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Nonlinear Optical (NLO) materials have gained increasing interest, particularly in the past decades, for their realized and potential applications in many fields of photonics, optical communication and laser technology. Along with metallophthalocyanines and mixed metal clusters [1], C60 and other fullerenes have emerged as promising candidate materials for the nonlinear optical applications owing to their intrinsic NLO properties which primarily originate from their largeπ electron conjugations and strong electron affinity [2]. However the ability to fabricate NLO devices based on C60 has been limited due to its poor processability and multiaddition of organic group [3]. Therefore, the main key to the development of C60-based NLO materials is to synthesize highly soluble C60 derivatives with excellent NLO properties under very mild conditions. Very recently, studies on the optical limiting (OL) property (one of the NLO responses) of simple blends of [60]fullerene and polymer (i.e., [60]fullerene-doped polymer) have grown rapidly. Although doping of C60 into polymer matrices may bring about enhancement of nonlinear response, there are, however, problems associated with this approach. These problems stem from the tendency for the dopant molecules to aggregate in the solid state, leading to difficulty in achieving homogeneous dispersions and ultimately phase separation at high loadings [4]. Polymeric modification of fullerene can overcome these problems. So far, only a few articles reported such work concerning C60 polymeric derivatives [5, 6]. For this reason, we synthesized the highly soluble [60]fullerene-based polyacrylonitrile (PAN) derivatives with different C60 contents using a previously reported one-pot experiment procedure [7, 8], and described initial results of an investigation into their third-order nonlinear optical response by optical-heterdyne-detected optical-Kerr-effect (OHDOKE) technique. The parent polymer PAN and the soluble C60acrylonitrile (C60-AN) copolymers with C60 wt % of ∼12% and ∼18% were synthesized as shown in Scheme 1 under a purified argon atmosphere. The resultant polymers were redissolved in N,N-dimethylformamide (DMF), filtered to remove any unreacted C60 and trace of cross-linking product (if any), and reprecipitated with methanol to give the powder product (the purification procedure was repeated twice). Its color is closely related to the fullerene content in the copolymer: the higher the content, the deeper the product’s color. These copolymer structures were characterized by a variety of physical methods, including ultraviolet-visible (UV-Vis) absorption, electron spin resonance (ESR), differential scanning calorimeter analysis (DSC), Fourier transform infra-red (FT-IR), scanning electron microscope (SEM) and X-ray powder diffraction (XRD). The UV-Vis absorption spectra in DMF of C60-AN copolymers differ greatly from that of pure PAN. For the former, its spectrum with only one sharp absorption peak at 295 nm(s) keeps essentially transparent at wavelengths longer than 400 nm, whereas in the copolymer with high C60 content, except for the peak at 295 nm, two new peaks at 257 nm (m, shoulder) and 264 nm(s), which are ascribed to the characteristic absorption for the covalent attachment of C60 to the PAN backbone, were observed. In contrast to the light-yellow exhibited by the pure PAN, the color of copolymers gradually changes from brown to black as the C60 content increases. Obviously, the covalent attachment of C60 to the PAN chains leads to the enhancement of the absorption degree at longer wavelengths. This implies that there should be somewhat electronic interaction between C60 and PAN chains. As discussed for the UV-Vis absorption spectra, there exists considerable difference in electronic structure

The clustering dynamics of SiO 2 -containing negative ion clusters generated from ultrafine amorphous SiO 2 powders with high specific surface area is investigated by XeCl excimer laser ablation time-of-flight mass spectrometry (TOF-MS). From the evolution of the mass spectra with the delay time and the number of laser irradiation shots, the key roles played by OH and OH − fragments from the surface silanol groups in the formation of SiO 2 -containing negative ion clusters are discussed.

Cycloisomalto-heptaose (CI-7) and cycloisomalto-octaose (CI-8) are two novel cyclodextrans. Treatment with C60 or C70 by kneading leads to the formation of four distinct water-soluble inclusion complexes: CI-7/C60 (2: 1), CI-8/C60 (2: 1), CI-7/C70 (2: 1) and CI-8/C70 (2: 1). Their formation and structures have been examined by UV vis spectroscopy, X-ray powder diffraction and fluorescence spectral studies. The reaction is a reversible process.

The coherent Raman mixing spectra from individual micrometer-sized droplets of ethanol and of water consist of regularly spaced peaks that correspond to the morphology-dependent resonances of a spherical droplet. In contrast, the coherent anti-Stokes Raman scattering spectra from droplets exhibit no morphology-dependent peaks. Both results are explained by the spatial overlap of the enhanced internal field distributions and by the phase-matching conditions associated with the droplet.

Asymmetrically broadened line shapes observed in the stimulated Raman and elastically scattered spectra from a CS(2) droplet are manifestations of phase modulation by means of the intensity-dependent index of refraction. Unique features of the droplet morphology in enhancing the internal fields at the input and Stokes wavelengths and in prolonging the decay time of the waves within the droplet, which acts as an optical cavity, are discussed.

Stimulated Raman scattering (SRS) from an individual liquid droplet (~30-microm radius) has been observed for H(2)O, D(2)O, and ethanol. The occurrence of a series of spectrally narrow peaks that are regularly spaced in wavelength is consistent with morphology-dependent resonances of the droplet, which acts as an optical resonator. The input intensity required to achieve the SRS threshold for the droplet is considerably less than that for the liquid in an optical cell.

A metal sulfide such as ZnS, CdS, Ag(2)S or PbS was coated on the sidewall of multiwalled carbon nanotubes (MWCNTs) by an in situ wet chemical synthesis approach via noncovalent functionalization of MWCNTs with a polyelectrolyte (polyethylenimine or poly(diallyldimethylammonium chloride)) without causing significant electronic and structural modification of the carbon nanotubes. Extensive characterizations of the fabricated nanocomposites have been performed using x-ray diffraction, transmission electron microscopy (TEM), high resolution TEM, energy dispersive x-ray spectroscopy, selected area electron diffraction, thermal gravimetric analysis, Fourier transform IR spectra, UV-vis spectra and x-ray photoelectron spectroscopy. The coating layers were composed of metal sulfide nanoparticles with a mean size of less than 10 nm. The optical limiting property measurements for some metal sulfide coated MWCNTs were carried out by the open-aperture z-scan technique. The results demonstrate that the samples suspended in water showed optical limiting behavior better than that of purified MWCNTs.

Three kinds of soluble polymer grafted multi-walled carbon nanotubes (MWNTs), including poly(N-vinylcarbazole)-MWNTs (MWNTs-PVK), polystyrene-MWNTs (MWNTs-PSt) and poly(methyl methacrylate)-MWNTs (MWNTs-PMMA) were synthesized. The TEM images of these samples show that polymers are coated outside the carbon nanotubes. The UV-Vis absorption spectra of the samples in CHCl3 were taken on a HP8452 spectrophotometer at room temperature. Compared with that of MWNTs suspension, there is a characteristic absorption peak in the ultraviolet region, which can be attributed to the polymers linked covalently with MWNTs. Their nonlinear optical properties and optical limiting (OL) performances were investigated by Z-scan method with 527 nm nanosecond laser pulses. These MWNTs dissolved in chloroform possess similar optical limiting properties, which are better than that of raw MWNT suspension and C60 in toluene solution. Nonlinear refraction, nonlinear absorption and nonlinear scattering mechanism were taken into consideration for explaining the observed results. The analysis of the experimental results shows that nonlinear absorption is the dominant mechanism behind the OL performance of these samples.

The decay curves of the emission at different wavelength were measured. One nanosecond of transition lifetime of interband was obtained. The transient dynamics of InP nanoparticles was investigated by one color femtosecond pump-probe method at the wavelength of 800 nm. The experimental result shows that the saturation of exciton resonance results in photobleaching at 800 nm The decay process of the bleaching includes two components, i.e. the fast one from free carries scattering and the slow one from trapped carriers scattering. The nonlinear optical properties of InP nanoparticles were investigated by using femtosecond optical Kerr effect. The magnitude of chi3 for InP nanoparticles embedded in SiO2 sol-gel glass was calculated, and its origin was analyzed.

The charge transfer (CT) process in PAN-C60 copolymer films was studied by absorption and picosecond time-resolved photoluminescence (TRPL) spectra. The CT process can be confirmed from the appearing of new absorption bands and fluorescence quenching of pure PAN in the copolymer films. The TRPL result revealed that excitation state relaxation obeyed biexponential decay process, which were 160 ps and 1,500 ps for the fast and slow decay process, respectively. The fast decay process results from the interaction of chains in the polymer, and a slow decay process comes from the singlet excition recombination. In the copolymer, the singlet excition state lifetime of PAN becomes shorter due to CT process between PAN and C60, which lead to PL quenching of PAN. Additionally, C60 molecules also affect the interchain interaction of PAN by its spacial shape, which closely relates with the fast decay process.

The ultrafast energy transfer process, which takes place in femtosecond time range, in bacterial photosynthetic reaction center RS601 was investigated using femtosecond pump-probe technique with selective excitation. Upon 755 nmexcitation, the excited state of bacteriopheophytin H decayed to bacteriochlorophyll B with a time constant of about 130 fs, while the excited state of B transported the energy to its energy acceptor, the dimeric bacteriochlorophyll P, in about 240 fs with the 800 nm excitation. The internal conversion process between the upper and lower exciton levels of special pair P might exist upon the excitation of 850 nm pulses. In addition, from the results obtained in our experiments, the charge separation and electron transfer from P to the acceptor H was also observed via the real intermediate B within a few picoseconds.

When dye-doped ethanol droplets are irradiated with an intense pulsed laser beam, the resulting laser emission from individual droplets highlights the liquid-air interface. Photographs of the lasing droplets in the micrometer size range taken in a single 10-nanosecond laser pulse clearly show the dynamic changes in droplet size, shape, and orientation.

Nonlinear optical interactions in micrometer-size liquid droplets are readily observable. New data on the stimulated Raman scattering of benzene droplets (up to the 6th-order Stokes), and water droplets containing KNO3 (up to the 2nd-order Stokes) will be presented, as well as data on the phase modulation broadened line shape of the 1st and 2nd Stokes of CS2 droplets, and the phase-matching angular dependence of the coherent anti-Stokes Raman scattering (CARS) signal of ethanol droplets. The phenomenological description of these nonlinear interactions involving x(3) will be presented in terms of the internal field distributions of the incident and Raman fields which are modified by the droplet interface and the feedback provided by the morphology-dependent resonances.

Preliminary studies on laser emission from individual ethanol (~30-μm radius) droplets doped with rhodamine 6G dye have been reported.1 Two striking features of this emission were (1) the existence of spectrally narrow peaks and (2) a substantially lowered lasing threshold. Both of these features are the result of optical feedback at specific resonant wavelengths, which occurs as a consequence of whispering gallery modes or more accurately morphology-dependent resonances of the internally generated fluorescence radiation.