Periodic generation of subfemtosecond pulses by modulated Raman coherence

We propose a scheme for periodic generation of subfemtosecond pulses on the basis of modulated Raman coherence. The detailed theoretical analyses and numerical simulations show that an oscillatory Raman coherence with periodically changed phase is established. It leads to periodic compression of the generated broadband sidebands in the same medium. As compared with the scheme by using nonmodulated driving fields where subfemtosecond pulses can be generated only with negative Raman detunings, the modulated Raman coherence scheme supports subfemtosecond pulse generation with positive, negative, or even opposite Raman detunings around the Raman resonance.