An 81-Gc/s zero-field maser

A zero magnetic field millimeter maser is described which uses the iron ion Fe³⁺in a host crystalline structure of rutile, TiO2, as the active material. The maser operates as a classical three-level maser [1] between three doubly degenerate zero-field spin levels of the iron ion at a frequency of 81.3 Gc/s and is pumped at a frequency of 124.5 Gc/s. Net gain in excess of 20 dB with instantaneous bandwidths of 3-6 Mc/s have been obtained in a dielectric cavity type configuration.