24 research outputs found
Demonstration of passive plasma lensing of a laser wakefield accelerated electron bunch
We report on the first demonstration of passive all-optical plasma lensing using a two-stage setup. An intense femtosecond laser accelerates electrons in a laser wakefield accelerator (LWFA) to 100Â MeV over millimeter length scales. By adding a second gas target behind the initial LWFA stage we introduce a robust and independently tunable plasma lens. We observe a density dependent reduction of the LWFA electron beam divergence from an initial value of 2.3Â mrad, down to 1.4Â mrad (rms), when the plasma lens is in operation. Such a plasma lens provides a simple and compact approach for divergence reduction well matched to the mm-scale length of the LWFA accelerator. The focusing forces are provided solely by the plasma and driven by the bunch itself only, making this a highly useful and conceptually new approach to electron beam focusing. Possible applications of this lens are not limited to laser plasma accelerators. Since no active driver is needed the passive plasma lens is also suited for high repetition rate focusing of electron bunches. Its understanding is also required for modeling the evolution of the driving particle bunch in particle driven wake field acceleration
The Vacuum Emission Picture Beyond Paraxial Approximation
Optical signatures of the effective nonlinear couplings among electromagnetic
fields in the quantum vacuum can be conveniently described in terms of
stimulated photon emission processes induced by strong classical, space-time
dependent electromagnetic fields. Recent studies have adopted this approach to
study collisions of Gaussian laser pulses in paraxial approximation. The
present study extends these investigations beyond the paraxial approximation by
using an efficient numerical solver for the classical input fields. This new
numerical code allows for a consistent theoretical description of optical
signatures of QED vacuum nonlinearities in generic electromagnetic fields
governed by Maxwell's equations in the vacuum, such as manifestly non-paraxial
laser pulses. Our code is based on a locally constant field approximation of
the Heisenberg-Euler effective Lagrangian. As this approximation is applicable
for essentially all optical high-intensity laser experiments, our code is
capable of calculating signal photon emission amplitudes in completely generic
input field configurations, limited only by numerical cost.Comment: 8 pages, 3 figures; talk given at LPHYS'18, Nottingham, United
Kingdo
Photon-Photon Scattering at the High-Intensity Frontier: Paraxial Beams
Our goal is to study optical signatures of quantum vacuum nonlinearities in
strong macroscopic electromagnetic fields provided by high-intensity laser
beams. The vacuum emission scheme is perfectly suited for this task as it
naturally distinguishes between incident laser beams, described as classical
electromagnetic fields driving the effect, and emitted signal photons encoding
the signature of quantum vacuum nonlinearity. Using the Heisenberg-Euler
effective action, our approach allows for a reliable study of photonic
signatures of QED vacuum nonlinearity in the parameter regimes accessible by
all-optical high-intensity laser experiments. To this end, we employ an
efficient, flexible numerical algorithm, which allows for a detailed study of
the signal photons emerging in the collision of focused paraxial high-intensity
laser pulses. Due to the high accuracy of our numerical solutions we predict
the total number of signal photons, but also have full access to the signal
photons' characteristics, including their spectrum, propagation directions and
polarizations. We discuss setups offering an excellent background-to-noise
ratio, thus providing an important step towards the experimental verification
of quantum vacuum nonlinearities.Comment: 7 pages, 2 figures; talk given at LPHYS'18, Nottingham, United
Kingdo