A variety of nonlinear media, each with tailored optical properties, could be produced using a gold-disk patterning method to perform four-wave mixing. Developed at Rice University, the method is the first to produce materials that can achieve four-wave mixing with a range of colored input and output. “Versatility is one of the advantages of this process,” said study co-author Naomi Halas, director of the university’s Laboratory for Nanophotonics (LANP). She is the Stanley C. Moore Professor in Electrical and Computer Engineering. “It allows us to mix colors in a very general way. That means not only can we send in beams of two different colors and get out a third color, but we can fine-tune the arrangements to create devices that are tailored to accept or produce a broad spectrum of colors.” By arranging optically tuned gold disks in a closely spaced pattern, Rice University scientists created intense electrical fields and enhanced the nonlinear optical properties of the system. Here, a computer model displays the plasmonic interactions that give rise to the intense fields. The investigators used electron beam lithography to etch the puck-shaped gold disks – a type of nonlinear media – then placed them on a transparent surface for optical testing. They designed each disk to harvest the energy from a particular light frequency; by arranging a baker’s dozen of the disks in a closely spaced pattern, the team enhanced the nonlinear properties of the system by creating intense electrical fields. “Our system exploits a particular plasmonic effect called a Fano resonance to boost the efficiency of the relatively weak nonlinear effect that underlies four-wave mixing,” said Peter Nordlander, a theoretical physicist at LANP and co-author of the new study. “The result is a boost in the intensity of the third color of light that the device produces.” “The value of this research goes beyond the design for this particular device,” Halas said. “The methods used to create this device can be applied to the production of a wide range of nonlinear media, each with tailored optical properties.” The technique was described in the Proceedings of the National Academy of Sciences (doi: 10.1073/pnas.1220304110).