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Real-time gas sensing using terahertz quantum-cascade lasers

PGR-P-1408

Key facts

Type of research degree
PhD
Application deadline
Tuesday 31 January 2023
Project start date
Sunday 1 October 2023
Country eligibility
International (open to all nationalities, including the UK)
Funding
Competition funded
Source of funding
University of Leeds
Supervisors
Dr Paul Dean and Dr Alexander Valavanis
Research groups/institutes
Pollard Institute
<h2 class="heading hide-accessible">Summary</h2>

This project will develop fast detection systems to provide the first real-time gas sensing and imaging in the terahertz (THz) band of the electromagnetic spectrum.<br /> The THz band lies between the infrared and microwave regions and represents a meeting between electronic and optical technologies. Although numerous potential applications for THz sensing exist, including atmospheric and space research, security and biomedical imaging, and industrial inspection, there has been limited practical use of THz systems outside specialised laboratories.<br /> One key reason for this is the reliance on relatively slow thermal detectors to measure and analyse THz signals. These are inadequate for studying rapidly changing systems, such as chemical reactions, or for video-rate imaging. They are also highly susceptible to background thermal noise, which degrades imaging quality, and limits the accuracy and dynamic range of measurements. In this project, the student will develop new high-speed THz gas-sensing techniques, taking advantage of recent developments in fast THz detector technology.<br /> They will initially use a fast, and sensitive TeraFET detector system, in collaboration with Goethe University Frankfurt, to detect and analyse rapidly changing chemical concentrations in a custom-built THz gas-cell. They will use the world-leading Bragg Nanotechnology cleanroom facilities to develop bespoke THz quantum-cascade laser sources (QCLs), and THz photonic-molecule lasers to target the spectral fingerprints of key atmospheric gases (e.g., O, NO, NH3 and OH) precisely in the 2&ndash;5 THz band, with dynamically-controllable laser emission. They will incorporate these into a step-scan Fourier-Transform interferometry system to provide spectral analysis of complex gas mixtures on microsecond timescales. In parallel, they will use TeraFET detectors to control the output power and frequency of THz QCLs, enabling their use in low-noise video-rate sensing for the first time.

<h2 class="heading hide-accessible">Full description</h2>

<p style="margin-bottom:11px">This project will develop fast detection systems to provide the first real-time gas sensing and imaging in the terahertz (THz) band of the electromagnetic spectrum.</p> <p>The THz band lies between the infrared and microwave regions and represents a meeting between electronic and optical technologies.&nbsp; Although numerous potential applications for THz sensing exist, including atmospheric and space research, security and biomedical imaging, and industrial inspection, there has been limited practical use of THz systems outside specialised laboratories.</p> <p>One key reason for this is the reliance on relatively slow thermal detectors to measure and analyse THz signals.&nbsp; These are inadequate for studying rapidly changing systems, such as chemical reactions, or for video-rate imaging.&nbsp; They are also highly susceptible to background thermal noise, which degrades imaging quality, and limits the accuracy and dynamic range of measurements.&nbsp; In this project, the student will develop new high-speed THz gas-sensing techniques, taking advantage of recent developments in fast THz detector technology.</p> <p>They will initially use a fast, and sensitive TeraFET detector system, in collaboration with Goethe University Frankfurt, to detect and analyse rapidly changing chemical concentrations in a custom-built THz gas-cell.&nbsp; They will use the world-leading Bragg Nanotechnology cleanroom facilities to develop bespoke THz quantum-cascade laser sources (QCLs), and THz photonic-molecule lasers to target the spectral fingerprints of key atmospheric gases (e.g., O, NO, NH3 and OH) precisely in the 2&ndash;5?THz band, with dynamically-controllable laser emission.&nbsp; They will incorporate these into a step-scan Fourier-Transform interferometry system to provide spectral analysis of complex gas mixtures on microsecond timescales.&nbsp; In parallel, they will use TeraFET detectors to control the output power and frequency of THz QCLs, enabling their use in low-noise video-rate sensing for the first time.</p> <p>The studentship enables a step-change in the speed and accuracy of THz sensing and imaging techniques, which have historically been limited by the availability of good THz detectors. Ultimately, this will allow real-time THz analysis of chemical reactions for the first time.&nbsp; This would provide key missing links in atmospheric chemistry (e.g., impact of volatile-organic compounds on the lifetimes of greenhouse gases), which currently introduce order-of-magnitude uncertainties in climate models.&nbsp; There are far wider potential impacts though, in terms of high-speed industrial emission monitoring and control, video-rate biomedical sensing, and the first potential satellite deployment of fast and low-noise THz receiver systems.</p> <p>Key objectives include:</p> <ul> <li><strong>Real-time analysis of chemical reactions using THz radiation:</strong> The PGR will use a broadband TeraFET detector to undertake analysis of gas reactions (e.g., deuteration of methanol) and flux rates (e.g., ammonia concentrations), leading ultimately to development of the first UV-pump/THz-probe reaction studies of atomic oxygen concentrations as an analytical chemistry technique.</li> <li><strong>Precision THz source development for gas analysis:</strong> The PGR will employ molecular spectroscopy catalogue data (HITRAN, JPL etc) to optimise QCL frequency selection to target atmospheric gas-phase species.&nbsp; They will use finite-element analysis (COMSOL MultiPhysics) to design photonic gratings and photonic-molecule structures and fabricate QCLs accordingly in the Bragg Nanotechnology cleanroom, for use in gas spectroscopy.</li> <li><strong>High-bandwidth control of THz sources: </strong>The student will exploit the high speed of TeraFET detectors to develop the high-bandwidth frequency and amplitude control of THz QCLs to date, enabling a ~100-fold improvement in gas analysis sensitivity and precision.&nbsp; Initially, they will use a commercial proportional&ndash;integral (PI) controller to modulate the QCL frequency directly using a known gas absorption feature as an FM&ndash;AM convertor.&nbsp; They will integrate a power modulator structure with the QCL ridge to provide an independent power-lock mechanism.&nbsp; They will also investigate the use of external liquid-crystal modulators (H.&nbsp;Gleeson, U.&nbsp;Leeds) and graphene modulators (C. Kosabas, U.&nbsp;Manchester) to provide long-term power stability.</li> </ul> <p>You can start your PhD from 1 August 2023 but you must be able to start by no later than 1 November 2023.</p>

<h2 class="heading">How to apply</h2>

<p>Formal applications for research degree study should be made online through the&nbsp;<a href="https://www.leeds.ac.uk/research-applying/doc/applying-research-degrees">University&#39;s website</a>. Please state clearly in the Planned Course of Study section that you are applying to <em><strong>PHD Electronic &amp; Electrical Engineering FT</strong></em> and in the research information section&nbsp;that the research degree you wish to be considered for is <em><strong>Real-time gas sensing using terahertz quantum-cascade lasers</strong></em> as well as <a href="https://eps.leeds.ac.uk/electronic-engineering/staff/375/alexander-valavanis">Dr Alexander Valavanis</a> as your proposed supervisor.</p> <p>If English is not your first language, you must provide evidence that you meet the University&#39;s minimum English language requirements (below).</p> <p><em>As an international research-intensive university, we welcome students from all walks of life and from across the world. We foster an inclusive environment where all can flourish and prosper, and we are proud of our strong commitment to student education. Across all Faculties we are dedicated to diversifying our community and we welcome the unique contributions that individuals can bring, and particularly encourage applications from, but not limited to Black, Asian, people who belong to a minority ethnic community, people who identify as LGBT+ and people with disabilities. Applicants will always be selected based on merit and ability.</em></p> <p class="MsoNoSpacing">Applications will be considered on an ongoing basis. &nbsp;Potential applicants are strongly encouraged to contact the supervisors for an informal discussion before making a formal application. &nbsp;We also advise that you apply at the earliest opportunity as the application and selection process may close early, should we receive a sufficient number of applications or that a suitable candidate is appointed.</p> <p>Please note that you must provide the following documents in support of your application by the closing date of 31 January 2023:</p> <ul> <li>Full Transcripts of all degree study or if in final year of study, full transcripts to date</li> <li>Personal Statement outlining your interest in the project</li> <li>CV</li> <li>Funding information including any alternative sources of funding that you are applying for or if you are able to pay your own fees and maintenance</li> </ul>

<h2 class="heading heading--sm">Entry requirements</h2>

Applicants to research degree programmes should normally have at least a first class or an upper second class British Bachelors Honours degree (or equivalent) in an appropriate discipline. The criteria for entry for some research degrees may be higher, for example, several faculties, also require a Masters degree. Applicants are advised to check with the relevant School prior to making an application. Applicants who are uncertain about the requirements for a particular research degree are advised to contact the School or Graduate School prior to making an application.

<h2 class="heading heading--sm">English language requirements</h2>

The minimum English language entry requirement for research postgraduate research study is an IELTS of 6.0 overall with at least 5.5 in each component (reading, writing, listening and speaking) or equivalent. The test must be dated within two years of the start date of the course in order to be valid. Some schools and faculties have a higher requirement.

<h2 class="heading">Funding on offer</h2>

<p class="MsoNoSpacing">A highly competitive School of Electronic &amp; Electrical Engineering Studentship consisting of the award of fees at the UK fee rate (currently &pound;4,596 in academic session 2022/23) or Non-UK fee rate (currently &pound;25,500 in academic session 2022/23) together with a maintenance grant (currently &pound;17,668 for session 2022/23) for 3.5 years.</p> <p>This opportunity is open to all applicants. All candidates will be placed into the School of Electronic &amp; Electrical Engineering Studentship Competition and selection is based on academic merit.<br /> <br /> <strong>Important:&nbsp;</strong> Any costs associated with your arrival at the University of Leeds to start your PhD including flights, immigration health surcharge/medical insurance and Visa costs are not covered under this studentship.</p> <p>Please refer to the&nbsp;<a href="https://www.ukcisa.org.uk/">UKCISA</a>&nbsp;website for&nbsp;information regarding Fee Status for Non-UK Nationals.</p>

<h2 class="heading">Contact details</h2>

<p>For further information about your application, please contact Doctoral College Admissions: e:&nbsp;<a href="mailto:EMAIL@leeds.ac.uk">phd@engineering.leeds.ac.uk</a></p> <p>For further information about this project, please contact Dr Alexander Valavanis: e:&nbsp;<a href="mailto:a.valavanis@leeds.ac.uk">a.valavanis@leeds.ac.uk</a>&nbsp;or t: + 44 (0) 113 343 3224.</p>


<h3 class="heading heading--sm">Linked funding opportunities</h3>
<h3 class="heading heading--sm">Linked research areas</h3>