Mode Selection in an Aperture-Limited Concentric Maser Interferometer

Interferometer-type resonators that are used in optical masers are inherently multimode devices. The resonant modes that can exist in such devices may be classified as longitudinal and transverse modes. The longitudinal mode order is determined by the number of field variations along the axis of the interferometer, while the transverse mode order is determined by the number of field variations in the plane of the mirrors. For each longitudinal mode order, there exists a set of transverse modes. The number of modes that can partake in the oscillations of an optical maser is dependent on the geometry and the losses of the resonator, the width of the atomic resonance of the active material and the degree of population inversion. Practically, an optical maser will oscillate in several modes simultaneously unless special steps are taken to suppress the unwanted ones. For applications such as optical communication it is desirable from the standpoint of noise, coherence, spectral purity, etc. to suppress all but one mode in a maser oscillator. There2609