Attosecond Electron Dynamics

With support from the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) Program in the Division of Chemistry, Professor Stephen Leone of the University of California, Berkeley, is using sophisticated laser techniques to study some of the shortest time processes in molecules. Short time measurements can only be accomplished by first creating X-ray pulses on time frames of one billion billionth of a second, namely one attosecond. This is achieved with laboratory table-top optical methods, producing multiple time-delayed laser pulses to first prepare, then initialize, and finally measure the time dynamics. Professor Leone and his students will analyze the rapid switching of charge from one part of a molecule to another and the extremely fast ensuing chemical transformations with site-specific characterization. Benefits to society arise through the fundamental elucidation of charge flow in molecules that is essential to the conversion of solar energy to electrical output and from the technical training of the future workforce in measurement science and experimental physical chemistry. The Leone group plans to engage middle school and high school teachers to participate in summer research and them team also plans to host high school students on guided visits to these ultrafast spectroscopy laboratories. Attosecond transient absorption in the X-ray is employed for time-resolved dynamics measurements that separate the electron dynamical timescales from those of nuclear motion. Core level spectroscopic transitions in reporter atoms are used. These are charge- and oxidation-state specific, bond-length-sensitive, and electronic-state-dependent, providing a site-selective probe of few-femtosecond time dynamics. Professor Leone and his group are studying attosecond time-resolved processes associated with charge transfer, charge migration, ion pair states, and electronic quantum state superpositions. Attosecond probe pulses are produced via the process of high harmonic generation using few-femtosecond driver laser pulses, and, under this award, three pulse experiments will be developed, to prepare, initialize, and probe, with high state specificity. Broader scientific impacts include the potential to develop tools that push the limits of time, particularly important tools as the dimensions and speed of devices decrease and computing architectures begin to become governed by quantum principles. 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.