| 1. |
- Antosiewicz, Tomasz, 1981, et al.
(författare)
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Bi-metal coated aperture SNOM probes
- 2011
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819486608 ; 8070
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Konferensbidrag (refereegranskat)abstract
- Aperture probes of scanning near-field optical microscopes (SNOM) offer resolution which is limited by a sum of the aperture diameter at the tip of a tapered waveguide probe and twice the skin depth in metal used for coating. An increase of resolution requires a decrease of the aperture diameter. However, due to low energy throughput of such probes aperture diameters usually are larger than 50 nm. A groove structure at fiber core-metal coating interface for photon-to-plasmon conversion enhances the energy throughput 5-fold for Al coated probes and 30-fold for Au coated probes due to lower losses in the metal. However, gold coated probes have lower resolution, first due to light coupling from the core to plasmons at the outside of the metal coating, and second due to the skin depth being larger than for Al. Here we report on the impact of a metal bilayer of constant thickness for coating aperture SNOM probes. The purpose of the bilayer of two metals of which the outer one is aluminum and the inner is a noble metal is to assure low losses, hence larger transmission. Using body-of-revolution finite-difference time-domain simulations we analyze properties of probes without corrugations to measure the impact of using a metal bilayer and choose an optimum bi-metal configuration. Additionally we investigate how this type of metalization works in the case of grooved probes.
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| 2. |
- Antosiewicz, Tomasz, 1981, et al.
(författare)
-
Magnetic probe for material characterization at optical frequencies
- 2011
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819486608 ; 8070
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Konferensbidrag (refereegranskat)abstract
- Rapid development of novel, functional metamaterials made of purely dielectric, plasmonic, or composite structures which exhibit tunable optical frequency magnetic responses creates a need for new measurement techniques. We propose a method of actively measuring magnetic responses, i.e. magnetic dispersion, of such metamaterials within a wide range of optical frequencies with a single probe by exciting individual elementary cells within a larger matrix. The probe is made of a tapered optical fiber with a radially corrugated metal coating. It concentrates azimuthally polarized light in the near-field below the apex into a subwavelength size focus of the longitudinal magnetic field component. An incident azimuthally polarized beam propagates in the core until it reaches the metal stripes of constant angular width running parallel to the axis. For a broad frequency range light-to-plasmon coupling is assured as the lattice constant changes with the radius due to constant angular width. Bound plasmonic modes in slits between the metal stripes propagate toward the apex where circular currents in stripes and displacement currents in slits generate a strong longitudinal magnetic field. The energy density of the longitudinal magnetic component in the vicinity of the axis is much stronger than that of all the other components combined, what allows for pure magnetic excitation of magnetic resonances rather than by the electric field. The scattered signal is then measured in the far-field and analyzed.
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| 3. |
- Antosiewicz, Tomasz, 1981, et al.
(författare)
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On the optical properties of plasmonic glasses
- 2014
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781628415568 ; 9441, s. Art. no. 94411G-
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Konferensbidrag (refereegranskat)abstract
- We report on the optical properties of plasmonic glasses which are metal-dielectric composites composed of metallic inclusions in a host dielectric medium. The investigated structures are of quasi-random nature, described by the pair correlation function, featuring a minimum center-to-center distance between metallic inclusions and long range randomness. Plasmonic glasses exhibiting short-range order only may be fabricated using bottom-up, self-assembly methods and have been utilized in a number of applications such as plasmonic sensing or plasmon-enhanced solar harvesting, and may be also employed for certain non-linear applications. It is therefore important to quantify their properties. Using theoretical methods we investigate optical of 1D, 2D, and 3D structures composed of amorphous distributions of metallic spheres. It is shown, that the response of the constituent element, i.e. The single sphere localized surface plasmon resonance, is modified by the scattered fields of the other spheres in such a way that its peak position, peak amplitude, and full-width at half-maximum exhibit damped oscillations. The oscillation amplitude is set by the particle density and for the peak position may vary by up to 0.3 eV in the optical regime. Using a modified coupled dipole approach we calculate the effective (average) polarizability of plasmonic glasses and discuss their spectra as a function of the dimensionality, angle of incidence and polarization, and the minimum center-to-center distance. The analytical model is complemented and validated by T-Matrix calculations of the optical cross-sections of amorphous arrays of metallic spheres obtained using a modification of the Random Sequential Adsorption algorithm for lines, surfaces, and volumes.
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| 4. |
- Antosiewicz, Tomasz, 1981, et al.
(författare)
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Optical activity of catalytic elements of hetero-metallic nanostructures
- 2015
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781628416237 ; 9502
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Konferensbidrag (refereegranskat)abstract
- Interaction of light with metals in the form of surface plasmons is used in a wide range of applications in which the scattering decay channel is important. The absorption channel is usually thought of as unwanted and detrimental to the efficiency of the device. This is true in many applications, however, recent studies have shown that maximization of the decay channel of surface plasmons has potentially significant uses. One of these is the creation of electron-hole pairs or hot electrons which can be used for e.g. catalysis. Here, we study the optical properties of hetero-metallic nanostructures that enhance light interaction with the catalytic elements of the nanostructures. A hybridized LSPR that matches the spectral characteristic of the light source is excited. This LSPR through coupling between the plasmonic elements maximizes light absorption in the catalytic part of the nanostructure. Numerically calculated visible light absorption in the catalytic nanoparticles is enhanced 12-fold for large catalytic disks and by more 30 for small nanoparticles on the order of 5 nm. In experiments we measure a sizable increase in the absorption cross section when small palladium nanoparticles are coupled to a large silver resonator. These observations suggest that heterometallic nanostructures can enhance catalytic reaction rates.
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| 5. |
- Antosiewicz, Tomasz, 1981, et al.
(författare)
-
Sensing (un)binding events via surface plasmons: Effects of resonator geometry
- 2016
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781510601291 ; 9884
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Konferensbidrag (refereegranskat)abstract
- The resonance conditions of localized surface plasmon resonances (LSPRs) can be perturbed in any number ways making plasmon nanoresonators viable tools in detection of e.g. phase changes, pH, gasses, and single molecules. Precise measurement via LSPR of molecular concentrations hinge on the ability to confidently count the number of molecules attached to a metal resonator and ideally to track binding and unbinding events in real-time. These two requirements make it necessary to rigorously quantify relations between the number of bound molecules and response of plasmonic sensors. This endeavor is hindered on the one hand by a spatially varying response of a given plasmonic nanosensor. On the other hand movement of molecules is determined by stochastic effects (Brownian motion) as well as deterministic flow, if present, in microfluidic channels. The combination of molecular dynamics and the electromagnetic response of the LSPR yield an uncertainty which is little understood and whose effect is often disregarded in quantitative sensing experiments. Using a combination of electromagnetic finite-difference time-domain (FDTD) calculations of the plasmon resonance peak shift of various metal nanosensors (disk, cone, rod, dimer) and stochastic diffusion-reaction simulations of biomolecular interactions on a sensor surface we clarify the interplay between position dependent binding probability and inhomogeneous sensitivity distribution. We show, how the statistical characteristics of the total signal upon molecular binding are determined. The proposed methodology is, in general, applicable to any sensor and any transduction mechanism, although the specifics of implementation will vary depending on circumstances. In this work we focus on elucidating how the interplay between electromagnetic and stochastic effects impacts the feasibility of employing particular shapes of plasmonic sensors for real-time monitoring of individual binding reactions or sensing low concentrations - which characteristics make a given sensor optimal for a given task. We also address the issue of how particular illumination conditions affect the level of uncertainty of the measured signal upon molecular binding.
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| 6. |
- Wróbel, P., et al.
(författare)
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Concentrator of magnetic field of light
- 2012
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819491152 ; 8423
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Konferensbidrag (refereegranskat)abstract
- In the recent decade metamaterials with magnetic permeability different than unity and unusual response to the magnetic field of incident light have been intensively explored. Existence of magnetic artificial materials created an interest in a scanning near-field magnetic microscope for studies of magnetic responses of subwavelength elementary cells of those metamaterials. We present a method of measuring magnetic responses of such elementary cells within a wide range of optical frequencies with single probes of two types. The first type probe is made of a tapered silica fiber with radial metal stripes separated by equidistant slits of constant angular width. The second type probe is similar to metal coated, corrugated, tapered fiber apertured SNOM probe, but in this case corrugations are radially oriented. Both types of probes have internal illumination with azimuthally polarized light. In the near-field they concentrate into a subwavelength spot the longitudinal magnetic field component which is much stronger than the perpendicular electric one.
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| 7. |
- Wróbel, P., et al.
(författare)
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Fabrication of corrugated probes for scanning near-field optical microscopy
- 2011
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819486608 ; 8070
-
Konferensbidrag (refereegranskat)abstract
- We present a method of fabricating aperture tapered-fiber metal-coated SNOM probes with a corrugated core surface which assures efficient photon-to-plasmon conversion and thus high energy throughput. High energy throughput allows for a small apex aperture and high resolution. The procedure consists of recording of Bragg grating in the to-be-tapered part of a Ge-doped silica fiber and chemical etching with the Turner method. Bragg gratings are recorded with UV light through nearly sinusoidal phase masks of chosen lattice constants. The refractive index contrast in the Bragg grating differentiates the etch rate of the Ge-doped hydrogenated fiber core in exposed and unexposed parts by about 100 nm/min at room temperature.
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| 8. |
- Wróbel, P., et al.
(författare)
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Optimization of transmission and focusing properties of plasmonic nanolenses
- 2011
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819486608 ; 8070
-
Konferensbidrag (refereegranskat)abstract
- We consider two kinds of plasmonic nanolenses which focus radially polarized Laguerre-Gauss beam into subwavelength spot. The first one is free-standing opaque metal layer with concentric grooves on both sides [Phys. Rev. Lett. 102, 183902 (2009)]. The second has slits instead of grooves thus concentric rings have to be integrated with dielectric matrix. Constructive interference of far-field radiation of SPPs scattered on the back side of the lenses gives subwavelength size foci approaching the Rayleigh resolution limit. We investigate transmission and focusing properties of considered metal structures. Choice of appropriate metal such as silver, gold, copper or aluminum strongly affects transmission. Parameters of surface structure determine efficient photon-plasmon coupling and plasmon scattering phenomenon thus influence both transmission and focusing effect. Finally, the choice of dielectric function of surrounding medium gives another degree of freedom to fulfill momentum matching condition for resonant photon-plasmon interaction. In this paper, taking into account the above parameters, we show an optimization procedure, which leads to high transmission, tight focal spot and large focal length of the considered plasmonic nanolenses.
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