Matter-radiation coupling

Imaginary terms The imaginary terms introduced by the complex variable z = cu +1 0 in (1.33) must vanish in a exact calculation of the eigenvalues of the coupled system. This is the case in (1.81), which is an exact expression. For systems with weak matter-radiation coupling, we are able to make in (1.33) the following approximation ... 

The vibrational motions of the chemically bound constituents of matter have fre-quencies in the infrared regime. The oscillations induced by certain vibrational modes provide a means for matter to couple with an impinging beam of infrared electromagnetic radiation and to exchange energy with it when the frequencies are in resonance. In the infrared experiment, the intensity of a beam of infrared radiation is measured before (Iq) and after (7) it interacts with the sample as a function of light frequency, w[. A plot of I/Iq versus frequency is the infrared spectrum. The identities, surrounding environments, and concentrations of the chemical bonds that are present can be determined. 

The success of this extended STIRAP scheme can be traced to the fact that the basis of the subset of dressed eigenstates of the coupled matter-radiation field is a stationary state representation. In this representation, all couplings are already taken into account via the identity of and the locations of the energy levels. The contribution of the background states to the population transfer process is then limited to effects associated with nonresonant coupling to the field, and if these background states are far off resonance such effects are small. 

S. A. Rice The coupled matter-radiation system considered in the control schemes can, indeed, be studied from the point of view of dressed potential-energy surfaces, as suggested by the remark by Prof. Quack. We find it more convenient to use the equivalent point of view of continuous transfer of amplitude back and forth between the undressed potential-energy surfaces, because the formalism we have developed calculates the temporally and spectrally shaped field for that dynamical representation. 

A powerful way of achieving this goal uses the coupled-channels expansion, a method widely used in calculations of scattering cross sections [6]. In the context of quantized matter-radiation problems, the coupled-channels method amounts to expanding E, n, N ) in number states. Concentrating on the expansion in the /th mode, we write E, n, N ) as... 

The above results may be interpreted as follows Figure 3.10 shows the dispersion diagrams co(/0 for the uncoupled and the coupled matter-radiation systems. Thus, the coupling induces, for cK < oj0, a splitting off of the lower state of the effective continuum, repelled to lower energies by its interaction with the matter state K>.126... 

Here, pm, Pr, Pi/, Pk are the densities of matter, radiation, scalar field (f 1 ), and vacuum, respectively a t) is the scale factor (H = aja)-, a> = He is the coupling constant of the dynamic Langrangian (I is a length scale of the theory) and is a dimensionless parameter that represents the fraction of mass in Coulomb energy of an average nucleon compared with the free proton mass. 

In conclusion of this section, we have thus presented a comprehensive theory of EIT in which both the structure and multiplicity of (coupled) continua are taken into account, which strongly emphasizes the fact that EIT is a manifestation of interferences in the continuum. As such, it is a property of the way the full continuum eigenfunctions are convoluted with the matter-radiation Hamiltonian and the initial bound states. The exact nature of this convolution depends on the type of spectroscopy used to probe the continuum whether it is linear or nonlinear, the EIT line shapes and especially the EIT dips are properties of the continuum. 

Photoacoustics is well established [36] for the investigation of optical and thermal properties of condensed matter, but it has only rather recently been applied to liquid crystals [37-41]. The photoacoustic technique is based on the periodic heating of a sample, induced by the absorption of modulated or chopped (electromagnetic) radiation. In the gas microphone detection configuration the sample is contained in a gas-tight cell (Fig. 6). The thermal wave produced in the sample by the absorbed radiation couples back to the gas above the sample and periodically changes the tempera-... 

The dipole moment is the total dipole of the sample, p = Y.i Pi The correlation function describes the response of the system to the weakly coupled radiation field. The effects of the field are modeled by the response of the individual atoms or molecules unaffected by the weak coupling. The Hamiltonian describes the interaction of the field and matter (first-order perturbatiuon theory). The correlation function describes how the perturbed system approaches equilibrium. 

Finally we must deal with perturbations not to pressureless matter but to baryons and photons. At early times, the universe is radiation dominated, and pr = p/3 for radiation. Before the epoch of recombination, the same Thomson scattering processes that keep the baryons ionized also keep the radiation tightly-coupled to the ions. The nuclei have pressure pb = (5kT/dmp)p [Pg.182]

In the case of an assembly of dipoles coupled to radiation and described by the hamiltonian (1.9), we must diagonalize a matrix of the type (1.24) which may be written with explicitly separated matter variables B, Bf and radiation variables... 

Therefore, our model of a surface with substrate is based on interactions, of purely retarded type, between surface and bulk dipoles via the radiation field, or, more formally, on a renormalization by the bulk matter of the photon continuum to which the surface is coupled, with consequent modifications of its radiative properties. 

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