Abstract
Subfemtosecond to attosecond pulses are highly desirable for elucidating ultrafast processes in atoms, molecules and condensed matter. One particularly promising approach to generating such pulses is the molecular modulation technique which has the potential for producing a broad comb of frequencies that can be used to synthesize optical pulses as short as a fraction of a fs [1]. When narrowband nanosecond driving fields were used in gas phase molecular modulation, long trains of ~106 relatively low-energy (nanojoule level) subcycle pulses were generated [2]. This gas phase molecular modulation method has been extended to Raman-active crystals pumped with mode-locked laser pulses, leading to a possibility of generating a pulse train of only a few ultrashort pulses [3]. In particular, by selectively operating near a Raman resonance of lead tungstate with a pair of time-delayed linearlychirped pulses, up to 40 anti-Stokes and 5 Stokes sidebands were generated, assisted by phase-matching and favorable near-resonance to the 191 cm-1 Raman mode of the crystal [4].