Optical response scattered waves

The optical response of a monomolecular layer consists of scattered waves at the frequency of the incident wave. Since the surface model is a perfect infinite layer, the scattered waves are reflected and transmitted plane waves. In the case of a 3D crystal, we have defined (Section I.B.2) a dielectric permittivity tensor providing a complete description of the optical response of the 3D crystal. This approach, which embodies the concept of propagation of dressed photons in the 3D matter space, cannot be applied in the 2D matter system, since the photons continue propagating in the 3D space. Therefore, the problem of the 2D exciton must be tackled directly from the general theory of the matter-radiation interaction presented in Section I. 

Typical electro-optical responses of the suspensions of spherical particles (CS81), recorded by the scattered light intensity are presented in Fig. 2. They are detected for the crystal state of the systems and for different intensities and frequencies of the applied sine-wave electric pulses. The low-frequency responses are modulated they follow the field frequency at sufficiently low field intensity and exhibit a double frequency modulation at higher field intensity. Two different time scales are involved in the decay of the responses (10 " and 1 s), which can be both exponential and oscillatory. At higher field intensity or frequency the effects cannot be distinguished by the responses of anisotropic colloids. 

The fundamental scattering mechanism responsible for ROA was discovered by Atkins and Barron (1969), who showed that interference between the waves scattered via the polarizability and optical activity tensors of the molecule yields a dependence of the scattered intensity on the degree of circular polarization of the incident light and to a circular component in the scattered light. Barron and Buckingham (1971) subsequently developed a more definitive version of the theory and introduced a definition of the dimensionless circular intensity difference (CID),... 

Figure 1. Laser-induced ultrasonic wave excitation and detection using ISLS. Two 100 picosecond infrared pulses converge spatially and temporally within a transparent sample medium. The time-dependant intensity or strength of the optical transient diffraction grating is monitored by a third frequency doubled pulse which, in the case for relatively low scattering strength, is systematically delayed in time. The time response of stronger gratings can be monitored using a CW laser.

Certainly the clearest conclusion from the examples of this chapter is the total absence of sharp features in the inelastic response function of anomalous lanthanide and metallic actinide materials. This contrasts strongly with the sharp dispersionless crystal-field excitations observed in most lanthanide compounds, in which the exchange interactions are weak (fig, 2), and with the sharp spin-wave excitations found in systems with strong exchange interactions. In many of the early studies with neutron inelastic scattering, for example of the heavy lanthanides or transition metals and their compounds, the width of the excitations was never an issue. It was almost always limited by the instrumental resolution, although it should be stressed that this resolution is relatively poor compared to that obtained by optical techniques. However, the situation is completely different in the materials discussed in this chapter. Now the dominant factor is often the width indeed in some materials the width of the over-damped response function is almost the only remaining parameter with which to characterize the response. 

The mechanism responsible for the formation of Cooper pairs in the superconductive state remains unsolved. Extensive spin-polarized inelastic neutron-scattering experiments have revealed a 41 meV resonance in the spin-excitation spectrum of the superconductive copper oxides that has caught theoretical attention [317]. Carbotte et al. [318] have noted that if these spin excitations are strongly coupled to the charge carriers, they should also be seen as a peak in the optical conductivity. They therefore calculated a((o) for a d-wave superconductor with inelastic scattering from the neutron data. Comparison with a-axis optical-conductivity data [319] showed that the... 

To summarize, the EOM-PMA considerably facilitates the computation of various optical signals and 2D spectra. With shght alterations, the EOM-PMA can also be applied to compute nonlinear responses in the infrared (IR). The three-pulse EOM-PMA can be extended to calculate the A-pulse-induced nonhnear polarization [51], which opens the way for the interpretation of fifth-order spectroscopies, such as heterodyned 3D IR [52], transient 2D IR [53, 54], polarizability response spectroscopy [55], resonant-pump third-order Raman-probe spectroscopy [56], femtosecond stimulated Raman scattering [57], four-six-wave-mixing interference spectroscopy [58], or (higher than fifth order) multiple quantum coherence spectroscopy [59]. 

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