Experimental evidence of radiation reaction in the collision of a high-intensity laser pulse with a laser-wakefield accelerated electron beam

TL;DR

This paper provides experimental evidence of radiation reaction effects during the collision of a laser-wakefield accelerated electron beam with an intense laser pulse, demonstrating quantum radiation reaction and generating high-energy gamma rays.

Contribution

First experimental observation of quantum radiation reaction in laser-electron collisions using laser wakefield acceleration and intense laser pulses.

Findings

Measured energy loss in electrons consistent with quantum radiation reaction.

Detected gamma rays with critical energy exceeding 30 MeV.

Demonstrated stochastic nature of radiation emission in the quantum regime.

Abstract

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 transition between the classical and quantum radiation reaction regimes. We report on the observation of radiation reaction in the collision of an ultra-relativistic electron beam generated by laser wakefield acceleration ($\varepsilon > 500$ MeV) with an intense laser pulse ($a_0 > 10$). We measure an energy loss in the post-collision electron spectrum that is correlated with the detected signal of hard photons ($\gamma$-rays), consistent with a quantum (stochastic) description of radiation reaction. The generated $\gamma$-rays have the highest energies yet reported from an all-optical inverse Compton scattering scheme, with critical energy $\varepsilon_{\rm crit} > $ 30 MeV.