic signal and a reference electronic signal having a frequency equal to Δf.

Claim 17

An apparatus for remotely sensing the angular displacement of a test surface, comprising: a. means for producing two collimated light beams of substantially the same intensity which are coherent with respect to one another, one of said beams having a different frequency from the other beam, the frequency difference, Δf, being within the radio frequency (RF) range; b. means for directing each of said light beams toward separate optically reflective, good optical quality target areas on said test surface, said light beams being directed to reflect off of their respective target areas and to converge at a distance from said test surface thus forming a fringe pattern at said distance in an interference zone and producing an optical radiation field which is spatially and temporally modulated by the Δf, said fringe pattern continuously moving laterally along a direction perpendicular to the fringe planes of the interference zone at a rate equal to Δf; c. sampling means positioned within the interference zone for sampling the laterally moving fringe pattern, said sampling means having at least one sampling aperture exposed to said interference zone, said at least one sampling aperture lying in a plane substantially perpendicular to a plane formed by the converging light beams, and having a width smaller than the effective spatial period of the fringe field, λ es , where λ es =λ s /cosφ, λ s being the spatial period of the fringe field and φ being the angular deviation of the plane of the sampling aperture from a plane which is perpendicular to said fringe planes; d. a light detector positioned to receive said modulated optical radiation which is sampled from the interference zone, said modulated optical radiation being converted into a sample electronic signal by associated electronic circuits; and e. comparing means for comparing the phase of said sample electronic signal to the phase of a reference electronic signal having a frequency equal to Δf and thereby sensing rotation of said test surface.

Claim 18

An apparatus for remotely sensing the angular displacement of a test surface, comprising: a. means for producing two collimated light beams of substantially the same intensity which are coherent with respect to one another, one of said beams having a different frequency from the other beam, the frequency difference, Δf, being within the radio frequency (RF) range; b. means for directing each of said light beams toward separate optically reflective, good optical quality target areas on said test surface, said light beams being directed to reflect off of their respective target areas and to converge at a distance from said test surface thus forming a fringe pattern at said distance in an interference zone and producing an optical radiation field which is spatially and temporally modulated by the Δf, said fringe pattern continuously moving laterally along a direction perpendicular to the fringe planes of the interference zone at a rate equal to Δf; c. sampling means positioned within the interference zone for sampling the laterally moving fringe pattern, said sampling means having at least one sampling aperture exposed to said interference zone, said at least one sampling aperture lying in a plane substantially perpendicular to a plane formed by the converging light beams, and having a width smaller than the effective spatial period of the fringe field, λ es , where λ es =λ s /cosφ, λ s being the spatial period of the fringe field and φ being the angular deviation of the plane of the sampling aperture from a plane which is perpendicular to said fringe planes; d. a light detector positioned to receive said modulated optical radiation which is sampled from the interference zone, said modulated optical radiation being converted into a sample electronic signal by associated electronic circuits; and e. comparing means for comparing the phase of said sample electronic signal to the phase of a reference electronic signal having a frequency equal to Δf and thereby sensing rotation of said test surface.

Claim 27

An apparatus for measuring the angular displacement of a test surface, comprising: a. means for producing two collimated light beams of substantially the same intensity which are coherent with respect to one another, one of said beams having a different frequency from the other beam, the frequency difference, Δf, being within the radio frequency (RF) range; b. means for directing each of said light beams toward separate optically reflective, good optical quality target areas on said test surface, said light beams being directed to reflect off of their respective target areas and to converge at a distance from said test surface thus forming a fringe pattern at said distance in an interference zone and producing an optical radiation field which is spatially and temporally modulated by the Δf, said fringe pattern continuously moving laterally along a direction perpendicular to the fringe planes of the interference zone at a rate equal to Δf; c. a slitted element positioned within the interference zone for sampling the laterally moving fringe pattern, said slitted element having at least one slit formed therein which is exposed to said interference zone, said at least one slit lying in a plane substantially perpendicular to a plane formed by the converging light beams, and having a width smaller than the effective spatial period of the fringe field, λ es , where λ es is equal to λ s /cosφ, λ s being the spatial period of the fringe field and φ being the angular deviation of the plane of the slitted element from a plane which is perpendicular to said fringe planes; d. a light detector positioned to receive said modulated optical radiation which is sampled from the interference zone, said modulated optical radiation being converted into a sample electronic signal by associated electronic circuits; and e. measuring means for measuring the magnitude and direction of the phase shift between said sample electronic signal and a reference electronic signal having a frequency equal to Δf for determining the extent and direction of the angular displacement of the test surface.

Claim 28

An apparatus for measuring the angular displacement of a test surface, comprising: a. means for producing two collimated light beams of substantially the same intensity which are coherent with respect to one another, one of said beams having a different frequency from the other beam, the frequency difference, Δf, being within the radio frequency (RF) range; b. means for directing each of said light beams toward separate optically reflective, good optical quality target areas on said test surface, said light beams being directed to reflect off of their respective target areas and to converge at a distance from said test surface thus forming a fringe pattern at said distance in an interference zone and producing an optical radiation field which is spatially and temporally modulated by the Δf, said fringe pattern continuously moving laterally along a direction perpendicular to the fringe planes of the interference zone at a rate equal to Δf; c. a slitted element positioned within the interference zone for sampling the laterally moving fringe pattern, said slitted element having at least one slit formed therein which is exposed to said interference zone, said at least one slit lying in a plane substantially perpendicular to a plane formed by the converging light beams, and having a width smaller than the effective spatial period of the fringe field, λ es , where λ es is equal to λ s /cosφ, λ s being the spatial period of the fringe field and φ being the angular deviation of the plane of the slitted element from a plane which is perpendicular to said fringe planes; d. a light detector positioned to receive said modulated optical radiation which is sampled from the interference zone, said modulated optical radiation being converted into a sample electronic signal by associated electronic circuits; and e. measuring means for measuring the magnitude and direction of the phase shift between said sample electronic signal and a reference electronic signal having a frequency equal to Δf for determining the extent and direction of the angular displacement of the test surface.