Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session N16: Focus Session: Optical Properties of Subwavelength Apertures and Nanoparticle Arrays |
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Sponsoring Units: DMP Chair: Bennett Goldberg, Boston University Room: LACC 404A |
Wednesday, March 23, 2005 8:00AM - 8:12AM |
N16.00001: Theoretical and experimental study of surface plasmon enhanced transmission of subwavelength apertures Ian Schick, John Yarbrough, Reuben Collins, Russell Hollingsworth, Greg Nuebel We present a study of surface plasmon (SP) enhanced transmission through subwavelength apertures in Au films on glass. Samples consisting of 100-500nm linear apertures flanked by periodic corrugations were prepared using e-beam lithography with subsequent ion milling. Transmission through these structures were studied experimentally and modeled numerically. Geometric parameters were varied in the numerical simulation which used a 2D Green's function approach and a frequency dependent Au dielectric function. Transmission with flanking corrugations was significantly enhanced related to an isolated aperture, at the wavelengths corresponding to SP resonance in the structure in agreement with the literature. Periodic corrugation also affected the spatial dependence of the transmitted field. Transmission through these structures was spectrally and spatially mapped using near-field scanning optical microscopy which revealed field intensity distributions consistent with those observed in the simulations. The authors acknowledge financial support from the NSF. [Preview Abstract] |
Wednesday, March 23, 2005 8:12AM - 8:24AM |
N16.00002: Transmission properties of an array of sub-wavelength holes in a metal film Kwangje Woo, Sinan Selcuk, Arthur F. Hebard, David B. Tanner It is known that the intensity of light transmitted through an array of holes can be surprisingly high at certain wavelengths, even when the holes are of sub-wavelength scales. The enhanced transmission is attributed to a coupling of surface plasmons on the two sides of the film. We have studied the systematics of this transmission of hole arrays in silver films. We have observed a scaling of the transmission wavelength with the hole spacing, and found that the effect can be observed at long wavelengths. We have also studied the effect of the angle of incidence of the light and found a very strong dependence of the transmission on this angle. In addition, significant polarization dependence is observed. Finally, the effect of the dielectric media on the surface-plasmon-enhanced transmittance will be addressed. [Preview Abstract] |
Wednesday, March 23, 2005 8:24AM - 8:36AM |
N16.00003: Enhancement of Light Transmission through Thin-Film Bull’s Eye Structures Sinan Selcuk, Kwangje Woo, David B. Tanner, Arthur F. Hebard Previous researchers have shown that light transmitted through a single hole in a silver film can be strongly enhanced by the presence of periodic concentric groove structures (bull's eye) on the film. We present a systematic study of the wavelength dependence (0.3 -- 2.0 $\mu $m) as measured by a Zeiss microscope photometer of the transmission of bull's eye structures with varying dimensions. A focused ion beam microscope is used to drill successively larger holes on the same structure thus facilitating the identification of transmission emanating from the hole compared to transmission associated with evanescent waves coupled through the opaque portions of the structure. The intensity and spectral distribution of the transmitted light is correlated with variation of sample parameters including the film thickness (40 -- 100 nm), groove periodicity (2.0- 4.0 $\mu $m), hole diameter (0.5 -- 10 $\mu $m) and phase difference between the entrance and exit groves. The relevance of surface plasmons to the enhanced transmission and the predictions of theory will be discussed. [Preview Abstract] |
Wednesday, March 23, 2005 8:36AM - 9:12AM |
N16.00004: Diffracted Evanescent Wave Model for Enhanced, Suppressed and Directional Transmission through Subwavelength Apertures Invited Speaker: The transmission spectrum of an array of subwavelength apertures in a metal film displays a set of peaks related to the periodicity. Extraordinary transmission efficiencies at these positions have been claimed and associated with discrete grating-coupling conditions that excite surface-plasmon polaritons (SPPs). In this talk, we re-evaluate the magnitude and origin of the effect by proper normalization of the as-collected transmission spectrum of the array to that of the corresponding isolated hole. The normalized spectrum then reveals a sequence of both enhancements and suppressions of modest and similar magnitude (less than a factor of ten). This continuous modulation is inconsistent with an SPP-based interpretation, but rather suggests an underlying mechanism based on interference. A subwavelength aperture couples inefficiently to a specific surface mode such as an SPP because it diffracts light into a continuum of evanescent surface waves with a large distribution of in-plane k-vectors. We show however that these components sum to form an effective surface wave which is coherent over a short range and phase-shifted with respect to the source. We confirm the presence of this composite diffracted evanescent wave (CDEW) via interferometric experiments involving pairs of subwavelength apertures. We propose a new model for the anomalous transmission of hole arrays in which enhancement and suppression result from the interference of light directly incident upon (or emerging from) a given hole with CDEWs launched by neighboring holes. This model successfully predicts equivalent effects in non-metallic systems. In addition, it accounts for the salient optical properties of single apertures surrounded by surface corrugations, such as efficient, low-divergence beaming. [Preview Abstract] |
Wednesday, March 23, 2005 9:12AM - 9:24AM |
N16.00005: Optical transmission through metallic bilayers with subwavelength apertures H. B. Chan, Z. Marcet, Kwangje Woo, D. B. Tanner, D.W. Carr The optical transmission through a periodical array of subwavelength apertures in a metal film can be strongly enhanced by resonance of the incident light with surface plasmon polaritons on the metal surfaces. The excitation of surface plasmons is accompanied by a dramatic enhancement of the local electromagnetic field on the metal surfaces. We have fabricated subwavelength structures consisting of two layers of metal. The metal layers are positioned sufficiently close to each other such that the evanescent fields of the surface plasmons generated in the first layer excite surface plasmons in the second layer. In some cases the two metal layers are laterally displaced such that no direct line of sight exists through the structure. Nevertheless, the transmission through a number of these devices remains remarkably high at resonance, comparable to the single layer value. We will discuss the dependence of the optical transmission on various sample parameters, including metal layer thickness, separation, lateral shift and incident angle of light. [Preview Abstract] |
Wednesday, March 23, 2005 9:24AM - 9:36AM |
N16.00006: Nonlinear and Active Optics in Nanolenses Kuiru Li, Mark Stockman, David Bergman We consider surface plasmon amplification by stimulated emission of radiation (SPASER) and second harmonic generation (SHG) in an effective nanolens. Such a nanolens is an aggregate of several nanospheres with progressively decreasing radii and separations .....[1]. It has a ``hottest spot'' of highly enhanced local fields between the smallest spheres. We show that such a system surrounded by semiconductor quantum dots is also an efficient SPASER that generates dark eigenmodes with gigantic, temporarily coherent local fields .()..()[2]. We also consider SHG in the nanolenses where we show that highly enhanced SHG local fields are generated at the nanofocus. Numerical data are presented for silver spheres .[1] K. Li, M. I. Stockman, and D. J. Bergman, \textit{Self-Similar Chain of Metal Nanospheres as an Efficient Nanolens}, Phys. Rev. Lett. \textbf{91}, 227402-1-4 (2003). [2] K. Li, X. Li, M. I. Stockman, and D. J. Bergman, \textit{Surface Plasmon Amplification by Stimulated Emission in Nanolenses}, Phys. Rev. B (2005 (In Print)). [Preview Abstract] |
Wednesday, March 23, 2005 9:36AM - 9:48AM |
N16.00007: Optical studies of plasmon resonances in Ag nanoparticle arrays. R. Valdes Aguilar, G. Evans, H. D. Drew, S. H. Guo, T. Corrigan, R. Phaneuf The optical (UV and visible) response of Ag nanoparticle arrays is studied in reflection measurements. The behavior (position and width) of the plasmon resonance is investigated as a function of size and shape of the nanoparticles. While the resonant frequencies can be understood in terms of the Mie type resonant response of ellipsoidal particles the widths of the resonances are controlled by radiation damping and is very sensitive to particle size. A model based on the Maxwell-Garnett effective medium theory is developed to comprehend the behavior of the resonance. [Preview Abstract] |
Wednesday, March 23, 2005 9:48AM - 10:00AM |
N16.00008: Harmonic generation from metal nanoparticle arrays Matthew McMahon, Rene Lopez, Leonard Feldman, Richard Haglund Metal nanoparticle arrays have optical coherence properties that are predicted to have interesting consequences for optical harmonic generation. We have prepared planar arrays of non-spherically symmetric silver-nanoparticle clusters using a combination of focused ion-beam lithography and pulsed laser deposition. The 150-fs amplified pulses of a Ti:sapphire laser were incident on the array, which was mounted on the rotatable sample stage of a dark-field confocal microscope; this arrangement permits the elimination of virtually all optical background so that the scattered harmonic signal from the array is easily detectable. We describe experiments designed to test a recent theoretical prediction [1] to the effect that the nanoparticle array should produce phase-matched second harmonics like those generated by bulk media without a center of inversion symmetry, and that the harmonic- generation efficiency should scale inversely as the square of the nanoparticle size.[1] N. I. Zheludev and , J. Opt. A: Pure Appl. Opt. 6 (2004) 26-28. [Preview Abstract] |
Wednesday, March 23, 2005 10:00AM - 10:12AM |
N16.00009: Electromagnetic energy transport through metallic nanoparticle arrays Stavroula Foteinopoulou, Jean-Pol Vigneron We investigate electromagnetic (EM) energy transport through arrays consisting of Au spheres, 50 nm in diameter, with the Finite Difference Time Domain (FDTD) method. We assume the Drude model for the dielectric response of the Au nanospheres. The Drude model is incorporated into the FDTD technique with the introduction of an appropriate time-dependent polarization current. This method is known as Auxillary Differential Equation (ADE) method [1]. In order to test the validity of our numerical findings, we first focus on the EM excitations on a single metallic nanoparticle [2]. We compare for the latter case the FDTD results with analytical calculations following Mie theory. Over all we found reasonably good agreement between the two. Our numerical results indicate EM energy transport through the Au nanochain. Nonetheless, a careful analysis of the field profiles suggests that nearest-neighbor tight-binding like models fail to describe certain aspects of the observed EM energy transport through the nanochain. [1] ``Computational Electrodynamics'' A. Taflove, S. C. Hagness, Artech House, Boston (2000). [2] ``Electromagnetic excitations on a single metallic nanoparticle'', S. Foteinopoulou, J. P. Vigneron and C. Vandenbem, unpublished. [Preview Abstract] |
Wednesday, March 23, 2005 10:12AM - 10:24AM |
N16.00010: Size-dependent optical properties of VO2 nanoparticle arrays Rene Lopez, Leonard C. Feldman, Richard F. Haglund Jr. Arrays of vanadium oxide nanoparticles with long-range order have been fabricated by pulsed laser deposition in an arbitrary pattern defined by focused ion-beam lithography. Interaction of light with the nanoparticles is controlled by the geometrical arrangement as well as by the differing optical properties displayed by the metallic and semiconducting phases of VO$_{2}$. Contrary to previous VO$_{2}$ studies, we observe that the optical contrast between the semiconducting and metallic phases is dramatically enhanced in the visible region, presenting size-dependent optical resonances and size dependent transition temperatures. The collective optical response as a function of temperature presents an enhanced scattering state during the evolving phase transition. The effects appear to arise because of the underlying VO$_{2}$ mesoscale optical properties, the heterogeneous nucleation behind the phase transition and the incoherent coupling between the nanoparticles undergoing an order-disorder-order transition. Arrays such as this open up new opportunities to study surface plasmon interactions for nanoparticles in close proximity, with the added advantage that the interaction can be switched on by the thermally driven metal-semiconductor phase transition in VO$_{2}$. This research was supported by the NSF-NIRT program (DMR0210785). [Preview Abstract] |
Wednesday, March 23, 2005 10:24AM - 10:36AM |
N16.00011: Long-Range Transmission of Evanescent Waves Simin Feng, John Elson, Pamela Overfelt Metal/dielectric periodic multilayer structures are shown to exhibit a new type of photonic transmission bands corresponding to resonant tunneling of evanescent waves. We show that evanescent fields can propagate over long distances as Bloch waves. This occurs by means of surface wave resonant coupling with electron plasma oscillations. Consistent with this, we also find that plane wave transmission across a metal/dielectric periodic multilayer structure oscillates periodically with increasing number of metal/dielectric pairs. The presence of the Bloch evanescent states provides a channel for optical tunneling and the long-range transmission of the evanescent waves. The structures considered here can be fabricated with existing nanotechnology. [Preview Abstract] |
Wednesday, March 23, 2005 10:36AM - 10:48AM |
N16.00012: The Physical Basis of Enhanced Transmission Through Small Apertures in Metallic Films Kevin Webb, Jia-Han Li While the coupling of electromagnetic radiation through small apertures in a conducting screen is well understood based on the work of Bethe and, more rigorously, through an eigenmode expansion in the intervening waveguide, there has been recent interest in enhanced transmission phenomena. Greater coupling through the hole than might be expected based on the theory of apertures in perfectly conducting screens has been found. Studies with physical metals have focused on surface plasmon waves on the top and bottom surfaces of the metal film. We present numerical results for two-dimensional apertures in silver films with various geometries. The transmission is a function of the aperture width and film thickness variables. An analytical model is provided that explains the effect for silver and other metals. [Preview Abstract] |
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N16.00013: FDTD modeling of the optical fields produced by nanoarrays of coaxial structures on gold films Michael Haftel, Carl Schlockermann, Girsh Blumberg Extraordinary optical transmission has been observed for nanoarrays of apertures in thin metallic films, originally attributed to coupling with surface plasmons (SP) [1]. More recently Baida et al. [2] have suggested that even larger enhancements can occur with nanoarrays of subwavelength coaxial structures at wavelengths much longer than those of the SP resonances. We employ the NRL HASP (FDTD) code to simulate the electromagnetic fields, in the 500-1500 nm wavelength range, produced by nanoarrays of silica coaxial cylinders (or rings) embedded in a thin gold film. We analyze the transmission spectrum as a function of ring geometry, film thickness, and periodicity. We contrast the results obtained from isolated rings and cylinders with those from arrays to assess the roles of SP and the resonances of the isolated structures in accounting for any field enhancements. We discuss the mechanisms of the field propagation in the real metal (versus an ideal metal) that may account for enhancements. [1] T. Ebbesen, H. Lezec, H. Ghaemi, T. Thio, and P. Wolff, Nature \textbf{391}, 667 (1998). [2] F. I. Baida and D. Van Labeke, Phys. Rev. B \textbf{67}, 155314 (2003). [Preview Abstract] |
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