Bulletin of the American Physical Society
41st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 55, Number 5
Tuesday–Saturday, May 25–29, 2010; Houston, Texas
Session L6: Attosecond Pulses: Generation, Characterization and Utilization |
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Chair: Gilles Doumy, The Ohio State University Room: Arboretum IV-V |
Thursday, May 27, 2010 2:00PM - 2:12PM |
L6.00001: Isolated Attosecond Pulses Generated Directly from a Femtosecond Chirped Pulse Amplifier Yi Wu, Steve Gilbertson, Sabih Khan, Michael Chini, Kun Zhao, Ximao Feng, Zenghu Chang Using a generalized version of double optical gating, we produced single isolated attosecond pulses with 2 mJ, 25 fs driving lasers directly from a multi-pass Chirped Pulse Amplifier. Through attosecond streaking, we characterized isolated 160 attosecond pulses with 170 pJ pulse energy. By varying the CE phase of the 25 fs driving lasers, the XUV spectrum exhibited a unique 2$\pi $ periodicity indicating the robustness of the sub-cycle gating. Spectral shaping inside the amplifier is implemented to reduce the laser pulse duration for improving the conversion efficiency from NIR to XUV photons. The GDOG technique will allow many labs to generate single attosecond pulses of XUV photons directly from an amplifier which should help further expand the field of attosecond science. [Preview Abstract] |
Thursday, May 27, 2010 2:12PM - 2:24PM |
L6.00002: Generation of phase-matched 20-25eV single attosecond pulse by double optical gating Shouyuan Chen, Qi Zhang, Kun Zhao, Michael Chini, Zenghu Chang Intensive single attosecond pulses near the ionization threshold of noble gas atoms and many molecules are desired to study nonlinear dynamics in these systems. Using double optical gating and Xenon gas target, we successfully produced high order harmonics with continuum spectra in this energy range with an 8 fs driving laser pulse. By scanning the CE phase of the driving laser, the XUV spectrum exhibited 2$\pi $ periodicity, which indicates the generation of the single attosecond pulse. The continuum spectrum supports a Fourier transform limited pulse duration of 420 as. The relation between the pressure of the gas target and harmonic yield shows single attosecond pulse generation in this regime is absorption-limited. [Preview Abstract] |
Thursday, May 27, 2010 2:24PM - 2:36PM |
L6.00003: OPTICAL: a new method for characterizing ultra-broadband isolated attosecond pulses Michael Chini, Steve Gilbertson, Sabih Khan, Zenghu Chang So far, the measurement of isolated attosecond pulses has been performed with the FROG-CRAB technique based on attosecond streaking. However, it is only applicable to pulses whose spectral width is much less the center photon energy. We show that the spectral phase of isolated attosecond pulses can instead be measured using spectral interference from laser-dressed photoemission signals, a technique we term OPTICAL (One Photon Transition Interference for Characterizing Attosecond Lasers), and we demonstrate that the technique can characterize broadband, very short attosecond pulses. Unlike streaking-based techniques, it requires only modest dressing laser intensities and is not limited by the attosecond spectrum bandwidth. [Preview Abstract] |
Thursday, May 27, 2010 2:36PM - 2:48PM |
L6.00004: Magnetic-bottle electron spectrometer for measuring 25 as pulses Qi Zhang, Kun Zhao, Zenghu Chang The duration of attosecond pulses is usually retrieved from streaked photoelectron energy spectra produced by XUV pulses. To resolve pre- or post-pulses, the resolution of the spectrometer should be better than 0.5 eV. A magnetic-bottle electron time-of-flight spectrometer (MBEES) is under development for such measurements. Simion simulation of the time of flight of the photoelectron in MBEES showed that in order to achieve the 0.5 eV resolution, a temporal resolution of 250 ps or less is required for the microchannel plate (MCP) and the data acquisition system (DAQ). Experimentally, the resolution was measured with 3$^{rd}$ harmonic photons produced by a 25fs, 800nm laser in air. The nominal resolutions of the MCP and the detection system (MCP plus DAQ) were found to be 170 and 200 ps, respectively. This result indicated that the requirement to retrieve a 25 as pulse can be met by our MBEES including MCP and DAQ. [Preview Abstract] |
Thursday, May 27, 2010 2:48PM - 3:00PM |
L6.00005: Using Ion-imaging to Measure Gouy Phase Shift and Wavefront Distortions for Attosecond Pump-Probe Experiments Niranjan Shivaram, Lei Xu, Adam Roberts, Arvinder Sandhu In typical attosecond experiments using extreme-ultraviolet (XUV) pulses produced by high harmonic generation, an infrared (IR)/visible laser pulse is used as a time delayed pump or probe. Such experiments are very sensitive to the phase between XUV and IR fields and it is of crucial importance that the phase difference remain constant over the entire region of observation. However, in practice, Gouy phase shift and wave-front distortions are inherently present in most experimental geometries which lead to phase ambiguities and it is thus important to measure them accurately. We present here a method for direct measurement of Gouy phase shift and wave-front distortions in the focus using two-pulse ionization of Xe. These quantities are measured for a TEM$_{00}$ mode reflected from a mirror with a hole using 2-D imaging of Xe ions produced in the focal region by a superposition of two IR pulses and for IR+XUV superposition. The resolution in this measurement is in principle limited only by the pixel size of the detector. [Preview Abstract] |
Thursday, May 27, 2010 3:00PM - 3:12PM |
L6.00006: Attosecond pulses from long wavelength sources: characterization and utilization Jonathan Wheeler, Razvan Chirla, Christoph Roedig, Stephen Schoun, Gilles Doumy, Louis DiMauro, Pierre Agostini We demonstrate the generation of attosecond pulse trains (APTs) from high harmonics of Ti:Sapphire (800 nm) and OPA-produced MidIR (1300 -- 2200 nm) fundamental driving wavelengths in a new apparatus capable of performing typical pump/probe experiments between a laser pulse of the fundamental and its harmonic APT. Both beams are overlapped spatially and temporally in a magnetic bottle electron time-of-flight spectrometer allowing for measurements with high collection efficiency and energy resolution for the photoelectrons produced. We are further characterizing such features as spectral amplitude and phase of the attosecond harmonic bursts produced at longer fundamental wavelengths while also utilizing them in imaging and photo-ionization studies. Current progress and experimental results will be presented. [Preview Abstract] |
Thursday, May 27, 2010 3:12PM - 3:24PM |
L6.00007: Intense sub-2 optical cycle laser pulses at 1.8 micron for high harmonic generation Francois Legare, Bruno E. Schmidt, Pierre B\'ejot, Mathieu Gigu\`ere, Andrew D. Shiner, Carlos Trallero-Herrero, \'Eric Bisson, Jerome Kasparian, Jean-Pierre Wolf, David M. Villeneuve, Jean-Claude Kieffer, Paul B. Corkum Shortening of attosecond pulse duration utilizing high harmonic generation (HHG) requires access to few cycle pulses in the infrared spectral range because the cut-off shifts towards higher photon energies proportional to the square of the driving field wavelength. Furthermore, the ability of performing time-resolved molecular orbital tomography of polyatomic molecules will benefit from longer wavelengths compared to 800 nm because of their low ionization potential. A simple scheme for generating 0.4 mJ 11.5 fs pulses at 1.8 $\mu $m is presented. Optical parametric amplified pulses were spectrally broadened in a hollow-core fiber and subsequently compressed by utilizing linear propagation through bulk material. The physical origin of the pulse compression scheme will be confirmed with numerical simulations of nonlinear propagation in the hollow-core fiber. Finally, high harmonic generation of noble gas atoms will be reported. [Preview Abstract] |
Thursday, May 27, 2010 3:24PM - 3:36PM |
L6.00008: Two-photon double ionization of helium by chirped attosecond XUV pulses R. Pazourek, S. Nagele, G. Schoissengeier, E. Persson, J. Burgd\"orfer, B.I. Schneider, L.A. Collins, J. Feist Above a photon energy of 54.4 eV, two-photon double ionization (TPDI) of helium occurs sequentially in two temporally separated steps, where each electron independently absorbs one photon. The temporal structure of this process can be controlled by the use of chirped laser pulses, in which the instantaneous frequency changes with time. The photoelectron energies therefore depend on the time of photoabsorption. For photon energies well above the sequential threshold, this leads to a shift of the sequential peaks in the electron spectra (cf. [1]). In addition, interference patterns become visible. For photon energies near the sequential threshold even the totally integrated TPDI yield becomes a function of the chirp, as the sign and strength of the chirp shifts the onset of sequentiality. We perform fully correlated \emph{ab initio} calculations to investigate the influence of different chirp parameters on the spectral and angular distributions of the ejected electrons. $[1]$ T.G.~Lee et al., \emph{PRA} \textbf{79}, 053420 (2009) [Preview Abstract] |
Thursday, May 27, 2010 3:36PM - 3:48PM |
L6.00009: Coulomb-Laser Coupling Effects in Attosecond Time-Resolved Photoelectron Spectra Chang-hua Zhang, Uwe Thumm Photoionization by attosecond (as) extreme ultraviolet pulses into the laser-dressed continuum of the ionized atom is commonly approximated in strong-field approximation, i.e., by neglecting the Coulomb interaction between the emitted photoelectron (PE) and the residual ion [1]. By solving the time-dependent Sch\"{o}dinger (TDSE) equation, we find a temporal shift in the streaked photoemission spectra that is due to the Coulomb-laser coupling in the final-state and reaches in excess of 50~as at small photoelectron kinetic energies. The examination of this shift enables i) the experimental scrutiny of effects that are due to the combined action of Coulomb and laser forces on the PE and ii) tests of theoretical approximations to the exact Coulomb-Volkov state of the PE. Within an eikonal approximation, we derive a simple analytical expression for this coupling effect and assess its accuracy by comparison with full TDSE numerical results.\\[4pt] [1] e.g., Zhang and Thumm, PRL 102, 123601 (2009).\\[0pt] [2] Submitted to PRL. [Preview Abstract] |
Thursday, May 27, 2010 3:48PM - 4:00PM |
L6.00010: Two-electron time-delay interference in atomic double ionization by attosecond pulses Alicia Palacios, Thomas N. Rescigno, C. William McCurdy Two-color two-photon atomic double ionization with subfemtosecond UV pulses is explored in the particular case that laser parameters are chosen such that the sequential two-color process dominates, and one electron is ejected by each pulse, emerging with overlapping energy distributions. Benchmark-level time-dependent ab initio numerical calculations for the case of a helium target show that a prominent interference pattern in the joint energy distribution of the ejected electrons is observed for short enough pulses. This pattern: (1) arises from electron indistinguishability,(2) depends on their spin coupling, (3) is a measure of the time delay between pulses and (4) occurs in two-photon double ionization when it is necessarily dominated by sequential ionization by the two pulses. Additionally, even if for very short time delays these interference oscillations are visible, suggesting sequential ejection, the associated angular distributions show important differences from those expected from a pure sequential mechanism. [Preview Abstract] |
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