Brumer-Shapiro method

M. N. Kobrak and S. A. Rice. Equivalence of the Kobrak-Rice photoselective adiabatic passage and the Brumer-Shapiro strong field methods for control of product formation in a reaction. J. Chem. Phys., 109(1) 1-10(1998). 

A more sophisticated version of the Tannor-Rice scheme exploits both amplitude and phase control by pump-dump pulse separation. In this case the second pulse of the sequence, whose phase is locked to that of the first one, creates amplitude in the excited electronic state that is in superposition with the initial, propagated amplitude. The intramolecular superposition of amplitudes is subject to interference whether the interference is constructive or destructive, giving rise to larger or smaller excited-state population for a given delay between pulses, depends on the optical phase difference between the two pulses and on the detailed nature of the evolution of the initial amplitude. Just as for the Brumer-Shapiro scheme, the situation described is analogous to a two-slit experiment. This more sophisticated Tannor-Rice method has been used by Scherer et al. [18] to control the population of a level of I2. The success of this experiment confirms that it is possible to control population flow with interference that is local in time. 

To determine how effective the method described is in controlling the concentrations of the products of a branching chemical reaction, Brumer and Shapiro have carried out [27] an extensive study of the branching reaction... 

Another strategy for optical control of chemical reaction dynamics has been investigated by Brumer and Shapiro. The simplest version of their scheme relies on quantum mechanical interference between one and three photon absorption pathways to a given final continuum state [16]. Thus a fixed relative optical phase between continuous wave light sources of different colors must be maintained. Some essential features of Brumer and Shapiro s proposed method have been implemented in recent experimental work [17]. 

Two main approaches to the control of molecules using wave interference in quantum systems have been proposed and developed in different languages . The first approach (Tannor and Rice 1985 Tannor et al. 1986) uses pairs of ultrashort coherent pulses to manipulate quantum mechanical wave packets in excited electronic states of molecules. These laser pulses are shorter than the coherence lifetime and the inverse rate of the vibrational-energy redistribution in molecules. An ultrashort pulse excites vibrational wave packets, which evolve freely until the desired spacing of the excited molecular bond is reached at some specified instant of time on a subpicosecond timescale. The second approach is based on the wave properties of molecules as quantum systems and uses quantum interference between various photoexcitation pathways (Brumer and Shapiro 1986). Shaped laser pulses can be used to control this interference with a view to achieving the necessary final quantum state of the molecule. The probability of production of the necessary excited quantum state and the required final product depends, for example, on the phase difference between two CW lasers. Both these methods are based on the existence of multiple interfering pathways from the initial... 

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