Reducing The Spectral Bandwidth Of Lasers

摘要

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.

主权项

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.