Matter/radiation interactions

Given this approximation, we can transform the Hamiltonian of Eq. (1.44) from the velocity gauge to the so-called length gauge in which the matter-radiation interaction term contains only the dot product of the dipole moment and the electric field. In order to do so we choose x [Eq. (1.5)] as... 

The molecule, initially in a state IE), J , Mf), is subjected to two cw fields. Once again J , Mf denote the angular momentum and its projection along the z axis. The matter-radiation interaction term is of the form, ... 

T ) obtain the Schrodinger equation for the interaction of a molecule with the quanted radiation field, that is, the Schrodinger equation for the (matter + radiation) fr steni. we need the quantum analog of 77MR, the matter-radiation interaction, hi the 1,1 pole approximation HMR depends, according to Eq. (1.51), on the transverse... 

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. 

Equations (3.21)—(3.22) satisfy the conservation law for elastic matter-radiation interactions, )rK(ct )j2 -1- tK(ct>) 2 = 1, and the very useful relation tK(co) = 1 + rK(o>), which accounts for the symmetry of the matter system (when the dipoles lie in the 2D layer) and which is valid for elastic and inelastic interactions. They are obtained if the expression for RK(to) has only a pure imaginary part, the real part being included in the eigenenergy ha>0. 

Even when the wavelength of the electromagnetic radiation is small relative to the length of the bulk molecular sample, it is often necessary to think of the matter ->radiation interaction in terms of a bulk polarization induced by the radiation and detected via one or more coherence terms of the sample polarization (Mukamel, 1995). When the wavelength is small relative to sample size,... 

The independent-photon and bulk-polarization spectroscopic communities use different aspects of the matter<- radiation interaction to form the cartoons that help them to understand their experiments. The concepts and language are so different that communication between members of the different communities is often difficult. 

The intensity of scattering can be modeled by the same equations developed for light scattering, provided that account is taken of the different matter-radiation interaction. For visible light, scattering is a result of differences in the refractive index of the solute and the solvent, and the optical constant K (Chapter 9, Equation 9.18) is proportional to n idh/dc). For SAXS, the scattered intensity is a function of the electron density, and the molar mass is then related to the excess electron density Ap of solute over solvent. For A, = 1.54 A, the Rayleigh ratio at 0 = 0, Rq is ... 

Christiansen tried to apply the description and the model of chain reactions to different mechanisms (Christiansen 1922) and wrote a paper with Kramers in 1923, cited previously, about unimolecular reactions confronting the activation mechanism due to thermal collisions and radiation absorption. They treated the radiation mechanism with the fundamental Einstein s quantum theory about matter-radiation interaction (Einstein 1917). Other work of Einstein and Smoluchowski will be necessary later for Christiansen-Kramers approach. After the paper the collaboration probably ended and the two researchers will reconsider separately these arguments aroxmd fifteen years later. 

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