Pump-dump control experiments

The pump-dump control concept [17,18] has been realized in different experiments in the gas and the condensed phase (see review [71] and references therein, [30]). The concept includes three successive steps. First step excitation of the system from the ground state (reactant) to an excited state with a femtosecond pump pulse short enough to create a wavepacket in the excited state. Second step field free evolution of the system. Third step interaction with a second pulse to dump the vibrational wavepacket to the target state/region on the electronic ground state. 

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. 

The sea water used in these experiments was San Francisco Bay water collected at the laboratory s salt water supply intake on the pier at the Richmond Field Station. Because of the diluting and polluting effect of the Sacramento River as well as other effluents dumped into the bay, the salinity of bay water at Richmond varies widely during the tide cycle. In order to obtain water of maximum salinity, the intake pump is controlled by float switches and permits the pump to operate only at or near high tide for approximately 3 hours in 24. Even with this limited pumping schedule the... 

The formation of a bound moleeule out of two colliding ultracold atoms is a simple example of a laser-induced ehemieal reaction at very low temperature. At room or even higher temperatures, as discussed in Chapter 8 by Evgueny Shapiro and Moshe Shapiro, the well-established field of coherent control relies upon the possibility of shaping laser pulses to eontrol the output of chemical reactions. Whether similar schemes ean be applied to the PA and stabilization reactions at low temperatures has been an open question. To give an answer, one should carefully explore the feasibility and the effieiency of pump-dump experiments to selectively create ultracold molecules in the w = 0 level of their ground elecfionic state. 

Dr. Roger Carlson has suggested an approach to testing the key concepts of the the Tannor-Rice scheme which is simpler, both conceptually and experimentally, than the alteration of product yields in the photofragmentation of a triatomic molecule. In the experiment suggested,a diatomic molecule is subjected to a femtosecond duration pump-dump pulse sequence. Since there is only one reaction coordinate, product selectivity can not be achieved. However, the delay between pulses can still be used to control the kinetic energy of the final wavepacket one should be able to switch the dissociation on and off as a function of delay. 

H. J. Neusser Choosing a special pulse sequence of the dump and the pump laser pulse leads to a complete blocking of the population transfer in the CIS experiment or else makes it very efficient. We can say that a special channel is open or closed, that is, controlled by the experimental parameter. This is similar to STIRAP experiments. However, it was shown by Band and Magnes [1] that the adiabatic passage population transfer in STIRAP experiments does not represent a solution of an optimal control problem. 

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