Effects of Laser Polarization on Target Focusing and Acceleration in a Laser-Ion Lens and Accelerator

TL;DR

This paper demonstrates that elliptically polarized laser pulses can effectively drive ion acceleration and focusing in a laser-ion lensing setup, challenging previous assumptions about polarization limitations.

Contribution

It extends the LILA framework to include elliptically polarized lasers and shows optimized target thickness enables efficient ion acceleration with different polarizations.

Findings

EP lasers can drive LILA with proper target optimization

Linearly polarized lasers can produce focused ion beams with non-uniform targets

Laser-to-ion energy conversion efficiency is comparable across polarizations

Abstract

We present the process of ion acceleration using ultra-thin foils irradiated by elliptically polarized, high-intensity laser pulses. Recently, efficient generation of monoenergetic ion beams was introduced using the concept of laser-ion lensing and acceleration (LILA). LILA is an innovative technique where the target's radially varying thickness enables simultaneous acceleration and focusing of a proton beam. In this work, we extend the LILA framework to incorporate elliptically polarized (EP) laser pulses. While it's commonly assumed that EP lasers are unsuitable for radiation pressure acceleration (RPA) due to excessive electron heating that compromises ion acceleration, our multidimensional particle-in-cell simulations challenge this notion. We show that, with proper optimization of the target's average thickness, EP laser pulses can successfully drive the LILA mechanism. We also demonstrate that with a non-uniform thickness target, even linearly polarized laser pulses can efficiently generate low-emittance focused ion beams, with the overall laser-to-ions energy conversion comparable to those predicted for circularly polarized laser pulses.