Laser heterodyne surface profiler
First Claim
1. A method for testing the deviation of the face of an object from a flat smooth surface comprising the steps ofgenerating a dual frequency beam of coherent light having a stable frequency difference with a constant reference phase,splitting said beam into first and second frequency components,directing said separating components onto spaced apart points on the face of said object,recombining said components into a single beam after reflection from said points,rotating said object about an axis normal to said face with respect to said first of said split components so as to have said second one of said components reflected from points along a circular track on said face while the first component is continually reflected from a stationary point on said axis at the center of rotation of said object, andmeasuring the phase shift of the difference frequency of said components in the recombined beam as a measure of the variation of said face from a flat smooth surface.
1 Assignment
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Accused Products
Abstract
A method and apparatus is disclosed for testing the deviation of the face of an object from a flat smooth surface using a beam of coherent light of two plane-polarized components, one of a frequency constantly greater than the other by a fixed amount to produce a difference frequency with a constant phase to be used as a reference. The beam also is split into its two components with the separate components directed onto spaced apart points onthe face of the object to be tested for smoothness. The object is rotated on an axis coincident with one component which is directed to the face of the object at the center which constitutes a virtual fixed point. This component also is used as a reference. The other component follows a circular track on the face of the object as the object is rotated. The two components are recombined after reflection to produce a reflected frequency difference of a phase proportional to the difference in path length which is compared with the reference phase to produce a signal proportional to the deviation of the height of the surface along the circular track with respect to the fixed point at the center.
42 Citations
15 Claims
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1. A method for testing the deviation of the face of an object from a flat smooth surface comprising the steps of
generating a dual frequency beam of coherent light having a stable frequency difference with a constant reference phase, splitting said beam into first and second frequency components, directing said separating components onto spaced apart points on the face of said object, recombining said components into a single beam after reflection from said points, rotating said object about an axis normal to said face with respect to said first of said split components so as to have said second one of said components reflected from points along a circular track on said face while the first component is continually reflected from a stationary point on said axis at the center of rotation of said object, and measuring the phase shift of the difference frequency of said components in the recombined beam as a measure of the variation of said face from a flat smooth surface.
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3. A method for testing the deviation of the face of an object from a flat smooth surface comprising the steps of
generating a beam of coherent light of two components, one of a frequency constantly greater than the other by a fixed amount to produce a difference frequency with a constant reference phase, splitting said beam into its two components and directing said separate components onto spaced apart reflecting points, at least one of which is on said face to be tested for smoothness, moving the face of said object to pass under at least said one component, recombining said two components after reflection from said points to produce a reflected frequency difference of a phase changed in proportion to the difference to path length of one component reflected from one point to the other component reflected from the other point, and comparing the phase of said reflected frequency difference with said constant reference phase to produce a signal proportional to the change of phase of said reflected frequency difference from said constant reference phase as said face is moved, and wherein the other of said points is selected to reflect light from a fixed position, thereby to produce a signal that is a measurement of the profile of said surface along a track over which said one component passes, and further wherein said fixed position is on said face, and movement of said face is rotational to pass said one component over a circular track on said face while the other component is reflected from a fixed position at the center of rotation, thereby to produce a phase which, upon being detected, provides a signal that is an absolute measurement of the profile of said surface along said circular track.
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7. A system for testing the deviation of the face of an object from a flat smooth surface comprising
means for generating a dual frequency beam of coherent light having a stable frequency difference, optical means for splitting said beam into first and second frequency components, for directing said separated components onto spaced apart points on the face of said object, and for recombining said components into a single beam after reflection from said points, means for rotating said object about an axis normal to said face with respect to said first of said split components so as to have said second one of said components reflected from points along a circular track on said face while said first component is continually reflected from a single point on said axis at the center of rotation of said object, and means for measuring the phase shift of the difference frequency of said components in the recombined beam as a measure of the variation of said face from a flat smooth surface.
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9. A system for testing the deviation of the face of an object from a flat smooth surface comprising
means for generating a beam of coherent light having two components of distinct frequencies which produce a constant frequency difference of fixed phase, optical means for splitting said beam into a measurement beam and a reference beam each with two frequency components, said measurement beam being split into its two frequency components, and directing said components of said measurement beam on two spaced apart focus points on the face of said object, and for recombining said two measurement beam components upon reflection from said face, means for rotating said object about an axis normal to said face at one of said focus points, thereby to vary the phase of the difference frequency of the recombined frequency components of the reference beam as a function of optical path length of said components, thereby to measure height deviation of said surface along a circular track reflecting one component with respect to the fixed point reflecting the other component, and means for continually comparing the phase of the frequency difference in said reference beam with the changing phase of the frequency difference in said measurement beam, thereby to obtain a signal proportional to height deviation of said face from a flat smooth surface along said circular track.
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13. Apparatus for testing the deviation of the face of an object from a flat smooth surface comprising
means for generating a beam of coherent light of two components, one of a frequency constantly greater than the other by a fixed amount to produce a difference frequency with a constant reference phase, means for optically splitting said beam into its two frequency components and directing said separate components onto spaced apart reflecting points, at least one of which is on said face to be tested for smoothness, and for recombining said two components after reflection from said points to produce a reflected frequency difference of a phase changed in proportion to the difference in path length of one component reflected from one point to the other component reflected from the other point, means for moving said object to pass said face under at least one component, and means for comparing the phase of said reflected frequency difference with said constant frequency phase to produce a signal proportional to the deviation of the phase of said reflected frequency difference from said constant reference phase as said face is moved, and wherein the other of said points is selected to reflect light from a fixed position, thereby to produce a signal that is a measurement of the profile of said surface along a track over which said one component passes, and further wherein said fixed position is on said face, and means for moving said object rotates said object on an axis passing through said fixed position, and said fixed position is on the face of said object, thereby to pass said one component over a circular track on said face while the other component is reflected from a point at the center of the track, thereby to produce a signal that is an absolute measurement of the profile of said surface along said circular track.
Specification