http://www.kitp.ucsb.edu/online/atto_c06/ KITP Conference: Attosecond Science: Status and Prospects KITP Conference: Attosecond Science: Status and Prospects en-us © 2006 by the individual authors doug@kitp.ucsb.edu webmaster@kitp.ucsb.edu Sat, 05 Aug 2006 17:00:58 -0700 Sat, 05 Aug 2006 17:00:58 -0700 Education http://blogs.law.harvard.edu/tech/rss 240 http://online.kitp.ucsb.edu/online/atto_c06/bandrauk/ Andre Bandrauk (U. Sherbrooke) (Andre Bandrauk (U. Sherbrooke)) Andre Bandrauk (U. Sherbrooke) Andre Bandrauk (U. Sherbrooke) Andre Bandrauk (U. Sherbrooke) (Thu, 03 Aug 2006 17:00) Recent advances in ultrashort intense laser pulse technology allows for unprecedented study of laser matter interaction on the time scale of a few optical cycles [1]. For few cycle pulses the electric field, E(t)=Eo(t) cos(?t+?) depends strongly on the phase ? of the carrier wave of frequency ? with respect to the pulse envelope Eo(t). ? is called the carrier envelope phase, CEP. Spatiotemporal variation of electromagnetic pulses E(t) consisting of very few cycles are now precisely known and can be shaped with attosecond precision via control over ?.We have previously demonstrated by numerical simulations that intense few cycle laser pulses produce asymmetries in strong-field ionization of one electron atomic 3-D model systems [2] and that such asymmetry follows a universal CEP dependence which can be used to measure the duration of subfemtosecond pulses [3]. We investigate in the present work double ionization in a 2-D model of H2 and HeH+ and its dependence on CEP effects. The 2-D model allows for calculation of the angular dependence of the double electron ejection by intense 800 nm laser pulses in molecules and to compare to recent experimental results in Ar atoms [4]. Comparisons are also made at large internuclear distances where Charge Resonance Enhanced Ionization, CREI, dominates [5].[1] T. Brabec, F. Krausz, Rev. Mod. Phys. 72, 545 (2000).[2] S. Chelkowski, A.D. Bandrauk, A. Apolonski, Phys. Rev. A71, 053815 (2005); Opt. Lett. 29, 1557 (2004).[3] A.D. Bandrauk, S. Chelkowski, H.S. Nguyen, Phys. Rev. A68, 041802 (2003).[4] X. Liu et al., Phys. Rev. Lett. 93, 263001 (2004).[5] G. Lagmago Kamta, A.D. Bandrauk, Phys. Rev. Lett. 94, 203003 (2005). http://online.kitp.ucsb.edu/online/atto_c06/bandrauk/ Thu, 03 Aug 2006 17:00:00 -0700 22:00 http://online.kitp.ucsb.edu/online/atto_c06/becker/ Wilhelm Becker (MBI-Berlin) (Wilhelm Becker (MBI-Berlin)) Wilhelm Becker (MBI-Berlin) Wilhelm Becker (MBI-Berlin) Wilhelm Becker (MBI-Berlin) (Fri, 04 Aug 2006 10:30) D. B. Milosevic1 and W. Becker21 Faculty of Science, University of Sarajevo, Sarajevo, Bosnia and Herzegovina2 Max-Born-Institut, Berlin, GermanyAbove-threshold ionization is the cleanest laser-atom effect, sinceexperiments observe, in principle, just one atom at any one time in thelaser field. Except very close to the ion, the electron dynamics aredominated by the laser field. This is exploited by the strong-fieldapproximation (SFA), which is largely analytical and complements numericalsolution of the time-dependent Schroedinger equation in the analysis ofthe experimental data. Even though the SFA is an S-matrix theory, in itsquantum-orbit formulation it affords insight into the temporal evolutionof the ionization process. This is particularly illuminating for theinvestigation of few-cycle pulses with fixed carrier-envelope phase.We review formalism and results of the quantum-orbit SFA, with specialemphasis on few-cycle pulses.This work was supported in part by VolkswagenStiftung and the FederalMinistry of Education and Science, Bosnia and Herzegovina. http://online.kitp.ucsb.edu/online/atto_c06/becker/ Fri, 04 Aug 2006 10:30:00 -0700 40:16 http://online.kitp.ucsb.edu/online/atto_c06/brabec/ Thomas Brabec (Univ. of Ottawa) (Thomas Brabec (Univ. of Ottawa)) Thomas Brabec (Univ. of Ottawa) http://online.kitp.ucsb.edu/online/atto_c06/brabec/ Wed, 02 Aug 2006 14:00:00 -0700 40:31 http://online.kitp.ucsb.edu/online/atto_c06/bucksbaum/ Philip H. Bucksbaum (Stanford) (Philip H. Bucksbaum (Stanford)) Philip H. Bucksbaum (Stanford) http://online.kitp.ucsb.edu/online/atto_c06/bucksbaum/ Wed, 02 Aug 2006 11:50:00 -0700 39:33 http://online.kitp.ucsb.edu/online/atto_c06/burgdoerfer/ Joachim Burgdoerfer (Vienna Univ.) (Joachim Burgdoerfer (Vienna Univ.)) Joachim Burgdoerfer (Vienna Univ.) Joachim Burgdoerfer (Vienna Univ.) Joachim Burgdoerfer (Vienna Univ.) (Thu, 03 Aug 2006 10:30) Advances in ultrashort-pulse technology have made it possible to generate electromagnetic pulses with duration as short as few hundred attoseconds. thus approaches the orbital period 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 discuss recent progress and open questions with the help of a few examples. Topics include time-resolved Fano resonances in atoms and quantum graphs, coherent excitation, time-resolved orbital motion in doubly-excited helium, and time-double slit interferences.Work performed in collaboration with D. Arbo, I. Barna, A. Barnthaler, M. Drescher, F. Krausz, E. Persson, S. Rotter, J. Wang, M. Wickenhauser http://online.kitp.ucsb.edu/online/atto_c06/burgdoerfer/ Thu, 03 Aug 2006 10:30:00 -0700 41:32 http://online.kitp.ucsb.edu/online/atto_c06/burke/ Kieron Burke (UC Irvine) (Kieron Burke (UC Irvine)) Kieron Burke (UC Irvine) Kieron Burke (UC Irvine) Kieron Burke (UC Irvine) (Thu, 03 Aug 2006 16:30) I will give a general review of density functional theory for non-experts and explain why time-dependent DFT holds such promise for strong fields. I will also explain why successes for electronic exitations do not imply success for strong field processes [1][1] Time-dependent density functional theory: Past, present, and future K. Burke, Jan Werschnik, and E.K.U. Gross, J. Chem. Phys. 123, 062206 (2005). http://online.kitp.ucsb.edu/online/atto_c06/burke/ Thu, 03 Aug 2006 16:30:00 -0700 38:50 http://online.kitp.ucsb.edu/online/atto_c06/dimauro/ Louis DiMauro (Ohio State Univ.) (Louis DiMauro (Ohio State Univ.)) Louis DiMauro (Ohio State Univ.) Louis DiMauro (Ohio State Univ.) Louis DiMauro (Ohio State Univ.) (Thu, 03 Aug 2006 11:10) Over the last decade, the tailoring of a light field for manipulating the dynamics of a system at the quantum level has taken a prevalent role in modern atomic, molecular and optical physics. As first described by Keldysh1, the ionization of an atom by an intense laser field will evolve depending upon the light characteristics and atomic binding energy. Numerous experiments have thoroughly investigated the dependence of the intensity and pulse duration on the ionization dynamics of inert gases. However, exploration of the wavelength dependence has been mainly limited to wavelengths ? 1 ?m or in the language of Keldysh to the multiphoton or mixed ionization regime. It is now technically possible to more thoroughly test scaling laws at longer mid-infrared wavelengths with the same sensitivity available at near-visible wavelengths. In addition, excitation with mid-infrared light augments the number of atomic systems which can be studied in the tunneling regime, as well as posing different model atomic structure, e.g. one- and two-electron like systems.In this talk, we will discuss two topics. The first topic examines the long wavelength scaling of the strong field physics and its utility for experiments investigations. In the experiment alkali metal atom interact with an intense mid-infrared (3-4 ?m) laser field. In a Keldysh picture this scaled interaction should show similar ionization dynamics to the more familiar situation of a near visible light interacting with inert gas atoms. However, the interpretation of the spectra is greatly simplified since the alkali metal atoms are "good" one-electron like systems. Both ionization and harmonic processes are currently under investigation. The results show many similarities with the more extensively studied inert gas atom spectrum but significant differences do exist.The second topic deals with inert gas atoms in large ponderomotive potentials. Both theoretical and experimental results will be presented that show neutral atoms experiencing nearly 400 eV of ponderomotive potential and ionization deep into the tunnel regime. These studies are fundamentally interesting but also provide a roadmap to light pulses that have both the atomic unit of time and length.1. L.V. Keldysh, Sov. Phys. JETP 20, 1307 (1965). http://online.kitp.ucsb.edu/online/atto_c06/dimauro/ Thu, 03 Aug 2006 11:10:00 -0700 36:14 http://online.kitp.ucsb.edu/online/atto_c06/ditmire/ Todd Ditmire (Univ. Texas-Austin) (Todd Ditmire (Univ. Texas-Austin)) Todd Ditmire (Univ. Texas-Austin) Todd Ditmire (Univ. Texas-Austin) Todd Ditmire (Univ. Texas-Austin) (Wed, 02 Aug 2006 15:20) In recent years, there has been quite substantial progress in the understanding of explosions of atomic clusters subject to intense laser irradiation. It is now well understood that single species clusters of low Z materials (such as hydrogen or deuterium) expand by a Coulomb explosion if they are irradiated with enough intensity. In this case, if irradiated with a pulse of sufficiently fast rise time and sufficiently high intensity to eject all free electrons from the cluster, the ejected ion energies will be simply the potential energy of the ions after ionization at their equilibrium position in the cluster. Large clusters irradiated at modest intensity exhibit different behavior. Experiments indicate that in this case collective electron oscillation phenomena are very important in determining the dynamics of such clusters. It has been found that in an intensely irradiated cluster, optically and collisionally-ionized electrons undergo rapid collisional heating for the short time (<1 ps) before the cluster disassembles in the laser field. Pump-probe experiments indicate that the cluster microplasma exhibits a resonance in the heating by the laser pulse similar to the giant resonance seen in metallic clusters. Charge separation of the hot electrons leads to a very fast expansion of the cluster ions.Quite recently, the nature of cluster interactions with intense, short wavelength light, ie vacuum ultraviolet and extreme ultraviolet, have come under study. Such studies have now become possible because of the development of a number of intense, ultrafast sources in the VUV range.These studies are motivated in part by the promise of XFEL imaging of large protein molecules, an experiment which is similar in many respects to the interaction of an intense XFEL pulse with a large cluster. The expansion time and mechanism of these large structures under intense short wavelength illumination is of great importance to ascertaining the likely success of such imaging experiments. As such, a complete understanding of the explosion mechanisms of large clusters (ie. proteins) under intense short wavelength illumination is critical. Furthermore, such interactions are of fundamental interest as collective effects, not manifested in long wavelength laser interactions, may play a part in the dynamics. Interactions with wavelengths shorter than 10 nm will be quite different from near IR interactions (at 800 to 1000 nm) since, even at high intensity, the ponderomotive forces (which scale as I?2) of the XUV pulses are much smaller than in the IR pulses. As a result, much of the electron heating and ponderomotive ejection of electrons, which we know to occur at high intensity in IR pulses, will likely not occur in the short wavelength pulses. Furthermore, short wavelength pulses will come into resonance with the giant dipole resonance of a cluster plasma at much higher density than do IR pulses. These are much more collisional plasmas and the absorption of energy from the pulse will differ dramatically.In my talk I will discuss various aspects of the physics of intense XUV and x-ray interactions with small clusters. I will discuss our plans for using femtosecond XUV light generated by high order harmonic generation to study these short wavelength-cluster interactions. I will also consider how very short pulses of XUV light (few fs) might be used to study the very early time dynamics of the cluster explosion. http://online.kitp.ucsb.edu/online/atto_c06/ditmire/ Wed, 02 Aug 2006 15:20:00 -0700 43:18 http://online.kitp.ucsb.edu/online/atto_c06/freeman/ Richard R. Freeman (Ohio State Univ.) (Richard R. Freeman (Ohio State Univ.)) Richard R. Freeman (Ohio State Univ.) Richard R. Freeman (Ohio State Univ.) Richard R. Freeman (Ohio State Univ.) (Tue, 01 Aug 2006 14:00) This presentation introduces the salient physics phenomena associated with the reaction of solid materials to their being hit with laser intensities in excess of 10^19 W/cm^2. Most of the interesting interactions happen within the first several picoseconds of the interaction, and several thoroughly unexpected results have been observed. This talk reviews these results, and attempts to put them in perspective in terms of their possible uses, which range from inertial fusion, to ultra-fast time-resolved radiography. http://online.kitp.ucsb.edu/online/atto_c06/freeman/ Tue, 01 Aug 2006 14:00:00 -0700 42:07 http://online.kitp.ucsb.edu/online/atto_c06/gross/ David Gross (KITP Director) (David Gross (KITP Director)) David Gross (KITP Director) http://online.kitp.ucsb.edu/online/atto_c06/gross/ Tue, 01 Aug 2006 08:45:00 -0700 08:39 http://online.kitp.ucsb.edu/online/atto_c06/keitel/ Christoph H. Keitel (MPI-K) (Christoph H. Keitel (MPI-K)) Christoph H. Keitel (MPI-K) Christoph H. Keitel (MPI-K) Christoph H. Keitel (MPI-K) (Wed, 02 Aug 2006 10:30) C. H. Keitel, A. Di Piazza, K. Z. Hatsagortsyan, M. Klaiber, C. Muller Relativistic quantum dynamics of atoms and ions is introduced inintense laser fields [1]. Emphasis is placed here on allowing forrelativistic recollisions via tailored attosecond pulses [2]. The feasibility of nuclear excitation dynamics is then shown to be realistic with XFEL light[3]. Quantum electrodynamical processes are investigated in extremely strong laser pulses, including nonlinearities of laser-driven vacuum [4]. Finally emphasis is placed on high-energy processes such as muon pair production from laser-driven positronium [5].[1] Y. I. Salamin et al., Phys. Rep. 427, 41 (2006)[2] M. Klaiber, K. Z. Hatsagortsyan, C. H. Keitel, submitted (2006)[3] T. J. Burvenich, J. Evers and C. H. Keitel, Phys. Rev. Lett. 96, 142501 (2006)[4] A. Di Piazza, K. Z. Hatsagortsyan and C. H. Keitel, arXiv.org: hep-ph/0602039[5] C. Muller, K. Z. Hatsagortyan, C. H. Keitel, arXiv.org: physics/0602106 http://online.kitp.ucsb.edu/online/atto_c06/keitel/ Wed, 02 Aug 2006 10:30:00 -0700 40:33 http://online.kitp.ucsb.edu/online/atto_c06/krausz/ Ferenc Krausz (MPI MPQ) (Ferenc Krausz (MPI MPQ)) Ferenc Krausz (MPI MPQ) Ferenc Krausz (MPI MPQ) Ferenc Krausz (MPI MPQ) (Tue, 01 Aug 2006 09:00) Fundamental processes in atoms, molecules, as well as condensed matter are triggered or mediated by the motion of electrons inside or between atoms. Electronic dynamics on atomic length scales tends to unfold within tens to thousands of attoseconds (1 attosecond [as] = 10-18 s). Recent breakthroughs in laser science are now opening the door to watching and controlling these hitherto inaccessible microscopic dynamics.The key to accessing the attosecond time domain is the control of the electric field of (visible) light, which varies its strength and direction within less than a femtosecond (1 femtosecond = 1000 attoseconds). Atoms exposed to a few oscillations cycles of intense laser light are able to emit a single extreme ultraviolet (xuv) burst lasting less than one femtosecond [1,2]. Full control of the evolution of the electromagnetic field in laser pulses comprising a few wave cycles [3] have recently allowed the reproducible generation and measurement of isolated 250-attosecond xuv pulses [4], constituting the shortest reproducible events and fastest measurement to date. These tools have enabled us to visualize the oscillating electric field of visible light with an attosecond "oscilloscope" [5] as well as steering and real-time observation of the motion of electrons in atoms [6] and molecules [7]. Recent experiments [8] hold promise for the development of an attosecond x-ray source, which may pave the way towards 4D electron imaging with sub-atomic resolution in space and time. [1] M. Hentschel et al., Nature 414, 509 (2001); [2] R. Kienberger et al., Science 291, 1923 (2002); [3] A. Baltuska et al., Nature 421, 611 (2003); [4] R. Kienberger et al., Nature 427, 817 (2004); [5] E. Goulielmakis et al., Science 305, 1267 (2004); [6] M. Drescher et al., Nature 419, 803 (2002). [7] J. Seres et al, Nature 433, 596 (2005). [8] M. Kling et al., Science 312, 246 (2006). http://online.kitp.ucsb.edu/online/atto_c06/krausz/ Tue, 01 Aug 2006 09:00:00 -0700 1:13:43 http://online.kitp.ucsb.edu/online/atto_c06/lhuillier/ Anne L'Huillier (Lund Univ.) (Anne L'Huillier (Lund Univ.)) Anne L'Huillier (Lund Univ.) Anne L'Huillier (Lund Univ.) Anne L'Huillier (Lund Univ.) (Thu, 03 Aug 2006 09:00) A. L'Huillier, J. Mauritsson, P. Johnsson. T. Remetter, E. Gustafsson, T. Ruchon and M. Swoboda, Department of Physics, Lund University, P. O. Box 118, SE-221 00 Lund, SwedenThe characteristic plateau region of the harmonic spectrum produced when an atom is ionized in an intense infrared laser field spans from the ultraviolet into the soft X-ray region, thus providing enough bandwidth to produce pulses of hundred attoseconds. However, the different frequency components in the harmonic spectrum are not naturally synchronized. Ensuring or imposing a sufficient degree of synchronization over a certain spectral bandwidth, combined with the filtering of this bandwidth is the biggest problem that must be overcome for the production of short attosecond pulses. In this communication, we report on the different technologies that can be used to spectrally filter and phase control high-order harmonics in order to produce sub-200 as pulses on target in a wide energy region [1-4].Applications of attosecond pulses are emerging. We will present applications of attosecond pulses to time-resolved studies of ionization of rare gas atoms by attosecond pulses in presence of an infrared laser pulse [3-5] and to interferometric measurements of electron wave packets [6]. Our experiments consist in measuring the angular and energy-resolved electron emission from atoms exposed to a train of attosecond pulses in presence of an infrared laser field using a velocity map imaging technique. The momentum distributions depend on the timing of injection of the electron wave packets in the continuum relative to the laser cycle. We will especially discuss the results presented in [6] where the interferences between wave packets created at a given time in the infrared cycle and those created half a cycle later are studied as a function of the relative delay between the infrared field and the attosecond pulses. In some cases, information on the phase of the electron wave packet can be extracted from the interferograms, in a way resembling spectral-shearing interferometry of optical pulses.[1] R. Lopez-Martens et al, Phys. Rev. Lett. 94, 033001 (2005) [2] A.-S. Morlens et al., Opt. Lett. 31, 1558 (2006) [3] P. Johnsson et al., in preparation [4] J. Mauritsson et al., Phys. Rev. Lett., in press (2006) [5] P. Johnsson et al., Phys. Rev. Lett. 95, 013001 (2005) [6] T. Remetter et al, Nature Physics 2, 323 (2006) http://online.kitp.ucsb.edu/online/atto_c06/lhuillier/ Thu, 03 Aug 2006 09:00:00 -0700 1:00:29 http://online.kitp.ucsb.edu/online/atto_c06/lin/ Chii-Dong Lin (Kansas State Univ.) (Chii-Dong Lin (Kansas State Univ.)) Chii-Dong Lin (Kansas State Univ.) Chii-Dong Lin (Kansas State Univ.) Chii-Dong Lin (Kansas State Univ.) (Wed, 02 Aug 2006 14:40) The natural time scale for the electronic interactions in matter is of the order of hundreds of attoseconds or less. In this talk, we show a few examples where the dynamics between two electrons can be probed with attosecond pulses, illustrating the temporal response of one electron to the other, in the time domain. The examples include the joint rotational and vibrational motions between two excited electrons, the response of one electron with the sudden removal of another electron, and the discrete nature of autoionization of a two-electron wave packet. http://online.kitp.ucsb.edu/online/atto_c06/lin/ Wed, 02 Aug 2006 14:40:00 -0700 35:34 http://online.kitp.ucsb.edu/online/atto_c06/marangos/ Jon Marangos (Imperial College) (Jon Marangos (Imperial College)) Jon Marangos (Imperial College) Jon Marangos (Imperial College) Jon Marangos (Imperial College) (Tue, 01 Aug 2006 11:50) J.P.Marangos, S.Baker, R.Torres, N.Kajumba, C.Haworth, J.Robinson, J.W.G. Tisch, Blackett Laboratory, Imperial College ,London SW7 2BW, United Kingdom C.Vozzi, F. Calegari, E. Benedetti, G. Sansone, S. Stagira, M. Nisoli, National Laboratory for Ultrafast and Ultraintense Optical Science-INFM, Dipartimento di Fisica, Politecnico, Milano, Italy C.Altucci and R.Velotta, Coherentia-INFM and Dipartimento di Scienze Fisiche, Universita di Napoli "Federico II", Napoli, Italy Our recent work has looked in particular at the signal from high order harmonic generation which contains rich information about the structure and intra-molecular dynamics of small molecules. This we will illustrate by two types of experiment; (a) measurements of HHG from aligned molecular samples to observe two-centre recombination interference and electronic structure dependence of the angle dependent yield, (b) reconstruction of intra-molecular proton dynamics from the spectral dependence of the HHG using the intrinsic chirp of recolliding electrons.We experimentally investigate the process of intramolecular quantum interference in high-order harmonic generation in impulsively aligned CO2 molecules. The recombination interference effect is clearly seen through the order dependence of the harmonic yield in an aligned sample. This confirms that the effective de Broglie wavelength of the returning electron wave is not significantly altered by acceleration in the Coulomb field of the molecular ion. For the first time, to our knowledge, we demonstrate that such interference effects can be effectively controlled by changing the ellipticity of the driving laser field [1]. We demonstrate a new technique using high order harmonic generation in molecules to probe nuclear dynamics and structural rearrangement on a sub-femtosecond timescale. The chirped nature of the electron wavepacket produced by laser ionization in a strong field gives rise to a similar chirp in the photons emitted upon electron-ion recombination. Use of this chirp in the emitted light allows information about nuclear dynamics to be gained with 100 attosecond temporal resolution, from excitation by an 8 fs pulse, in a single laser shot. Measurements on H2 and D2 agree well with calculations of ultra-fast nuclear dynamics in the H2+ molecule, confirming the validity of the method. Guided by this result, we have measured harmonic spectra from CH4 and CD4 to demonstrate a few-femtosecond timescale for the onset of proton rearrangement in methane upon ionization [2]. [1] C.Vozzi et al., "Controlling two-center interference in molecular high harmonic generation", Phys. Rev. Lett., 95, 153902 (2005). [2] S.Baker, et al., "Probing proton dynamics in molecules on an attosecond timer scale", Science, 312 424 (2006). http://online.kitp.ucsb.edu/online/atto_c06/marangos/ Tue, 01 Aug 2006 11:50:00 -0700 41:37 http://online.kitp.ucsb.edu/online/atto_c06/merdji/ Hamed Merdji (CEA, Saclay) (Hamed Merdji (CEA, Saclay)) Hamed Merdji (CEA, Saclay) Hamed Merdji (CEA, Saclay) Hamed Merdji (CEA, Saclay) (Wed, 02 Aug 2006 16:00) H. Merdji, W. Boutu, R. Fitour, P. Monchicourt, P. Breger, B. Carre and P. SalieresService des Photons, Atomes et Molecules, CEA-Saclay, 91191 Gif-sur-Yvette, FranceRecently, a number of papers have demonstrated the interest of high-order harmonic generation (HHG) from molecules aligned with respect to the laser polarization. Itatani et al. (Nature 432, 867 (2004)) have shown that a precise characterization of the harmonic emission allows performing a tomographic reconstruction of the molecular orbitals that radiate. Kanai et al. (Nature 435, 470 (2005)) have evidenced quantum interferences in the recombination process of HHG that are directly related to the molecular structure. In all of these papers, only the HHG intensity was measured. The relative harmonic phase, though more difficult to measure, contains important information on the interference process, and is needed for an ab initio tomographic reconstruction. Finally, while the attosecond emission from atoms has been thoroughly studied, in particular by our group (Mairesse et al., Science 302, 1540 (2003)), it has not been investigated in molecules.In a recent experiment, we have measured for the first time the harmonic amplitude and relative phase for aligned molecules. In order to align the molecules, we used the so-called nonadiabatic technique: a rotational wavepacket is created by a strong enough and short aligning pulse, so that a field-free alignment is obtained at the revival (a few ps after the aligning pulse). The measurement of phase locking between neighboring harmonics was performed through the photoionization of a target gas by the harmonic beam in presence of a sufficiently intense "dressing" laser beam (RABITT technique).The harmonic emission times measured when the CO2 molecules are aligned parallel to the generating laser polarization (at the revival of the rotational wavepacket, 22 ps after the aligning laser pulse) are significantly different from the Krypton case (which has a similar ionization potential). Up to sideband 22, their behavior is extremely similar, with a constant time shift between consecutive harmonic (~100 as). From sideband 22 to 24 this time shift suddenly increases to 350 as around harmonic 23 in the CO2 case, while it remains the same for the krypton. Finally a saturation for the last sideband is observed. The observed time shift around harmonic 23 corresponds to a shift of the harmonic phase of roughly 2 radians. This is close to the phase jump of pi that is predicted when destructive interference occurs in the recombination process. Our measurement would thus be consistent with that of Kanai et al. (Nature 435, 470 (2005)), where the quantum interference in the harmonic amplitude was observed around order 23.The temporal profiles of the generated attosecond pulses has been reconstructed for both gases. They reveal the complex electron dynamics involved in the recombination process. While the trains reconstructed from harmonics 15 to 21 (i.e. before the phase jump) are quite similar, their comportment differs when one selects harmonics 23 to 29 due to the phase shift.Corresponding author: Hamed Merdji, merdji@drecam.cea.fr http://online.kitp.ucsb.edu/online/atto_c06/merdji/ Wed, 02 Aug 2006 16:00:00 -0700 28:23 http://online.kitp.ucsb.edu/online/atto_c06/mevel/ Eric Mevel (CELIA) (Eric Mevel (CELIA)) Eric Mevel (CELIA) Eric Mevel (CELIA) Eric Mevel (CELIA) (Fri, 04 Aug 2006 11:10) When interacting with a molecule or an atom, an intense ultra short laser field periodically drives electron wave packets away and back to the parent ion. At each return, the electron bunch may recombine to the initial electronic state producing an XUV light burst of attosecond duration. The characteristics of the XUV radiation is therefore directly mapped out from the temporal and spectral structure of the electrons wave packets while recolliding. Controlling the laser field to allow only one recollision event is the key to produce a single attosecond pulse. Here, for the first time, we have unambiguously achieved the temporal confinement of XUV harmonic radiation down to an isolated attosecond burst using the technique of polarization gating with (CEP) phase-stabilized few-optical-cycle driving pulses [1]. The signature of a single attosecond pulse emission has been observed in two gases, argon and neon, for three different broad spectral ranges, 25-40 eV in argon and 35-70 eV or 50-100 eV in neon. While earlier work was limited to attosecond pulse bandwidth of few eV hence to pulse longer than 100 as, polarization gating provides access to the full bandwidth of the recolliding EWP and potentially enables the generation of isolated pulses of few attoseconds. Isolated attosecond pulses are thus becoming accessible in new spectral and temporal ranges and will benefit to new attosecond science such as time resolved tomographic imaging of electron wave packet motion or electron-electron interaction dynamics at the atomic unit time scale.[1] I. Sola, E. Mevel, L. Elouga, E. Constant, V. Strelkov, L. Poletto, P . Villoresi, E. Benedetti, J.-P. Caumes, S. Stagira, C. Vozzi, G. Sansone and M. Nisoli, "Controlling attosecond electron dynamics by phase-stabilized polarization gating", Nature Physics, 2, 319 (2006) http://online.kitp.ucsb.edu/online/atto_c06/mevel/ Fri, 04 Aug 2006 11:10:00 -0700 34:35 http://online.kitp.ucsb.edu/online/atto_c06/mourou/ Gerard Mourou (LOA-ENSTA) (Gerard Mourou (LOA-ENSTA)) Gerard Mourou (LOA-ENSTA) Gerard Mourou (LOA-ENSTA) Gerard Mourou (LOA-ENSTA) (Fri, 04 Aug 2006 09:00) The generation of ultrahigh intense pulse has open up a new field in optics, the field of relativistic nonlinear optics, where the nonlinearity is dictated by the relativistic character of the electron. This young field has already produced a series of landmark experiments. Among them are the generation of energetic beams of particles (electrons, protons, ions, positrons), as well as beams of X-ray and gamma-ray.More recently it was shown by PIC simulations, that the light-induced large pressure on the critical surface could move the critical surface at relativistic velocity hence producing simultaneously short attosecond electron and attosecond electromagnetic pulses by relativistic compression. This novel approach to attosecond generation offers a new and efficient route to attosecond generation with some unique features: efficiency, pulse isolation and the potential to accommodate arbitrarily large amount of energy, since the plasma cannot be damaged. It has also been shown that the process of attosecond generation is accompanied by the generation of synchronized attosecond electron and photon pulses. In addition there is the possibility to scatter the laser pulse itself on the ultra short electron pulses to produce by coherent Thomson scattering ultra bright X-ray beams.Finally, the efficient relativistic compression of laser pulses offers the possibility to produce pulses 1000 times shorter (few as) in the nm range without any limit in energy. The energy density would be such that nonlinear QED effects such as vacuum polarization or pair generation could be observed.In summary this overview will show that ultra relativistic optics could be a new gateway to attosecond physics, that could unify, Nuclear Physics High Energy Physics, astrophysics, General Relativity, Cosmology and Nonlinear QED http://online.kitp.ucsb.edu/online/atto_c06/mourou/ Fri, 04 Aug 2006 09:00:00 -0700 1:02:43 http://online.kitp.ucsb.edu/online/atto_c06/murnane/ Margaret Murnane (JILA) (Margaret Murnane (JILA)) Margaret Murnane (JILA) Margaret Murnane (JILA) Margaret Murnane (JILA) (Tue, 01 Aug 2006 11:10) In this talk, we will discuss the observation of intramolecular vibration dynamics using electrons rescattered during the process of high-order harmonic generation.[1] We excite coherent vibrations in molecules (both spherically-symmetric and non-spherically-symmetric molecules) using impulsive Raman scattering (ISRS) with a short laser pulse. A second, more-intense laser pulse generates high-order harmonics of the fundamental laser, at wavelengths of ~20-50 nm. The high-order harmonic yield is observed to oscillate, at frequencies corresponding to all the Raman-active modes of the molecules. In the case of SF6, an asymmetric breathing mode is most visible. This is in contrast to conventional ISRS, where only the symmetric breathing mode of the molecule is observed. The SF6 data also show evidence of relaxation dynamics following impulsive excitation of the molecule. Our results indicate that high harmonic generation is a very sensitive probe of vibrational dynamics and yields more information simultaneously than conventional ultrafast spectroscopic techniques. Since the de Broglie wavelength of the recolliding electron is on the order of interatomic distances, i.e. ~ 1.5 A, small changes in the shape of the molecule lead to large changes in the high harmonic yield. This work therefore demonstrates a new spectroscopic technique for probing ultrafast internal dynamics in molecules, and in particular on the chemically-important ground state potential surface that is difficult to probe using other techniques. High harmonic generation from excited molecules is also sensitive in theory to Raman-active as well as infrared-active vibrational modes. 1. Nick Wagner et al., to be published in PNAS (2006). http://online.kitp.ucsb.edu/online/atto_c06/murnane/ Tue, 01 Aug 2006 11:10:00 -0700 35:30 http://online.kitp.ucsb.edu/online/atto_c06/mysyrowicz/ Andre Mysyrowicz (LOA-ENSTA) (Andre Mysyrowicz (LOA-ENSTA)) Andre Mysyrowicz (LOA-ENSTA) http://online.kitp.ucsb.edu/online/atto_c06/mysyrowicz/ Thu, 03 Aug 2006 11:50:00 -0700 32:56 http://online.kitp.ucsb.edu/online/atto_c06/organizers/ Conference Organizers (Conference Organizers ) Conference Organizers http://online.kitp.ucsb.edu/online/atto_c06/organizers/ Fri, 04 Aug 2006 12:30:00 -0700 07:26 http://online.kitp.ucsb.edu/online/atto_c06/pukhov/ Alexander Pukhov (Univ. Duesseldorf) (Alexander Pukhov (Univ. Duesseldorf)) Alexander Pukhov (Univ. Duesseldorf) Alexander Pukhov (Univ. Duesseldorf) Alexander Pukhov (Univ. Duesseldorf) (Tue, 01 Aug 2006 14:40) We show analytically and numerically that the spectrum of high harmonics produced when a relativistically intense laser pulse interacts with an overdense plasma surface is a slow decaying power law In/I0 ~ 1/n-8/3. This spectrum has been recently confirmed in the experiment done by Dromey et al on the VULCAN laser [1]. The high harmonics emerge as a train of (sub-)attosecond pulses [2]. Laser polarization control allows to select a single attosecond pulse out of this train [3]. [1] Dromey, B. et al. "High harmonic generation in the relativistic Limit," Nature Phys. 2, 456-459 (2006). [2] A. Pukhov X-rays in a flash, Nature Phys. 2, 439 (2006) [3] T. Baeva, S. Gordienko, A. Pukhov, "Theory of high harmonic generation in relativistic laser interaction with overdense plasma," arXiv:physics/0604228 v1, 28 Apr (2006) http://online.kitp.ucsb.edu/online/atto_c06/pukhov/ Tue, 01 Aug 2006 14:40:00 -0700 33:45 http://online.kitp.ucsb.edu/online/atto_c06/rost/ Jan-Michael Rost (MPI PKS) (Jan-Michael Rost (MPI PKS)) Jan-Michael Rost (MPI PKS) Jan-Michael Rost (MPI PKS) Jan-Michael Rost (MPI PKS) (Tue, 01 Aug 2006 15:20) While uncertainty relations in quantum mechanics are based on non commuting operators, the energy-time "uncertainty" is an exception since time is a (classical) parameter.There have been many unsuccessful attempts to construct a general "time operator" which would give the energy-time uncertainty the same operator based justification as the other uncertainty relations. Here, we accept that the energy-time uncertainty is for some reason not as fundamental as the operator based uncertainties and we find a reason by arguing that time is a useful but "man-made" concept which actually arises from separation in space. Without resorting to relativistic arguments we can construct the time-dependent Schroedinger equation from the time-independent one by separation of system and environment in space using a semiclassical approach. http://online.kitp.ucsb.edu/online/atto_c06/rost/ Tue, 01 Aug 2006 15:20:00 -0700 36:19 http://online.kitp.ucsb.edu/online/atto_c06/schafer/ Kenneth J. Schafer (LSU) (Kenneth J. Schafer (LSU)) Kenneth J. Schafer (LSU) Kenneth J. Schafer (LSU) Kenneth J. Schafer (LSU) (Tue, 01 Aug 2006 10:30) Attosecond pulses, generated as either single bursts or a train of pulses, are among the most celebrated offspring of strong field physics. They are also among the most exciting new tools available for studying and controlling strong field phenomena. In this talk we highlight some of the single atom as well as macroscopic strong field physics which is crucial for the generation of single attosecond pulses. We also discuss how attosecond pulse trains can be tailored for specific applications such as non sequential double ionization and the creation of novel attosecond electron wave packets. http://online.kitp.ucsb.edu/online/atto_c06/schafer/ Tue, 01 Aug 2006 10:30:00 -0700 41:33 http://online.kitp.ucsb.edu/online/atto_c06/scrinzi/ Armin Scrinzi (Vienna Univ.) (Armin Scrinzi (Vienna Univ.)) Armin Scrinzi (Vienna Univ.) Armin Scrinzi (Vienna Univ.) Armin Scrinzi (Vienna Univ.) (Thu, 03 Aug 2006 14:40) The dynamics of molecular electrons in a strong laser fielddiffers from that in atoms in several important aspects: for largermolecules, in general, several electrons equally interact with theexternal field, time scales can be comparable to the 800 nm laser cycle,and electronic wave functions may be delocalized. For attosecondphysics this has important consequences. The single-active-electronapproximation becomes questionable and with it much of ourknowledge about laser ionization. For commonly used laserintensities the limit between multi-photon and tunnelionization may be pushed to much longer wavelength.Finally, emitted and re-colliding electron wavepacketsand harmonic radiation reflect the multi-centeredbound electron orbital.We have developed the MCTDHF method for the fully correlatedtreatement of molecular electrons [1-3]. The method will bebriefly introduced and basic effects of correlation willbe pointed out. We show the time and momentum structure of electronemission and re-collision. In simple models a dramatic effectof orientation and orbital symmetry on the re-colliding electronsis found [4].[1] J. Zanghellini, M. Kitzler, T. Brabec, and A. Scrinzi,J. Phys. B37, 763 (2004)[2] J. Caillat, J. Zanghellini, M. Kitzler, O. Koch, W. Kreuzer,and A. Scrinzi, Phys. Rev. A 71, 12712 (2005)[3] G. Jordan, C. Ede, J. Caillat, and A. Scrinzi,J. Phys. B39, 341 (2006)[4] Xinhua Xie, G. Jordan, M. Wickenhauser, and A. Scrinzi, J. Mod. Opt.Special Issue on \\"Ultra-Fast Dynamic Imaging of Matter\\", submitted. http://online.kitp.ucsb.edu/online/atto_c06/scrinzi/ Thu, 03 Aug 2006 14:40:00 -0700 33:32 http://online.kitp.ucsb.edu/online/atto_c06/sergeev/ Alexander M. Sergeev (IAP) (Alexander M. Sergeev (IAP)) Alexander M. Sergeev (IAP) Alexander M. Sergeev (IAP) Alexander M. Sergeev (IAP) (Thu, 03 Aug 2006 14:00) M.Yu.Emelin, M.Yu.Ryabikin, and A.M.SergeevInstitute of Applied Physics, Russian Academy of Sciences, 46 Ul'yanov st, Nizhny Novgorod, 603950 RussiaKey points on the way of bringing attosecond sources into practice are to enhance the efficiency of HHG and to control spectral and temporal characteristics of attosecond pulses. These enhancement and control can be based in many respects on the concept of electron wave-packet engineering, which implies the control of the ionization process and electron propagation in the continuum by means of optimal preparation of the initial state of atom or molecule and laser pulse shaping. Possible ways to provide this control on microscopic level are the use of symmetry of molecular valence orbital by appropriate choice of molecular species, molecular alignment, and optimization of the internuclear separation. The control can be implemented by using, for example, molecular vibrational or rotational wave packets. In addition, an essential enhancement of attosecond SXR pulse production can be achieved for atoms and molecules prepared initially in excited electronic states to provide much slower diffusion of the released electronic wave packet. The control over above-mentioned stages of HHG using the phenomenon of quantum mechanical interference of coherent electron wavepackets detached from the molecule allows tuning the yield of harmonics in the desired spectral range. Constructive and destructive interferences caused by coherent superposition of the contributions to X-ray radiation from scattering of different parts of the electron wave packet by different centers in a molecule is also exploited for this purpose.In this report we will demonstrate that combining all the above ideas can result in increase by several orders of magnitude the efficiency of laser pulse energy conversion to the attosecond range, tuning the spectrum of attosecond bursts over a whole SXR wavelength band, and pulse shortening down to 10 attosecond duration. http://online.kitp.ucsb.edu/online/atto_c06/sergeev/ Thu, 03 Aug 2006 14:00:00 -0700 41:22 http://online.kitp.ucsb.edu/online/atto_c06/sokolov/ Alexei V. Sokolov (Texas A&M) (Alexei V. Sokolov (Texas A&M)) Alexei V. Sokolov (Texas A&M) Alexei V. Sokolov (Texas A&M) Alexei V. Sokolov (Texas A&M) (Thu, 03 Aug 2006 15:50) I will review the technique of Molecular Modulation and describe our recent results on efficient Raman generation in multi-level molecular systems, where excitations of adjacent transitions can interfere with each other. We use several (two or three) laser pulses at wavelengths such that their difference frequencies are tuned close to Raman resonances, so as to excite substantial molecular coherence. We use few-nanosecond pulses when we work with gasses, and sub-picosecond pulses when we work with Raman-active crystals. In both experiments we observe efficient generation of multiple mutually-coherent frequency sidebands that span infrared, visible, and ultraviolet spectral regions, opening possibilities for synthesis of subfemtosecond light waveforms, and for further studies of ultrafast molecular dynamics and molecular structure. http://online.kitp.ucsb.edu/online/atto_c06/sokolov/ Thu, 03 Aug 2006 15:50:00 -0700 39:57 http://online.kitp.ucsb.edu/online/atto_c06/umstadter/ Donald P. Umstadter (Univ. Nebraska) (Donald P. Umstadter (Univ. Nebraska)) Donald P. Umstadter (Univ. Nebraska) Donald P. Umstadter (Univ. Nebraska) Donald P. Umstadter (Univ. Nebraska) (Wed, 02 Aug 2006 11:10) Attosecond pulses are generally at the single-cycle limit. In a recent theoretical study, we found an exact solution for the fields of a focused laser for arbitrary spot size [1] and pulse duration [2]. For example, in comparison with monochrome fields, the inclusion of longer wavelengths reduces the fraction of laser energy in the focus from 86.5% to 72.7% in a single-cycle Ti:Sapphire laser pulse. Thus, unlike light with long pulse duration (many optical cycles), the transverse distribution of the field is found to depend on the longitudinal field profile.These theoretical predictions, along with others pertaining to the generation of ultrashort pulses of x-rays or electrons [3] with ultra-intense laser light, will be tested with newly built laser at UNL that operates at a peak power of >100 TW, pulse duration of <30 fs, and repetition rate of 10 Hz To support the stringent demands of such a state-of-the-art laser system, a 5,000-sq-ft laboratory has recently been renovated to provide a high degree of stability in terms of temperature (< +/- 0.25 degree C), humidity (< 5%) and vibration. Details of the laser system and the various methods in which it will be used to produce significant fluxes of ultrashort duration radiation will be discussed.1. S. Sepke and D. Umstadter, "Exact analytical solution for the vector electromagnetic field of Gaussian, flattened Gaussian, and annular Gaussian laser modes," Opt. Lett. 31, 1447 (2006).2. S. Sepke and D. Umstadter, "Analytical solutions for the electromagnetic fields of tightly focused laser beams of arbitrary pulse length", Opt. Lett., (accepted).3. S. Banerjee, S. Sepke, R. Shah, A. Valenzuela, and D. Umstadter, "Optical deflection and temporal characterization of an ultra-fast laser-produced electron beam", Phys. Rev. Lett. 95, 035004 (2005). http://online.kitp.ucsb.edu/online/atto_c06/umstadter/ Wed, 02 Aug 2006 11:10:00 -0700 28:46 http://online.kitp.ucsb.edu/online/atto_c06/vrakking/ Marc Vrakking (FOM) (Marc Vrakking (FOM)) Marc Vrakking (FOM) Marc Vrakking (FOM) Marc Vrakking (FOM) (Wed, 02 Aug 2006 09:00) In the past two decades femtosecond time-resolved experiments have allowed the observation of molecular rotations and vibrations, and of photo-induced chemical processes. However, these experiments often tell only half the story: they show the motion of atoms moving under the influence of potential energy curves that result from a time-average over the motion of all electrons in the system. The natural time-unit for this electronic motion itself is the atomic unit of time (1 a.u. = 0.024 fsec = 24 attoseconds). Real-time observation of this motion therefore requires recently developed attosecond laser techniques. When considering motions of electrons we may distinguish between motion that results from driving the electrons with a strong laser field and motion that results from photo-absorption in a weak laser field. In strong laser fields the electron motion can be quite intuitive. Eventually, studies of photo-absorption in weak laser fields will be more important though, since all photo-absorption processes in nature (i.e. outside a laser laboratory) occur in this regime. In my talk I will present a personal perspective on the current status of attosecond science, discussing a number of requirements for both further experimental and theoretical developments of the field. I will discuss how there is both a utility for isolated attosecond pulses and attosecond pulse trains, and will argue that interesting attosecond science already starts at the level of perturbative atom-light field interactions. I will discuss ongoing experiments aimed at observing the motion of electrons on attosecond timescales in strong laser fields. An interesting example is the dissociative ionization of the hydrogen molecule (into a proton and a neutral atom), where we have recently observed that the dissociation process can be controlled by the carrier envelope phase of a few-cycle laser pulse. [1] [1] M.F. Kling, Ch. Siedschlag, A.-J. Verhoef, J.I. Khan, M. Schultze, Th. Uphues, Y. Ni, M. Uiberacker, M. Drescher, F. Krausz and M.J.J. Vrakking, Science (in press, 2006). http://online.kitp.ucsb.edu/online/atto_c06/vrakking/ Wed, 02 Aug 2006 09:00:00 -0700 1:04:08 http://online.kitp.ucsb.edu/online/atto_c06/zholents/ Alexander A. Zholents (LBNL) (Alexander A. Zholents (LBNL)) Alexander A. Zholents (LBNL) Alexander A. Zholents (LBNL) Alexander A. Zholents (LBNL) (Fri, 04 Aug 2006 11:50) Several technique for generation of attosecond x-ray pulses with peak power up to 100 GW will be discussed. Key provision for most of the technique is the modulation of the electron energy in the wiggler due to electron beam interaction with a short few cycle lasre pulse. http://online.kitp.ucsb.edu/online/atto_c06/zholents/ Fri, 04 Aug 2006 11:50:00 -0700 38:10