Selective probing of electronic and nuclear coherences using time-resolved off-resonant excitation of Raman-active vibration modes

In this presentation the underlying theoretical analysis of the four wave mixing (FWM) efficiency is given for the resembling experiment of three-level quantum system (TLQS), where the transition from |1> to |3> correspond to a Raman active vibration mode and is forbidden in the dipole approximation. In this case quantum state |3> (vibration mode) is excited by combined resonance and, subsequently, quantum state |2> is driven by a (delayed) weak field. Notable, that during off-resonance FWM experiments significant excited state probability amplitude and, consequently, FWM exists only as long as the perturbing fields overlap. Actually, in this presentation we discuss efficiency of the FWM process, which exist for long (as compared to the pump and probe pulses) times, and appears dependent on the both electronic and nuclear excitations, stored in the TLQS. The induced material variables (coherences and populations) in the TLS were considered by means of the density matrix, and in order to account for Raman transition |1> → |3> we used an approach closely related to that exploited previously. Considerable impact of the created in TLQS electronic and nuclear coherences on the frequency conversion for specific (negative and positive) time delays will be demonstrated.