Dipole, radiating

The theoretical analysis of a radiating dipole at a dielectric interface is quite involved and its full description is beyond the scope of this chapter. Instead, an outline of the most salient features of the model is presented. The complete analysis can be found in Ref. 25. 

The computation of far-field radiation from a collection of incoherently radiating dipoles is in general quite a complicated problem. To calculate the angular dependence of the far-field intensity, the volume distribution of excited states must first be obtained, which, as we have seen, depends on the volume distribution of the absorbers and the electromagnetic field which stimulates them. The fields in turn depend on the frequency and linewidth of the exciting light source. Then the emission problem for the excited-state distribution (both spatial and frequency) must be solved including reorientation and depolarization effects. 

We will assume that all the incident fields are polarized in the x-direction. The pump and Stokes focal fields, which each look like the complex fields depicted in Figure 9.1, set up an effective CARS excitation field E = (r) (r). The anti-Stokes polarization in the excitation volume induced by the effective excitation field can be considered as a collection of radiating dipoles. The resulting CARS amplitude at any far-field point Q with coordinates R = (R, 6, (j)) is a sum of the amplitude contributions form all these dipoles and is given by... 

Equation (7.34) is the leading term in a near field expansion of the electric field generated from a radiating dipole. Substituting equations (7.34) and (7.33) into equation (7.32), and multiplying the result by the mean polarizability ot- of segment i, the following... 

The basic principle of SPP mediated emission involves two steps, SPP coupling and scattering. When radiating dipole is placed in close proximity to the... 

If a field with a value diflerent from that for resonance conditions is applied perpendicularly to the axis of the ferrite. Fig. 5.25, the microwave signal is propagated with a phase change. Phase shifters are typically used in microwave antenna systems. These systems are formed of radiating dipoles control of the phase shift between them allows accurate control of the emitted beam direction. 

It is known that fluorescing fluorophores behave like radiating dipoles. The intensity of light radiated from a... 

Figure 10.3. Radiating dipole in a coordinaie system. The dipde is oriented along the r-axis, and the intensity /(O of the emission in any direction is proportional tocas C where is the angle from the x-yplane.

Superradiance. We consider a system of several two-level atoms occupying a volume the dimension of which is small compared to A. In this case the total radiating dipole is given by eq. (36), multiplied by the difference of atom populations in the excited state and in die ground state. If the external resonant field is stopped at t-nHQa, we shall create a macro dipole given by ... 

The effect of such metal cluster and cluster related but also plain metal films is explained on one hand by the strong enhancement of the field strength of light due to surface plasmons and Mie plasmons (not for plain metals), which are driven by the irradiation of the cluster layer. The resonant interlayer now is driven by the plasmons, and the fluorophore is exposed to this enhanced light field of the interlayer and has consequently an enhanced absorption probability. On the other hand during emission the fluorophore acts as radiating dipole and oscillator, thereby influenced by the nearby resonant layer. Thus, an additional charge is induced and the emission process is enhanced. 

Buchler, B. C., Kalkbrenner, T, Hettich, C., and Sandoghdar, V (2005] Measuring the quantum efficiency of the optical emission of single radiating dipoles using a scanning mirror, Phys. Rev. Lett., 95, 063003/ 1-4. 

Raman scattering arises from the radiating dipole moment induced by the electric field of incident electromagnetic radiation. The laws of momentum and energy conservation govern the interaction between a phonon and a photon. When we consider a solid containing numerous Bravais unit cells and each cell contains n atoms, there will be 3n modes of vibrations. Among the 3n modes, there will be three acoustic modes, LA, TAj and TA2 and 3(n — 1) optical modes. The acoustic mode represents the in-phase motion of the mass center of the unit cell or the entire solid. 

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