Lasers provide first evidence that light can stop electrons
This article is a republication from the Chalmers University of Technology.
Chalmers researcher Mattias Marklund, together with his colleagues, has developed the theoretical calculations for the laser experiment where extremely bright laser beams were collided with high-energy electrons. The illustration shows how electrons (blue) collide with a laser beam (green/magenta) and emit gamma rays (yellow). Illustration: Tom Blackburn
By hitting electrons with an ultra-intense laser, researchers have revealed dynamics that go beyond ‘classical’ physics and hint at quantum effects.
“The real result then came when we compared this detection with the energy in the electron beam after the collision. We found that these successful collisions had a lower than expected electron energy, which is clear evidence of radiation reaction.” Study co-author Professor Alec Thomas, from Lancaster University and the University of Michigan, added: “One thing I always find so fascinating about this is that the electrons are stopped as effectively by this sheet of light, a fraction of a hair’s breadth thick, as by something like a millimetre of lead. That is extraordinary.” The data from the experiment also agrees better with a theoretical model based on the principles of quantum electrodynamics, rather than Maxwell’s equations, potentially providing some of the first evidence of previously untested quantum models.
Study co-author Professor Mattias Marklund of Chalmers University of Technology, Sweden, whose group were involved in the study, said: “Testing our theoretical predictions is of central importance for us at Chalmers, especially in new regimes where there is much to learn. Paired with theory, these experiments are a foundation for high-intensity laser research in the quantum domain.” However more experiments at even higher intensity or with even higher energy electron beams will be needed to confirm if this is true. The team will be carrying out these experiments in the coming year. The team were able to make the light so intense in the current experiment by focussing it to a very small spot (just a few micrometres – millionths of a metre – across) and delivering all the energy in a very short duration (just 40 femtoseconds long: 40 quadrillionths of a second). To make the electron beam small enough to interact with the focussed laser, the team used a technique called ‘laser wakefield acceleration’. The laser wakefield technique fires another intense laser pulse into a gas. The laser turns the gas into a plasma and drives a wave, called the wakefield, behind it as it travels through the plasma. Electrons in the plasma can surf on this wake and reach very high energies in a very short distance.
Read the scientific article ‘Experimental evidence of radiation reaction in the collision of a high-intensity laser pulse with a laser-wakefield accelerated electron beam’ in Physical Review X.
The research at Chalmers University of Technology has been funded by the Knut och Alice Wallenberg Foundation and the Swedish Research Council.
