Experimental signatures of quantum electrodynamics in the strong field regime

Introduction

Quantum Electrodynamics (QED) is the theory that unifies electromagnetism and quantum mechanics to describe how light and matter interact. Considered as one of the most accurately tested theories, it led Richard Feynman to call it “the jewel of physics.” Yet, in the strong-field (SF) regime, when the light fields are ultra-intense, this theory is only treated perturbatively, and the non-perturbative regime of SF-QED remains a terra incognita as even no theory exists to predict the behaviour of nature.

Current State of Research

The advent of multi-PW laser infrastructures now makes the SF-QED regime within experimental reach when considering the collision of relativistic electrons with such light pulses focused above 10^22 W/cm². Yet, all planned experiments to probe SF-QED with current technologies only propose to investigate its perturbative regime, expected to be well described by theory.

Proposed Experiments

In the EXAFIELD project, I propose a new concept of experiments to exceed the perturbative limit of SF-QED in the lab. This will be achieved by reflecting an ultra-intense laser pulse off a plasma mirror at relativistic speed.

Mechanism of Action

The strong Doppler effect occurring upon reflection up-converts the near-infrared laser pulse down to the extreme ultraviolet range, which enables both:

1. Temporal compression to the attosecond timescale
2. Spatial compression down to sub-micron size

This results in a considerable intensity boost at the focus of more than three orders of magnitude, up to a few 10^25 W/cm².

Expected Outcomes

The collision of such a “Doppler-boosted beam” with ultrashort electron bunches generated from laser-plasma accelerators will allow us to access regimes where the SF-QED can no longer be treated perturbatively, producing very strong signatures in the lab.

Implications for Research

Characterizing how the observations deviate from the perturbative theory will enable us to determine the limits of validity of the perturbative models and will open a new area of research toward the understanding of the non-perturbative regime of SF-QED.