Electron acceleration by femtosecond laser interaction with micro-structured plasmas

Abstract

Laser-driven accelerators are a promising and compact alternative to RF accelerator technology for generating relativistic electron bunches for medical, scientific, and security applications. This dissertation presents three experiments using structured plasmas designed to advance the state of the art in laser-based electron accelerators, with the goal of reducing the energy of the drive laser pulse and enabling higher repetition rate operation with current laser technology. First, electron acceleration by intense femtosecond laser pulses in He-like nitrogen plasma waveguides is demonstrated. Second, significant progress toward a proof of concept realization of quasi-phasematched direct acceleration (QPM-DLA) is presented. Finally, a laser wakefield accelerator at very high plasma density is studied, enabling relativistic electron beam generation with ~10 mJ pulse energies. Major results from these experiments include:

• Acceleration of electrons up to 120 MeV from an ionization injected wakefield accelerator driven in a 1.5 mm long He-like nitrogen plasma waveguide

• Guiding of an intense, quasi-radially polarized femtosecond laser pulse in a 1 cm plasma waveguide. This pulse provides a strong drive field for the QPM-DLA concept.

• Wakefield acceleration of electrons up to ~10 MeV with sub-terawatt, ~10 mJ pulses interacting with a thin (~200 µm), high density (>1020 cm-3) plasma.

• Observation of an intense, coherent, broadband wave breaking radiation flash from a high plasma density laser wakefield accelerator. The flash radiates > 1% of the drive laser pulse energy in a bandwidth consistent with half-cycle (~ 1 fs) emission from violent unidirectional acceleration of electron bunches from rest.

These results open the way to high repetition rate (>~kHz) laser-driven generation of relativistic electron beams with existing laser technology.