Frequency Up-Conversion Detection System for Space Based Lidar

We review some of our recent results on frequency upconversion. Frequency upconversion of laser pulses at 10.26 mu m to those at 1.187 mu m was measured in the presence of Nd:YAG laser pulses based on difference-frequency generation in a 10-mm-long GaSe crystal. The highest power conversion efficiency for the parametric conversion was determined to be 20.9%, corresponding to the photon conversion efficiency of 2.42%. This value is two orders of magnitude higher than the highest value reported on GaSe in the literature. The saturation of the output power at 1.187 mu m as the input power at 10.26 mu m was increased, due to the back conversion, i.e. 1.187 mu m + 10.26 mu m -> 1.064 mu m, was clearly evidenced. Besides the midinfrared region, we have also investigated frequency upconversion of the input signals at 1.27 mu m and 1.57 mu m in the presence of the pump beam at 1.064 mu m in bulk periodically-poled LiNbO3 (PPLN) crystals. The quantum efficiencies of 11.2% and 13.2% have been achieved at these two input wavelengths. The detections of low-level photons at these two wavelengths are important to the NASA Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) mission.