Laser with intense beam Stops Electrons in a Quantum Experiment. Researchers says a big leap in Quantum world.

Scientists have experimentally verified an extraordinary property of light arising straight from the realms of the field of Quantum Electro-Dynamics.

The dynamics of energetic particles in strong electromagnetic fields can be heavily influenced by the energy loss arising from the emission of radiation during acceleration, known as radiation reaction. When interacting with a high-energy electron beam, today’s lasers are sufficiently intense to explore the transitionbetween the classical and quantum radiation reaction regimes. Finally after a long run, Scientists have now presented evidence of radiation reaction in the collision of an ultra relativistic electron beam. We measure an energy loss in the post collision electron spectrum that is correlated with the detected signal of hard photons (γ rays), consistent with a quantum description ofradiation reaction. The generated γ rays have the highest energies yet reported from an all-optical inverse Compton scattering scheme, with critical energy greater than 30 MeV.

While we all have studied that accelerating charges radiate and therefore lose energy.The effective force on charged particles resulting from these losses, known as radiation reaction (RR), scalesquadratically with both particle energy and applied electro-magnetic field strength.

EXPERIMENTAL ANALYSIS :

In order to get a more clear view of the phenomenon, let's see how the Scientists performed the experiment.

The team were able to make the light so intense in the current experiment by focusing it to a very small spot (just a few micrometres) and delivering all the energy in a very short duration (just 40 femtoseconds long. i.e., about 40 quadrillionths of a second).

To make the electron beam small enough to interact with the focused 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.

The experiment was conducted using the Gemini laser of the Central Laser Facility, Rutherford Appleton Laboratory, UK.
Gemini is a Ti:sapphire laser system delivering twosynchronized linearly polarized beams of 800 nm central wavelength and pulse durations of 45 fs FWHM. One of the beams, used to drive a laser wakefield accelerator, wasfocused with an f=40 spherical mirror to a focal spot
FWHM size of 37 × 49 μm. This pulse was focused at the leading edge of a 15-mm-diameter supersonichelium gas jet, which produced an approximately trapezoidal density profile with 1.5 mm linear ramps at the leading and trailing edges.
The second Gemini beam was focused at the rear edge of the gas jet, counterpropagating with respect to the first.As the laser-wakefield generated electron beam interacted with the second focused laser pulse, inverse Compton- scattered γ rays were generated, copropagating with the electron beam. By colliding close to the rear of the gas jet, the electron bunch did not have time to diverge before the collision and so the overlap between the electron bunch and laser was maximized.

Researchers involved in the Experiment concluded :While the results obtained represent statistically significant evidence of radiation reaction occurring duringthe collision of a high-intensity laser pulse with a high-energy electron beam, they are not a systematic study of radiation reaction. The QED model currently appears to provide a more self-consistent description of the data than apurely classical one; however, this is only at the 1σ level. Afuture study systematically varying the quantum parameter
η through either the electron beam energy or laser intensitywhich extends to higher values of η than achieved in thisexperiment will allow detailed comparisons of different
models and a proper assessment of their range of validity.Laser-wakefield accelerators have already demonstratedsufficient beam stability, and higherbeam energies, and higher laser intensitiesare readily achievable with existing lasers, so that thenecessary η to clearly observe quantum radiation reaction iswithin reach of existing laser systems. The main remaining
challenge is therefore to achieve all of these simultaneouslyin an experiment which maintains femtosecond andmicrometer level alignment over extended periods of time,so as to allow sufficient data to be collected for a systematicstudy of radiation reaction in the quantum regime.

Credits :
J. M. Cole, K. T. Behm, E. Gerstmayr, T. G. Blackburn, J. C. Wood, C. D. Baird, M. J. Duff, C. Harvey, A. Ilderton, A. S. Joglekar, K. Krushelnick, S. Kuschel, M. Marklund, P. McKenna, C. D. Murphy, K. Poder, C. P. Ridgers, G. M. Samarin, G. Sarri, D. R. Symes, A. G. R. Thomas, J. Warwick, M. Zepf, Z. Najmudin, S. P. D. Mangles. Experimental Evidence of Radiation Reaction in the Collision of a High-Intensity Laser Pulse with a Laser-Wakefield Accelerated Electron Beam. Physical Review X, 2018; 8 (1) DOI: 10.1103/PhysRevX.8.011020

Note. The image shows just an illustration of a laser device and is not related to the original experiment.