The spectrum of the radiation emitted spontaneously along the axis of a gas laser can be expected to exhibit a fine structure of narrow, Doppler-shifted lines which are substantially free of normal thermal broadening. The widths of these lines depend on the energies and lifetimes of all three of the atomic levels involved in the successive stimulated and spontaneous transitions and on the nonlinear response of the atoms to the laser radiation. Expressions are given for these dependencies for laser oscillations near and far above threshold in the limits that the quanta of energy emitted spontaneously are either much larger or much smaller than the quanta emitted coherently. It is suggested that the fine structure might be useful for precise spectroscopic determinations of a few atomic energy level separations and natural lifetimes and for studies of broadenings arising from atomic collisions and interactions with intense radiation.
© 1965 Optical Society of AmericaFull Article | PDF Article
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