Scientists at the University of Toronto and at Carleton University in Ottawa have produced polyurethane optical films containing buckyballs that exhibit third-order optical nonlinearity at near-IR telecommunications wavelengths up to 100 times higher than in other C60 derivatives. The material, on which they reported in the Sept. 15 issue of Applied Physics Letters, may have applications in optical switching and signal processing.They used a picosecond Ti:sapphire laser and an optical parametric amplifier to measure the nonlinear refractive index and nonlinear absorption of the material at wavelengths from 1150 to 1600 nm, separated by 50 nm. The third-order susceptibility was found to be 1.4 X 10–18 m2/V2. They suggest that the films, which featured a fullerene concentration of 19.1 percent by weight, display enhanced third-order nonlinearity because of a strong charge-transfer process in which the C60and the polymer act as an electron acceptor and donor, respectively.