Relativistic plasma apertures: Generating ultraintense structured light with orbital angular momentum

When matter is irradiated by a high-power laser pulse it transforms into plasma, creating extreme temperatures and strong electric and magnetic fields. At high laser intensities, the fields induced in the plasma generate pulses of energetic particles and radiation with useful properties, opening up new frontiers in science as well as novel applications.

The ability to produce structured beams of ultraintense light opens up new degrees of freedom in control of the energetic particles and radiation generated, and thus further possibilities for applications of these promising laser-driven sources.

The scientific push for ever more intense light typically requires ever larger optical elements to control it, due to limitations in the energy density that solid-state optical materials can sustain before they damage. This motivates research into the use of plasma optics to manipulate laser light, as plasma can sustain more intense light and thereby overcome these limitations.

Such optics are typically compact and the possibility to engineer the properties of the plasma to tune specific properties of light, opens up new scientific possibilities. One such possibility is the generation of ultraintense light structured with helical phase-fronts (optical vortices) carrying orbital angular momentum (OAM). Ultraintense light pulses carrying OAM are difficult to generate and control with large solid-state optics, but new mechanisms become available via plasma optics.

In this project, we shall take major steps towards addressing the challenge of generating ultraintense structured light with adjustable intensity and polarisation distributions, and potentially tuneable OAM, through investigation of a new type of plasma optic based on structured plasma apertures. We will deliver this via the following scientific objectives:

Investigate direct electron acceleration and the generation of intense harmonic light with tuneable beam structure from circular micro-aperture targets.

Demonstrate harmonic generation with independent control of frequency and OAM, using apertures with defined periodic structure. Elucidate the physics of self-generated plasma apertures for dynamic control of structured light. Investigate the potential for OAM transfer to directly accelerated, relativistic electrons.

In parallel, we will undertake a programme of regular outreach activities to disseminate the concepts and results produced via this project to the wider public. We aim to raise awareness of how new developments in physics can produce original approaches to addressing societal challenges.

The project is primarily discovery science and will make a substantial contribution to advancing the field of high-power laser-plasma interactions, on topics such as plasma optics and photonics, high harmonic generation and particle acceleration. Tailoring plasma to produce structured light fields pushes the boundaries of plasma optics, which contributes to the development of future plasma-based high-power lasers.

Our plasma optics approach to produce ultraintense light with OAM could contribute new capabilities to frontier high-power laser systems, such as the UKRI-funded EPAC and Vulcan 20-20 facilities. Beyond laser-plasma science, the results on harmonic generation and demonstration of OAM transfer to relativistic electrons is of fundamental interest to nonlinear optics and could be applied as a powerful tool for nuclear physics.

Thus, there is potential for a wide range of academic beneficiaries. The longer-term application of the structured light fields to enhance control of laser-plasma accelerators could also benefit the growing industrial user base of laser-driven radiation sources, as well as potential future use in areas such as medicine.