Physics colloquium – “Watching Electrons Move”

Kathryn R. Hamilton

University of Colorado at Denver

Abstract: Since their discovery in the late 1800’s, electrons have been a constant source of curiosity for scientists. Their properties and behavior have been studied and harnessed to produce some of the greatest inventions of the past century, including electron microscopes and particle accelerators. However one fundamental question about their behavior still remains: how do electrons move inside atoms and molecules? Electron motion within atoms has proved difficult to study due to the incredibly short timescale it occurs on (the attosecond timescale, or 10^-18 seconds). One method of capturing electron motion is to use very short laser pulses to take a series of snapshots of the system. This requires laser pulses shorter than the duration of the dynamics we want to observe (similar to using a short flash on a camera to obtain an image of a fast-moving object). The means to do this have only become possible in the past decade with the advent of new ultrashort (less than 100 as) lasers, which have become feasible due to a process called high‐harmonic generation (HHG). Harmonic generation occurs when an atom is exposed to a short laser pulse. Electrons are removed from the atom by the laser field, accelerated, and then recombine with the parent atom emitting high-energy harmonic light. This light can then be manipulated to produce the attosecond pulses required to image electronic motion. Analysis of the spectra produced by harmonic generation can also give an insight on the attosecond‐scale dynamics of electrons. An accurate theoretical description of high harmonic generation would therefore be extremely beneficial for the advancement of attoscience. To this end, a world‐leading computational method, known as RMT (R‐Matrix with Time dependence), has been developed at Queen’s University Belfast to model accurately and efficiently the behavior of electrons in many‐electron atoms. In this seminar I will present recent results obtained using the RMT method, firstly to treat high-harmonic generation in two-color laser fields, and then on applications of the attosecond pulses generated during the HHG process to measure ionization delays.

Figure 1: High-harmonic spectrum of neon atoms irradiated by a two-color (800nm + 400nm) laser field. The red “v” shapes are spectral caustics, formed by the coalescence of two or more electron trajectories in the same energy space.

Biography: Kathryn Hamilton is a new Assistant Professor at the University of Colorado Denver. Previously she was a Postdoctoral Research Scholar at Drake University in Des Moines, Iowa, where she worked alongside Prof. Klaus Bartschat on applying R-Matrix methods to treat a variety of atomic physics problems. She obtained her PhD in 2019 under the supervision of Dr. Andrew Brown and Prof. Hugo van der Hart at Queen’s University Belfast with a thesis entitled “R-Matrix calculations for ultrafast two-color spectroscopy of noble gas atoms”. Her current research focuses on observing and controlling multielectron dynamics in atoms exposed to external laser fields, and electron collisions with atomic species. When she is not running code on supercomputers all over the world, she likes to play traditional Irish music and domesticate feral cats. Both activities produce very similar sounds.

All lectures held in CoorsTek 140 unless otherwise noted