Control and Characterization of Intramolecular Dynamics with Chirped Femtosecond Three-Pulse Four-Wave Mixing

Abstract

Experimental control and characterization of intramolecular dynamics are demonstrated with chirped femtosecond three-pulse four-wave mixing (FWM). The two-dimensional (spectrally dispersed and timeresolved) three-pulse FWM signal is shown to contain important information about the population and coherence of the electronic and vibrational states of the system. The experiments are carried out on gas-phase I 2 and the degenerate laser pulses are resonant with the X (ground) to B (excited) electronic transition. In the absence of laser chirp, control over population and coherence transfer is demonstrated by selecting specific pulse sequences. When chirped lasers are used to manipulate the optical phases of the pulses, the two-dimensional data demonstrate the transfer of coherence between the ground and excited states. Positive chirps are also shown to enhance the signal intensity, particularly for bluer wavelengths. A theoretical model based on the multilevel density matrix formalism in the perturbation limit is developed to simulate the data. The model takes into account two vibrational levels in the ground and the excited states, as well as different pulse sequences and laser chirp values. The analytical solution allows us to predict particular pulse sequences that control the final electronic state of the population. In a similar manner, the theory allows us to find critical chirp values that control the transfer of vibrational coherence between the two electronic states. Wave packet calculations are used to illustrate the process that leads to the observation of ground-state dynamics. All the calculations are found to be in excellent agreement with the experimental data. The ability to control population and coherence transfer in molecular systems is of great importance in the quest for controlling the outcome of laser-initiated chemical reactions.

The manipulation of massive ro-vibronic superpositions using time–frequency-resolved coherent anti-Stokes Raman scattering (TFRCARS): from quantum control to quantum computing

“…The latter aspect, for the important case of single-color four-wave mixing has been recently explored. 61,64 A useful application of quantum control is to be expected in quantum computation, or quantum information transfer, which we explore here.…”

What Role Can Four-Wave Mixing Techniques Play in Coherent Control?

“…63,64 When τ ab is 614 fs (Figure 2b) (twice the vibrational period of I 2 in the B state), the dynamics show 160 fs oscillations, reflecting predominately the ground state contribution. 63,64,66,67 By changing the fixed time delay between fields E a and E b , the observation of excited or ground state dynamics of I 2 can be controlled.…”

“…The FWM emission contains valuable spectral information. 66,67,80 Figure 5 shows spectrally dispersed data obtained as a function of τ for a VE steup. When transform-limited pulses were applied with (a) τ ab = 460 fs, the spectrally dispersed signal can be assigned to the dynamics of the excited excited state with an oscillation period of τ e = 307 fs corresponding to vibrational levels ν′ = 6-11.…”

“…64,65 More recently, we have shown that coherently combined chirped femtosecond pulses can be used to control intramolecular dynamics of the system and developed a technique for the characterization of these dynamics based on spectrally dispersed FWM. 66,67 Realizing that coherent control can only be achieved while the system maintains its coherence, we have carried out coherence relaxation measurements that use some of the pulse sequences we have identified to provide information from ground or excited state coherence.…”

A molecular logic gate

“…Then the pump (or probe) can also be tailored up to and including interference between the pump (or probe) pulses. Such spectroscopies include the three-pulse four-wave mixing technique (31).…”