Highly efficient single-longitudinal-mode beta-BaB(2)O(4) optical parametric oscillator with a new cavity design

A new coupled-cavity design for single-longitudinal-mode operation of an optical parametric oscillator (OPO) is presented. The OPO is based on a beta-BaB(2)O(4) crystal and is pumped by the third harmonic of a Nd:YAG laser. With this design, we achieved single-longitudinal-mode operation of the OPO with a decrease in the threshold and an increase in external efficiency compared with those of a conventional grazing-incidence OPO. A mathematical model that describes the mode spacings for this cavity is given.