Monolithic ring resonator with PPLN crystal for efficient cw SHG of 976 nm emitted by a diode laser

摘要

A new setup for efficient blue light generation that consists of two passively coupled optical resonators is presented. The first resonator is based on a broad area laser diode (BAL) in a Littrow external cavity with a special off-axis design. This external cavity diode laser provides more than 450 mW diffraction limited and narrow bandwidth emission at 976 nm. A compact cavity design with 40 mm length could be realized. The second resonator is a monolithic high finesse ring cavity containing a 10 mm bulk periodically poled lithium niobate (PPLN) crystal for resonant second harmonic generation. This ring resonator consists of four small mirrors with appropriate reflectivities and two GRIN lenses for stability reasons. All parts of this ring cavity are mounted monolithically on a glass substrate with a size of 19.5 mm × 8.5 mm. First experiments showed good passive matching of both cavities without any active closed-loop control. With this setup efficient SHG was achieved. A maximum optical output power of 70 mW blue light at 488 nm was obtained. The conversion efficiency was better than 15%.