Damping optical mode frequency

Fig. tt.5-23 BaTiOs. Avq and F versus T, obtained from hyper-Raman scattering in the cubic phase. Avq and F are the optical mode frequency and damping constant, respectively. The different symbols brown and gray) show results from different authors. Avq decreases as the temperature decreases to the Curie point, showing the presence of mode softening, c ligth velocity... 

We now want to study the consequences of such a model with respect to the optical properties of a composite medium. For such a purpose, we will consider the phenomenological Lorentz-Drude model, based on the classical dispersion theory, in order to describe qualitatively the various components [20]. Therefore, a Drude term defined by the plasma frequency and scattering rate, will describe the optical response of the bulk metal or will define the intrinsic metallic properties (i.e., Zm((a) in Eq.(6)) of the small particles, while a harmonic Lorentz oscillator, defined by the resonance frequency, the damping and the mode strength parameters, will describe the insulating host (i.e., /((0) in Eq.(6)). 

Fig. 7. Model calculations for the reflectivity (a) and the optical conductivity (b) for a simple (bulk) Drude metal and an effective medium of small metallic spherical particles in a dielectric host within the MG approach. The (bulk) Drude and the metallic particles are defined by the same parameters set the plasma frequency = 2 eV, the scattering rate hr = 0.2 eV. A filling factor/ = 0.5 and a dielectric host-medium represented by a Lorentz harmonic oscillator with mode strength fttOy, 1 = 10 eV, damping ftF] = I eV and resonance frequency h(H = 15 eV were considered for the calculations.

Let us consider an optical system with two modes at the frequencies oo and 2oo interacting through a nonlinear crystal with second-order susceptibility placed within a Fabry-Perot interferometer. In a general case, both modes are damped and driven with external phase-locked driving fields. The input external fields have the frequencies (0/, and 2(0/,. The classical equations describing second-harmonic generation are [104,105] ... 

Let us consider a quantum optical system with two interacting modes at the frequencies coi and ff>2 = respectively, interacting by way of a nonlinear crystal with second-order susceptibility. Moreover, let us assume that the nonlinear crystal is placed within a Fabry-Perot interferometer. Both modes are damped via a reservoir. The fundamental mode is driven by an external field with the frequency (0/ and amplitude F. The Hamiltonian for our system is given by [169,178] ... 

Note that the main dissimilarities seen in Fig. 5 are related with the Independence of dispersions and damping coefficients of optic-like mode at small k domain. For example, for LiF the characteristic frequency of these excitations decreases when k increases. An inverse situation is observed for KrAr. One may suppose that such a dissimilarity is caused for finite k mainly by an antiferromagnetic type of interactions in a mixture of charged particles, whereas the long-range characte of Coulombic potential becomes a crucial fac-... 

The frequency dependence of the damping and shift of the TO-mode at q = 0 has also been calculated for NaCl [5.50]. A breathing shell model was used to provide frequencies and eigenvectors necessary for these calculations. The influence of anharmonicity on the TO and LO optical phonons at q = 0 has been studied experimentally by means of the far-infrared dielectric response for 18 alkali and thallium halides [5.51], for the silver and thallium halides... 

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