All-Optical Electron Acceleration with Ultrafast THz Pulses

Abstract

This thesis discusses a series of advances toward - and resulting in -the demonstration of the first ultrafast THz-driven electron gun, a technology with the potential to deliver unprecedented electron beam quality to scientists studying matter at the ultrafast and ultrasmall scale via electron diffraction or x-ray imaging. In Part 1, we discuss various advances in generation of high energy pulsed THz radiation, a spectral regime uniquely effective at accelerating electrons but historically lacking in effcient sources. In particular, through various improvements to thegrating-based tilted pulse front (TPF) technique, we demonstrate a record conversion effciency of 1%. We also implement echelon-based TPF, achieving 3.5x higher effciency than grating-based TPF for short (~100 fs) pulses. Finally, we reuse the residual pump to obtain a recycled effciency around half to a quarter that of the original. This reduced effciency can be linked spatio-spectral distortions in the residual pump, and we visualize these distortions to better understand the asymmetric dynamics of the THz generation process. In Part 2, we discuss the design, testing, and commissioning of an electron gun driven exclusively by THz radiation. The accelerating structure, capable of broadband, dispersionless THz propagation and sub-wavelength confinement, is analyzed through electromagnetic simulations and experimental characterization. We also characterize the accelerated electrons in absolute charge and spectrum as a functionof emission phase and THz energy, while showing that the behavior matches well with theory and simulation. Our first-version THz gun delivers near 1 keV electrons accelerated by field strengths surpassing that of the best operational RF guns. The gun also delivers narrowband electron spectra which can already be used for low-energy electron diffraction