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US 4,215,578 AGranted
Dipole mass laser-based gravity gradiometer
AssigneeStandard Oil Company (Indiana)
InventorTheodore V. Lautzenhiser
Life of this patent
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Abstract
A gravity gradiometer using at least one mass dipole mounted in a laser force-measurement system to detect the torque on the mass dipole generated by gravity gradient. The mass dipole is mounted on one end of a photoelastic modulator element positioned in the laser beam to differentially modulate circular polarization modes in response to application of a torque. In a preferred form, two mass dipoles are mounted on opposite ends of the modulator element which is rigidly supported at its center to improve noise rejection.
Claims15
A gravity gradiometer comprising:
- a laser for generating a laser beam having a plurality of circular polarization modes;
- a modulator comprising a photoelastic element positioned in the path of the laser beam for differentially altering the characteristics of the polarization modes in response to the application of a stress, said modulator fixedly supported at its center relative to the path of the laser beam;
- first and second mass dipoles bonded to first and second ends of the modulator, said dipoles positioned at substantially right angles to each other, whereby a gravity gradient in a plane perpendicular to the path of the laser beam produces torques in said mass dipoles which are coupled to said modulator to produce a frequency difference between said modes;
- and
- means for detecting said frequency difference.
2 more elements
A gravity gradiometer comprising:
- a laser for generating a laser beam having a plurality of circular polarization modes;
- a modulator comprising a photoelastic element positioned in the path of the laser beam for differentially altering the characteristics of the polarization modes in response to the application of a stress, said modulator being fixedly supported at a first end relative to the path of the laser beam;
- a mass dipole bonded to a second end of the modulator with the axis of the dipole perpendicular to the path of the laser beam whereby a gravity gradient in the plane perpendicular to the laser beam produces a torque in the dipole which is coupled to the modulator to produce a frequency difference between said modes;
- means for detecting said frequency difference;
- and
- a biasing element positioned within the path of the laser beam, said biasing element comprising photoelastic material pre-stressed by application of a permanent torque wherein the axis of the torque is parallel to the axis of the laser beam, whereby said biasing element causes an essentailly constant frequency difference between the polarization modes in addition to that caused by said modulator and causes said gradiometer to operate in a linear response range.
3 more elements
A method for determining gravity gradients comprising the steps of:
- generating a laser beam having a plurality of circular polarization modes;
- positioning a modulator comprising a photoelastic element in the path of said laser beam for differentially altering the characteristics of the polarization modes in response to the application of a stress, said modulator being fixedly supported at its center relative to the path of said laser beam;
- attaching first and second mass dipoles to first and second ends of said modulator, said dipoles being positioned at substantially right angles to each other, whereby a gravity gradient in a plane perpendicular to the path of said laser beam will produce torques on said mass dipoles which are coupled to said modulator, thus producing a frequency difference between said modes;
- detecting said frequency difference.
1 more element
A method for determining gravity gradients comprising the steps of:
- generating a laser beam having a plurality of circular polarization modes;
- positioning a modulator comprising a photoelastic element in the path of said laser beam for differentially altering the characteristics of the polarization modes in response to the application of a stress, said modulator being fixedly supported at a first end relative to the path of said laser beam;
- attaching a mass dipole to a second end of said modulator with the axis of said dipole being perpendicular to the path of said laser beam, whereby a gravity gradient in the plane perpendicular to said laser beam produces a torque in the dipole which is coupled to the modulator to produce a gravity gradient caused frequency difference between said modes;
- positioning a biasing element within the path of said laser beam, said biasing element comprising photoelastic material pre-stressed by application of a permanent torque wherein the axis of said torque is parallel to the axis of said laser beam, whereby said biasing element causes an essentially constant frequency difference between the polarization modes in addition to that caused by said modulator and causes said method to provide a linear response to said gravity gradients;
- and
- detecting said gravity gradient caused frequency difference.
3 more elements
Dependencies are inferred from the claim text.