Ultrafast Imaging and the Phase Problem for Inelastic X-Ray Scattering

• Published in: Advanced materials (Weinheim) Vol. 22; no. 10; pp. 1141 - 1147
• Main Authors: Abbamonte, Peter, Wong, Gerard C. L., Cahill, David G., Reed, James P., Coridan, Robert H., Schmidt, Nathan W., Lai, Ghee Hwee, Joe, Young Il, Casa, Diego
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 12.03.2010; WILEY‐VCH Verlag
• Subjects: Algorithms; Condensed matter; Dynamics; Elasticity; Electron density; Electrons; Fourier Analysis; Fourier transformation; Imaging; Inelastic scattering; Inelastic X-Ray Scattering; Neutron scattering; Neutrons; Phase Problem; Scattering, Radiation; Ultrafast imaging; X-Rays
• ISSN: 0935-9648; 1521-4095; 1521-4095
• DOI: 10.1002/adma.200904098

A new method for imaging ultrafast dynamics in condensed matter using inelastic X‐ray scattering (IXS) is described. Using the concepts of causality and irreversibility a general solution to the inverse scattering problem (or “phase problem”) for IXS is illustrated, which enables direct imaging of dynamics of the electron density with resolutions of ∼1 attosecond (10−18 s) in time and <1 Å in space. This method is not just Fourier transformation of the IXS data, but a means to impose causality on the data and reconstruct the charge propagator. The method can also be applied to inelastic electron or neutron scattering. A general outline of phenomena that can and cannot be studied with this technique and an outlook for the future is provided. A space–time image of valence excitation in a model insulator, LiF, is shown in the figure. The quantity shown is the “density Green's function”, which can be imagined as a ripple of density generated by an idealized point source (depicted as bright light in the image). The image was reconstructed from inelastic X‐ray scattering experiments and has an effective time resolution of 26 as (2.6 × 10−17 s).