A. Existence of two types of effects in atom-photon interactionsConsider first a light beam with frequency L propagating through a medium consisting of atoms with resonance frequency A .The index of refraction describing this propagation has an imaginary part and a real part which are associated with two types of physical processes.The incident photons can be absorbed, more precisely scattered in all directions.The corresponding attenuation of the light beam is maximum at resonance.It is described by the imaginary part of the index of refraction which varies with L Ϫ A as a Lorentz absorption curve.We will call such an effect a dissipative (or absorptive) effect.The speed of propagation of light is also modified.The corresponding dispersion is described by the real part n of the index of refraction whose difference from 1, nϪ1, varies with L Ϫ A as a Lorentz dispersion curve.We will call such an effect a reactive (or dispersive) effect.
A. Existence of two types of effects in atom-photon interactionsConsider first a light beam with frequency L propagating through a medium consisting of atoms with resonance frequency A .The index of refraction describing this propagation has an imaginary part and a real part which are associated with two types of physical processes.The incident photons can be absorbed, more precisely scattered in all directions.The corresponding attenuation of the light beam is maximum at resonance.It is described by the imaginary part of the index of refraction which varies with L Ϫ A as a Lorentz absorption curve.We will call such an effect a dissipative (or absorptive) effect.The speed of propagation of light is also modified.The corresponding dispersion is described by the real part n of the index of refraction whose difference from 1, nϪ1, varies with L Ϫ A as a Lorentz dispersion curve.We will call such an effect a reactive (or dispersive) effect.
Abstract The present chapter deals with the macroscopic theory of light-matter interaction. By using the Maxwell’s equations, the wave equation is developed first for free space, and then for a dielectric, and a conductor. The relationship between refractive index and absorption coefficient is then established. The phase and group velocities of the EM wave are defined. The well-known damped harmonic oscillator model is then used to find expressions for real and imaginary parts of the susceptibility. At the end, the two-level atomic system is used to illustrate fundamental processes of light-matter interaction, namely, absorption, spontaneous, and stimulated emissions, and the rates of these processes in terms of Einstein’s A and B coefficients. Absorption, gain, and self-sustained oscillation in a medium with a Fabry–Perot resonator are discussed using the two-level atomic model.
The control of the optical properties of a medium by atomic coherence and quantum interference effects is an important area of research, not only for its fundamental aspects in the understanding of radiation and matter interaction, but also for its potential applications in the design of optical devices. Atomic coherence can emerge in a medium through the coupling of a strong coherent field to an atomic transition. This coupling affects the optical properties of the medium in a very interesting ways. For example, it may yield light amplification without population inversion. Also, it can modify the traditional dispersion of an optical medium in such a way that maximum variations of the refractive index occur around a spectral region of vanishing absorption. In the first part of this work we investigate some fundamental aspects of this coherent dynamics. We investigate how this non-inversion gain is affected by the presence of atomic motion. The coherent interaction between atom and radiation can lead to the interference between optical paths of decay. We report on an atomic setting where the interference structures depend upon the phase of the coherent field, an new effect which is absent in other resonance fluorescent phenomena. As a potential application, we investigate a novel approach for the modulation of optical signal. This approach consists of injecting atomic coherence in the medium in order to tailor its optical properties so it is a more suitable medium for modulation.
The refractive index of a system is often viewed as the collective response of a medium to an electromagnetic field. Nevertheless, even if targeted at a single atom, the incoming light undergoes the dispersion. By studying the propagation of a single photon interacting with a two-level atom, we examine the dispersion behavior, calculate the phase and group velocity of the photon wave packet, and further analyze the dispersion experienced by the photon. These findings are critical for advancing long-distance quantum communications.
The propagation of narrow packets of electromagnetic waves (EMWs) in frequency dispersive medium with the consideration of the complex refractive index is studied. It is shown that counting in the dispersion of the complex refractive index within the context of the conventional expression of the group velocity of narrow wave packets of EMWs propagating in a dispersive medium results in the appearance of additional constraints on the group velocity, which dictates that the physically acceptable group velocity can only be realized in the case of a negligible imaginary part of the group index. In this paper, the conditions that allow one to realize the physically acceptable group velocity are formulated and analyzed numerically for the relevant model of the refractive index of a system of two-level atoms in the optical frequency range. It is shown that in the frequency band where superluminal light propagation is expected, there is a strong dispersion of the refractive index that is accompanied with strong absorption, resulting in a strongly attenuated superluminal light.
The propagation of narrow packets of electromagnetic waves(EMWs) in frequency dispersive medium with the consideration of the complex refractive index is studied. It is shown that counting in the dispersion of the complex refractive index within the context of the conventional expression of the group velocity of narrow wave packets of EMWs propagating in a dispersive medium results in the appearance of additional constraints on the group velocity, which dictates that the physically acceptable group velocity can only be realized in the case of a negligible imaginary part of the group index. In this paper, the conditions that allow one to realize the physically acceptable group velocity are formulated and analyzed numerically for the relevant model of the refractive index of a system of two-level atoms in the optical frequency range. It is shown that in the frequency band where superluminal light propagation is expected, there is a strong dispersion of the refractive index that is accompanied with strong absorption, resulting in a strongly attenuated superluminal light.
Introduction We have already encountered situations in which light of one frequency falling on an atomic system gives rise to light of different frequencies (cf. Section 15.6). The atom may here be considered to play the role of a (noisy) nonlinear transducer for the incident field. Even stronger nonlinear effects arise when one is dealing with a large number of atoms, or a nonlinear medium . Under these circumstances it is sometimes permissible to ignore the atomic structure and to treat the medium as a continuum, as in Maxwell's electromagnetic theory. The subject of the interaction of the incident field with the nonlinear medium is usually known as nonlinear optics. The subject had its beginnings in an experiment in which a strong beam of red light (wavelength 6943 Å) from a ruby laser was allowed to fall on a quartz crystal, and a faint beam of blue light at a wavelength of 3472 Å, the first harmonic of the red, was produced (Franken, Hill, Peters and Weinreich, 1961). The development of the subject of nonlinear optics into a mature field is due largely to the work of Bloembergen and his collaborators. In the following we shall consider only a few simple illustrative examples of phenomena in nonlinear optics. More topics and more detail can be found in the books by Bloembergen and others (Bloembergen, 1965; Yariv, 1967, Chap. 21; Shen, 1984; Schubert and Wilhelmi, 1986; Butcher and Cotter, 1990; Boyd, 1992).