Abstract: A radial flow laser having an unstable resonator configuration with a standing wave optical path is disclosed. The gain medium forms a cylindrical sheath which is symmetric about a centerline axis through the resonator and the output beam is annular in cross section. The resonator geometry is based on a circular end mirror, an annular end mirror, an annular folding mirror having a reflective surface conforming to the inside of a cone geometry and conical folding mirror conforming to the outside of a cone geometry. Various embodiments are disclosed whereby the width of the resonant mode is either held constant or expanded to accommodate various power density loadings on the mirrors. In one configuration, the standing wave travels in a complete loop through the cylindrical sheath of gain medium.