Spectral properties and conversion efficiency of 355-nm-pumped pulsed optical parametric oscillators of β-barium borate with noncollinear phase matching

We report on a theoretical and experimental investigation of the spectral properties and the conversion efficiency of 355-nm-pumped pulsed optical parametric oscillators (OPO’s) of β-barium borate with noncollinear phase matching. If the noncollinear phase matching is tangential, the pump wave’s angular acceptance—which is approximately 0.3 mrad cm-1 for collinear excitation—is increased as much as 9 mrad cm-1. Because of the large angular acceptance the OPO output energy increases to a factor of 4 greater than that for conventional collinear excitation when the OPO is pumped by a laser beam with a divergence of 3 mrad. Besides an increase in efficiency, the noncollinear phase matching provides a broadening of the spectral width of the OPO signal radiation of as much as 20 nm in the whole tuning range of 420–700 nm. The measured spectral widths are in good agreement with the results of an analysis that takes into account the influence of the divergence of the resonant OPO wave.