Intense laser experiments provide first evidence that light can stop electrons

February 7, 2018 by Hayley Dunning, Imperial College London
Illustration of the effect. Credit: Imperial College London/Stuart Mangles

By hitting electrons with an ultra-intense laser, researchers have revealed dynamics that go beyond 'classical' physics and hint at quantum effects.

Whenever light hits an object, some of the light scatters back from the surface of the object. However, if the object is moving extremely fast, and if the light is incredibly intense, strange things can happen.

Electrons, for example, can be shaken so violently that they actually slow down because they radiate so much energy. Physicists call this process 'radiation reaction'.

This radiation reaction is thought to occur around objects such as black holes and quasars ( surrounded by a disc of gas). Being able to measure radiation reaction in the lab will therefore provide insights into processes that occur in some of the most extreme environments in the universe.

Radiation reaction is also interesting to physicists studying effects beyond 'classical' physics, as the equations (known as Maxwell's equations) that traditionally define the forces acting on objects fall short in these .

Now, a team of researchers led by Imperial College London have demonstrated radiation reaction in the lab for the first time. Their results are published today in the journal Physical Review X.

They were able to observe this radiation reaction by colliding a laser beam one quadrillion (a billion million) times brighter than light at the surface of the Sun with a high-energy beam of electrons. The experiment, which required extreme precision and exquisite timing, was achieved using the Gemini laser at the Science and Technology Facilities Council's Central Laser Facility in the UK.

Photons of light that reflect from an object moving close to the speed of light have their energy increased. In the extreme conditions of this experiment, this shifts the reflected light from the visible part of the spectrum all the way up to high energy gamma rays. This effect let the researchers know when they had successfully collided the beams.

Senior author of the study, Dr. Stuart Mangles from the Department of Physics at Imperial, said: "We knew we had been successful in colliding the two beams when we detected very bright high energy gamma-ray radiation.

"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 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 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 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.

Explore further: Where does laser energy go after being fired into plasma?

More information: 'Experimental evidence of radiation reaction in the collision of a high-intensity laser pulse with a laser-wakefield accelerated electron beam' by J. M. Cole et al. is published in Physical Review X, … 03/PhysRevX.8.011020

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1 / 5 (2) Feb 07, 2018
The full maxwell's equations have some very fine outlier asymmetrical resonant field effects.

The cut or curtailed maxwell's equations are the ones that everyone knows.

Heaviside cut out the complex outliers so that the equations could be used to engineer motors, etc. The math of the time - was all done by hand.

The full complex equations are so little known, that until recently, the original treatise, with the full equations, generally sold for about $5,000 US. If you could find one. The full math was unpublished and held like a 'secret weapon' by those who possessed it.

When Einstein did his work with relativity, he worked with the shortened and incomplete equations.

This shortened equation set is why there is a unsolvable discrepancy between quantum and relativity/Newtonian works.

It's not 'laws', etc, it's about incorrect mathematics and theory.

The more difficult a problem to solve, the more fundamental the mistake in the formulation of the question.
1 / 5 (2) Feb 07, 2018
And that is why you end up with quotes from a dying Ben Rich, the ex-head of Lockheed Martin's Skunkworks, when he had a deadly cancer (no longer cared-threats did not work on him) speeches to students, etc..said things like (I paraphrase) 'now we can take ET home'. And 'Anything you can imagine, we can do, and have, but it would take an act of god to get it released to the world'.

And the most important part, relating to my original post, he said, 'we found an error in the equations, and now we can do anything'.
1 / 5 (1) Feb 07, 2018
I don't get it. We know photons have momentum, so if they hit electrons the latter are going to be affected. Isn't this just the Compton Effect? What am i missing?
1 / 5 (1) Feb 07, 2018
It just turned the electron beam into more photons which accounted for missing electrons in the electron beam
1 / 5 (2) Feb 07, 2018
The field is affected, the field initiates charge motion, the degrees of freedom of the system and feed back, i.e. Superposition, only the Fields exist there ripples are due to their motion, the field centers we call charge! That's it! An immortal Universe! Charge, never created, or destroyed, all fields are created by the motion of the centers, centers follow Coulomb, Fields follow Maxwell, Gauss define's all when one can see any instant of time! Can a superimposed field appear as a charge?
1 / 5 (2) Feb 07, 2018
That's all the math you need, field centers, initial conditions,
1 / 5 (2) Feb 07, 2018
Just make sure you know what you are talking about and not a Theory that is easily disproved! There is nothing in t5he center, i.e. neutrons! So the wrinkle moves away at Lambda Nu, best guess, while the object holding the oscillator moves, at an acceleration, and the observer, accelerating, solve that, then the steady state!
1 / 5 (2) Feb 07, 2018
Now we have tools that can control the microscopic interpretation, I see how I would use QM and the define the target structure. Each line is separable, as a set, and add! Wonder what we could do with just one charge seeing a phantom charge appear and disappear? Or a laser show with modulated laser and power with feedback from ...
1 / 5 (2) Feb 07, 2018
Experiments!? Simulate what you control? A Gaussian Beam, spot size, ... Construct the fields!

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