Dressed photon

Plasmon-phonon coupling represents mixing of two quasi-particles. The coupling of three quasi-particles has also been observed. The term plasmariton was used by Alfano 45) for a coupled state of a TO phonon and a dressed photon , namely, a photon surrounded by an electron cloud (a coupled state of a plasmon and a photon). The quasi-particle dressed photon is also called a transverse plasmon. Because the coupled state of a photon and a TO phonon has been termed polariton, a plasmariton can also be regarded as coupled state of a plasmon and a polariton. Earlier the term plasmariton was used in a more restricted sense, namely, when a partly transverse character of the plasmon is induced by an external magnetic field. 

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. 

The nature of media effects relates to the fact that, since the microscopic displacement field is the net field to which molecules of the medium are exposed, it corresponds to a fundamental electric field dynamically dressed by interaction with the surroundings. The quantized radiation is in consequence described in terms of dressed photons or polaritons. A full and rigorous theory of dressed optical interactions using noncovariant molecular quantum electrodynamics is now available [25-27], and its application to energy transfer processes has been delineated in detail [10]. In the present context its deployment leads to a modification of the quantum operators for the auxiliary fields d and h, which fully account for the influence of the medium—the fundamental fields of course remain unchanged. Expressions for the local displacement electric and the auxiliary magnetic field operators [27], correct for all microscopic interactions, are then as follows... 

In Eq. (25) the prime on the summation denotes its limitation to those molecules whose transitions are engaged either directly or indirectly in the optical response. The double prime on the summation in Eq. (26) denotes the exclusion of those molecules. The eigenstates of Ho thus contain products of the eigenstates of the optically prominent molecules and the dressed-photon eigenstates of //bath- As usual, if the system is in an eigenstate of IIq at time 0, the wavefunction at any later time f is expressible as... 

Nanophotonics Dressed Photon Technology for Qualitatively Innovative Optical Devices, Fabrication, and Systems... 

Nanophotonics, proposed by the author in 1993 [1-3], is a novel optical technology that utilizes the optical near-field. The optical near-field is the dressed photons that mediate the interaction between nanometric particles located in close proximity to each other. Nanophotonics allows the realization of qualitative innovations in photonic devices, fabrication techniques, and systems by utilizing novel functions and phenomena enabled by optical near-field interactions that would otherwise be impossible if only conventional propagating light were used. In this sense, the principles and concepts of nanophotonics are completely different from those of conventional wave-optical technology, encompassing photonic crystals, plasmon-ics, metamaterials, and silicon photonics. This review describes these differences and shows examples of such qualitative innovations. 

Coupled state of electron and photon (Dressed photon)... 

The dressed photon is theoretically described by assuming a multipolar quantum electro-dynamic Hamiltonian in Coulomb gauge and single-particle states in a finite... 

The real system is more complicated because the nanometric subsystem (composed of the two nanometric particles and the dressed photons) is urie m a macroscopic subsystem composed of the macroscopic substra e ma eria an e... 

Because the extent of localization of the dressed photon is equivalent to the nanometric particle size, the long-wavelength approximation, which has always been employed for conventional light-matter interaction theory, is not valid. This means that an electric dipole-forbidden state in the nanometric particle can be excited as a result of the dressed photon exchange between closely placed nanometric particles, which enables the operation of novel nanophotonic devices. Details of such devices will be reviewed in Sect. 1.4. 

A real nanometric material is composed not only of electrons but also of a crystal lattice. In this case, after a dressed photon is generated on an illuminated nanometric particle, its energy can be exchanged with the crystal lattice, as shown by the Feynman diagram of Fig. 1.3a. By this exchange, the crystal lattice can excite the vibration mode coherently, creating a coherent phonon state. As a result, the dressed photon and the coherent phonon can form a coupled state, as is schematically explained by Fig. 1.3b. The creation operator a] of this novel form of elementary excitation is expressed as... 

Fig. 1.3 Feynman diagrams representing the coupling of a dressed photon with phonons, (a) Generation of a dressed photon and exchange with the crystal lattice, (b) A coupled state of a dressed photon and a coherent phonon...

It is easily understood that the energy of the DP-CP, vdp-cp, is higher than that of the dressed photon. It is also higher than the free photon energy, hv p, incident on the nanometric particle. The relation between these energies is represented by... 

Nanophotonics is a promising candidate for meeting the above requirements for two reasons (1) a signal can be transferred by the dressed photon exchange between nanometric particles without using any wires and (2) a non-invasive attack is impossible because the signal intensity is fixed by the energy dissipation inside the nanometric particles [30]. This section reviews the principles, operations, and applications of these nanophotonic devices. 

Because the long-wavelength approximation is not valid due to the localized nature of the dressed photon (refer to Sect. 1.2), an electron in the nanometric particle can be excited even to an electric dipole-forbidden energy level as a result of the dressed photon exchange between closely spaced nanometric particles, which enables novel nanometer-scale wireless optical devices with dimensions beyond the diffraction-limit, low energy consumption, and resistance to non-invasive attacks. 

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