Cavity and traveling-wave maser using ruby at S-band

Several three-level solid-state masers using ruby have been operated at frequencies near 3000 Mc/s, using a high-efficiency cavity having TEM modes in a rectangular geometry, or a meander-line slow-traveling-wave circuit with low group velocity over the signal pass band. Various possible maser operating points in the energy-level spectrum of ruby have been studied with both structures. At good operating points, i.e. points where the observed inversion at the signal frequency is large when the pump is turned on, large gain-bandwidth products are obtained in the cavity maser and large gains/unit length in the traveling-wave maser. Although the cavity gain-bandwidth products obtained are two orders of magnitude larger than were obtained in early maser work, and are sufficiently large for some practical applications, the traveling-wave maser appears to have much more promise due to its inherently broader bandwidth, stability and built-in nonreciprocity.