Exciton-photon coupling

This equation in o)2, which is exact if we consider the dependence K of oje and of de, determines all the eigenenergies of the exciton-photon coupled system. However, it is preferable to put it in the classical form, which privileges the photon subspace, by introducing the transverse dielectric tensor1213... 

First, we envisage the weak exciton-photon coupling (which allows an intuitive description of the phonon effects on the nature of the secondary emissions). Therefore we write the hamiltonian of the total system as sums of free photons (Hy), free excitons (He), and free phonons (Hp), with the appropriate interactions Hey (Section I) and Hep (see Sections II, A, B, C.), including intramolecular vibrations too. 

Let us now consider the case of strong exciton-photon coupling, which is that in the singlet state of the anthracene crystal. As shown in Section I, we have to consider as zero-order hamiltonian H that of the polaritons, and the transition between polaritons will be induced by the exciton-phonon coupling Hep. Let us denote by Jf and the hamiltonian of the total system and of its... 

Thus, flK(co) is imaginary for K < (o/c and real for K > cu/c these two cases correspond, respectively, to a radiatively unstable 2D exciton and to a radiatively stable 2D polariton. Solution of equations (1.3) and (3.12) provides the complete description of the 2D polariton dynamics. We analyze below the 2D polariton at different orders of exciton-photon coupling. 

Figure 3.7. Dispersion of the 2D monolayer polariton real part (left) and imaginary part (right) of the excitonic energy renormalization RK(

Assemblies of molecules can be seen in a first approximation as assemblies of transition dipoles subject to electromagnetic interactions. If only the coulombic part of the interaction is kept, new eigenstates of the assembly are found with real energies (the excitonic states). To account for the spontaneous emission, we have to include the retardation (to consider the exciton-photon coupling), which amounts to taking the classical problem of... 

In the exciton-photon interaction, the translational molecular motions have negligible effects owing to the small amplitude of the translation compared to the optical wavelength. In contrast, the molecular rotations may cause an important variation of the transition dipole the librations may be strongly coupled to the incident photon via its coupling to the exciton. If DX(R) is the transition dipole of an a molecule in a unit cell, the first-order expansion in the libration coordinate 8 around the u axis will give... 

State (exciton) is coupled with the multiexciton states and creates a superposition of single and multiexcitons. Below, the theory is applied to PbSe NCs, in which the onset of very efficient MEG occurs at photon energies of 3Eg, corresponding to a 2Ph -A 2Pe transition (Shabaev et al, 2006) (but note that the threshold for the onset of MEG is 2Eg). 

The appearance of an enhanced radiative width and renormalization of the exciton dispersion are the main effects arising in one- and two-dimensional structures under the influence of retardation (21). Qualitatively these effects are valid for Frenkel as well as for Wannier-Mott excitons. In contrast to 3D structure where in the exciton-photon interaction all three components of the momentum have to be conserved and as a result a picture with 3D polaritons arises, for structures of lower dimensionality only the in-plane momentum for 2D structures is conserved and only one component for the ID structure. An exciton in both cases is coupled to a continuum of photon states. There is no possibility of reversible strong... 

FlG. 13.15. (a) Dispersion curve for cavity polariton and energy relaxation of Wan-nier-Mott excitons (b) coupling coefficient of the lower branch to cavity photon and to exciton. 

Excitonically Coupled Oligomers and Dendrimers for Two-Photon Absorption... 

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