[60]Fullerene-Containing Polyurethane Films with Large Ultrafast Nonresonant Third-Order Nonlinearity at Telecommunication Wavelengths

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Abstract
A significantly enhanced, ultrafast third-order optical nonlinearity at the wavelengths of 1150−1600 nm was demonstrated with cross-linked C60-containing polyurethane films using the Z-scan technique. Good-quality polymer films with a high loading of C60 derivative were obtained by cross-linking of the hydroxyl-containing C60 derivative and a triisocyanate. The positive Kerr coefficient with nonresonant nonlinear refractive index n2 falls in the range of (3.7 ± 0.80) × 10-4 to (2.0 ± 0.6) × 10-3 cm2/GW, and the calculated χ(3) and γ values are up to 9.7 × 10-11 and 9.6 × 10-32 esu at 1550 nm, which are several orders of enhancement in third-order optical nonlinearity over pristine C60 in solution and 1−2 orders of enhancement over recently reported C60 derivatives and conjugated polymers.