Physicists receive ERC Synergy Grant to create extreme light pulses

Members of the Synergy team, from left to right: the main project leader Prof. Matt Zepf from Helmholtz-Institute Jena, and the three co-project leaders: Prof. Brendan Dromey from Queen’s University Belfast, Prof. Alexander Pukhov from Heinrich Heine University Düsseldorf, and Prof. László Veisz from Umeå University.

ImageMatt Zepf

The project is a collaboration between researchers in Germany, the United Kingdom and Sweden. Professor László Veisz from the Department of Physics at Umeå University is a co-project leader with expertise in high-power lasers. He and his colleagues have built Sweden’s most powerful laser, LWS100, which will be used in the ExtremeField experiments.

When an extremely powerful, ultrashort laser pulse strikes a glass surface, the surface transforms into a plasma and electrons are released from the atomic nuclei. The electrons move at nearly the speed of light, acting like a mirror, reflecting the light and producing unimaginably short flashes of light. The pressure of the light can also curve the mirror, concentrating the light into an extremely small single point.

Pushing the limits of light

The basic idea behind this method is that the energy of the laser pulse is focused simultaneously in both space and time. Calculations predict that this method can increase the intensity of the light pulse by a factor of a million compared to what today’s lasers achieve at the focal point. Such intensities are close to the so-called Schwinger limit, named after the American physicist Julian Seymour Schwinger (1965 Nobel Laureate in Physics). 

Theory predicts that fields this strong could cause electrons and their antiparticles, positrons, to emerge spontaneously from the vacuum, and that light particles can be scattered by other light particles.

To date, these predictions have not been tested experimentally because the generation of such high electric fields has not been possible. 

The idea behind ExtremeField: An intense, very short laser pulse (red) from the right creates a plasma mirror, causing its surface to curve and oscillate with velocities close to the speed of light (green on the left). The oscillating surface reflects short flashes of light with much shorter wavelengths and focuses them all into a tiny point (bright spot in the center). At that point, field strengths are expected that allow quantum effects of the vacuum to become measurable.

ImageMatt Zepf using Gemini

“With ExtremeField, we aim to create, for the first time, experimental conditions near the Schwinger limit where quantum effects in a vacuum can be measured,” explains project coordinator Professor Matt Zepf of the Helmholtz Institute Jena, a branch of GSI. “We plan to conduct experiments at our high-power laser JeTi in Jena, Taranis in Belfast, Light Wave Synthesizer 100 (LWS100) in Umeå and develop a new class of lasers to achieve the maximum possible performance with the team members in Umeå.” 

Computer models and experiments go hand in hand

At Heinrich Heine University in Düsseldorf, the team led by Professor Alexander Pukhov develops computer models that show how laser light transforms the material into plasma and generates light at higher frequencies. The models are continuously compared with measurements from experiments.

“The simulations tell the experimenters where to look, and the experiments show us where our models are still off,” says Pukhov. “Closing this loop is at the heart of the project.”

At Queen’s University Belfast in Northern Ireland, Professor Brendan Dromey will investigate how the glass surface transitions into plasma at the start of the laser pulse.

László Veisz is setting up the new laser SUPER there.

“LWS100 is the best existing tool to efficiently compress laser pulses to extreme dimensions, both in time and space. But we envisage an even better laser with pulses as short as half an optical cycle and almost ten times more peak power than LWS100. This would bring us closer to the Schwinger limit,” says László Veisz.