Here we demonstrate a novel surface plasmon polariton (SPP) microscope which is capable of imaging below the optical diffraction limit. A plasmonic lens, generated through phase-structured illumination, focuses SPPs down to their diffraction limit and scans the focus with steps as small as 10 nm. This plasmonic lens is implemented on a metallic nanostructure consisting of alternating hole array gratings and bare metal arenas. We use subwavelength scattering holes placed within the bare metal arenas to determine the resolution of our microscope. The resolution depends on the size of the scanning SPP focus. This novel technique has the potential for biomedical imaging microscopy, surface biology, and functionalization chemistry.

We study and actively control the coherent properties of Surface Plasmon Polaritons (SPPs) optically exited on a nano-hole array. Amplitude and phase of the optical excitation are externally controlled via a digital spatial light modulator (SLM) and SPP interference fringe patterns are observed with high contrast. Our interferometric observations revel SPPs dressed with the Bloch modes of the periodic nano-structure. The momentum associated with these Dressed Plasmons (DP) is highly dependent on the grating period and fully matches our theoretical predictions. We show that the momentum of DP waves can in principle exceed the SPP momentum. Actively controlling DP waves via programmable phase patterns offers the potential for high field confinement applicable in sensing, Surface Enhanced Raman Scattering and plasmonic structured illumination microscopy.

We present a study of optical transport properties of powder layers with submicrometer, strongly scattering gallium arsenide (GaAs) particles. Uniform, thin samples with well controlled thicknesses were created through the use of varying grinding times, sedimentation fractionation, annealing, and a new sedimentation technique. These fabrication parameters were optimized to produce maximum scattering and minimum absorption. The physical properties were characterized using scanning electron microscopy (SEM) and x-ray diffraction. The optical transport mean-free path, absorption length, and the diffusion constant were determined for each sample using both continuous wave and time-resolved methods. The samples scatter strongly in the near infrared region. Total reflection and transmission measurements show that all of these samples have high absorption. X-ray diffraction results suggest that the source of this absorption is grinding induced strain and/or defects in the crystal structure. For all the different grinded GaAs powder samples that we investigated, the absorption length was less than ten micrometers.

We study and actively control the coherent properties of surface plasmon polaritons (SPPs) optically excited on a nanohole array. Amplitude and phase of the optical excitation are externally controlled via a digital spatial light modulator (SLM) and SPP interference fringe patterns are designed and observed with high contrast. Our interferometric observations reveal SPPs dressed with the Bloch modes of the periodic nanostructure. The momentum associated with these dressed plasmons (DP) is highly dependent on the grating period and fully matches our theoretical predictions. We show that the momentum of DP waves can, in principle, exceed the SPP momentum. Actively controlling DP waves via programmable phase patterns offers the potential for high field confinement applicable in lithography, surface enhanced Raman scattering, and plasmonic structured illumination microscopy.

McGregor, Stephen J PhD; Johnson, Patrick M MS; Madrigal, David MS; Levine, Sheldon MS; Rubenfire, Melvyn MD Author Information

We introduce a new approach for measuring both the transport and the efiective medium proper- ties of light propagation in inhomogeneous media. These properties include the difiusion constant, the path length distribution, and the efiective index of refraction. Our method utilizes the equiv- alence of frequency variation with a change in the index of refraction. A new correlation function that describes correlations in both frequency and index of refraction is introduced. Experimentally, we measure this correlation via spectrally resolved refractive index tuning (RIT), controlling the latter via changes in the ambient pressure. Our new generic measurement technique can be used to characterize a wide variety of materials, including photonic crystals, random photonic media, photonic meta-materials, and certain porous biological samples like bone and wood. Optical properties of quenched random samples are dominated by speckle, a highly irregular intensity pat- tern dependent upon spatial (or angular) or time (or fre- quency) coordinates and brought about by interference. Correlations, which are inherent properties of speckle de- spite the apparent irregularity, provide important infor- mation about transport parameters. In fact, the descrip- tion of intensity correlations is at the heart of under- standing transport theory (1). In the past, correlations have been measured in time (2) and frequency (3) as a means of, for example, determining the difiusion constant of light. What is often overlooked is the degree to which ef- fective medium properties are essential for determining correlation functions, and thereby transport properties. Indeed, the importance of the efiective medium, in some sense, exceeds that of the transport properties as the lat- ter only becomes important when the material is turbid. Furthermore, when developing a theory of transport, the efiective medium is used as a building block. That is to say, the difiusion constant of light depends on the average index of refraction but not the other way around. In this letter we propose a new correlation function de- pendent on both the efiective index of refraction and the frequency. By tuning the efiective index and measuring intensity-intensity correlations, we show that a variety of transport properties of the sample can be measured in an entirely new way. Furthermore, by combining mea- surements of refractive index correlations with frequency correlations, the concept of efiective medium is directly tested. This type of efiective medium measurement is unprecedented, in that it is not afiected by surface irreg- ularities, does not require a coherently transmitted beam, and can be measured for any irregular sample shape. This new parameter allows for transport properties to be determined without resorting to gross approximations for the efiective medium. Given the importance of un- derstanding disorder in a wide variety of flelds including biology (4), advanced materials (5), solar cells (6), and in general modern photonics, we expect our approach to have broad cross-disciplinary application. Our method is based on controlled change of the op- tical path length distribution by refractive index tuning (RIT). It is the optical analogue of a class of experiments in condensed matter physics that control the elongation of electron trajectories by using magnetic fleld. Those ex- periments resulted in the observation of electronic weak localization and universal conductance ∞uctuations (7). Due to its simplicity and high precision, RIT measure- ments can be applied to a diverse set of rigid samples, which cannot be analyzed by other dynamic methods due to the limitation of time (or frequency) resolution. The concept of changing the optical path length distri- bution has also been exploited for difiusing wave spec- troscopy (8, 9), and for other types of waves in evolving media (10{12). We begin by deflning the following correlation func- tion:

We introduce a new approach for measuring both the effective medium and the transport properties of light propagation in heterogeneous media. Our method utilizes the conceptual equivalence of frequency variation with a change in the effective index of refraction. Experimentally, we measure intensity correlations via spectrally resolved refractive index tuning, controlling the latter via changes in the ambient pressure. Our experimental results perfectly match a generalized transport theory that incorporates the effective medium and predicts a precise value for the diffusion constant. Thus, we directly confirm the applicability of the effective medium concept in strongly scattering materials.

atrick M. Johnson d Lagendijk OM Institute for Atomic and Molecular Physics AMOLF cience Park 113 msterdam 1098 XG he Netherlands Abstract. We have developed several new experimental model systems that demonstrate anisotropic diffusion of light. These systems, consisting of aligned fibers, stretched plastic foam, and stretched plastic frit, have relatively simple microstructures and are easily sliced, making them ideal for testing theoretical models of diffusion. We demonstrate that the solution to the diffusion equation for arbitrary orientation of the diffusion tensor is consistent with experimental measurements. We also show that simple models of microstructure, based on cylindrical and planar scatterers, are consistent with the experimental results. These models provide simple analytical expressions for predicting the degree of alignment of the scatterers from diffuse transmission measurements. The combination of experimental results and theoretical support demonstrates both the power and the limitations of the diffusion model for providing information about microstructure via simple experiments and modeling. © 2009 Society of PhotoOptical Instrumentation Engineers. DOI: 10.1117/1.3253332

We have experimentally measured the distribution of the second-harmonic intensity that is generated inside a highly scattering slab of porous gallium phosphide. Two complementary techniques for determining the distribution are used. First, the spatial distribution of second-harmonic light intensity at the side of a cleaved slab has been recorded. Second, the total second-harmonic radiation at each side of the slab has been measured for several samples at various wavelengths. By combining these measurements with a diffusion model for second-harmonic generation that incorporates extrapolated boundary conditions, we present a consistent picture of the distribution of the second-harmonic intensity inside the slab. We find that the ratio l(2w)/L-c of the mean free path at the second-harmonic frequency to the coherence length which was suggested by some earlier calculations, cannot describe the second-harmonic yield in our samples. For describing the total second-harmonic yield, our experiments show that the scattering parameter at the fundamental frequency k(1w)l(1w) is the most relevant parameter in our type of samples. (C) 2009 Optical Society of America

We demonstrate a method for fully characterizing diffuse transport of light in a statistically anisotropic opaque material.Our technique provides a simple means of determining all parameters governing anisotropic diffusion.Anisotropy in the diffusion constant, the mean free path, and the extrapolation length are, for the first time, determined independently.These results show that the anisotropic diffusion model is effective for modeling transport in anisotropic samples, providing that the light is allowed to travel several times the transport mean free path from the source.

We describe the synthesis and characterization of stable suspensions of monodisperse fluorescently labeled silica dumbbell particles. Pure dispersions of silica dumbbells with center-to-center lengths from 174 nm to 2.3 microm were produced with a variety of aspect ratios. Individual particles in concentrated dispersions of these particles could be imaged with confocal microscopy. These particles can be used as a colloidal model system for addressing fundamental questions about crystal and glass formation of low-aspect-ratio anisotropic particles. They also have potential in photonic applications and electro-optical devices.

We describe the synthesis and the physical properties of suspensions of colloidal silicon and silica rodlike particles. In addition to pure silicon and pure silica rods, we have also synthesized silicon rods with a silica shell and silica rods with a fluorescent silica layer. Pre-patterned p-type (100) silicon wafers were electrochemically etched in electrolyte solutions containing hydrogen fluoride. By the current density being varied while etching, macropores were etched with controllable modulated pore diameters. These silicon structures were transformed into rods with indentations 5.5 mum apart and with lengths up to 100 mum using iterative oxidation in air and dissolution of the silica by HF. Complete oxidation of these rods was also achieved. Sonication of the modulated rods resulted in monodisperse particles of 5.5 mum length and 300 nm width. A high yield of 10(12) particles, or more, is possible with this method. At high concentrations, these particles show nematic ordering in charge-stabilized suspensions. The oxidized silica outer layer of the silicon rods makes the further growth of silica in solution or on a wafer possible. This allows for control of the particles' interaction potential. Labeling with a fluorescent dye and index matching of the complete silica rods enable the study of concentrated dispersions quantitatively, on a single particle level, with confocal microscopy. Because of their high refractive index in the near-IR, the nematic phases of rods with a silica core are also interesting for photonic applications.

0599 PURPOSE: The purpose of this investigation was to determine the activity of MyoD, p53 and creatine kinase (CK) in confluent myoblasts and differentiating myotubes, and to quantify the effect of myostatin (MSTN) treatment on these factors in confluent myoblasts. MSTN, a member of the transforming growth factor beta (TGF-â) family of cytokines, negatively regulates skeletal muscle growth by inhibiting both skeletal muscle proliferation and differentiation. Expression of the muscle regulatory factor MyoD is down regulated by MSTN, and this has been proposed as the underlying mechanism of MSTN's effect on skeletal muscle differentiation. Expression of another transcription factor, the tumor suppressor protein p53, is increased with MSTN over-expression in myoblasts. Because p53 cooperates with MyoD and promotes expression of the muscle specific gene creatine kinase (CK), it was of interest to determine if MSTN treatment would affect activity of either of these transcription factors. METHODS: Nuclear extracts of C2C12 skeletal myoblasts were obtained at 80 % confluence and after 1 through 7 days of differentiation to establish time of greatest transcription factor activity using the TransAm assay (Active Motif, Carlsbad, CA). CK activity was determined using CK reagent (Sigma Diagnostics, St. Louis, MO). Activity of all factors was corrected for protein content using a BCA protein assay. RESULTS: MyoD activity exhibited a biphasic pattern, which peaked at confluence, declined from days 1–6, and increased again at day 7 of differentiation (p = 0.008). Activity of p53 exhibited a similar pattern to that of MyoD, with peak activity occurring at confluence. Because maximal MyoD and p53 activity were determined to occur at 80 % confluence, treatment with recombinant MSTN (10 ug/ml) was initiated 24 h after seeding and maintained for 48 h, while PBS was added to control cultures. In confluent myoblasts, MSTN treatment decreased the activity MyoD (p = 0.002), p53 (p = 0.007), and CK (P = 0.046). CONCLUSIONS: These data provide unique evidence of the biphasic pattern of activity exhibited by MyoD in the transition from proliferation to, and during the progression of differentiation in cultured myocytes. Additionally, it is shown that MSTN inhibits MyoD, p53, and CK activity in confluent myoblasts. Future studies will examine the effect of MSTN in myotubes during the later stages of differentiation, during concurrent peak MyoD, p53 and CK activity.

The transport of light in complex dielectric materials is a rich and fascinating topic of research. With complex dielectrics we intend dielectric structures with an index of refraction that has variations on a length scales that is very roughly comparable to the wavelength. Such structures strongly scatter light. A possible building block for constructing a complex dielectric is a micro sphere of diameter comparable to the wavelength and of a certain refractive index that is different from its surrounding medium. The single scattering from such a sphere has a rich structure due to internal resonances in the sphere, but its behaviour is well-understood and can be calculated using the formalism of Mie-scattering [1]. A complex dielectric material can then be realized by micro-assembly of several micro spheres.

Measurements of the angular-resolved-optical transmission through strongly scattering samples of porous gallium phosphide are described. Currently porous GaP is the strongest-scattering material for visible light. From these measurements the effective refractive index and the average reflectivity at the sample interface can be obtained. These parameters are of great importance for an accurate interpretation of optical experiments, and are for the first time determined in strongly scattering samples.

Light transport in macroporous gallium phosphide, perhaps the strongest nonabsorbing scatterer of visible light, is studied using phase-sensitive femtosecond pulse interferometry. Phase statistics are measured at optical wavelengths in both reflection and transmission and compared with theory. The diffusion constant of light is measured in both reflection and transmission as a function of thickness and compared with theories for diffusive transport and localization. An unusually high energy velocity due to the bicontinuous structure of the porous network is reported. For such strongly scattering samples, we show that surface properties and the effective index of refraction need to be treated carefully.

A high resolution null-transmission ellipsometry system has been developed for measurement of the optical properties of liquid crystal free-standing films. The ellipsometric parameters are measured to within a resolution of 0.002degrees from samples held in a sealed, temperature-controlled environment. By measuring the ellipsometric parameters as a function of applied electric field orientation, the optical symmetry and molecular orientations of free-standing liquid crystal films can be determined in some cases. Three carefully selected applications of this technique are presented.