Breakthroughs in scientific discovery, especially in the experimental realm, often are preceded by breakthroughs in scientific instrumentation. The development of these revolutionary instruments has allowed researchers to accurately capture the world of the ultra-fast and ultra-small.
The emerging field of ultrafast electron diffraction has made incredible progress in the last two decades, paving the way for studying ultrafast structural dynamics with electron probes. Modern ultrafast electron diffractometers now routinely break the sub-picosecond time resolution by either using the compact design principle or via electron pulse compression. This thesis details the development of two distinct UED apparatuses, one that involves the novel implementation of semiconductor photocathodes, and the other is a more conventional compact design electron gun.
Semiconductor cathodes have been a staple in photoinjectors technology, providing ultrabright beams for various accelerator applications. The appeal of semiconductor cathodes is their superior quantum efficiency and initial emittance at the source, corresponding to a higher spatial resolution for more complex systems such as proteins and nanoparticles. The design of this electron gun must accommodate the stringent vacuum requirements of semiconductors, adding extra complexity and cost.
The compact UED takes a more minimalist approach, aiming to shorten the electrons' transit distance from the cathode to the sample, being the most straightforward approach for achieving ultrashort pulse durations. The lack of beamline elements and pulse compression devices eliminates sources of jitter in electron beam propagation.
My last project proposes a novel time-zero determination method for UED that exploits a system with a known response function. Here we used polycrystalline bismuth (Bi) deposited on a home-built silicon nitride (SiN) chip for its ultrafast non-thermal melting time response. The advantage of this time-zero determination method over others is that it closely matches actual UED experimental conditions while determining time-zero with a precision better than the native temporal resolution of our UED instrument. In this development, we also investigate the effect of the silicon nitride substrate on the melting dynamics. This thesis work explored the next generation of high-brightness ultrafast electron sources and provided a robust, simple-to-implement timing tool that greatly facilitates the application of UED.