Low-threshold BBO OPO with cylindrical focusing

Abstract

ABSTRACT The design ofa BBO OPO cavity based on cylindiical focusing ofthe pump beam in the insensitive plane ofthe non-linear cr is presented and characterized. A variety ofbeam sizes in the sensitive plane of theBBO ciystal are investigated, and in all cases this cavity design is found to significantly lower the operationalthreshold pulse energy of355 nm pumped type I BBO OPOs. With optimal beam focussing parameters, themeasured threshold intensity of45 MW/cm2 is similar to that ofconventional OPOs, but the threshold pulseenergy ofO.4 mJ is some twenty times lower than that found in circularly symmetric pump beams. Pumppulse energies in this range can now be routinely achieved with diode-pumped Q-switched lasers, and thecombination ofthese sources with cylindrically-focussed OPO cavities (COPOs) should result in a new classofall-solid-state high repetition rate and high average power non-linear light sources that can be tuned overthe entire visible wavelength region.Key words: BBO OPO, cylindrical focusingOptical Parametric Oscillators (OPOs) based on BBO crystals have been demonstrated to be powerful,widely tunable solid state light sources in the visible and near-JR regions of the electromagnetic spectrum 1.However, because ofits inherently large walk-offangle and small acceptance angle, BBO crystals are limitedat present to studies that require high pulse energies and/or low repetition rates. For many scientific andindustrial applications, average power and repetition rate are as or more important, and for such applicationsmaterials such as periodically-poled LiNbO3 have become increasingly important 2