Showing papers in "Journal of Nanophotonics in 2011"

Electric and magnetic dipolar response of germanium nanospheres: interference effects, scattering anisotropy, and optical forces

Abstract: Thecoherentcombinationofelectricandmagneticresponsesisthebasisoftheelectro- magnetic behavior of new engineered metamaterials. The basic constituents of their meta-atoms usually have metallic character and consequently high absorption losses. Based on standard "Mie" scattering theory, we found that there is a wide window in the near-infrared (wavelengths 1t o 3μm), where light scattering by lossless submicrometer Ge spherical particles is fully described by their induced electric and magnetic dipoles. The interference between electric and magneticdipolarfieldsisshowntoleadtoanisotropicangulardistributionsofscatteredintensity, including zero backward and almost zero forward scattered intensities at specific wavelengths, which until recently was theoretically established only for hypothetically postulated magnetodi- electric spheres. Although the scattering cross section at zero backward or forward scattering is exactly the same, radiation pressure forces are a factor of 3 higher in the zero forward condition.

Optical properties of nanostructured materials: a review

Abstract: Depending on the size of the smallest feature, the interaction of light with structured materials can be very different. This fundamental problem is treated by different theories. If first order theories are sufficient to describe the scattering from low roughness surfaces, second order or even higher order theories must be used for high roughness surfaces. Random surface structures can then be designed to distribute the light in different propagation directions. For complex structures such as black silicon, which reflects very little light, the theory needs further development. When the material is periodically structured, we speak about photonic crystals or metamaterials. Different theoretical approaches have been developed and experimental tech- niquesarerapidlyprogressing.However,someworkstillremainstounderstandthefullpotential of this field. When the material is structured in dimension much smaller than the wavelength, the notion of complex refractive index must be revisited. Plasmon resonance can be excited by a progressing wave on metallic nanoparticles inducing a shaping of the absorption band and of the dispersion of the extinction coefficient. This addresses the problem of the permittivity of such metallic nanoparticles. The coupling between several metallic nanoparticles induces a field enhancement in the surrounding media, which can increase phenomena like scattering, absorption, luminescence, or Raman scattering. For semiconductor nanoparticles, electron con- finement also induces a modulated absorption spectra. The refractive index is then modified. The bandgap of the material is changed because of the discretization of the electron energy, which can be controlled by the nanometers size particles. Such quantum dots behave like atoms and become luminescent. The lifetime of the electron in the excited states are much larger than in continuous energy bands. Electrons in coupled quantum dots behave as they do in molecules. Manyapplicationsshouldbeforthcominginthenearfutureinthisfieldofresearch. C � 2011Society

Thin-film growth dynamics with shadowing and re-emission effects

Abstract: Growth dynamics of thin-films involves both shadowing and re-emission effects. Shadowing can originate from obliquely incident atoms being preferentially deposited on hills of the surface, which leads to a long range geometrical effect, as well as from an atomic shadowing process that can occur even during normal angle deposition. Re-emission effect is a result of nonsticking atoms, which can bounce off from hills and deposit on valleys of the surface. In the case of an energetic incident flux, re-emission can also originate from a resputtering process that includes a surface atom being knocked off by an incident ion/atom followed by redeposition to another surface point. Due to their long-range nonlocal nature, both the shadowing effect (which tries to roughen the surface) and re-emission effect (which has a smoothening effect) have been shown to be more dominant over local effects such as surface diffusion, and have been proven to be critical processes in accurately determining the dynamic evolution of surface roughness. Recent Monte Carlo simulation methods that involve shadowing, re-emission, surface diffusion, and noise effects successfully predicted many experimentally relevant surface roughness evolution results reported in the literature. For example, root-mean-square surface roughness (ω) of Monte Carlo simulated thin-films have evolved with time t according to a power law behavior ω ∼ t β , with β values ranging from about 0 to 1 for a growth with strong re-emission effects (i.e., low sticking coefficients) and a growth with dominant shadowing effects (i.e., with high sticking coefficients), respectively. Potential future thin-film growth modeling studies are also discussed. These include advanced simulation approaches that can incorporate atomistic details of physical and chemical processes and a recently developed network growth model that can potentially capture some universal aspects of thin-film growth dynamics independent of the details of growth process. C 2011

Nonlinear laser dynamics : from quantum dots to cryptography

Abstract: Part I Nanostructured Devices Modeling Quantum-Dot-Based Devices Kathy Ludge Exploiting Noise and Polarization Bistability in Vertical-Cavity Surface-Emitting Lasers for Fast Pulse Generation and Logic Operations J. Zamora-Munt and Cristina Masoller Mode Competition Driving Laser Nonlinear Dynamics Marc Sciamanna Quantum Cascade Laser: An Emerging Technology Andreas Wacker Controlling Charge Domain Dynamics in Superlattices M. T. Greenaway, Alexander G. Balanov, E. Scholl, and T.M. Fromhold Bifurcation Study of a Semiconductor Laser with Saturable Absorberand Delayed Optical Feedback Bernd Krauskopf and Jamie J. Walker Modeling of Passively Mode-Locked Semiconductor Lasers Andrei G. Vladimirov, Dmitrii Rachinskii, and Matthias Wolfrum Dynamical and Synchronization Properties of Delay-Coupled Lasers C.M. Gonzalez, M.C. Soriano, M.C. Torrent, J. Garcia-Ojalvo, and Ingo Fischer Complex Networks Based on Coupled Two-Mode Lasers Andreas Amann Part III Synchronization and Cryptography Noise Synchronization and Stochastic Bifurcations in Lasers Sebastian M. Wieczorek Emergence of One- and Two-Cluster States in Populations of Globally Pulse-Coupled Oscillators Leonhard Lucken and Serhiy Yanchuk Broadband Chaos Kristine E. Callan, Lucas Illing, and Daniel J. Gauthier Synchronization of Chaotic Networks and Secure Communication Ido Kanter and Wolfgang Kinzel Desultory Dynamics in Diode-Lasers: Drift, Diffusion, and Delay K. Alan Shore

Single photon emission and detection at the nanoscale utilizing semiconductor nanowires

Abstract: We report recent progress toward on-chip single photon emission and detection in the near infrared utilizing semiconductor nanowires. Our single photon emitter is based on a single InAsP quantum dot embedded in a p-n junction defined along the growth axis of an InP nanowire. Under forward bias, light is emitted from the single quantum dot by electrical injection of electrons and holes. The optical quality of the quantum dot emission is shown to improve when surrounding the dot material by a small intrinsic section of InP. Finally, we report large multiplication factors in excess of 1000 from a single-Si-nanowire avalanche photodiode comprised of p-doped, intrinsic, and n-doped sections. The large multiplication factor obtained from a single Si nanowire opens up the possibility to detect a single photon at the nanoscale.

Nanoreplicated positive and inverted submicrometer polymer pyramid array for surface-enhanced Raman spectroscopy

Abstract: We demonstrated gold-coated polymer surface enhanced Raman scattering (SERS) substrates with a pair of complementary structures—positive and inverted pyramid array struc- turesfabricatedbyamultiple-stepmoldingandreplicationprocess.TheuniformSERSenhance- ment factors over the entire device surface were measured as 7.2×10 4 for positive pyramid sub- strates while 1.6×10 6 for inverted pyramid substrates with Rhodamine 6G as the target analyte. Based on the optical reflection measurement and finite difference time domain simulation result, the enhancement factor difference is attributable to plasmon resonance matching and to SERS "hot spots" distribution. With this simple, fast, and versatile complementary molding process, we can produce polymer SERS substrates with extremely low cost, high throughput, and high repeatability. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). (DOI: 10.1117/1.3663259)

Preparation of nanostructured ultrathin silver layer

Abstract: Silver is widely used for a fabrication of plasmonic devices due to its unique optical constants. Nanostructured Ag layer can exhibit strong localized surface plasmon resonance, which mainly affects its optical behavior in visible and near infrared spectra. The nanostructure of the Ag layer is mainly influenced during the initial stage of the silver nucleation. Therefore we focused our attention on the study of this stage of the silver growth. The nanostructured ultra-thin silver layers were prepared by means of the magnetron sputtering. The nucleation mode and the resulting nanostructure was controlled by the deposition conditions. The initial stage of the nucleation and the layer growth was studied by means of an optical monitoring, which is based on a principle of spectrophotometric measurement of sample reflectivity. The measured data were fitted to a model of layered structure. The non-continual (Volmer-Weber) mode of the layer nucleation was clearly distinguished in the monitored data. Thus we were able to estimate the point of the non-continual layer coalescence as well as the subsequent evolution of the surface roughness. The prepared nanostructured Ag layers were analyzed by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). Optical properties were studied by spectroscopic ellipsometry and spectrophotometry. The aim of this work was to study the formation of nanostructured Ag layer and its correlation to the optical behavior.

Fabrication and realistic modeling of three-dimensional metal-dielectric composites

Abstract: Historically, the methods used to describe the electromagnetic response of random, three-dimensional (3D), metal-dielectric composites (MDCs) have been limited to approximations such as effective-medium theories that employ easily-obtained, macroscopic parameters. Full-wave numerical simulations such as finite-difference time domain (FDTD) calculations are difficult for random MDCs due to the fact that the nanoscale geometry of a random composite is generally difficult to ascertain after fabrication. We have developed a fabrication method for creating semicontinuous metal films with arbitrary thicknesses and a modeling technique for such films using realistic geometries. We extended our two-dimensional simulation method to obtain realistic geometries of 3D MDC samples, and we obtained the detailed near- and far-field electromagnetic responses of such composites using FDTD calculations. Our simulation results agree quantitatively well with the experimentally measured far-field spectra of the real samples.

Spectroscopic ellipsometry of few-layer graphene

Abstract: The optical properties of few-layer graphene (FLG) films were measured in the ultraviolet and visible spectrum using a spectroscopic ellipsometer equipped with a 50-mu m nominal microspot size. The FLG thickness was found by atomic force microscopy. Measurements revealed that the microspot is larger than the FLG flake. The ellipsometric data was interpreted using the island-film model. Comparison with graphite and recently published graphene data showed reasonable agreement, but with some features that could not be explained. The error margin for the optical constants was estimated to be +/- 10%.

Designing super-resolution metalenses by the combination of metamaterials and nanoscale plasmonic waveguide couplers

Abstract: We recently demonstrated a phase compensated metalens that cannot only achieve super-resolution, but also possesses the Fourier transform capability. The metalens consists of a metamaterial slab and a plasmonic waveguide coupler (PWC). We have now ascertained the requirements for the metamaterial and the detailed design principles for the PWCs. Simulations of metalenses with a new type of PWC geometry have confirmed that the new metalenses also possess super-resolution and the Fourier transform function. The hyperbolic metalens shows an anomalous focus shifting behavior, which may be used to design exotic optical systems with new functionalities.

Nonlinear absorption spectra for intersubband transitions of CdSe/ZnS spherical quantum dots

Abstract: The electronic structure and optical properties of a one-electron quantum dot (QD) were investigated by assuming a spherically symmetric confining potential of finite depth. In this particular case CdSe is surrounded by ZnS. The energy eigenvalues and wave functions dependence on QD dimension were calculated by using effective mass approximation. We also calculated energies of s, p, and d states, oscillator strengths, and the linear and third-order nonlinear intersubband optical absorption coefficients as a function of the QD dimension, incident photon energy, and incident optical intensity for the 1s-1p, 1p-1d, and 1p-2s transitions. Even in a simple composition, QD correct calculation of oscillator strength differs from the simplified approach in the most sensitive QD radius region below one Bohr radius.

Effective constitutive parameters of linear nanocomposites in the long-wavelength regime

Abstract: By the process of homogenization, judiciously designed nanocomposite materials can offer unprecedented degrees of material enhancement and/or novel material properties that may be usefully exploited in nanophotonic applications. Recently, there have been significant developments in the theory of such homogenized nanocomposite materials (HNMs), within the context of linear bianisotropic scenarios for particulate nanocomposites. These developments involve: the incorporation of depolarization dyadics, which represent component particles of nonzero volume, and the implementation of the strong-property-fluctuation theory wherein scattering interactions between neighboring component particles are treated on a statistical basis. Four recent areas of application are notable: (i) HNMs that support the propagation of plane waves with negative phase velocity (while their component materials do not); (ii) HNMs that support Voigt wave propagation (while their component materials do not); (iii) modeling the infiltration of certain sculptured thin films with a view to optical sensing applications; and (iv) simulation of the electromagnetic properties of vacuum in curved spacetime via HNMs as Tamm mediums. Forward homogenization is implemented in applications (i) and (ii); inverse homogenization is implemented in application (iv); and both forward and inverse homogenization are implemented in application (iii).

Nanoprecision algorithm for surface plasmon resonance determination from images with low contrast for improved sensor resolution

Abstract: A forward-projection algorithm based on Radon transform for two-dimensional surface plasmon imaging was devised to achieve nanoscale precision in determining the surface plasmon signal. A diverging laser beam at the chosen frequency was used to overcome the angular scanning in the well-known Kretschmann configuration. Multichannel sensing with improved resolution was realized. The technique was also used to find the lateral resolution of the sensor using a patterned layer of 40-nm thick SiO2 layer on top of the metallic surface. As a surface plasmon resonance signal detector, the use of the proposed Radon transform algorithm shows nanoprecision accuracy in cases of single and multichannel sensing. The method also provides the filtered output of the signal without any extra modification and therefore, it is nonsensitive to noise.

Detailed experimental analysis of the structural fluorescence in the butterfly Morpho sulkowskyi (Nymphalidae)

Abstract: The Morpho sulkowskyi concentrates on its dorsal wings complementary features contributing to its visual attraction: predominantly translucent, their wings display a blue coloration due to light interference. Fluorescent molecules, producing a violet-blue coloration when irradiated by ultraviolet light, are embedded in the scales which present a two-dimensional photonic structure. We investigate i. the effects of the fluorophores confinement in the structure on the variation of the emission intensity and coloration with the observation direction and ii. the correlation between the reflection and emission processes that control the surface optical response. Three types of measurements have been carried out. The morphology of the butterfly was examined with a scanning electron microscope. Then, the spatial distribution of the reflected light was measured with a viewing angle instrument, providing bidirectional reflectance distribution function data. Finally, an automatic method coupling an ultraviolet source to a gonio-spectrophotometer allowed for an extensive fluorescent emission characterization and provided angular emission maps. We find a spatial variation of the emission intensity and coloration and also an exhaustion behavior of the fluorophores. Moreover, we reveal that the spatial distribution of the emitted and reflected light is mainly governed by the photonic structure.

Field enhancement at metallic interfaces due to quantum confinement

Abstract: We point out an apparently overlooked consequence of the boundary conditions obeyed by the electric displacement vector at air-metal interfaces: the continuity of the normal component combined with the quantum mechanical penetration of the electron gas in the air implies the existence of a surface on which the dielectric function vanishes. This, in turn, leads to an enhancement of the normal component of the total electric field. We study this effect for a planar metal surface, with the inhomogeneous electron density accounted for by a Jellium model. We also illustrate the effect for equilateral triangular nanoislands via numerical solutions of the appropriate Maxwell equations, and show that the field enhancement is several orders of magnitude larger than what the conventional theory predicts.

Dual-surface plasmon excitation with thin metallic nanoslits

Abstract: Based on the experimental results and comparison between analytical and rigorous calculations, we have found that dual-surface plasmon (SP) waves are excited at both interfaces of a periodic array of thin metallic nanoslits: one at the grating-substrate interface and one at the grating-superstrate interface. Dual plasmons are excited for each diffraction order at two different wavelengths when the substrate differs from the superstrate. The splitting of the plasmons was investigated as a function of the refractive index difference between the substrate and superstrate. Verification of the extended nature of the double SPs is presented by comparing the rigorous calculation and analytic dispersion relation of extended SPs.

Silicon-on-insulator microring resonator defect-based photodetector with 3.5-GHz bandwidth

Abstract: We have devised and fabricated high-speed silicon-on-insulator resonant microring photodiodes. The detectors comprise a p-i-n junction across a silicon rib waveguide microring resonator. Light absorption at 1550 nm is enhanced by implanting the diode intrinsic region with boron ions at 350 keV with a dosage of 1 × 10 13 cm −2 . We have measured 3-dB band- widths of 2.4 and 3.5 GHz at 5 and 15 V reverse bias, respectively, and observed an open-eye diagram at 5 gigabit/s with 5 V bias. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).

In-situ monitoring of the growth of nanostructured aluminum thin film

Abstract: Metal thin film functional properties depend strongly on its nanostructure, which can be manipulated by varying nucleation and growth conditions. Hence, in order to control the nanostructure of aluminum thin films fabricated by RF magnetron sputtering, we made use of in-situ monitoring of electrical and optical properties of the growing layer as well as plasma characterization by mass and optical emission spectroscopy. The electrical conductivity and I-V characteristics were measured. The optical constants were obtained from optical monitoring basedonspectralellipsometry.Therelevantmodels(basedononeortwoLorentzoscillatorsand B-splinefunctions)weresuggestedtoevaluatethedataobtainedfromthemonitoringtechniques. Theresultsofthein-situmonitoringwerecorrelatedwithscanningelectronmicroscopeanalyses. Wedemonstratedthemonitoringwasabletodistinguishthegrowthmodeinreal-time.Wecould estimate the percolation threshold of the growing layer and control layer nanostructure. The nanostructure was effectively manipulated by RF power variation. Optical functions exhibiting plasmonic behavior in the UV range and a strong nonlinear character of I-V curves were obtained for an ultrathin Al film deposited at a lower growth rate. C 2011 Society of Photo-Optical

Limitations and potentials of metamaterial lenses

Abstract: The seminal discovery that an ideal negative-index lens may overcome Abbe's diffraction limit has raised enormous interest in the field of metamaterials and of subwavelength focusing. This finding is based on the anomalous wave propagation in ideally isotropic and homogeneous metamaterials with negative index of refraction and low loss, provided they are available. We have designed a metamaterial lens based on one of the simplest metamaterial geometries, a cubic array of spheres, with the aim of verifying its imaging properties in a practical configuration. After a rigorous homogenization, we have shown that, for suitable designs, the effective bulk parameters may indeed provide a quasi-isotropic negative-index response, ideal for imaging applications. We have then tested the imaging properties for finite-size lenses, analyzing challenges and potentials of going beyond the diffraction limit in a practical setup. We have also explored an alternative venue to exploit the negative-index property of the designed metamaterial in a concave lens, in order to resolve subwavelength features in the far-field. Our results indicate that, although subwavelength resolution and evanescent-wave amplification are possible in metamaterial arrays, practical imaging beyond the diffraction limit is challenging and a careful design should consider the granularity, degree of isotropy, and transverse size of the metamaterial lens.

Study of adsorption behavior of aminothiophenols on gold nanorods using surface-enhanced Raman spectroscopy

Abstract: A comparative study of the adsorption behavior of 4, 3, and 2 aminothiophenol on gold nanorod (AuNRs) solution and film substrates is carried out using surface-enhanced Raman spectroscopy (SERS) to provide information about the adsorption mechanisms of aminothiophenols on AuNRs. SERS from gold nanorods in solution form could reveal the distribution of aminothiophenol molecules adsorbed on different facets of gold nanorods. Significant and sudden changes in the relative intensities of some of the vibrational bands are observed above a particular concentration of aminothiophenol, which could be related to adsorption of molecules on different facets of nanorods. The enhancement factor is found to be maximum for the excitation wavelength close to the absorption maximum of gold nanorods. Our results are not only useful for the application of nanorods as sensors and in molecular electronics, but also depict the potential of gold nanorods as the effective SERS substrate.

Nanomembrane-based plasmonics

Abstract: This paper reviews the main properties and applications of nanomembrane-based plasmonic structures, including some results presented here for the first time. Artificial nanomembranes are a novel building block in micro- and nanosystems technologies. They represent quasi-two-dimensional (2D) freestanding structures thinner than 100 nm and with giant aspect ratios that often exceed 1,000,000. They may be fabricated as various quasi-2D metal-dielectric nanocomposites with tailorable properties; they are fully symmetric in an electromagnetic sense and support long-range surface plasmon polaritons. This makes nanomembranes a convenient platform for different plasmonic structures such as subwavelength plasmonic crystals and metamaterials and applications such as plasmon waveguides and ultrasensitive bio/chemical sensors. Among other advantages of nanomembrane plasmonics is the feasibility to fabricate flexible, transferable plasmonic guides applicable to different substrates and dynamically tunable through stretching. There are various approaches to multifunctionalization of nanomembranes for plasmonics, including the use of transparent conductive oxide nanoparticles, but also the incorporation of switchable ion channels. Since the natural counterpart of the artificial nanomembranes are cell membranes, the multifunctionalization of synthetic nanomembranes ensures the introduction of bionic principles into plasmonics, at the same time extending the toolbox of the available nanostructures, materials and functions.

Columnar-thin-film acquisition of fingerprint topology

Abstract: Fingerprint visualization obtained from physical evidence taken from crime scenes for subsequent comparison typically requires the use of physical and chemical techniques. One physical technique to visualize or develop sebaceous fingerprints on various surfaces employs the deposition of metals such as gold and zinc thereon. We have developed a different vacuum technology: the conformal-evaporated-film-by-rotation technique to deposit dense columnar thin films (CTFs) on latent fingerprints on different types of surfaces. Sample fingerprints, acting as nonplanar substrates, deposited on different surfaces were placed in a vacuum chamber with the fingerprint side facing a boat containing an evaporant material such as chalcogenide glass. Thermal evaporation of the solid material led to the formation of a dense CTF on the fingerprint, thereby capturing the topographical texture with high resolution. Our results show that it is possible to acquire the topology of latent fingerprints on nonporous surfaces. Additionally, deposition of CTFs on overlapping fingerprints suggested ours may be a technique for elucidating the sequence of deposition of the fingerprints at the scene.

Photonic crystal slab waveguide-based infiltrated liquid sensors: design and analysis

Abstract: Infiltrated liquid sensors based on a 2D photonic crystal waveguide were devised. This waveguide is designed by taking into account lowering of the radius of the central air holes in a single row and the optical resonance shifts due to refractive index change of these holes by selectively filling with different liquids. The transmission spectrum of the infiltrated liquid sensor was obtained with the use of a finite difference time domain method. At the working wavelength of 1550 nm, the waveguide mode gap edge shifts with sensitivity of 200 nm per refractive index unit. The mode gap shifts are consistent with dispersion diagrams.

Low-energy single-optical-cycle soliton self-compression in air-silica nanowires

Abstract: We investigated and optimized the process of soliton self-compression in few millimeters-long air-silica nanowires. A 100 fs prechirped input pulse was compressed to a 1.4 fs pulse by pumping at very low energy of 2.5 nJ an air-silica nanowire. More than one octave spanning coherent broadband supercontinuum extending from 260 to 1800 nm was

Subwavelength optical imaging with an array of silver nanorods

Abstract: Tailoring the parameters of a silver nanorod array for subwavelength imaging of arbitrary coherent sources is of recent interest. We evaluated the operational bandwidth of this type of superlens, and also the impact of source-offset in order to understand the level of tolerance offered by the superlens with regard to source location. The performance of the device was analyzed numerically both through analysis of transmission and reflection coefficients and by full-wave simulation for a particular sample source arrangement. We observed that such a device exhibited better imaging performances with the sources spread wider, offering a bandwidth of around 13.5%.

Enhanced resonance tuning of photonic crystal nanocavities by integration of optimized near-field multitip nanoprobes

Abstract: A compact and low power control of photonic crystal nanocavity resonance was devised, simulated, and experimentally validated utilizing a hybrid integration of a microelec- tromechanical systems driven nanoprobe. The experimental results demonstrated a reversible resonance tuning up to 5.4 nm with minimal Q-factor degradation. C 2011 Society of Photo-Optical

Lossy gradient index metamaterial with sinusoidal periodicity of refractive index: case of constant impedance throughout the structure

Abstract: We used an exact analytical approach to investigate the electromagnetic wave propagation across an isotropic metamaterial composite with i. a sinusoidally periodic gradient of the real parts of the effective permittivity and permeability, ii. spatially uniform imaginary parts of the effective permittivity and permeability, and iii. spatially uniform impedance. The real part of the effective refractive index can be positive and negative along the direction of nonhomogeneity. A remarkably simple direct solution for the field distribution was obtained.

Tuning the effective dielectric function of thin film metal-dielectric composites by controlling the deposition temperature

Abstract: . The influence of the substrate temperature on the effective optical behavior ofAg-SiO 2 composites obtained by electron beam evaporation was studied. Optical characteriza-tion of the composites was performed by means of spectroscopic ellipsometry measurements.Theeffectivedielectricfunctionofthecomposites,modeledusingamultipleoscillatorapproach,could be widely tuned by controlling the deposition temperature. The spectral dependence ofthe composite absorption appeared to be better described with a Gaussian line shape than withthe classical Lorentz oscillator model. The description of the effective dielectric function usingstandard effective medium theories failed and the experimental results could be explained onlyin the general framework of the Bergman spectral density theory. C 2011 Society of Photo-OpticalInstrumentation Engineers (SPIE) . [DOI: 10.1117/1.3590238] Keywords: metal-dielectric composites; metal island films; surface plasmon resonance; opticalconstants; effective medium theory; spectroscopic ellipsometry.Paper 11015SSR received Jan. 28, 2011; revised manuscript received Apr. 15, 2011; acceptedfor publication Apr. 15, 2011; published online May 13, 2011.

Nontypical photoinduced optical nonlinearity of dielectric nanostructures

Abstract: The recently discovered ultralow-threshold nonlinear refraction of low-intensity laser radiation in dielectric nanostructures has an atypical dependence on radiation intensity in the pulsedandcontinuousmodes.Wefirstcarryoutquantitativemeasurementsofthedependenceof the nonlinear response of liquid dielectric nanostructures on the low-intensity radiation and then devise a theoretical explanation. The theory suggests that the nonlinearity is of photoinduced nature instead of a thermal one and depends directly on the nanoparticles electronic structure and the relationship between permittivities of dielectric matrix and nanoparticles. C � 2011 Society