title: Current vs Charge Density Contributions to Nonlinear X-ray Spectroscopy.
abstract: Stimulated (coherent) and spontaneous (incoherent) nonlinear X-ray signals are expressed using a spatially nonlocal response tensor which directly connects them to the time evolving current j and charge σ densities rather than to electric and magnetic multipoles. The relative contributions of the σA(2) and j · A minimal coupling terms, where A is the vector potential, are demonstrated. The two dominate off-resonant and resonant scattering, respectively, and make comparable contributions at near resonant detunings.
authors.affiliation: Department of Chemistry, University of California , Irvine, California 92697-2025, United States.
authors.forename: Jérémy R
authors.initials: JR
authors.lastname: Rouxel
authors.affiliation: Department of Chemistry, University of California , Irvine, California 92697-2025, United States.
authors.forename: Markus
authors.initials: M
authors.lastname: Kowalewski
authors.affiliation: Department of Chemistry, University of California , Irvine, California 92697-2025, United States.
authors.forename: Shaul
authors.initials: S
authors.lastname: Mukamel