Self-triggered strong-field QED collisions in laser-plasma interaction

Exploring quantum electrodynamics in the most extreme conditions, where electron-positron pairs can emerge in the presence of a strong background field, is now becoming possible in Compton collisions between ultraintense lasers and energetic electrons. In the strong-field regime, the colliding electron emits <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mi>γ</a:mi></a:math> rays that decay into pairs in the strong laser field. While the combination of conventional accelerators and lasers of sufficient power poses significant challenges, laser-plasma accelerators offer a promising alternative for producing the required multi-GeV electron beams. To overcome the complexities of colliding these beams with another ultraintense laser pulse, we propose a scheme in which a single laser pulse both accelerates the electrons and collides with them after self-focusing in a dedicated plasma section and reflecting off a plasma mirror. The laser intensity boost in the plasma allows the quantum interaction parameter to be greatly increased. Using full-scale numerical simulations, we demonstrate that a single <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mrow><b:mn>100</b:mn><b:mspace width="0.28em"/><b:mi mathvariant="normal">J</b:mi></b:mrow></b:math> laser pulse can achieve a deep quantum regime with electric fields in the electron rest frame as high as <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:mrow><e:msub><e:mi>χ</e:mi><e:mi>e</e:mi></e:msub><e:mo>∼</e:mo><e:mn>5</e:mn></e:mrow></e:math> times the Schwinger critical field, resulting in the production of about 40 pC of positrons.