NSF Award
2409183
Photoelectron emission is a fundamental light-matter interaction process. It occurs when light with an appropriate wavelength and intensity strikes a material object, interacts with the electrons in it, and gives some of them enough energy to eventually leave the material altogether. These emitted photoelectrons carry information about the dynamics of the process and the electronic properties of the target material. For more than a century, the measurement and analysis of their energy and momentum distribution has been one of the most prolific methods for determining the electronic structure of matter, importantly promoting the development of laser and detection technologies as well as accurate quantum-mechanical theoretical methods. Traditional energy-domain spectra image the sample's time-averaged internal electronic dynamics during the photoemission process, but do not resolve the ultrafast time-dependent electronic dynamics during the photoelectron-release process. The PI and graduate student’s theoretical modeling of time-resolved photoelectron emission from solid surfaces and plasmonic nanoparticles is motivated by extraordinary progress in ultrafast laser technology that enabled the generation of ultrashort light pulses and their accurate control and synchronization. These pulses allow for investigations of the electronic dynamics in isolated atoms and condensed matter systems with temporal resolution at the natural timescale of the electronic motion in matter and with atomic spatial resolution. In the same way as making a movie of a fast-moving object, such as a bullet in flight, requires the stroboscopic assembly of many frames, each constituting a momentary image of the object, time-domain spectroscopy is about to provide “electronic movies”, capable of displaying the motion of electrons in and their emission from matter with atomic spatiotemporal resolution.<br/><br/>Attosecond (1 as = 10-18 seconds) time-resolved spectroscopy has led to impressive time-domain studies of ionization processes on isolated (gaseous) atoms and is anticipated to significantly advance our understanding of electronic properties of layered-semiconductor structures and nanoparticles. However, the physical interpretation of time-resolved photoemission spectra faces significant conceptual challenges and necessitates comprehensive theoretical investigations, even for simple atomic systems. For complex systems, such as plasmonic nanoparticles and solid surfaces, additional severe technical difficulties in describing the transiently photoexcited electronic dynamics must be overcome. The PI and graduate student’s work addresses these challenges. It focuses on the numerical modeling of time- and spatially resolved emission of electrons and the generation of up-converted high-harmonic (HH) radiation from adsorbate-covered metal surfaces and nanoparticles. It proceeds by developing and applying complementary quantum-mechanical methods, including numerical solutions of the time-dependent Schrödinger equation, and physically more transparent semi-classical methods. It will assess the fidelity with which time- and emission-angle-resolved photoelectron and HH spectra can reveal information on (a) electronic forces and dynamics in solids and (b) non-homogenous nano-plasmonic electric-field enhancements of incident light pulses. These investigations will advance our understanding of (i) single-electron and collective electronic excitations and (ii) the dynamics of electrons and fields in layered semiconductors, adsorbate-covered surfaces, and nanoparticles. It thus promotes emerging technologies, such as light-wave computing, nano-catalysis, and artificial photosynthesis, thereby contributing to the development of novel computers and catalytic devices for securing our energy supply and preserving our environment.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
