We report on the time-dependent light scattering from single gold nanospheres (diameter about 90 nm) and nanorods (15x25 nm). Unlike the recent report by S&diaero;nnichsen and Alivisatos (Nano Lett. 5, 301-304, 2005), we observed the dynamic modulation of scattering intensity by using unpolarized dark field microscopy equipped with a digital camera. The changes in light scattering intensity from gold nanorods were caused by 3-dimensional rotational diffusion by contrast to 2-dimensional polarized-scattering modulation observed previously. In the case of 90-nm gold nanospheres, the light scattering modulation was related to the translational diffusion only. By using T-matrix method and Rayleigh approximation, we describe the time-dependent variations in light scattering intensity caused by rotation of nanorods at several scattering and orientation geometry. Finally, we present preliminary data on real-time visualization of active interaction between the living rat peritoneal macrophages and gold nanorods.

The sensitivity of the gold nanoshell localized plasmon resonance (LPR) to the local dielectric environment is studied in terms of a multilayered sphere with a silica core, gold nanoshell, and two dielectric modeling the primary functionalization of gold surface and the secondary binding of target biomolecules. The adsorption-induced changes in the extinction and scattering spectra are analyzed by the dipolar Rayleigh approximation and multilayered Mie codes for gold shell diameters 20-160 nm and (gold shell thickness)/(gold shell diameter) ratios 0.025-0.75. The dependence of the LPR extinction and scattering spectral shifts on the conjugate structure can be well described by an analytical expression derived in the dipole approximation. Our analysis predicts greater sensitivity of nanoshell's LPR to the local dielectric environment as compared to the solid gold spheres, whereas the absolute changes in spectral maxima are less than those for the equivolume spheres. By contrast, the differential extinction and scattering spectra of gold nanoshells can be used as a sensitive tool for optical monitoring of biomolecular binding onto nanoshell surface. The maximal local-environment sensitivity has been found for the gold (shell/radius) ratios within the range 0.2-0.4.

Recently, the first applications of gold nanoshells (Halas and co-workers, 2003), nanospheres and nanosphere clusters (Anderson and co-workers, 2003; Zharov and co-workers, 2003) to the cancer cell diagnostics and laser killing of cancer cells (LKCC) have been reported. However, to be clinically relevant, existing technologies must overcome fundamental problems related with limitations of current understanding the relationship between the nanoparticle/cluster parameters (size, shape, particle/cluster structure, etc.) and the efficiency of LKCC therapy, as well as with limitations of the available methods for synthesis and in situ characterization of new advanced nanoparticles and clusters with unique synergistic properties which are crucial for selective LKCC therapy. Here we report on preliminary simulation results aimed at finding the optimal cluster structures for maximal absorption efficiency of laser radiation. We consider also alternative possibilities related with using gold nanorods and nanoshells instead of spherical particles. Two types of nanostructures are studied: (1) bioconjugates of single nanoparticles (spheres, nanoshells, and nanorods); (2); linear chains, 2D lattice arrays, and 3D clusters of gold spheres or conjugates that mimic aggregation of nanoparticles on or within cancer cells. By using the generalized multiparticle Mie solution and different versions of the cluster T-matrix method, we calculated the absorption efficiency of nanostructures under study. The gold nanoshells and nanorods with tunable spectral resonances are shown to be more effective photothermal labels as compared to usual solid gold spheres. In the case of 1D-3D clusters, the interparticle separations and short linear chain fragments are the main structural parameters determining the absorption efficiency

A new variant of a technique for in vivo production of antibodies to various antigens with colloidal-gold nanoparticles as carrier is discussed. With this technique we obtained highly specific and relatively high-titre antibodies to different antigens. The antibodies were tested by an immunodot assay with gold nanoparticle markers. Our results provide the first demonstration that immunization of animals with colloidal gold complexed with either haptens or complete antigens gives rise to highly specific antibodies even without the use of complete Freund's adjuvant. These findings may attest to the adjuvanticity of gold nanoparticles itself. We provide also experimental results and discussion aimed at elucidation of possible mechanisms of the discovered colloidal-gold-adjuvanticity effect.

We present analytical solutions for polarizability of small metal particles such as nanoshells, nanorods, and bispheres. The optical model of the gold nanoshell conjugates with biopolymers is treated in terms of a multilayered spherical particle with a silica core covered by a gold shell and by two inhomogeneous dielectric shells that simulate effect of primary adsorption of recognizing molecules followed by the target molecules binding. To calculate the optical polarizability of the multilayered particle, we develope a simple analytical method based on a principle of the dipole equivalency of the multilayered conjugate and its homogeneous counterpart. This is used to derive simple relations between the parameters of the local dielectric environment and the gold nanoshell structure. To calculate the optical polarizability of axially symmetrical metal nanorods, we use the electrostatic limit of the extended boundary conditions method (EBCM) to derive an integral formula for the geometrical depolarization factor. This solution is exemplified by application to the right circular cylinders and s-cylinders with semi-spherical ends. Finally, we derive analytical solutions for the electrodynamic and electrostatic optical polarizabilities of a small metal bisphere by using the discrete dipole approximation (DDA). The electrostatic solution is examined by the comparison of extinction spectra with the exact T-matrix calculations.

The optical properties of emulsion nanocomposite materials based on powder silicon are studied. The method of creation of a new type of emulsion composite, allowing the control of the spectral structure of transmitted electromagnetic radiation is reported. Two series of powder silicon, containing SiO_x (type 1) and SiO_x + SiN_x (type 2) depending on conditions were obtained and investigated. The results of FTIR-spectroscopy of powder silicon claimed the formation of SiO₂ and SiO_x phases on the surface layer of sample type 1 and the formation of nitride phase on the surface layer of sample type 2. The Raman Spectroscopy investigation of two series samples allowed to appreciate the dimensions of nanoparticles and phase structure in powder silicon. The Raman Spectra of samples type 1 and type 2 at the region of 500-600 cm^-1 demonstrated that our powder silicon is nanocristalline silicon with dimension of d=10±2 nm for type 1 and d=13±2 nm for type 2. We prepared emulsion composite samples with nanocristalline silicon; the test run of these materials was performed. The Spectra of optical density as well as the spectra of transmission and diffusive reflection into integrative sphere were measured for both types of samples. It was shown that the samples of type 2 are preferable as main protective ingredients of sunscreens.

We have experimentally investigated for the first time the electro-optical response of polymer dispersed liquid crystals (PDLC) doped with multi-wall carbon nanotubes (MWCNT). Undoped PDLC and PDLC doped with MWCNT were studied. Principal transmittances of the films and angular distributions of scattered light were measured as the functions of applied voltage. Anomalous electro-optical response of PDLC doped with MWCN was observed with cross-polarized light. Carbon nanotubes influence on the droplet director orientation in PDLC was found. The obtained results are discussed in terms of the model which takes into account the partial orientation of liquid crystal droplets in PVA matrix together with the presence of carbon nanotubes.

The properties of dichroic objects are discussed for a number of special cases where a specific constituent anisotropy is arbitrary. It is shown that a dichroic behavior in general may allow for the presence of birefringent mechanisms provided that they satisfy certain limitations. Corresponding Mueller matrices and their eigenpolarizations are derived for each case.

On the basis of the generalized Mueller matrix (Mar'enko and Savenkov, Optics and Spectroscopy, 76, 94-96, 1994), the structure of the incomplete Mueller matrix has been proposed for solving the inverse problem for homogeneous anisotropic medium. The expressions for the anisotropy parameters are obtained. The stability of the obtained expressions is considered.

Polarized light interaction with inhomogeneous linear birefringent crystalline medium in single scattering approach has been built. Mueller matrix of the medium has been calculated theoretically. Polarization characteristics of the scattered light behind the screen have been investigated.

In this paper an influence of imperfections of polarizing elements imaging Muller-polarimeter on accuracy of measurement is investigated. The operating of polarimeter is based on three probing polarization method (). The optimal scheme of polarimeter was chosen and recommendations on a selection of its parameters were produced.

Some recent advances in the optical analysis of anisotropic media, especially those, related with work of our group at National Institutes of Health, are presented. Comparison of theoretical formulas, obtained from random walk theory with available time-resolved (transmission mode) and polarization CW (reflectance mode) experimental data is discussed.

The statistics of light deflection by interfaces between two media is analytically related with the angular probability density between the normal to the interface and the incident beam. In the proposed model all reflection and refraction events are considered as independent with statistical weights equal to Fresnel intensity coefficients. The calculus of phase matrixes of light deflection resulting in the interaction with the randomly oriented interface is proposed. The balance of integrated probabilities of reflected and refracted photons from both sides of the interface allowed quantitative estimates of the probability of photons to be situated in different phases of inhomogeneous media.

Paper samples with a grammage between 50-200 g/m² were compressed from 313 to 1105 kg/m³. During pressing, laser pulses were shot through them and delays in pulse propagation and light transmission in the compressed paper were observed with a streak-camera. The results show that the transmitted intensity depends mainly on the paper's grammage and is inversely proportional to it. Contrary to earlier TOF lidar measurements conducted during compression, delays in the propagation of photons decreased in paper samples with a grammage smaller than 280 g/m². This result suggests that there is a grammage limitation at about 100 g/m². When a streak-camera is used it allows the transmittance and propagation delay of photons to be obtained concurrently. As a result, changes in grammage and thickness can be evaluated separately. In addition, the paper presents a light transmittance and propagation delay dependent equation for porosity.

The transport properties of densely packed layers of titanium dioxide (rutile) powder are studied in visible and near infrared region by measuring coherent backscattering (CBS). Fitting of the experimental data with the coated coherent potential approximation led to evaluation of the transport parameters (such as transport mean free path and effective refractive index) of studied samples without a-priori knowledge of the optical properties of scattering particles.

Application of polarized probe light and polarization discrimination of backscattered light give the additional possibilities for characterization and imaging of various diseases localized in superficial layers of tissues because of the high sensitivity of polarization state of multiply scattered light, which is detected in the backscattering mode, to alterations in optical parameters of the probed tissue. In this work we compare two methods of analysis of multiple scattering anisotropic media (demineralized bone), such as laser videoreflectometry and method of coherent backscattering. The agreement between results obtained with these two techniques is satisfactory.

The reconstruction method of the human skin intrinsic fluorescence spectra distorted by "the screen effect" was proposed. The method is based on the fact that fluorescence and reflectance spectra are formed by the same absorption and scattering properties of the media. Therefore diffuse reflectance spectrum can be used for fluorescence spectrum reconstruction. The intrinsic fluorescence spectral profiles restoration was tested experimentally using scattering media (phantoms, solutions) with a fluorescent dye and hemoglobin as a strong absorber producing inner-filter distortions. The correction produces the fluorescence spectrum profiles same to the one measured from the corresponding sample with an infinitely low absorption. In this paper we present the results of the fluorescence spectra reconstruction using coefficient &sqrt;R_d(λ) as a correction factor.

The low-coherence reflectometry (LCR) technique was used to examine the transport properties of dense suspensions of scattering particles in the course of particle sedimentation and aggregation. The shapes of backscattered signal and the reflectance of the layers of sedimented particles measured with the use of an OCT system in A-scan mode at various stages of sedimentation were analyzed in order to characterize the time-dependent alterations in transport properties (the transport mean free path and the transport albedo) of studied scattering media (water suspensions of polystyrene beads). The role of the static structure factor of the examined scattering systems in transport of light at high scatter concentrations is discussed. The influence of scattering anisotropy on the scatter correlation effect is analyzed on the base of experimental data obtained with various values of the scatter size and the wavelength of probe light. The potential of LCI technique for characterization of the structure of sedimented substances is discussed.

Features of simultaneous manifestation of longitudinal spatial coherence and temporal coherence under different viewing conditions - angular spectrum width and form, frequency spectrum width and thickness of nondispersive layer in one of the arms of the interferometer - are discussed.

Dynamic Light Scattering together with Diffusing Wave Spectroscopy are common and well acknowledged techniques to study micro and macro dynamics of a complex media. In the past these methods were successfully applied for the characterization of colloidal particles of different kind, foam, sand, interfacial boundaries, blood cells etc. The shape and decay of auto-correlation function (ACF) of scattered light intensity fluctuations are used to study the type and time scale of scatters dynamics. This is usually done by collecting the light by a point-like detector for a time period much larger than the correlation time. But in case of slow or arrested scatter motion the obtained time-averaged ACF may depend on the detector position (non-ergodicity problem). Special averaging techniques required for this case are presented in the current paper.

The method of increasing the resolution of an optical addressing system is proposed. To increase the resolution, a nonlinear element, a cell filled with dye solution, is placed in the focal plane of the focusing lens. A dynamic lens induced by a controllable light beam in a photochrome dye is used. The performance of the dynamic lens formed in the photochrome medium was investigated. The results of investigation of a reversible light-sensitive crown-bearing medium are presented. It was found experimentally that the resolution of the optical addressing system can be increased by an order of magnitude if the solution of a phitichrome crown-bearing dye is used. The article is arranged as follows. In p. 2, the principle of the new addressing system with the increased resolution is described; its main advantages compared to conventional systems are illustrated. In p. 3, a new nonlinear element is described. The prototype of the element is implemented. Its properties are investigated. In p. 4, the results of experiments are presented.

In this paper we present the model of photographic image formation and the light leakage at emulsion layers of photographic materials. Result of modelling is spatial distribution of exposed silver grains at photographic emulsion layers. We found the influence of some photographic material parameters to image characteristics. Distribution of optical density for real images and results of modeling are also presented.

CMOS APS Active Pixel Sensors (APS) are very important among others because of their possible technical innovations leading to ultra-low power image acquisition or efficient on-chip image preprocessing. The design of the novel CMOS is presented in the first part of the paper. The general principle of analog interpixel subtraction is described. The edge detection algorithm for analog realization and patented focal plane circuits for analog image preprocessing (signals subtraction, addition, and edge detection) are described. Implementation of the image processing tasks (focal plane preprocessing and subsequent image processing) can be done effectively only with the consideration of known transfer characteristics of the imager itself. In the second part of the paper we present analysis of those characteristics. Geometrical Point Spread Function (PSF) depends on the certain geometric shape of active area in the particular design of CMOS APS. In this paper the concept of Modulation Transfer Function (MTF) analysis is generalized to be applicable to the sampled structures of CMOS APS. Recalling theoretical results we have analytically derived the detector MTF in the closed form for some special active area shapes.

Some results obtained with developed high resolution scanning acoustical microscope are shown in the present paper. Created systems are provided with the set of acoustical objectives for working frequencies from 25 MHz to 1 GHz having different apertures of sound beam and different focus distances. Designed and developed system is capable for capturing both bulk acoustical images, as well as the plane images obtained as cuts in desirable section of an object; so, so-called B-scan as well as C-scan are realized. The presence of noise strongly reduces their quality. To solve this problem it is possible to use methods of mathematical processing. The application of this method allows receiving bulk acoustic images with very high resolution. In the present work the application of four such methods in comparison is considered.

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We propose an effective elastography technique in which an acoustic radiation force is used for remote palpation to generate localized tissue displacements, which are directly correlated to localized variations of tissue stiffness and are measured using a light probe in the same direction of ultrasound propagation. The experimental geometry has provision to input light beam along the ultrasound propagation direction, and hence it can be prealigned to ensure proper interception of the focal region by the light beam. Tissue-mimicking phantoms with homogeneous and isotropic mechanical properties of normal and malignant breast tissue are considered for the study. Each phantom is insonified by a focusing ultrasound transducer (1 MHz). The focal volume of the transducer and the ultrasound radiation force in the region are estimated through solving acoustic wave propagation through medium assuming average acoustic properties. The forward elastography problem is solved for the region of insonification assuming the Lame's parameters and Poisson's ratio, under Dirichlet boundary conditions which gives a distribution of displacement vectors. The direction of displacement, though presented spatial variation, is predominantly towards the ultrasound propagation direction. Using Monte Carlo (MC) simulation we have traced the photons through the phantom and collected the photons arriving at the detector on the boundary of the object in the direction of ultrasound. The intensity correlations are then computed from detected photons. The intensity correlation function computed through MC simulation showed a modulation whose strength is found to be proportional to the amplitude of displacement and inversely related to the storage (elastic) modulus. It is observed that when the storage modulus in the focal region is increased the computed displacement magnitude, as indicated by the depth of modulation in the intensity autocorrelation, decreased and the trend is approximately exponential.

In this paper, we present a wavelet-based approach to solve the non-linear perturbation equation encountered in optical tomography. A particularly suitable data gathering geometry is used to gather a data set consisting of differential changes in intensity owing to the presence of the inhomogeneous regions. With this scheme, the unknown image, the data, as well as the weight matrix are all represented by wavelet expansions, thus yielding the representation of the original non-linear perturbation equation in the wavelet domain. The advantage in use of the non-linear perturbation equation is that there is no need to recompute the derivatives during the entire reconstruction process. Once the derivatives are computed, they are transformed into the wavelet domain. The purpose of going to the wavelet domain, is that, it has an inherent localization and de-noising property. The use of approximation coefficients, without the detail coefficients, is ideally suited for diffuse optical tomographic reconstructions, as the diffusion equation removes most of the high frequency information and the reconstruction appears low-pass filtered. We demonstrate through numerical simulations, that through solving merely the approximation coefficients one can reconstruct an image which has the same information content as the reconstruction from a nonwaveletized procedure. In addition we demonstrate a better noise tolerance and much reduced computation time for reconstructions from this approach.

Reconstructions in optical tomography involve obtaining the images of absorption and reduced scattering coefficients. The integrated intensity data has greater sensitivity to absorption coefficient variations than scattering coefficient. However, the sensitivity of intensity data to scattering coefficient is not zero. We considered an object with two inhomogeneities (one in absorption and the other in scattering coefficient). The standard iterative reconstruction techniques produced results, which were plagued by cross talk, i.e., the absorption coefficient reconstruction has a false positive corresponding to the location of scattering inhomogeneity, and vice-versa. We present a method to remove cross talk in the reconstruction, by generating a weight matrix and weighting the update vector during the iteration. The weight matrix is created by the following method: we first perform a simple backprojection of the difference between the experimental and corresponding homogeneous intensity data. The built up image has greater weightage towards absorption inhomogeneity than the scattering inhomogeneity and its appropriate inverse is weighted towards the scattering inhomogeneity. These two weight matrices are used as multiplication factors in the update vectors, normalized backprojected image of difference intensity for absorption inhomogeneity and the inverse of the above for the scattering inhomogeneity, during the image reconstruction procedure. We demonstrate through numerical simulations, that cross-talk is fully eliminated through this modified reconstruction procedure.