Generation of intense frequency-tunable few-cycle femtosecond pulses in hollow fiber

We theoretically show an approach to generate intense frequency-tunable few-cycle femtosecond pulses by molecular phase modulation combined with self-phase modulation. An intense pump pulse propagates through a gas-filled hollow fiber to excite alignment of the gas molecule, which induces temporal modulation of the refractive index. Then the spectrum of a time-delayed intense probe pulse is continuously tuned by the alignment and broadened simultaneously by self-phase modulation. The modification to the pump-induced alignment by the intense probe pulse is considered. Frequency-tunable intense few-cycle pulses in the visible and near-infrared spectrum range are obtained using initial 20 fs, 800 nm pulses. (C) 2009 Optical Society of America