Bulletin of the American Physical Society
53rd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 67, Number 7
Monday–Friday, May 30–June 3 2022; Orlando, Florida
Session S08: Dynamics at the Attosecond TimescaleRecordings Available

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Chair: Michael Chini, Central Florida Room: Salon 7/8 
Thursday, June 2, 2022 10:30AM  10:42AM 
S08.00001: Twophoton doubleionization of polyelectronic atoms with a virtual sequential model Siddhartha Chattopadhyay, Luca Argenti Pumpprobe experiments with new XUV sources [1] permit to observe correlated electron dynamics with attosecond resolution. The quantitative description of twophoton double ionization (2PDI) dynamics in these experiments is numerically expensive [2,3]. Still, a virtual sequential model (VSM) with only singleionization intermediate states and no finalstate interaction can capture qualitative aspects of this process even below the sequential regime [4]. In this work, we extend the VSM to finite pulses [5] and polyelectronic atoms. The photoionization cross section of the ground state and of the intermediate ionic states are computed ab initio with the NewStock closecoupling code. This model includes the contribution from final autoionizing states as well as finitepulse effects. The joint energy distribution for the 2PDI of helium compares well with available results in the literature for both single and sequences of multiple ultrashort pulses. Preliminary results for the application of this approach to the neon atom will be presented. 
Thursday, June 2, 2022 10:42AM  10:54AM 
S08.00002: Strongfield dissociation of CO_{2}^{+} VanHung Hoang^{1} and Uwe Thumm^{1} ^{1}Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA Hung V Hoang, Uwe Thumm We theoretically investigated strongfield XUVIR pumpprobe dissociative ionization of CO_{2}. Employing the multiconfigurational selfconsistentfield quantumchemistry code GAMESS to ab initio calculate CO_{2}^{+ }adiabatic potential energy surfaces and dipole couplings, we numerically propagated the timedependent Schrödinger equation for the nuclear motion. Distinguishing the effects of (velocitydependent) nonadiabatic and external IRfield dipole couplings, we (A) calculated the population of the predissociative C ^{2}Σ_{g}^{+} state and kinetic energy release (KER) in the O + CO^{+} dissociation channel and (B) investigated the imprint on KER spectra of the nuclear dynamics near the A^{2}Π_{u} and B^{2}Σ_{u}^{+} conical intersection. Accounting for all vibrational normal modes (bending, symmetrical and antisymmetrical stretch), our simulated fragment KER spectra and pumpprobedelay dependent CO^{+} yield oscillation period are in good agreement with the experiment of Timmers et al., Phys. Rev. Lett. 113, 113003 (2014). This agreement persists for reduceddimensionality calculations with linear molecules (disregarding bending). 
Thursday, June 2, 2022 10:54AM  11:06AM 
S08.00003: AngleDependent Continuum Transitions in MultiSideband RABBITT on Argon: Experiment and Theory Divya Bharti, Kathryn R. Hamilton, Klaus R Bartschat, Anne Harth The reconstruction of attosecond beating by interference of twophoton transitions (RABBITT) [1,2] is a commonly used technique for the study of photoionization dynamics in atomic, molecular, and solid systems with attosecond pulses [3]. Recently, a threesideband (3SB) scheme was suggested [4] and analyzed in detail theoretically for atomic hydrogen [5]. We present recently obtained results from a 3SB RABBITT experiment with argon as the target gas. The dependence of the continuumcontinuum transition phase on the orbital angular momenta of the continuum states is revealed in the angular variation of the three sideband phases. We also directly show an effect of Fano resonances on these phases. Argon is experimentally more readily accessible than atomic hydrogen, but its multielectron character presents a major challenge to theory. Since singleactive electron (SAE) calculations do not adequately reproduce the photoionization cross section of argon, we use the multielectron Rmatrix with time dependence (RMT) method [6] to generate theoretical predictions. These are compared with the latest experimental data. 
Thursday, June 2, 2022 11:06AM  11:18AM 
S08.00004: Time delay in XUV photon driven ionization of C_{60} giant plasmon Maia Magrakvelidze, Mohamed ElAmine Madjet, Himadri Chakraborty Large scale coherent electron correlations play the dominant role to induce a giant plasmon excitation in fullerenes driven by extreme ultraviolet (XUV) light absorption. This excitation primarily decays via the singleelectron continuum channels to create a broad resonance in the ionization spectrum. The underlying manybody mechanism induces a temporary attractive force to affect the time delay of the photoelectrons to reach the detector. In order to determine this delay, the socalled EisenbudWignerSmith delay, for the C_{60} fullerene molecule, we apply a scheme of linear response timedependent density functional theory [1] where the C_{60} ioncore is frozen in a spherical jellium charge distribution. We find a delay approximately within the range of 100200 attoseconds over the plasmon resonance energy range. This is comparable to the average dephasing time obtained from the linewidth of the resonance. The result served as an essential ingredient to describe recent real time measurements by photoelectron chronoscopy [2]. [1] Choi et al., Phys. Rev. A, 95, 023404 (2017); [2] Biswas et al., arXiv:2111.14464 [physics.atomph] 
Thursday, June 2, 2022 11:18AM  11:30AM 
S08.00005: ASTRA, a transitiondensitymatrix method for attosecond molecular dynamics Luca Argenti, Carlos Marante, Juan M Randazzo, Heman Gharibnejad, Barry I Schneider, Jeppe Olsen The push of ultrashort light sources to and beyond the water window [1], to high intensity [2], and to ever shorter durations has opened the way to the sitespecific xraypump xrayprobe study of electron dynamics in molecules of chemical relevance. Theoretical tools able to quantitatively resolve in time the correlated and entangled character of molecular ionization processes are necessary to guide these experiments. Here we present ASTRA (AttoSecond TRAnsitions), a program based on an innovative approach to the closecoupling method for molecular ionization. ASTRA makes use of highorder transition density matrices between largescaleCI ionic states with arbitrary symmetry and multiplicity, obtained with an extension of the LUCIA code [3], and on hybrid GaussianBspline integrals [4,5]. These essential features allow ASTRA to reach coreexcitation/decay energies, to account for exchange effects exactly, and to scale independently of the size of the parention configuration space. The talk will focus on ASTRA theory, its current applications, and its future directions. 
Thursday, June 2, 2022 11:30AM  11:42AM 
S08.00006: Photoelectron – ion entanglement in streaked direct and shakeup photoemission from helium: an ab initio approach Uwe Thumm, Hongyu Shi We applied our FEDVR code for the ab initio calculation of single and doubleionization of gaseous helium atoms [1] to explore the effects of electronic correlation on attosecond time and angleresolved photoemission. Our calculated spectra and relative photoemission time delays for IR streaked direct and He+ (n=2) shakeup XUV emission agree well with experimental and theoretical data in [2]. To scrutinize the influence of the transient induced oscillating residual excited He+ (n=2,3) charge distribution, we compared our abinitio streaking calculations with single active electron (SAE) calculations. By adjusting effective multipole SAE potentials to ab initio calculated He+* charge distributions, we assessed to role of individual multipole components of the residual He+* ion on spectra and photoemission delays. 
Thursday, June 2, 2022 11:42AM  11:54AM 
S08.00007: Direct Electric Field Measurement of Femtosecond TimeResolved FourWave Mixing Signals in Molecules Francis F Walz, Siddhant Pandey, Liang Tan, Niranjan Shivaram We measure the third order nonlinear response in molecules such as CO_{2 }and ethylene, by fully reconstructing the emitted signal electric field. Using a spectral interferometrybased technique for measuring ultraweak femtosecond pulses, called TADPOLE, we measure the real and imaginary parts of the nonlinear response in a single measurement. The nonlinear signal is generated using the Optical Kerreffect (OKE), where a pair of femtosecond pulses (gate and probe) generate a signal that copropagates with the probe beam having a polarization orthogonal to the probe polarization. Properties of the reconstructed signal electric field, such as the pulse envelope fullwidth half maximum and chirp of the temporal phase, can provide detailed information about ultrafast dynamics in these systems. We present results from measurement of nonlinear signal electric fields generated from purely electronic response in neutral CO_{2 }molecules and ionized ethylene molecules. A further extension of these experiments to measure higher order nonlinear response, such as the fourth order nonlinear response in chiral molecules will be discussed. 
Thursday, June 2, 2022 11:54AM  12:06PM 
S08.00008: Measurement of molecularframe electronic nonlinear response in aligned carbon dioxide and nitrogen molecules Siddhant Pandey, Francis F Walz, Varun S Makhija, Niranjan Shivaram We report the measurement of the molecular frame thirdorder nonlinear response tensor (second hyperpolarizability) in impulsively aligned carbon dioxide and nitrogen molecules. A moderately strong femtosecond nearinfrared laser pulse is used to impulsively align gas molecules, and a set of weaker femtosecond pulses subsequently probe the nonlinear response using nondegenerate fourwave mixing (NDFWM). The emitted electric field is directly measured, using a spectral interferometry technique for measuring ultraweak femtosecond pulses, called TADPOLE. The measured amplitude and phase of the signal electric field is combined to get the real and imaginary parts of the signal in a single measurement. By suppressing the rotational and ionization grating contributions, NDFWM exclusively measures the electroniconly nonlinearity. By analyzing the nonlinear signal as a function of time delay between the alignment pulse and the fourwave mixing pulses, the molecular frame nonlinear response is extracted using the previously established technique of Orientation Resolution through Rotational Coherence Spectroscopy (ORRCS). Using the transformation properties of a tensor under rotation, a few tensor components measured as a function of the molecular alignment angle can be converted into multiple tensor components for a fixed molecular orientation. Knowledge of these multiple tensor components are used to distinguish the symmetries of the ground state electronic character in different molecules. We discuss these results for carbon dioxide and nitrogen. The roadmap for extending these nonlinear response tensor measurements to study ultrafast dynamics on electronically excited states in molecules is discussed. 
Thursday, June 2, 2022 12:06PM  12:18PM 
S08.00009: Improved initial conditions of the electron ionized by a strong, linearly polarized laser field and their reconstruction from the detected momentum of the electron Szabolcs Hack, Szilárd Majorosi, Mihaly Benedict, Sándor Varró, Attila Czirják Tunneling time and exit momentum are of outstanding importance regarding both quantum theory and attosecond metrology. Several research groups published relevant experimental results, and the explanatory theoretical models often employ classical dynamics, where the choice of proper initial conditions is an important open question. 
Thursday, June 2, 2022 12:18PM  12:30PM 
S08.00010: Onthefly ab initio semiclassical evaluation of electronic coherences in polyatomic molecules reveals a simple mechanism of decoherence Jiri J Vanicek, Nikolay Golubev, Tomislav Begusic Irradiation of a molecular system by an intense laser field can trigger dynamics of both electronic and nuclear subsystems. The lighter electrons usually move on much faster, attosecond time scale but the slow nuclear rearrangement damps ultrafast electronic oscillations, leading to the decoherence of the electronic dynamics within a few femtoseconds. We show that a simple, singletrajectory semiclassical scheme can evaluate the electronic coherence time in polyatomic molecules accurately by demonstrating an excellent agreement with fulldimensional quantum calculations. In contrast to numerical quantum methods, the semiclassical one reveals the physical mechanism of decoherence beyond the general blame on nuclear motion. In the propiolic acid, the rate of decoherence and the large deviation from the static frequency of electronic oscillations are quantitatively described with just two semiclassical parametersthe phase space distance and signed area between the trajectories moving on two electronic surfaces. Because it evaluates the electronic structure on the fly, the semiclassical technique avoids the "curse of dimensionality" and should be useful for preselecting molecules for experimental studies. 
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