Poster Session II

#P2-1: A Vlasov Code Simulation of Plasma-Based Backward Raman Amplification in Underdense Plasmas, M. SHOUCRI, J-P. MATTE, F. VIDAL.

#P2-2: Ionization Modulation of H by Two Time-delayed Strong IR Pulses, SHU-NA SONG, JI-WEI GENG, LIZHONG LI, HONG-BING JIANG, AND LIANG-YOU PENG, Considering a pair of identical but time delayed one-cycle infrared (IR) laser pulses in the nonperturbative tunneling regime theoretically, we find that the total ionization yield of hydrogen atom is modulated by the time delay. The modulation is mainly due to the interference of ionizing electron wave  packets respectively generated by both pulses which has some similarities to and differences from the usual quantum control that has been well explained by the second-order time-dependent perturbation theory. Finally, we also extend our study of ionization modulation to the one multi-cycle laser pulse case with different wavelengths in the tunneling regime.

#P2-3: Applications of Elliptically-Polarized, Few-Cycle Attosecond Pulses, J.M. NGOKO DJIOKAP, N.L. MANAKOV, A.V. MEREMIANIN, S.X. HU, L.B. MADSEN, AND ANTHONY F. STARACE, A new nonlinear dichroic effect is predicted as a first application of our ability to solve the six-dimensional two-electron, time-dependent Schrödinger equation for He interacting with an elliptically-polarized XUV pulse. Specifically, we demonstrate control of double ionization of He by means of the polarization and carrier-envelope-phase (CEP) of an intense, few-cycle attosecond XUV pulse. Other applications of circularly- and elliptically-polarized few-cycle attosecond pulses may also be presented.

#P2-4: 31-fs OPCPA front-end at 1.55 μm, A. THAI , A. VAN DE WALLE, M. HANNA, P. GEORGES, AND N. FORGET, We present an OPCPAe front-end at 1.55 μm pumped by an Yb CPA at kHz repetition rates. The front-end delivers 40 μJ and pulse duration of 31 fs.

#P2-5: Three-dimensional characterization of sub-2-cycle laser pulses, T. WITTING, TIM JACOBS, PATRICK SCHYGULLA, JON P. MARANGOS, J.W.G. TISCH, We extend the SEA-F-SPIDER technique to include an additional spatial dimension to allow reconstruction of the full electric field in two transverse spatial dimensions E(x,y,t). We show the full 3D characterization of sub-2-cycle near infrared pulses generated in a hollow fibre compressor.

#P2-6: Multi-Pass Relativistic High Harmonic Generation, MATTHEW R. EDWARDS AND JULIA M. MIKHAILOVA, We consider here the enhancement of relativistic high harmonic generation (HHG) from solid-density targets using multi-ple interactions to create efficient driving beams. Since the higher frequencies added by HHG are phaselocked to the reflected fun-damental beam, the resulting waveform is better suited to driving HHG than the original single frequency. Particle-in-cell simulations demonstrate that a multiple-interaction system can produce attosecond pulses four orders of magnitude more intense than a single-pass configuration at the same conditions, and that a chain of interactions at a0 = 5 can create brighter attosecond pulses than a single interaction at a0 = 30.

#P2-7: Electron correlation effects in enhanced ionization of molecules: A timedependent generalizedactive-space configuration-interaction study, S. CHATTOPADHYAY, S. BAUCH, AND L. B. MADSEN, We present a study of electron correlation effects in enhanced-ionization of diatomic molecules based on the time-dependent generalized-active-space configuration-interaction (TD-GASCI) method. To incorporate the electron correlation as accurately as possible poses a great challenge in time-dependent many-electron theories. We numerically studied models of H2 and LiH molecules, aligned collinearly with the polarization of the external field, to elucidate the possible role of correlation in the enhanced-ionization (EI) phenomena. The results of our studies show that correlation is important and they also demonstrate significant deviations between the results of single-activeelectron (SAE) approximation and more accurate configuration-interaction methods.

#P2-8: Decomposition of phase-matched signals from nonlinear wave mixing experiments calculated with the Multiconfiguration Time-Dependent Hartree-Fock method, DANIEL J. HAXTON , ZACH WALTERS, AND C. WILLIAM MCCURDY, We have developed an open-source computer code ( that calculates allelectrons-active time-dependent wave functions for polyatomic molecules. With the method of Domcke et al. , we calculate signals generated by hypothetical nonlinear wave-mixing experiments. We decompose the signals fully with respect to the number of photons absorbed and the number emitted, not merely the net number absorbed/emitted. We speculate and inquire about experiments that could perform this total decomposition, which would chart the paths through which laser light may direct energy in a molecule in a particularly specific manner.

#P2-9: Attosecond Transient Absorption Spectroscopy (ATAS) of highly excited core level electrons in Krypton and Xénon, ANAND MAILAM, OJOON KWON, STEFAN PABST, DONG EON KIM, We report the attosecond transient absorption study of Xe and Kr in the XUV region at the attosecond beamline for atomic physics at the Max Planck Center for Attosecond Science (MPC-AS), POSTECH. We have used the attosecond transient absorption spectroscopy (ATAS) setup to make time resolved measurements on highly excited inner shell core electrons of krypton and xenon atoms. The excited atoms in the presence of few cycle IR pulses of intensities about 10-20 x 1012 Wcm-2 show several interesting features such as AC stark shift and sub cycle oscillation in the absorption spectra. The observed features have been explained using time dependent configuration interaction singles (TDCIS) calculations.

#P2-10: Theoretical Study of Ultrafast Electron Dynamics in Amino Acids, D. AYUSO, A. PALACIOS, P. DECLEVAY, F. MARTIN, Prompt ionization of large biological molecules may induce ultrafast charge migration along the molec- ular  skeleton, preceding any nuclear rearrangement. This phenomenon has been recently observed in the amino acid phenylalanine in a two-color pump probe experiment, where the production of ionic fragments was measured as a function of the time delay between the two pulses and charge fluctuations manifested as sub-4.5 fs oscillations in the quantum yield of a specific doubly charged fragment. We present our latest results in glycine, and compare with previous findings in phenylalanine. We seek to perform a systematic study including larger aminoacids such as tryptophan.

#P2-11: Creating coherent hole wave packets with strong-field pulses, STEFAN PABST AND HANS JAKOB WÖRNER, A new approach is identified that can generate highly coherent hole wave packets with multi-cycle strong-field pulses and stands in contrast to the usual idea of making the ionizing pulse as short as possible. The effect is demonstrated in atomic xenon with a spin-orbit wave packet involving the 5p3/2 -1 and 5p1/2 -1 ionic states.

#P2-12: Coupled electron-nuclear dynamics following valence ionization of toluene, MORGANE VACHER, ANDREW J. JENKINS, JAN MEISNER, DAVID MENDIVE-TAPIA, LEE STEINBERG, MICHAEL J. BEARPARK AND MICHAEL A. ROBB, Photoionization can initiate electron dynamics in molecules. Theoretical studies at a single fixed nuclear geometry have demonstrated oscillatory charge migration. Here, we show how nuclear motion and the initial nuclear distribution affect the outcome of electron dynamics. In toluene, only a few fs are necessary for the nuclear geometry to distort enough to affect both the time scale and nature of electron dynamics following valence ionization. We also show how by choosing the initial weight and phase of a superposition of electronic states, one can control the initial nuclear dynamics.

#P2-13: XUV-initiated high harmonic spectroscopy, DORON AZOURY, MICHAEL KRÜGER, BARRY D. BRUNER AND NIRIT DUDOVICH, High-harmonic generation (HHG) spectroscopy is a powerful tool to image atomic and molecular structure on ångström length and attosecond time scales. However, conventional HHG employs tunneling ionization and therefore addresses outer-shell electrons. In XUV-initiated HHG, tunneling ionization is replaced by photoionization by an XUV attosecond pulse. The new mechanism enables unprecedented control of timing and initial energy of the ionization step. In a proof-of-principle experiment, we observe XUV-initiated HHG from groundstate helium and demonstrate its control capability. Since photoionization can induce inner-shell electron dynamics, we expect that the new scheme will enable precise investigations of such processes.

#P2-14: Probing Nuclear Motion by Frequency Modulation of Molecular High-Order Harmonic Generation, XUE-BIN BIAN, ANDRE D. BANDRAUK, Amplitude modulation (AM) and frequency modulation (FM) in molecular high-order harmonic generation (MHOHG) can be used to retrieve the nuclear motion in molecules. The former is an intracycle dynamics, and the latter is an intercycle dynamics. This work concentrates on the mechanism on FM. Its applications in the motion of light molecules are investigated. Angstrom space resolution can be achieved by using FM. Isotope effect is also studied.

#P2-15: Mapping molecular rotational dynamics from the time-dependent spectral minimum, XIAOSONG ZHU, MEIYAN QIN, YANG LI, PEIXIANG LU, The interference of the harmonic emissions from molecules aligned at different angles can significantly modulate the spectra and result in the anomalous harmonic cutoffs observed in a recent experiment. The shift of the structural minimum position with decreasing the degree of alignment is also explained by this interference effect of the harmonic emissions. In this work, we investigate the delay-dependent harmonic spectra generated from non-adiabatically aligned molecules around the first half rotational revival. It is found that the evolution of the molecular alignment is encoded in the structural minima. To reveal the relation between the molecular alignment and the structural minimum in the high-order harmonic spectrum, we perform an analysis based on the two-center interference model. Our analysis shows that the structural minimum position depends linearly on the inverse of the alignment parameter <cos2θ>. This linear relation indicates the possibility of probing the rotational wave-packet dynamics by measuring the spectral minima.

#P2-16: High Harmonics Spectroscopy in molecules: reconstructing emission time for below threshold harmonics and electron localization, F. MORALES, P. RIVIERE, M. RICHTER, A. GUBAYDULLIN, L. MEDISAUSKAS, M. IVANOV , O. SMIRNOVA, F.MARTIN, We present quantum mechanical simulations of the H2 + molecule, with fully correlated electronic and nuclear degrees of freedom. Applying a strong infrared laser field, we analyse the resulting HHG spectra. Taking advantage of the fast Coulomb explosion that removes the contribution of long trajectories, we are able to peek into below threshold harmonics, and gain new insight on their behaviour. We also show how field induced correlated electron-nuclear dynamics in H2 + can lead to the generation of even harmonics, breaking the symmetry of the system. High-Harmonic Spectroscopy, electron localization.

#P2-17: Disentangling Contributing Factors to Electron Trajectories in Two-Colour High Harmonic Generation using Semiclassical Simulations, C. HOFMANN, A. S. LANDSMAN, H. SOIFER, D. SHAFIR, B. BRUNER, N. DUDOVICH, U. KELLER, Simulations based on a semiclassical model of strong field tunnel ionization of Helium followed by classical propagation reveal the contributions and influences of the fundamental strong IR driving field, the ionic Coulomb field and a perturbative second harmonic field on the electron trajectories involved in High Harmonic Generation (HHG). Comparison to experimental HHG spectra uncovers the relative contribution of long trajectories to low harmonic orders.

#P2-18: Cooper Minimum in the high-harmonic generation spectra from argon atoms, XUANYANG LAI, The Cooper minimum (CM) in high harmonic generation (HHG) spectrum has recently attracted much attention in strong field physics community. Numerous experimental results indicate that the position of the minimum in HHG spectrum is associated with the electronic structure of the atom rather than with its dynamics in the laser field. In this work, we study HHG spectra generated from argon atom by solving time-dependent Schrödinger equation (TDSE). The time-frequency analysis has been employed to separate the spectra from long and short orbits. Our results show that the position of the CM in the spectrum from short orbit is approximately independent of the laser intensity, while the minimum in the spectrum from long orbit depends on the laser intensity. We explain this finding in the context of the semi-classical theory.

#P2-19: Probing Molecular Dynamics with Sub-Cycle Techniques: PES vs ATI vs HHG, ALBERT STOLOW

#P2-20: Characterization of Molecular Breakup by Super-Intense, Femtosecond XUV Laser Pulses, LUN YUE AND LARS BOJER MADSEN, We study the breakup of H2 + exposed to super-intense, femtosecond laser pulses with laser frequencies greater than that corresponding to the ionization potential. By solving the time-dependent Schrödinger equation in an extensive field parameter regime, it is revealed that highly nonresonant dissociation channels can dominate over ionization. By considering field-dressed Born-Oppenheimer potential energy curves in the Kramer-Henneberger (KH) frame, we propose a simple physical model that characterizes this dissociation mechanism.

#P2-21: Subcycle interference and recollision dynamics of photoelectron holography in the nonadiabatic tunneling regime, WEIFENG YANG, ZHIHAO SHENG, XIANHUAN YU, PENG LIU, AND XIAOHONG SONG, Using a generalized quantum-trajectory Monte Carlo (GQTMC) method which includes both non-adiabatic tunneling ionization contribution and Coulomb potential effects, we investigate interference and recollision dynamics of strong-field photoelectron holography in different Keldysh parameter regimes. We achieve good agreement with both the experimental and the time-dependent Schrӧdinger equation (TDSE) results. It is shown that in the nonadiabatic tunneling regime (૪-1), non-adiabatic ionization and long-range Coulomb potential play important roles on the holographic interference structures. Multiple backscatterings of electrons are found to leave obvious imprints on the photoelectron spectrum in the low energy regime (< 2Up). Our results have implications for decoding time-resolved electron-dynamics from strong-field photoelectron momentum spectra.

#P2-22: Tunneling ionization of molecules including nuclear motion, JENS SVENSMARK, OLEG I. TOLSTIKHIN, LARS BOJER MADSEN, Tunneling ionization is an important process in the description of the interaction of atoms and molecules with strong laser fields. The Born-Oppenheimer (BO) approximation is ubiquitous in quantum chemistry for describing molecules. It has however been shown that the BO approximation breaks down in the description of tunneling ionization for weak fields. In this weak-field limit the recently developed weak-field asymptotic theory (WFAT, see Introduction of) provides an accurate description.

#P2-23: Slalom in complex time: dealing with the imaginary position of a quantum orbit, EMILIO PISANTY AND MISHA IVANOV, Intuition suggests that the main effect of the Coulomb interaction between a photoelectron and its parent ion should be an additional term in the action, but a rigorous first-principles approximation of this type was lacking until recently. We explore this approximation, the analytical R-matrix theory, and the imaginary position it imposes on quantum orbits. This imaginary part can dominate during a recollision, forcing contour changes in the complex time plane, and it can create large amplitudes if the recollision velocity is low, naturally predicting the known Low Energy Structures and a second structure at even lower energies.

#P2-24: Ionization and excitation with quasi sub-cycle laser pulses, B. WITZEL, G.GINGRAS AND C. MARCEAU, Ionization processes triggered by polarization gated laser pulses are studied. We show for the first time excitation processes and double ionization processes occurring in effective sub-cycle laser.

#P2-25: Femtosecond x-ray induced fragmentation of fullerenes using IR and FELs. N. BERRAH, H. XIONG , B. MURPHY , L. FANG , T. OSIPOV , E. KUKK , M. GUEHR , R. FEIFEL , V. S. PE-TROVIC, K. R. FERGUSON, J. D. BOZEK , C. BOSTEDT , L. J. FRASINSKI , P. H. BUCKSBAUM , J. C. CASTAGNA, The new class of x-ray lasers, the intense-femtosecond FELs, has opened up new opportunities to study AMO physics with atomic spatial resolution and femtosecond temporal resolution. The understanding of physical and chemical changes at an atomic spatial scale and on the time scale of atomic motion is crucial not only for AMO physics but also for a broad range of other scientific fields. We report here on the photoionization and fragmentation dynamics of gas phase fullerenes using intense femtosecond IR and x-ray pulses from the Linac Coherent Light Source (LCLS) free electron laser (FEL).

#P2-26: On a spin specific time delay with an eye on a “Larmor clock” calibration, VALERIY K. DOLMATOV AND ANATOLI KHEIFETS, Recently, time delay in the 3d and 4s photoionization of Mn was predicted to be enhanced drastically in the region of the 3p → 3d auto-ionization resonance. Moreover, the 4s photoionization time delay was found to depend strongly on the spin of the ion-remainder. It is argued in the present communication that the above findings can be utilized for calibration of the so-called “Larmor clock” which relates the attosecond time delay with the spin precession angle.

#P2-27: Attosecond imaging applications based on Fourier transform holography using high order harmonics, B. IWAN, A. I. GONZALEZ, H. MERDJI, W. BOUTU, G. O. WILLIAMS, S. KÜNZEL, L. LI, M. LOZANO, E. OLIVA,S. DABOUSSI, M. FAJARDO, PH.ZEITOUN, Diffractive imaging techniques theoretically offer spatial resolutions limited only by the wavelength. We report on an imaging method based on Fourier transform holography that exploits the spectral and temporal properties of attosecond high harmonic order emission in the XUV range. With sub-100 nm resolution, we reconstructed diffraction pattern obtained through illumination of a target with a discrete frequency comb of high order harmonics. Carefully selected combinations of object and reference positions enable us to obtain spatially and spectrally resolved images of the target through a single 2D Fourier transform. Adjusting the reference/sample configuration allows nanometer-scale attosecond time resolved imaging.

#P2-28: Ab-initio TD-ADC(1) electron dynamics in CO2 molecule interacting with strong IR laser pulses: HHG spectra and coherences between the final ionic states, M.RUBERTI, V.AVERBUKH, J.P.MARANGOS AND P. DECLEVA, We have performed a fully ab-initio 3-D TDSE calculation for the electron dynamic of the CO2 molecule interacting with high-intensity ultra-short infrared (IR) laser pulses. Specifically, we have calculated the high order harmonic generation spectra (HHG), quantitatively investigating the effects of its multi-channel nature on its dynamical minimum. We also present the first calculation of the reduced ionic density matrix (R-IDM) resulting from the ionization of CO2 by strong IR laser fields. We show that the final coherence between the produced ionic states is strongly affected by the IR pulse duration and moderately affected by the IR peak intensity.. We also show that high coherence between the final ionic channels can be obtained with a moderately high IR intensity for very short pulses. The calculation has been performed using the recently developed [1] molecular time-dependent version of the ab-initio algebraic diagrammatic construction (ADC) many-body Green’s function method, in the Bspline single-electron basis.

#P2-29: High-order optical processes in intense laser field: towards nonperturbative nonlinear optics, VASILY V. STRELKOV, We develop an approach describing nonlinear-optical processes in the domain of nonperturbative field-with-matter interaction. The atomic polarization calculated with the help of numerical solution of the Schrödinger equation agrees with our analytical findings. For the case of one strong laser field and several weaker fields we derive and analytically solve propagation equations describing high-order (HO) wavemixing, HO parametric amplification and HO stimulated scattering. These processes provide a way of efficient coherent XUV generation. Some properties of HO processes are new in nonlinear optics: essentially complex values of the coefficients in the propagation equations, the super-exponential (hyperbolic) growing solutions, etc.

#P2-30: Nonsequential double ionization of Helium in IR+XUV two-color laser pulses, FACHENG JIN, MIN LIU, YUANYE TIAN, AND BINGBING WANG, In this work, we investigate the nonsequential double ionization of Helium in IR+XUV two-color laser field. We that the momentum distribution of the two ionized electrons present a step-like structure, which can be explained by the quantum channel contributions.

#P2-31: Mechanisms of Strong-Field Double Ionization of Xe, XUFEI SUN, MIN LI, DIFA YE, GUOGUO XIN, LIBIN FU, XIGUO XIE, YONGKAI DENG, CHENGYIN WU, JIE LIU, QI-HUANG GONG AND YUNQUAN LIU, We perform a fully differential measurement on strong-field double ionization of Xe by 25 fs, 790 nm laser pulses in intensity region (0.4–3)×1014 W/cm2. We observe that the two-dimensional correlation momentum spectra along the laser polarization direction show a nonstructured distribution for double ionization of Xe when decreasing the laser intensity from 3×1014 to 4×1013 W/cm2. The experimental observation indicates that multiple rescatterings play an important role for the  generation of high energy photoelectrons.

#P2-32: High order harmonic generation in two electrons systems by inhomogeneous fields, ALEXIS CHACÓN, MARCELO CIAPPINA AND MACIEJ LEWENSTEIN, When an ultra-short infrared (IR) laser field is focused on a metal nanostructure  the free charge oscillations create a plasmon field. It is an amplified version of the incoming laser pulse, usually of modest intensity, and consequently it is now possible to generate high-order harmonics out of atomic gases. In this work, we present theoretical studies of the High Harmonic Generation (HHG) in two electron atoms, namely He and H−, driven by inhomogeneous field. By numerically integrating the time-dependent Schrödinger equation (TDSE) in reduced two electrons 1D-1D, the electron-electron correlation effects is investigated in the HHG process. It is demonstrated that the inhomogeneity of the enhanced plasmonic field plays an important role in the HHG process.

#P2-33: Relativistic Photoionization Delays and the Role of Auto-ionizing Resonances, M. HUPPERT, I. JORDAN, S. PABST, H.J. WÖRNER, We measured the relative ionization delays into the two spin-orbit components of the electronic ground states of Xe+ and Kr+ under the influence of auto-ionizing intermediate and final states. The results are in good agreement with state-of-the-art calculations based on the time-dependent configuration interaction singles (TDCIS) approach.

#P2-34: Account of the endpoint contribution to the instantaneous ionization rate, I. A. IVANOV, CHANG HEE NAM, KYUNG TAEC KIM, We examine the instantaneous ionization amplitudes and instantaneous ionization rates for the process of tunelling ionization. We show that the end point contribution usually neglected in the asymptotic evaluation of the amplitudes, may be significant. For weak fields the instantaneous ionization rate is largely defined by this contribution. For higher field strengths of the order of 0.1 a.u., the account of this contribution allows to reproduce numerically computed instantaneous ionization rates with higher accuracy.

#P2-35: Attosecond Photoionization Delays of Liquid and Gaseous Water, INGA JORDAN, MARTIN HUPPERT, SEBASTIAN HARTWEG, HANS JAKOB WÖRNER, Photoionization delays reveal electron dynamics on ultrashort time scales. Here, we measure photoionization delays between the outermost valence shells of water in the gas phase, as well as relative delays between the gas and the liquid phases.

#P2-36: Observation of Bloch oscillations and dynamical localization within the quantum rotor, A. KAMALOV, J. FLOẞ , D.W. BROEGE, P.H. BUCKSBAUM, AND I. SH. AVERBUKH, Molecular alignment improves when multiple pulse kicks are used. Pulse trains consisting of a moderate number of kicks are known to amplify alignment when periodically spaced. We present experimental evidence that after a sufficient number of kicks the molecular alignment begins to oscillate and decay with the increasing kicks and that introducing aperiodicity into the pulse train can lead to improved population alignment.

#P2-37: Molecular alignment control of filamentation, N. KAYA, G. KAYA, M. SAYRAC, S. ANUMULA, Y. BORAN, A. A. KOLOMENSKII,M. AMANI, AND H. A. SCHUESSLER, Effect of nonadiabatic laser-induced molecular alignment on filamentation is studied by measuring the rotational wavepacket evolution of N2 molecules after passing of a femtosecond laser pump pulse by observating the nonlinear propagation dynamics of a variably delayed filamentproducing probe pulse.

#P2-38: Reconstruction of attosecond pulses by ptychography, M. LUCCHINI, M. BRÜGMANN, A. LUDWIG, L. GALLMANN, U. KELLER, T. FEURER, The characterization of the temporal properties of ultrafast pulses is often a prerequisite for a correct interpretation of pump-probe experiments. Isolated attosecond pulses are characterized in cross-correlation measurements involving a strong infrared pulse and reconstructed from the data by an iterative algorithm. Here, we present a new algorithm based on time-domain ptychography, which allows for robust and fast reconstruction even of sparsely sampled spectrograms for which the existing algorithms fail.

#P2-39: Macroscopic optimization of high harmonic generation for high power laser pulses, K KOVÁCS, B MAJOR, B MANSCHWETUS, E BALOGH, S MACLOT, L RADING, P RUDAWSKI, CM HEYL, H COUDERT-ALTEIRAC, B FARKAS, V TOSA, P JOHNSSON, A L’HUILLIER, K VARJÚ, We study upscaling of gas high harmonic generation, to make efficient use of the ever increasing laser pulse powers. Loose focusing geometries optimizing phasematching are investigated and compared in HHG efficiency to shorter focusing arrangements. Numerical results obtained in a full 3D code are presented, verified by experimental results.

#P2-40: Strong-Field Electron Holography in Aligned Molecules using COLTRIMS, MORITZ MECKEL, ANDRÉ STAUDTE, SERGUEI PATCHKOVSKII, DAVID M. VILLENEUVE, PAUL B. CORKUM, REINHARD DÖRNER, AND MICHAEL SPANNER, We performed laser induced electron holography on aligned N2 molecules using COLTRIMS and 800nm, 40fs laser pulses. We find that molecules act as tiny antennas that not only shape the amplitude but also the spatial phase of the tunnel ionized wave packet.