Application of XUV and Soft-x-ray Attosecond Spectroscopies to Quantify Vibronic Couplings and Charge Dynamics

The primary quantum process behind many phenomena in our daily lives is the light-driven motion of electrons. Important examples of this include photosynthesis, vision, vitamin D synthesis from sunlight, DNA damage by UV light, and more. As a first step towards developing a better understanding of such phenomena, it is important investigate and harness the electronic motions inside atoms and simple molecules with light pulses. However, the electrons are extremely fast, and can move on the timescale of an attosecond – a billionth of a billionth of a second! To capture the images of what transpires in the quantum realm at such dizzying speeds, one needs to use a sophisticated camera alongside an extremely fast flash or strobe light. The PI’s team employs advanced technologies such as a charged particle velocity imaging detector, which serves the purpose of a camera film, and ultrafast laser pulses that play the role of a strobe light. The proposed research project will investigate how electronic charge gets distributed after excitation by light, and how the changes in atomic positions within a molecule impact this process. Graduate and undergraduate students working on this this project will develop an important scientific skillset and will be empowered to generate new ideas and devise applications of their research. This impact will multiply as they move to the next stage of their careers in universities, national labs, and tech companies, thus fostering scientific innovation and productivity in the society. Attosecond extreme ultraviolet and soft-x-ray spectroscopy techniques form a very powerful toolkit for fundamental, real-time investigations of electron dynamics. In the proposed work, the PI and graduate students will employ these approaches for time-resolved study of coherent electronic wavepacket motion. Specifically, they will investigate XUV induced Rydberg, ionic, and many-electron excitations in atoms and molecules. To quantify the vibronic couplings that mix electronic states due to nuclear motion, the research team will conduct pump-probe measurements near conical intersections in small molecules. They will also aim to perform elementally specific transient absorption studies to monitor the coherent evolution of charge in photoionized molecules. Results obtained here will guide the development of theoretical methods that can accurately model the light-matter interaction, and the coupled and correlated evolution of electron and nuclei. The spatio-temporal mapping of charge dynamics in complex systems will serve to establish attosecond science as a versatile spectroscopy technique. These objectives will be achieved while training the graduate and undergraduate students in the frontier fields of attosecond science, laser technologies, and optical and x-ray spectroscopies. The PI will also place an emphasis on the participation of students from minority and underrepresented groups. Annual outreach events will be used to engage and educate the community about the importance and impact of physics research. 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.