Multigrating quasi-phase-matched optical parametric oscillator in periodically poled LiNbO_3

We report a widely tunable quasi-phase-matched optical parametric oscillator that uses periodically poled LiNbO(3)with a multigrating structure. The device is tuned by translation of the crystal through the resonator and pump beam, with no realignment needed. With a 1.064-microm acousto-optically Q-switched Nd:YAG pumplaser, we produced noncritically phase-matched tunable IR output from 1.36 to 4.83 microm. The threshold was 6 microJ for a 26-mm interaction length. The extraordinary polarization of LiNbO(3) has better IR transmission than does the ordinary polarization, permitting operation at longer wavelengths with d(33) quasi-phase matching than with conventional Type I birefringent phase matching.