Pushing the boundaries of laser plasma acceleration

July 13, 2026

Simon Hooker, Professor of Atomic & Laser Physics at the University of Oxford, highlights the work of his Laser-Plasma Accelerator Group

Laser plasma acceleration holds major promise for particle physics, producing an electric field more than three orders of magnitude larger than those found in conventional radiofrequency (RF) accelerators. When an intense laser pulse propagates through a plasma, the ponderomotive force pushes electrons away from the front and back of the pulse, thereby forming a trailing longitudinal density wave. This ‘laser wakefield accelerator’ is particularly promising for generating beams of short pulse, high-energy electrons for applications in femtosecond electron diffraction, medical imaging, and miniature free-electron X-ray lasers.

A key challenge associated with these accelerators is the distance over which the intensity of the driving laser can be maintained, which can limit the energy to which particles can be accelerated. This is one of the main issues that the Laser-Plasma Accelerator Group at the University of Oxford has set out to tackle. The group has developed several techniques for channelling laser pulses with peak intensities of up to 10¹⁸ Wcm^-2, over distances which are much longer than the limit set by diffraction.

The group’s work on laser-driven plasma accelerators is focused on four key areas:

Investigation of techniques for controlling the injection of electrons into the plasma wakefield;
Development of new techniques for driving plasma accelerators, such as multi-pulse laser wakefield acceleration;
Development of techniques for guiding the intense driving laser pulse over hundreds of millimetres; and
Development of applications of laser-driven plasma accelerators, particularly their application to the generation of X-rays.

To learn more about the work of the group and its standout achievements so far, The Innovation Platform spoke to Group Lead, Professor Simon Hooker.

Can you explain more about the Laser-Plasma Accelerator Group and its main objectives?

The Laser-Plasma Accelerator Group currently comprises three post-doctoral researchers and six graduate students. I lead the group, with invaluable input from Emeritus Professor Roman Walczak.

The group focuses on experimental work, although we also undertake a large number of numerical simulations, typically with particle-in-cell (PIC) codes run on computer clusters. Our experiments are performed in our own radiation-shielded high-power laser lab, the Oxford Plasma Accelerator Laboratory (OPAL), which houses a 25 TW (1 J, 40 fs) Ti:sapphire laser, and at international facilities, such as those at the Central Laser Facility at Harwell Campus.

What are the main challenges that you are working to overcome?

Many groups around the world have demonstrated that laser-driven plasma accelerators (LPAs) can – in just a few centimetres – accelerate electrons to energies of several GeV, which is in the range of the electron beams used in synchrotrons and free-electron lasers. The current challenges for the field, as I see it, are generating high-energy electron bunches of high quality at high repetition rates – and doing this in a highly reproducible way. Each of these four goals – high energy, quality, repetition rate, and reproducibility – has been achieved by several groups, but realising all of them at the same time is still a challenge for the field.

We have therefore set ourselves the over-arching objective of working towards the development of plasma accelerators capable of reproducibly delivering high-quality, GeV-scale electron bunches at pulse repetition rates in the kilohertz range. This is far from trivial, but it is something that the community can achieve in the next five to ten years.

Most LPAs today are driven by Ti:sapphire lasers that deliver laser pulses with an energy of a few joules. These systems are currently limited to pulse repetition rates of around 10 Hz, and increasing this is technically challenging. In an attempt to circumvent this limit, we proposed the plasma-modulated plasma accelerator (P-MoPA) concept. This exploits commercially available thin-disk lasers (TDLs) that can already provide joule-scale pulses at kilohertz repetition rates, but the pulse duration is too long to drive a LPA directly. The P-MoPA concept aims to get around this by converting each picosecond TDL pulse into a train of short pulses. In outline, the P-MoPA comprises three stages. In the first stage, the ‘Modulator’, a long, high-energy pulse from a TDL co-propagates with the low-amplitude plasma wave driven by a short (< 100 fs), low-energy pulse. Co-propagation with the plasma wave causes the spectrum of the TDL pulse to develop sidebands spaced by the frequency of the plasma wave. In the second stage, the ‘Compressor’, the spectral phase of the modulated TDL spectrum is removed, which converts the TDL pulse into a train of short pulses separated by the period of the plasma wave. Finally, in the third stage, ‘the Accelerator’, the pulse train is used to resonantly excite a large-amplitude plasma wave, which can be used to accelerate electrons to GeV-scale energies.

What have been the key achievements so far?

An important step towards this goal is the hydrodynamic optical-field-ionised (HOFI) plasma channel, which my group played a key role in developing. These channels can guide very intense laser pulses over the tens of centimetres needed to accelerate electrons to multi-GeV energies, and since they are freestanding, they are ‘indestructible’. As they are optically generated, they can operate at high repetition rates, and indeed we have demonstrated kilohertz operation over many hours with no degradation in performance. It is very pleasing to see that HOFI channels have been adopted by several groups around the world, and that they have been used to accelerate electrons to energies as high as 10 GeV.

We have also demonstrated experimentally the operation of the Accelerator stage of a P-MoPA. This was achieved in experiments at the Central Laser Facility, in which we mimicked a P-MoPA pulse train by modulating the spectrum of pulses from the Astra-Gemini Ti:sapphire laser. This work was able to show that a train of pulses with a total energy of around 1 J could resonantly excite plasma waves of amplitude 3 – 10 GV / m, corresponding to a particle energy gain of order 1 GeV over the 11 cm stage length.

What are the group’s main priorities/ focuses for the year ahead?

Our main current priority is to demonstrate the operation of the first two stages of the P-MoPA scheme.

This work is undertaken in collaboration with Professor Stefan Karsch of Ludwig Maximilians-Universiät München, whose laboratories at the Centre for Advanced Laser Applications (CALA) have available the thin-disk lasers needed for this work.

We have already used CALA’s lasers to guide joule-scale TDL laser pulses through long HOFI channels, and we are now preparing to demonstrate spectral modulation of the TDL pulses by co-propagating them with a low-amplitude plasma wave driven by a short, low-energy pulse derived from a TDL pulse. In parallel, we are developing optical systems to compress spectrally modulated TDL pulses into a train of short pulses. We would then be in a position to test the entire P-MoPA concept, which will be an exciting moment.