NONRESONANT OPTICAL NONLINEARITY OF ZNO COMPOSITE NANOPARTICLES WITH DIFFERENT INTERFACIAL CHEMICAL ENVIRONMENTS

ZnO nanoparticles coated by surfactant molecules were synthesized by m icroemulsion method. Under proper thermal treatment, a new ZnO/surfact ant composite nanoparticles were formed and exhibited an unique optica l property. The third-order optical nonlinearity chi((3)) of ZnO compo site nanoparticles with different interfacial chemical environment wer e measured by single-beam Z-scan technique, the sign and magnitude of both the real and imaginary parts of chi((3)) at 790 nm were measured to be: -5.2x10(-16) m(2)/W and 11.6 cm/Gw for ZnO/DBS composite nanopa rticles (DBS, dodecyl benzene sulfonate, anionic surfactant); and -2.2 x10(-17) m(2)/W, 0.45 cm/Gw for ZnO/CTAB composite nanoparticles (CTAB , cetyltrimethyl ammonium bromide, cationic surfactant). The ultrafast nonlinear response time (similar to 250 fs) measured by time-resolved pump-probe technique at excitation wavelength of 647 nm suggests that the optical nonlinearity below band-gap originate mainly from a rapid electronic polarization process or virtual process such as the optica l Stark effect.