Researchers at the Leibniz Universität Hannover (Hannover, Germany) have achieved a new efficiency high for the frequency doubling of continuous-wave laser light. In the experiment, 1.10 W of light at a 1550 nm wavelength was externally doubled in a cavity containing a periodically poled potassium titanyl phosphate crystal (PPKTP), yielding 1.05 W of light at 775 nm, for a conversion efficiency of 95%. Aside from general use, the technique is suitable for low-decoherence frequency conversion of quantum states of light; the researchers’ interest is in quantum information experiments in which quantum information is mapped from one system to another.
A fiber laser produced the 1550 nm light, which passed through a mode-cleaning resonator and was mode-matched into an actively length-stabilized standing-wave cavity containing the PPKTP crystal. The plano-convex crystal was 1 × 2 × 9.3 mm3 in size and was antireflection coated on the plano surface and high-reflection coated on the curved surface, which served as a cavity mirror (the other cavity mirror was 24 mm away from the crystal and had a 25 mm curvature). The researchers believe that an efficiency of 98% can be reached, and that nonclassical states of light can be frequency doubled at a comparable efficiency.
Contact Roman Schnabel at [email protected].