The Blackett Laboratory, Department of Physics, Imperial College London, London, UK
The metamaterial concept has in recent years inspired scientists to conceive perfect lenses, new lasers, ‘invisibility’ and acoustic cloaks and opened the door to slow and stopped broadband light with applications in quantum science and technology, sensing and nanochemistry. At the same time, quantum nano-photonics promotes an extreme control of light and matter interaction and empowers novel femto- and attosecond and nano-photonic phenomena, forming the basis for quantum photonics and innovative nano-photonic lasers. The Quantum Theory of Matter and Light (QTML) group (Professor Ortwin Hess) in the Blackett Laboratory (Department of Physics) at Imperial College London explores these research frontiers, studying the physics of nanophotonics, optical and electronic metamaterials, and investigating the (ultrafast) nonlinear and quantum dynamics of nano-plasmonic particles, nano-photonic nano-devices and complex systems with gain. Concurrently the group is striving to embed metamaterials in new realms of applications in information and laser technology, nano-photovoltaics and the biomedical sciences.
Nonlinear Nanophotonic Active Metamaterials
Ever since their conception, metamaterials have fascinated both researchers and the wider public alike, due to the prospect of a unique realisation of photonic properties such as a negative refractive index or functionalities such as optical clo ing that are not accessible otherwise. While initially many proofs of concept realisations have been made at microwave frequencies, the quest for miniaturisation has opened up both new challenges (such as the compensation of losses) as well as opportunities for new functionalities such as ultrafast nonlinearities. Incorporating gain molecules into the fabric of the metamaterials, the QTML group has shown that it is realistically possible to overcome dissipative losses, even in the exotic negative index regime. Moreover, the strong coupling of the excited (bright) modes of optical metamaterials to the radiative continuum has been shown to open up a broad window within which we can achieve full loss compensation and amplification in the steady-state regime. When the gain supplied by the active medium embedded, e.g. within the fabric of an active nano fishnet metamaterial structure is beyond a level that is sufficient to overcome dissipative and radiative losses, the nano-fishnet structure can function as a coherent emitter of surface plasmons and light over the whole ultrathin 2D area, well below the diffraction limit for visible light.
Nanoplasmonic Metamaterial Thermal-Emitter Improves CO2 Gas-Sending Devices
Over the last two decades, surface plasmon polaritons have been intensely studied from a theoretical and applied physics perspective and many promising applications in sensing have been proposed. Examples are Surface-enhanced Raman spectroscopy (SERS) or single molecule sensing. They both take advantage of huge field enhancements, while nano-lasers or stopped light lasing use field confinement and localisation to replace cavities. While some applications are hindered by the resistive losses that occur in the metal, an application of plasmonics to thermal emitters, in contrast, even calls for absorption (i.e. losses in the metal), because Kirchhoff’s law dictates that only good absorbers make good thermal emitters. The QTML group recently demonstrated that a plasmonic thermal emitter, fabricated in collaboration with using an industrial CMOS process that enables a 400% increase in emission intensity at the CO2 absorption wavelength used for non-dispersive infrared gas-sensing device, compared to a standard non-plasmonic device.
Stopped-Light Nanolasing
Since their first conception nearly 50 years ago, lasers have evolved from a scientific curiosity in the laboratory to take a place at centre stage in today’s society. Lasers do come in all kinds of sizes and for an incredible variety of wavelengths but all have two vital components: a (laser) gain material and coherent feedback of the emitted light. In normal lasers feedback is provided by placing the gain material between mirrors – i.e. inside a cavity. Now, could we accomplish such feedback by keeping photons that have just been emitted from an active laser medium, simply from propagating away? Light is normally the fastest ‘object’ in the universe, but researchers have, indeed, recently conceived ways of slowing it down considerably, even long enough to consider it as having been stopped altogether.
The QTML group has recently demonstrated that lasing does not require modes pre-defined by a resonator with a particular geometry but only a feedback mechanism: providing feedback by stopped-light singularities in the density of states stopped-light lasing can be realised on subwavelength (nano-) scales. Extensive fulltime domain Maxwell–Bloch Langevin simulations in combination with (semi-) analytic theory have uncovered that in the absence of cavity induced feedback a phase-locked superposition of quasi dispersion-free waveguide mode promotes the dynamic formation of a subwavelength lasing mode with a remarkably high in-coupling of (amplified) spontaneous emission into the lasing mode. The realisation of trapped/condensed non-equilibrium surface-plasmon polaritons at stopped-light singularities. The recently proposed nano-plasmonic stopped-light lasing principle conceivably thus not only opens the door to ultrafast cavity-free nano lasing, ultra-thin lasing surfaces and cavity-free quantum-electrodynamics but, applied to surface-plasmon polaritons, also provides an entry point to SPP-condensation, quantum gain in quantum plasmonics and quantum fluids of light.
Research Publications (selected)
1 O. Hess et al., Nature Materials, 11, 573 – 584 (2012).
2 O. Hess and K.L. Tsakmakidis, Science 339, 654 (2013).
3 J. M. Hamm and O. Hess, Science 340, 1298 (2013).
4 S. Wuestner and O. Hess, “Active Optical Metamaterials”, Progress in Optics, 59, 1-88 (2014).
5 T. Pickering, J. M. Hamm, A. F. Page, S. Wuestner and O. Hess, Nature Communications 5, 4971 (2014).
6 A. Pusch et al., Scientific Reports 5, 1751 (2015).
Professor Ortwin Hess
Leverhulme Chair in Metamaterials
Imperial College London
Tel : +44 20 7594 7586
o.hess@imperial.ac.uk
