The effect of nonuniform population distributions in masers

The inverted population in a cavity maser has spatial dependence, produced by standing waves in the cavity, if the maser material is of the order of the cavity dimensions. It is shown that higher order mode operation of a maser, in which many nodes exist in the signal and pump fields, does not appreciably degrade the small-signal performance and, in fact, improves the saturation behavior of the maser amplifier. However, higher pump powers are required. A dielectric cavity maser (DCM), composed of a ruby rod separating two metal end plates, is described which exploits this phenomenon. Both the strength of the maser action, as measured by the paramagnetic filling factor and the saturation behavior of the device have been calculated and measured. When operated as an -band amplifier, pumped at 35 Gc/s, gain bandwidth products up to 141 Mc/s have been observed. Power outputs greater than 0.1 mW have been measured using the DCM as an amplifier or an oscillator. Improvement in the saturation behavior of ∼20 dB compared to other masers is reported.