Efficiency improvement in MgO:PPLN based optical parametric generation using soft-edge top-hat transverse intensity profile for the pump beam

Pulsed nanosecond optical parametric generators (OPGs), in general, are pumped by a direct laser beams having Gaussian intensity profiles in temporal and spatial domains. This limits the conversion efficiency due to long build-up time of signal and idler intensities, and back-conversion effects. Efficiency optimization in an OPG involves reducing these effects; however, spatial and temporal distribution of pulse intensity across the pump beam limits the achievable conversion efficiency. We show that by using a spatially uniform intensity profile for the input pump beam, one can achieve significantly higher optimized efficiency because of uniform conversion over larger area of cross section of the pump beam. We present simulation results for MgO:PPLN based OPG with soft-edge top-hat (SETH) and Gaussian profiles which shows an improvement of about 27% in the optimized pump conversion efficiency, in the case of a pump beam with SETH transverse intensity profile. We also discuss the requirements for efficient conversion in an OPG using a SETH profile for the pump beam. Further, we present results of our study on the effect of pump pulse duration on the conversion efficiency for a given set of pump power and OPG parameters.