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 K2: Attosecond Electron Physics |
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Chair: Markus Guehr, SLAC National Accelerator Laboratory Room: Imperial Center |
Thursday, May 27, 2010 10:30AM - 11:00AM |
K2.00001: Attosecond Spectral Interferometry and Quantum Control of Electron Dynamics Invited Speaker: The direct time-resolved observation of electron dynamics in atoms and molecules is a key goal of attosecond physics. To this end, several pioneering spectroscopic techniques have been conceived and experimentally demonstrated by a number of research groups in the past, including the optical streak camera in the gas phase and on surfaces of solids, tunneling spectroscopy, as well as recollision tomography and related methods. All these schemes, however, require strong laser fields for probing the dynamics and thus potentially distort the ``natural'' field-free energy-level structure and dynamic evolution of the system to be studied. In this talk, some novel spectroscopic routes and first experiments are presented that allow the measurement of coherent electron dynamics in field-free environments. The key idea is the usage of interferometric methods, e.g. realized by two interferometrically stable and time-delayed attosecond pulses. Combined with coincidence detection techniques (reaction microscopes, COLTRIMS), these interferometric methods will enable the attosecond time-resolved measurement of multi-electron correlation in atoms and molecules. In addition, experimental results for coherent control of electron dynamics will be presented. Also here, we focus on the low-intensity regime, where we directly control electronic quantum-path interference instead of quasi-classical trajectories that typically prevail at higher intensities. Multiphoton N/N+1 absorption-pathway interference is controlled by varying the carrier--envelope phase (CEP) of few-cycle light fields in a generalized Brumer-Shapiro control scheme. The results yield important conclusions for laser control with shaped ultrashort pulses, proving the necessity of CEP stabilization to exert full control over quantum systems. [Preview Abstract] |
Thursday, May 27, 2010 11:00AM - 11:30AM |
K2.00002: Probing and Controlling Electronic Dynamics on the Attosecond Scale Invited Speaker: With the advent of sub-femtosecond ultrashort XUV pulses and of phase-stabilized few-cycle IR pulses with sub-cycle time resolution, novel pathways have opened up for studying time-resolved electronic processes on the attosecond scale. These experimental advances pose challenges for theory: How do short pulses interact with matter? Which novel information can be extracted from such time-resolved spectroscopies that is difficult or even impossible to access in the spectral domain? In this talk, these issues will be addressed with the help of a few examples. Attosecond streaking allows a direct look at electronic correlations and rearrangement processes including the formation of shake-up states during photoionization. Photoemission from a tungsten surface reveals an attosecond time delay between conduction and core electrons and provides time-resolved information on electron transport and plasmon excitation near the surface. Attosecond pulses cannot only probe electronic dynamics but also actively control and manipulate the electronic dynamics. Examples include the modification of the angular distribution of two-electron emission by variation of the attosecond pulse duration and the control of the emission direction in molecular break-up by unidirectional attosecond pulse trains. [Preview Abstract] |
Thursday, May 27, 2010 11:30AM - 12:00PM |
K2.00003: Attosecond dynamics in simple molecular systems Invited Speaker: Isolated attosecond pulses have been used to excite and ionize H$_{2}$ and D$_{2}$ molecules. The interplay among the large variety of states of the neutral molecule and of the molecular ion that can be accessed, determines a complex dynamics that can be probed using a synchronized infrared field. A complete quantum mechanical calculation including nuclear and electronic wave-packets has been applied to interpret the experimental outcome. In the analysis particular attention will be devoted to the role of the doubly excited states of H$_{2}$/ D$_{2.}$ [Preview Abstract] |
Thursday, May 27, 2010 12:00PM - 12:30PM |
K2.00004: Generation of isolated attosecond pulses with double optical gating and electronic dynamics in molecules studied via attosecond pump-probe experiment Invited Speaker: Single isolated attosecond pulses are useful tools for studying electron dynamics. Previously, such as pulses can be generated by few cycle 5 fs driving lasers. It is still a technical challenge to reproduce daily such pulses. In order to allow longer driving laser pulses, two optical gating methods of polarization gating and two-color gating are combined. This approach is dubbed double optical gating. Due to less depletion of the ground state population by the leading edge of the field, this technique can produce isolated 250 as pulses using up to $\sim $25 fs driving laser pulses. Also, the supercontinuous spectra (28-620 eV) can in principle support a 16 as pulse duration, obtained from 8 fs driving lasers. Because of the relaxation on the driving laser requirements, more laboratories can enter the isolated attosecond pulse science field. Pump-probe experiments with such isolated attosecond pulses and IR pulses can provide quantitative information on electronic dynamics. In recent work, the photoelectron spectra of sulfur hexafluoride (SF$_{6})$ clearly indicates the precise shape of the IR driving pulse (1.5 eV), verifying that isolated $\sim $400 as pulses (93 eV) are achieved and these pulses produce an instantaneous inner valence ionization in the molecule. The pump-probe spectra of cation fragments resulting from double and triple ionization show 6-7 fs rise times (SF$_{4}^{2+}$, SF$_{3}^{2+}$, SF$_{2}^{2+}$ and S$^{2+})$ or decay times (SF$^{+}$ and S$^{+})$ times governed by the overlap of the IR and XUV pulses. A suppression or enhancement of certain fragmentation channels is tentatively interpreted as resulting from the IR laser exciting the initial cations to higher states that exhibit different decay channels. This type of pump-probe experiment with isolated attosecond pulses is powerful for the study of electronic dynamics as well as resulting nuclear fragmentation measurements. [Preview Abstract] |
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