High repetition rate nanosecond optical parametric oscillator pumped by the third harmonic of a DPSSL

A high repetition rate (5 kHz), nanosecond, type-I phase matched β-BaB₂O₄ (BBO) crystal-based optical parametric oscillator (OPO), pumped by the third harmonic (355 nm) of a diode-pumped solid state laser, is demonstrated for the first time. The high threshold pump pulse energy, which impedes the high repetition rate operation of OPO, is reduced to ≤ 1 mJ using cylindrical focusing of the pump beam. The performance of the OPO is compared for different gain lengths of the type-I BBO crystal and the optimum length of the crystal for efficient operation of the OPO is determined. We have obtained a stable output power of ~ 2.6 W at a signal wavelength of 492 nm, and at a conversion efficiency of 26%, when operated with pump laser at 5 kHz. Furthermore, the narrowband (~ 0.15 nm) operation of the OPO at a repetition rate of 2 kHz was achieved by employing type-II phase-matched BBO crystal in double pass pump beam configuration. Thermal loading in the BBO crystal arising due to high repetition rate operation was studied by measuring the temperature of the crystal for determining the average power scaling limit of visible nanosecond OPOs.