Unstable-resonator flashlamp-pumped dye laser

A negative-branch confocal unstable resonator has been found to significantly improve the beam quality of a coaxial flashlamp-pumped rhodamine 6G dye laser. In a performance comparison with a conventional parallel-plane mirror resonator, over an order-of-magnitude increase in laser beam radiance has been measured. The negative-branch unstable resonator demonstrated relatively uncritical alignment sensitivity.