Bulletin of the American Physical Society
38th Annual Meeting of the Division of Atomic, Molecular, and Optical Physics
Volume 52, Number 7
Tuesday–Saturday, June 5–9, 2007; Calgary, Alberta, Canada
Session G3: Attosecond Science: The Next Frontier |
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Chair: A. Bandrauk, University of Sherbrooke Room: TELUS Convention Centre Glen 201-203 |
Thursday, June 7, 2007 8:00AM - 8:36AM |
G3.00001: Probing proton dynamics in molecules on an attosecond timescale Invited Speaker: A new technique for probing the ultrafast structural rearrangements of light molecules following ionization was demonstrated by our group earlier this year. This technique, termed PACER (\textbf{p}robing \textbf{a}ttosecond \textbf{d}ynamics by \textbf{c}hirp \textbf{e}ncoded \textbf{r}ecollision), interrogates the motion of intramolecular nuclei following ionization via the process of high-harmonic generation (HHG). The strength of harmonic emission on return of the continuum electron wavepacket is weaker the more nuclear motion has occurred in the short time window since ionization. Moreover, since different harmonic orders are emitted at different times, dynamical information is gained by simply recording an harmonic spectrum and examining the change in signal as a function of order (which maps directly to time). Previously the nuclear dynamics of H$_{2}^{+}$ and D$_{2}^{+}$ were reliably determined at a temporal resolution limited by the difference in emission time of successive harmonic orders (roughly 100 as). The time window accessed in the measurement was 0.9 -- 1.5 fs following ionization. Enlargement of this time window would be a valuable extension to the PACER technique. To this end, we have now performed a PACER measurement in H$_{2}$ and D$_{2}$ at longer pump wavelengths (increasing the average electron return time). This work was conducted at the Advanced Laser Light Source facility, using a HE-TOPAS system producing 110 fs pulses in the mid-IR. We observed multiple harmonic orders at pump wavelengths of 1300 nm and 1450 nm using on-target intensities of $<$ 1 x 10$^{14}$ Wcm$^{-2}$. Data at the two pump wavelengths was found to be in qualitative agreement with the known nuclear dynamics of the H$_{2}^{+}$ and D$_{2}^{+ }$ions to a time 2.1 fs after ionisation. Extension of the time window accessed by the PACER measurement is therefore promising, however, at the pulse durations employed we expect partial alignment of the molecules during the pulse, and therefore the effect of two-centre interference must be carefully examined. [Preview Abstract] |
Thursday, June 7, 2007 8:36AM - 9:12AM |
G3.00002: Coulomb and polarization effects in dynamic imaging with strong laser fields Invited Speaker: Interaction of few-cycle intense infrared laser pulses and attosecond XUV pulses with atoms and molecules opens new avenues for imaging electronic dynamics and molecular structures with sub-Angstrom spatial and sub-femtosecond temporal resolution. These approaches are based on either (i) photo-ionization by an attosecond pulse in the presence of a strong IR field or (ii) on laser-field driven electron recollision with its parent molecule following strong-field ionization of the molecule. Information about electronic dynamics and molecular structures can be recorded either in photoelectron spectra or in the high-frequency radiation emitted during electron recollision with the parent ion. The combination of high temporal and spatial resolution does not come for free. In all approaches, strong laser field is present during the interaction, affecting dynamics of both bound and continuum electrons in a complex way. Quantitative analysis of strong-field approaches requires understanding of both laser-induced polarization effects (bound dynamics) and interplay of ionic potential and strong laser field in the electron motion in the continuum. In this talk I will describe theoretical approaches to analyzing these effects and show how they manifest themselves in photo-electron spectra and in high-frequency emission spectra. In particular, I will describe how electron localization affects spectra of high-frequency emission and how attosecond dynamics of laser-induced polarization can be visualized in photo-electron spectra. Finally, I will analyze scattering phase-shifts and modifications in the photo-electron spectra due to the interplay of the Coulomb field of the parent ion and the strong laser field. This analysis provides foundation and limitations for simple recipes of reconstructing molecular structures in strong-field approaches. [Preview Abstract] |
Thursday, June 7, 2007 9:12AM - 9:48AM |
G3.00003: Two-electron atomic response on the attosecond time-scale Invited Speaker: Over the past decade or so we have developed methods [1] that now allow accurate two-electron solutions of the full-dimensionality Time-dependent Schroedinger equation to be constructed and temporally followed as they evolve on the attosecond time-scale. A survey of the achievements of this work will be presented. These range from the prediction of Double Above Threshold Ionisation [2] brought about by intense light in the EUV; through the prediction of uni-lateral double ionization by longer wavelength light [3] to the prediction of a surprising energy-partition between the two electrons ionizing as a result of a recollision process at Ti:sapphire wavelengths [4]. The talk will go on to describe new theoretical investigations pertinent to the imminently-available XFEL sources and also to FEL and IR lasers in combination. \newline References: \newline [1] Smyth ES, Parker JS and Taylor KT Comput Phys Commun 114 1 (1998) \newline [2] Parker JS, Moore LR, Meharg KJ, Dundas D and Taylor KT. J Phys B: Atom Molec Opt Phys 34 L69 (2001) \newline [3] Taylor KT, Parker JS, Dundas D, Smyth ES and Vivirito S Laser Physics 9 98 (1999) \newline [4] Parker JS, Doherty BJS, Taylor KT, Schultz KD, Blaga CI and DiMauro LF Phys Rev Lett 96 133001 (2006) [Preview Abstract] |
Thursday, June 7, 2007 9:48AM - 10:24AM |
G3.00004: Generation and control of attosecond pulses. Invited Speaker: Generating attosecond (1 as = 10$^{-18}$ s) pulses both as trains of pulses or as isolated sub-femtosecond pulses is now possible with high order harmonic generation combined with temporal confinement techniques. As this source gets available, diverse applications of these pulses are emerging. To fulfil the requirements imposed by these applications (tunability, bandwidth, pulse duration and so on), the attosecond pulses have to be controlled. During this talk I will present how manipulating the polarization of an intense short pulse allows us to generate isolated attosecond pulses (or short burst of attosecond pulses) and what are the required characteristics for the fundamental pulse. I will describe the opportunities offered by this polarization gating approach in terms of control of the attosecond pulses, especially for their tunability, duration and bandwidth of the attosecond pulse or pulse train. Using these pulses for performing time resolved experiment with attosecond accuracy is also a challenge and I will present some tools that we developed for high resolution pump-probe experiments like for instance a simple ultra-stable interferometer that offers a temporal resolution of few as. [Preview Abstract] |
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