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

We present the process of ion acceleration with ultra-thin foils irradiated by elliptically polarized, highly intense laser pulses. Recently, efficient generation of monoenergetic ion beams was introduced using the concept of laser-ion lensing and acceleration (LILA)[1]. LILA is a novel scheme where the target has a radially-dependent thickness, resulting in simultaneous acceleration and focusing of a proton beam. We extend the LILA concept to include elliptically polarized (EP) laser pulses. It is widely believed that an elliptically polarized (EP) laser is unacceptable for radiation pressure acceleration (RPA) because strong electron heating compromises ion acceleration [2].  By multidimensional particle-in-cell simulations, we demonstrate that the LILA scheme can be driven by EP laser pulses as long as the average target thickness is optimized. 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.

[1] Tianhong Wang, Vladimir Khudik and Gennady Shvets, Phys. Rev. Lett. 126, 024801(2021).

[2] S G Rykovanov et al, New J. of Phys. 10 (2008) 113005