Speaker
Konstantin Ivanov
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2013.pdf
Relativistic laser pulse peak intensity evaluation based on vacuum
acceleration of electrons
K.A. Ivanov1, I.N. Tsymbalov1, O.E. Vais2, S.G. Bochkarev2 and A.B. Savel’ev1
1
Physics faculty of M.V. Lomonosov MSU, Moscow, Russia
2
P.N. Lebedev Physical Institute of RAS, Moscow, Russia
Recent results on acceleration of electrons in the electromagnetic field of tightly focused
relativistically strong femtosecond laser radiation are presented. The vacuum acceleration of
free electrons by laser pulse is characterized by direct connection between laser radiation
characteristics and accelerated electron distributions with no influence of additional plasma
collective effects. It opens the opportunity to evaluate the main pulse parameters for ultra-high
power laser systems by means of measurement of high energy electrons properties.
In our work we used the radiation of a Ti:Sa laser system (805nm, 10Hz, 100 mJ, 50 fs) focused
by an off-axis parabolic mirror (F/D=3) to a focal diameter D=2.2 microns (FWHM), which
provided the estimated peak intensity >1019 W/cm2. The focusing optics was mounted inside a
vacuum chamber filled with noble gas (Helium or Argon) at pressure of ~10-1 mb (gas purity
>99%). Electrons appearing due to nonlinear ionization by the EM field of the pulse were
registered in the polarization plane by energy calibrated MediPix matrix detector which
covered angles from 0o to 90o in respect to the beam propagation axis. It was found that
electrons are dominantly emitted in a relatively narrow range of angles. With the growth of
laser pulse energy the direction of electron scattering moves closer to the beam axis. Particles
residual energy exceeded 500 keV.
Numerical simulations of relativistic laser interaction with particles using two independent
models (PIC code and test particles method) revealed that electrons gain energy dominantly due
to the ponderomotive action of the pulse. A good agreement between numerical and
experimental data was observed for electrons angular and energy distributions. Moreover in the
considered range of laser peak intensity (1018-1020 W/cm2) the results are weakly depended on
beam transvers profile and we found a direct correlation between the peak intensity and the
scattered particles properties. This gives the opportunity to build a simple method of in-situ
single shot peak intensity measurement at full energy of the pulse. With the use of our technique
the peak intensity of the laser pulse with 70 mJ energy was evaluated on the level of 2.9x1019
W/cm2, being very close to 2.6x1019 W/cm2, obtained from beam diameter and energy. The
work was supported by RFBR grant 16-32-60174.
