Cold optical injection producing monoenergetic, multi-GeV electron bunches.

Area of Science:

• Plasma Physics
• Particle Acceleration
• Laser Technology

Background:

• Laser-plasma accelerators (LPAs) are promising for compact, high-gradient particle acceleration.
• Current optical injection schemes often rely on electron heating, leading to broad energy spreads.
• Developing injection methods that produce high-quality electron beams is crucial for LPA applications.

Purpose of the Study:

• To introduce and analyze a novel cold optical injection mechanism for LPAs.
• To demonstrate injection without relying on electron heating.
• To achieve electron bunches with a narrow absolute energy spread.

Main Methods:

• Utilizing a short, circularly polarized, low-energy laser pulse counterpropagating with a main circularly polarized pulse in a low-density plasma.
• Employing the collision of these pulses to generate a spatially periodic, time-independent beat force.
• Simulating the acceleration process and analyzing electron bunch properties.

Main Results:

• The beat force effectively blocks longitudinal electron motion, facilitating injection into the plasma wake.
• Demonstrated acceleration of a 60 MeV, 50 pC electron bunch with a 0.7 MeV rms energy spread over 0.6 mm.
• Computed acceleration to 3 GeV with a sub-1% rms energy spread over 3.8 cm in a plasma channel.

Conclusions:

• The proposed cold optical injection scheme offers a viable alternative to heating-based methods.
• This mechanism enables the production of high-quality electron bunches with significantly reduced energy spread.
• The results highlight the potential of this scheme for advanced LPA applications requiring precise electron beam characteristics.