Dispersion of refractive properties of solvents: Chloroform, toluene, benzene, and carbon disulfide in ultraviolet, visible, and near-infrared

Refractive indexdispersion formulas have been derived for chloroform, toluene, benzene, and carbon disulfide from a broad range of the experimental refractive index data at 20 °C. The data were examined with the linear least-squares method. The dispersion equations allow one to calculate the values of refractive index required for analysis of nonlinear optical measurements in the UV, visible, and near-IR wavelength range (0.3–2.5 μm) in these liquids and solutions. The indices were compared to those estimated from quantum chemical calculations. A survey of the experimental data revealed that the measurement results published recently [Opt. Mater. 20, 81 (2002); Rev. Sci. Instrum. 65, 2056 (1994); 66, 38 (1995); 69, 1243 (1998)] were significantly different from other data reported in the literature.Australian Photonics CRC is acknowledged for support

Self-reconstructing all-optical poling in polymer fibers

Self-sustained all-optical poling second-harmonic generation (SHG) experiments are conducted in single-core and multicore dye-doped poly(methyl methacrylate) optical fibers. By tuning the polarization of the fundamental beam, the SHG signal is degraded and is reconstructed spontaneously up to its initial level. We found a new situation in which the photo-induced self-organization of azo polymers creates a well-ordered periodic structure

Ab initio studies of two-photon absorption of some stilbenoid chromophores

Two-photon absorption of a series of donor-acceptor trans-stilbene derivatives is studied by means of density functional theory applied to second-order response function. Several important issues in modeling are highlighted which must be addressed for a reliable reproduction of the experimental results. It is evident that the correct order of magnitude of calculated two-photon absorption cross sections can only be obtained if proper account is taken of vibrational broadening of the absorption profiles. A comparison of the theoretical results with the experimental ones indicates that the computed two-photon absorption cross sections are in rough agreement with our previous report, although the observed systematic increase of the cross sections with the electron acceptor strength is not well reproduced. It is suggested that this disagreement may be due not only to the deficiencies of the computations but also to a variety of factors contributing to the experimental value of the effective two-photon absorption cross section, which are not taken into account in the ab initio calculations

Charge carrier mobility in an organic-inorganic hybrid nanocomposite

Organic-inorganic hybrid materials are media for electronic and optoelectronic applications. We present a study of the electronic transport in such a modelnanoparticle-sensitizedhybridorganic-inorganic photorefractive host system, consisting of poly(N-vinylcarbazole) doped with quantum dots of cadmium sulfide, using standard time-of-flight techniques. The photocurrent transients exhibit features typical of dispersive transport in an amorphous semiconductor. The hole mobility depends strongly on the electric field and temperature indicating Poole–Frenkel-like activated hopping transport; a thickness dependence of the mobility is observed. The presence of nanoparticles does not lead to increased trapping of holes. Conversely, a surprising result is observed: the mobility actually increases with the increase of nanoparticle concentration even though it is well below the percolation limit.This study was supported by a NSF, DMR Solid State and Polymer Chemistry Grant No. DMR0075867. Partial support by a Defense Research Initiative on Nanotechnology (DURINT), Contract No. F496200110358, through the Directorate of Chemistry and Life Sciences of the Air Force Office of Scientific Research is also acknowledged

Multiphoton absorption in amyloid protein fibres

Fibrillization of peptides leads to the formation of amyloid fibres, which, when in large aggregates, are responsible for diseases such as Alzheimer's and Parkinson's. Here, we show that amyloids have strong nonlinear optical absorption, which is not present in native non-fibrillized protein. Z-scan and pump-probe experiments indicate that insulin and lysozyme β-amyloids, as well as α-synuclein fibres, exhibit either two-photon, three-photon or higher multiphoton absorption processes, depending on the wavelength of light. We propose that the enhanced multiphoton absorption is due to a cooperative mechanism involving through-space dipolar coupling between excited states of aromatic amino acids densely packed in the fibrous structures. This finding will provide the opportunity to develop nonlinear optical techniques to detect and study amyloid structures and also suggests that new protein-based materials with sizable multiphoton absorption could be designed for specific applications in nanotechnology, photonics and optoelectronics

DNA-Ormocer based biocomposite for fabrication of photonic structures

We report microfabrication of high quality photonicstructures such as two-dimensional photonic crystals and beam splitters from a high DNA load, photosensitive Ormocer nanocomposite. This nanocomposite combines the high dye loading capacity of DNA with the photopatternability and hardness of the Ormocer. The fabrication is performed with the two-photon lithography method. Detailed studies of the deoxyribonucleic acid distribution in the fabricatedstructures are conducted with Raman microscopy. We also demonstrate that the deoxyribonucleic acid based nanocomposite films cast on glass substrates are of high enough quality to support amplified spontaneous emission from dyes intercalated in the deoxyribonucleic acid

Synthesis and optical power limiting properties of heteroleptic Mo3S7 clusters

Substitution of the halide ligands in (Bu4N)2[Mo3S7X6] (X = Cl, Br) by diimine ligands, such as 4,4′-dimethyl-2,2′-bipyridine (dmbpy), 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen), affords the neutral heteroleptic clusters Mo3S7Cl4(dmbpy) (1), Mo3S7Br4(dmbpy) (2), Mo3S7Br4(bpy) (3), and Mo3S7Br4(phen) (4). Further substitution of the halide ligands in Mo3S7Br4(diimine) clusters by dmit (1,3-dithiole-2-thione-4,5-dithiolate) allows the preparation of the mixed diimine–dithiolene neutral cluster complexes Mo3S7(dnbpy)(dmit)2 (5, dnbpy = 4,4′-dinonyl-2,2′-bipyridine), Mo3S7(dcmbpy)(dmit)2 (6, dcmbpy = 4,4′-dimethoxycarbonyl-2,2′-bipyridine), and Mo3S7(dcbpy)(dmit)2 (7, dcbpy = 2,2′-bipyridine-4,4′-dicarboxylic acid). The optical limiting properties of complexes 1–7 have been assessed by the open-aperture Z-scan technique at 570 nm, employing a nanosecond optical parametric oscillator. In order to investigate the effect of increasing the π-system, complexes 1–4, with the general formula Mo3S7X4(diimine), (X = Cl, Br), were compared to clusters 5–7, containing the dmit ligand. The influence of the metal content on the optical power limiting properties was also investigated by comparing the trinuclear series of complexes prepared herein with the bis(dithiolene) dinuclear cluster (Et4N)2[Mo2O2S2(BPyDTS2)2], which has been recently prepared by our group. All trinuclear clusters 1–7 are efficient optical limiters (σeff > σ0) with the threshold limiting fluence F15% decreasing on proceeding from dinuclear to trinuclear clusters and, generally, on extending the π-system.Financial support from the Spanish Ministerio de Economia y Competitividad (MINECO) (Grant CTQ2011-23157), UJI (research project P1.1B2013-19) and Generalitat Valenciana (Prometeo/2014/022 and ACOMP/2014/274) is gratefully acknowledged. The authors also thank Serveis Centrals d ’ Instrumentació Cientifica (SCIC), within Universitat Jaume, I for providing them with materials characterization facilities. D. R. thanks the Spanish Ministerio de Economía y Competividad for a predoctoral fellowship. M. G. H. thanks the Australian Research Council for support. M. S. acknowl- edges the NCN grant DEC-2013/10/A/ST4/0011