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New horizons in nanophotonics

Scientific meeting

Event downloads

Starts:

May
232016

09:00

Ends:

May
242016

17:00

Location

Kavli Royal Society Centre, Chicheley Hall, Newport Pagnell, Buckinghamshire, MK16 9JJ

Overview

Theo Murphy scientific meeting organised by Professor Yuri Kivshar, Professor Nikolay Zheludev, Professor Ortwin Hess and Professor Bill Barnes.

Nanoscale waterlily, courtesy of R.Waters, University of Southampton

This meeting will bring together leading researchers from different areas of nanoscale physics to explore the confluence of subwavelength photonics, metamaterials, graphene physics, and nonlinear optics. Whilst a number of breakthroughs can be already anticipated, such as energy saving metadevices for optical technologies, the primary objective of this meeting is to catalyse the creation of new exciting areas in nanophotonics.

Speaker biographies, abstracts, and recorded audio of the presentations is available below. Papers from the meeting will be published in a future issue of Philosophical Transactions A.

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Event organisers

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Schedule of talks

23 May

Session 1 09:00-12:30

Session 1

4 talks Show detail Hide detail

Chairs

Professor Yuri Kivshar, Australian National University, Australia

09:05-09:30 Sculpting waves for desired functionalities

Professor Nader Engheta, University of Pennsylvania, USA

Abstract

Owing to the recent advances in nanoscience, nanotechnology, and materials science and engineering, it has become possible to engineer materials and platforms with unprecedented features and characteristics that allow unconventional control and manipulation of waves and fields at subwavelength scales.  In my group, we are exploring electromagnetic and optical wave interaction in platforms with extreme scenarios, such as materials with near-zero parameters (e.g., near-zero permittivity and near-zero permeability), and with extreme features such as very high phase velocity, very low group velocity, one-way vortices at the nanoscale, giant anisotropy and nonlinearity, “near-zero photonics”, nanoscale computation with optical nanocircuits, and more.  Such “extreme control” on fields and waves provides us with exciting features and functionalities for wave-based paradigms such as optics, acoustics, and thermodynamics.

In this presentation, I will present most recent results from some of our ongoing efforts in these areas, and will forecast some future directions and possibilities.

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09:45-10:15 Non-Hermitian light matter interactions: exploiting the optical loss

Professor Xiang Zhang, University of California at Berkeley, USA

Abstract

Optical loss is usually undesirable. Recently, judiciously designed balanced gain and loss structures, so called parity-time (PT) symmetric synthetic systems, are explored due to their extraordinary properties. In this talk I will discuss the notion of PT symmetry in optical systems. Especially I will discuss how to achieve nano-scale spectrometer by designing an anti-Hermitian light matter interactions. This will be also useful for spectrum splitting in solar applications. Finally, I will discuss a single mode lasing scheme using PT symmetric periodically modulation in a micro ring lasers.

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11:00-11:30 Nanosystems in ultrafast and superstrong fields: attosecond phenomena

Professor Mark Stockman, Georgia State University, USA

Abstract

We present our latest results for a new class of phenomena in condensed matter nanooptics when a strong optical field ∼1-3 V/Å changes a solid within optical cycle. Such a pulse drives ampere-scale currents in dielectrics and adiabatically controls their properties, including optical absorption and reflection, extreme UV absorption, and generation of high harmonics in a non-perturbative manner on a 100-as temporal scale. Applied to a metal, such a pulse causes an instantaneous and, potentially, reversible change from the metallic to semimetallic properties. We will also discuss our latest theoretical results on graphene that in a strong ultrashort pulse field exhibits unique behavior. New phenomena are predicted for buckled two-dimensional solids, silicene and germanine. These are fastest phenomena in optics unfolding within half period of light. They offer potential for petahertz-bandwidth signal processing, generation of high harmonics on a nanometer spatial scale, etc.

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11:45-12:15 Cooling and amplification of a vacuum-trapped nanoparticle

Professor Lukas Novotny, ETH Zürich, Switzerland

Abstract

I discuss our experiments with optically levitated nanoparticles in ultrahigh vacuum.Using an active parametric feedback scheme we cool the particle’s center-of-mass temperature to ~ 500μK and reach mean quantum occupation numbers of ~ 50. I show that mechanical quality factors of Q = 109 can be reached and that damping is dominated by photon recoil heating. The vacuum-trapped nanoparticle forms an ideal model system for studying non-equilibrium processes, nonlinear interactions, and ultrasmall forces.

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12:30-13:30

Lunch

Session 2 13:30-17:00

Session 2

4 talks Show detail Hide detail

Chairs

Professor Nikolay Zheludev, University of Southampton, UK

13:30-14:15 Nanophotonic energy conversion mechanisms

Professor Harry Atwater, California Institute of Technology, USA

Abstract

Plasmonics has long suffered a reputation as the province of lossy structures for nanophotonic applications – to be reluctantly tolerated and carefully managed. However plasmon decay processes harbor interesting opportunities for new photonic energy conversion structures and mechanisms. First principles calculations of decay rate for surface plasmon polaritons via phonon-mediated processes indicate that the prompt distribution of generated carriers is extremely sensitive to the energy band structure of the plasmonic material. In particular, the onset of interband transitions, occurring in the visible regime for the noble plasmonic metals (Au, Cu, Ag), and is expected to significantly modify the hot-carriers distribution. Results of experiments that test these calculations, using wide bandgap/noble-metal nanoscale heterostructures, will be presented. Resonant excitation of periodic antenna arrays coupled to waveguides in a guided mode resonance configuration give rise to narrowband absorption with resonant absorption wavelength defined by the array geometrical parameters. When these antennas are defined as thermoelectric junctions on a low thermal conductivity membrane substrate, the temperature rise associated with resonant optical absorption induces a measurable thermoelectric potential. These resonant thermoelectric antennas have potential to serve as component elements of resonant photodetectors with sensitivity over a very broad spectral range. Near-resonant excitation of metallic antennas induces a plasmoelectric potential, distinct from the thermoelectric potential, due to changes in the carrier antennas in response to excitation. We describe a theoretical framework and several experiments to measure plasmoelectric potentials in metal nanostructures.

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14:15-15:30 Quantum plasmonics and hot carrier induced processes

Professor Peter Nordlander, Rice University, USA

Abstract

Plasmon resonances with their dramatically enhanced cross sections for light harvesting have found numerous applications in a variety of applications such as single particle spectroscopies, chemical and biosensing, subwavelength waveguiding and optical devices. Recently it has been demonstrated that quantum mechanical effects can have a pronounced influence on the physical properties of plasmons. Examples of such effects is the charge transfer plasmon enabled by conductive coupling (tunneling) between two nearby nanoparticles and nonlocal screening of the plasmonic response of small nanoparticles. One relatively recent discovery is that plasmons can serve as efficient generators of hot electrons and holes that can be harvested in applications. The physical mechanism for plasmon-induced hot carrier generation is plasmon decay. Plasmons can decay either radiatively or non-radiatively with a branching ratio that can be controlled by tuning the radiance of the plasmon mode. Non-radiative plasmon decay is a quantum mechanical process in which one plasmon quantum is transferred to the conduction electrons of the nanostructure by excitation of an electron below the Fermi level of the metal into a state above the Fermi level but below the vacuum level. In particular I will discuss external control of charge transfer plasmons for active plasmonic devices, molecular plasmonics, hot carrier generation, decay and fluorescence, and hot carrier induced processes and applications such as photodetection, photocatalysis, and phase changing of nearby media.

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15:30-16:00 Replacing metals with alternative plasmonic substances in plasmonics and metamaterials: how good an idea?

Professor Jacob B Khurgin, The John Hopkins University, USA

Abstract

Metals, which dominate the fields of plasmonics and metamaterials suffer from large ohmic losses. New plasmonic materials, such as doped oxides and nitrides, have smaller material loss, and using them in place of metals carries a promise of reduced-loss plasmonic and metamaterial structures, with sharper resonances and higher field concentration.  This promise is put to a rigorous analytical test in this work and it is revealed that having low material loss is not sufficient to have a reduced modal loss in plasmonic structures, unless the plasma frequency is significantly higher than the operational frequency. Using examples of nanoparticle plasmons and gap plasmons one comes to the conclusion that even in the mid-infrared spectrum metals continue to hold advantage over the alternative media.  And yet, the new materials may still find application niche where the high absorption loss is beneficial rather than detrimental  while cost and thermal stability are important factors. Such applications may be in medicine and thermal photovoltaics.

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16:15-16:45 Light-matter interactions in plasmonic lattices

Professor Päivi Törmä, Aalto University, Finland

Abstract

We have proposed the concept of quantum plasmonic lattices, that is, arrays of metal nanoparticles combined with emitters, as a platform to study quantum many-body physics, especially quantum fluids. Here we present our experimental work towards its realization. We have studied strong coupling in nanoparticle arrays combined with organic molecules. We briefly discuss our work on strong coupling involving three different types of resonances in plasmonic nanoarrays: surface lattice resonances (SLRs), localized surface plasmon resonances on single nanoparticles, and excitations of organic dye molecules, and spatial coherence properties of a plasmonic nanoarrays. We also show with magnetic nanoparticles how the intrinsic spin-orbit coupling of the material interplays with the symmetries of the nanoparticle array. Finally, we present some of our newest results on light-matter interactions in plasmonic lattices.

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17:00-17:45

Poster Session

24 May

Session 3 09:00-12:30

Session 3

4 talks Show detail Hide detail

Chairs

Professor Ortwin Hess, Imperial College London, UK

09:00-09:30 Device applications of metafilms

Professor Mark Brongersma, Geballe Laboratory for Advanced Materials, USA

Abstract

Many conventional optoelectronic devices consist of thin, stacked films of metals and semiconductors. In this presentation, I will demonstrate how one can improve the performance of such devices by nano-structuring the constituent layers at length scales below the wavelength of light.

The resulting metafilms and metasurfaces offer opportunities to dramatically modify the optical transmission, absorption, reflection, and refraction properties of device layers. This is accomplished by encoding the optical response of nanoscale resonant building blocks into the effective properties of the films and surfaces. To illustrate these points, I will show how nanopatterned metal and semiconductor layers may be used to enhance the performance of solar cells, photodetectors, and enable new imaging technologies. I will also demonstrate how the use of active nanoscale building blocks can facilitate the creation of active metafilm devices.

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09:45-10:15 Dielectric Huygens metasurfaces – fundamentals and applications

Professor Dragomir Neshev, Australian National University, Australia

Abstract

The concept of Huygens metasurfaces has recently emerged as a powerful platform for complete manipulation of light properties, including phase, amplitude, polarisation, and even colour. Their operation is based on the interference of the electric and magnetic dipolar responses of the constituent metasurface elements, called meta-atoms, such that they can only scatter in forward direction, while back-scattering is inhibited. Dielectric Huygens metasurfaces stand out as a prominent example, due to their negligible optical losses and easy fabrication. Such dielectric metasurfaces are composed of small high-refractive-index nano-particles, which exhibit Mie-type resonances of both electric and magnetic origin and comparable strength. By designing the geometry of the individual meta-atoms it is possible to exactly match the spectral position of these resonances, thus enabling unitary transmission through the Huygens metasurface, while simultaneously being able to control the phase of transmitted light in the full range of 0-2π.

This talk will review the fundamental designs and principles of operation of such dielectric metasurfaces, as well as will overview the plethora of their functionalities, including frequency selectivity, wavefront shaping, and polarization control. In particular, we demonstrate experimentally beam shaping in complex holographic shapes with near unity transmission efficiency. We further utilise our Huygens metasurfaces for generation of beams carrying orbital angular momentum, including vortex and vectors beams with azimuthal/radial polarisations operating over a broad spectral range. Finally, we will present some of their recent applications in nonlinear light sources, biosensing, and quantum optics.

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11:00-11:30 Silicon-based metasurfaces for near-infrared optics

Professor Jason Valentine, Vanderbilt University, USA

Abstract

Absorption loss continues to be one of the primary impediments to the application of plasmonic metamaterials and metasurfaces at optical frequencies. Dielectric metamaterials offer one potential solution to this issue by eliminating ohmic loss, allowing the realization of highly transparent materials. As with their plasmonic counterparts, manipulation of the unit cell structure of all-dielectric metasurfaces also offers a means to engineer a wide variety of optical functionalities. 

In this talk, I will discuss our recent experimental efforts to demonstrate silicon-based metasurfaces within the telecommunications band. I will talk about how simple unit cell geometries allow these metasurfaces to be scaled to large areas using self-assembly based patterning techniques. Importantly, defects in such materials are found to have little effect on the performance of the surfaces. On the other hand, I will discuss how more complicated unit cells can be used to realize wavefront control as well as high quality factor resonances. The high-Q resonances can be used for sensing and the large local field enhancement within the silicon unit cells results in a third harmonic conversion enhancement factor of 105 with respect to an unstructured silicon slab. Such surfaces could potentially be applied for all-optical switches in the future.

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11:45-12:15 Active graphene-integrated plasmonic metasurfaces and their applications: from motion detection to polarization control of infrared light

Professor Gennady Shvets, The University of Texas at Austin, USA

Abstract

Plasmonic metasurfaces enhance light-matter interaction by focusing light into extremely subwavelength dimensions. These carefully designed structures have been used in extremely thin optical component which can mold the wavefront, with exciting applications in optical lenses, beam steering, and biosensing applications. Adding dynamic tunability to these devices opens up the possibility for new application in single pixel detection and 3D imaging as well as optical modulators and switches. However the existing approaches for designing active optical devices in infrared, are either slow or have small refractive index change. Integrating plasmonic metasurfaces with single-layer graphene (SLG) opens exciting opportunities for developing active plasmonic devices because the amplitude and phase of the transmitted and reflected light can be rapidly modulated by injecting charge carriers into graphene using field-effect gating. I will describe our recent experimental results demonstrating strong phase modulation of mid-infrared light. The phase shifting due to electric gating of the SLG was measured using a Michelson interferometer, and further utilized to demonstrate an electrically controlled (i.e. no moving parts) interferometry capable of measuring distances with sub-micron accuracy. Because of the potentially nanosecond-scale measurement time, active metasurfaces represent a promising platform for ultra-fast standoff detection. Finally, we demonstrate that, by the judicious choice of a strongly anisotropic metasurface, the graphene-controlled phase shift of light can be rendered polarization-dependent, thereby modulating the polarization state (e.g., the ellipticity) of the reflected light. These results pave the way for novel high-speed graphene-based optical devices and sensors such as polarimeters, ellipsometers, and frequency modulators.

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12:30-13:30

Lunch

Session 4 13:30-17:00

Session 4

4 talks Show detail Hide detail

Chairs

Professor Bill Barnes, University of Exeter, UK

13:30-14:00 Short-range surface plasmonics and its (sub-)femtosecond dynamics

Professor Harald Giessen, Universität Stuttgart, Germany

Abstract

We use single crystalline gold flakes on atomically flat silicon substrates to generate ideally suitable metals for plasmon propagation. By electrochemical means, the thickness is tunable from a few tens to over 100 nm. Using sub-20 fs laser pulses around 800 nm, we excite surface plasmons, whose dynamics can be observed using time-resolved two-photon excitation electron emission (PEEM).

Plotting the dispersion of surface plasmons in a thin gold slab on silicon, one finds that excitation at 800 nm can lead to extreme wavelength reduction due to the dispersion slop of over five. Using focused ion beam for cutting rings with appropriate periodicity into the samples, we can excite concentric surface plasmons that create a nanofocus of only 60 nm width for 800 nm excitation.

Using Archimedean spirals with broken n-fold radial symmetry, it is possible to excite surface plasmons with angular orbital momentum on the gold flakes. This leads in case of 4-fold symmetry to cloverleaf-type nanofoci on the order of 100 nm, which rotate during four optical cycles by 360 degrees.

Using two-pulse experiments with a subwavelength-stabilized Michelson interferometer, it is possible to observe the dynamics of the surface patterns with a (sub-)femtosecond resolution, thus giving insight into the dynamics of the nanofocus formation as well as on the plasmonic spin-orbit coupling.

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14:15-14:30 Non-linear optical excitation of surface plasmons in graphene

Professor Euan Hendry, University of Exeter, UK

Abstract

We present recent optical wave-mixing measurements showing the excitation of surface plasmons in planar graphene. A large enhancement of non-linear signal in regions of high density of states suggests a strong coupling to propagating plasmons in graphene for a variety of in-plane wave-vectors. Estimates regarding the non-linearity of graphene and the efficiency of the DFG process are inferred from our experiment. These results demonstrate a promising route to efficient generation of surface plasmons in graphene using free-space radiation.

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15:30-16:00 Deep UV plasmonics and bio-photonics

Professor Satoshi Kawata, Osaka University, Japan

Abstract

Recent development of deep UV light sources opens a new world of nanophotonics, as exemplified by deep UV photo-lithography, photo-catalysis, sterilization, and molecular-sensing, analysis and imaging. If deep UV optics is combined with Raman scattering microscopy, the distribution of nucleotides and proteins in a cell is imaged and analyzed without labelling. However, the use of deep UV light for bio-imaging is limited because it can destroy or denature target bio-molecules. Recently, we proposed a method for suppressing the photo-degradation of molecules using lanthanide ions in solution as energy quenchers. This approach directly removes excited energy at the fundamental origin of cellular photo-degradation. For sub-wavelength imaging, we need a plasmonic tip that effectively works in deep UV to enhance Raman scattering at molecules. We have found that aluminum is one of the best metals that exhibit plasmonic field enhancement in deep-UV, while not in visible range because the imaginary part of the dielectric constant for aluminum is very large in visible. We also found that Indium is another good candidate in deep UV and is useful in practice for vapour deposition due to the relatively low melting point, which is important for producing multi-grain tips for highly reproducible enhancement. Experimental results of this topics will be shown for bio-photonic nano-imaging.

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16:15-16:45 Nanophotonics with high refractive index materials

Professor Boris Luk'yanchuk, Agency of Science, Technology and Research (A*STAR), Singapore

Abstract

Recently, a new field of resonant dielectric nanostructures has emerged demonstrating a huge promise to substitute plasmonic elements with low-loss high-refractive index dielectric materials. A unique advantage of dielectric nanostructures over nanometallic or plasmonic structures is the low dissipative losses which provide new and competitive alternatives for nanoantennas and metamaterials. Another unique peculiarity of high-refractive index dielectric nanoparticles is their ability to scatter light unidirectionally, i.e. mainly in a preferred direction. This property is a consequence of far-field Kerker-type interference of electric and magnetic dipoles that can be excited coherently inside such nanoparticles. These high-refractive index dielectric nanostructures can substitute plasmonics in some applications. Resonant properties of dielectric particles with high refractive index together with weak dissipation permit to form efficient dielectric antennas and 2D metasurfaces. These 2D artificial interfaces can be designed to possess specialized electromagnetic properties which do not occur in nature. For example recently it was shown that such metasurfaces permit to realize generalized Brewster effect for any polarization and arbitrary angle of incidence. Structured dielectric surfaces permit to provide locally phase control on subwavelength scale which yields many promising applications. The last but not least we should mention an anapole mode which can be viewed as a composition of electric and toroidal dipole moments, resulting in destructive interference of the radiation fields due to similarity of their far-field scattering patterns. Such anapole excitations exist in most of high-index dielectric nanostructures with relatively large size parameter.

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New horizons in nanophotonics

Theo Murphy scientific meeting organised by Professor Yuri Kivshar, Professor Nikolay Zheludev, Professor Ortwin Hess and Professor Bill Barnes.

Kavli Royal Society Centre, Chicheley Hall Newport Pagnell Buckinghamshire MK16 9JJ
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