Abstract
QED cascades are complex avalanche processes of hard photon emission and electron-positron pair creation driven by ultrastrong electromagnetic fields. They play a fundamental role in astrophysical environments such as a pulsars’ magnetosphere, rendering an earth-based implementation with intense lasers attractive. In the literature, QED cascades were also predicted to limit the attainable intensity in a set-up of colliding laser beams in a tenuous gas such as the residual gas of a vacuum chamber, therefore severely hindering experiments at extreme field intensities. Here, we demonstrate that the onset of QED cascades may be either prevented even at intensities around 1026 W/cm2 with tightly focused laser pulses and low-Z gases, or facilitated at intensities below 1024 W/cm2 with enlarged laser focal areas or high-Z gases. These findings pave the way for the control of novel experiments such as the generation of pure electron-positron-photon plasmas from laser energy, and for probing QED in the extreme-intensity regime where the quantum vacuum becomes unstable.
Highlights
As a consequence of the dramatic progress in high-power laser technology intensities of the order of 1024 W/cm[2] may become accessible in the few years[1, 2], opening up the investigation of unexplored regimes of laser-matter interaction[3,4,5,6,7]
We show the crucial role played by the laser field structure on the onset of seeded QED cascades when accounting for realistic laser pulse set-ups
In the following we investigate the conditions for the onset of e−e+γ cascades initiated by stray electrons in the presence of two counter-propagating laser pulses both for aligned linear polarization (LP||), i.e. the electric fields of the two pulses are parallel to each other, and for crossed linear polarization (LP⊥), i.e. the electric fields of the tEgwr0oobwepitunhlgsinethstehopertenhauokmgfoibenledarl,otoofreet−haeec+hppooawtihreesrrw,Pdit≈ehpteπhnwed0c2iIrn/eg2atooinfoentahocehnwbaaveieasrmtarg.aQedoEiufDsatwclae0saacsnatddoenesietahpreearicrhthpaeeraricnintteeirtniizasieltdeylbeIcy=tarnocnEe1x072p,/28o6π.nO,enwthtiiteahrl scenarios where e−e+ pairs are produced but the above-mentioned conditions are not fulfilled are termed “e−e+ γ gases”
Summary
As a consequence of the dramatic progress in high-power laser technology intensities of the order of 1024 W/cm[2] may become accessible in the few years[1, 2], opening up the investigation of unexplored regimes of laser-matter interaction[3,4,5,6,7]. Copious e−e+γ production in the collision of two laser pulses may be initiated either by the initial presence of seed particles in the focal volume (seeded QED cascades), or by the spontaneous creation of e−e+ pairs out of the quantum vacuum (self-seeded QED cascades) when the laser field invariant E = (F 2 + G2)1/2 + F approaches the the QED critical field Fcr = me2c3/ e ≈ speed of light in vacuum, and ħ is the. The generated pairs are accelerated by the laser fields and originate a new generation of particles Such avalanche process was predicted to develop in the collision of two laser pulses with intensities around15 1024 W/cm[2]. The determination of a mechanism to control the onset of seeded QED cascades is essential at ultra-high laser intensities
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