Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.

The THz part of the electromagnetic spectrum has a number of potential applications which include oncology (skin cancer imaging), security imaging, THz bandwidth photonics, production monitoring and astronomy. The U.K. has been one of the pioneering countries in THz research but also in the exploitation of the technology with a number of companies including TeraView, QMC Instruments and Thruvision. At present most commercial imaging and spectroscopy systems use expensive femtosecond lasers with photoconductive antenna which fundamentally limits the power output to the microWatt level. Virtually all the applications referenced above require room temperature sources with over 10 mW of output power if parallel, fast, high performance imaging and/or spectroscopy systems are to be developed.While interband recombination of electrons and holes in Si and Ge are inefficient due to the indirect bandgap of the semiconductors, intersubband transitions provide an alternative path to a laser for low energy radiation such as THz frequencies. Intersubband unipolar lasers in the form of quantum cascade lasers have been demonstrated using III-V materials. Powers up to 248 mW at 10 K have been demonstrated at THz frequencies but due to polar optical phonon scattering and the associated reduction in intersubband lifetimes as the temperature is increased, such devices only operate at cryogenic temperatures. Previous work has been undertaken on p-type Si/SiGe quantum cascade lasers but due to large non-parabolicity and large effective mass (0.3 to 0.4 m_0) in the valence band, significant gain above 10 cm^-1 is difficult to engineer.In this proposal, we propose to use pure Ge quantum well designs and L-valley electrons for the first experimental demonstration of a n-type Si-based quantum cascade laser grown on top of a Si substrate. We demonstrate that the low effective of 0.118 m_0 and long non-polar lifetimes in the Ge/SiGe system potentially provide gain close to values demonstrated in GaAs THz quantum cascade lasers at 4 K and also potentially allow 300 K operation. Further the cheap and mature available Si process technology will allow at least a x100 reduction in the cost of THz quantum cascade lasers compared to GaAs devices. Such devices could be further developed into vertical cavity emitters (i.e. VCSELs) for parallel imaging applications or integrated with Si photonics to allow THz bandwidth telecoms. Finally we propose optically pumped structures which have the potential for broadband tunability, higher output powers and higher operating temperatures than THz quantum cascade lasers.This programme has brought together the modelling and design toolsets at Leeds University with the CVD growth expertise at Warwick University combined with the fabrication and measurement expertise of SiGe devices at Glasgow University to deliver internationally leading research. We have a number of industrial partners (AdvanceSis, Kelvin Nanotechnology and TeraView) who provide direct exploitation paths for the research. Successful room temperature quantum cascade lasers are an enabling technology for many new markets for THz applications including oncology (skin cancer imaging), security imaging, production monitoring, proteomics, drug discovery and astronomy.

The incidence of skin cancer in the UK and globally is increasing. There are two main types of skin cancer: melanoma and non-melanoma skin cancer. Basal Cell Carcinoma (BCC) is a non-melanoma skin cancer, and is the most common type (> 80%) of all UK skin cancer cases. It is well known that applying sunscreen helps to protect the skin from the sun but many people are unaware of the need for UVA (315-400 nm) as well as UVB (280-315 nm) protection. Although lower in energy than UVB, the amount of UVA reaching the earth's surface is 30 times more than for UVB. Furthermore, UVA penetrates the skin more deeply, contributing to both carcinogenesis and skin aging via oxidative stress pathways. One of the most common UVA filters is avobenzone, as it is industrially cheap and thus affordable to the consumer. However, it is now well-established that avobenzone photodegrades, which is a serious concern. In this project, a highly interdisciplinary team consisting of investigators at the University of Warwick in the Departments of Physics, Chemistry, Life Sciences and Medicine, as well as industry partners from Lubrizol (major skin-care provider) and TeraView Ltd (major terahertz (THz)-based instrument provider) will join forces to attack the problem of increasing skin cancer 'prevention' and 'treatment' using a multi-pronged approach. We will improve skin cancer prevention by developing a new UVA, nature-inspired, sunscreen offering longer lasting and more photostable protection than existing sunscreens. To achieve this, we will repurpose the photoprotection mechanisms of other living organisms, specifically those of cyanobacteria and microalgae. These organisms protect themselves from radiation by producing mycosporine-like amino acids (MAAs), a family of molecules which are strong UVA absorbers and are ideal candidates for sunscreen agents, owing to their dual action as UVA filter and antioxidant. We recognise that sunscreens are composed of a UV filter blended with a moisturiser (emollient); this can make up to 80% of the composition of the sunscreen. We also recognise that sunscreens are applied to skin. Therefore, to optimise the sunscreen composition, we will develop a revolutionary characterisation tool, the 'THz skinometer', which is able to measure parameters of skin in vivo that other techniques cannot. In this way, we will determine the best UV filter/emollient blend. We will investigate whether different skin conditions such as eczema and psoriasis will benefit from a different emollient blend. THz radiation is non-ionising, using low power levels such that thermal effects are insignificant and consequently safe for in vivo imaging of humans as well as non-destructive testing of materials. It is very sensitive to intermolecular interactions such as hydrogen bonds, and probes molecular processes (eg vibrations, chemical reactions) that occur on picosecond (millionth millionth of a second) timescales. In this project we will employ THz techniques to evaluate the effectiveness of emollients and sunscreens in vivo with a view to developing a single sunscreen that covers both the UVA and UVB regions of the solar spectrum. Furthermore, as a powerful additional feature of our invention, we will also use our THz skinometer to improve the surgical removal, or 'treatment', of skin cancers such as BCC, which often spread out beneath the surface of the skin such that their entirety cannot be detected until surgery. The THz skinometer will be designed to accurately characterise skin in vivo such that it will be able to determine the likely extent of any tumour beneath the surface. In this way, we will identify the full extent of the tumour prior to surgery which will improve skin grafting planning as well as reduce the likelihood of missing any tumour and tumour recurrence. Thus by attacking skin cancer through 'prevention' as well as 'treatment', we aim to reduce 'incidence' and 'morbidity' of skin cancer in the UK & globally.

Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.

Semiconductor lasers are compact, low-cost sources of short pulses of light - and this is used in many applications, e.g. CD players (CD lasers operate at frequencies of a few MHz) and optical communications. For applications in optical communications ultra-short pulses are required at very high repetition frequencies, i.e. tens of GigaHertz (tens of billions of cycles per second) / and in the future even higher repetition rates are likely to be required. It is possible to switch semiconductor lasers on-and-off, directly, at frequencies up to about 40 GHz by using a pulsed current source but not much higher. Future optical communications systems are likely to need higher repetition frequencies - and these frequencies can be reached by using a method called mode-locking, where a special absorbing section within the laser cavity helps to form pulses, with the time between adjacent pulses being controlled by the round trip time for the cavity. But such pulses from mode-locked lasers have relatively low average power levels and are relatively long (typically a few picoseconds). For optical communications applications, lasers with shorter pulses and higher output power levels need to be developed.Another potential use of mode-locked lasers is in the generation of terahertz radiation. The Terahertz part of the electromagnetic frequency spectrum lies between the spectra for visible light and for microwaves. This non-ionising radiation is able to penetrate through materials that are opaque to light, such as paper, plastic, cloth and skin / so it can be used in security and medical applications. It can detect explosives and tumours - it is safer than x-rays because it does not ionise the material through which it passes and is better at differentiating between different types of soft tissue. Terahertz waves are typically generated by conversion from pulsed light sources that presently are both large and expensive to buy and to run. One of the aims of this project is to develop semiconductor lasers that produce pulses at very high frequencies (300 to 2000 Gigahertz) with enough output power to be used to generate Terahertz and sub-Terahertz waves with much increased efficiency. Lasers are needed that emit shorter pulses at higher repetition frequencies and with higher power output levels. This need can be met by using structures already designed to emit high powers and then adapting them for pulsed operation. We shall bring together high-power semiconductor lasers with mode-locked operation to develop lasers that emit short higher-power pulses at world-record repetition frequencies. We shall also investigate structures that can be integrated with the laser that can compress the light pulses even further - and also investigate exactly how the light interacts with the semiconductor material, thereby finding optimum designs of the laser structures for specific applications.