Bulletin of the American Physical Society
51st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 65, Number 4
Monday–Friday, June 1–5, 2020; Portland, Oregon
Session H04: FOCUS: Theoretical Advances in Strong-Field and Ultrafast Physical Processes (Memorial Session to Honor the Legacy of Anthony Starace)Focus Live
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Chair: Jean Marcel Ngoko-Djiokap, University of Nebraska Lincoln Room: D137-138 |
Wednesday, June 3, 2020 10:30AM - 11:00AM Live |
H04.00001: Attosecond Time-resolved Photoemission Invited Speaker: Joachim Burgdörfer With recent advances in ultrafast laser technologies featuring phase controlled few-cycle strong-field near infrared pulses as well as XUV pulses of attosecond duration, the dream of watching electronic dynamics, charge transfer, bond breaking and making, or electron ejection in real time is becoming reality. Challenges ahead in fully reaching the goal to steer and control electronic motion and the attosecond scale will be discussed. Such attosecond chronoscopy allows a novel look at a wide range of fundamental photophysical and photochemical processes in the time domain, including Auger and autoionization processes, photoemission from atoms, molecules and surfaces, completing conventional energy-domain spectroscopy. Attosecond chronoscopy raises fundamental conceptual and theoretical questions as which novel information becomes accessible and which dynamical processes can be controlled and steered. In this talk, we will focus on a few prototypical examples in the field of time-resolved photoionization, a field to which Antony Starke has significantly contributed. Examples include time-resolved Fano resonances, correlation effects and chirality in double ionization, and non-linear many-particle interferences in strong-field attosecond pulses. * Work in collaboration with I. Brezinova, S. Donsa, C. Lemell, W.-C. Jiang, H. Ni, and L. Argenti. [Preview Abstract] |
Wednesday, June 3, 2020 11:00AM - 11:30AM Live |
H04.00002: Multielectron polarization and nondipole effects in strong-field ionization Invited Speaker: Lars Bojer Madsen In theoretical strong-field and attosecond physics, we are faced with a number of fundamental and computational challenges. Two central related research themes are \begin{enumerate} \item How to deal with the time-dependent nonperturbative driving of a multielectron system? \item How to deal with situations where the nature of the external laser pulses leads to a breakdown of conventional approximations, like, e.g., the electric dipole approximation? \end{enumerate} In this talk, I will discuss recent progress addressing certain aspects of points 1 and 2. Specifically, I will (i) give a status on formulation and numerical implementation of the tunneling theory for large molecules. I will (ii) show how multielectron polarization effects may lead to a simplification of the response of a many-electron system facilitating the formulation of effective single-active electron models. Finally, I will (iii) show how an approximate nondipole approach, which is described by a nondipole strong-field approximation Hamiltonian, accounts for nondipole effects in an accurate and effective manner. [Preview Abstract] |
Wednesday, June 3, 2020 11:30AM - 11:42AM Live |
H04.00003: Attosecond ionization dynamics: finding the best path Loren Greenman Attosecond processes can frequently be understood from the perspective of time-dependent perturbation theory. Ionization is either a feature of the processes of interest through the information gained from photoelectron yields and angular distributions, or it is a byproduct of the broad bandwidths required for attosecond resolution that must be described to understand the more interesting features. The necessity of including electronic continua in our perturbative states makes the connection between accurate descriptions of correlated states and continuum states more difficult. Recent attempts have had some success at combining perturbation theory, scattering methods, and bound-state quantum chemistry. I will describe our contributions to these methods, along with some examples of their use. One of the key issues in the implementation of such methods is the combination of quantum chemistry and scattering theory at the same level of accuracy, and the evaluation of the necessary integrals mixing bound and continuum states and local and grid basis functions. I will discuss extending these methods by addressing these issues using ideas from variational perturbation theory, which for time-independent states was explored in the 1980s and 1990s by Prof. Anthony Starace. [Preview Abstract] |
Wednesday, June 3, 2020 11:42AM - 11:54AM Live |
H04.00004: Ellipticity dependence of frustrated tunneling ionization in argon atoms. Kathryn Hamilton, Thomas Pauly, Klaus Bartschat Following tunneling ionization by a strong, few-cycle infrared pulse, a portion of the ionized electrons can recombine into a bound state through Frustrated Tunneling Ionization (FTI)~[1,2]. A recent joint experimental and theoretical study on argon atoms, with emphasis on metastable production by linearly polarized light, was reported by Chetty et al.~[3]. By increasing the ellipticity of the driving laser pulse, the liberated electron is driven further away from the ion, thereby reducing the probability of recombination into a bound state. The ellipticity dependence of FTI was previously studied both theoretically~[1] and experimentally~[4] in helium. Here we present predictions for the theoretically more challenging argon target, employing both multi-electron~[4] and single-active electron~[5] theoretical techniques to compliment experimental efforts currently in progress~[7]. [1] T.~Nubbemeyer et al., Phys.\ Rev.\ Lett.~{\bf 101} (2008) 233001. [2] H.~Zimmermann et al., Phys.\ Rev.\ Lett.~{\bf 118} (2017) 013003. [3] D.~Chetty et al., arXiv:1912.06280v1 (2019). [4] H.~Yun et al., Nat.\ Phot.~{\bf 12} (2018) 620-624. [5] A.~C.~Brown et al., Comput.\ Phys.~(2019) 107062. [6] N.~Douguet et al., Phys.\ Rev.\ A~{\bf 93} (2016) 033402. [7] I.~Litvinyuk, priv.\ commun.~(2020). [Preview Abstract] |
Wednesday, June 3, 2020 11:54AM - 12:06PM Live |
H04.00005: \textbf{Control of Electron Recollision and Molecular Nonsequential Double Ionization} Marcos Dantus, Shuai Li, Itzik Ben-Itzhak Control over non-sequential double ionization (NSDI) via spectral-phase pulse shaping of strong femtosecond laser pulses was measured on ethane molecules. The shaped pulses having either a positive or a negative \textthreequarters $\pi $ phase step that is scanned across the spectrum of the pulse, while all other parameters fixed, and the yield of all resulting ions generated by the field are measured. We find that the shaped pulses can enhance or suppress the yield of dications resulting from electron recollision by factors of 3 to 6, the maximum degree of control is observed when the phase step is near /2 of the Gaussian laser spectrum. Identifying molecular NSDI from other ionization processes, such as multiphoton ionization, allow us to time-resolve roaming chemical reactions such as those producing H$_{\mathrm{3}}^{\mathrm{+}}$. [Preview Abstract] |
Wednesday, June 3, 2020 12:06PM - 12:18PM Live |
H04.00006: Generation of vortex electrons in high energy ionization Katarzyna Krajewska, Felipe Cajiao V\'elez, Jerzy Kami\'nski Electron beams with a well-defined longitudinal orbital angular momentum (OAM), known as twisted or vortex electrons, are attracting considerable interest in both fundamental and applied physics. Their unique features (such as helical wavefronts, circulating probability density currents, etc.) make these beams ideal tools for studies in various fields of modern physics. For instance, scattering of twisted electrons on a solid target can provide detailed information about the magnetic properties of the target material. The same concerns helical properties of crystals or nanomolecules. Here, we investigate a possibility of generating vortex electrons in high-energy ionization. We show that photoelectrons of unprecedented large OAM can be emitted when a high-intensity laser pulse interacts with atomic targets. In order to analyze how OAM of photoelectrons may influence the ionization spectrum we use the quasi-relativistic strong-field approximation. This approach (with the binding potential neglected during the electron dynamics in a laser field) is particularly well suited for describing high-energy ionization. In addition, it accounts for relativistic effects, including the electron recoil due to the interaction with the laser field and the relativistic mass correction. [Preview Abstract] |
Wednesday, June 3, 2020 12:18PM - 12:30PM On Demand |
H04.00007: Violation of centrosymmetry in time-resolved coherent x-ray diffraction from ro-vibrational states of diatomic molecules Hua-Chieh Shao, Anthony F. Starace Owing to increasing applications of x-ray scattering for the investigation of molecular reaction dynamics, we theoretically study coherent x-ray diffraction to characterize features in time-resolved diffraction images that reflect nuclear motion in molecules.\footnote{H.-C. Shao and A.F. Starace, Phys. Rev. A \textbf{99}, 033413 (2019).} Contrary to the conventional theory of time-independent x-ray diffraction, our model shows that the diffraction images can exhibit asymmetric angular distributions when the nuclei are in motion. In order to illustrate this violation of centrosymmetry (VOC), we simulate the diffraction images from two oriented diatomic molecules undergoing ro-vibrational motion: deuterated lithium hydride (LiD) and hydrogen (HD). We further investigate how the VOC relates to the nuclear motion and the nature of such asymmetry. Our analysis indicates that the VOC is a general phenomenon in time-resolved coherent diffraction whenever a molecular motion breaks the inversion symmetry. [Preview Abstract] |
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