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Theory and Advanced Computation

  Shining Light on Metamaterials and Condensed Matter on the Nanoscale

The Theory and Advanced Computation Group (TAC)

explores the nano-space and ultrafast dynamics in

metamaterials and plasmonics, slow light and novel lasers, nanoelectronics and semiconductor device physics, spatio-temporal bio-dynamics and soft-matter photonics

by means of theory and advanced computation.  

At the beginning of the twenty-first century research and technology have embarked on a journey into nano- and femto-space and to the ultrafast worlds of atto- and femtosecond dynamics. The remarkable progress towards the very small has allowed the conception of photonic metamaterials with exciting new properties such as a negative refractive index, quantum dot nanomaterials or carbon nanotubes becoming the basis of novel advanced devices as well as the visualization and controlled manipulation of the function of biological molecules. Just as revolutionary has been the progress towards harnessing of the quantum nature of electrons and photons on ultrafast timescales heralding the new field of lightwave nanoelectronics.

The Theory and Advanced Computation Group (TAC) headed by  Professor Ortwin Hess explores these frontiers by means of analytic theory and advanced computer simulation.

 

Highlights

Negative Refraction in Sight

Ortwin Hess.
Optics: Farewell to Flatland
Nature 455, 299 (2008).

Optical metamaterials are the key to perfect lenses, 'invisibility' cloaks and slow and stored broadband light. A three-dimensional optical metamaterial with a negative refractive index has recently been created [ Valentine, J. et al. Nature 455, 376–379 (2008) ].

                                                                             [from: Nature 455, 299 (2008); with kind permission]

The difference in the optical density of air and 'normal' water (glass on the left) causes a straw in a glass of water to appear shifted at the interface and slightly enlarged inside the liquid. In (hypothetical) 'negative-index water' in the glass on the right, the straw would seem to continue in 'the wrong direction'.

For more details: Negative Refractive Index Materials: En Route from Flatland to Spaceland

 

Watch Your Back

Kosmas Tsakmakidis and Ortwin Hess, Optics: Watch your back, Nature 451, 27 (2008)

A proposal for transporting photons invisibly between two unconnected points in space seems worthy of a Star Trek plot. But it is in principle wholly realizable, and could open up new vistas — literally.

[from: Nature 451, 27 (2008); with kind permission]

It's behind you. a, The invisibility cloak devised by Pendry et al. uses specially structured 'metamaterials' to open up a 'hole' in photon-space, inside which one can place an object. Photons are naturally redirected around the object, rendering it invisible, at least when viewed with photons at a certain wavelength. b, An electromagnetic wormhole is a natural extension of the invisibility idea, with exciting potential applications. For example, in principle two flexible wormholes attached to the frame of a specially designed pair of half-moon spectacles could project the photon-space behind the head to the half-moon area of the lenses, providing a seamless 360° view.

 

 

Novel principle for broadband storage of light: 

The Trapped Rainbow Effect

Kosmas L Tsakmakidis, Alan D Boardman and Ortwin Hess.
'Trapped rainbow' storage of light in metamaterials.

Here we demonstrate theoretically that an axially varying heterostructure with a metamaterial core of negative refractive index can be used to efficiently and coherently bring light to a complete standstill. In contrast to previous approaches for decelerating and storing light, the present scheme simultaneously allows for high in-coupling efficiencies and broadband, room-temperature operation. Surprisingly, our analysis reveals a critical point at which the effective thickness of the waveguide is reduced to zero, preventing the light wave from propagating further. At this point, the light ray is permanently trapped, its trajectory forming a double light-cone that we call an 'optical clepsydra'. Each frequency component of the wave packet is stopped at a different guide thickness, leading to the spatial separation of its spectrum and the formation of a 'trapped rainbow'. Our results bridge the gap between two important contemporary realms of science—metamaterials and slow light. Combined investigations may lead to applications in optical data processing and storage or the realization of quantum optical memories.

 

The 'Trapped Rainbow' in the Press

Recent Press Coverage of Metamaterials and Slow Light

 

 

Research: Dynamics of Light and Matter

TAC brings together a broad range of fundamental and applied theoretical research activities on ultrafast spatio-temporal dynamics of ("soft" and "hard") nanomaterials with the physics of light and dynamics of advanced lasers and a large variety of advanced computational tools are developed and used on the dedicated high-performance computing platforms of the Nano-Modelling High-Performance Computing Lab (NM-HPCL) run by the TAC group.

Current foci of TAC's research interests are:

  • metamaterials

    Metamaterials are the key to perfect lenses, 'invisibility' cloaks and slow and stored broadband light and promise novel magnetoelectronic phenomena. We study the unique properties of metamaterials with a negative or negligibly small refractive index, research new ways how they can be realized and explore novel nanoelectronic and nanophotonic phenomena of metamaterials.

  • nano-photonics and plasmonics

    Metal surfaces and interfaces can support surface plasmons - density waves of free electrons. These plasmon waves can interact with photons, opening the way to a novel realm of optics - plasmonics. When the metal surfaces are nanostructured, the possibility for true nanoscale photonics emerges at optical wavelengths. Using theoretical and advanced computational approaches that take on board microscopic spatio-temporal properties TAC studies the light-matter interaction in nanostructured metals and (molecular/nanoparticle) light scattering in structured polymer films and explores the ultrafast (sub-) femtosecond dynamics.

  • physics of photonic crystals

    Photons propagating in materials that are (periodically) structured on scales of about half or quater of the wavelength may experience them as "photonic crystals"  in a way similar to how electrons experience "normal" crystals. This may lead to novel effects such as the formation of so-called photonic band-gaps. We model the materials properties of ordered and disordered photonic "crystals" and explore the possiblity of photonic functionalities on the materials level.


 

  • femto- and attosecond dynamics of materials

    The conception and realisation of pulses of light that are as short as femto- or attoseconds has started to open up exciting new possibilities to observe and control the dynamics of electrons in atoms, nano-structures, biological media and the solid-state.

    TAC studies the physics of ultrafast femto- and attosecond dynamics of semiconductors, plasmonic nanomaterials and bio-molecular media by a combination of theoretical and advanced computational simulation schemes involving and taking into account the propagation of coherent electromagnetic waves (with wavelengths from the THz to the soft X-ray regimes) and matter (on various levels of sophistication).

    • coherent femtosecond dynamics of semiconductors
    • attosecond dynamics in nanoplasmonics
    • ultrafast bio-molecular media

 

  • physics of advanced lasers and spatio-temporal laser dynamics

    The TAC group has pioneered the field of spatio-temporal dynamics and quantum fluctuations of semiconductor lasers and continues to study the physics of advanced lasers, focussing on mirocavity or nano-lasers, new active materials and nonlinear dynamics and exploring novel concepts such as the "thermal laser".  We develop new theoretial approchaes for innovative gain materials (such as quantum dots), quantum fluctuations or novel laser concepts (such as the "thermal laser") and laser cavities (such as photonic crystal fibres) that may emit coherent radiation at new wavelengths and optical pulses with durations as short as femto- or attoseconds.

  • spatio-temporal bio-dynamics and soft-matter photonics

    TAC has pionered the theory for and modelling of the spatio-temporal dynamics of optical molecular motors. We study the way light interacts with (non-crystallised and disordered) molecular and biological materials in space and time and how light can be used to explore their dynamic structure and harnessed for control on the molecular level. 

  • structural dynamics of "soft" materials

    The physics of noncrystalised ("soft") materials as well as the realization of novel photonic "crystals" such as polymer opals involve complex spatio-temporal processes all the way from macroscopic scales down to the "flow" of single molecules (such as water) through carbon nanotubes.

    The TAC group developes new effective theoretical models (such as a nonlinear Maxwell model) describing the highly nonlinear flow and structural dynamics of anisotropic fluids (such as polymers) and simulates the microscopic (nonequilibrium) molecular dynamics of nano-confined water and formation of polymer opal films from (core-shell) polymer spheres on the basis of equilibrium and nonequilibrium molecular dynamics computer simulation.

    • rheo-chaos in Maxwell model fluids
    • 3D elastic turbulence in complex fluids
    • molecular transport through carbon nanotubes
    • formation of polymer opal films

 

Strong and mult-faceted collaboration within the ATI as well as with academic partners and companies in the UK, Finland, Germany, Japan and the USA integrate our theoried and computer simulations with experimental and technological efforts and link them with innovative application.

Further Information
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Theory and Advanced Computation Group Prof. Ortwin Hess 68 2745 Prof. Ortwin Hess

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The University of Surrey, Guildford, Surrey, GU2 7XH | Tel: +44 (0)1483 300800 | Fax: +44 (0)1483 300803 |

 

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