This chapter uses the density matrix methods of Chap. 4 to find the polarization induced by one or two cw plane waves in two-level media. The density matrix is extended in a form known as the population matrix, which treats collections of atomic responses simply. Section 5-1 deals with homogeneously-broadened media, while Sec. 5-2 includes inhomogeneous broadening. The induced polarization is used as a source in the slowly-varying Maxwell equations to yield a nonlinear Beer’s law for propagation. The population matrix equations of motion are solved in the important rate equation approximation, which assumes that the dipole lifetime T 2 is short compared to times for which the field envelope or population difference vary appreciably. The concepts of power-broadening and spectral hole burning are developed.
KeywordsBurning Recombination Coherence GaAs Eter
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