Speaker
Prof.
Alexander Titov
(JINR, BLTP)
Description
We have performed a simultaneous analysis of two essentially
non-linear QED processes in circular and linear polarized short and intensive
e.m. (laser) pulses: (i) non-linear Breit-Wheeler $e^+e^-$ pair creation
in the interaction of probe photon with such a pulse and
(ii) the photon emission or the non-linear Compton scattering
when an initial electron interacts with
the short and intensive e.m. (laser) pulse.
Both processes are analyzed in the multi-photon region,
where several photons at the same time participate in the
process. In case of non-linear Breit-Wheeler $e^+e^-$ pair emission, the multi-photon
region is determined uniquely by the variable $\zeta>1$ or $s < s_{\rm sthr}=4m^2$.
For the non-linear Compton scattering we use the partially integrated cross section
where the integration starts from the dynamical parameter $\kappa>1$
which selects the multi-photon events and
is an analog of the variable $\zeta$ in the Breit-Wheeler process.
Our analysis shows the step like $\zeta$ ($\kappa$) behavior of the total
cross sections for Breit-Wheeler (Compton) process in the case of relatively
long pulses with the number of oscillations in a pulse $N\geq 2$, similar to the
prediction for the infinitely long pulse.
In case of sub-cycle pulse ($N=1/2$), the cross sections exhibit
an exponential dependence
$\exp[-b_\zeta\zeta]$ ($\exp-[b_\kappa\kappa]$).
The slopes $b_\zeta$, $b_\kappa$ depend on the field intensity and
the pulse duration.
The azimuthal angle distributions are very sensible and, in particularly,
depend on the carrier envelope phase $\phi_{CEP}$.
In addition to the processes occurring in the circularly polarized
e.m.\ pulses considered earlier, the case of linear
polarization leads to the qualitative modification of the azimuthal
distributions of outgoing electrons. These distributions are
non-monotonic functions %of the azimuthal angle of outgoing electrons
with peculiar maxima and minima.
Their positions, heights, and depths are determined by the
structure of the phase factor ${P}^{(L)}$ of the basis functions $\widetilde A_m$,
and they depend on the reduced field intensity $\xi^2$,
dynamic variables $\zeta,\,\kappa$, and $\phi_{CEP}$
and the pulse width ($\Delta=\pi N$) as well.
In the case of non-linear Compton scattering, the angular distributions are
determined by a nontrivial destructive interference of
the terms in the partial probability $w^{(L)}(\ell)$.
Our results may be used as a unique
and powerful method for studying the multi-photon dynamics of
elementary non-linear QED processes.
Primary author
Prof.
Alexander Titov
(JINR, BLTP)
Co-authors
Dr
A. Otto
(HZ Dresden-Rossendorf, Dresden, Germany)
Prof.
Burkhard Kampfer
(HZ Dresden-Rossendorf, Dresden Germany)
