Bulletin of the American Physical Society
2005 36th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 17–21, 2005; Lincoln, Nebraska
Session F2: Ultra Short Pulse Physics (Attosecond, Femtosecond) |
Hide Abstracts |
Chair: Anthony F. Starace, University of Nebraska-Lincoln Room: Burnham Yates Conference Center Ballroom II |
Thursday, May 19, 2005 10:30AM - 11:06AM |
F2.00001: Attosecond pulse train control of strong field processes Invited Speaker: Attosecond pulse trains (APTs) are a natural tool for studying and controlling strong field processes driven by an infrared (IR) laser. This control originates in the short duration of the individual pulses in the train, and their periodicity, which is half the IR laser period. This allows us to fix the ionization to a particular point in each IR half cycle and to select which quantum paths are available for the ionized electron to follow. This splitting of responsibilities: the APT drives the ionization and the IR laser drives the continuum dynamics, is, we will argue, a valuable new paradigm in strong field physics. In this talk we present calculations that demonstrate these principles by manipulating the time-frequency properties of high order harmonics at the single atom level. Solutions of the time-dependent Schr\"{o}dinger equation for a helium atom subject to a combined APT/IR field show that both the yield and the coherence properties of the harmonics are improved when the APT is timed to launch the electron along the shortest quantum path, which exhibits a slow phase dependence and therefore gives rise to well behaved harmonics. We have also carried out non-adiabatic phase matching calculations which demonstrate that there are phase matching conditions where the single atom quantum path selection has a very large impact on the macroscopic harmonic signal. Finally, we examine how the electron wave packet created by APT-driven ionization gains energy from a strong IR laser field. In particular, we show that both the timing and the time-frequency characteristics of the APT influence the energy-resolved angular distributions of the ionized electrons. [Preview Abstract] |
Thursday, May 19, 2005 11:06AM - 11:42AM |
F2.00002: Dynamics of Multiple Ionization in Strong Laser Fields Invited Speaker: We will review recent experiments on multiple ionization of atoms by femtosecond laser pulses in the $10^{14}-10^{15} W/cm^2 $ regime. The dynamics of the multiple ionization process via rescattering is unravelled on a subfemtosecond time scale. This is achieved by imaging the momenta of electrons and ions in coincidence using the COLTRIMS technique. [Preview Abstract] |
Thursday, May 19, 2005 11:42AM - 12:18PM |
F2.00003: Attosecond Control and Spectroscopy of Electrons Invited Speaker: The generation of ever shorter pulses is a key to exploring the dynamic behavior of matter on ever shorter time scales. Over the past decade novel ultrafast optical technologies have pushed the duration of laser pulses close to its natural limit, to the wave cycle, which lasts about one femtosecond (1 fs = 10$^{-15}$ s) in the visible spectral range. Time-resolved measurements with these pulses are able to trace atomic motion in molecules and related chemical processes. However, electronic dynamics \textit{inside }atoms often evolve on an attosecond (1 as = 10$^{-18}$ s) timescale and require sub-femtosecond pulses for capturing them. This talk will review the recent generation, measurement and first applications of sub-femtosecond soft-X-ray pulses (near 100 eV). These X-ray pulses together with the few-cycle laser pulses used for their generation have opened the way to the development of a technique for attosecond sampling of electrons ejected from atoms. This is accomplished by probing electron emission with the oscillating electric field of the few-cycle laser pulse following an excitation of the atom by the synchronized sub-femtosecond X-ray pulse. Sampling the emission of photo electrons in this manner -- with an apparatus that may be regarded as an optical-field-driven ``streak camera'' -- allows time-resolved measurement of the X-ray pulse duration as well as of the laser field oscillations. Tracking the evolution of secondary (Auger) electron emission in addition to that of the primary (photo) electrons with the same system provides time-domain access to inner-shell atomic electron dynamics. Measurement of the duration of sub-fs X-ray pulses and their timing with respect to the few-cycle laser waves has opened the way to using this two-colour sampling system for taking ``snapshots'' of atomic electron dynamics with an exposure time of less than 1 femtosecond. From the recorded snapshots plasma formation by optical-field ionization and the decay of inner-shell atomic excitations has been reconstructed for the first time directly in the time domain. As a result, atomic dynamics can now be watched in slow-motion replay, with time dilated by $\approx $10$^{15}$. Microscopy in time (time-resolved spectroscopy) is now being extended into the sub-atomic domain and holds promise for breaking new grounds in the research of the microcosm. [Preview Abstract] |
Thursday, May 19, 2005 12:18PM - 12:54PM |
F2.00004: Imaging a Molecular Orbital Wave Function Using High Harmonic Emission Invited Speaker: Single-electron molecular orbital wave functions are mathematical constructs that are used to describe the multi-electron wave function of molecules. The highest lying orbitals are of particular interest since they are responsible for the chemical properties of molecules. To observe them change as molecular bonds are formed and broken is to observe the essence of chemistry. Yet single orbitals are difficult to observe experimentally --- until now impossible on the time scale of chemical reactions. We show that the full 3-dimensional structure of a single orbital can be imaged using a seemingly unlikely technique --- high harmonic generation from aligned molecules using intense femtosecond laser pulses. We show how the broadband harmonic spectra, measured for a series of molecular alignments, lead to a tomographic reconstruction of the single electron orbital wave function of dinitrogen. This leads to ontological discussions about the meaning of a wave function, particularly in a multielectron system. A non-ionizing femtosecond laser pulse creates a rotational wavepacket that causes periodic molecular alignment. A more intense pulse induces high harmonic emission from the aligned molecules. The recollision electron current pulse is characterized as it returns to a reference argon atom. Assuming that we know the shape of the 3p orbital of argon, we can determine the spectral phase and amplitude of the recollision current. The phase of the harmonic emission from nitrogen is referenced to the phase of argon by measuring the interference in a mixed target gas. The polarization of the emission is also recorded by polarimetry. All of these measurements lead to the reconstruction of the nitrogen sigma-g orbital shape. We also show that attosecond dynamics of an electron wave packet can be measured in the high harmonic spectrum. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700