| 21. |
- Antosiewicz, Tomasz, 1981, et al.
(författare)
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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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| 22. |
- 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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| 23. |
- 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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| 24. |
- 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
-
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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| 25. |
- Ardeberg, Arne, et al.
(författare)
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Clusters as probes of distance, evolution, and chemistry of galaxies
- 2003
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Ingår i: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 5382:1, s. 47-56
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Konferensbidrag (refereegranskat)abstract
- Stellar clusters are highly useful as tools for determination of distances, ages and abundances of heavy elements of galaxies, also at larger distances. Their utility for these purposes has, so far, been severely limited, mainly due to image crowding. The introduction of Extremely Large Telescopes (ELTs) with full adaptive optics (AO) and near diffraction limited performance should imply a drastic improvement concerning the usefulness of clusters and the limiting distances of high quality data. We have made a study of stellar clusters as probes of distance, evolution and chemistry of galaxies at distances from one to twenty Mpc. From data on the Stromgren uvby system, partly from direct measurements taken from the literature, we have synthesized test clusters, one open and one globular, as well as galactic backgrounds. The clusters have been embedded in the backgrounds and located at distances between one and twenty Mpc. Here, vby data have been measured, reduced and analyzed. Color-magnitude diagrams (CMDs), metallicity diagrams (MDs) and luminosity functions (LFs) have been constructed. They have been evaluated absolutely and compared to the corresponding template data. We conclude that with a 50 m AO ELT, for open as well as globular clusters, MDs are of high quality for clusters out to and beyond 5 Mpc and useful out to 10 Mpc. CMDs are of very high quality well beyond 5 Mpc. They are of high scientific value out to and beyond 10 Mpc and valuable for clusters even out to 20 Mpc. LFs are highly informative well beyond 10 Mpc and still rather valuable at 20 Mpc. With sufficient measurement data available, LFs are useful for clusters in galaxies even beyond 20 Mpc
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| 26. |
- Ardeberg, Arne, et al.
(författare)
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Diffraction-limited light collection: Promises and challenges of a 50 m ELT
- 2004
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 5489:PART 1, s. 23-34
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Konferensbidrag (refereegranskat)abstract
- Programmes driving ELT design are discussed. The nature and evolution of circum-stellar shells and planetary discs are attractive, while the small angular sizes place basic properties, asymmetry and warps, beyond VLT capability. An ELT is neeed to reveal the conversion processes shell - disc - planets, planetary systems, Earth-like planets, habitability and life signatures. Formation and evolution of massive stars are dicussed as are stellar rotation and shape, surface spatial and temporal resolution and evolution. Stellar clusters are discussed as probes of galactic evolution, resolving CMDs for Virgo and Fornax cluster galaxies. High-resolution studies of AGNs are discussed as are supernovae with bearing on early star formation, galactic activity and cosmology. Finally, the requirements defined from the prime science drivers are confronted with technical realities.
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| 27. |
- Ardeberg, Arne, et al.
(författare)
-
ELTs, adaptive optics and wavelengths - art. no. 698608
- 2008
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Ingår i: Extremely Large Telescopes: Which Wavelengths? Retirement Symposium for Arne Ardeberg. - : SPIE. - 1996-756X .- 0277-786X. ; 6986, s. 98608-98608
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Konferensbidrag (refereegranskat)abstract
- A number of Extremely Large Telescopes for visual-infrared and adjacent wavelengths are in various degrees of progress. All have primary mirrors with equivalent diameters larger than 20 m and are intended for operation with adaptive optics systems. We discuss several ELT observing parameters as functions of wavelength. Stellar energy distributions and atomic line spectra are inspected as are the transmission of the Earth's atmosphere, the emissivity of the sky and telescope and instruments as well as detector sensitivity, resolution and signal-to-noise ratio. The spatial resolution depending on the size of the diffraction limited adaptive optics point spread function is discussed. We have evaluated the ELT efficiency in terms of Johnson V to N band photometry, simulating diffraction-limited ELT images of a stellar field at 4 Mpc and 4 kpc, respectively. We conclude that the information content at shorter wavelengths is of dominant nature and that there is every reason to do the utmost to include shorter wavelengths in the AO regime. We propose to adopt a short-wave length goal of 1 000 nm for first light AO with later updates reaching down to visual wavelengths.
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| 28. |
- Ardeberg, Ame, et al.
(författare)
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ELTs, AO wavelengths and science output
- 2008
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Ingår i: GROUND-BASED AND AIRBORNE TELESCOPES II, PTS 1-3. - 0277-786X .- 1996-756X. ; 7012, s. 121-121
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Konferensbidrag (refereegranskat)abstract
- A study is presented of the impact on science data from extremely large telescopes of a transformation of wavelength base for optimization of actuator architecture from 2 200 to 1250 nm. From the optical path difference (OPD) data for Euro50, we transform to E-ELT OPDs. We compute the corresponding power spectrum, in which we simulate a higher actuator density via high-pass filtering to convert from K to J band actuator-pitch optimization. From the modified power spectrum we derive the correspondingly modified OPDs, PSFs and Strehl ratios. A massive improvement is demonstrated resulting from converting from AO@K to AO@J. This result is followed up by model-based E-ELT imaging in a field in a galactic disc at a distance of 4 Mpc. The improvements in image quality, background and limiting magnitude are very large as are the increases in photometric precision derived from the field imaging. Further, the great science benefit and large opportunities provided by partial AO is demonstrated. In conclusion, while admittedly challenging, pushing AO optimization to wavelengths as short as possible is of prime concern for the science output of ELTs.
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| 29. |
- Ardeberg, Arne, et al.
(författare)
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Evolution of distant galaxies from cluster photometry: a program for a 50-m ELT
- 2004
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Ingår i: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5489:1, s. 72-83
-
Konferensbidrag (refereegranskat)abstract
- The formation, shaping and evolution of galaxies are processes of high interest but poorly known. This is true also for our closest galactic neighbours. Of key importance is a representative sample of all major types of galaxies with solid evolutionary parameters. Stellar clusters are excellent probes of galactic evolution, albeit so far useful at smaller distances only, mainly due to the limiting effects of image crowding. With extremely large telescopes (ELTs) with full adaptive optics (AO) and near diffraction limited performance, the effects of image crowding will be drastically reduced. Thus, the excellence of clusters of stars as evolutionary probes can be extended out to cosmological distances. We have studied this extension. With data on the Str
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| 30. |
- Ardeberg, Arne, et al.
(författare)
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From Euro50 towards a European ELT
- 2006
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 6267 II, s. 26725-26725
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Konferensbidrag (refereegranskat)abstract
- With Euro50 as a convenient telescope laboratory, the Euro50 team has continued development aiming at a European extremely large telescope (ELT). Here, we give a progress report. The needs of science and instrumentation are briefly discussed as is the importance of photometric stability and precision. Results are reported from work on integrated modelling. Details are given concerning point-spread functions (PSFs) obtained with and without adaptive optics (AO). Our results are rather encouraging concerning AO photometry and compensation of edge sensor noise as well as regarding seeing-limited ELT operation. The current status of our development of large deformable mirrors is shown. Low-cost actuators and deflection sensors have been developed as have hierarchic control algorithms. Fabrication of large thin mirror blanks as well as polishing and handling of thin mirrors has been studied experimentally. Regarding adaptive optics, we discuss differential refraction and the limitations imposed by dispersive optical path differences (OPDs) and dispersive anisoplanatism. We report on progress in laser guide star (LGS) performance and a real-time online experiment in multi-conjugate AO (MCAO). We discuss ELTs, high-resolution spectroscopy and pupil slicing with and without use of AO. Finally, we present some recent studies of ELT enclosure options.
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