Generation of an ultrabroadband optical pulse with a fluent frequency dependency of the phase is important for creating a monocyclelike optical pulse and for shaping multiwavelength optical pulses. A previously proposed method that uses induced phase modulation between a femtosecond fundamental wave ω<sub>1</sub> and its second-harmonic wave ω<sub>2</sub>=2ω<sub>1</sub> in a fused-silica fiber is applied to a capillary fiber filled with noble gas. Analytic results of chirps without dispersion but with loss in the fiber are shown, and the optimum conditions relating to a delay time between two pulses and to input peak powers are found for fully covering the spectrum between ω<sub>1</sub> and ω<sub>2</sub>. Furthermore, numerical calculations, including dispersion effects of the fundamental and the second-harmonic waves from a Ti:sapphire laser-amplifier system with experimentally realizable parameters, are presented. These calculations show that it is possible to generate an ultrabroadband optical pulse whose spectrum ranges from 300 to 900 THz (330 to 1000 nm) with quasi-linear chirp by this method.
© 1999 Optical Society of America
(060.4370) Fiber optics and optical communications : Nonlinear optics, fibers
(060.7140) Fiber optics and optical communications : Ultrafast processes in fibers
(320.5520) Ultrafast optics : Pulse compression
(320.5540) Ultrafast optics : Pulse shaping
(320.7140) Ultrafast optics : Ultrafast processes in fibers
Naoki Karasawa, Ryuji Morita, Lin Xu, Hidemi Shigekawa, and Mikio Yamashita, "Theory of ultrabroadband optical pulse generation by induced phase modulation in a gas-filled hollow waveguide," J. Opt. Soc. Am. B 16, 662-668 (1999)