%0 Journal Article %T Weak-signal conversion from 1550nm to 532nm with 84% efficiency %A Aiko Samblowski %A Christina E. Vollmer %A Christoph Baune %A Jaromir Fiurasek %A Roman Schnabel %J Physics %D 2013 %I arXiv %R 10.1364/OL.39.002979 %X We report on the experimental frequency conversion of a dim, coherent continuous-wave light field from 1550nm to 532nm with an external photon-number conversion efficiency of (84.4 +/- 1.5)%. We used sum-frequency generation, which was realized in a standing-wave cavity built around a periodically poled type I potassium titanyl phosphate (PPKTP) crystal, pumped by an intense field at 810 nm. Our result is in full agreement with a numerical model. For optimized cavity coupler reflectivities it predicts a conversion efficiency of up to 93% using the same PPKTP crystal. %U http://arxiv.org/abs/1310.0712v2