# US 7,304,746 B2 · Common-path point-diffraction phase-shifting interferometer > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,304,746 B2 - Document ID: US7304746B2 - Status: Granted - Kind: B2 - Application number: 11/501,413 - Filed: 2006-08-09 - Published: 2006-12-07 - Granted: 2007-12-04 - Earliest claimed: 2002-01-09 - Assignees: Interphase Technologies, Inc. - Inventors: William J. Cottrell - Web page: https://patentgrep.com/patent/US7304746B2 ## CPC - G01J 9/02: by interferometric methods (using interferometers for measuring optically the linear dimensions of objects G01B9/02) - G01M 11/005: {Testing of reflective surfaces, e.g. mirrors} - G01M 11/331: {by using interferometer} - G01M 11/333: {using modulated input signals} - G01J 2009/0223: {Common path interferometry; Point diffraction interferometry} - G01J 2009/0261: {polarised} - G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N) - G01M: TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR ## Abstract A common-path, point-diffraction, phase-shifting interferometer uses a half wave plate having a diffractive element, such as pin hole. A coherent, polarized light source simultaneously generates a reference beam from the diffractive element and an object beam from remaining portions of the light going through the half wave plate. The reference beam has a nearly spherical wavefront. Each of the two beams possesses a different polarization state. The object and reference beams are then independently phase modulated by a polarization sensitive phase modulator that shifts phase an amount depending on applied voltage and depending on polarization state of the incident light. A polarizer is then used to provide the object and reference beams in the same polarization state with equal intensities so they can interfere to create an interferogram with near unity contrast. ## Claims ### Claim 1 A interferometric device, comprising: a polarizing point diffraction plate for receiving an incident beam, said plate including a first diffractive polarizer adjacent to a second polarizer, said first polarizer for generating a reference beam and said second polarizer for generating an object beam. ### Claim 2 (depends on 1) A device as recited in claim 1, wherein said first polarizer is a polarizing film. ### Claim 3 (depends on 1) A device as recited in claim 1, wherein said second polarizer is a polarizing film. ### Claim 4 (depends on 1) A device as recited in claim 1, wherein said first polarizer is embedded in said second polarizer. ### Claim 5 (depends on 1) A device as recited in claim 1, wherein said first polarizer is circumscribed by said second polarizer. ### Claim 6 (depends on 1) A device as recited in claim 1, wherein the polarization axis of said second polarizer is oriented at 90 degrees to the polarization axis of said first polarizer. ### Claim 7 (depends on 1) A device as recited in claim 1, wherein said first and second polarizers are for generating mutually perpendicular reference and object beams. ### Claim 8 A interferometric device, comprising: an incident beam; a polarization point diffraction plate for receiving said incident beam, said plate including a first diffractive polarizer adjacent to a second polarizer and splitting said incident beam into a reference beam and an object beam; and a polarization filter for combining a portion of said reference beam and a portion of said object beam into the same polarization state. ### Claim 9 (depends on 8) A device as recited in claim 8, wherein said object beam and said reference beam travel along a common axis. ### Claim 10 (depends on 8) A device as recited in claim 8, wherein said object beam and said reference beam have mutually orthogonal polarizations. ### Claim 11 (depends on 8) A device as recited in claim 8, wherein the polarization axis of said second polarizer is oriented at 90 degrees to the polarization axis of said first polarizer. ### Claim 12 (depends on 8) A device as recited in claim 8, wherein the polarization axis of said incident beam is oriented at 45 degrees to said polarization axes of both said first and second polarizer. ### Claim 13 (depends on 8) A device as recited in claim 8, wherein said reference beam has a spherical wavefront. ### Claim 14 (depends on 8) A device as recited in claim 8, wherein said polarization filter comprises a linear polarizer. ### Claim 15 (depends on 8) A device as recited in claim 8, wherein said polarization filter is adjustable. ### Claim 16 (depends on 8) A device as recited in claim 8, further comprising a detector for imaging interferograms. ### Claim 17 (depends on 8) A device as recited in claim 8, further comprising a modulator for shifting phase of said reference beam relative to phase of said object beam. ### Claim 18 (depends on 17) A device as recited in claim 17, wherein said modulator comprises an anisotropic electro-optic material. ### Claim 19 (depends on 8) A device as recited in claim 8, further comprising means for adjusting the amount of polarization shift introduced by said polarization point diffraction plate. ### Claim 20 A method of characterizing an optical wavefront with an interferometric device comprising: transmitting a wavefront through a test system; splitting said wavefront into an object wavefront and a reference wavefront traveling along a common axis so that said object wavefront has a first intensity and first polarization and said reference wavefront has a second intensity and a second polarization; shifting the phase of said object wavefront relative to the phase of said reference wavefront; and adjusting said first intensity of said object wavefront relative to said second intensity of said reference wavefront to be in substantially the same polarization state to generate an interferogram that provides information about said wavefront. ### Claim 21 (depends on 20) A method as recited in claim 20, wherein said shifting occurs by an electro-optic device. ### Claim 22 (depends on 20) A method as recited in claim 20, wherein said splitting occurs by a point diffraction plate including a diffractive non-polarizer region adjacent to a polarizer. ### Claim 23 (depends on 20) A method as recited in claim 20, wherein said splitting occurs by a point diffraction plate including a first diffractive polarizer adjacent to second polarizer. ### Claim 24 (depends on 20) A method as recited in claim 20, wherein said splitting occurs by a point diffraction plate including a diffractive non-birefringent region adjacent to a birefringent region. ### Claim 25 (depends on 20) A method as recited in claim 20, wherein said splitting occurs by a point diffraction plate including a diffractive polarizer adjacent to a birefringent region. ### Claim 26 (depends on 20) A method as recited in claim 20, wherein said splitting occurs by a point diffraction plate including a diffractive birefringent region adjacent to a polarizer. ### Claim 27 (depends on 20) A method as recited in claim 20, wherein said splitting occurs by a point diffraction plate including a diffractive first birefringent region adjacent to a second birefringent region. ### Claim 28 An interferometric measurement device for characterizing an input wavefront comprising a polarizing point-diffraction plate positioned along an optical axis of the device, wherein the plate includes two regions and one of the regions includes a first polarizing element adapted to split the input wavefront into a reference wavefront and a test wavefront with mutually orthogonal polarizations; and wherein the other of said two regions includes a second polarizing element perpendicular to the first polarizing element. ### Claim 29 (depends on 28) The interferometric measurement device of claim 28, further comprising a phase-shifting interferometer that includes a temporal phase-shifting section to impart different relative temporal phase shifts between the reference and test wavefronts, an interference section to combine the temporally phase-shifted reference and test wavefronts to produce corresponding interferograms, and a detector section to temporally sample the interferograms. ### Claim 30 (depends on 28) The interferometric measurement device of claim 28, further comprising means for changing a relative position between a source of said input wavefront and said polarizing point-diffraction plate. ### Claim 31 An interferometric measurement device for characterizing an input wavefront comprising a polarizing point-diffraction plate positioned along an optical axis of the device, wherein the plate includes two regions and one of the regions includes a first polarizing element adapted to split the input wavefront into a reference wavefront and a test wavefront with mutually orthogonal polarizations; and wherein said one region is circumscribed by the other of said two regions of the plate. ### Claim 32 (depends on 31) The interferometric measurement device of claim 31, further comprising a phase-shifting interferometer that includes a temporal phase-shifting section to impart different relative temporal phase shifts between the reference and test wavefronts, an interference section to combine the temporally phase-shifted reference and test wavefronts to produce corresponding interferograms, and a detector section to temporally sample the interferograms. ### Claim 33 An interferometric measurement device for characterizing an input wavefront comprising a polarization shifter positioned along an optical axis of the device, wherein the shifter includes two regions for splitting the input wavefront into a first polarized and a second polarized wavefront with mutually orthogonal polarizations, wherein one of the regions includes a means for rotating said first polarized wavefront to produce said second polarized wavefront; wherein said means for rotating the first polarized wavefront includes an output polarization element. ### Claim 34 (depends on 33) The interferometric measurement device of claim 33, further including an input polarizing element in line with said two regions to convert the input wavefront into said first polarized wavefront. ### Claim 35 An interferometric measurement method for characterizing the shape of an input wavefront comprising the following steps: passing the input wavefront through a polarizing point-diffraction plate that includes two regions, one of the regions including a first polarizing element adapted to spilt the input wavefront into a reference wavefront and a test wavefront having a common optical path and mutually orthogonal polarizations; passing the reference and test wavefronts through a phase-shining interferometer maintaining said common optical path; imaging an interferogram produced by the interferometer onto a detector; and analyzing the interferogram to characterize the shape of the input wavefront wherein the other of said two regions includes a second polarizing element perpendicular to the first polarizing element. ### Claim 36 (depends on 35) The interferometric measurement method of claim 35, wherein said phase-shifting interferometer is a temporal phase-shifting interferometer. ### Claim 37 An interferometric measurement method for characterizing the shape of an input wavefront comprising the following steps: passing the input wavefront through a polarizing point-diffraction plate that includes two regions, one of the regions including a first polarizing element adapted to split the input wavefront into a reference wavefront and a test wavefront having a common optical path and mutually orthogonal polarizations; passing the reference and test wavefronts through a phase-shifting interferometer maintaining said common optical path; imaging an interferogram produced by the interferometer onto a detector; and analyzing the interferogram to characterize the shape of the input wavefront; wherein said one region is circumscribed by the other of said two regions of the plate. ### Claim 38 (depends on 37) The interferometric measurement method of claim 37, wherein said phase-shifting interferometer is a temporal phase-shifting interferometer.