Raman self-conversion of femtosecond laser pulses and generation of single-cycle radiation

Stimulated Raman scattering of light in the regime of laser pulse durations shorter than the period of Raman-active vibrational mode $2\pi /{\Omega }_R$ is investigated. Using full equations for the field and the medium polarization, we obtain an insight into the stage of frequency conversion where the slowly varying amplitude approximation is inapplicable. It is found that the laser pulse experiences a continuous downshift of its spectrum, resulting in the formation of an intense single-cycle electromagnetic pulse. The role of the competing processes is analyzed.