When we speak of oscillations at optical frequencies and their amplification, we are indeed a long way from the world of swinging pendulums and oscillating balance wheels. It is true that classical theory based on Newton’s laws of motion and Maxwell’s theory of electromagnetic radiation are inappropriate to deal with the interaction of radiation with atoms and molecules; for this we need the quantum theory. However, from a background of classical theory, certain aspects can be sketched in a semiclassical way, in which quantum ideas are superimposed on a classical base. Historically, this characterized the early development of the theory of radiation and the general features of the theory of optical dispersion. In this context “dispersion” refers to the dependence of the refractivity of a medium on the wavelength, which leads to the dispersion of, for example, white light by a glass prism into the colors of the rainbow.
KeywordsAngular Momentum Valence Band Quantum Number Orbital Angular Momentum Total Angular Momentum
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