Chair: Michael Spanner, NRC Ottawa, Canada

  • Martin Schultze
  • Marieke Jager
  • Marcus Ossiander
  • Tobias Witting
  • Lamia Kasmi

#63, 13:30 – 14:00 Attosecond band gap dynamics, M. SCHULTZE, K. RAMASESHA, E. BOTHSCHAFTER, A. SOMMER, C.D. PEMMARAJU, S.A. SATO, D. WHITMORE, A. GANDMAN, J.S. PRELL, L. J. BORJA, D. PRENDERGAST, K. YABANA, D.M. NEUMARK, F. KRAUSZ, AND S.R. LEONE, The transfer of electronic population from valence to conduction band states in a semiconductor is the basis of modern electronics. Now attosecond spectroscopy allows to resolve this process in real-time. The excitation of electrons across the band-gap of silicon by few-cycle laser pulses is found to induce lasting modifications to the XUV absorbance spectrum in steps in synchrony with the laser electric field oscillations, indicative of light-field induced electron tunneling [1]. All regions of the density of states across the conduction band show persistent broadening and the electronic response is readily resolved from a slower phonon induced broadening.

#64, 14:00 – 14:15 Attosecond Transient Absorption Spectroscopy of an Insulator-to-Metal Phase Transition Material: Vanadium Dioxide, MARIEKE JAGER, CHRISTIAN OTT, CHRISTOPHER KAPLAN, ROBERT MARVEL, RICHARD HAGLUND, DANIEL NEUMARK, AND STEPHEN LEONE, Changes in the vanadium 3p core level spectrum are observed with attosecond transient absorption upon excitation of carriers into the 3d conduction band of vanadium dioxide (VO 2 ) using few cycle 800 nm near infrared (NIR) pulses. By observing ultrafast photoinduced changes to the spectrum, measurements are sensitive to the rapid rearrangements in the density of states that can result from strong electron correlation and the insulator to metal phase transition (IMT). VO 2 displays a near-instantaneous spectral response over a broad range around the vanadium M-edge, followed by a fast reshaping of the spectrum. The fast and persisting rise in absorbance at the Fermi level is suggestive of transition to a metal, and the noncongruence of the fast spectral response with thermally induced changes hints at the importance of intermediate states in mediating the material’s photoinduced response.

#65, 14:15 – 14:30 Attosecond electron dynamics on surfaces and layered systems, J. RIEMENSBERGER, M. OSSIANDER, R. KIENBERGER, Attosecond stereaking experiments performed on different solids, e.g. tungsten (110) and (100), rhenium, and magnesium (0001), leading to different delays – also depending on the excitation photon energy, will be disussed. We show results from time-resolved transport of different types of electrons through defined adlayers on a bulk material on attosecond timescale.

#66, 14:30 – 14:45 Temporal broadening of attosecond photoelectron wavepackets from Au and WO3 surfaces, W.A. OKELL, T. WITTING, D. FABRIS, C.A. ARRELL, J. HENGSTER, S. IBRAHIMKUTTY, A. SEILER, M. BARTHELMESS, S. STANKOV, D. Y. LEI, Y. SONNEFRAUD, M. RAHMANI, TH. UPHUES, S. A. MAIER, J. P. MARANGOS, AND J. W. G. TISCH, We performed attosecond streaking measurements on amorphous WO3 and polycrystalline gold films. The measurements reveal the temporal structure of the near infrared electric field at the surface Furthermore FROG-CRAB analysis yields the photoelectron wavepacket temporal broadening associated with a spread of photoelectron transport times to the surface.

#67, 14:45 – 15:00 Probe Field in Photoemission Delay Measurements on a Cu(111)-Surface: Validity of Macroscopic Laws on Atomic and Attosecond Scales, L. KASMI, M. LUCCHINI, L. CASTIGLIONI, P. KLIUIEV, A. LUDWIG, M. GREIF, M. HENGSBERGER, J. OSTERWALDER, L.GALLMANN, AND U. KELLER, An infrared (IR) pulse reflected on a copper (111) surface creates a local transient grating. The phase of this field distribution, which depends on the metal properties, is imprinted in the electron phase in a two-color photoemission process. We isolate this phase from other contributions by using the RABBITT technique. A semiclassical model describing the reflected and transmitted IR field at the surface using the Fresnel equations successfully reproduces the results, therefore indicating the validity of these equations down to the atomic and attosecond level. Due to the efficient electron screening, the transmitted field contributes negligibly to the photoelectron phase.