Enhanced electron acceleration in aligned nanowire arrays irradiated at highly relativistic intensities

Abstract

We report a significant enhancement in both the energy and the flux of relativistic electrons accelerated by ultra-intense laser pulse irradiation (>1×10 21 W cm −2 ) of near solid density aligned CD 2 nanowire arrays in comparison to those from solid CD 2 foils irradiated with the same laser pulses. Ultrahigh contrast femtosecond laser pulses penetrate deep into the nanowire array creating a large interaction volume. Detailed three dimensional relativistic particle-in-cell simulations show that electrons originating anywhere along the nanowire length are first driven towards the laser to reach a lower density plasma region near the tip of the nanowires, where they are accelerated to the highest energies. Electrons that reach the lower density plasma experience direct laser acceleration up to the dephasing length, where they outrun the laser pulse. This yields an electron beam characterized by a 3× higher electron temperature and an integrated flux 22.4× larger respect to foil targets. Additionally, the generation of>1 MeV photons were observed to increase up to 4.5×.

Enhanced laser-driven proton acceleration using nanowire targets

“…The high aspect ratio between length and diameter of NWs favors an increased laser absorption due to a greater effective interaction surface area with the incoming electromagnetic (EM) wave, occurring within a few laser cycles such as to maximize the interaction with the intact NW forest. This increased interaction ejects electrons from the NW boundaries mainly through Brunel-type and absorption processes, which are further accelerated in the gaps between the NWs by Direct Laser Acceleration (DLA) before re-collision with the target bulk 49 , where the electrons seed a cascade of impact ionization events. This leads to a denser and hotter electron cloud at the rear side of the target and generates a more intense accelerating sheath electric field driving the TNSA mechanism.…”

Deuterated polyethylene nanowire arrays for high-energy density physics

“…Optical field ionization initially generates a plasma concentrated at the tip of the NWs. The electrons ripped from the material are accelerated in the space between the NWs by a strong ponderomotive interaction [29] . The accelerated electrons are characterized by a three times higher electron temperature and an integrated flux 22 times larger with respect to foil targets [29] .…”

“…The electrons ripped from the material are accelerated in the space between the NWs by a strong ponderomotive interaction [29] . The accelerated electrons are characterized by a three times higher electron temperature and an integrated flux 22 times larger with respect to foil targets [29] . Electrons accelerated in the laser backward direction form a space charge sheath in front or the target, where ions are accelerated to multi-megaelectronvolt energy towards the laser by transverse normal sheath acceleration (TNSA) [30] .…”

Intense proton acceleration in ultrarelativistic interaction with nanochannels

“…Recently, relativistic interaction of ultrashort laser pulses with nano-or micro-structured targets has attracted interest, mainly because of the enhanced efficiency of laser absorption. Depending on the target geometry, the improved laser-target coupling can result in a volumetric heating of the plasma up to extreme temperatures [5], in a more efficient x-ray emission [6] or in an efficient production of HE [7][8][9]. It was shown that for aligned arrays of micropillars or microchannels, the interaction can lead to mega-Ampere currents of relativistic electrons propagating into the target [10], resulting in the self-generation of a mega-Gauss magnetic field on its rear surface [11].…”