Femtosecond nearly degenerate four-wave mixing in C 60 films between 0.55 and 0.70 μm

Abstract

We used femtosecond nearly degenerate four-wave mixing (nDFWM) to measure the instantaneous third-order nonlinear optical susceptibility function χ 1111[−( ω− δω), ω, ω,−( ω+ δω)] near the absorption edge of C 60 films with absorption reaching up to 2.0×10 4 cm −1 . The frequency shift was set to ℏ δω=0.07±0.01 eV, smaller than the width of the spectral feature studied but large enough to suppress non-instantaneous signal contributions. Our data are orders of magnitude below previous DFWM results but connect smoothly to data at longer wavelengths where absorption is low (<≈100 cm −1).