Description
State-of-the-art high-power laser systems are now enabling the exploration of quantum electrodynamics (QED) in the nonperturbative, strong-field regime, where electromagnetic fields approach or surpass the so-called critical “Schwinger” limit of QED [1]. In this extreme regime, phenomena such as nonlinear Breit-Wheeler pair production, vacuum birefringence, and quantum radiation reaction effects are predicted to emerge — effects that remain experimentally unobserved under controlled laboratory conditions. Achieving the required field strengths demands laser intensities around 2.3×10²⁹ W/cm², which greatly exceed the current maximum of 10²³ W/cm² [2]. A promising approach to access this regime involves nonlinear Compton scattering between ultra-relativistic electron beams and ultra-intense laser pulses, offering a practical platform to investigate strong-field QED effects. Resent advances in laser-plasma accelerator technology, particularly laser wakefield acceleration (LWFA) [3], has opened new possibilities for all-optical investigation of strong-field QED, now actively pursued by several research groups worldwide. In our previous study, we experimentally investigated nonlinear Compton scattering in intense laser fields, where a multi-GeV electron simultaneously interacts with hundreds of laser photons. Using LWFA, we generated an ultra-relativistic electron beam and collided it with a high-intensity laser pulse, reaching the quantum nonlinearity parameter corresponding to about half of Schwinger field strength. This interaction produced GeV-scale gamma rays via multiphoton Compton scattering, extending well beyond the linear Compton limit and marking the onset of the strongly nonlinear regime [4].
Here, we present our latest experimental results demonstrating interactions at effective field intensity exceeding the Schwinger limit. We utilized CoReLS 1 PW beamline for scattering laser, increasing its ɑ0 by a factor of four, and collided with 2.2 GeV LWFA-driven electron using another multi PW beamline. The resulting post-collision electron spectra show signatures consistent with radiation reaction effects, calculated using experimental parameters.
This work was supported by the Institute for Basic Science grant (IBS-R038-D1).
References
[1] A. Di Piazza, et al. "Extremely high-intensity laser interactions with fundamental quantum systems." Rev. Mod. Phys. 84, 1177-1228 (2012).
[2] Yoon, Jin Woo, et al. "Realization of laser intensity over 1023 W/cm2." Optica 8.5, 630-635 (2021).
[3] M. Mirzaie et al. "Demonstration of self-truncated ionization injection for GeV electron beams." Sci. Rep. 5, 14659 (2015).
[4] M. Mirzaie et al. "All-optical nonlinear Compton scattering performed with a multi-petawatt laser." Nat. Photon. 18, 1212-1217 (2024).