Abstract: In a laser, the optical cavity includes a pair of spaced-apart electrode plates which are RF excited transversely and a pair of substantially identical spherical mirrors having a radius of curvature, spacing and alignment selected to cause a beam within the cavity to make a plurality of round trips and mirror encounters along a set of off-axis paths, before returning, in phase, to its starting point. The multiple traversals of the cavity result in a long effective gain path equivalent to the number of round trips times the mirror spacing. The plurality of off-axis traversals of the laser beam trace out a plane around the gain region before exiting through the aperture in the first spherical mirror, permitting an effective utilization of the wide excitation region defined by the electrodes. In a CO2 laser, the electrodes are separated by an electrode spacing such that the modes perpendicular to the electrodes are waveguide in nature to form a stable cavity resonator.