Code: TOD	Time Slot/Poster Number: 10:30 - 11:00 am	Session: Attosecond/X-ray & Raman
The effective fine structure constant of graphene, measured with inelastic x-ray scattering
Peter Abbamonte
University of Illinois at Urbana-Champaign, Urbana, IL
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Summary
Electrons in graphene behave like relativistic, Dirac Fermions. A key question is whether they are noninteracting or critically influenced by correlations. I will describe inelastic x-ray scattering experiments on graphite, to which we have applied inversion algorithms to image screening in a graphene sheet (time resolution=10.3 attoseconds). We found that an electron is screened by 1 nm-sized cloud of charge originating from two Van Hove singularities residing beyond the Dirac spectrum, which renormalize the fine structure constant to alpha_g = 0.14 +/i 0.092 ~ 1/7. This suggests a weak influence of correlations on the properties of graphene.

Code: TOD	Time Slot/Poster Number: 11:00 - 11:30 am	Session: Attosecond/X-ray & Raman
Molecular Dynamics Probed by Ultrafast Coherent X-Rays
Margaret Murnane; Henry Kapteyn
University of Colorado, Boulder, CO
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Summary
High-order harmonic generation is a unique source of coherent, ultrashort-pulse, soft x-rays, useful for applications in ultrafast molecular and materials spectroscopy and in high-resolution imaging. Until recently, the useful range of HHG was limited to < 130 eV, due to the inability to fully phase match the HHG process. In recent work we extended fully phase-matched, coherent, high harmonic beams to the soft x-ray region of the spectrum, to photon energies > 0.5 keV, for the first time.

Code: TOD	Time Slot/Poster Number: 11:30 am - 12:00 pm	Session: Attosecond/X-ray & Raman
Stimulated Raman Spectroscopy with Femtosecond Optical or Attosecond X-ray Pulses
Shaul Mukamel; Saar Rahav; Haitao Wang
UC Irvine, Irvine, CA
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Summary
Coherent nonlinear optical signals are commonly calculated using a semiclassical approach that assumes quantum molecules interacting with classical fields. We present an alternative approach based on a quantum description of both matter and field. The signals are recast in terms of transition amplitudes which provide a clearer picture for the underlying molecular processes. Using this approach we show that stimulated coherent anti-stokes Raman spectroscopy (CARS) resonances originate from double-slit interference of two-photon Stokes pathways.

Code: TOD	Time Slot/Poster Number: 12:00 - 12:30 pm	Session: Attosecond/X-ray & Raman
Raman Probes of Molecules at Extreme Pressures and Temperatures
Russell Hemley; Timothy Strobel; Maddury Somayazulu; Alexander Goncharov; Natarajan Subramanian; Yue Meng; Ho-kwang Mao
Geophysical Lab., Carnegie Inst. of Washington, Washington, DC
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Summary
Raman spectroscopy is a key tool in studies of materials in extreme environments, particularly at high pressures and temperatures. The behavior of molecular systems under these conditions is of great interest because of their large compressibility, marked changes in bonding and electronic properties, and dramatic alterations in physical and chemical behavior leading to novel states of matter. Optical Raman scattering, including time resolved and non-linear techniques, are used as well as synchrotron x-ray Raman and resonance inelastic x-ray scattering methods. Examples will include hydrogen related diatomic molecules, hydrogen-rich and van der Waals compounds and more complex materials including biological systems.