Ion-exchange membranes (IEMs) are required for a diversity of applications across many fields spanning clean energy, environmental remediation, and healthcare. Examples include: green hydrogen producing electrolysers and low temperature fuel cells; carbon dioxide electrolysis into high value chemicals; salinity gradient power; hydrogen peroxide generation; redox flow batteries; actuators; batteries and supercapacitors; electrodialysis and diffusion dialysis for the recovery, extraction, and separation of inorganics including heavy metals ions and acid and bases; chromatography materials for protein purification; biomaterials for tissue engineering; and fouling resistant membranes for microfiltration. The Lancaster University team will develop a novel table-top facility using terahertz time-domain spectroscopy (THz-TDS) to routinely and non-destructively quantify the different states of water (bound, bulk, and free) in IEMs in environments with both relative humidity (RH) and temperature control. Previously, water states and contents have only been measured in uncontrolled environments using either pulse field gradient nuclear magnetic resonance experiments or with destructive techniques like differential scanning calorimetry. The developed THz-TDS system will be used to gain a more extensive TRL1-2 level fundamental understanding of how the states of water vary in IEMs with different composition characteristics. These IEMs will be either commercial types (including those provided by a project partner) or those fabricated at the University of Surrey (see below). Underpinning preliminary work at Lancaster University has shown that THz-TDS derived water state information can be collected at different RHs, but this was only possible at ambient temperatures. A more comprehensive development of a system, that can collect such data with both RH and temperature control, is required. Commercial ion-exchange membrane developers and users, including project partners, have indicated that they would like to see this knowledge deficiency rectified, where routinely collected water-state data is available over a wider range of conditions. Radiation grafting is a useful method for bulk functionalisation of polymers with defined characteristics (films, powders, fibres). The University of Surrey will supply a range of small-scale (10 × 10 cm) samples of radiation-grafted cation- and anion-exchange membranes with a diversity of: (1) ion-exchange capacities; (2) chemistries; (3) thicknesses, and (4) nano-morphologies (distribution and size of crystallites). This will aid the generation of new fundamental scientific knowledge related to how IEM characteristics affect their water contents and states. In the latter stages, the Surrey team will then conduct TRL3 scale-up work on down-selected radiation-grafted IEMs, an effort that will be supported by the developed Lancaster University-based THz-TDS capability. For initial translation to impact, the scaled-up RG-IEMs will be those that have the right balance of properties for application in peroxide generating cells, an interest of our aerospace partner. It is well known that the in situ performances of IEMs (in numerous electrochemical systems) is as much a function of water contents (and mobility) as they are of ion-conductivity. Hence it will be important to elucidate the homogeneity of the distribution of water states across different areas of scaled-up (30+ × 30+ cm) batches of IEM, as well as the consistency of water states across multiple repeat batches. It is currently unknown if homogeneous ion-exchange capacities actually lead to homogeneous water states.

This project targets the realization of an innovative class of optoelectronic devices operating in the terahertz frequency range. The THz spectral region (1-10 THz correspond to vacuum wavelengths between 30 and 300 micrometers), lies between the electronics and the photonics range. This frequency range is vastly unexplored despite its huge potential in many applications, ranging from spectroscopy to communications, to imaging and astronomy. The full potential of the THz range is limited by the intrinsic hurdles inherent to working at these frequencies and by the lack of efficient devices. In particular, the basic optoelectronic building blocks, such as frequency and polarization modulators, capable of actively manipulating this radiation are currently missing, thus hindering its full exploitation in fundamental research and in industrial applications. This proposal aims to provide such tools by realizing a novel class of active integrated and efficient devices based on the interplay between metamaterial resonances and graphene. Because of their unique versatility and performance in terms of power consumption, efficiency and reconfiguration speed, these devices will be readyly implemented with already established academic /industrial environments. The main research areas where this project finds application are identified as terahertz imaging, spectroscopy, communications and quantum electronics. Terahertz imaging represents a mature technology which is currently used in diverse key sectors, ranging from security and defense, to semiconductor inspections, to non-destructive testing of pharmaceutical tables and imaging of biological samples. THz gas and solid-state spectroscopy have several applications as well: it is widely known that drugs or explosives present strong absorption features in the THz range while, conversely, plastic material are transparent to this radiation. This lends itself naturally into security screening, e.g. at airport, and into applications in drug detection. Common pollutants and greenhouse gases have unique spectral fingerprints in this frequency range, thus finding obvious applications in environmental monitoring. These devices in combination with already established sources such as the quantum cascade laser or time domain spectroscopic systems will increase the imaging capability and allow novel spectroscopic methodologies and experimental configurations. The interest in THz wireless communication stems from the saturation of the present communication frequencies and from the ambition of higher communication speed. The THz range uniquely addresses both issues, being an unallocated frequency region and with high carrier frequencies, mandatory prerequisite for achieving fast data transfer. The development of future THz communication platform, necessary passes through the development of fast and integrated frequency and polarization modulators, which are the basic components in many communication protocols. Therefore, the success of this proposal will uniquely address several future challenges in strategic public/private sectors, capable of impacting on the layman quality of life. At the same time, this proposal has the ambition to contribute to the health and progress of different academic environments such as the research area investigating novel carbon-based materials, and the quantum cascade laser community. This research in fact will help finding novel concrete implementations for 2D materials in electronic devices and establishing their utilization in the THz range. Finally, in combination with the quantum cascade laser, these devices will provide a formidable tool set for exploring novel concepts and configurations in fundamental quantum electron field, and increase the breadth of spectroscopic operations for this particular source.

The generation of ultrafast and intense light pulses is an underpinning technology across the electromagnetic spectrum enabling time-resolved measurements, nonlinear photonics, coherent control of matter, and frequency comb synthesis for high-precision metrology and spectroscopy. Yet in the terahertz (THz) region of the electromagnetic spectrum (~0.5-5THz), which spans the frequency range between microwaves and the mid-infrared, a compact semiconductor-based technology platform for intense and ultrafast pulse generation has yet to be realised. Established pulse generation schemes, based on excitation of photoconductive emitters or nonlinear crystals using bulky and expensive near-infrared lasers systems, offer only low frequency modulation, or broadband emission with little control of the spectral bandwidth and pulse width. These limitations are significantly hindering the development of the THz field not only in the UK but internationally, with adverse consequences for both fundamental scientific research and the development of future applications in metrology, materials analysis and molecular spectroscopy, and ultra-high speed THz communications. One promising solution to closing this technological gap is the THz frequency quantum cascade laser (QCL) - a compact and high-power semiconductor laser based on a quantum-engineered semiconductor superlattice. However, modelocking these sources is inherently difficult to achieve due to the very fast gain recovery time in these structures. Indeed, active modelocking approaches adopted to date have succeeded only in achieving pulse widths down to ~4ps, and only low output powers are possible. In this programme we will explore a radically new approach to pulse generation in lasers, based on the phenomenon of self-induced transparency in which pulses of the correct energy and pulse duration propagate without loss in the laser cavity whilst the growth of continuous waves is supressed. Although this concept has been discussed since the 1960s, the observation of this effect in semiconductor devices has remained elusive owing to the typically short coherence times of inter-band laser transitions. QCLs, however, are the ideal tool to realize SIT-modelocking owing to their large dipole moments, relatively long inter-subband coherence times, and, importantly, the possibility of combining resonant gain and absorbing periods with engineered dipole moments. We will explore the coherent interaction of intense, ultrafast THz pulses with intersubband semiconductor heterostructures and THz QCL devices for the first time. Although these measurements are of fundamental interest in their own right, the investigation of such systems will lead to the development of the first modelocked semiconductor laser exploiting self-induced transparency. Through this approach, we will bring about a step change in QCL modelocked technology and develop THz QCLs into a foundational, compact semiconductor technology for generating intense and ultrafast THz pulses, with inherent advantages of high powers, broad spectral coverage and the ability to electrically-control the emission properties. This will pave the way for the application of modelocked THz QCLs across a wide range of areas of academic and industrial relevance, including non-linear THz science, quantum optics, ultra-high-speed THz communications, and high-precision metrology and molecular spectroscopy. But that is not all. We will also demonstrate proof-of-principle applications of these new QCL sources for molecular spectroscopy, leading to a compact, all-solid-state and electrically-controlled multi-heterodyne THz spectrometer offering >500 GHz spectral coverage and sub-millisecond acquisition times. Through this goal we will translate to the THz region the unequalled combination of broad spectral coverage, high detection sensitivity, narrow spectral resolution and fast acquisition enabled by laser frequency combs at mid- and near-infrared frequencies.

This Fellowship application will provide support for a leading Photonics Engineering Academic, Prof Peter Smith, University of Southampton, to build a research team to address industry and academic led challenges in Quantum Technologies. The project is entitled QuINTESSEnCE - standing for Quantum Integrated Nonlinear Technology Enabling Stable, Scaleable Engineered for Commercial Exploitation. This title reflects our desire to develop technology that will be stable and applicable in real-world applications, and move that towards developing a supply chain to take Quantum Technologies towards commercial reality. The work will focus on building optical components and photonic manufacturing capability for the next generation of science and, by working closely with companies, to provide the components needed to underpin the application of quantum enabled technology to address a wide range of societal and economic challenges. Two core technologies will be developed, the first being lasers that are exceptionally stable and low noise, and ideally suited for use in a wide range of science applications. The second technology will see the development of new optical materials capable of converting the wavelength (colour) of laser light, efficiently and cheaply. The approach will use high reflecting cavities to enhance the light fields, giving high conversion efficiency and, importantly, exploiting the laws of quantum science to create photons with unique properties. The highlight of the project will be manufacturing demonstrators of our quantum enabled optical technology to take to companies and end-users that will act to prove their value. Two demonstration areas are planned, firstly detectors that will be able to see extremely low light levels in the infra-red without the need for expensive cooling to prevent noise. The second will be to use our lasers and cavities to show advantage in measuring optical fibre links while they are in use, improving data reliability on the internet and increasing down-load speeds. Detectors and other devices will be based on fundamental quantum properties, in which two photons can be fused together to create a single photon with higher energy but preserving fundamental quantum information in the photons themselves.

Pulsed terahertz (THz) radiation has proved particularly powerful in applications such as spectroscopy, materials characterisation, security screening, communications, quality control and medical imaging. Considerable information is encoded in the polarisation state of a THz pulse, yet to date most terahertz spectrometers and imaging systems do not record full polarisation information. Thus, the ability to record and harness polarisation information, which can double the information encoded on a THz pulse, offers huge potential benefits to existing applications of THz systems as well as new applications. We recently developed a new technology based on semiconductor nanowires (NWs) that promises to open up an exciting and powerful new field of terahertz polarimetry. This project will capitalise on our discovery by using the NW-technology to create an ultrafast THz polarimeter, that will firmly establish this new field and make it accessible to a range of disciplines. The power of the ultrafast THz polarimeter will be demonstrated in two key areas: (i) the extraction of the electronic properties of nanoscale and novel thin-film semiconductors and (ii) the development and characterisation of terahertz metasurfaces.