High-Harmonic Generation in Complex Systems

Louisiana State University, Baton Rouge LA

Investigators

Abstract

Since the invention of the laser, the development of ever more controlled pulses of light has facilitated progress in science, technology, and medicine. As an example, light pulses with very short temporal durations allow scientists to make “movies” of how electrons and atoms move around inside molecules, for instance during chemical reactions. The 2023 Nobel Prize in Physics was awarded for the development of attosecond pulses of light (the shortest ever made), which are produced in the process of high harmonic generation (HHG). HHG happens as a result of the interaction between an intense laser pulse and almost any nonlinear medium, and has proven to be a versatile source of short-pulse, well-controlled light in the ultraviolet (UV) and extreme UV (XUV) spectral region. This project is centered on the further development of HHG as a source of UV and XUV light, in particular in systems that are more complex than atomic gases, for which the majority of work has been done up to now. The PI and her group will work on the development of theoretical tools for simulating the HHG process and the light it generates, as well as applications of these tools to model results in collaboration with experimental colleagues. The proposed work will be relevant to open questions at the forefront of ultrafast science and will contribute to workforce development through the training of junior researchers at the undergraduate and postgraduate levels. The PI will continue to serve the AMO and broader physics community through service roles at the national level. The work in this project entails specific developments and applications for HHG in semi-conductor crystals, as well as for HHG in organic molecules. In crystals, the PI and her group will continue their on-going development of a versatile theory tool that is capable of describing the coupled microscopic and macroscopic dynamics of HHG in crystalline solids, through the build-up and phase matching of the HHG light. This tool is based on the coupled solutions of the semi-conductor Bloch equations and the Maxwell wave equation, and will require high-performance computing resources. The understanding and macroscopic control of the properties of HHG in crystals, similar to what is routinely done in gas-phase HHG, has been largely unexplored even though it is essential for the development of solid-state HHG as a probe of ultrafast dynamics. For example, in order to interpret features in the HHG spectrum in terms of the structure and dynamics of the host material it is necessary to know what role macroscopic effects play in shaping those features. In organic molecules, accurate calculations of HHG are extremely challenging because there are so many degrees of freedom involved. The group will use time-dependent density functional theory (TDDFT) to simulate the HHG process, with the goal of developing TDDFT as a reliable tool for molecular HHG calculations, allowing more direct comparisons between calculated and experimentally measured results. 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.