Attosecond Time-Resolved Quantum Dynamics: From Atoms Towards Nanostructures

Kansas State University, Manhattan KS

Investigators

Abstract

Over the past decade, extraordinary advances in the field of time-resolved photoelectron spectroscopy have enabled investigations of simple atoms with an unprecedented time resolution of the electron motion within the atoms, resolution that approaches one attosecond (one attosecond is a billionth of a billionth of a second). This project extends these investigations to more complex targets, such as adsorbate-covered solid surfaces and nanoparticles. These investigations of the dynamics of electron emission from atoms and complex target at the natural time scale of the electronic motion in matter relates to both established and emerging fields of research and technology. Time-resolved studies of the electronic dynamics in matter will promote the comprehensive understanding of i) elementary physical processes, such as single-electron and collective electronic excitations and ii) the dynamics of electrons and electric fields in metals, semiconductors, and catalytic surfaces, (bio-) molecules, and nanoparticles. These research projects are thus likely to deepen our insight into photochemical processes and chemical reaction dynamics at surfaces. They have a strong educational component by training students and postdocs in applying concepts as well as mathematical and numerical techniques used in modern atomic, optical, surface, and computational physics. Our research efforts may have a transformative impact on emerging technologies, such as ultrafast light-wave computing, nanocatalysis, and artificial photosynthesis, thereby contributing to the development of novel ultrafast computers and efficient catalytic devices needed to secure our energy supply. Attosecond streaking spectroscopy has led to impressive time-resolved studies of atomic ionization and is anticipated to significantly advance our understanding of electronic properties of molecules, layered--semiconductor structures, and nanoparticles. However, the detailed physical interpretation of streaked spectra faces significant conceptual challenges and necessitates comprehensive theoretical investigations, even for simple atomic systems. For complex systems, additional severe technical difficulties in describing the transiently photoexcited electronic dynamics in molecules and solids must be overcome. This research addresses these challenges and focuses on the modeling of time-resolved photoemission from atoms, adsorbate-covered metal surfaces, and nanoparticles. It examines streaked photoemission spectra in order to systematically analyze the role of (i) electronic correlation, (ii) electron propagation, and (iii) collective electronic excitation and relaxation effects during and after the photoemission process. We will develop and apply complementary quantum--mechanical methods: exact numerical solutions of the time--dependent Schrödinger equation and physically more transparent analytical (S--matrix) quantum-mechanical methods. Effective potentials for surfaces and nanoparticles will be modeled based on density-functional theory. They will serve as input for full three--dimensional calculations of the electronic dynamics during the interaction of intense IR and XUV light pulses with matter. New numerical methods will be explored and implemented, allowing for the modeling of increasingly complex samples. Furthermore, we will assess the degree to which streaked photoelectron spectroscopy can reveal information on (a) electronic forces and dynamics in solids and at solid interfaces and (b) non?homogenous nanoplasmonic electric--field enhancements in response to an incident IR streaking pulse. Supported by numerical modeling, attosecond time-resolved measurements promise novel methods to prepare, probe, and control electronic excitations and the formation and breaking of chemical bonds in complex systems.