arXiv subjects

Shikha Bhadoria

Publications and source records attributed to Shikha Bhadoria.

5 recordsLinked to original sources

arXiv2023

Unforeseen advantage of looser focusing in vacuum laser acceleration

Acceleration of electrons in vacuum directly by intense laser fields, often termed vacuum laser acceleration (VLA), holds great promise for the creation of compact sources of high-charge, ultrashort, relativistic electron bunches. However, while the energy gain is expected to be higher with tighter focusing (i.e. stronger electric field), this does not account for the reduced acceleration range, which is limited by diffraction. Here, we present the results of an experimental investigation of VLA, using tungsten nanotips driven by relativistic-intensity few-cycle laser pulses. We demonstrate the acceleration of relativistic electron beams with typical charge of 100s pC to 15 MeV energies. Two different focusing geometries (tight and loose, with f-numbers one and three respectively) produced comparable results, despite a factor of ten difference in the peak intensities, which is evidence for the importance of post-injection acceleration mechanisms around the focus. Our results are in good agreement with the results of full-scale, three-dimensional particle-in-cell simulations.

physics.plasm-ph↗

arXiv2023

Energy enhancement of laser-driven ions by radiation reaction and Breit-Wheeler pair production in the ultra-relativistic transparency regime

The impact of radiation reaction and Breit-Wheeler pair production on acceleration of fully ionized Carbon ions driven by an intense linearly-polarized laser pulse has been investigated in the ultra-relativistic transparency regime. Against initial expectations radiation reaction and pair production at ultra-high laser intensities is found to enhance the energy gained by the ions. The electrons lose most of their transverse momentum and the additionally produced pair plasma of Breit-Wheeler electrons and positrons co-stream in the forward direction as opposed to the existing electrons streaming at an angle above zero. We discuss how these observations could be explained by the changes in the phase velocity of the Buneman instability, that is known to aid ion acceleration in the Breakout-Afterburner regime, by tapping the free energy in the relative electron and ion streams. We present evidence that these non-classical effects can further improve the highest Carbon ion energies in this transparency regime.

physics.plasm-ph↗

arXiv2022

Mapping the power-law decay of high-harmonic spectra from laser-plasma interactions

Visible or near infra-red light can be manipulated to produce bursts of coherent extreme ultraviolet (XUV) or X-rays via the relativistic high-order harmonic generation process when a laser irradiates a solid plasma target. The intensity of the spectral components of the reflected signal decays with increase of harmonic order and the efficiency of this non-linear process largely hinges on how prompt this decay is. This is governed by the conditions of the laser-plasma interaction for which various models have been proposed. At relativistic intensities, a spectrum exhibiting a power-law decay with an exponent of 8/3 or 4/3 is often stated. Here, we analyse the dependence of this exponent on interaction parameters including the angle of incidence, the carrier envelope phase, intensity of the laser and the pre-plasma length, and discuss opportunities for optimization. Our simulations show that, rather than there being one universal exponent, the spectral decay is a continuous function of the laser-plasma interaction parameters.

physics.plasm-ph↗

arXiv2019

Collisionless shocks in laboratory astrophysics experiments

Influence of the plasma collisions on the laser-driven collisionless shock formation and subsequent ion acceleration is studied on the basis of two different collisional algorithms and their implementations in two well-known particle-in-cell codes EPOCH and SMILEI. In this setup, an ultra-intense incident laser pulse generates hot-electrons in a thick target, launching an electrostatic shock at the laser-plasma interface while also pushing the interface through the hole-boring effect. We observe, to varying degrees, the weakening of the space-charge effects due to collisions and improvements ($\ge 10\%$) in the energy spectra of quasi-monoenergetic ions in both PIC codes EPOCH and SMILEI. These results establish the `collisionlessness' of the collisionless shocks in laboratory astrophysics experiments.

physics.plasm-ph↗

arXiv2019

Collisionless shock acceleration of quasi-monoenergetic ions in ultra-relativistic regime

Collisionless shock acceleration of carbon ions (C$^{6+}$) is investigated in the ultra-relativistic regime of laser-plasma interaction by accounting for the radiation reaction force and the pair production in particle-in-cell simulations. Both radiation reaction force and pair plasma formation tend to slow down the shock velocity, reducing the energy of the accelerated ions, albeit extending the time scales of the acceleration process. Slab plasma target achieves lower energy spread while target with a tailored density profile yields higher ion acceleration energies.

physics.plasm-ph↗