Speaker: Sason Sofer
Program Description:
Nonlinear interactions between x-rays and long wavelengths can be used as a
powerful atomic scale probe for light-matter interactions and for properties of valence
electrons. This probe can provide novel microscopic information in solids that existing
methods cannot reveal, hence, to advance the understanding of many phenomena in
condensed matter physics. However, thus far, reported x-ray nonlinear effects were very
small and their observations required tremendous efforts. In this talk, I will present the observation
of unexpected strong nonlinearities in parametric down-conversion (PDC) of x-rays to long
wavelengths in gallium arsenide (GaAs) and in lithium niobate (LiNbO3 ) crystals, with
efficiencies that are about 4 orders of magnitude stronger than the efficiencies measured
in any material studied before. These strong nonlinearities cannot be explained by any
known theory and indicate on possibilities for the development of a new spectroscopy
method that is orbital and band selective. In this work we demonstrate the ability to use
PDC of x-rays to investigate the spectral response of materials in a very broad range of
wavelengths from the infrared regime to the soft x-ray regime.
