# US 7,608,808 B2 · Injection-locked pulsed laser with high wavelength stability > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,608,808 B2 - Document ID: US7608808B2 - Status: Granted - Kind: B2 - Application number: 11/935,035 - Filed: 2007-11-05 - Published: 2008-05-08 - Granted: 2009-10-27 - Earliest claimed: 2006-11-07 - Assignees: Canon Kabushiki Kaisha - Inventors: Yoshiyuki Kuramoto - Web page: https://patentgrep.com/patent/US7608808B2 ## CPC - H01S 3/1394: {by using an active reference, e.g. second laser, klystron or other standard frequency source} - G03F 7/706: {Aberration measurement} - H01S 3/005: {Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping (shaping laser beam for working metal or other materials B23K26/06; optical elements, systems or apparatus in general G02B)} - H01S 3/083: Ring lasers {(fibre ring lasers H01S3/06791)} - H01S 3/094038: {End pumping} - H01S 3/10092: {Coherent seed, e.g. injection locking} - H01S 3/1305: {Feedback control systems} - H01S 3/1392: {by using a passive reference, e.g. absorption cell (H01S3/1396, H01S3/1398 take precedence)} - H01S 3/1398: {by using a supplementary modulation of the output} - H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL - G03F: PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR; (phototypographic composing devices B41B; photosensitive materials or processes for photographic purposes G03C; electrophotography, sensitive layers or processes therefor G03G) ## Abstract An injection-locked laser is disclosed. The injection-locked laser comprises a seed laser, an oscillator into which a certain component of light output from the seed laser is injected as seed laser light, a frequency converter which shifts a frequency of the remaining component of the light output from the seed laser, a photodetector which detects light obtained by synthesizing the light output from the oscillator and the light output from the frequency converter, and a controller which controls an optical path length of the oscillator based on a beat signal component contained in the signal output from the photodetector. ## Claims ### Claim 1 An injection-locked pulsed laser comprising: a seed laser; an oscillator into which a first portion of light output from said seed laser is injected as seed laser light; a frequency converter which shifts a frequency of a second portion of the light output from said seed laser; wherein the second portion is different from the first portion; a photodetector which detects light obtained by synthesizing the light output from said oscillator and the light output from said frequency converter; and a controller which controls an optical path length of said oscillator based on a beat signal component contained in the signal output from said photodetector. ### Claim 2 (depends on 1) The laser according to claim 1, wherein a frequency shift amount used in said frequency converter is larger than a spectral width of the light output from said oscillator. ### Claim 3 (depends on 1) The laser according to claim 1, wherein said frequency converter includes an acoustic optical modulator. ### Claim 4 (depends on 1) The laser according to claim 1, further comprising a stabilization unit which stabilizes a wavelength of the light output from said seed laser. ### Claim 5 (depends on 1) An interferormeter comprising: an injection-locked pulsed laser defined in claim 1; and an interferometer which generates a reference light beam and a test light beam using light output from said injection-locked pulsed laser so that the reference light beam and the test light beam interfere with each other. ### Claim 6 (depends on 1) An exposure apparatus comprising: an injection-locked pulsed laser defined in claim 1; an interferometer which generates a reference light beam and a test light beam using light output from said injection-locked pulsed laser so that the reference light beam and the test light beam interfere with each other; and a projection optical system which projects a pattern of an original onto a substrate, wherein said interferometer measures an aberration of said projection optical system. ### Claim 7 (depends on 6) A device manufacturing method comprising the steps of: forming a latent image pattern on a photosensitive agent applied to a substrate, using an exposure apparatus defined in claim 6; and developing the latent image pattern. ### Claim 8 (depends on 1) The laser according to claim 1, wherein said controller computes a frequency difference between the light output from said oscillator and the light output from said frequency converter based on a Fourier-transformation for the beat signal, and controls the optical path length of said oscillator based on the frequency difference. ### Claim 9 (depends on 4) The laser according to claim 4, wherein said stabilization unit includes a reference resonator and stabilizes the wavelength of the light output from said seed laser using a wavelength of the light output from said reference resonator as a reference. ### Claim 10 (depends on 4) The laser according to claim 4, wherein said stabilization unit includes a wavemeter which measures the wavelength of the light output from said seed laser, and stabilizes, on the basis of the output from said wavemeter, the wavelength of the light output from said seed laser.