Advanced particle acceleration mechanisms from laser solid interactions

Abstract

Advanced particle acceleration mechanisms in laser solid interactions are promising to generate high-energy particle beams with improved beam quality via enhanced laser energy coupling with the target. This thesis presents theoretical and numerical investigations of two advanced particle acceleration mechanisms. The Light Sail - Radiation Pressure Acceleration (LS-RPA) mechanism dominant in accelerating bulk ions from nm thin foil target and Surface Plasmon-driven electron and proton acceleration without grating coupling are investigated.

In the first investigation, the effect of tight focusing of a circularly polarised laser beam on carbon ion acceleration from ultra-thin (tens of nm) foils has been explored. Carbon ion energy is highly target thickness and laser polarisation dependent, suggesting that LS-RPA is the dominant mechanism while using a circularly polarised laser on a nm thin target. The increase in the ion energy while increasing the intensity of the laser via tightly focusing the beam is investigated. The effects related to the small spot size of the laser, such as target bending and the presence of the laser’s relativistic longitudinal electric field, have been explored. In spite of some unfavourable electron heating caused by these small spot-related effects, LS-RPA is still the dominant mechanism. Carbon ions with energy > 70 MeV/nucleon can be expected from a laser system, such as Gemini with an intensity of 2.4 × 10²¹ W/cm² achievable through tightly focusing the beam. Furthermore, the use of a frequency doubling crystal to achieve ultra-high contrast of the laser needed with these nm thin targets has been considered. The effect of the frequency-doubled laser on carbon ion acceleration has been investigated.

In the second investigation, the excitation of Surface Plasmons (SP) using a high-intensity laser on a flat foil target without grating coupling has been proposed theoretically. Simulations show that electrons are accelerated efficiently by the longitudinal electric field of the SP along the target surface when the laser is incident at a grazing angle to the target. Furthermore, an extended investigation of the laser incidence at the edge of the target, parallel to the surface, is carried out. These high-charge and high-energy electrons are used to accelerate protons present in the contaminant layer of the rear edge of the target. Proton beams with narrow energy spread peak at the high energy end of the spectrum are observed in simulations. A detailed characterisation of these proton beams is presented here.

Thesis is embargoed until 31 July 2025.

Date of Award	Jul 2024
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Tezpur University
Supervisor	Satyabrata Kar (Supervisor), Marco Borghesi (Supervisor) & Nilakshi Das (Supervisor)