Variations of nonlinear optical characteristics of C 60 thin films at 532 nm R.A. Ganeev a, * , A.I. Ryasnyansky b , V.I. Redkorechev a , K. Fostiropoulos c , G. Priebe d , T. Usmanov a a NPO Akadempribor, Akademgorodok, Tashkent 700125, Uzbekistan b Samarkand State University, Samarkand 703004, Uzbekistan c Hahn-Meitner-Institut Berlin, D-14109 Berlin, Germany d Max Born Institute, Max-Born-Str. 2A, D-12489 Berlin, Germany Received 14 April 2003; received in revised form 22 July 2003; accepted 23 July 2003 Abstract We present our investigations of the real and imaginary parts of third-order nonlinear susceptibility ðv ð3Þ Þ of C 60 thin films (100 nm) by the Z-scan technique at the wavelength of Nd:YAG laser second harmonic radiation (532 nm, s ¼ 55 ps). Our studies have shown that the sign of Rev ð3Þ 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 ab- sorption. We attribute the high values of Rev ð3Þ ((4.8  1)  10 8 esu) and Imv ð3Þ ((1.1  0.2)  10 8 esu) obtained in these studies to surface-enhanced effect. Ó 2003 Published by Elsevier B.V. PACS: 42.65; 42.70 Jk; 78.20.)e Keywords: Nonlinear refractive index; Nonlinear absorption; Fullerenes; Thin films 1. Introduction Nonlinear optical properties of fullerenes were actively investigated during last decade due to their possible applications as optical limiters [1,2] and switching elements [3]. Such materials dem- onstrate high nonlinearity and fast response [4]. These investigations were carried out using de- generate four wave mixing (DFWM) technique [5], second [6] and third [6–8] harmonic generation, Z-scan [9–13]. Excited-state nonlinearities seem to be the main nonlinear mechanisms for realizing optical limiting and switching [14]. Fullerenes attracted much interest in the context of optical limiting due to its strong reverse saturable Optics Communications 225 (2003) 131–139 www.elsevier.com/locate/optcom * Corresponding author. Present address: Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan. Tel.: +81-471-363367; fax: +81-471-363366. E-mail address: r_ganeev@issp.u-tokyo.ac.jp (R.A. Ganeev). 0030-4018/$ - see front matter Ó 2003 Published by Elsevier B.V. doi:10.1016/j.optcom.2003.07.019