ABSTRACT: The microscopic structure and dynamics of valence electrons determine many of a material's properties, including its optical ones. Conventional x-ray scattering can resolve the angstrom-scale electronic structure, but it is difficult to separate the valence electrons from the more localized core electrons. Here we report nonlinear x-ray scattering measurements from optically-driven valence electrons using the LCLS hard x-ray free-electron laser. We measure the phase-matched x-ray-optical sum frequency generation between two optical photons and a single x-ray photon in bulk centrosymmetric silicon. We show that a single higher-order wave-mixing measurement gives critical information on the optically inaccessible nonlinear driven valence electron density. In particular, we measure the reduced site symmetry of the bonding electrons including their local inversion-symmetry breaking. Additionally, we report the first phase sensitive measurement of x-ray optical wave-mixing and the first measurement of x-ray optical mixing in an imperfect crystal. The results have implications for understanding optically driven materials in both the strong field regime and with exotic properties.

BIO: Chance completed his undergraduate degree in electrical engineering at the University of California, Irvine and then started his PhD in the electrical engineering department at Stanford University in 2019. His thesis research is centered around performing nonlinear x-ray scattering experiments at hard x-ray free electron lasers to image the local optical response of materials with Professor David Reis and Professor Jerry Hastings.

This seminar is sponsored by the Department of Applied Physics and the Ginzton Laboratory