Abstract: An improved microwave cavity resonator for use in vapor-cell atomic frequency standards. The resonator comprises a generally-rectangular hollow metallic body designed to support the TE.sub.101 mode of standing wave. A dielectric element is positioned within the cavity to concentrate electro-magnetic field so that a compact design is achieved and so that a preselected, substantially uniform magnetic field will be coupled into an alkali metal vapor absorption cell within the resonator. Means are provided for mounting elements of an excitation circuit to preferentially excite the desired TE.sub.101 mode.

Abstract: A cylindrical coil form, for magnetic coupling with an irradiated nuclear magnetic resonance gas sample, is provided with peripheral and longitudinal grooves. The peripheral grooves are not helical in form, but are perpendicular to the axis of the coil form to give a precisely directed longitudinal magnetic field. A first coil for providing strong magnetic coupling along the axis of the coil form is wound in the peripheral grooves, the adjacent turns being interconnected by short longitudinal sections of wire in one of the longitudinal grooves. Additional coils are provided for magnetic coupling transverse to the axis of the coil through the use of wires extending down one of the longitudinal slots and back in another longitudinal slot. The form may be of phenolic material, or may be transparent so that the nuclear magnetic resonance sample may be irradiated directly through the coil form.