Visible and infrared (incl THz)
Traditionally, making molecules with new properties, e.g. dyes of different colours, has been the province of chemistry, new properties are based on making new molecules. Our approach is fundamentally different, we use light to alter the way molecules interact with each other, something that can lead to radical changes in their properties, without changing their chemical composition. We use two related techniques known as strong coupling and weak coupling, and are investigating this approach to controlling molecular excitonic resonances.
Conventional metamaterials and metasurfaces (the 2D form of metamaterials) are ‘fixed-by-design’, with performance determined by the form of their resonating structures and the properties of the materials of which they are made. Far greater functionality and application would be available if we could develop active versions, i.e. metamaterials whose response can be dynamically adapted, tuned or reconfigured. At Exeter we are doing just this, using chalcogenide phase-change materials to deliver active optical metasurfaces that can work from the UV right out to the THz, and with applications ranging from LiDAR to multispectral imaging, optoelectronic displays, chemical sensing and much more.
We explore the potential for developing new THz components and sensors to fill the so called “THz gap”, utilizing novel magnetic and plasmonic responses of many materials in this region, and are currently working on novel methods for imaging in this difficult spectral region. We also work in plasmoncs, and explore the possibility of replacing coinage metals with new materials such as graphene and ITO. These materials have tuneable electromagnetic responses, as free electrons can controllably introduced by chemical, electrical or photo- doping, making the manipulating light on extreme sub-wavelength length scales possible, and we focus on enhancing nonlinear optical responses for optical switching etc.
The mechanical properties of biological tissues are central to their function and impairment is implicated in ageing and disease. Changes in the macroscopic mechanical properties and tissue structure and composition are both well characterised, but the causal relationships between them are largely unclear. A novel microscopy technique based on Brillouin light scattering from acoustic waves at GHz frequencies has emerged for the contactless 3-D probing of tissue mechanics at the microscopic and subcellular levels. In Exeter we advance the development and applications of Brillouin microscopy as a novel optical technique within biophotonics and the clinical environment.
Sensor systems have emerged that exhibit extraordinary sensitivity for detecting physical, chemical, and biological entities at the micro/nanoscale. Particularly exciting is the detection and analysis of molecules on miniature devices that have many possible applications in health, environment, analysis, and security.
Within the NEST group we explore the fascinating characteristics of new materials including 2D materials, for example graphene, and metasurfaces. We both investigate fundamental phenomena, such as the interaction of light with molecules, but also aim to exploit these phenomena to create novel technology.
Disorder is often considered to be a hindrance. It reduces the performances of otherwise carefully designed devices, scatters and scrambles signals, and it is difficult to describe with simple deterministic models. But as much as people try to minimize disorder, it is impossible to ever completely remove it. Instead, our research aim is to understand and exploit disorder.
Our approach is to study the correlations due to the fact that, despite difficult to completely characterize, disordered system are still deterministic at a fundamental level, and use them to extract information that is usually considered lost. In particular we focus on the problem of imaging in turbid and highly scattering media.
My research expertise spans across applied research in nanotechnology, electronic and optoelectronic devices to fundamental research in nanoscience (quantum phenomena, molecular electronics, nano electronics, spintronics) and materials science.
In particular, I am currently focused on the study of 2D materials such as graphene, functionalized graphene and layered dichalcogenides (e.g. MoS2, WS2), and of their hybrids with other emerging materials (e.g. organic semiconductors, perovskites). The aim is to create new materials and devices with unique electronic and optoelectronic properties not available in any other systems. In particular, we explores novel devices that can be used in emerging technologies such as electronic textiles, multifunctional smart coatings, or in a new generation of highly efficient solar cells and light emitting devices.
- Graphene-based flexible and transparent electronic devices.
- Novel technologies for fabricating suspended and double gated graphene transistors to access the electric field tuneable low-energy band structure in few-layer graphene and the electro-mechanical properties.
- Search for highly conductive and transparent materials.
- Superconducting-graphene hybrid structures.
I work on spatial structuring of infra-red and visible light for a variety of applications to imaging, optical trapping and optical communications. Dynamic light shaping is achieved using liquic crystal spatial light modulators and digital micro-mirror devices. We are also developing new methods to create compact light transforming optics using direct laser writing (microscale 3D printing).
Our research focusses on providing theoretical understanding of thermodynamics at the nanoscale. Specifically, we investigate the importance of small scale fluctuations and non-equilibrium effects within stochastic thermodynamics and investigate the impact quantum effects, such as coherences and entanglement, have on thermodynamic processes.
My work enables a better understanding and manipulation of heat/energy at the nanoscale. I am working on quantum theoretical modelling of low energy light-matter interactions and am currently also involved in a project that may, one day, lead to single molecule sensing for diagnostics in the healthcare sector.
Previously, I focussed on quantum cryptography which can find applications in communication and security.
I am a theoretical physicist with a broad range of research interests spanning from exactly-solvable problems in quantum and statistical mechanics and anyon excitons in the fractional quantum Hall effect regime to THz applications of carbon-based nanostructures and modelling white light-emitting diodes. My most recent work is related to electronic waveguides and zero-energy states in graphene and THz gain and excitons in narrow-gap carbon nanotubes as well as optoelectronic applications and quantum optics of quantum rings.
View Mikhail's publications.
Design of electromagnetic materials: Suppose you want to do something to a wave; perhaps redirect a radio wave, or absorb a sound wave. I use mathematics to look for the materials you need.
I am interested in the theory of electromagnetism and wave physics in general. Recently I've been thinking about how waves reflect from metamaterial structures, but I also work on the theory of quantum electromagnetism in dielectric media (I am interested in understanding how macroscopic bodies affect the quantum properties of the electromagnetic field, and how these in turn affect the motion of the object).
We explore different techniques for non-invasively observing live biological samples to recover three dimensional image data. These techniques include exploiting linear and non-linear optical effects, phase conjugation techniques or using active optical devices to generate structured light patterns to provide image data with high spatial and temporal resolution.
Key research challenges include expanding the three dimensional field of view of these imaging system to study larger samples, the development of new probes to improve contrast, imaging depth and chemical specificity, increasing sample throughput to generate reliable statistics of specimen behaviour and finally generating new image processing algorithms (including AI) to extract meaningful information from large data sets.
Calum's research aims to understand & control light-matter interactions in photonic nanostructures, and to build next-generation optical devices that make use of this understanding.
He is specifically interested in unconventional imaging and sensing systems (visible-to-mid-infrared wavebands) enabled through the development of new nanofabrication tools, tunable optical (active) materials, and multifunctional optical metasurfaces. Application areas include biomedical diagnostics, environmental monitoring and remote sensing. Research challenges lying at the interface between disciplines are particularly exciting.
In most nanotechnology contexts, we design structures with ordered geometries and model how electromagnetic waves interact with these perfect geometries. However, manufacturing devices with nanometre-level tolerance can be expensive and time-consuming. Furthermore, even with state-of-the-art fabrication facilities, imperfections in the manufacturing process are inevitable, leading to a performance degradation from the original design.
In Changxu's research, he is focusing on both sides of the coin: designing optical systems with specific features (topology) that are robust to fabrication errors or, more interestingly, harnessing intrinsic disorder within nanostructures as a benefit for various applications, ranging from energy harvesting, optical sensing to light manipulation.
We study the generation, control and interaction between sound, heat and electricity in materials. The focus of our experimental research is to study the fundamental physics of acoustic, thermal and electrical transport both within materials and across interfaces between materials. This has direct application in sound production, heat management in electronics, and improved efficiency of electronic devices. We also investigate the ways in which these properties can be used for active sensing, which includes detection of gas and fluids as well as electrical and thermal features of materials. Our work extends into biological systems, including biomimetics, thermoregulation in insects and electrical signalling in plants and animals.
My research spans different areas of condensed matter theory, with particular focus on the properties of correlated states in reduced dimensionality. These include quantum transport in two dimensional (2D) electron systems in the fractional Quantum Hall regime, the electronic and electromechanical properties of graphene and carbon nanotubes [e.g. Phys. Rev. Lett. 100, 076801 (2008)], as well as nano-electromechanical systems [e.g. Nature Physics 5, 327 - 331 (2009)] and suspended Josephson junction resonators.
Within the field of metamaterials I recently started investigating the properties of tunable Dirac-like and topological polaritons in 2D arrays of dipolar resonators embedded in optical cavities. Here we showed that the photon-mediated interactions between the resonators give rise to a tunable polariton bandstructure, with the emergence of type I and II chiral Dirac-like quasiparticles [Nature Communications 9, 2194 (2018)]. In parallel, we have recently unveiled how strained metasurfaces embedded in optical cavities lead to tunable fictitious magnetic fields for light [Nature Photonics 14, 669 (2020)].
Optoelectronic devices, which generate, manipulate and measure light, underpin modern communication and have enabled the internet to revolutionise the modern world. A new generation of quantum optoelectronic devices, which process light at the single photon level promise a further revolution in the way we communicate, measure and process data. Individual photons, the elementary particles of light, are the building blocks of this technology, but must first be generated by single photon sources. For practical applications the photons must be generated on-demand, at high repetition rates and must be indistinguishable, in other words identical in all degrees of freedom (for example energy and polarisation). My research is centred around the development of such devices through the exploration of novel materials and their nanophotonic integration.
