Exploring novel photoemission regimes with laser-driven terahertz fields for next-generation electron sources

Applications are invited for a fully funded studentship starting Oct 2025 aiming to enhance the performance of electron sources by exploiting novel photoemission schemes using nano-structured photocathodes driven by strong-field terahertz (THz) pulses. Electron sources underpin numerous technologies including electron microscopy, X-ray imaging, lithography, vacuum microwave devices and of course particle accelerators. However, limitations in their performance (such as quantum efficiency, emittance, coherence, repetition rate, stability) are preventing the next technological advances in these areas.

This project will explore an emerging area of research in electron source development exploiting photoemission in the strong-field regime. Electron sources based on the photoelectric effect are typically driven by short-wavelength (UV) laser pulses and operate in either continuous DC or pulsed radio-frequency (RF) accelerating fields, which are limited by material breakdown to less than 10 MV/m and 100 MV/m, respectively. By using THz frequencies (1000x higher than RF), fields >10 GV/m can be applied to the photocathode, unlocking new regimes of photoemission through THz field-assisted work-function control.  This has the potential to significantly boost the photocathode quantum efficiency (higher charge) while maintaining low beam emittance (higher beam quality), in addition to enabling the use of visible-wavelength drive lasers (more efficient than UV) with long pulse lengths (higher damage threshold), transforming the performance and underpinning technology of electron sources.

Recent developments in ultrashort THz pulse generation mean such strong fields are now accessible using high-power drive lasers. However, there is also potential to achieve this with moderate THz sources in combination with nano-structuring of the photocathode, by providing field enhancement through localised confinement of the THz pulse intensity below the diffraction limit. In addition to strong-field effects, the ps-scale THz fields provide unique opportunities to control the electron source properties, using single- or multi-cycle THz pulses to generate either individual electron bunches or THz-frequency bunch trains for high-repetition rate applications.

The project will build collaborations with ASTeC’s Photocathode R&D team and the Photoemission Laboratory at CERN to provide expertise in photocathode technology, including the design and manufacture of nano-structured photocathodes. Experimental facilities such as the Transverse Energy Spread Spectrometer (TESS) at Daresbury Laboratory and the CTF2 electron beamline at CERN will provide the ideal environments to explore THz-assisted photoemission experiments.

The project will be predominantly experimental in nature, enabling you to gain hands-on experience across a wide range of laser and accelerator physics, including using high-power femtosecond lasers, designing complex optical setups, generating/detecting THz pulses, developing structured photocathodes and working with low/high energy electron beams. The project will be based primarily at Daresbury Laboratory with occasional work undertaken in the laser lab at The University of Manchester but will also involve the opportunity to re-locate and work at CERN for up to 12 months during the course of the PhD. It is anticipated that the student will publish papers in peer-reviewed journals and present their work at national and international conferences.

Applicant information

You will be expected to have a first or upper second-class degree in physics or other appropriate qualification, with a keen interest in experimental work in the field of laser and accelerator physics. Experience in either of these areas is desirable but not essential. A full graduate programme of training and development will be provided by the Cockcroft Institute. For more information, potential applicants are strongly encouraged to contact Dr Morgan Hibberd ([email protected]) and provide an up-to-date CV tailored to the project. This position will remain open until filled but it is typical to interview students in Feb 2024 for start in Oct 2024, so interested candidates should submit applications as soon as possible.