Reducing the spectral bandwidth of lasers
First Claim
1. A fiber-based fundamental light source for generating fundamental light at a nominal fundamental frequency a laser system, the fiber-based fundamental light source comprising:
- one or more seed lasers including means for generating seed light having an initial peak power and an initial spectral bandwidth, and for transmitting the seed light along an optical path;
one or more amplifiers disposed in the optical path and including means for amplifying the seed light generated by said one or more seed lasers such that amplified light output from the one or more amplifiers has a fundamental peak power that is substantially higher than the initial peak power; and
one or more nonlinear chirp elements disposed in the optical path and including means for modifying one of the seed light and the amplified light to include one or more nonlinear chirps that compensate for Self Phase Modulation (SPM) characteristics of the one or more amplifiers,wherein each of said one or more nonlinear chirp elements comprises one of a Bragg grating, a fiber Bragg grating and an electro-optic modulator, andwherein said one or more nonlinear chirp elements comprise means for generating said nonlinear pre-chirp with a nonlinearity on the order of x2 or higher.
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Abstract
A laser system for semiconductor inspection includes a fiber-based fundamental light source for generating fundamental light that is then converted/mixed by a frequency conversion module to generate UV-DUV laser light. The fundamental light source includes a nonlinear chirp element (e.g., a Bragg grating or an electro-optic modulator) that adds a nonlinear chirp to the seed light laser system prior to amplification by the fiber amplifier(s) (e.g., doped fiber or Raman amplifiers). The nonlinear chirp includes an x2 or higher nonlinearity and is configured to compensates for the Self Phase Modulation (SPM) characteristics of the fiber-based amplifiers such that fundamental light is generated that has a spectral E95 bandwidth within five times that of the seed light. When multiple series-connected amplifiers are used, either a single nonlinear chirp element is provided before the amplifier string, or a chirp elements are included before each amplifier.
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Citations
18 Claims
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1. A fiber-based fundamental light source for generating fundamental light at a nominal fundamental frequency a laser system, the fiber-based fundamental light source comprising:
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one or more seed lasers including means for generating seed light having an initial peak power and an initial spectral bandwidth, and for transmitting the seed light along an optical path; one or more amplifiers disposed in the optical path and including means for amplifying the seed light generated by said one or more seed lasers such that amplified light output from the one or more amplifiers has a fundamental peak power that is substantially higher than the initial peak power; and one or more nonlinear chirp elements disposed in the optical path and including means for modifying one of the seed light and the amplified light to include one or more nonlinear chirps that compensate for Self Phase Modulation (SPM) characteristics of the one or more amplifiers, wherein each of said one or more nonlinear chirp elements comprises one of a Bragg grating, a fiber Bragg grating and an electro-optic modulator, and wherein said one or more nonlinear chirp elements comprise means for generating said nonlinear pre-chirp with a nonlinearity on the order of x2 or higher. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A fiber-based fundamental light source for generating fundamental light at a nominal fundamental frequency a laser system, the fiber-based fundamental light source comprising:
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one or more seed lasers including means for generating seed light having an initial peak power and an initial spectral bandwidth, and for transmitting the seed light along an optical path; one or more amplifiers disposed in the optical path and including means for amplifying the seed light generated by said one or more seed lasers such that amplified light output from the one or more amplifiers has a fundamental peak power that is substantially higher than the initial peak power; and one or more nonlinear chirp elements disposed in the optical path and including means for modifying one of the seed light and the amplified light to include one or more nonlinear chirps that compensate for Self Phase Modulation (SPM) characteristics of the one or more amplifiers, wherein said one or morenonlinear chirp elements includes means for generating said nonlinear chirp such that the nonlinear chirp compensates for said SPM characteristics of the one or more amplifiers such that said fundamental light generated by said laser system has a fundamental spectral bandwidth that is in a range defined by five times said initial spectral bandwidth of said seed light.
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14. A method for generating fundamental light using a fiber-based laser system, the method comprising:
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generating seed light having an initial spectral bandwidth; amplifying the seed light using one or more fiber-based amplifiers to produce amplified light having a peak power that is substantially higher than the initial peak power; and modifying one of the seed light and the amplified light to include a nonlinear chirp, wherein the nonlinear chirp has a nonlinearity on the order of x2 or higher and substantially entirely compensates for Self Phase Modulation (SPM) characteristics of said one or more fiber-based amplifiers such that said fundamental light has a fundamental spectral bandwidth that is within a range defined by five times said initial spectral bandwidth. - View Dependent Claims (15, 16, 17, 18)
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Specification