Abstract
A hydrogen cyanide molecular beam-type maser has been successfully operated as an oscillator. The maser oscillates at two lines of a hyperfine triplet at 88.633 and 88.631 kMc. The maser uses an interferometer-type confocal resonant cavity. Many molecular beams eject from two circular beam sources radially towards the center of the circle where the cavity is located. The focusers, which separate molecules in the first excited state of the rotational energy spectrum from those in the ground state, consist of two planes. Each plane is composed of radially arranged rods which are charged alternatingly to high positive and negative potentials.