Abstract

The laser-pumped ⁸⁷Rb maser showed many new experimental features.¹ A precise understanding of the maser behavior is obtained by considering a simple three-level atom, located inside a microwave cavity, interacting with a frequency-modulated laser. This simple model is based on the density operator formalism within a semi-classical approach. We show that moderately rapid modulation of the laser frequency results in sustained large hyperfine coherence, thus high gain, due to reduced light broadening, even for a high intensity pump. This is optimally achieved with a given modulation depth which is proportional to the light intensity. This last result has also been obtained when considering only the maximization of the population inversion.² On the other hand the modulation greatly decreases the dependence of the maser frequency upon the laser frequency (through the variation of the light shift), therefore reducing the requirements for the mid- and the long-term frequency stability of the pumping laser. Finally the maser frequency suffers a small modulation, relatively insensitive to the modulation depth, which becomes negligible for sufficiently high modulation frequencies.

© 1993 Optical Society of America