Speaker
Martin Jirka
Description
QED cascade in a tightly focused standing wave
M. Jirka1,2,3
, O. Klimo1,2
, M. Vranic3
, S. Weber1
, G. Korn1
1
Institute of Physics of the CAS, ELI-Beamlines project, Prague, Czech Republic
2 Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in
Prague, Prague, Czech Republic
3 GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de
Lisboa, Lisbon, Portugal
The advent of laser technology is opening exciting opportunities for testing new physical
regimes. A possibility to generate an electron-positron cascade via the Breit-Wheeler process in
the field of an ultra-intense laser beam has attracted considerable attention. One possible interaction
scenario leading to a prolific pair production is the interaction of seed particles with an
intense standing wave formed by two colliding laser pulses [1]. To efficiently generate electronpositron
pairs in this configuration, the intensities of the order of 1023−24 W/cm2
are required
[2].
To achieve such intense laser fields with the upcoming generation of 10 PW laser beams,
the laser pulse has to be focused to a λ scale spot size. However, as the laser pulse is focused
more tightly, the ponderomotive force becomes stronger and seed particles are expelled more
rapidly from the interaction region, so the focusing acts against an efficient cascade seeding.
That prevents cascade development even at very high laser intensities in case of low-density
targets [3].
Nevertheless, here we show that using a target with an appropriate density can help balance
the effect of expelling seed particles from the high-intensity region [4]. We also show how tight
focusing affects the cascade development for a wide set of initial conditions. Optimising the target
density lowers the threshold power required for cascade pair production, which is favourable
for experiments at upcoming 10 PW-class laser facilities that are now under construction and
will become accessible soon.
References
[1] A. R. Bell and J. G. Kirk, Phys. Rev. Lett. 101 , 200403 (2008)
[2] J. P. Zou et al., High Power Laser Science and Engineering 3, e2 (2015)
[3] M. Tamburini, A. Di Piazza and C. H. Keitel, Scientific Reports 7, 5694 (2017)
[4] M. Jirka, O. Klimo, M. Vranic, S. Weber and G. Korn, Scientific Reports 7, 15302 (2017)
