A group at Max Born Institut in Berlin have produced ultrashort optical pulses by molecular phase modulation in Raman-active gases. Unlike self-phase modulation, the technique should enable the control of the time-dependent phase of the pulses it generates.

To produce the pulses, the researchers illuminated a 1-m waveguide filled with H₂ or SF₆ with 30-fs, 800-nm pump and 27- or 15-fs, 400-nm probe pulses from a Ti:sapphire laser. According to the team's calculations, the technique could generate 3.5-fs pulses; in the experiments, reported in the May 20 issue of Physical Review Letters, it produced pulses shorter than 4 fs.