Special narrowing of ultrashort laser pulses by self-phase modulation in optical fibers

We demonstrate experimentally and theoretically that frequency-modulated femtosecond laser pulses can be spectrally narrowed by self-phase modulation in optical fibers. We obtain a reduction of the spectral linewidth from 10.6 down to 2.7 nm, limited only by the laser power in the fiber. Applications for extracavity conversion of femtosecond lasers to narrow-linewidth picosecond sources are discussed.