High intensity mid-infrared laser development for laser wakefield acceleration
File(s)
Author(s)
Gunn, Annabel
Type
Thesis
Abstract
This thesis presents a detailed investigation into the feasibility of a laser wakefield acceleration (LWFA) experiment driven by the 3.7 μm centred mid-infrared (MIR) arm of Chimera, a high-power, short-pulse, multi-beam optical parametric chirped pulse amplification system under development at Imperial College London. The work addresses the challenges of commissioning a developmental laser system for routine experimental operation, with emphasis on front-end stability, and the theoretical viability of MIR-driven LWFA through particle-in-cell (PIC) simulations. MIR drivers offer potential advantages for LWFA, including higher normalised vector potentials at lower intensities and increased accelerated charge, though experimental implementation remains limited by the scarcity of suitable high-power sources.
Guided by PIC simulations, MIR-driven LWFA is shown to be feasible within Chimera’s current design constraints. Self-injection and acceleration of electrons to energies of ~20 MeV are achieved at a plasma density of n_e=5.8×10^18 cm^(-3), provided the laser delivers at least 15 mJ with a pulse duration below 70 fs. Pulse energy is identified as the dominant parameter, while pulse duration is comparatively forgiving, indicating that future development should prioritise energy scaling. Although the bandwidth at MIR generation -- via difference-frequency generation in PPLN -- could support compressed pulses as short as 30 fs, higher-order phase accumulation and bandwidth reduction in subsequent optical parametric amplifiers suggest an initial compressed pulse duration near ~70 fs.
Simulations also reveal electron energies exceeding established scaling predictions, along with substantial accelerated charge. This is attributed to operation in a high-density regime enabled by short-pulse, long-wavelength laser-drivers. Early beam-loading effects suggest the onset of a hybrid beam-driven phase, potentially enhancing laser-plasma efficiency and beam current. The apparent insensitivity of this regime to acceleration length could simplify experimental implementation. If confirmed experimentally, this could position mid-infrared drivers as promising sources of high-charge, high-current electron beams for future medical and industrial applications.
Guided by PIC simulations, MIR-driven LWFA is shown to be feasible within Chimera’s current design constraints. Self-injection and acceleration of electrons to energies of ~20 MeV are achieved at a plasma density of n_e=5.8×10^18 cm^(-3), provided the laser delivers at least 15 mJ with a pulse duration below 70 fs. Pulse energy is identified as the dominant parameter, while pulse duration is comparatively forgiving, indicating that future development should prioritise energy scaling. Although the bandwidth at MIR generation -- via difference-frequency generation in PPLN -- could support compressed pulses as short as 30 fs, higher-order phase accumulation and bandwidth reduction in subsequent optical parametric amplifiers suggest an initial compressed pulse duration near ~70 fs.
Simulations also reveal electron energies exceeding established scaling predictions, along with substantial accelerated charge. This is attributed to operation in a high-density regime enabled by short-pulse, long-wavelength laser-drivers. Early beam-loading effects suggest the onset of a hybrid beam-driven phase, potentially enhancing laser-plasma efficiency and beam current. The apparent insensitivity of this regime to acceleration length could simplify experimental implementation. If confirmed experimentally, this could position mid-infrared drivers as promising sources of high-charge, high-current electron beams for future medical and industrial applications.
Version
Open Access
Date Issued
2025-10-02
Date Awarded
2026-03-01
Copyright Statement
Attribution-Non Commercial-No Derivatives 4.0 International Licence (CC BY-NC-ND)
Advisor
Smith, Roland
Mangles, Stuart
Publisher Department
Department of Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)