Quasi-monoenergetic Deuteron Acceleration via Boosted Coulomb Explosion by Reflected Picosecond Laser Pulse

Abstract

Generation of quasi-monoenergetic ions by intense laser is one of long-standing goals in laser-plasma physics. However, existing laser-driven ion acceleration schemes often produce broad energy spectra and limited control over ion species. Here we propose the acceleration mechanism, boosted Coulomb explosion, initiated by a standing wave, which is formed in a pre-expanded plasma by the interference between a continuously incoming main laser pulse and the pulse reflected by a solid target, where the pre-expanded plasma is formed from a thin layer on the solid target by a relatively strong pre-pulse. This mechanism produces a persistent Coulomb field on the target front side with field strengths on the order of TV/m for picoseconds. We experimentally demonstrate generation of quasi-monoenergetic deuterons up to 50 MeV using an in-situ D$_2$O-deposited target. Our results show that the peak energy can be tuned by the laser pulse duration.

Figures (6)

• Figure 1: (a)-(b) Raw data of TPISs for shot L5167. Only low-energy deuterons are measured on the target laser-facing side. (c)-(d) Raw data of TPISs for shot L5165. Shot with pre-pulse, $\sim$ 40 MeV quasi-monoenergetic deuterons are measured at the laser-facing side. (e)-(g) The deuteron spectra at laser-facing side for 3 different shots. Structured deuterons from 20 to 50 MeV are measured. (h) The measured highest energy profile by RCF, the corresponding deuteron energy is 33.0 MeV. (i) The spot is nearly an ellipse with size of 4.4 mm$\times$2.2 mm.
• Figure 2: The proton spectra at laser-facing side for the same 3 shots with TPIS
• Figure 3: (a)Simulation set-up, self-focused main pulse incident into the solid target with pre-expanded deuterons. (b) Energy spectra at different simulation time. Experimental spectra of L5165 and L5158 are also included.(c) The deuteron peak energy time evolution. (d) Laser pulse duration dependence of the deuteron peak energy.
• Figure 4: (a)Electron density while laser incident on the solid target. Electrons are kicked off by the laser pulse at the laser-facing side of target. (b)-(d) The B$_z$ field, indicate the laser pulse position during simulation. (e)-(g)The deuteron energy distribution and E$_x$ field at the center, deuterons are accelerated by a TV/m level Coulomb Explosion field lasting multi-picoseconds.
• Figure 5: (a)Simulations for oblique incidence, standing wave is formed at the overlapping area of incident and reflected pulses. (b)Deuterons are able to accelerated into several tens of MeV on the laser-facing side at normal direction.