EFFICIENT, LOW-THRESHOLD COLLINEAR AND NONCOLLINEAR BETA-BARIUM BORATE OPTICAL PARAMETRIC OSCILLATORS

The performance of collinear and noncollinear pulsed barium berate opt ical parametric oscillators with third-harmonic Nd:YAG pumping is anal yzed. The effects of tangential phase matching and pump Poynting vecto r walk-off compensation are shown to enhance noncollinear operation. H owever, we show that these effects are mutually exclusive for a type I beta-barium berate optical parametric oscillator and furthermore that tangential phase matching is dominant. The selection of a collinear o r a noncollinear configuration is determined by pump divergence and sp ot size as well as by crystal aperture. With a pump divergence of 4 mr ad, noncollinear operation is optimal. The highest slope efficiency, 3 7%, and the lowest threshold, 5 mJ, are obtained with nearly perfect t angential phase matching. For a pump divergence of less than 2 mrad an d a similar spot size, collinear operation gives the lowest threshold, 3.2 mJ, and the highest slope efficiency, 33%. (C) 1997 Optical Socie ty of America.