Unidirectional unstable ring lasers

The properties of traveling-wave unstable ring resonators are discussed with respect to conventional standing-wave unstable resonator geometries. As a consequence of the inherent geometric magnification, the mode diameters associated with clockwise and counterclockwise traveling waves can differ substantially within various regions of the unstable ring resonator. Tailoring of the CO(2) active medium within an unstable ring laser is demonstrated as an effective technique in suppressing the oscillation associated with one of the traveling waves and achieving near unidirectional operation.