Multiple-Region Hydrogen Maser with Reduced Wall Shift

The magnitude of the atom-wall collision frequency shift in the hydrogen maser has been reduced tenfold by confining the hydrogen atoms in a Teflon-coated cylindrical vessel that is 5 ft long and 5 ft in diam. The wall shift of this large maser was measured to be - (2.3±0.8) × ${10}^{-3\mathrm{}}$ Hz at 27°C. Oscillation is achieved by a prestimulation method in which radiant atoms that have been prestimulated in the high rf field of one microwave cavity maintain a maser oscillation in a second cavity. A signal is extracted from the low-level cavity, amplified to a suitable value, and coupled into the high-level cavity to maintain the rf field there. A detailed theory of a multiple-region maser system is presented.