Song Yinglin

Transformation of Sign of Nonlinear Refraction between Mo(W)/S/Cu Planar Metal Clusters

Optical nonlinear refractive properties of a series of Mo(W)/S/Cu planar square clusters are investigated using the Z-scan technique with the ns laser pulses at the wavelength of532nm. The result shows that the planar metal clusters containing the halogen ligands demonstrate the self-focusing effect, and the other planar metal clusters demonstrate the self-defocusing effect. These facts indicate that the halogen ligands can act as crucial factors in determining the sign of the nonlinear refraction of the Mo(W)/S/Cu planar metal clusters. The analysis of the experimental data shows that the planar clusters with halogen ligands possess greater refraction volume of the excited state than that of the ground state, while the other planar clusters possess the smaller refraction volume of the excited state than that of the ground state.

Novel metallo-phthalocyanine with high performances for ns optical limiting in solution

Abstract The optical limiting performances of metallo-phthalocyanines of (C12H25O)8PcNi and (C12H25O)8PcPb were investigated in toluene, in which the optical limiting threshold and clamped value of the (C12H25O)8PcPb were much lower than those of C60 at same conditions in toluene and the optical limiting threshold and clamped value of the (C12H25O)8PcNi were also comparable to the C60 for 8 ns pulses at 532 nm. The photophysical parameters were calculated according to a multiple levels model, which indicated that the reverse saturable absorption in the excited triplet state is responsible for the optical limiting mechanism for (C12H25O)8PcNi and (C12H25O)8PcPb with improved stability.

Third-order optical nonlinearities and optical limiting of octa-octyloxy phthalocyanine free base in toluene

The third-order nonlinear optical properties of the octa-octyloxy phthalocyanine free base were studied by Z-scan using 35-ps laser pulses at 532 nm in toluene. The nonlinear refractive index or the refractive cross section, and the excited singlet state absorption cross section were determined. The optical limiting performances at both nanosecond and picosecond time scales have been investigated. The results suggest that the octa-octyloxy phthalocyanine free base is promising for optical limiting materials.

Nonresonant Saturation Absorption in Electrostatic Self-Assembly Films Containing Methanofullerene

Ultrathin films containing methaofullerene are prepared by electrostatic layer-by-layer self-assembly of a positively charged trifluoroacetic acid salt of monoamino-substituted methanofullerene (TMAF) derivative and a negatively charged poly (sodium 4-styrenesulfonate) (PSS). Absorptive optical nonlinearities of 30 bilayer TMAF/PSS films and TMAF in water solution are measured using the Z-scan technique at 532 nm. Nonresonant saturation absorption is observed in the film sample, whereas reverse saturation absorption was for TMAF in water. The saturation-absorption behaviour is interpreted by a special formula. The saturation intensity is extracted to be 15.2±0.8 MW/cm2. The mechanism of saturation absorption in the TMAF/PSS film is discussed.

Localization and Threshold of Bistable Switching by Gap-Edge Shifting

We numerically investigate the localization behaviour of light propagation in a one-dimensional nonlinear photonic crystal (1D-NPC). It is found that the localization of a high gap-edge mode is better than that of a low one, so that the switching threshold of the 1D-NPC with plus Kerr L-layers is much lower than that with minus Kerr H-layers. For a structure of 16 periods, the threshold of the structure with nonlinear L-layers is about 1/10 of that with nonlinear H-layers in the same level of nonlinear refractive coefficient.

Enhanced Excited-State Optical Nonlinearities in a Novel Metallophthalocyanine Compound (C12H25O)8PcPb

Nonlinear absorption in a novel metallophthalocynine compound (C12H25O)8PcPb was investigated by the Z-scan technique with the irradiation of 8 ns laser pulses at the wavelength of 532 nm. The large optical limiting response was observed. The nonlinear absorption cross section was obtained by the simulation with a simplified rate equation model in which excited triplet-triplet state absorption is dominant. The excited-state absorption cross section and its effective ratio to the ground-state absorption cross section are larger than those of C60. The attenuation factor for (C12H25O)8PcPb is 2.5 times larger than that of C60, which is induced by the heavy atom lead interposition.

Excited state refraction of C70/toluene studied by using 4f coherent imaging system with phase object

Dynamic nonlinearities of C70/toluene solution are measured and analysed by an improved picosecond time-resolved pump-probe system based on a nonlinear imaging technique with phase object. The photophysical parameters are determined by the five-level model, which is adopted to interpret the experimental data. The change of refraction index per unit density of the excited state obtained by a numerically simulation is a critical factor to determine the nonlinear behaviour of C70 in picosecond time regime.

Preparation and nonlinear optical properties of Au colloid

Colloidal Au less than 20 nm was prepared in an aqueous solution of HAuCl4 by irradiation with a near-infrared femtosecond laser. The absorption peak around 526 nm in the absorption spectra and the peaks 2θ = 38.3° and 2θ = 44.3° in the x-ray diffraction (XRD) pattern indicated the formation of Au colloid. Nonlinear optical properties of Au colloid were investigated by using the Z-scan technique with 8 ns pulses at 532 nm. The transition characteristics from self-defocusing to self-focusing and from saturable absorption (SA) to reverse saturable absorption (RSA) were observed for the Au colloid.

Properties and stability of nanosecond optical limiting of gold nanoclusters

Optical limitation (OL) performances of the gold nanoclusters protected by C60-tpy have been investigated with 8 ns pulses at 532 nm. The experimental results show that the nanocomposite possesses OL effects superior to C60 in toluene. The main mechanism of OL is attributed to the nonlinear absorption and subsequently induced nonlinear scattering during excitation of the pulse. Ageing of the nanocomposite chloroform solution in air lowers the OL performances by a factor of 2.4, which can be due to the formation of aggregates of large gold particles.

Nonlinear optical properties in double-sided nonlinear media with Z-scan technique based on the Huygens--Fresnel principle

We present a theoretical model to analyse the propagation of a Gaussian laser beam through double-sided nonlinear media. This model is based on the Huygens?Fresnel diffraction integral method. This theoretical model is not only consistent with the cascade structure model for a small nonlinear phase-shift but also can be used for a large nonlinear phase-shift. It has been verified that it is suitable to characterize the double-sided nonlinear media compared with the cascade structure model. A good agreement between the experimental data and the results from the theoretical model is obtained. It will be useful for the design of multi-sided nonlinear materials.