Chair: Anthony Starace, The University of Nebraska, Lincoln, USA

#73, 8:30 – 9:00 Ultrafast molecular structure determination from aligned polyatomic molecules using laser-induced electron diffraction, M. G. PULLEN, B. WOLTER, A.-T. LE, M. BAUDISCH, M. HEMMER, A. SENFTLEBEN, M. SCLAFANI, C. D. SCHRÖTER, J. ULLRICH, R. MOSHAMMER, C.-D. LIN, AND J. BIEGERT, Laser-induced electron diffraction is a developing dynamical imaging technique that can probe molecular dynamics at fewfemtosecond temporal resolutions and has the potential to reach the sub-femtosecond level. We have developed the recipe to extend the technique to polyatomic molecules and we demonstrate the method by extracting the structure of aligned and anti-aligned acetylene (C2H2). We show that multiple bond lengths can be simultaneously imaged at high accuracy including elusive hydrogen containing bonds. Our results open the door to the investigation of larger complex molecules and the realization of a true molecular movie.

#74, 9:00 – 9:15 Carrier-Envelope Phase Mapping of Laser-Induced Electron Rescattering, HENNING GEISELER, NOBUHISA ISHII, FLORIAN GEIER, KEISUKE KANESHIMA, TERUTO KANAI, AND JIRO ITATANI, We present an experimental technique to probe the energy-dependence of elastic scattering cross sections for electron-ion collisions in laser-induced electron rescattering. When high-energy photoelectrons are produced through ionization in intense few-cycle IR pulses, rescattered electrons originating from a single half-cycle under the rapidly varying pulse envelope are spectrally isolated. Through CEP-control, the scattering energy is scanned over an extended interval, and assisted by a theoretical description, the scattering cross section is extracted. The technique is demonstrated for the case of xenon, revealing a localized enhancement at 17 eV.

#75, 9:15 – 9:30 Retrieval of two-dimensional molecular structure with laser-induced electron diffraction from laser-aligned polyatomic molecules, CHAO YU, HUI WEI, XU WANG, ANH-THU LE, RUIFENG LU, AND C. D. LIN, Imaging the transient process of molecules has been a basic way to investigate chemical reactions and dynamics. Based on laser-induced electron diffraction with partially 1D-aligned molecules, here we provide two efficient methods for reconstructing 2D structure of polyatomic molecules. We demonstrate that electron diffraction images in both scattering angles and broadband energy can be utilized to retrieve complementary structure information, including positions of light atoms. With picometer spatial resolution and the inherent femtosecond temporal resolution of lasers, laser-induced electron diffraction method offers significant opportunities for probing atomic motion in large molecules in a typical pump-probe measurement.

#76, 9:30 – 9:45 Atomic-scale diffractive imaging of subcycle electron dynamics in graphene, V. S. YAKOVLEV, M. I. STOCKMAN, F. KRAUSZ, AND P. BAUM, Using graphene as an example material, we show with simulations that ultrafast electron and X-ray diffraction can provide a time-dependent record of charge-density maps in condensed matter. Such real-space measurements promise subcycle and sub-atomic resolutions, and they can reveal light-driven electron  dynamics that are not easily accessible by conventional spectroscopic methods.

#77 9:45 – 10:00, Resolving tunneling dynamics in attosecond electron holography, G. PORAT, G. ALON, M. KRÜGER, B. D. BRUNER, N. DUDOVICH, Attosecond and strong-field physics offer new insights into ultrafast quantum phenomena, the most fundamental of which is quantum tunneling. We apply attosecond electron holography as a new mechanism to resolve the tunneling dynamics. By adding a weak second harmonic field we map the dynamical properties of the hologram. Specifically, we show that the holographic measurement serves as a differential measurement resolving, with extremely high sensitivity, subtle differences in the ionization times associated with the different electron trajectories.


Chair: Caterina Vozzi, CNR, Milano, Italy

#78, 10:30 – 11:00 High order harmonic generation in solid argon, GEORGES NDABASHIMIYE, DAVID A. REIS, AND SHAMBHU GHIMIRE, We report on comparisons of high-order harmonic generation in solid argon with the atomic response in a dilute argon gas. The harmonic spectrum in the solid exhibits a secondary plateau and a subsequent cut-off extending beyond the gas phase cut-off at the peak intensity of 1.8x1013W/cm2. These observations point to solid-state effects beyond single-band coherent Bloch oscillations in strongly-driven periodic media.

#79, 11:00 – 11:15 Linking high harmonics from gases and solids, G. VAMPA, T. J. HAMMOND, N. THIRÉ, B. E. SCHMIDT, F. LÉGARÉ, C. R. MCDONALD, T. BRABEC, AND P. B. CORKUM, In the generation of high harmonics from a ZnO crystal we find a “generalized recollision” between the electron and the hole to dominate the emission. Further, we report on high harmonic generation from GaN, quartz and silicon. The generation process is extremely sensitive to perturbing fields and we suggest using this sensitivity to image time-dependent fields in circuits and nanoplasmonic devices. Finally, we develop a method to reconstruct the material’s momentum-dependent bandgap by decoding this information from the spectral phase of the harmonics. This all-optical method can be applied when photoelectrons are not accessible, such as in high-pressure physics experiments.

#80, 11:15 – 11:30 High harmonic generation from Bloch electrons in solids, MENGXI WU, SHAMBHU GHIMIRE, DAVID A. REIS, KENNETH J. SCHAFER, AND METTE B. GAARDE, We study the generation of high harmonic radiation by Bloch electrons in a model transparent solid driven by a strong mid-infrared (MIR) laser field. We solve the single-electron time-dependent Schrödinger equation (TDSE) using a velocity-gauge method. The resulting harmonic spectrum exhibits a primary plateau, due to the coupling of the valence band to the first conduction band, with a cutoff energy that scales linearly with field strength and laser wavelength.

#81, 11:30 – 11:45 Ultrafast semi-metallization transition in quartz and sapphire induced by strong few-cycle optical field, OJOON KWON, TIM PAASCH-COLBERG, VADYM APALKOV, FERENC KRAUSZ, MARK I. STOCKMAN, AND D. KIM, We demonstrate that quartz and sapphire undergo an ultrafast semi-metallization transition induced by strong few-cycle optical pulses, allowing current to flow within a femtosecond time interval. The similarity in response of both materials, despite the significant differences in their physical properties, confirms a physical picture of formation of localized Wannier-Stark states. This study suggests that optical-field-induced semi-metallization offers a means of ultrafast control of dielectric media and currents in them, opening up the doors to further developments.


Chair: André Staudte, NRC Ottawa, Canada

  • Stefan Pabst
  • Matthias Kübel-Schwarz
  • Johann Förster
  • Igor Litvinyuk
  • Allan Johnson

#82, 12:15 – 12:30 Creating coherent hole wave packets with strong-field pulses, STEFAN PABST AND HANS JAKOB WÖRNER, A new approach is identified that can generate highly coherent hole wave packets with multi-cycle strong-field pulses and stands in contrast to the usual idea of making the ionizing pulse as short as possible. The effect is demonstrated in atomic xenon with a spin-orbit wave packet involving the 5p3/2 -1 and 5p1/2 -1 ionic states.

#83, 12:30 – 12:45 Controlling and Tracing Bond Rearrangements in Hydrocarbons with Few-Cycle Laser Pulses, M. KÜBEL-SCHWARZ, R. SIEMERING, C. BURGER, H. LI, NORA G. KLING, A.S. ALNASER, K.J. BETSCH, J. SCHMIDT, U. KLEINEBERG, I. BEN-ITZHAK, R. MOSHAMMER, R. DE VIVIE-RIEDLE, AND M.F. KLING, In this work, strongfield control of photochemical reactions is combined with Coulomb explosion imaging (CEI) using a reaction microscope. Structural rearrangements in hydrocarbons are induced by phase-controlled few-cycle laser pulses, where the direction of the bound-nuclei motion is steered by the carrier-envelope phase of the driving laser pulse. Quantum mechanical calculations reveal that the laser waveform creates a superposition of vibrational modes that leads to a preferential direction in the hydrogen migration. The temporal evolution of the hydrogen migration is monitored experimentally by CEI in up to four ionic fragments, providing a benchmark for the calculated wavepacket dynamics.

#84, 12:45 – 13:00 Geometry-Dependent Ionization of the Ammonia Molecule and its Application to the Creation and Imaging of Nuclear Wave Packets, JOHANN FÖRSTER AND ALEJANDRO SAENZ, We investigate the ionization behavior of the ammonia molecule as a function of the inversion coordinate (umbrella motion). Different approaches for obtaining the ionization yield are compared, all of them showing a strong dependence of the ionization yield on the inversion coordinate, especially at long wavelengths (above 800 nm). We show how this effect can be exploited to create and probe a nuclear wave packet in neutral ammonia. Furthermore, we propose dedicated experiments to image this motion by measuring the ionization yield or high-harmonic spectra.

#85, 13:00 – 13:15 Effect of Nuclear Mass in Strong-Field Ionization of Hydrogen Molecules and Dissociation of Hydrogen Molecular Ions, IGOR V. LITVINYUK, XIAOSHAN WANG, HAN XU, D. KIELPINSKI, R.T. SANG, We measure isotope effect in strong-field ionization and dissociation of molecular hydrogen using a mixedgas target in a Reaction Microscope (REMI). We compare experimental results with theoretical predictions.

#86, 13:15 – 13:30 High Harmonic Spectroscopy of Substituted Benzenes with a mid-IR source, ALLAN S JOHNSON, FELICITY MCGRATH, MARTA CASTILLEJO, PETER HAWKINS, LUKAS MISEIKIS, THOMAS SIEGEL, EMMA SIMPSON, CHRISTIAN STRÜBER, RICARDO TORRES, DAVID WOOD, DANE R AUSTIN, AND JONATHAN P MARANGOS, We present a comparative study of the high harmonic spectrum of benzene and various substituted benzenes using the idler of an OPA centered at 1.8 microns. We find qualitative differences between the high harmonic spectra of the various organic molecules, and by using benzene as a reference perform comparative studies. Differences are consistent with contributions from multiple electronic states in fluorobenzene, and rapid nuclear motion in methyl-substituted groups.