Nonlinear Optical Properties of Large-Sized Gold Nanorods

The nonlinear optical properties of single gold nanorods (GNRs) with a large diameter of ～200 nm and a long length of ～800 nm were investigated by using a focused femtosecond (fs) laser light with tunable wavelength. While the linear and nonlinear optical properties of small-sized GNRs have been extensively studied, the nonlinear optical properties of large-sized GNRs and the effects of high-order surface plasmon resonances remain unexplored. Second harmonic generation (SHG) or/and two-photon-induced luminescence (TPL) were observed in the nonlinear response spectra, and their dependences on excitation wavelength and polarization were examined. The scattering and absorption spectra of the small- and large-sized GNRs were compared by using the discrete dipole approximation method. It was found that the extinction of large-sized GNRs is dominated by scattering rather than absorption, which is dominant in small-sized GNRs. In addition, it was revealed that the excitation wavelength-dependent SHG of a GNR is governed by the linear scattering of the GNR and the maximum SHG is achieved at the valley of the scattering spectrum. In comparison, the excitation wavelength dependence of TPL is determined by the absorption spectrum of the GNR. The polarization-dependent SHG of a GNR exhibits a strong dependence on the dimension of the GNR, and it may appear as bipolar distributions parallel or perpendicular to the long axis of the GNR or multipole distributions.     

Optical studies of CdS:Mn nanoparticles

Cadmium sulphide nanoparticles were grown using a wet chemical method, by dissolving the reactants, cadmium chloride and sodium sulphide in water, in the presence of mercaptoethanol (ME), which was used as a capping agent. Manganese chloride was used to dope the nanoparticles. It was found that the particle size varied with different concentrations of ME. At higher concentrations of ME, smaller sized nanoparticles were synthesized. This method also reveals the high stability of nanoparticles in water. Nanoparticle properties were investigated using UV–vis absorption, photoluminescence spectroscopy, X‐ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The particle sizes were measured by the XRD technique, SEM and optical absorption spectra and were in the range 2–6 nm. Copyright © 2011 John Wiley & Sons, Ltd.     

Plasmonic, Low-Frequency Raman, and Nonlinear Optical-Limiting Studies in Copper–Silica Nanocomposites

Nanocomposite thin films consisting of Cu nanoparticles embedded in silica matrix were synthesized by atom beam co-sputtering technique. Plasmonic, optical, and structural properties of the nanocomposite films were investigated by using ultraviolet (UV)–visible absorption spectroscopy, nonlinear optical transmission, X-ray diffraction (XRD), and low-frequency Raman scattering. UV–visible absorption studies revealed the surface plasmon resonance absorption at 564 nm which showed a red shift with increase in Cu fraction. XRD results together with surface plasmon resonance absorption confirmed the presence of Cu nanoparticles of different size. Low-frequency Raman studies of nanocomposite films revealed breathing modes in Cu nanoparticles. Nanocomposites with lower metal fractions were found to behave like optical limiters. The possibility of controllably tuning the optical nonlinearity of these nanocomposites could enable them to be the potential candidates for applications in nanophotonics.     

Development of LSPR-Based Optical Fiber Dopamine Sensor Using L-Tyrosine-Capped Silver Nanoparticles and Its Nonlinear Optical Properties

Facile synthesis of L-tyrosine-capped silver nanoparticles (Tyr-AgNPs) was carried out, and its linear and nonlinear optical properties were investigated. Further, the sensing properties of Tyr-AgNPs toward dopamine were explored. Tyr-AgNPs exhibit a decrease in fluorescence intensity while a linear increase in absorption spectrum against increase in dopamine (DA) concentration (0–50 μM) at room temperature. Tyr-AgNPs are used as the sensing material for the fabrication of fiber optic dopamine sensor. Sensitivity, selectivity, and limit of detection of the sensor are evaluated. This proposed fiber optic sensor may offer sensitive and low-cost strategy for DA detection.

     

Investigation on Optical Properties of Ag–Au Alloy Nanoparticles

The outstanding chemical stability of Au and intense localized surface plasmon resonance of Ag make it possible to obtain a nanostructure with a good balance of good chemical stability and optical response. In this paper, we investigated the relationship between optical properties and the composition and size of Ag–Au alloy nanoparticle with numerical calculation by applying experimental data. Simplified empirical formulas are proposed through numerical simulation. The properties of extinction efficiency and the relative contribution of scattering and absorption efficiency to the extinction efficiency have been researched in detail. The calculated result and experimental data has been compared, and good agreement is obtained. Our work contributes greatly to catalysis application of Au–Ag alloy NPs in specific regions.     

Influence of Femtosecond Laser Ablated Silver Nanoparticles on the Nonlinear Optical Properties of Basic Fuchsin dye

We investigate the linear and nonlinear optical properties of Basic Fuchsin influenced by femtosecond laser ablated silver nanoparticles in deionised water. Single beam z-scan technique using a Q-switched Nd:YAG laser (Spectra PhysicsLAB-1760, 532 nm, 7 ns, 10 Hz) is used for the present study. Quenching of fluorescence is observed in the presence of silver nanoparticles. Transmission electron microscopic observation reveals that the nanoparticles are spherical in shape, with an average size of 7 nm. The samples show self-defocusing nonlinearity and better nonlinear absorption behavior in the presence of silver sol. The nonlinear absorption varies with varying input fluence and concentration. The results show that the variations in the nonlinear parameters are also due to the surface plasmon resonance of silver nanoparticles. The nonlinearity of the dye is increased in the presence of silver nanoparticles, which makes the material suitable for various photonic and optoelectronic applications.     

The Optical Absorption Coefficient of Maize Seeds Investigated by Photoacoustic Spectroscopy

The knowledge about a seed??s optical parameters is of great relevance in the seed technology practice. Such parameters provide information about its absorption and reflectance, which in turn is related to its color, quality, and health condition. The objective of the present study was to determine the optical absorption coefficient ?? for maize seeds (Zea mays L.) by means of the photoacoustic spectroscopy (PAS). Untreated seeds (I) and seeds dyed with methyl red (II) were used in this investigation. In addition, conventional reflectance measurements (obtained with the integrating sphere) were performed to validate PAS absorption measurements. The results show that the absorption spectra and reflection data of the seed samples are complementary. When used with thermally thick and optically opaque seeds, PAS may be considered as a potential diagnostic tool for the characterization of the seeds.     

Optical and electronic coupling of the redox copper Azurin on ITO-coated quartz substrate

We have investigated the hybrid system constituted by the redox copper protein Azurin integrated with the semiconductor indium tin oxide (ITO) coated on quartz substrate. The system appears to be a good candidate for bio-sensing and bio-optoelectronics applications, especially due to the coupling between the optical and electron transfer features of Azurin with the conductive properties and optical transparency of ITO. The optical, morphological and electrical properties of the system have been investigated by combining optical absorption and transmission, steady-state fluorescence, resonance Raman spectroscopy and scanning probe microscopies. We found that Azurin molecules are firmly anchored on ITO and retain their structural and optical features underlying the physiological electron transfer activity. Scanning tunnelling spectroscopy evidenced a good electric coupling between the protein molecules and the substrate and a concomitant modulation of the ITO semiconductor properties upon deposition of Azurin. Some interplay between the conduction and valence bands of ITO and the electronic levels of Azurin is therefore suggested. These results are of a significant relevance in the perspective of developing bio-nanodevices able to process both optical and electrical signals, in conjugation also with the biorecognition capability of the protein molecules.     

Influence of synthesis parameters on the optical and photocatalytic properties of solvo/hydrothermal CuS and ZnS nanoparticles

Copper sulfide and zinc sulfide nanostructures were synthesized using a solvo/hydrothermal method and a thio Schiff base ligand, N‐benzylidene ethanethioamide, as a source of sulfide ions. The effects of different synthesis parameters including the type of solvent, temperature, and duration of reactions on the morphology of the CuS and ZnS products were investigated using field emission scanning microscopy and transmission electron microscopy, respectively. The structural aspects of the samples were characterized using powder X‐ray diffraction, Fourier transform infrared spectroscopy, and energy dispersive X‐ray analysis. The optical properties of the samples were studied through their optical absorption and photoluminescence spectra. The photocatalytic ability of the as‐synthesized sulfides was explored by studying the colour removal of methylene blue under ultraviolet light irradiation.     

DFT study of linear and nonlinear optical properties of donor-acceptor substituted stilbenes, azobenzenes and benzilideneanilines

A theoretical analysis of the linear and nonlinear optical properties of six push–pull π-conjugated molecules with stilbene, azobenzene and benzilideneaniline as a backbone is presented. The photophysical properties of the investigated systems were determined by using response functions combined with density functional theory (DFT). Several different exchange-correlation potentials were applied in order to determine parameters describing the one- and two-photon spectra of the studied molecules. In particular, the recently proposed Coulomb-attenuated model (CAM-B3LYP) was used to describe charge-transfer (CT) excited states. In order to compare theoretical predictions with available experimental data, calculations with inclusion of solvent effects were performed. The BLYP and the CAM-B3LYP functionals were found to yield values of two-photon absorption (TPA) probabilities closer to experimental values than the B3LYP functional or the HF wavefunction. Moreover, molecular static hyperpolarisabilities were determined using both DFT and second-order Møller-Plesset perturbation (MP2) theory. Likewise, the CAM-B3LYP functional was found to outperform other applied exchange-correlation potentials in determining first hyperpolarisability (β). Moreover, it was confirmed on a purely theoretical basis that the presence of a –C=C– bridge between the phenyl rings leads to a much larger nonlinear optical response in comparison with a –N=N– bridge.     

Synthesis, X-ray crystal structures and linear and nonlinear optical characterization of a series of nickel(II) and copper(II) salicylaldiminato complexes

A series of nickel(II) and copper(II) salicylaldiminato complexes containing side arms with either potentially coordinating (OH) or non-coordinating (Cl) functional groups have been prepared and characterized by X-ray crystallography. The Cu(II) complexes are square planar, but the Ni(II) complexes prefer octahedral coordination. Linear absorption spectra depend on the metal and on its coordination geometry, with the octahedral Ni(II) complexes being the most weakly absorbing at 532 nm and the square planar Cu(II) complexes being the most strongly absorbing at 532 nm. The third-order nonlinear optical properties of the complexes have been characterized using degenerate four-wave mixing (DFWM) and Z-scan. Two different Z-scan experimental configurations were used, one of which employs a Gaussian beam in a tightly focused geometry while the other employs a top-hat beam and a more relaxed focus. The observed third-order optical nonlinearity is primarily due to transient thermal (photo-acoustic) effects associated with linear absorption in the samples. The dependence of the third-order nonlinear optical properties on the linear absorption means that the nonlinear optical properties vary substantially between the complexes even though they all contain the same chromophore. The hyperpolarizability of one of the complexes, γ = 1.3 × 10⁻³⁰ esu, rivals the nonlinearities measured at 532 nm in expanded porphyrin and phthalocyanine complexes.     

Changes in absorption,fluorescence, dichroism,and birefringence in stained giant axons: Optical measurement of membrane potential

Summary The absorption, fluorescence, dichroism, and birefringence of stained squid axons were measured during action potentials and voltage clamp steps in an effort to find large optical signals that could be used to monitor membrane potential. Changes in all four optical properties were found that were linearly related to membrane potential and, with several new dyes, the signal-to-noise ratios were larger than any obtained previously. The problem of photodynamic damage was greatly diminished; with a merocyaninerhodanine dye, the photodynamic damage associated with intense light and the presence of oxygen was negligible. The absorption change obtained with this dye was relatively large; it could be measured with a signal-to-noise ratio of 1001 during a single action potential.     

无损光学法测量人胃粘膜/粘膜下层组织的光衰减特性

研究了人正常胃粘膜及粘膜下层组织对640 nm,690 nm,740 nm,790 nm,840 nm和890 nm波长的钛宝石激光的光衰减特性以及光学穿透深度,实验采用激光斜入射式空间分辨反射光和CCD探测器以及非线性拟合确定组织光学特性。结果表明:人正常胃粘膜及粘膜下层组织对六个波长的激光的有效衰减系数和光学穿透深度都是随着激光波长的变化而变化的。其有效衰减系数的最大值在640 nm,其值为1.12 mm-1,最小值在790 nm,其值为0.901 mm-1,最大差异在790 nm和890 nm之间,其值为19.9%,最小差异在690 nm和740nm之间,其值为2.83%。其光学穿透深度的最大值在790 nm,其值为1.11 mm,最小值在640 nm,其值为0.890 mm,最大差异在640 nm和790 nm之间,其值为24.7%,最小差异在690 nm和740 nm之间,其值为2.97%。     

Optical investigation of three‐dimensional human skin equivalents: A pilot study

Human skin equivalents (HSEs) are three‐dimensional living models of human skin that are prepared in vitro by seeding cells onto an appropriate scaffold. They recreate the structure and biological behaviour of real skin, allowing the investigation of processes such as keratinocyte differentiation and interactions between the dermal and epidermal layers. However, for wider applications, their optical and mechanical properties should also replicate those of real skin. We therefore conducted a pilot study to investigate the optical properties of HSEs. We compared Monte Carlo simulations of (a) real human skin and (b) two‐layer optical models of HSEs with (c) experimental measurements of transmittance through HSE samples. The skin layers were described using a hybrid collection of optical attenuation coefficients. A linear relationship was observed between the simulations and experiments. For samples thinner than 0.5 mm, an exponential increase in detected power was observed due to fewer instances of absorption and scattering.      

Optical properties of mice's stool in 550 to 1000 nm wavelength range

The aim of this work was to measure optical properties of stool of mice to provide this relevant wavelength‐dependent behavior for optical imaging modalities such as fluorescent molecular tomography and near‐infrared optical tomography. BALB/c nude female mice were studied and optical properties of the stool were determined by employing the inverse adding‐doubling approach. The animals were kept on chlorophyll‐free diet. Nine stool samples were measured. The wavelength‐dependent behavior of absorption and scattering in 550 to 1000 nm range is presented. The reduced scattering spectrum is fitted to the Mie scattering approximation in the near‐infrared (NIR) wavelength range and to the Mie + Rayleigh approximation in visible/NIR range with the fitting coefficients presented. The study revealed that the absorption spectrum of stool can lead to crosstalk with the spectrum of hemoglobin in the NIR range.      

Optical characteristics of the phototroph Thiocapsa roseopersicina and implications for real-time monitoring of the bacteriochlorophyll concentration.

Optical characteristics of a Thiocapsa roseopersicina culture and environmental samples containing T. roseopersicina were investigated in the spectral range of 400 to 1,100 nm (absorption coefficient, diffuse attenuation coefficient, and reflectance). Specific absorption coefficients of T. roseopersicina at wavelengths of 480, 520, 550, 580, 805, 860, and 880 nm were determined. It is suggested that the optical properties of T. roseopersicina in the near-infrared range of 800 to 930 nm, confirmed in this study, may be used for development of remote sensing techniques for real-time monitoring of T. roseopersicina and other bacteriochlorophyll a-containing microbes.     

Optical Saturable Absorption in Gold Nanoparticles

In this work, we present the experimental study of the nonlinear absorption of gold nanospheres and nanorods in aqueous suspension, using picosecond white-light supercontinuum open-aperture Z-scan. We demonstrate a saturable absorption effect in all particle suspensions at low-pulse energy. In the high-pulse energy regime, the apparent reverse-saturable absorption, observed in gold nanorods, was determined to be induced by photodegradation. Using the Lorentzian deconvolution method for the absorption spectra, we explain the variations on nonlinear optical effects and prove that saturable absorption only occurs within the plasmonic bands.     

The Mirror Image Symmetry in the Optical Absorption/Luminescence Spectra of Silver Nanoparticles in Ag/Ag2O Composites Synthesized by Oxygen Plasma Treatment of Silver Thin Films

The aim of this paper is to compare the spectral features of the response plasmon peak in both the optical absorption and photoluminescence spectra of the Ag/Ag₂O composites synthesized by treating silver thin films manufactured by thermal evaporation method with oxygen plasma afterglow. Results show that close values of the relative area and spectral width of the plasmon response peaks in the optical absorption/photoluminescence spectra were obtained in the case of samples with high oxygen content. In addition, the intensity ratio (I_absorption/I_luminescence) of these samples decreases linearly with increasing silver oxide grain size.

     

Optical Characteristics of the Phototroph Thiocapsa roseopersicina and Implications for Real-Time Monitoring of the Bacteriochlorophyll Concentration

Optical characteristics of a Thiocapsa roseopersicina culture and environmental samples containing T. roseopersicina were investigated in the spectral range of 400 to 1,100 nm (absorption coefficient, diffuse attenuation coefficient, and reflectance). Specific absorption coefficients of T. roseopersicina at wavelengths of 480, 520, 550, 580, 805, 860, and 880 nm were determined. It is suggested that the optical properties of T. roseopersicina in the near-infrared range of 800 to 930 nm, confirmed in this study, may be used for development of remote sensing techniques for real-time monitoring of T. roseopersicina and other bacteriochlorophyll a-containing microbes.