Intrinsic Nonlinearity of the Interaction between Radiation Fields and Atoms
The purpose of this article is to present the background material necessary to deal with the nonlinear effect of the interaction between light and atomic systems.
The first section of this article is an introduction to the treatment of nonlinear effects in solids. The experimental conditions in which they are observed are first considered. The usage of nonlinear spectroscopy is reviewed. This usage takes place at three levels: 1) It may deal with the phenomena themselves, 2) it may deal with information about the nonlinear coupling of light to different classes of material systems, and 3) it may be used to probe the material properties themselves.
The second section presents a treatment of the density matrix formalism, first in a general context, and then for two-level systems. The formalism is applied to the treatment of the interaction of radiation with atoms and molecules. The optical Bloch equations, the Rabi oscillations and the connections of steady state solutions with transition rates are examined. The two characteristic relaxation times, T 1 and T 2, and the mechanisms responsible for them, are introduced.
The third section deals with the quantum treatment of the radiation field. The energy levels and the eigenfunctions of this field are derived.
The fourth section treats the interaction of the quantized radiation field with atomic systems. The special effects of the quantization of the radiation field, such as spontaneous emission, are considered.
In the last two sections two applications are presented, one dealing with the spontaneous emission of two photons from the metastable 2s state of the hydrogen atom, and the other with the radiative (Lamb) shift of atomic levels.
KeywordsDensity Matrix Spontaneous Emission Atomic System Virtual Photon Rabi Oscillation
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