Variations of nonlinear optical characteristics of C60 thin films at 532 nm

We present our investigations of the real and imaginary parts of third-order nonlinear susceptibility (chi((3))) of C-60 thin films (similar to100 nm) by the Z-scan technique at the wavelength of Nd:YAG laser second harmonic radiation (532 nm, tau = 55 ps). Our studies have shown that the sign of Rechi((3)) changed from negative (at 2-Hz pulse repetition rate) to positive (at 0.5-Hz pulse repetition rate). Sign variations of the real part of third-order susceptibility were attributed to the influence of thermal lens. The reverse saturable absorption was found to be responsible for the nonlinear absorption. We attribute the high values of Rechi((3)) ((4.8 +/- 1) x 10(-8) esu) and Imchi((3)) ((1.1 +/- 0.2) x 10(-8) esu) obtained in these studies to surface-enhanced effect. (C) 2003 Published by Elsevier B.V.