ACCELERATION AND CONTROL OF MULTI-MEV ELECTRON BUNCHES WITH FEW-CYCLE LASER PULSES

Abstract

Conventional radio frequency (RF) electron accelerators can be kilometers long and extremely expensive to build and maintain. Laser wakefield acceleration (LWFA) of electrons was first proposed in 1979 as a way to reduce the cost and size of these devices. In the past four decades, the laser plasma physics community has made great improvements to the implementation of LWFA. In the process of doing so, they have found that LWFA-driven electron bunches can have ultrashort durations, constitute kiloamp-scale transient currents that generate megagauss-scale magnetic fields, and produce short-pulse beams of spatially coherent x-rays. This has led to increased interest in methods for controlling these electron bunches.In this dissertation, I will present the laser-based techniques we have developed for fine control of laser-driven electron bunches with mega-electron volt (MeV) energies. I will first discuss the nonlinear dynamics of elliptically polarized pulses in helium filled hollow core fibers, which are used for spectral broadening, followed by compression, to generate few-cycle duration LWFA driver pulses. These pulses accelerate electrons with two orders of magnitude lower divergence than linearly polarized pulses of the same few-cycle duration. I will then discuss our development of a new loss-free pulse shaping technique for generating delay-adjustable pairs of exactly collinear few-cycle pulses with the same polarization, spatial mode, and central wavelength. This is followed by application of this technique to the resonant driving of near critical density plasmas for the acceleration of electron bunch pairs with controllable femtosecond scale delay. Finally, I discuss the necessary improvements for using these electron bunch pairs to perform ultrafast pump-probe experiments.