The University of Southampton

Computational Nonlinear Optics

The Computational Nonlinear Optics group is developing theoretical and numerical models for a wide range of photonics systems, from single-quantum interactions in optical resonators to high-power laser propagation in fibres. 

This work is supporting various experimental and fabrication activities across the ORC with the aim to identify and explore underlying nonlinear and quantum optical phenomena as well as material and structural effects. The results find applications in novel and improved short-pulse lasers, frequency converters, sensors, microstructured fibres, telecom systems, and even quantum logic circuits.

All PhD Projects: 

  • Entry Requirements: A very good undergraduate degree (at least a UK 2:1 honours degree, or its international equivalent) in physics or a related discipline. 
  • Funding: Full tuition plus, for UK students, an enhanced stipend of £20,000 tax-free per annum for up to 3.5 years. Limited funding for international applicants may be available. Overseas students who have secured or are seeking external funding are also welcome to apply.
  • How to apply: Applications should be made online
  • Closing date: Applications are accepted throughout the year and several start dates throughout the year are possible. Applications for the typical Sept./Oct. 2023 start should be received no later than 31 August 2023.


PhD Projects:

Exploring the application of low loss UV-guiding hollow core fibres for an enhanced gas-phase Raman instrument

Supervisory Team: Dr Natalie WheelerDr Peter HorakDr Ian Davidson

We are looking for a new PhD student, with a background in Physics, Chemistry or Engineering, to join our friendly team, working on a novel gas sensor for applications including next generation energy networks, sustainable process monitoring and point of care medical diagnosis. If you are looking for hands-on, primarily experimental project, working with an exciting new technology, which spans between academic research and commercial instrument development, then this project could be for you. 

The key element of our novel gas sensor is a specialty fibre known as hollow core optical fibre. Within our group we work on all aspects of these fibres, from fundamentals, including design and fabrication, to applications, where we work with a range of internal and external collaborators. 

Hollow core fibres are an exciting platform for gas-light interactions as they can be filled with the target gas sample to provide a huge interaction length between the confined gas molecules and the guided light. This means that using a hollow core fibre for gas sensing opens up a pathway to high sensitivity, multispecies gas detection, which has a range of applications. The sensor will detect Raman scattered light from the gas sample contained in the hollow core fibre which will provide a unique spectral fingerprint of the target gas. In this project, you will explore the potential of this concept in the ultraviolet spectral region, where further sensitivity enhancement is possible. 

In this project you will have the opportunity to learn how to design and simulate the properties of these fibres as well as to develop hands-on experience of fibre characterisation and applications. You will work within our research team and have opportunities to develop and test new ideas and to collaborate more broadly with the wide range of researchers working in our department. We will work closely with an industrial partner, and you will spend time working with them to develop a prototype instrument in their facilities. This will provide you with first-hand experience of how academic research can translate into a commercial product and maximise the impact of your research. You will also have opportunities to present your work at international conferences and publish in academic journals.


Spatial effects in high-power fibre lasers and amplifiers

Supervisory Team: Dr Peter Horak, Prof Michalis Zervas

We are looking for a PhD student to work on the design and numerical simulation of the next generation of high-power fibre lasers. The project is part of a major new initiative funded by the UK Research Council at the Optoelectronics Research Centre, University of Southampton, that will combine new fibre technology with state-of-the-art control mechanisms, including machine learning, to reach unprecedented laser powers with full control over the beam shape. 

As fibre lasers get more and more powerful, the fibre core size must increase to minimise optical nonlinearities and avoid material damage. This adds spatial degrees of freedom to the laser beam that have to be controlled in order to obtain a clean, well-behaved laser output. This project will exploit computer simulations to investigate the dynamics of the generation of light in such large, few-mode or multimode, optical fibres. We will analyse the dynamics of the spatial light profile and its dependence on the gain medium, fibre losses, optical nonlinearities, chromatic dispersion, and thermal and acoustic effects. These numerical and theoretical investigations will be performed in close collaboration with corresponding high-power laser experiments in our labs and at our industrial partners. 

If you have an interest in computational physics and research in the exciting area of high-power lasers, you would be highly suitable for this project. You will benefit from our world-leading expertise in these fields and exploit state-of-the-art computer hardware for your research on a PhD project which is highly relevant for the future development of the next generation of fibre lasers and their applications in, for example, advanced digital manufacturing and medical surgery.


Vacuum hollow-core optical fibres

Supervisory Team: Dr Peter Horak, Prof Radan Slavik, Dr Natalie Wheeler

We are looking for a PhD student to join our team on a project which aims to push the limits of what is possible with optical fibres by evacuating novel hollow-core optical fibres. Your project can focus on developing theoretical and numerical models or the experimental aspects or a mixture of both. 

Hollow-core optical fibres guide light in a central hole inside a silica microstructure. These newly developed fibres exceed traditional solid fibres used in the past 40 years in every metric: lower attenuation, nonlinearity, latency, and better high-power laser transmission. However, the central hole where light is transmitted is typically filled with air and for several applications even air limits the fibre performance. 

We have recently been awarded funding to investigate techniques to overcome these limits by removing the air from the core, that is, by evacuating the fibres. We will:

  • investigate, both theoretically and experimentally, techniques for evacuation (which is not straightforward for km-length fibres);
  • develop tools and methods to measure the gas pressure distribution;
  • study how these evacuated fibres can push the limits of what is possible with optical fibres.

Finally, we aim to use these fibres to demonstrate, for example, new record laser power delivery in fibres, interferometers with the minimum possible noise added by the fibre (of interest, e.g., for ultra-sensitive detection of gravitational waves), and transmission at wavelengths where air-filled hollow-core fibres or standard fibres have too strong absorption. 

In this PhD project you will either develop simulations of the various evacuation and characterisation methods or build set-ups based on such designs or combine both. This will mainly include optical methods exploiting linear and nonlinear laser pulse propagation in such fibres where the hollow core exhibits a non-uniform and (during evacuation) time-dependent air pressure. Additionally, you may investigate the pressure-driven gas flow inside these novel fibres. You can also choose to use the evacuated fibres with one of the applications they enable, as discussed above. Independently of what you choose, your work will be in close collaboration with our fabrication, theoretical, and experimental teams. 

If you have an interest in optical fibres, their physics, and their applications, you would be highly suitable for this project. You will benefit from the world-leading expertise in these fields at the ORC and work in a supportive group of like-minded researchers, leading you to a PhD in an exciting new area of physics and technology.


High-performance computer simulation of laser-driven coherent X-ray generation for imaging applications

Supervisory Team: Dr Peter Horak, Dr Bill Brocklesby

Generation of femtosecond and attosecond X-ray pulses using intense laser pulses has transformed ultrafast science. The ability to produce coherent ultrafast X-ray pulses has applications in many areas, from the investigation of ultrafast molecular dynamics to biomedical imaging. In this PhD project, you will exploit computer simulations to further develop and optimise X-ray sources for coherent imaging, in close collaboration with experimental work already happening in the Ultrafast Laser X-Ray group. 

This project will investigate theoretically all effects that contribute to X-ray generation in our setup: the propagation of ultrashort intense laser pulses through a dilute gas, the ionisation of the gas by these pulses, and the interaction of the resulting plasma with the laser and subsequent X-ray radiation generation by atomic recombination. For example, we will look at novel pump lasers and hollow-core optical fibres as gas-filled waveguides and investigate the effects of laser pulse shaping in space and time to optimise the generation of X-rays. 

You will be using a complex computer model that our group has recently developed as the basis for this project. The code is written in C++ and Python and runs on the Southampton supercomputer cluster Iridis. The project is therefore best suited for a student with a strong interest in programming and high-performance computing as well as a background in physics, nonlinear optics and/or lasers. You will benefit from the world-leading expertise in these fields at the ORC and work in a supportive group of like-minded researchers, leading you to a PhD in an exciting new area of physics and technology.


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