Nonadiabatic effects induced by the coupling between vibrational modes via Raman fields

Abstract

We study the effect of coupling between molecular vibrational modes attendant the excitation of Raman transitions using ultrafast chirped laser pulses. We model Raman-active vibrational modes by two-level systems (TLSs) with nondegenerate ground states and a predetermined initial relative phase. Chirp of the pump and Stokes pulses is the same in magnitude and opposite in sign for the whole pulse duration. To reveal the nonadiabatic effects induced by the coupling between the vibrational modes, we compare the model of two uncoupled TLSs with the one of two TLSs coupled by the external fields. The first model shows population inversion. Within the second model, the coupling induces nonadiabatic effects leading to a mixed population distribution. By introducing the time delay between the Stokes and pump pulses, nearly complete population transfer is realized in both coupled TLSs.

Orientation of adsorbed molecules under the influence of electric fields

“…If the barrier height V 0 is increased, the specific properties of the energy levels will display clearly. Furthermore, the anticrossing feature is also observed in various physical systems [30][31][32]. It is anticipated that the system manifests a great variation on the population under the circumstance of anticrossings being induced by the external control.…”

Quantum control via chirped coherent anti-Stokes Raman spectroscopy

“…A method for selective excitation in a multimode system using a transform-limited pump pulse and a lineraly chirped Stokes pulse in stimulated Raman scattering is proposed in [54]. The effects of chirped pump and Stokes pulses on the nonadiabatic coupling between vibrational modes are discussed in [55]. A 'roof ' method of chirping to maximize coherence is introduced in [56] based on adiabatic passage in an effective two-level system.…”