Break-out afterburner ion acceleration in the longer laser pulse length regime

Abstract

Kinetic simulations of break-out-afterburner (BOA) ion acceleration from nm-scale targets are examined in a longer pulse length regime than studied previously. It is shown that when the target becomes relativistically transparent to the laser, an epoch of dramatic acceleration of ions occurs that lasts until the electron density in the expanding target reduces to the critical density in the non-relativistic limit. For given laser parameters, the optimal target thickness yielding the highest maximum ion energy is one in which this time window for ion acceleration overlaps with the intensity peak of the laser pulse. A simple analytic model of relativistically induced transparency is presented for plasma expansion at the time-evolving sound speed, from which these times may be estimated. The maximum ion energy attainable is controlled by the finite acceleration volume and time over which the BOA acts.

Simultaneous observation of angularly separated laser-driven proton beams accelerated via two different mechanisms

“…As described in Ref. 18, BOA features an optimum target thickness for given laser parameters and target material. A target which is thinner than this optimum becomes classically transparent at an early time compared to the impact of the laser pulse maximum due to plasma expansion hence deteriorating the efficiency of the acceleration process.…”

Dynamics of relativistic transparency and optical shuttering in expanding overdense plasmas

“…Earlier experiments in TOR have measured time-integrated light transmission 20,21 as well as ion [22][23][24] and electron spectra 25 . In those measurements the dynamics of relativistic transparency could only be inferred from corresponding simulations [7][8][9][10] . Here, we observe the laser-plasma dynamics in TOR with ∼50 fs temporal resolution by measuring the reflected and transmitted laser intensities and associated temporal phases, from laser interactions with 10-100 nm carbon nano-foils.…”

Towards Laser Driven Hadron Cancer Radiotherapy: A Review of Progress

“…However recent developments both theoretical and experimental in laser driven ion acceleration have shown considerable promise for increasing the maximum energy efficiency of the acceleration process taking advantage of the so-called transparent overdense regime [13,[36][37][38][39][40]. The transition to this regime occurs when the target is thin enough-typically tens to hundreds of nanometers-and the laser intensity and contrast are high enough, for all of the target electrons to be removed from the material during the laser-target interaction.…”