arXiv subjects

Alexey V. Arefiev

Publications and source records attributed to Alexey V. Arefiev.

8 recordsLinked to original sources

arXiv2020

Strong surface magnetic field generation in relativistic short pulse laser-plasma interaction with an applied seed magnetic field

While plasma often behaves diamagnetically, we demonstrate that the laser irradiation of a thin opaque target with an embedded target-transverse seed magnetic field $B_\mathrm{seed}$ can trigger the generation of an order-of-magnitude stronger magnetic field with opposite sign at the target surface. Strong surface field generation occurs when the laser pulse is relativistically intense and results from the currents associated with the cyclotron rotation of laser-heated electrons transiting through the target and the compensating current of cold electrons. We derive a predictive scaling for this surface field generation, $B_\mathrm{gen} \sim - 2 πB_\mathrm{seed} Δx/λ_0$, where $Δx$ is the target thickness and $λ_0$ is the laser wavelength, and conduct 1D and 2D particle-in-cell simulations to confirm its applicability over a wide range of conditions. We additionally demonstrate that both the seed and surface-generated magnetic fields can have a strong impact on application-relevant plasma dynamics, for example substantially altering the overall expansion and ion acceleration from a $μ$m-thick laser-irradiated target with a kilotesla-level seed magnetic field.

physics.plasm-ph↗

arXiv2020

Laser reflection as a catalyst for direct laser acceleration in multipicosecond laser-plasma interaction

We demonstrate that laser reflection acts as a catalyst for superponderomotive electron production in the preplasma formed by relativistic multipicosecond lasers incident on solid density targets. In 1D particle-in-cell simulations, high energy electron production proceeds via two stages of direct laser acceleration, an initial stochastic backward stage, and a final non-stochastic forward stage. The initial stochastic stage, driven by the reflected laser pulse, provides the pre-acceleration needed to enable the final stage to be non-stochastic. Energy gain in the electrostatic potential, which has been frequently considered to enhance stochastic heating, is only of secondary importance. The mechanism underlying the production of high energy electrons by laser pulses incident on solid density targets is of direct relevance to applications involving multipicosecond laser-plasma interactions.

physics.plasm-ph↗

arXiv2019

Extreme Nonlinear Dynamics in Vacuum Laser Acceleration with a Crossed Beam Configuration

A relatively simple model problem where a single electron moves in two relativistically-strong obliquely intersecting plane wave-packets is studied using a number of different numerical solvers. It is shown that, in general, even the most advanced solvers are unable to obtain converged solutions for more than about 100 fs in contrast to the single plane-wave problem, and that some basic metrics of the orbit show enormous sensitivity to the initial conditions. At a bare minimum this indicates an unusual degree of non-linearity, and may well indicate that the dynamics of this system are chaotic.

physics.plasm-ph↗

arXiv2016

Self-aligning concave relativistic plasma mirror with adjustable focus

We report an experimental-computational study of the optical properties of plasma mirrors (PMs) at the incident laser frequency when irradiated directly at relativistic intensity (1e18 < I_0 < 1e19 W/cm^2) by near-normally incident (4 degree), high-contrast, 30 fs, 800 nm laser pulses. We find that such relativistic PMs are highly reflective (0.6 to 0.8), and focus a significant fraction of reflected light to intensity as large as 10I_0 at distance f as small 25 microns from the PM, provided that pre-pulses do not exceed 1e14 W/cm^2 prior to 20 ps before arrival of the main pulse peak. Particle-in-cell simulations show that focusing results from denting of the reflecting surface by light pressure combined with relativistic transparency, and that reflectivity and f can be adjusted by controlling pre-plasma length L over the range 0.5 < L < 3 microns. Pump-probe reflectivity measurements show the PM's focusing properties evolve on a ps time scale.

physics.plasm-ph↗

arXiv2015

Compact tunable Compton x-ray source from laser-plasma accelerator and plasma mirror

We present an in-depth experimental-computational study of the parameters necessary to optimize a tunable, quasi-monoenergetic, efficient, low-background Compton backscattering (CBS) x-ray source that is based on the self-aligned combination of a laser-plasma accelerator (LPA) and a plasma mirror (PM). The main findings are: (1) an LPA driven in the blowout regime by 30 TW, 30 fs laser pulses producesnot only a high-quality, tunable, quasi-monoenergetic electron beam, but also a high-quality, relativistically intense (a0~1) spent drive pulse that remains stable in profile and intensity over the LPA tuning range. (2) A thin plastic film near the gas jet exit retro-reflects the spent drive pulse efficiently into oncoming electrons to produce CBS x-rays without detectable bremsstrahlung background. Meanwhile anomalous far-field divergence of the retro-reflected light demonstrates relativistic "denting" of the PM. Exploiting these optimized LPA and PM conditions, we demonstrate quasi-monoenergetic (50% FWHM energy spread), tunable (75 to 200 KeV) CBS x-rays, characteristics previously achieved only on more powerful laser systems by CBS of a split-off, counter-propagating pulse. Moreover, laser-to-x-ray photon conversion efficiency ~6e12 exceeds that of any previous LPA-based quasi-monoenergetic Compton source. Particle-in-cell simulations agree well with the measurements.

physics.plasm-ph↗

arXiv2014

A Relativistic Plasma Polarizer: Impact of Temperature Anisotropy on Relativistic Transparency

3D particle-in-cell simulations demonstrate that the enhanced transparency of a relativistically hot plasma is sensitive to how the energy is partitioned between different degrees of freedom. For an anisotropic electron distribution, propagation characteristics, like the critical density, will depend on the polarization of the electromagnetic wave. Despite the onset of the Weibel instability in such plasmas, the anisotropy can persist long enough to affect laser propagation. This plasma can then function as a polarizer or a waveplate to dramatically alter the pulse polarization.

physics.plasm-ph↗

arXiv2014

Temporal resolution criterion for correctly simulating relativistic electron motion in a high-intensity laser field

Particle-in-cell codes are now standard tools for studying ultra-intense laser-plasma interactions. Motivated by direct laser acceleration of electrons in sub-critical plasmas, we examine temporal resolution requirements that must be satisfied to accurately calculate electron dynamics in strong laser fields. Using the motion of a single electron in a perfect plane electromagnetic wave as a test problem, we show surprising deterioration of the numerical accuracy with increasing wave amplitude $a_0$ for a given time-step. We go on to show analytically that the time-step must be significantly less than $λ/c a_ 0$ to achieve good accuracy. We thus propose adaptive electron sub-cycling as an efficient remedy.

physics.plasm-ph↗

arXiv2013

Enhancement of laser-driven electron acceleration in an ion channel

A long laser beam propagating through an underdense plasma produces a positively charged ion channel by expelling plasma electrons in the transverse direction. We consider the dynamics of a test electron in a resulting two-dimensional channel under the action of the laser field and the transverse electric field of the channel. A considerable enhancement of the axial momentum can be achieved in this case via amplification of betatron oscillations. It is shown that the oscillations can be parametrically amplified when the betatron frequency, which increases with the wave amplitude, becomes comparable to the frequency of its modulations. The modulations are caused by non-inertial (accelerated/decelerated) relativistic axial motion induced by the wave regardless of the angle between the laser electric field and the field of the channel. We have performed a parameter scan for a wide range of wave amplitudes and ion densities and we have found that, for a given density, there is a well pronounced wave amplitude threshold above which the maximum electron energy is considerably enhanced. We have also calculated a time-integrated electron spectrum produced by an ensemble of electrons with a spread in the initial transverse momentum. The numerical results show that the considerable energy enhancement is accompanied by spectrum broadening. The presented mechanism of energy enhancement is robust with respect to an axial increase of ion density, because it relies on a threshold phenomenon rather than on a narrow linear resonance.

physics.plasm-ph↗