Theory of ultrabroadband optical pulse generation by induced phase modulation in a gas-filled hollow waveguide

Generation of an ultrabroadband optical pulse with a fluent frequency depen dency of the phase is important for creating a monocyclelike optical pulse and for shaping multiwavelength optical pulses. A previously proposed metho d that uses induced phase modulation between a femtosecond fundamental wave omega(1) and its second-harmonic wave omega(2) = 2 omega(1) in a fused-sil ica fiber is applied to a capillary fiber filled with noble gas. Analytic r esults of chirps without dispersion but with loss in the fiber are shown, a nd the optimum conditions relating to a delay time between two pulses and t o input peak powers are found for fully covering the spectrum between omega (1) and omega(2). Furthermore, numerical calculations, including dispersion effects of the fundamental and the second-harmonic waves from a Ti:sapphir e laser-amplifier system with experimentally realizable parameters, are pre sented. These calculations show that it is possible to generate an ultrabro adband optical pulse whose spectrum ranges from 300 to 900 THz (330 to 1000 nm) with quasi-linear chirp by this method. (C) 1999 Optical Society of Am erica [S0740-3224(99)01604-5] OCIS codes: 060.4370, 060.7140, 320.5520, 320 .5540, 320.7140.