# US 12,768,746 B2 · Apparatus, measurement method, and manufacturing method > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,768,746 B2 - Document ID: US12768746B2 - Status: Granted - Kind: B2 - Application number: 19/041,496 - Filed: 2025-01-30 - Published: 2025-08-07 - Granted: 2026-10-20 - Earliest claimed: 2024-02-06 - Assignees: Canon Kabushiki Kaisha - Applicants: Canon Kabushiki Kaisha - Inventors: Tomohiro Sugimoto - Web page: https://patentgrep.com/patent/US12768746B2 ## CPC - G01M 11/0271: {by using interferometric methods} - G01B 9/0209: Low-coherence interferometers - G01M 11/0207: {Details of measuring devices} - G01M 11/0221: {by determining the optical axis or position of lenses} - G01M: TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR - G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS ## Abstract An apparatus includes a first light source for illuminating a chart including an index surface on which an index is provided, an objective lens for guiding index light emitted from the chart to an optical system, a first element for receiving the index light reflected on an optical surface in the optical system, an interferometer configured to include a second light source and a second element, and acquire a wavefront of measurement light, the measurement light being test light reflected on the target surface, and a reduction unit for reducing an intensity of a signal of light reflected on an optical surface other than the target surface, of the test light reflected on the plurality of optical surfaces and received by the second element. ## Claims ### Claim 1 An apparatus configured to measure eccentricity of an optical system based on a wavefront acquired for each target surface in a plurality of optical surfaces in the optical system, the apparatus comprising: a first light source configured to illuminate a chart including an index surface on which an index is provided; an objective lens configured to guide index light emitted from the chart to the optical system; a first element configured to receive the index light reflected on an optical surface in the optical system; an interferometer including a second light source and a second element, and configured to split light from the second light source into test light and reference light and to receive measurement light via the objective lens and the reference light with the second element, to acquire a wavefront of the measurement light, the measurement light being the test light reflected on the target surface; and a reduction unit configured to reduce an intensity of a signal of light reflected on an optical surface other than the target surface, of the test light reflected on the plurality of optical surfaces and received by the second element. ### Claim 2 (depends on 1) The apparatus according to claim 1, wherein the reduction unit is a spatial filter. ### Claim 3 (depends on 2) The apparatus according to claim 2, wherein the spatial filter is a pinhole. ### Claim 4 (depends on 1) The apparatus according to claim 1, wherein the reduction unit is configured to adjust a position of the second element. ### Claim 5 (depends on 1) The apparatus according to claim 1, wherein the interferometer includes a beam splitter, and wherein the reduction unit is configured to acquire a first signal obtained by receiving the reference light and the measurement light reflected by the beam splitter and a second signal obtained by receiving the reference light and the measurement light having passed through the beam splitter and acquire the wavefront based on a difference between the first signal and the second signal. ### Claim 6 (depends on 1) The apparatus according to claim 1, wherein the reduction unit is configured to reduce the intensity of the signal of light reflected on the optical surface other than the target surface to be smaller than an intensity of a signal of the measurement light. ### Claim 7 (depends on 1) The apparatus according to claim 1, further comprising a first adjustment unit configured to adjust a relative position between the objective lens and the optical system based on a position of an image formed by index light received by the first element. ### Claim 8 (depends on 7) The apparatus according to claim 7, wherein eccentricity of the target surface is measured based on a first adjustment amount and the wavefront, the first adjustment amount being acquired in a case where the first adjustment unit adjusts the relative position. ### Claim 9 (depends on 8) The apparatus according to claim 8, further comprising a second adjustment unit configured to adjust a tilt component of the wavefront, wherein eccentricity of the target surface is measured based on the first adjustment amount and a second adjustment amount that is acquired in a case where the second adjustment unit adjusts the relative position. ### Claim 10 (depends on 1) The apparatus according to claim 1, wherein the interferometer includes a change unit configured to change a light path length of the reference light. ### Claim 11 (depends on 1) The apparatus according to claim 1, further comprising a diaphragm in a light path from the second light source to the objective lens. ### Claim 12 An apparatus configured to measure eccentricity of a system based on a wavefront acquired for each target surface in a plurality of optical surfaces in the optical system, the apparatus comprising: an interferometer configured to include a light source and an element, split light from the light source into test light and reference light, and receive light via an objective lens and the reference light with the element, and acquire a wavefront of the measurement light, the measurement light being the test light reflected on the target surface; and a reduction unit configured to reduce intensity of a signal of light reflected on an optical surface other than the target surface, of the test light reflected on the plurality of optical surfaces and received by the element. ### Claim 13 An apparatus configured to measure eccentricity of an optical system based on a wavefront acquired for each target surface in a plurality of optical surfaces in the optical system, the apparatus comprising: a first light source configured to illuminate a chart including an index surface on which an index is provided; an objective lens configured to guide index light emitted from the chart to the optical system; a first element configured to receive the index light reflected on an optical surface in the optical system; and an interferometer configured to include a second light source and a second element, split light from the second light source into test light and reference light, receive light via the objective lens and the reference light with the second element, and acquire a wavefront of the measurement light, the measurement light being the test light reflected on the target surface. ### Claim 14 A method for measuring eccentricity of an optical system based on a wavefront acquired for each target surface in a plurality of optical surfaces in the optical system, the method comprising: illuminating a chart including an index surface on which an index is provided; capturing an image by making index light emitted from the chart to enter the optical system via an objective lens and receiving the index light reflected on the plurality of optical surfaces in the optical system with a first element; splitting light emitted from a second light source into test light and reference light, receiving, with a second element, the reference light and measurement light that is the test light having passed through the objective lens and reflected on the target surface, and acquiring a wavefront of the measurement light; and reducing intensity of a signal of light reflected on an optical surface other than the target surface of the test light reflected on the plurality of optical surfaces and received by the second element in the acquiring. ### Claim 15 (depends on 14) The method according to claim 14, further comprising: acquiring a first signal obtained by receiving the reference light and the measurement light reflected by the beam splitter and a second signal obtained by receiving the reference light and the measurement light having passed through the beam splitter and acquiring the wavefront based on a difference between the first signal and the second signal. ### Claim 16 (depends on 14) The method according to claim 14, wherein the reducing adjusts a position of the second element. ### Claim 17 (depends on 14) The method according to claim 14, wherein the reducing reduces the intensity of the signal of light reflected on the optical surface other than the target surface to be smaller than an intensity of a signal of the measurement light. ### Claim 18 (depends on 14) The method according to claim 14, further comprising adjusting a relative position between the objective lens and the optical system based on a position of an image formed by index light received by the first element. ### Claim 19 (depends on 14) The method according to claim 14, further comprising changing a light path length of the reference light. ### Claim 20 (depends on 14) A method for manufacturing an optical system comprising: measuring eccentricity of the optical system by using the method according to claim 14; and adjusting the optical system by using a measured result of the eccentricity of the optical system.