The field in a closed optical cavity with no absorption present can oscillate only at a sequence of discrete normal mode frequencies. When absorption is present, each of these normal mode frequencies is broadened into a band of finite width. An excited atom, placed within such a cavity, radiates only into those modes with which it posseses appreciable coupling. In an approximate sense then, if the frequency with which it radiates is v0, and its own spectral decay width is Г, it can only couple to modes possessing appreciable spectral density within the band from v0-Г to v0+Г. (Those must furthermore be modes with non-vanishing amplitudes at the atomic position.)
KeywordsDecay Width Cavity Mode Excited Atom Secular Equation Normal Mode Frequency
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