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Excitation energy transfer in the isolated light-harvesting chlorophyll (Chl)-a/b protein complex of photosystem II (LHC II) was studied by the one-colour pump-probe technique with femtosecond time resolution. After exciting Chl-b by 638 nm beam, the dynamic behaviour shows that the ultrafast energy transfer from Chl-b at positions of B2, B3, and B5 to the corresponding Chl-a molecules in monomeric subunit of LHC II is in the time scale of 230 fs. While with the excitation of Chl-a at 678 nm, the energy transfer between excitons of Chl-a molecules has the lifetime of about 370 fs, and two other slow decay components are due to the energy transfer between different Chl-a molecules in a monomeric subunit of LHC II or in different subunits, or due to change of molecular conformation.

Energy dissipation techniques, widely used in solid physics previously, are proven to be sensitive also to changes in liquid structure. It has been suggested from relative energy dissipation that changes in liquid structure can occur as a function of temperature in some ordinary binary systems such as Pb-Sn, In-Sn and In-Bi. This finding may be helpful to understand liquid structure changing patterns, therefore enriching the phenomenology of liquid state physics. This is significant for engineering practices.

In recent years, azobenzene derivates have received much attention for their potential application in optical data storage, biophotonics, holographic memories and waveguide switches optical sensors, and sensitive optical components from laser damage in both civilian and military applications. Experimental and theoretical studies demonstrate clearly the effect of the sonor-pi-acceptor (D- -A) conjugation on the steady-state and time-resolved PL spectra of azobenzene derivate films in multifarious situations, but comparatively little is concerned about the two-photon absorption and refraction involved in a single benzene ring. Furthermore, the excitation laser source on the azobenzene derivates in some investigations is continuum laser or nanosecond pulsed laser, where it is hard to avoid thermal effect on nonlinear optical (NLO) process produced by these lasers. To explore the origin of the azobenzene derivates' D- -A conjugation-dependent NLO process is a challenging task and has great signicance in describing the molecular structures of these azobenzene nanostructures as well as improving the performance of azobenzene derivates' devices. The D- -A conjugation of azobenzene functional material can be modified by mixing the azobenzene derivates with metal nanoparticles, so it is convenient to study how the D- -A conjugation affects the NLO properties by using the azobenzene derivate-metal composites. In this letter, the D- -A conjugation-dependent NLO absorption and refraction of the two kinds of azobenzene derivates 4-((4'-hydroxybenzene) azo) benzyl acid(BN) and N-(3, 4, 5-octanoxyphnyl)-N'-4-[(4-hydroxyphenyl) azophenyl]1, 3, 4-oxadiazole (AOB-t8) are investigated by Z-scan technology using 32 ps laser pulse width at 532 nm. The azobenzene derivates' surface is modified using the D- -A conjugation control and overcoating Au nanoparticles on the azobenzene derivates; and the Au/AOB-t8 composites, BN and AOB-t8 are characterized by Z-scans and absorption/fluorescence spectrum, and also calculated based on plasma resonance. The third-order NLO susceptibility of AOB-t8 is enhanced as compared with BN due to the growing conjugate chain and the increasingly extended bond. However, the third-order NLO susceptibility of AOB-t8 is decreased in the composite(Au/AOB-t8) for the cooperation of the local field effect induced by the gold nanoparticles and the extended bond of organic molecules. This work may be helpful to the understanding of the physical mechanism of the surface states and the surface-related optical nonlinearity of semiconductor QDs.

The energy transfer pathways from the excited accessory bacteriochlorophylls (B*) within native and modified (pheophytin-exchanged) reaction centres isolated from Rhodobacter sphaeroides (RS601) have been investigated by using the femtosecond pump-probe technique. For native RS601, B* decays with a time constant of 240 fs, followed by a partial recovery of the ground-state bleaching with a timescale of about 2 ps. In modified RS601(Phe), however, B* decays with a time constant of 800 fs for magic angle (54.7°) polarization configuration. In addition to the general assumption of energy transfer pathway from B* to the special pair P, an alternative pathway for energy transfer probably operates as well.

The photoconductive properties of MBB-PPV/C60 composite films fabricated by the physical jet deposition (PJD) technique have been studied on the basis of the photoinduced charge transfer process. Under the photoexcitation, the transverse photoconductivity of the composite films is greatly enhanced by 4 orders of magnitude due to the efficient excitation transfer process from MBB-PPV (as donor) to C60 (as acceptor) occurring at the interface, the separation of charges and the existence of in-layer free carriers. The results indicate that the conjugated polymer/fullerene composite films optimized by an appropriate configuration have potential applications in photoelectric devices and photonic fields.

On the basis of measurement and theoretical analysis, the linear and nonlinear optical properties of the CdSe quantumn dots with different nanoparticle sizes were investigated. The relation between the nanoparticle size and the absorption peak of CdSe quantumn dots was characterized by UV-VIS-NIR spectroscopy, and the dependence of third-order nonlinear susceptibility of quantumn dots on nanoparticle size was investigated by picosecond Z-scan technique with different excitation wavelengths (532nm and 1064nm,resp.). The analysis of optical properties of the films was carried out using the theory of localized field enhancement. The experimental and theoretical results showed the dependence of third-order nonlinear susceptibilities χ(3) on the CdSe nanoparticle size. With CdSe nanoparticle size around 4.3nm and the excitation wavelength of 532nm, which was close to the resonance, the third-order nonlinear susceptibility χ(3) showed a maximum value of 2.0×10-11 esu.

On the basis of measurements and theoretical analysis, linear and nonlinear optical properties on the Ag:Bi2O3 composite films with different Ag concentrations were investigated. The relationship between the Ag concentrations and the surface plasmon resonance (SPR) of Ag:Bi2O3 composite films were characterized by UV-VIS-NIR spectroscopy, and the dependence of third-order nonlinear susceptibility of composite films on Ag concentrations was investigated by picosecond Z-scan technique with different excitation wavelength (532nm and 1064nm). The analysis of optical properties of these films was carried out using the theories of surface plasmon resonance and localized field enhancement respectively. From the experimental and theoretical results, the dependence of third-order nonlinear susceptibilities χ(3) on Ag concentration was shown. With Ag concentration around 35％ and the excitation wavelength at 532nm near the surface plasmon resonance (560nm—622nm), the third-order nonlinear susceptibility χ(3) showed a maximum value of 2.4×10-9 esu.