Compression and acceleration of ions by ultra-short ultra-intense azimuthally-polarized light

An efficient plasma compression scheme by azimuthally-polarized (AP) light is proposed. An AP light possesses a donut-like intensity pattern, enabling it to compress and accelerate ions toward the optical axis across a wide range of parameters. When the light intensity reaches the relativistic regime of $10^{18}$ $\mathrm{W}/\mathrm{cm}^{2}$, and the plasma density is below the critical density, protons can be compressed and accelerated by the toroidal soliton formed by the light. The expansion process of the soliton can be well described by the snow-plow model. Three-dimensional (3D) particle-in-cell (PIC) simulations show that within the soliton regime, despite the ion density surpassing ten times of the critical density, their energy is relatively low for efficient neutron production. When the light intensity increases to $10^{22}$ $\mathrm{W}/\mathrm{cm}^{2}$, and the plasma density is tens of the critical density, deuterium ions can be compressed to thousands of the critical density and meanwhile accelerated to the MeV level by a tightly-focused AP light during the hole-boring (HB) process. This process is far more dramatic compared to the soliton regime, and can produce up to $10^{4}$ neutrons in a few light cycles. Moreover, in the subsequent beam-target stage, neutron yield is assessed to reach over $10^{8}$. Finally, we present a comparison with the results by a radially-polarized (RP) light to examine the influence of light polarization.