Thirdhyphen;order nonlinearity and twohyphen;photonhyphen;induced molecular dynamics: Femtosecond timehyphen;resolved transient absorption, Kerr gate, and degenerate fourhyphen;wave mixing studies in poly (phyphen;phenylene vinylene)/solhyphen;gel silica film

摘要

Femtosecond response and relaxation of the thirdhyphen;order optical nonlinearity in a newly developed poly (phyphen;phenylene vinylene)/solhyphen;gel silica composite are investigated by timehyphen;resolved forward wave degenerate fourhyphen;wave mixing, Kerr gate, and transient absorption techniques using 60 fs pulses at 620 nm. Using a theoretical description of twohyphen; and fourhyphen;wave mixing in optically nonlinear media, it is shown that the results obtained from simultaneous use of these techniques yield valuable information on the real and imaginary components of the thirdhyphen;order susceptibility. In the composite material investigated here, the imaginary component is derived from the presence of a twohyphen;photon resonance at the wavelength of 620 nm used for the present study. This twohyphen;photon resonance is observed as transient absorption of the probe beam induced by the presence of a strong pump beam. It also provides fifthhyphen;order nonlinear response both in transient absorption and in degenerate fourhyphen;wave mixing. The fifthhyphen;order contributions are derived from the twohyphen;photon generated excited species which can absorb at the measurement wavelength and therefore modify both the absorption coefficient and the refractive index of the medium.