Pulse compression of white-light continuum generated by induced phase modulation in a conventional glass fiber

The 530–880-nm continuum pulse with a greatly asymmetric temporal profile over 500 fs and a spectral phase variation over 150 rad, which was generated by induced phase modulation (IPM) as well as self-phase modulation in a conventional fused-silica fiber, was compressed to 7.8 fs by a feedback technique. Fundamental (a center wavelength of 800 nm, a duration of 80 fs, a pulse energy of 64 nJ) and signal pulses (a center wavelength of 670 nm, a duration of 80 fs, a pulse energy of 65 nJ) produced by one common femtosecond source with an optical parametric amplifier were copropagated in the fiber under an optimum delay time between the two pulses. The computer-controlled feedback system that combines a 4-f phase compensator with a spatial light modulator and a modified spectral phase interferometry for a direct electric-field reconstruction, automatically compensated for not only the conventional nonlinear chirp (group-delay dispersion and its higher-order dispersion) but also the frequency-independent group-delay (first-order phase dispersion), both of which are essential for pulse compression by use of the IPM effect.