1
|
Sun X, Adamo G, Eginligil M, Krishnamoorthy HNS, Zheludev NI, Soci C. Topological insulator metamaterial with giant circular photogalvanic effect. Sci Adv 2021; 7:eabe5748. [PMID: 33811072 PMCID: PMC11057521 DOI: 10.1126/sciadv.abe5748] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2020] [Accepted: 02/12/2021] [Indexed: 06/12/2023]
Abstract
One of the most notable manifestations of electronic properties of topological insulators is the dependence of the photocurrent direction on the helicity of circularly polarized optical excitation. The helicity-dependent photocurrents, underpinned by spin-momentum locking of surface Dirac electrons, are weak and easily overshadowed by bulk contributions. Here, we show that the chiral response can be enhanced by nanostructuring. The tight confinement of electromagnetic fields in the resonant nanostructure enhances the photoexcitation of spin-polarized surface states of topological insulator Bi1.5Sb0.5Te1.8Se1.2, leading to an 11-fold increase of the circular photogalvanic effect and a previously unobserved photocurrent dichroism (ρcirc = 0.87) at room temperature. The control of spin transport in topological materials by structural design is a previously unrecognized ability of metamaterials that bridges the gap between nanophotonics and spin electronics, providing opportunities for developing polarization-sensitive photodetectors.
Collapse
Affiliation(s)
- X Sun
- Centre for Disruptive Photonic Technologies, TPI, SPMS, Nanyang Technological University, Singapore 637371, Singapore
- Division of Physics and Applied Physics, Nanyang Technological University, Singapore 637371, Singapore
| | - G Adamo
- Centre for Disruptive Photonic Technologies, TPI, SPMS, Nanyang Technological University, Singapore 637371, Singapore
- Division of Physics and Applied Physics, Nanyang Technological University, Singapore 637371, Singapore
| | - M Eginligil
- Division of Physics and Applied Physics, Nanyang Technological University, Singapore 637371, Singapore
| | - H N S Krishnamoorthy
- Centre for Disruptive Photonic Technologies, TPI, SPMS, Nanyang Technological University, Singapore 637371, Singapore
- Division of Physics and Applied Physics, Nanyang Technological University, Singapore 637371, Singapore
| | - N I Zheludev
- Centre for Disruptive Photonic Technologies, TPI, SPMS, Nanyang Technological University, Singapore 637371, Singapore
- Division of Physics and Applied Physics, Nanyang Technological University, Singapore 637371, Singapore
- Optoelectronics Research Centre and Centre for Photonic Metamaterials, University of Southampton, Southampton SO17 1BJ, UK
| | - C Soci
- Centre for Disruptive Photonic Technologies, TPI, SPMS, Nanyang Technological University, Singapore 637371, Singapore.
- Division of Physics and Applied Physics, Nanyang Technological University, Singapore 637371, Singapore
| |
Collapse
|
2
|
Krishnamoorthy HNS, Adamo G, Yin J, Savinov V, Zheludev NI, Soci C. Infrared dielectric metamaterials from high refractive index chalcogenides. Nat Commun 2020; 11:1692. [PMID: 32245976 PMCID: PMC7125163 DOI: 10.1038/s41467-020-15444-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2019] [Accepted: 02/28/2020] [Indexed: 11/09/2022] Open
Abstract
High-index dielectric materials are in great demand for nanophotonic devices and applications, from ultrathin optical elements to metal-free sub-diffraction light confinement and waveguiding. Here we show that chalcogenide topological insulators are particularly apt candidates for dielectric nanophotonics architectures in the infrared spectral range, by reporting metamaterial resonances in chalcogenide crystals sustained well inside the mid-infrared, choosing Bi2Te3 as case study within this family of materials. Strong resonant modulation of the incident electromagnetic field is achieved thanks to the exceptionally high refractive index ranging between 7 and 8 throughout the 2-10 μm region. Analysis of the complex mode structure in the metamaterial allude to the excitation of circular surface currents which could open pathways for enhanced light-matter interaction and low-loss plasmonic configurations by coupling to the spin-polarized topological surface carriers, thereby providing new opportunities to combine dielectric, plasmonic and magnetic metamaterials in a single platform.
Collapse
Affiliation(s)
- H N S Krishnamoorthy
- Centre for Disruptive Photonic Technologies, TPI, SPMS, Nanyang Technological University, Singapore, 637371, Singapore.
| | - G Adamo
- Centre for Disruptive Photonic Technologies, TPI, SPMS, Nanyang Technological University, Singapore, 637371, Singapore
| | - J Yin
- Centre for Disruptive Photonic Technologies, TPI, SPMS, Nanyang Technological University, Singapore, 637371, Singapore
| | - V Savinov
- Optoelectronics Research Centre & Centre for Photonic Metamaterials, University of Southampton, London, SO17 1BJ, UK
| | - N I Zheludev
- Centre for Disruptive Photonic Technologies, TPI, SPMS, Nanyang Technological University, Singapore, 637371, Singapore
- Optoelectronics Research Centre & Centre for Photonic Metamaterials, University of Southampton, London, SO17 1BJ, UK
| | - C Soci
- Centre for Disruptive Photonic Technologies, TPI, SPMS, Nanyang Technological University, Singapore, 637371, Singapore.
| |
Collapse
|
3
|
Papasimakis N, Fedotov VA, Savinov V, Raybould TA, Zheludev NI. Electromagnetic toroidal excitations in matter and free space. Nat Mater 2016; 15:263-71. [PMID: 26906961 DOI: 10.1038/nmat4563] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2015] [Accepted: 01/08/2016] [Indexed: 05/20/2023]
Abstract
The toroidal dipole is a localized electromagnetic excitation, distinct from the magnetic and electric dipoles. While the electric dipole can be understood as a pair of opposite charges and the magnetic dipole as a current loop, the toroidal dipole corresponds to currents flowing on the surface of a torus. Toroidal dipoles provide physically significant contributions to the basic characteristics of matter including absorption, dispersion and optical activity. Toroidal excitations also exist in free space as spatially and temporally localized electromagnetic pulses propagating at the speed of light and interacting with matter. We review recent experimental observations of resonant toroidal dipole excitations in metamaterials and the discovery of anapoles, non-radiating charge-current configurations involving toroidal dipoles. While certain fundamental and practical aspects of toroidal electrodynamics remain open for the moment, we envision that exploitation of toroidal excitations can have important implications for the fields of photonics, sensing, energy and information.
Collapse
Affiliation(s)
- N Papasimakis
- Optoelectronics Research Centre &Centre for Photonic Metamaterials, University of Southampton, Highfield SO17 1BJ, UK
| | - V A Fedotov
- Optoelectronics Research Centre &Centre for Photonic Metamaterials, University of Southampton, Highfield SO17 1BJ, UK
| | - V Savinov
- Optoelectronics Research Centre &Centre for Photonic Metamaterials, University of Southampton, Highfield SO17 1BJ, UK
| | - T A Raybould
- Optoelectronics Research Centre &Centre for Photonic Metamaterials, University of Southampton, Highfield SO17 1BJ, UK
| | - N I Zheludev
- Optoelectronics Research Centre &Centre for Photonic Metamaterials, University of Southampton, Highfield SO17 1BJ, UK
- TPI and Centre for Disruptive Photonic Technologies, Nanyang Technological University, Singapore 637378, Singapore
| |
Collapse
|
4
|
|
5
|
Zhu WM, Liu AQ, Bourouina T, Tsai DP, Teng JH, Zhang XH, Lo GQ, Kwong DL, Zheludev NI. Microelectromechanical Maltese-cross metamaterial with tunable terahertz anisotropy. Nat Commun 2013; 3:1274. [PMID: 23232404 PMCID: PMC3535344 DOI: 10.1038/ncomms2285] [Citation(s) in RCA: 193] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2012] [Accepted: 11/14/2012] [Indexed: 11/09/2022] Open
Abstract
Dichroic polarizers and waveplates exploiting anisotropic materials have vast applications in displays and numerous optical components, such as filters, beamsplitters and isolators. Artificial anisotropic media were recently suggested for the realization of negative refraction, cloaking, hyperlenses, and controlling luminescence. However, extending these applications into the terahertz domain is hampered by a lack of natural anisotropic media, while artificial metamaterials offer a strong engineered anisotropic response. Here we demonstrate a terahertz metamaterial with anisotropy tunable from positive to negative values. It is based on the Maltese-cross pattern, where anisotropy is induced by breaking the four-fold symmetry of the cross by displacing one of its beams. The symmetry breaking permits the excitation of a Fano mode active for one of the polarization eigenstates controlled by actuators using microelectromechanical systems. The metamaterial offers new opportunities for the development of terahertz variable waveplates, tunable filters and polarimetry.
Collapse
Affiliation(s)
- W M Zhu
- School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore
| | | | | | | | | | | | | | | | | |
Collapse
|
6
|
Buchnev O, Ou JY, Kaczmarek M, Zheludev NI, Fedotov VA. Electro-optical control in a plasmonic metamaterial hybridised with a liquid-crystal cell. Opt Express 2013; 21:1633-8. [PMID: 23389148 DOI: 10.1364/oe.21.001633] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
We experimentally demonstrate efficient electro-optical control in an active nano-structured plasmonic metamaterial hybridised with a liquid-crystal cell. The hybridisation was achieved by simultaneously replacing the polarizer, transparent electrode and molecular alignment layer of the liquid-crystal cell with the metamaterial nano-structure. With the control signal of only 7 V we have achieved a fivefold hysteresis-free modulation of metamaterial transmission at the wavelength of 1.55 µm.
Collapse
Affiliation(s)
- O Buchnev
- Optoelectronics Research Centre, University of Southampton, SO17 1BJ, UK
| | | | | | | | | |
Collapse
|
7
|
Savinov V, Fedotov VA, Anlage SM, de Groot PAJ, Zheludev NI. Modulating sub-THz radiation with current in superconducting metamaterial. Phys Rev Lett 2012; 109:243904. [PMID: 23368321 DOI: 10.1103/physrevlett.109.243904] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2012] [Indexed: 06/01/2023]
Abstract
We show that subterahertz transmission of the superconducting metamaterial, an interlinked two-dimensional network of subwavelength resonators connected by a continuous superconducting wire loop, can be dynamically modulated by passing electrical current through it. We have identified the main mechanisms of modulation that correspond to the suppression of the superconductivity in the network by magnetic field and heat dissipation. Using the metamaterial fabricated from thin niobium film, we were able to demonstrate a transmission modulation depth of up to 45% and a bandwidth of at least 100 kHz. The demonstrated approach may be implemented with other superconducting materials at frequencies below the superconducting gap in the THz and subterahertz bands.
Collapse
Affiliation(s)
- V Savinov
- Optoelectronics Research Centre and Centre for Photonic Metamaterials, University of Southampton, Southampton SO17 1BJ, United Kingdom.
| | | | | | | | | |
Collapse
|
8
|
Adamo G, Ou JY, So JK, Jenkins SD, De Angelis F, MacDonald KF, Di Fabrizio E, Ruostekoski J, Zheludev NI. Electron-beam-driven collective-mode metamaterial light source. Phys Rev Lett 2012; 109:217401. [PMID: 23215613 DOI: 10.1103/physrevlett.109.217401] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2012] [Indexed: 05/12/2023]
Abstract
We demonstrate experimentally that the energy from a highly localized free-electron-beam excitation can be converted via a planar plasmonic metamaterial to a low-divergence free-space light beam. This emission, which emanates from a collectively oscillating coupled metamolecule nanoantenna ensemble much larger in size than the initial excitation, is distinctly different from cathodoluminescence and bears some similarity with laser light. It offers a novel, flexible paradigm for the development of scalable, threshold-free light sources.
Collapse
Affiliation(s)
- G Adamo
- Optoelectronics Research Centre and Centre for Photonic Metamaterials, University of Southampton, Highfield, Southampton SO17 1BJ, United Kingdom
| | | | | | | | | | | | | | | | | |
Collapse
|
9
|
Yang Y, Chin LK, Tsai JM, Tsai DP, Zheludev NI, Liu AQ. Transformation optofluidics for large-angle light bending and tuning. Lab Chip 2012; 12:3785-3790. [PMID: 22868356 DOI: 10.1039/c2lc40442g] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Transformation optics is a new art of light bending by designing materials with spatially variable parameters for developing wave-manipulation devices. Here, we introduce a transformation optofluidic Y-branch splitter with large-angle bending and tuning based on the design of a spatially variable index. Differing from traditional splitters, the optofluidic splitter is achieved in an inhomogeneous medium by coordinate transformation. The designed bidirectional gradient index (GRIN) distribution can be achieved practically by the convection-diffusion process of liquid flowing streams. The transformation optofluidic splitter can achieve a much larger split angle with little bend loss than the traditional ones. In the experiments, a large tunable split angle up to 30° is achieved by tuning the flow rates, allowing optical signals to be freely transferred to different channels. Besides the symmetrical branch splitting, asymmetrical Y-branch splitting with approximately equal power splitting is also demonstrated by changing the composition of the liquids. The optofluidic splitter has high potential applications in biological, chemical and biomedical solution measurement and detection.
Collapse
Affiliation(s)
- Y Yang
- School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798.
| | | | | | | | | | | |
Collapse
|
10
|
Abstract
We show that a plasmonic metamaterial can act as a far-field to near-field transformer that focuses a free-space beam of light into a subwavelength energy hot spot at a prescribed location with a spot size only a small fraction of the wavelength. The hot spot position on the metamaterial can be prescribed and moved at will from one metamolecule of the array to another in a "digital" fashion simply by modulating the input phase profile, thus providing new opportunities for imaging and optical data processing.
Collapse
Affiliation(s)
- T S Kao
- Optoelectronics Research Centre and Centre for Photonic Metamaterials, University of Southampton, Southampton SO17 1BJ, United Kingdom
| | | | | | | |
Collapse
|
11
|
Abstract
We introduce mechanically reconfigurable photonic metamaterials (RPMs) as a flexible platform for realizing metamaterial devices with reversible and large-range tunable characteristics in the optical part of the spectrum. Here we illustrate this concept for a temperature-driven RPM exhibiting reversible relative transmission changes of up to 50%.
Collapse
Affiliation(s)
- J Y Ou
- Optoelectronics Research Centre and Centre for Photonic Metamaterials, University of Southampton, SO17 1BJ, United Kingdom.
| | | | | | | |
Collapse
|
12
|
Kao TS, Jenkins SD, Ruostekoski J, Zheludev NI. Coherent control of nanoscale light localization in metamaterial: creating and positioning isolated subwavelength energy hot spots. Phys Rev Lett 2011; 106:085501. [PMID: 21405581 DOI: 10.1103/physrevlett.106.085501] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2010] [Indexed: 05/27/2023]
Abstract
We show the strong optically induced interactions between discrete metamolecules in a metamaterial system and coherent monochromatic continuous light beam with a spatially tailored phase profile can be used to prepare a subwavelength scale energy localization. Well-isolated energy hot spots of a fraction of a wavelength can be created and positioned on the metamaterial landscape offering new opportunities for data storage and imaging applications.
Collapse
Affiliation(s)
- T S Kao
- Optoelectronics Research Centre and Centre for Photonic Metamaterials, University of Southampton, Southampton SO17 1BJ, United Kingdom
| | | | | | | |
Collapse
|
13
|
Tanaka K, Plum E, Ou JY, Uchino T, Zheludev NI. Multifold enhancement of quantum dot luminescence in plasmonic metamaterials. Phys Rev Lett 2010; 105:227403. [PMID: 21231422 DOI: 10.1103/physrevlett.105.227403] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2010] [Indexed: 05/15/2023]
Abstract
We report that hybridizing semiconductor quantum dots with plasmonic metamaterial leads to a multifold intensity increase and narrowing of their photoluminescence spectrum. The luminescence enhancement is a clear manifestation of the cavity quantum electrodynamics Purcell effect and can be controlled by the metamaterial's design. This observation is an essential step towards understanding loss compensation in plasmonic metamaterials with gain media and for developing metamaterial-enhanced gain media.
Collapse
Affiliation(s)
- K Tanaka
- Optoelectronics Research Centre and Centre for Photonic Metamaterials, University of Southampton, Southampton SO17 1BJ, United Kingdom.
| | | | | | | | | |
Collapse
|
14
|
Abstract
Toroidal multipoles are fundamental electromagnetic excitations different from those associated with the familiar charge and magnetic multipoles. They have been held responsible for parity violation in nuclear and particle physics, but direct evidence of their existence in classical electrodynamics has remained elusive. We report on the observation of a resonant electromagnetic response in an artificially engineered medium, or metamaterial, that cannot be attributed to magnetic or charge multipoles and can only be explained by the existence of a toroidal dipole. Our direct experimental evidence of the toroidal response brings attention to the often ignored electromagnetic interactions involving toroidal multipoles, which could be present in naturally occurring systems, especially at the macromolecule level, where toroidal symmetry is ubiquitous.
Collapse
|
15
|
Denisyuk AI, Adamo G, MacDonald KF, Edgar J, Arnold MD, Myroshnychenko V, Ford MJ, García de Abajo FJ, Zheludev NI. Transmitting hertzian optical nanoantenna with free-electron feed. Nano Lett 2010; 10:3250-3252. [PMID: 20731411 DOI: 10.1021/nl1002813] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
A pair of coupled gold nanorods excited by a beam of free electrons acts as a transmitting Hertzian antenna in the optical part of the spectrum. Significantly enhanced resonant emission is observed from the antenna when the electron beam is injected around the junction between the rods, where the local density of electromagnetic states is elevated.
Collapse
Affiliation(s)
- A I Denisyuk
- Optoelectronics Research Centre, University of Southampton, Southampton SO17 1BJ, UK
| | | | | | | | | | | | | | | | | |
Collapse
|
16
|
Fedotov VA, Papasimakis N, Plum E, Bitzer A, Walther M, Kuo P, Tsai DP, Zheludev NI. Spectral collapse in ensembles of metamolecules. Phys Rev Lett 2010; 104:223901. [PMID: 20867169 DOI: 10.1103/physrevlett.104.223901] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2009] [Revised: 04/20/2010] [Indexed: 05/27/2023]
Abstract
We report on the first direct experimental demonstration of a collective phenomenon in metamaterials: spectral line collapse with an increasing number of unit cell resonators (metamolecules). This effect, which is crucial for achieving a lasing spaser, a coherent source of optical radiation fuelled by coherent plasmonic oscillations in metamaterials, is linked to the suppression of radiation losses in periodic arrays. We experimentally demonstrate spectral line collapse at microwave, terahertz and optical frequencies.
Collapse
Affiliation(s)
- V A Fedotov
- Optoelectronics Research Centre, University of Southampton, SO17 1BJ, United Kingdom.
| | | | | | | | | | | | | | | |
Collapse
|
17
|
|
18
|
Tikhomirov VK, Adamo G, Nikolaenko AE, Rodriguez VD, Gredin P, Mortier M, Zheludev NI, Moshchalkov VV. Cathodo- and photoluminescence in Yb(3+)-Er(3+) co-doped PbF(2) nanoparticles. Opt Express 2010; 18:8836-8846. [PMID: 20588728 DOI: 10.1364/oe.18.008836] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
We have prepared and studied the PbF(2):(Yb(3+),Er(3+)) co-doped nanoparticles, with chemical formula (Yb-Er)(x)Pb(1-x)F(2+x), where x = 0.29, Yb(3+)/Er(3+) = 6, and estimated the energy efficiency for their cathodoluminescence, mostly of Yb(3+), and up-conversion photoluminescence of Er(3+) to reach more than 0.5% and 20%, respectively, which may be the highest to date for rare-earth doped nanoparticles. Electron beam induced temperature rise in the nanoparticles has been estimated by measuring the ratio of green emission bands of Er(3+). These high efficiencies are due to high doping level of nanoparticles and due to low phonon energy of the PbF(2) host.
Collapse
Affiliation(s)
- V K Tikhomirov
- INPAC - Institute for Nanoscale Physics and Chemistry, Catholic University Leuven, Belgium.
| | | | | | | | | | | | | | | |
Collapse
|
19
|
Fedotov VA, Tsiatmas A, Shi JH, Buckingham R, de Groot P, Chen Y, Wang S, Zheludev NI. Temperature control of Fano resonances and transmission in superconducting metamaterials. Opt Express 2010; 18:9015-9019. [PMID: 20588747 DOI: 10.1364/oe.18.009015] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Losses are the main evil that limits the use of metamaterials in practical applications. While radiation losses may be controlled by design, Joule losses are hereditary to the metamaterial structures. An exception is superconducting metamaterials, where Joule losses can be uniquely controlled with temperature in a very wide range. We put this in use by demonstrating temperature-dependent transmission in the millimeter-wave part of the spectrum in high-Tc superconducting cuprate metamaterials supporting sub-radiant resonances of Fano type.
Collapse
Affiliation(s)
- V A Fedotov
- Optoelectronics Research Centre, University of Southampton, SO17 1BJ, UK.
| | | | | | | | | | | | | | | |
Collapse
|
20
|
|
21
|
Adamo G, MacDonald KF, Fu YH, Wang CM, Tsai DP, de Abajo FJG, Zheludev NI. Light well: a tunable free-electron light source on a chip. Phys Rev Lett 2009; 103:113901. [PMID: 19792372 DOI: 10.1103/physrevlett.103.113901] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2009] [Revised: 08/17/2009] [Indexed: 05/12/2023]
Abstract
The passage of a free-electron beam through a nanohole in a periodically layered metal-dielectric structure creates a new type of tunable, nanoscale radiation source--a "light well". In the reported demonstration, tunable light is generated at an intensity of approximately 200 W/cm(2) as electrons with energies in the 20-40 keV range are injected into gold-silica well structures with a lateral size of just a few hundred nanometers.
Collapse
Affiliation(s)
- G Adamo
- Optoelectronics Research Centre, University of Southampton, Southampton, SO17 1BJ, United Kingdom
| | | | | | | | | | | | | |
Collapse
|
22
|
Papasimakis N, Fedotov VA, Marinov K, Zheludev NI. Gyrotropy of a metamolecule: wire on a torus. Phys Rev Lett 2009; 103:093901. [PMID: 19792797 DOI: 10.1103/physrevlett.103.093901] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2009] [Revised: 07/29/2009] [Indexed: 05/10/2023]
Abstract
Sharing topology with numerous organic molecules, a wire helix bend into a torus gives a curious object with a gyrotropic behavior which is far from obvious. While a continuous constant current in opposite sections of the torus would create mutually cancelling contributions to its gyrotropic response, an array of tori can show strong circular dichroism linked to the excitation of standing current waves. Here we present the experimental study of optical activity in a chiral toroidal metamaterial and discuss its response in terms of multipole moments, including the elusive toroidal moment.
Collapse
Affiliation(s)
- N Papasimakis
- Optoelectronics Research Centre, University of Southampton, SO17 1BJ, United Kingdom.
| | | | | | | |
Collapse
|
23
|
Plum E, Fedotov VA, Kuo P, Tsai DP, Zheludev NI. Towards the lasing spaser: controlling metamaterial optical response with semiconductor quantum dots. Opt Express 2009; 17:8548-8551. [PMID: 19434188 DOI: 10.1364/oe.17.008548] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We report the first experimental demonstration of compensating Joule losses in metallic photonic metamaterial using optically pumped PbS semiconductor quantum dots.
Collapse
Affiliation(s)
- E Plum
- Optoelectronics Research Centre, University of Southampton, Southampton, United Kingdom.
| | | | | | | | | |
Collapse
|
24
|
|
25
|
Plum E, Liu XX, Fedotov VA, Chen Y, Tsai DP, Zheludev NI. Metamaterials: optical activity without chirality. Phys Rev Lett 2009; 102:113902. [PMID: 19392202 DOI: 10.1103/physrevlett.102.113902] [Citation(s) in RCA: 182] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2008] [Revised: 01/22/2009] [Indexed: 05/10/2023]
Abstract
We report that the classical phenomenon of optical activity, which is traditionally associated with chirality (helicity) of organic molecules, proteins, and inorganic structures, can be observed in artificial planar media which exhibit neither 3D nor 2D chirality. We observe the effect in the microwave and optical parts of the spectrum at oblique incidence to regular arrays of nonchiral subwavelength metamolecules in the form of strong circular dichroism and birefringence indistinguishable from those of chiral three-dimensional media.
Collapse
Affiliation(s)
- E Plum
- Optoelectronics Research Centre, University of Southampton, SO17 1BJ, United Kingdom
| | | | | | | | | | | |
Collapse
|
26
|
Papasimakis N, Fedotov VA, Zheludev NI, Prosvirnin SL. Metamaterial analog of electromagnetically induced transparency. Phys Rev Lett 2008; 101:253903. [PMID: 19113710 DOI: 10.1103/physrevlett.101.253903] [Citation(s) in RCA: 221] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2008] [Revised: 11/12/2008] [Indexed: 05/27/2023]
Abstract
We demonstrate a classical analog of electromagnetically induced transparency in a planar metamaterial. We show that pulses propagating through such metamaterials experience considerable delay. The thickness of the structure along the direction of wave propagation is much smaller than the wavelength, which allows successive stacking of multiple metamaterial slabs leading to increased transmission and bandwidth.
Collapse
Affiliation(s)
- N Papasimakis
- Optoelectronics Research Centre, University of Southampton, SO17 1BJ, United Kingdom.
| | | | | | | |
Collapse
|
27
|
Schwanecke AS, Fedotov VA, Khardikov VV, Prosvirnin SL, Chen Y, Zheludev NI. Nanostructured metal film with asymmetric optical transmission. Nano Lett 2008; 8:2940-3. [PMID: 18720979 DOI: 10.1021/nl801794d] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
We demonstrate for the first time a nanostructured planar photonic metamaterial transmitting light differently in forward and backward directions.
Collapse
Affiliation(s)
- A S Schwanecke
- Optoelectronics Research Center, University of Southampton, SO17 1BJ, United Kingdom
| | | | | | | | | | | |
Collapse
|
28
|
|
29
|
|
30
|
Aleksandrovskiĭ AL, Akhmanov SA, Dyakov VA, Zheludev NI, Pryalkin VI. Efficient nonlinear optical converters made of potassium titanyl phosphate crystals. ACTA ACUST UNITED AC 2007. [DOI: 10.1070/qe1985v015n07abeh007276] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
|
31
|
Fedotov VA, Rose M, Prosvirnin SL, Papasimakis N, Zheludev NI. Sharp trapped-mode resonances in planar metamaterials with a broken structural symmetry. Phys Rev Lett 2007; 99:147401. [PMID: 17930720 DOI: 10.1103/physrevlett.99.147401] [Citation(s) in RCA: 299] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2007] [Indexed: 05/04/2023]
Abstract
We report that a resonance response with a very high quality factor can be achieved in a planar metamaterial by introducing symmetry breaking in the shape of its structural elements, which enables excitation of trapped modes, i.e., modes that are weakly coupled to free space.
Collapse
Affiliation(s)
- V A Fedotov
- Optoelectronics Research Centre, University of Southampton, UK
| | | | | | | | | |
Collapse
|
32
|
Bashevoy MV, Jonsson F, Macdonald KF, Chen Y, Zheludev NI. Hyperspectral imaging of plasmonic nanostructures with nanoscale resolution. Opt Express 2007; 15:11313-11320. [PMID: 19547488 DOI: 10.1364/oe.15.011313] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We report on the first realization of a hyperspectral imaging technique for surface plasmon polaritons on metallic nanostructures. The technique uses a scanning electron beam and allows for simple visualization of light emission from decoupled plasmons, providing information on decay lengths and feature sizes with nanometer resolution.
Collapse
|
33
|
|
34
|
Soares BF, Bashevoy MV, Jonsson F, Macdonald KF, Zheludev NI. Polymorphic nanoparticles as all-optical memory elements. Opt Express 2006; 14:10652-10656. [PMID: 19529470 DOI: 10.1364/oe.14.010652] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
A nanoparticle undergoing light-induced transformations between structural phases with different optical properties is an inheritably bistable structure and this bistability can be used to create a resonator-free optical memory element, operating at very low power levels. We experimentally demonstrate this memory functionality using a film of gallium nanoparticles, and we present a method for differentially accessing the logic state of the memory using a modulated optical probe beam.
Collapse
|
35
|
Rogacheva AV, Fedotov VA, Schwanecke AS, Zheludev NI. Giant gyrotropy due to electromagnetic-field coupling in a bilayered chiral structure. Phys Rev Lett 2006; 97:177401. [PMID: 17155505 DOI: 10.1103/physrevlett.97.177401] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2006] [Indexed: 05/12/2023]
Abstract
We report experimental evidence that electromagnetic coupling between physically separated planar metal patterns located in parallel planes provides for extremely strong polarization rotatory power if one pattern is twisted with respect to the other, creating a chiral object. In terms of a rotary power per sample thickness equal to one wavelength, the bilayered structure rotates 5 orders of magnitude stronger than a gyrotropic crystal of quartz in the visible spectrum.
Collapse
Affiliation(s)
- A V Rogacheva
- EPSRC NanoPhotonics Portfolio Centre, School of Physics and Astronomy, University of Southampton, SO17 1BJ, United Kingdom
| | | | | | | |
Collapse
|
36
|
Fedotov VA, Mladyonov PL, Prosvirnin SL, Rogacheva AV, Chen Y, Zheludev NI. Asymmetric propagation of electromagnetic waves through a planar chiral structure. Phys Rev Lett 2006; 97:167401. [PMID: 17155432 DOI: 10.1103/physrevlett.97.167401] [Citation(s) in RCA: 204] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2006] [Indexed: 05/12/2023]
Abstract
We report that normal incidence transmission of circularly polarized waves through the lossy anisotropic planar chiral structure is asymmetric in the opposite direction. The new effect is fundamentally distinct from conventional gyrotropy of bulk chiral media and the Faraday effect, where the eigenstates are a pair of counterrotating elliptical states, while the eigenstates of the lossy anisotropic planar chiral structure are two corotating elliptical polarizations.
Collapse
Affiliation(s)
- V A Fedotov
- EPSRC Nanophotonics Portfolio Centre, School of Physics and Astronomy, University of Southampton, UK.
| | | | | | | | | | | |
Collapse
|
37
|
Bashevoy MV, Jonsson F, Krasavin AV, Zheludev NI, Chen Y, Stockman MI. Generation of traveling surface plasmon waves by free-electron impact. Nano Lett 2006; 6:1113-5. [PMID: 16771563 DOI: 10.1021/nl060941v] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
The injection of a beam of free 50 keV electrons into an unstructured gold surface creates a highly localized source of traveling surface plasmons with spectra centered below the surface plasmon resonance frequency. The plasmons were detected by a controlled decoupling into light with a grating at a distance from the excitation point. The dominant contribution to the plasmon generation appears to come from the recombination of d-band holes created by the electron beam excitation.
Collapse
Affiliation(s)
- M V Bashevoy
- EPSRC Nanophotonics Portfolio Centre, School of Physics and Astronomy, University of Southampton, SO17 1BJ, United Kingdom
| | | | | | | | | | | |
Collapse
|
38
|
Fedotov VA, Mladyonov PL, Prosvirnin SL, Zheludev NI. Planar electromagnetic metamaterial with a fish scale structure. Phys Rev E Stat Nonlin Soft Matter Phys 2005; 72:056613. [PMID: 16383777 DOI: 10.1103/physreve.72.056613] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2005] [Indexed: 05/05/2023]
Abstract
We report on a continuous electromagnetic metal planar metamaterial, which resembles a "fish scale" structure. Apart from the one isolated wavelength, it is highly transparent to electromagnetic radiation throughout a broad spectral range and becomes completely "invisible" at some frequency inflicting no transmission losses and phase delay. When the structure is superimposed on a metallic mirror it becomes a good broadband reflector everywhere apart from one wavelength where the reflectivity is small. At this wavelength the reflected wave shows no phase change with respect to the incident wave, thus resembling a reflection from a hypothetical zero refractive index material, or "magnetic wall." We also discovered that the structure acts as a local field concentrator and a resonant "amplifier" of losses in the underlying dielectric.
Collapse
Affiliation(s)
- V A Fedotov
- EPSRC Nanophotonics Portfolio Centre, School of Physics and Astronomy, University of Southampton, High Field, Southampton, SO17 1BJ, United Kingdom
| | | | | | | |
Collapse
|
39
|
Prosvirnin SL, Zheludev NI. Polarization effects in the diffraction of light by a planar chiral structure. Phys Rev E Stat Nonlin Soft Matter Phys 2005; 71:037603. [PMID: 15903646 DOI: 10.1103/physreve.71.037603] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/22/2003] [Revised: 08/31/2004] [Indexed: 05/02/2023]
Abstract
We analyze polarization changes of light diffracted on a planar chiral array from the standpoint of the Lorentz reciprocity lemma and find biorthogonality in the polarization eigenstates for waves diffracting though the grating in the opposite direction. Both reciprocal and nonreciprocal components in the polarization azimuth rotation of the diffracted light are identified. The structural chirality of the array arrangement and the chirality of individual elements of the array give rise to polarization effects.
Collapse
Affiliation(s)
- S L Prosvirnin
- Institute of Radio Astronomy, National Academy of Sciences of Ukraine, Kharkov, Ukraine
| | | |
Collapse
|
40
|
|
41
|
Pochon S, MacDonald KF, Knize RJ, Zheludev NI. Phase coexistence in gallium nanoparticles controlled by electron excitation. Phys Rev Lett 2004; 92:145702. [PMID: 15089555 DOI: 10.1103/physrevlett.92.145702] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2003] [Indexed: 05/24/2023]
Abstract
In gallium nanoparticles 100 nm in diameter grown on the tip of an optical fiber from an atomic beam we observed equilibrium coexistence of gamma, beta, and liquid structural phases that can be controlled by e-beam excitation in a highly reversible and reproducible fashion. With 2 keV electrons only 1 pJ of excitation energy per nanoparticle is needed to exercise control, with the equilibrium phase achieved in less than a few tenths of a microsecond. The transformations between coexisting phases are accompanied by a continuous change in the nanoparticle film's reflectivity.
Collapse
Affiliation(s)
- S Pochon
- School of Physics and Astronomy, University of Southampton, SO17 1BJ, United Kingdom
| | | | | | | |
Collapse
|
42
|
Schwanecke AS, Krasavin A, Bagnall DM, Potts A, Zayats AV, Zheludev NI. Broken time reversal of light interaction with planar chiral nanostructures. Phys Rev Lett 2003; 91:247404. [PMID: 14683156 DOI: 10.1103/physrevlett.91.247404] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2003] [Indexed: 05/12/2023]
Abstract
We report unambiguous experimental evidence of broken time-reversal symmetry for the interaction of light with an artificial nonmagnetic material. Polarized color images of planar chiral gold-on-silicon nanostructures consisting of arrays of gammadions show intriguing and unusual symmetry: structures, which are geometrically mirror images, lose their mirror symmetry in polarized light. The symmetry of images can be described only in terms of antisymmetry (black-and-white symmetry) appropriate to a time-odd process. The effect results from a transverse chiral nonlocal electromagnetic response of the structure and has some striking resemblance with the expected features of light scattering on anyon matter.
Collapse
Affiliation(s)
- A S Schwanecke
- School of Physics and Astronomy, University of Southampton, SO17 1BJ, United Kingdom
| | | | | | | | | | | |
Collapse
|
43
|
Potts A, Bagnall DM, Zheludev NI. A new model of geometric chirality for two-dimensional continuous media and planar meta-materials. ACTA ACUST UNITED AC 2003. [DOI: 10.1088/1464-4258/6/2/007] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
44
|
Fedotov VA, Emel yanov VI, MacDonald KF, Zheludev NI. Optical properties of closely packed nanoparticle films: spheroids and nanoshells. ACTA ACUST UNITED AC 2003. [DOI: 10.1088/1464-4258/6/2/001] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
45
|
|
46
|
MacDonald KF, Fedotov VA, Pochon S, Soares BF, Zheludev NI, Guignard C, Mihaescu A, Besnard P. Oscillating bubbles at the tips of optical fibers in liquid nitrogen. Phys Rev E Stat Nonlin Soft Matter Phys 2003; 68:027301. [PMID: 14525154 DOI: 10.1103/physreve.68.027301] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2002] [Revised: 03/31/2003] [Indexed: 05/24/2023]
Abstract
We report that a bubble with a radius of a few micrometers may be created at a precise location on a metal-coated optical fiber tip immersed in liquid nitrogen by microsecond optical pulses with peak powers of less than 20 mW. Dynamic optical measurements reveal that after termination of the optical pulse the bubble exhibits stable oscillations for several tens of microseconds, at frequencies up to several megahertz, as it slowly collapses.
Collapse
Affiliation(s)
- K F MacDonald
- Department of Physics and Astronomy, University of Southampton, Southampton SO16 7DH, United Kingdom
| | | | | | | | | | | | | | | |
Collapse
|
47
|
Papakostas A, Potts A, Bagnall DM, Prosvirnin SL, Coles HJ, Zheludev NI. Optical manifestations of planar chirality. Phys Rev Lett 2003; 90:107404. [PMID: 12689032 DOI: 10.1103/physrevlett.90.107404] [Citation(s) in RCA: 149] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2002] [Indexed: 05/24/2023]
Abstract
We report that planar chiral structures affect the polarization state of light in a manner similar to three-dimensional chiral (optical active) media. In experiments with artificial metal-on-silicon chiral planar gratings of 442 wallpaper group symmetry, containing millions of chiral elements per square centimeter, we observed rotation of the polarization azimuth in excess of 30 degrees of light diffracted from it. The rotation was found to change its sign for two enantiomeric forms of the media and to have components associated with both the structural arrangement and the chirality of individual structural elements.
Collapse
Affiliation(s)
- A Papakostas
- Department of Physics and Astronomy, University of Southampton, SO17 1BJ, United Kingdom
| | | | | | | | | | | |
Collapse
|
48
|
Rode AV, Samoc M, Luther-Davies B, Gamaly EG, Macdonald KF, Zheludev NI. Dynamics of light-induced reflectivity switching in gallium films deposited on silica by pulsed laser ablation: errata. Opt Lett 2001; 26:852. [PMID: 18040472 DOI: 10.1364/ol.26.000852] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
|
49
|
Rode AV, Samoc M, Luther-Davies B, Gamaly EG, Macdonald KF, Zheludev NI. Dynamics of light-induced reflectivity switching in gallium films deposited on silica by pulsed laser ablation. Opt Lett 2001; 26:441-443. [PMID: 18040347 DOI: 10.1364/ol.26.000441] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
We present what is to our knowledge the first experimental study of light-induced reflectivity changes at an alpha-Ga/Si interface irradiated by femtosecond and picosecond laser pulses. After exposure, the reflectivity can increase from R?0.55 , which is typical for alpha-Ga , to R?0.8 , which is close to that of liquid Ga. The initial step in the reflectivity change of 2-4 ps is resolved with 150-fs laser pulses. The light-induced reflectivity change relaxes during 100ns-10 mus , depending strongly on the background temperature of the Ga mirror and the laser fluence.
Collapse
|
50
|
Albanis V, Bratfalean RT, Dhanjal S, Zheludev NI, Emel'yanov VI, Petropoulos P, Richardson DJ. Light-induced specular-reflectivity suppression at a gallium/silica interface. Opt Lett 2000; 25:1594-1596. [PMID: 18066287 DOI: 10.1364/ol.25.001594] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
The reflectivity of a gallium/silica interface formed on an optical flat or at the tip of a cleaved optical fiber can be reduced in a reversible fashion when the interface is excited by a few milliwatts of laser power. This phenomenon occurs at temperatures just below gallium's melting point. We believe that the effect can be attributed to light-induced structuring at the interface.
Collapse
Affiliation(s)
- V Albanis
- Department of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK
| | | | | | | | | | | | | |
Collapse
|