Matter-radiation field interactions electrodynamics

AN OVERVIEW OF QUANTUM ELECTRODYNAMICS AND MATTER-RADIATION FIELD INTERACTION... 

We now consider the effect of exposing a system to electromagnetic radiation. Our treatment will involve approximations beyond that of replacing (3.13) with (3.16). A proper treatment of the interaction of radiation with matter must treat both the atom and the radiation field quantum-mechanically this gives what is called quantum field theory (or quantum electrodynamics). However, the quantum theory of radiation is beyond the scope of this book. We will treat the atom quantum-mechanically, but will treat the radiation field as a classical wave, ignoring its photon aspect. Thus our treatment is semiclassical. 

Dirac s 1929 comment [227] The underlying physical laws necessary for the mathematical theory for a large part of physics and the whole of chemistry are thus completely known, and the difficulty is only that the exact application of these laws leads to equations much too difficult to be soluble has become a part of the Delphic wisdom of our subject. To this confident statement Richard Feynman [228] added in 1985 a codicil But there was still the problem of the interaction of light and matter , and . .. the theory behind chemistry is quantum electrodynamics . He goes on to say that he is writing of non-covariant quantum electrodynamics, for the interaction of the radiation field with the slow-moving particles in atoms and molecules. 

As a second example for modifications of the quantum electrodynamical interaction between matter and the radiation field originating from controlled mode engineering in the following we discuss the spontaneous decay of a two-level system, such as an ion [24], in a half-open cavity with a... 

Hans Albrecht Bethe (1906-2005) was an American physicist, a professor at Cornell University, and a student of Arnold Sommerfeld. Bethe contributed to many branches of physics, such as crystal field theory, interaction of matter with radiation, quantum electrodynamics, and the structure and nuclear reactions of stars (for the latter achievement, he received the Nobel Prize in physics in 1967). 

As stated by Milonni [73], An arbitrarily large number n of photons may occupy the same state, and when this situation obtains, it is accurate to regard the photon wave function as defining a classical field distribution. Thus the quantum electrodynamic view of radiation for intense laser fields can be described classically. Overall, the light-matter interaction is treated semi-classically where the diatomic molecule is quantum mechanical and the laser pulse is classical in nature. The electric dipole approximation [74] is also used which reduces the form of the electric field due to the comparative size of the electric field wavelength compared to the molecule. The classical description of the laser field, E r,t), can be written in complex form according to... 

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