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 μm to those at 1.187 μm 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 μm as the input power at 10.26 μm was increased, due to the back conversion, i.e. 1.187 μm + 10.26 μm → 1.064 μm, was clearly evidenced. Besides the midinfrared region, we have also investigated frequency upconversion of the input signals at 1.27 μm and 1.57 μm in the presence of the pump beam at 1.064 μm in bulk periodically-poled LiNbO 3 (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 CO 2 Emissions over Nights, Days, and Seasons (ASCENDS) mission.