Rough surface profiler and method

Claim 1

A method of profiling a rough surface of an object, comprising the steps of: (a) positioning the object along an optical axis so that a predetermined feature of the rough surface is optically aligned with an imaging device; (b) producing an interference pattern of the rough surface by means of an interferometer; (c) varying an optical path difference between the object and a reference surface of the interferometer; (d) operating an imaging device to scan the rough surface to produce intensity data for each pixel of an image of the rough surface for a plurality of frames each shifted from the other by a preselected phase difference; (e) extracting a modulation envelope from the intensity data for each pixel; (f) locating a preselected characteristic of the modulation envelope for each pixel; (g) correlating the preselected characteristic of the modulation envelope to a relative height of the rough surface for each pixel, wherein step (e) includes (1) eliminates a constant or slow-charging component from the intensity data, as the optical path difference is varied, to produce a first digital signal; (2) rectifying the first digital signal to produce a second digital signal; and (3) separating the modulation envelope from the second digital signal, the fist and second digital signals and the modulation envelope being successive values of digital words.

Claim 2

A method of profiling a rough surface of an object, comprising the steps of: (a) positioning the object along an optical axis so that a predetermined feature of the rough surface is optically aligned with an imaging device; (b) producing an interference pattern of the rough surface by means of an interferometer; (c) varying an optical path difference between the object and a reference surface of the interferometer; (d) operating an imaging device to scan the rough surface to produce intensity data for each pixel of an image of the rough surface for a plurality of frames each shifted from the other by a preselected phase difference; (e) extracting a modulation envelope from the intensity data for each pixel; (f) locating a preselected characteristic of the modulation envelope for each pixel; (g) correlating the preselected characteristic of the modulation envelope to a relative height of the rough surface for each pixel, wherein step (e) includes (1) eliminates a constant or slow-charging component from the intensity data, as the optical path difference is varied, to produce a first digital signal; (2) rectifying the first digital signal to produce a second digital signal; and (3) separating the modulation envelope from the second digital signal, the fist and second digital signals and the modulation envelope being successive values of digital words.

Claim 6

A method of profiling a surface of an object, comprising the steps of: (a) moving the object along an optical axis so that a predetermined feature of the surface is optically aligned with an imaging device; (b) producing an interference pattern of the surface by means of an interferometer; (c) varying an optical path difference between the object and a reference surface at the interferometer; (d) operating an imaging device of the interferometer to scan the surface to produce intensity data for each pixel of an image of the surface for a plurality of frames each shifted from the other by a preselected phase difference; (e) computing phase information from the intensity data for each pixel; (f) determining a relative height corresponding to the phase information for each pixel, and using the relative heights as the profile of the surface if the surface is of a predetermined smoothness; (g) extracting a modulation envelope from the intensity data for each pixel; (h) locating a preselected characteristic of the modulation envelope for each pixel; (i) correlating the preselected characteristic of the modulation envelope to a relative height of the rough surface for each pixel, and using the relative heights as the profile of the surface if the surface is of roughness greater than a predetermined high roughness; and (j) combining the phase information with the relative height of the peak to obtain a relative height of improved accuracy for the surface at each pixel, and using the relative heights as the profile of the surface if the surface is of a predetermined intermediate roughness, wherein step (g) includes (1) eliminating a slow-charging component from the intensity data as the optical path difference is varied to produce a first digital signal; (2) rectifying the first digital signal to produce a second digital signal; and (3) separating the modulation envelope from the second digital signal, the first and second digital signals and the modulation envelope being successive values of digital words.

Claim 7

A method of profiling a surface of an object, comprising the steps of: (a) moving the object along an optical axis so that a predetermined feature of the surface is optically aligned with an imaging device; (b) producing an interference pattern of the surface by means of an interferometer; (c) varying an optical path difference between the object and a reference surface at the interferometer; (d) operating an imaging device of the interferometer to scan the surface to produce intensity data for each pixel of an image of the surface for a plurality of frames each shifted from the other by a preselected phase difference; (e) computing phase information from the intensity data for each pixel; (f) determining a relative height corresponding to the phase information for each pixel, and using the relative heights as the profile of the surface if the surface is of a predetermined smoothness; (g) extracting a modulation envelope from the intensity data for each pixel; (h) locating a preselected characteristic of the modulation envelope for each pixel; (i) correlating the preselected characteristic of the modulation envelope to a relative height of the rough surface for each pixel, and using the relative heights as the profile of the surface if the surface is of roughness greater than a predetermined high roughness; and (j) combining the phase information with the relative height of the peak to obtain a relative height of improved accuracy for the surface at each pixel, and using the relative heights as the profile of the surface if the surface is of a predetermined intermediate roughness, wherein step (g) includes (1) eliminating a slow-charging component from the intensity data as the optical path difference is varied to produce a first digital signal; (2) rectifying the first digital signal to produce a second digital signal; and (3) separating the modulation envelope from the second digital signal, the first and second digital signals and the modulation envelope being successive values of digital words.

Claim 11

A device for profiling a rough surface of an object, comprising in combination: (a) an imaging device; (b) means for moving the object along an optical axis so that a highest point of the rough surface is optically aligned with the imaging device; (c) an interferometer, and means for producing an interference pattern of the rough surface by means of the interferometer; (d) means for operating an imaging device of the interferometer to scan the rough surface to produce intensity data for each pixel of an image of the rough surface for a plurality of frames each shifted from the other by a preselected phase difference; (e) means for extracting modulation envelope from the intensity data for each pixel; (f) means for locating a preselected characteristic of the modulation envelope for each pixel ;and (g) means for correlating the preselected characteristic of the modulation envelope to a relative height of the rough surface at the peak for each pixel to obtain the profile of the rough surface.

Claim 12

A device for profiling a rough surface of an object, comprising in combination: (a) an imaging device; (b) means for moving the object along an optical axis so that a highest point of the rough surface is optically aligned with the imaging device; (c) an interferometer, and means for producing an interference pattern of the rough surface by means of the interferometer; (d) means for operating an imaging device of the interferometer to scan the rough surface to produce intensity data for each pixel of an image of the rough surface for a plurality of frames each shifted from the other by a preselected phase difference; (e) means for extracting modulation envelope from the intensity data for each pixel; (f) means for locating a preselected characteristic of the modulation envelope for each pixel ;and (g) means for correlating the preselected characteristic of the modulation envelope to a relative height of the rough surface at the peak for each pixel to obtain the profile of the rough surface.