High-efficiency frequency doubling of continuous-wave laser light
  We report on the observation of high efficiency frequency doubling of 1550 nm continuous-wave laser light in a nonlinear cavity containing a periodically poled potassium titanyl phosphate crystal (PPKTP). The fundamental field had a power of 1.10 W and was converted into 1.05 W at 775 nm, yielding a total external conversion efficiency of (95 \pm 1)%. The latter value is based on the measured depletion of the fundamental field being consistent with the absolute values derived from numerical simulations. According to our model, the conversion efficiency achieved was limited by the non-perfect mode-matching into the nonlinear cavity and the pump power available. Our result shows that cavity-assisted frequency conversion based on PPKTP is well suited for low-decoherence frequency conversion of quantum states of light. 
Stefan Ast, Ramon Moghadas Nia, Axel Sch\"onbeck, Nico Lastzka,   Jessica Steinlechner, Tobias Eberle, Moritz Mehmet, Sebast...
quant-ph physics.optics