Highly efficient frequency doubling with a doubly resonant monolithic total-internal-reflection ring resonator

Doubly resonant second-harmonic generation is demonstrated in a monolithic total-internal-reflection MgO:LiNbO(3) ring resonator. The coating-free cavity is kept resonant for both the 1.06-microm fundamental wave and the harmonic by control of the resonator temperature and the laser frequency. Independent input coupling of the fundamental and output coupling of the harmonic wave are realized by the use of two calcite coupling prisms that frustrate total internal reflection. Using mechanically optimized coupling, we achieve external conversion efficiencies of more than 50% at input powers exceeding 5 mW.