Publications by authors named "Worawut Khunsin"

9 Publications

  • Page 1 of 1

Quantitative and Direct Near-Field Analysis of Plasmonic-Induced Transparency and the Observation of a Plasmonic Breathing Mode.

ACS Nano 2016 Feb 1;10(2):2214-24. Epub 2016 Feb 1.

Max-Planck-Institut für Festkörperforschung , Heisenbergstraße 1, 70569 Stuttgart, Germany.

We investigated experimentally and numerically in the optical near-field a plasmonic model system similar to a dolmen-type structure for phenomena such as plasmon-induced transparency. Through engineering of coupling strength, structure orientation, and incident angle and phase of the excitation source it was possible to control near-field excitation of the dark modes. We showed that quantitative analysis of near-field amplitude and excitation strength provided essential information that allowed identifying the interaction between the bright and the dark mode and how it causes the formation of plasmon-induced transparency features and a Fano resonance. In addition, we introduced a mechanism to excite field distributions in plasmonic structures that cannot be accessed directly using far-field illumination and demonstrated the excitation of a dark mode akin to a symmetry-forbidden plasmonic breathing mode using a linearly polarized far-field source.
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http://dx.doi.org/10.1021/acsnano.5b06768DOI Listing
February 2016

Order quantification of hexagonal periodic arrays fabricated by in situ solvent-assisted nanoimprint lithography of block copolymers.

Nanotechnology 2014 May 10;25(17):175703. Epub 2014 Apr 10.

Institut Catala de Nanociencia i Nanotecnologia, Campus de la UAB, Barcelona 08193, Spain.

Directed self-assembly of block copolymer polystyrene-b-polyethylene oxide (PS-b-PEO) thin film was achieved by a one-pot methodology of solvent vapor assisted nanoimprint lithography (SAIL). Simultaneous solvent-anneal and imprinting of a PS-b-PEO thin film on silicon without surface pre-treatments yielded a 250 nm line grating decorated with 20 nm diameter nanodots array over a large surface area of up to 4' wafer scale. The grazing-incidence small-angle x-ray scattering diffraction pattern showed the fidelity of the NIL stamp pattern replication and confirmed the periodicity of the BCP of 40 nm. The order of the hexagonally arranged nanodot lattice was quantified by SEM image analysis using the opposite partner method and compared to conventionally solvent-annealed block copolymer films. The imprint-based SAIL methodology thus demonstrated an improvement in ordering of the nanodot lattice of up to 50%, and allows significant time and cost reduction in the processing of these structures.
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http://dx.doi.org/10.1088/0957-4484/25/17/175703DOI Listing
May 2014

Ordered 2D colloidal photonic crystals on gold substrates by surfactant-assisted fast-rate dip coating.

Small 2014 May 3;10(10):1895-901. Epub 2014 Mar 3.

Department of Chemistry, University College Cork, Cork, Ireland.

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http://dx.doi.org/10.1002/smll.201303616DOI Listing
May 2014

Plasmonic grating as a nonlinear converter-coupler.

Opt Express 2012 Jan;20(2):1392-405

Photonics Research Laboratory, Center of Excellence for Applied Electromagnetic Systems, School of Electrical and Computer Engineering, University of Tehran, Tehran, Iran.

The paper introduces a wavelength converter composed of a metallic finite 2-dimensional particle grating on top of an optical waveguide. The particles sustain plasmonic resonances which will result in the near-field enhancement and therefore, high conversion efficiency. Due to near-field interaction of the grating field with the propagating modes of the waveguide, the generated third harmonic wave is phase-matched to a propagating mode of the waveguide, while the fundamental frequency component is not coupled into the output waveguide of the structure. The performance of this structure is numerically investigated using a full-wave transmission line method for the linear analysis and a three-dimensional finite-difference time-domain method for the nonlinear analysis.
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http://dx.doi.org/10.1364/OE.20.001392DOI Listing
January 2012

Long-distance indirect excitation of nanoplasmonic resonances.

Nano Lett 2011 Jul 8;11(7):2765-9. Epub 2011 Jun 8.

Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, 70569 Stuttgart, Germany.

In nanoscopic systems, size, geometry, and arrangement are the crucial determinants of the light-matter interaction and resulting nanoparticles excitation. At optical frequencies, one of the most prominent examples is the excitation of localized surface plasmon polaritons, where the electromagnetic radiation is coupled to the confined charge density oscillations. Here, we show that beyond direct near- and far-field excitation, a long-range, indirect mode of particle excitation is available in nanoplasmonic systems. In particular, in amorphous arrays of plasmonic nanodiscs we find strong collective and coherent influence on each particle from its entire active neighborhood. This dependency of the local field response on excitation conditions at distant areas brings exciting possibilities to engineer enhanced electromagnetic fields through controlled, spatially configured illumination.
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http://dx.doi.org/10.1021/nl201043vDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3136109PMC
July 2011

Near-field dynamics of optical Yagi-Uda nanoantennas.

Nano Lett 2011 Jul 27;11(7):2819-24. Epub 2011 May 27.

4. Physikalisches Institut und SCoPE Forschungszentrum, Pfaffenwaldring 57, Universität Stuttgart, 70569 Stuttgart, Germany.

We present near-field measurements of optical Yagi-Uda nanoantennas that are used in receiving mode. The eigenmode imaging of amplitude and phase by apertureless scanning near-field optical microscopy allows us to investigate the dynamics of the local out-of-plane electric field components and to visualize the temporal evolution of this time-harmonic reception process. The antenna directionality manifests itself by the dependence of the local field enhancement at the feed element on the illumination direction. Simulations taking into account the substrate confirm our observation of the directionality. Our work demonstrates the possibility to characterize multielement nanoantennas by electromagnetic antenna near-field scanners.
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http://dx.doi.org/10.1021/nl201184nDOI Listing
July 2011

Plasmonic nanowire antennas: experiment, simulation, and theory.

Nano Lett 2010 Sep;10(9):3596-603

Max-Planck-Institut für Festkorperförschung, Heisenbergstrasse 1, 70569 Stuttgart, Germany.

Recent advances in nanolithography have allowed shifting of the resonance frequency of antennas into the optical and visible wavelength range with potential applications, for example, in single molecule spectroscopy by fluorescence and directionality enhancement of molecules. Despite such great promise, the analytical means to describe the properties of optical antennas is still lacking. As the phase velocity of currents at optical frequencies in metals is much below the speed of light, standard radio frequency (RF) antenna theory does not apply directly. For the fundamental linear wire antenna, we present an analytical description that overcomes this shortage and reveals profound differences between RF and plasmonic antennas. It is fully supported by apertureless scanning near-field optical microscope measurements and finite-difference time-domain simulations. This theory is a starting point for the development of analytical models of more complex antenna structures.
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http://dx.doi.org/10.1021/nl101921yDOI Listing
September 2010

Resonance amplification of defect emission in ZnO-inverted opal.

Opt Lett 2009 May;34(10):1519-21

Tyndall National Institute, University College Cork, Lee Maltings, Cork, Ireland.

Transformation of broadband emission of oxygen defects in the carcass of ZnO-inverted opal into a multiple-mode amplified spontaneous emission band has been observed in the spectral interval of a photonic bandgap upon increasing excitation intensity. The mode structure has been assigned to amplification of emission coupled to resonance modes of the self-selected distributed Bragg resonator. The surprisingly low 2 W/cm(2) onset of amplification has been explained by the long radiative decay time of defect states populated according to the three-level excitation scheme. The decrease of emission intensity between amplified peaks has been associated with the saturation of the ZnO defect emission.
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http://dx.doi.org/10.1364/ol.34.001519DOI Listing
May 2009

Chemosorption-related shift of a photonic bandgap in photoconductive ZnO inverse opal.

Opt Lett 2008 Mar;33(5):461-3

Tyndall National Institute, University College Cork, Lee Maltings, Cork, Ireland.

A change of up to 40% of the relative transmission at the photonic bandgap edge has been observed in photoconductive inverted ZnO opals under ultraviolet laser irradiation. This effect has been related to the irradiation-stimulated change of the refraction index of the photonic crystal. The desorption (chemosorption) of oxygen molecules on the surface of the ZnO backbone leading to destruction (formation) of a depletion layer at the ZnO surface has been suggested as the mechanism responsible for the slow variation of polarizability of the inverted ZnO opal.
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http://dx.doi.org/10.1364/ol.33.000461DOI Listing
March 2008
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