Terahertz near-field imaging of electric and magnetic resonances of a planar metamaterial

Bitzer, Andreas; Merbold, Hannes; Thoman, Andreas; Feurer, Thomas; Helm, H.; Walther, Markus

doi:10.1364/oe.17.003826

Cited by 118 publications

(78 citation statements)

References 27 publications

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“…The Freibourg group took a similar approach for a measurement on a metamaterial structure [84]. These structures exhibit specific resonances in transmission when measured in the far-field.…”

Section: Metamaterialsmentioning

confidence: 99%

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Review of Near-Field Terahertz Measurement Methods and Their Applications

Adam

2011

J Infrared Milli Terahz Waves

202

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In the last decades, many research teams working at Terahertz frequencies focused their efforts on surpassing the diffraction limit. Numerous techniques have been investigated, combining methods existing at optic wavelength with THz system such as Time Domain Spectroscopy. The actual development led on one side to a resolution as high as λ/3000 and one the other side to a video-rate recording. The purpose of this paper is to give an overview of the history of the field, to describe the different approaches, to give examples of existing applications and to draw the perspective for this research area.

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Section: Metamaterialsmentioning

confidence: 99%

“…17, taken from [84] for four different resonances. The two higher resonances, given in at A3 and A4 present an electric quadrupole excitation while the two lower show a rotational field oscillating around the center of the structure.…”

Section: Metamaterialsmentioning

confidence: 99%

Review of Near-Field Terahertz Measurement Methods and Their Applications

Adam

2011

J Infrared Milli Terahz Waves

202

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“…To illustrate further the dependence of the resonant response on the size of the coherent metamaterial, we studied the spatial distribution of the magnetic field in a single split-ring meta-molecule and a meta-molecule that is a part of a regular array containing N = 400 unit cells. For this we employed a THz near-field imaging technique with sub-wavelength resolution described in [6]. The technique enabled accurate mapping of orthogonal components of the electrical field E in the plane of the unit cell (as illustrated in the inset to Fig.…”

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confidence: 99%

Spectral Collapse in Ensembles of Metamolecules

et al. 2010

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We report on a new collective phenomenon in metamaterials: spectral line collapse with increasing number of the unit cell resonators (meta-molecules). Resembling the behaviour of exotic states of matter, such as Bose-Einstein condensates of excitons and magnons, this new effect is linked to the suppression of radiation losses in periodic arrays. We demonstrate experimentally spectral line collapse at microwave, terahertz and optical frequencies. It emerges as a universal and truly scalable effect underpinned by classical electromagnetic interactions between the excited meta-molecules.The burgeoning field of metamaterials provides unique opportunities to engineer the electromagnetic properties of artificial media and achieve exotic functionalities, such as negative refraction [1] and cloaking [2]. Similarly to natural crystals, which are created by arranging individual atoms and molecules in a regular grid, periodic ensembles of subwavelength electromagnetic resonators present an effective medium to an incident with properties not available in natural materials. Here, we study the dependence of the metamaterial properties on the number of meta-molecules in the microwave, THz and optical domain, and demonstrate a new collective phenomenon in metamaterials: in contrast to solid state crystals, where bulk arrangements result in broadening of the individual element spectral line, leading eventually to the formation of absorption bands, regular ensembles of meta-molecules can exhibit the opposite effect, i.e. spectral line collapse. The reported phenomenon is characteristic to a novel class of artificial media, which we call "coherent" metamaterials [3] and are characterized by very strong interactions between the electromagnetically excited metamolecules that provide for a low rate of energy loss due to scattering and lead to a high-quality resonant response. An example of a coherent metamaterial is an array of ASRs, where the meta-molecular excitation corresponds to an oscillating magnetic dipole perpendicular to the plane of the array that does not interact directly with the magnetic field of the incident wave, thus creating a nearly thermodynamically isolated ensemble of strongly interacting coherent "molecules" with interesting physical properties. To illustrate this behavior we present a comparison with an "incoherent" metamaterial: a twodimensional array formed by pairs of concentric conducting rings that also supports a high-quality resonant response. In this case, however, the response of the array is a sum of the individual meta-molecule responses, rather than a collective property.The coherent microwave metamaterial was manufactured as a regular planar array of asymmetric split rings (ASR) etched from a 35 µm thick copper layer on a 1.6 mm thick FR4 substrate. The diameter of the ASR was 6 mm with a line width of 0.4 mm and was split in two segments corresponding to 140 • and 160 • arcs. The unit cell of 7.5 × 7.5 mm 2 rendered the arrays nondiffracting at normal incidence for frequencies of up to 40 GHz. I...

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“…An intriguing Fourier-spectroscopic variant of pumpprobe techniques has been shown to resolve electromagnetic vector field components of THz-pumped SPP resonances with the spatial resolution of optical probe pulses. [98][99][100][101][102][103][104] During the writing of this Minireview, mapping plasmonic resonances with simultaneous electron and photon pulses has also been demonstrated. 105 It allows observation of higher-order EELS processes as well as electron energy gain spectroscopic (EEGS) imaging of plasmons.…”

Section: Discussionmentioning

confidence: 99%

Real-space imaging of nanoplasmonic resonances

Vogelgesang

Dmitriev

2010

Analyst

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Resonant nanoplasmonic structures have long been recognized for their unique applications in subwavelength control of light for enhanced transmission, focussing, field confinement, decay rate management, etc. Increasingly, they are also integrated in electro-optical analytical sensors, shrinking the active volume while at the same time improving sensitivity and specificity. The microscopic imaging of resonances in such structures and also their dynamic variations has seen dramatic advances in recent years. In this Minireview we outline the current status of this rapidly evolving field, discussing both optical and electron microscopy approaches, the limiting issues in spatial resolution and data interpretation, the quantities that can be recorded, as well as the growing importance of time-resolving methods.

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Terahertz near-field imaging of electric and magnetic resonances of a planar metamaterial

Cited by 118 publications

References 27 publications

Review of Near-Field Terahertz Measurement Methods and Their Applications

Review of Near-Field Terahertz Measurement Methods and Their Applications

Spectral Collapse in Ensembles of Metamolecules

Real-space imaging of nanoplasmonic resonances

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