Theory of a Gas Laser with Internal Absorption Cell

Abstract

A single‐mode gas laser containing an internal absorption cell is described theoretically, with special emphasis on those properties that make this configuration appropriate as a frequency standard. No use is made of perturbation theory, since its applicability to this problem is of restricted validity. Primary attention is devoted to (a) the ``inverted Lamb dip,'' the conditions for its existence, and its size, width, and shape, (b) the frequency ``self‐stabilization'' effects, which are a consequence of the dispersive properties of the absorption medium, and (c) the nature of the solutions to the gain equation, including the hysteresis and ``hard‐excitation'' effects. The parameter that measures the relative saturability of the absorption and gain media plays a central role in the theory, and it is found that those properties of interest from the point of view of frequency stabilization are generally optimized if the gain and absorption media saturate at comparable rates.