Nonresonant optical nonlinearity of ZnO composite nanoparticles with different interfacial chemical environments

ZnO nanoparticles coated by surfactant molecules were synthesized by microemulsion method. Under proper thermal treatment, a new ZnO/surfactant composite nanoparticles were formed and exhibited an unique optical property. The third-order optical nonlinearity χ⁽³⁾ of ZnO composite nanoparticles with different interfacial chemical environment were measured by single-beam Z-scan technique, the sign and magnitude of both the real and imaginary parts of χ⁽³⁾ at 790 nm were measured to be: -5.2×10^-16 m²/W and 11.6 cm/Gw for ZnO/DBS composite nanoparticles (DBS, dodecyl benzene sulfonate, anionic surfactant); and -2.2×^-17 m²/W, 0.45 cm/Gw for ZnO/CTAB composite nanoparticles (CTAB, cetyltrimethyl ammonium bromide, cationic surfactant). The ultrafast nonlinear response time (∼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 optical Stark effect.