Polarization-Dependent Self-Injection by Above Threshold Ionization Heating in a Laser Wakefield Accelerator

Area of Science:

• Plasma Physics
• Laser-Plasma Interactions
• Particle Acceleration

Background:

• Laser wakefield acceleration (LWFA) is a promising technique for generating high-energy particle beams.
• The self-injection process is crucial for LWFA but often requires specific conditions.
• Linear polarization has been the standard for laser pulses in LWFA experiments.

Purpose of the Study:

• To investigate the effect of laser pulse polarization on self-injection in LWFA.
• To compare the electron beam charge and injection threshold for circular versus linear polarization.
• To elucidate the underlying physical mechanisms responsible for any observed differences.

Main Methods:

• Experimental observation of LWFA using laser pulses with circular and linear polarization in nonpreformed plasma.
• Quasi-3D particle-in-cell simulations to model the laser-plasma interaction and electron dynamics.
• Spectroscopy of XUV plasma emission to diagnose plasma properties, including temperature.

Main Results:

• A decreased self-injection threshold was experimentally observed for circularly polarized laser pulses compared to linear polarization.
• Significantly higher electron beam charge was achieved with circular polarization across a range of experimental parameters.
• Simulations indicated that circular polarization leads to a different injection mechanism, involving larger electron momentum gain during above-threshold ionization.

Conclusions:

• Laser pulse polarization critically influences self-injection and electron beam characteristics in LWFA.
• Circularly polarized pulses offer a pathway to more efficient electron trapping and higher beam charges due to enhanced ionization momentum gain.
• The findings provide insights into optimizing LWFA performance by controlling laser polarization.