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 K1: Attosecond and High Energy Density Physics |
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Sponsoring Units: DLS Chair: Zenghu Chang, Kansas State University Room: Burnham Yates Conference Center Ballroom I |
Friday, May 20, 2005 10:30AM - 11:06AM |
K1.00001: Dynamics of Attosecond Electron Wave Packets Invited Speaker: We present results from some of the first experimental studies of attosecond electron wave packets created via the absorption of ultrashort extreme ultraviolet (XUV) light pulses [1]. The pulses, made via high harmonic generation, form an attosecond pulse train (APT) whose properties we can manipulate by a combination of spatial and spectral filtering. For instance, we show that on-target attosecond pulses of 170 as duration, which is close to the single cycle limit, can be produced [2]. The electron wave packets created when such an APT is used to ionize an atom are different from the tunneling wave packets familiar from strong field ionization. We show how to measure the dynamics of these wave packets in a strong infrared (IR) field, where the absorption of energy above the ionization threshold is found to depend strongly on the APT-IR delay [3]. We also demonstrate that altering the properties of the initial electron wave packet by manipulating the APT changes the subsequent continuum electron dynamics. Finally, we show how the phase of a longer, femtosecond electron wave packet can be modulated by a moderately strong IR pulse with duration comparable to or shorter than that of the electron wave packet. This experiment reveals how the normal ponderomotive shift of an XUV ionization event is modified when the IR pulse is shorter than the XUV pulse.\newline [1] The experiments were done at Lund Institute of Technology, Sweden.\newline [2] R. López-Martens, \textit{et al.}, Phys. Rev. Lett. \textbf{94}, 033001 (2005)\newline [3] P. Johnsson, \textit{et al.}, submitted to Phys. Rev. Lett. [Preview Abstract] |
Friday, May 20, 2005 11:06AM - 11:42AM |
K1.00002: Molecules in Intense Laser Fields and Electron-Nuclear Dynamics form Femto Attosecond Time Scales Invited Speaker: The photophysic of atoms with high intensity lasers is dominated by the process of electron ionization and laser induced electron recollision, with the parent ion [1]. The recollision time can be tuned as a function of laser frequency to span few femtoseconds (fs) (10$^{-15}$sec) to attoseconds (asec) (10$^{-18}$sec) times. Molecules introduce a new complexity, nuclear time scales which for protons occur in the region 8-10 fs. In intense fields, dissociative ionization, allows for molecules to reach large internuclear distances where Charge Resonance Enhanced Ionization (CREI) occurs thus increasing by several orders of magnitude ionization rates [2-3]. During recollision in molecules, electrons will undergo Coulomb refocusing. Both nonlinear effects, enhanced ionization and refocusing of the recollision electron leads to new efficient sources of high order harmonic generation (HOHG) from symmetric and nonsymmetric molecules [4]. Molecular electron recollision can lead to Laser Induced Electron Diffraction (LIED) [5] and molecular orbital tomography by inversion of HOHG spectra [6]. Finally, using asec pulses synthetized from HOHG spectra [7], one can create coherent molecular electron wavepackets. These are localized on asec time scales on various nuclei. Methods of detection and characterization of such electron wavepackets in molecules will be proposed from numerical solutions of the time-dependent Schroedinger equation for the molecular ion, [8]. \newline \newline \textbf{REFERENCES:} \newline [1] P.B. Corkum, Phys. Rev. Lett. \textbf{71}, 1994 (1993). \newline [2] T. Zuo, A.D. Bandrauk, Phys. Rev. \textbf{A52}, 2511 (1995). \newline [3] T. Seideman, M.Y. Ivanov, P.B. Corkum, Phys. Rev. Lett\textbf{. 75,} 2819 (1995). \newline [4] G. Lagmago Kamta, A.D. Bandrauk, P.B. Corkum, Phys. Rev. Lett. (submitted 2005). \newline [5] T. Zuo, A.D. Bandrauk, P.B. Corkum, Chem. Phys. Lett. \textbf{259}, 313 (1996). \newline [6] J. Itatani et al., Nature \textbf{ 432, }867 (2004). \newline [7] A.B. Yedder et al., Phys. Rev. \textbf{A69}, 041802 (2004). \newline [8] G. Yudin et al., (submitted to Phys. Rev. Lett. 2005). [Preview Abstract] |
Friday, May 20, 2005 11:42AM - 12:18PM |
K1.00003: Attosecond nonlinear optics Invited Speaker: Attosecond pulse generation was realized through high harmonic generation and has made it possible to observe attosecond phenomena [1]. Another interesting application of attosecond pulses is nonlinear optics in the XUV and soft x-ray region However, the pulse energy of attosecond pulses available so far is not intense enough to cause nonlinear optical phenomena. In this work, intense attosecond pulses were nonadiabatically generated by using 8-fs blue laser pulses. We present the observation of the above-threshold ionization (ATI) of rare gases by XUV pulses . [2] and demonstrate the autocorrelation measurement of isolated attosecond pulses. 8-fs blue laser pulses were generated by broadband frequency doubling (BFD) of Ti:sapphire laser pulses (photon energy 1.55 eV). BFD enables us to shorten the pulse duration with high efficiency. The blue laser induces relatively larger nonlinear dipole moment. At the same time, high harmonic pulses rises rapidly nonadiabatically and the field ionization shuts off the harmonic generation, producing intense isolated attosecond pulses. The ninth harmonic pulses of the blue laser (photon energy 27.9 eV) were generated by focusing the blue laser pulses into Ar gas and were characterized by the autocorrelation technique, in which the two-photon ATI process in helium atoms was used. The ATI process was confirmed by observing photoelectrons ejected from helium atoms, recorded as a function of the relative delay time of two high harmonic pulses to form an autocorrelation trace. The shortest pulse duration was 950 as with pulse energy of 2 nJ [3]. References .[1] E. Goulielmakis et al., Science 305, 1267 (2004)., [2] N. Miyamoto, M. Kamei, D. Yoshitomi, T.Kanai,T,Sekikawa, T. Nakajima, and S. Watanabe, Phys. Rev. Lett. 93, 083903 (2004). [3] T. Sekikawa, A. Kosuge, T. Kanai, and S. Watanabe, Nature ,432,604 (2004). [Preview Abstract] |
Friday, May 20, 2005 12:18PM - 12:54PM |
K1.00004: Ultrashort-Pulse-Duration Laser and Charged-Particle Beams from High-Intensity Laser-Plasma Interactions Invited Speaker: Discussed are novel approaches to using high-intensity laser-plasma interactions to generate ultrashort duration (femtosecond or attosecond) pulses of energetic (keV---MeV) x-ray and charged-particle beams. These include (1) Thomson scattering of laser-accelerated electron beam by a laser wiggler, (2) Ultrashort-duration betatron emission from electron beams by a laser-driven plasma wiggler, (3) pulse-compression of laser light in plasmas via laser-induced index-of-refraction modification, (4) ponderomotive deflection of a laser-accelerated electron beam by a short-pulse high-intensity laser pulse, (5) laser-driven ion acceleration. Comparisons between theoretical predictions and experimental results will also be discussed. [Preview Abstract] |
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