Jan 14 2016
Scientists from the University of Strathclyde have discovered that the charged particle motion can be controlled by the diffraction of ultra-intense laser light, traveling via a thin foil. The findings in the fundamental physics of the laser-plasma interactions, may have a major impact in the fields of security, industry, and medicine. This breakthrough holds immense potential in advancing compact, cost-effective, laser-powered particle accelerators.
The researchers demonstrate that a localized region, termed relativistic plasma aperture, is produced at the peak of the laser intensity which is transparent to the laser light. This happens when an interaction occurs between the foil target and the ultra-intense laser pulse. Control of the particle motion can be achieved by manipulating the diffraction of light through the aperture.
The results of the study have been reported in the physics journal, Nature Physics. The study was a collaborative effort between Queen’s University Belfast and the Central Laser Facility, and was headed by Professor Paul McKenna of the University of Strathclyde. McKenna is also an EPSRC Leadership Fellow.
The development of compact laser-driven particle accelerators and high-energy radiation sources relies on controlling the motion of plasma electrons displaced by the intense laser fields.
Our discovery that diffraction via a self-induced plasma aperture not only controls this motion but also drives the production of twisting plasma structures opens a new pathway to controlling charged particle dynamics. The results have immediate application in the development of laser-driven ion sources and can potentially be used to model astrophysical phenomena such as helical field structures in jets originating from the rotation of black hole accretion disks.
The plasma electrons are accelerated to close to the speed of light, gaining mass due to Einstein’s mass-energy conservation principle. This effect can make a region of an opaque foil transparent, creating a relativistic plasma aperture, and in the process induce diffraction of the laser light – similar to how normal light waves diffract though a pin-hole. Unlike normal diffraction however, the plasma aperture adapts in response to the laser light, enabling control of the plasma electron motion.
Paul Mckenna, Professor, University of Strathclyde
The researchers observed that when the polarization of the light beam was changed the structure of the electron beam was able to rotate at different rotational frequencies, based on the level of ellipticity of the laser polarization. This resulted in twisted or spiral-shaped plasma structures. When the researchers performed 3D simulations and modeling it was revealed that the new concept was able to induce the helical magnetic fields, which could possibly be used in laboratory investigations of similar field structures in astrophysical jets.
The Gemini laser at the Central Laser Facility was used to conduct the experiment, and the ARCHIE-WeSt (University of Strathclyde) and ARCHER (Edinburgh) high performance computers were used to perform the simulations.
EPSRC funding supported the study.