Showing papers by "David R. Smith published in 2002"
TL;DR: In this article, the authors analyzed the reflection and transmission coefficients calculated from transfer matrix simulations on finite lengths of electromagnetic metamaterials, to determine the effective permittivity and permeability.
Abstract: We analyze the reflection and transmission coefficients calculated from transfer matrix simulations on finite lengths of electromagnetic metamaterials, to determine the effective permittivity ~«! and permeability ~m! .W e perform this analysis on structures composed of periodic arrangements of wires, split ring resonators ~SRRs!, and both wires and SRRs. We find the recovered frequency-dependent« and m are entirely consistent with analytic expressions predicted by effective medium arguments. Of particular relevance are that a wire medium exhibits a frequency region in which the real part of « is negative, and SRRs produce a frequency region in which the real part of m is negative. In the combination structure, at frequencies where both the recovered real parts of « and m are simultaneously negative, the real part of the index of refraction is also found to be unambiguously negative.
2,689 citations
TL;DR: In this paper, the effect of size and shape on the spectral response of individual silver nanoparticles was studied and it was shown that specific geometrical shapes give distinct spectral responses.
Abstract: We present a systematic study of the effect of size and shape on the spectral response of individual silver nanoparticles. An experimental method has been developed that begins with the detection and characterization of isolated nanoparticles in the optical far field. The plasmon resonance optical spectrum of many individual nanoparticles are then correlated to their size and shape using high-resolution transmission electron microscopy. We find that specific geometrical shapes give distinct spectral responses. In addition, inducing subtle changes in the particles’ morphology by heating causes a shift in the individual particle spectrum and provides a simple means of tuning the spectral response to a desired optical wavelength. Improved colloidal preparation methods could potentially lead to homogeneous populations of identical particle shapes and colors. These multicolor colloids could be used as biological labels, surface enhanced Raman scattering substrates, or near field optical microscopy sources cove...
1,687 citations
TL;DR: In this article, the sensitivity of the subwavelength focus to various slab parameters, pointing out the connection to slab plasmon modes, is discussed, and a paradox associated with the perfect imaging of a point source is resolved.
Abstract: Recently it has been proposed that a planar slab of material, for which both the permittivity and permeability have the values of -1, could bring not only the propagating fields associated with a source to a focus, but could also refocus the nonpropagating near-fields, thereby achieving a subdiffraction image. In this work we discuss the sensitivity of the subwavelength focus to various slab parameters, pointing out the connection to slab plasmon modes. We also note and resolve a paradox associated with the perfect imaging of a point source. We conclude that subwavelength resolution is achievable with available technology, but only by implementation of a critical set of design parameters.
361 citations
TL;DR: In this paper, the polarization-dependent scattering of light from homogeneous and multisegment silver, gold, and nickel nanowires is analyzed using an optical microscope configured for single particle spectroscopy.
Abstract: We present an experimental study of the polarization-dependent scattering of light from homogeneous and multisegment silver, gold, and nickel nanowires. The metallic nanowires are prepared within a polycarbonate membrane template by a combination of electroplating (gold and nickel) and electroless (silver) growth processes. The size range of the nanowire segments is such that surface plasmon resonances are supported, dominating the optical spectra. We characterize the light scattering properties of individual composite nanowires using an optical microscope configured for single particle spectroscopy. Because of the scattering efficiency associated with the plasmon resonance, very narrow (∼30 nm diameter) nanowires can be readily observed under white-light illumination, with the spectral characteristics of each subsection easily distinguishable. Because of their compactness, these simply prepared multiisegment plasmon resonant nanowires are capable of hosting a large number of segment sequences over a comp...
172 citations
TL;DR: In this article, a slab of a medium with negative refractive index bounded by media of different positive refractive indices was shown to act as a near-perfect lens for evanescent waves.
Abstract: We extend the ideas of the perfect lens recently proposed [J.B. Pendry, Phys. Rev. Lett. 85, 3966 (2000)] to an alternative structure. We show that a slab of a medium with negative refractive index bounded by media of different positive refractive index also amplifies evanescent waves and can act as a near-perfect lens. We examine the role of the surface states in the amplification of the evanescent waves. The image resolution obtained by this asymmetric lens is more robust against the effects of absorption in the lens. In particular, we study the case of a slab of silver, which has a negative dielectric constant, with air on one side and other media such as glass or GaAs on the other side as an ‘asymmetric’ lossy near-perfect lens for p-polarized waves. It is found that retardation has an adverse effect on the imaging due to the positive magnetic permeability of silver, but we conclude that subwavelength image resolution is possible in spite of it.
163 citations
TL;DR: In this article, it was shown that a modulated Gaussian beam undergoes negative refraction at the interface between a positive and negative refractive index material, and the interference fronts appear to bend in a manner suggesting positive refraction, such that the true direction of the energy flow associated with the refracted beam is not obvious.
Abstract: We show that a modulated Gaussian beam undergoes negative refraction at the interface between a positive and negative refractive index material. While the refraction of the beam is clearly negative, the modulation interference fronts are not normal to the group velocity, and thus exhibit a sideways motion relative to the beam—an effect due to the inherent frequency dispersion associated with the negative index medium. In particular, the interference fronts appear to bend in a manner suggesting positive refraction, such that for a plane wave, the true direction of the energy flow associated with the refracted beam is not obvious.
137 citations
TL;DR: In this paper, a method of fabricating single crystal silver nanowires based on the electroless deposition of silver into the pores of the polycarbonate membranes by the metal amplification process is presented.
Abstract: We present a method of fabricating single crystal silver nanowires based on the electroless deposition of silver into the pores of the polycarbonate membranes by the metal amplification process. A gold film on one side of the nanoporous membrane is used as the initiation layer for the silver crystal growth, while the pores of the membrane are used for guiding the growth of the silver crystal into a cylindrical nanostructure. Optical microscopy and spectroscopy of individual nanowires, transmission electron microscopy (TEM), and TEM diffraction crystallography were used to characterize the silver nanostructures. The metal amplification technique presents an electroless, simple, and inexpensive solution to the challenge of fabricating silver nanowires for electronic, optical, and biological applications.
128 citations
TL;DR: These measurements are performed utilizing a SD2 source coupled to a spallation source of neutrons, providing a demonstration of UCN production in this geometry and permitting systematic studies of the influence of thermal up-scatter and contamination with para-deuterium on the UCN survival time.
Abstract: We present the first measurements of the survival time of ultracold neutrons (UCNs) in solid deuterium (SD2). This critical parameter provides a fundamental limitation to the effectiveness of superthermal UCN sources that utilize solid ortho-deuterium as the source material. These measurements are performed utilizing a SD2 source coupled to a spallation source of neutrons, providing a demonstration of UCN production in this geometry and permitting systematic studies of the influence of thermal up-scatter and contamination with para-deuterium on the UCN survival time.
65 citations
07 Aug 2002
TL;DR: In this article, an indirect holographic method was used to record simple intensity patterns formed by a combination of the antenna near field signal and an offset reference signal and is similar to methods employed at optical frequencies.
Abstract: This work describes a new technique for the determination of antenna radiation patterns and the imaging of antenna aperture fields. It uses an indirect holographic method to record simple intensity patterns formed by a combination of the antenna near field signal and an offset reference signal and is similar to methods employed at optical frequencies. This is as an alternative to the traditional direct holographic method of measuring complex amplitude and phase values. It outlines how previous practical difficulties, which have prevented this method being usefully employed at microwave frequencies, can be overcome by the synthesis of an offset reference plane wave. It describes how far field antenna radiation patterns can be obtained from knowledge of the resultant intensity pattern and how the information contained within this pattern can be further processed to provide images of the antenna aperture fields. It includes the results of mathematical simulations which strongly support the ideas outlined. Currently, an experimental system is being assembled to provide practical measurements and preliminary experimental results are expected to be available shortly.
25 citations
07 Nov 2002
TL;DR: In this article, a high-pass THz filter was used to fabricate the 2D lattice of thin metal cylinders and the reflection property of the filter was characterized by FTIR, and the plasma frequency was determined at 0.7 THz.
Abstract: Terahertz imaging systems have applications for explosives detection, aircraft guidance and landing in zero-visibility weather condition, as well as terrestrial and astronomical remote sensing. These critical applications need a variety of optical elements in the THz frequency, which has yet to be explored. In this paper, we demonstrate a high pass THz filter which utilizes the lowered plasma frequency of thin metal wire structures. The microstereolithography technique is applied to fabricate the 2D lattice of thin metal cylinders. The reflection property of the filter is characterized by FTIR, and the plasma frequency is determined at 0.7 THz, which agrees with the approximate theory.
3 citations
TL;DR: In this paper, it was shown that a slab of a medium with negative refractive index bounded by media of different positive refractive indices also amplifies evanescent waves and can act as a near perfect lens.
Abstract: We extend the ideas of the recently proposed perfect lens [J.B. Pendry, Phys. Rev. Lett. {\bf 85}, 3966 (2000)] to an alternative structure. We show that a slab of a medium with negative refractive index bounded by media of different positive refractive index also amplifies evanescent waves and can act as a near-perfect lens. We examine the role of the surface states in the amplification of the evanescent waves. The image resolution obtained by this asymmetric lens is more robust against the effects of absorption in the lens. In particular, we study the case of a slab of silver, which has negative dielectric constant, with air on one side and other media such as glass or GaAs on the other side as an `asymmetric' lossy near-perfect lens for P-polarized waves. It is found that retardation has an adverse effect on the imaging due to the positive magnetic permeability of silver, but we conclude that subwavelength image resolution is possible inspite of it.
01 Oct 2002
TL;DR: The large scattering cross section of plasmon resonant gold and silver nanoparticles functionalized with the appropriate ligand allows for sensitive and specific detection of nucleic acids and proteins.
Abstract: The large scattering cross section of plasmon resonant gold and silver nanoparticles functionalized with the appropriate ligand allows for sensitive and specific detection of nucleic acids and proteins. By varying the size, shape, and material morphology populations with a specific peak plasmon resonance can be prepared. By varying the order and length of plasmon resonant bar segment in a composite nanowire one can obtain a large number of particle populations. Distinct populations can be used for labels for multiplexing or as a platform for biological assays. An larger number of color populations can be obtained with composite nanowires that are fabricated with various lengths of silver, gold, or nickel segments. The order and length of the different plasmon resonance rod segments can be used to uniquely identify a rod population allowing for a large degree of multiplexing within a single sample.