Bulletin of the American Physical Society
2006 37th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 16–20, 2006; Knoxville, TN
Session V2: Attosecond Physics |
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Chair: Louis DiMauro, Ohio State University Room: Knoxville Convention Center Ballroom EFG |
Friday, May 19, 2006 1:30PM - 2:06PM |
V2.00001: Generation and manipulation of attosecond light pulses Invited Speaker: Attosecond pulses of light can be generated in the extremely non-linear interactions between an ultrashort, intense laser pulse and a gas of atoms, via the process of high harmonic generation [1,2]. In one approach, a number of odd harmonics of rougly equal strength are combined to form a train of sub-femtosecond pulses. If the harmonics are locked in phase to each other, the train will consist of the emission of one attosecond pulse every half cycle of the driving laser field [1,3]. It is in general not trivial to ensure that the harmonics are phase-locked as they are generated with intrinsically different phases. These phases originate in the strong field dynamics of the light-matter interaction [4].\\ \\ We will discuss different ways of generating and manipulating attosecond pulses via high harmonic generation. We will show how the harmonics can be phase-locked and better synchronized so as to form optimal pulse trains [3]. We will also show that it is possible to generate trains of pulses separated by a full laser cycle, by combining the driving laser field with its second harmonic [5]. The strong field continuum dynamics driven by the two-color field is very different from that of the one-color field and varies strongly with the delay between the two laser fields [6]. \\ \\ (1) P. M. Paul {\it et al}, Science {\bf 292}, 1689 (2001).\\ (2) M. Hentschel {\it et al}, Nature {\bf 414}, 509 (2001).\\ (3) R. Lopez-Martens {\it et al}, PRL {\bf 94}, 033001 (2005).\\ (4) P. Antoine, A. L'Huillier, and M. Lewenstein, PRL {\bf 77}, 1234 (1996).\\ (5) J. Mauritsson {\it et al}, in preparation (2006).\\ (6) M. B. Gaarde {\it et al}, in preparation (2006). [Preview Abstract] |
Friday, May 19, 2006 2:06PM - 2:42PM |
V2.00002: Attosecond double-slit experiment Invited Speaker: Gerhard G. Paulus A novel application of intense few-cycle laser pulses is demonstrated. Taking advantage of the unique properties of phase-controlled few-cycle pulses, a close analogue of the double-slit scheme has been realized in the time domain. It is distinguished from conventional schemes by a combination of characteristics: {\it (i)} The double slit is realized not in position-momentum but in time-energy domain. {\it (ii)} The role of the slits is played by windows in time of attosecond duration. {\it (iii)} These ``slits'' can be opened or closed by changing the temporal evolution of the field of a few-cycle laser pulse. {\it (iv)} At any given time there is only a single electron in the double-slit arrangement leading to the presence or absence of interference depending on emission direction. The experimental scheme is of similar plainness as the one of the double slit: Few-cycle laser pulses of given absolute phase are focused into a field-free vacuum chamber and intersect a beam of Argon atoms. Photoelectrons emitted parallel to the axis of polarization are detected by two electron detectors located at a distance of about 400\,mm at either side of the focus. The time-of-flight is used to determine the energy of the electrons. The photoelectron spectra exhibit a fringe pattern whose visibility depends on the temporal evolution of the pulses as well as on the emission direction. [Preview Abstract] |
Friday, May 19, 2006 2:42PM - 3:18PM |
V2.00003: Atomic Dynamics on the Attoscecond Scale Invited Speaker: Advances in ultrashort-pulse technology have made it possible to generate electromagnetic pulses with duration $\tau_P$ as short as few hundred attoseconds. $\tau_P$ thus approaches the orbital period $\tau_0$ of a classical atomic electron. This advance holds the promise to map out electronic dynamics inside atoms in real time. It poses a considerable challenge to theory to identify observables and novel information that can be accessed and mapped out by attosecond pulses. We will review recent progress with the help of a few examples including time- resolved atomic resonances and double ionization of helium. [Preview Abstract] |
Friday, May 19, 2006 3:18PM - 3:54PM |
V2.00004: Measuring the Electronic Structure of Molecules Using High Harmonic Emission Invited Speaker: Electronic structure is commonly measured by photoelectron spectroscopy, in which short wavelength radiation detaches an electron from a molecule. The kinetic energy of the electron labels the orbital from which it came. The angle of the electron relative to the polarization direction gives further information about the orbital through a partial wave expansion. \par When a molecule is exposed to an intense femtosecond laser field, selective ionization of the highest orbital occurs, but the electron contains no molecular information because its subsequent motion is completely dominated by the laser field. However, there is a very small probability that the electron will recombine with the parent ion, and liberate its kinetic energy into an xuv photon. This process is known as high harmonic generation, and produces a coherent, collimated xuv beam that is composed of a train of attosecond pulses. It can be viewed as time-reversed photoelectron spectroscopy. The xuv spectrum contains both amplitude and phase information about the ionized orbital. \par I will show how we can reconstruct the shape of a single orbital from nitrogen molecules. This technique can also be used to observe dynamical changes to the electronic structure during chemical reactions using pump-probe techniques with a time resolution of 5-30 fs. Because the high harmonic process occurs within a fraction of an optical cycle, and because the attosecond bursts are chirped in frequency, it is possible to map attosecond electron wave packet motion onto the spectrum. Thus attosecond electron motion may be visible to this process. [Preview Abstract] |
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