Variations of nonlinear optical characteristics of C 60 thin films at 532 nm

Abstract

We present our investigations of the real and imaginary parts of third-order nonlinear susceptibility ( χ (3)) of C 60 thin films (∼100 nm) by the Z-scan technique at the wavelength of Nd:YAG laser second harmonic radiation (532 nm, τ=55 ps). Our studies have shown that the sign of Re χ (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 Re χ (3) ((4.8 ± 1) × 10 −8 esu) and Im χ (3) ((1.1 ± 0.2) × 10 −8 esu) obtained in these studies to surface-enhanced effect.