Reducing the spectral bandwidth of lasers
First Claim
1. A laser system for generating laser output light having a nominal UV-DUV output frequency, the laser system comprising:
- a fiber-based fundamental light source for generating fundamental light at a nominal fundamental frequency including;
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 for combining one of the seed light and the amplified light with one or more nonlinear chirps; and
a frequency conversion module including means for converting said fundamental light from said nominal fundamental frequency to said laser output light L having said nominal output frequency,wherein the one or more amplifiers have inherent Self Phase Modulation (SPM) characteristics, andwherein 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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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 compensate 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 chirp elements are included before each amplifier.
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Citations
15 Claims
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1. A laser system for generating laser output light having a nominal UV-DUV output frequency, the laser system comprising:
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a fiber-based fundamental light source for generating fundamental light at a nominal fundamental frequency including; 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 for combining one of the seed light and the amplified light with one or more nonlinear chirps; and a frequency conversion module including means for converting said fundamental light from said nominal fundamental frequency to said laser output light L having said nominal output frequency, wherein the one or more amplifiers have inherent Self Phase Modulation (SPM) characteristics, and wherein 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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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Specification