Pump-dump pulse separation

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. 

VARIATION OF PRODUCT YIELD IN DISSOCIATION OF HgAr WITH PUMP-DUMP PULSE SEPARATION. 

In general, the results of the calculations establish that it is possible to guide the reaction to preferentially form one or the other product with high yield. Note that, unlike the original Tannor-Rice pump-dump scheme, in which the pulse sequences that favor the different products have different temporal separations, the complex optimal pulses occupy about the same time window. Indeed, the optimal pulse shape that generates one product is very crudely like a two-pulse sequence, which suggests that the mechanism of the enhancement of product formation in this case is that the time delay between the pulses is such that the wavepacket on the excited-state... 

Consider then a system irradiated by two pulses, termed the pump-and-dump pulse. These pulses are assumed to be temporally separated by a time delay Ad. The analysis below shows that under these circumstances control over the photodissocia-tion yields is obtained by vaiying the central frequency of the pump pulse and the tune delay between the two pulses. 

Consider now the pump-dump scenario where, for generality, we assume a pump pulse whose spectral width is sufficiently large to encompass a large number of levels. As in Section 3.5, a molecule with Hamiltonian HM is subjected to two temporally separated pulses e(t) = sx(t) + ed(t). The probability of forming channel q at energy E is now given by the extension of Eq. (3.77) to many level excitations by ex(l), that is,... 

Further, as discussed in Section 3.1, the inability to control the product ratio by shaping the pulse can be overcome by photodissociating not just one EX) bound . state but a superposition of several bound states )) (as was done, e.g., with bichro-, matic control). Such a superposition state can be created separately by an initial preparation pulse, as in the case of pump-dump control scenario Sections 3.5 and. 4.1). Alternatively, the superposition state can be created by the photolysis pulse itself (by, e.g., a stimulated Raman process), provided that the bandwidth of the -pulse is comparable to the energy spacings between the Ef) levels. r, ... 

The weak-field control discussed here must be achieved in two steps. First, if necessary to create the cD(f) superposition state of Eq. (13.65). This state k th irradiated with the pulse satisfying Eq. (13.64). This is the essence of the weak fil pump-dump scenario. However, in the strong-field domain these two procei cannot be separated since the factorization of Eq. (13.62) does not hold. In case the control conditions become 1 ... 

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