# US 4,391,525 A · Interferometer > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,391,525 A - Document ID: US4391525A - Status: Granted - Kind: A - Application number: 06/083,315 - Filed: 1979-10-10 - Granted: 1983-07-05 - Earliest claimed: 1979-10-10 - Assignees: Ball Corporation - Inventors: Robert A. Woodruff - Web page: https://patentgrep.com/patent/US4391525A ## CPC - G01J 3/4535: {Devices with moving mirror (G01J3/4532 takes precedence)} - G01B 9/02018: Multipass interferometers, e.g. double-pass - G01B 9/02058: {by particular optical compensation or alignment elements, e.g. dispersion compensation} - G01B 2290/15: Cat eye, i.e. reflection always parallel to incoming beam - 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) - G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS ## Abstract An interferometer having beamsplitting and reflective coatings on the same surface of a beamsplitter member. The fixed length path of the interferometer includes a compensator matched to the beamsplitter member, a Cat's Eye Retroreflector, the reflective coating and a retro-mirror. The variable length path of the interferometer includes a moving coil mirror, a movable Cat's Eye Retroreflector and the retro-mirror. ## Claims ### Claim 1 An interferometer comprising: a beamsplitter member including a surface; a beamsplitting coating disposed on a first portion of said beamsplitter member surface for splitting incident light into a transmitted beam and a reflected beam, said transmitted beam propagating along a first optical path of said interferometer and said reflected beam propagating along a second optical path of said interferometer; a compensator positioned in said first optical path; a first reflector for reflecting light transmitted by said beamsplitter; a second reflector formed by a coating positioned upon a second portion of said surface of said beamsplitter member, such that said second reflector and said beamsplitting coating are substantially coplanar, said second reflector for reflecting light from said first reflector; a retro-reflector for reflecting light transmitted thereto from said second reflector back toward said second reflector, said light retracing its optical path back to said beamsplitter; a third reflector for reflecting light reflected by said beamsplitter; a fourth reflector for reflecting light reflected by said third reflector back to said third reflector and then to said retroreflector, said retroreflector reflecting light back toward said third reflector, said light retracing its optical path back to said beamsplitting coating along said second optical path, said transmitted beam and said reflected beam being recombined at said beamsplitting coating. ### Claim 2 (depends on 1) An interferometer according to claim 1 wherein said fourth reflector is movable. ### Claim 3 (depends on 2) An interferometer according to claim 2 wherein said fourth reflector is a Cat's Eye Retroreflector. ### Claim 4 (depends on 1) An interferometer according to claim 1 wherein said third reflector comprises a moving coil mirror. ### Claim 5 (depends on 1) An interferometer according to claim 1 wherein said first reflector comprises a Cat's Eye Retroreflector. ### Claim 6 (depends on 1) An interferometer according to claim 1 wherein said fourth reflector comprises a Cat's Eye Retroreflector. ### Claim 7 (depends on 1) An interferometer according to claim 1 wherein said compensator is positioned between said beamsplitter member and said first reflector. ### Claim 8 (depends on 1, 7) An interferometer according to claims 1 or 7 wherein said beamsplitter member and said compensator are wedged in like amounts to eliminate channel spectral interference. ### Claim 9 (depends on 1) An interferometer according to claim 1 wherein the angle of incidence of said incident light is less than 45.degree.. ### Claim 10 (depends on 1) An interferometer according to claim 1 wherein said beamsplitter member comprises a KBr plate and a layer of germanium affixed thereto. ### Claim 11 (depends on 10) An interferometer according to claim 10 wherein said compensator is made of KBr. ### Claim 12 (depends on 1) An interferometer according to claim 1 wherein said beamsplitter member and compensator are made of NaCl. ### Claim 13 (depends on 1) An interferometer according to claim 1 wherein said beamsplitter member and compensator are made of CsI. ### Claim 14 An interferometer comprising: a flat or wedge-shaped plate having two approximately parallel planar surfaces and a beamsplitter disposed on a portion of one planar surface thereof for splitting the wavefront of optical radiation incident thereon into a first optical wavefront and a second optical wavefront; a first plurality of optical elements constituting a first optical path for said first optical wavefront to propagate through, said first plurality of optical elements including at least one optical reflector element that is coplanar with said beamsplitter and formed on another portion of said one planar surface of said plate; a second plurality of optical elements constituting a second optical path for said second optical wavefront to propagate through; and said first and second pluralities of optical elements positioned such that said first and second optical wavefronts, having propagated through said first and second optical paths respectively, recombine at said beamsplitter. ### Claim 15 (depends on 14) An interferometer according to claim 14 wherein said first optical path traverses said plate only once and wherein said first plurality of optical elements includes a separate compensator plate which is twice traversed by said first optical path. ### Claim 16 (depends on 15) An interferometer according to claim 15 wherein said reflector is a reflective coating formed on another portion of said one planar surface of said plate. ### Claim 17 (depends on 14) An interferometer according to claim 14 wherein said beamsplitter comprises: a beamsplitting coating disposed on a portion of said one surface of said plate. ### Claim 18 (depends on 17) An interferometer according to claim 17 wherein said plate is a KBr plate. ### Claim 19 (depends on 17) An interferometer according to claim 17 wherein said plate is a NaCl plate. ### Claim 20 (depends on 17) An interferometer according to claim 17 wherein said plate is a CsI plate. ### Claim 21 (depends on 18, 19, 20) An interferometer according to any of claims 18-20 wherein said beamsplitting coating is a layer of germanium. ### Claim 22 In an interferometer having a beamsplitter element disposed on a flat or wedge-shaped plate and also using other optical elements to define distinct transmitted and reflected optical paths, the improvement comprising the use in combination with the other optical elements of the interferometer of a flat or wedge-shaped compensating element in one of said paths and the beamsplitter element in both of said paths, said optical paths passing through said plate only at the location of said beam splitter element, and wherein: said beamsplitter element comprises a beamsplitter coating disposed on a portion of a first planar surface of said plate; and said optical elements in said transmitted optical path comprises a reflective coating disposed on another portion of said first planar surface of said plate. ### Claim 23 (depends on 22) The improvement according to claim 22 wherein said plate is a KBr plate. ### Claim 24 (depends on 22) The improvement according to claim 22 wherein said plate is a NaCl plate. ### Claim 25 (depends on 22) The improvement according to claim 22 wherein said plate is a CsI plate. ### Claim 26 (depends on 23, 24, 25) The improvement according to any of claims 23-25 wherein said beamsplitting coating is a layer of germanium. ### Claim 27 In an interferometer of the type having a flat or wedge-shaped plate means having two approximately parallel planar surfaces for splitting an incident wavefront into two separate wavefronts and directing said wavefronts along separate paths of differing lengths, and for combining said separate wavefronts after said separate wavefronts have traversed said separate paths, the improvement comprising; a beamsplitting coating disposed on a first portion of a first planar surface of said plate which first portion of the plate is the only portion thereof through which both said optical paths pass; and a reflective coating disposed on a second portion of said first planar wurface of said plate, said reflective coating for use as an optical element in the beamsplitter transmitted optical path. ### Claim 28 (depends on 27) The improvement according to claim 27 wherein said plate is a KBr plate. ### Claim 29 (depends on 27) The improvement according to claim 27 wherein said plate is a NaCl plate. ### Claim 30 (depends on 27) The improvement according to claim 27 wherein said plate is a CsI plate. ### Claim 31 (depends on 28, 29, 30) The improvement according to claim 28, 29 or 30 wherein said beamsplitting coating is a layer of germanium.