Strong Field Interactions

Important aspects of the interaction of strong laser fields with molecules can be missed in standard TOF experiments, most notably the population of electronically excited states. However, by studying vibrational excitation, the frequency and dephasing of the vibrational motion can be used to identify the electronic state undergoing the vibrational motion. In some cases, this turns out to be a ground state, and in others, an excited state. Once we have identified an excited state, we are left with the question of how and why the state was populated by the strong field. In one example above (the Ij A state discussed in Sect. 1.3.3), the excited state is formed by the removal of an inner orbital electron, in this case a iru electron. This correlates with the measured angular dependence for the ionization to this state. 

In the case of vibrational motion in the ground electronic state produced by LF, the study of the vibrational motion can provide information about how the ionization rate of the state depends on R. For I2, certain theoretical calculations predicted that the ionization rate would decrease as R increased, at least near Req [28]. However, the experimental results showed the opposite trend. 

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Electro-optic The liquid crystal plastics exhibit some of the properties of crystalline solids and still flow easily as liquids (Chapter 6). One group of these materials is based on low polymers with strong field interacting side chains. Using these materials, there has developed a field of electro-optic devices whose characteristics can be changed sharply by the application of an electric field. 

The vibrational and electronic excitation of molecules has received less attention over the years, but the understanding of excitation processes is important for a number of reasons. Thus, in this paper, we will review the various mechanisms leading to vibrational and/or electronic excitation of molecules in strong laser fields. As we do this, it will become clear that exploring these mechanisms (1) reveals new features of the strong field interaction ... 

The identification of excited states in strong field interactions with molecules has lead to some novel forms of molecular spectroscopy, allowing previously inaccessible states to be studied. For the most part, this comes from the ability to do transient spectroscopy in the time domain with ultrashort pulses. But, the strong field interaction also allows for new population mechanisms. 

In order to describe strong-field interaction of the five-state system in Figure 6.9 with intense shaped femtosecond laser pulses, the theoretical formalism prepared in Section 6.3.2.1 is readily extended. The RWA Hamiltonian H f) for the five-state system in Figure 6.9 in the frame rotating with the carrier frequency reads... 

If we are to study strong field interactions using Rydberg states of = 20 it is apparent that the strongest field required is the classical ionization field, 2 kV/cm. In addition, we must work at frequencies far below the 27cm ... 

We have shown, in agreement with the results presented in Ref. 21, that the method of classical trajectories gives very good predictions in the case of strong-field interactions (i.e., for the photon numbers larger than 10). The calculation speed of the method does not depend on numbers of interacting... 

If we consider the optical response of a molecular monolayer of increasing surface density, the fomi of equation B 1.5.43 is justified in the limit of relatively low density where local-field interactions between the adsorbed species may be neglected. It is difficult to produce any rule for the range of validity of this approximation, as it depends strongly on the system under study, as well as on the desired level of accuracy for the measurement. The relevant corrections, which may be viewed as analogous to the Clausius-Mossotti corrections in linear optics, have been the... 

Other hand, when the dislocation density is high, the dislocations do interact and they become tangled up with each other dislocation motion is then difficult and the material is therefore strong. The interaction of dislocations with each other and with other structural features in metals is a very complex field it is also, however, extremely important, since it greatly affects the strength of metals. 

In the previous section we assumed that disorder results in random fluctuations of the order parameter around some average value A<). Such an approach is, essentially, a mean field treatment of the lattice. It requires sufficiently strong interchain interactions, whose role is to establish a coherence between the phases of the order parameter in different chains. 

First, consider an octahedral nickel(ii) complex. The strong-field ground configuration is 2g g- The repulsive interaction between the filled 2g subshell and the six octahedrally disposed bonds is cubically isotropic. That is to say, interactions between the t2g electrons and the bonding electrons are the same with respect to x, y and z directions. The same is true of the interactions between the six ligands and the exactly half-full gg subset. So, while the d electrons in octahedrally coordinated nickel(ii) complexes will repel all bonding electrons, no differentiation between bonds is to be expected. Octahedral d coordination, per se, is stable in this regard. 

When we include the Zeeman interaction term, gpBB-S, in the spin Hamiltonian a complication arises. We have been accustomed to evaluating the dot product by simply taking the direction of the magnetic field to define the z-axis (the axis of quantization). When we have a strong dipolar interaction, the... 

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