Ultrafast nonlinear optical property of the C60(CH3)x(PAN)x copolymer

Abstract

ABSTRACT We have fabricated thin film of the star-like C60(CH3)(PAN) copolymer. Optical property and ultrafast nonlinear optical response of the copolymer films were measured. The absorption and photoluminescence spectra showed the intramolecular excitation transfer process existed in thecopolymer. From the femtosecond optical Kerr effect measurement, third-order nonlinear opticalsusceptibility of the copolymer film was found bigger than that of pure PAN and fullerene molecule which result from a new lower excited state and the redistribution of the electron cloud in the copolymer.Keywords: femtosecond, fullerene, copolymer, nonlinear optics, charge transfer, absorption 1JNTRODUCTION Materials with large nonlinear optical response are much attractive for photonic applications includingoptical switching, modulator, optical information processing and optical communication.1The rapiddevelopment of the optical communication requires the ultrafast response of the nonlinearity in thepicosecond(ps) and even subpicosecond domain for fabricating the ultrafast optical switching andprocessing devices. For these purposes, research of ps and femtosecond(fs) nonlinear optical propertyof many kinds of the materials has attracted much aftention.5 For a lot of existing inorganic andorganic materials, though some materials show large nonlinear optical response and are used in thenonlinear optical devices, many materials have medium or small nonlinear optical susceptibility whichis not good enough for the application. One possible way to improve the nonlinear optical response ofthe materials is to modify the structure of the material, such as to implant the metal nanocluster into thesilica leading to a increase of nonlinear optical parameter about six orders than that of unimplantedsilica,7 or to make composite material. For the organic materials, the donor-acceptor structure werewidely used to get the improved second-order and third-order nonlinear optical response. Marder et atreported that for several acceptor-substituted carotenoids, large enhancement of the third-order opticalnonlinearity has been achieved.6 The intramolecular charge transfer from the polyenic chain to theacceptor moiety is one important reason for this enhancement. By combining the fullerene with the