Bulletin of the American Physical Society
54th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 68, Number 7
Monday–Friday, June 5–9, 2023; Spokane, Washington
Session C04: Focus Session: Probing Electronic Dynamics thru PhotoemissionFocus Live Streamed
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Chair: Alexandra Landsman, Ohio State University Room: Conference Theater |
Tuesday, June 6, 2023 10:45AM - 11:15AM |
C04.00001: Molecular frame photoemission time delay Invited Speaker: Robert R Lucchese The time delay in one-photon emission is given by the energy derivative of the phase of the transition matrix element for the process. In molecular systems, the transition matrix element depends on the emission direction, relative to the orientation of the molecule, i.e. in the molecular frame, and on the polarization direction of the radiation. As a consequence, the time delay can have a complicated direction dependence in the molecular frame. The molecular frame photoemission time delay provides insights into the attosecond dynamics induced by one-photon absorption, including the role of continuum resonant states, hole localization, and diffractive scattering. Here, we report the angular dependence of single-photon ionization delays across a shape resonance in the photoionization of NO [1] studied both in theory and experiment. The angle-dependent time delay variations of a few hundreds of attoseconds, resulting from the interference of the resonant and non-resonant contributions to the dynamics of the ejected electron, are well described using a multichannel Fano model where the time delay of the resonant component is angle-independent. A theoretical study of the photoionization of Kr2 shows the effect of both hole localization and diffractive scattering on molecular-frame time delays, which are related to experimental laboratory-frame measurements [2]. Additionally, we consider the behavior of the photoemission time delay in molecular photodetachment. In this case, the absence of the long-range Coulomb interaction in the resulting electron-neutral molecule scattering yields more detailed information about the low-energy photoemission dynamics. A theoretical study of the detachment from core levels of CN– shows that the asymmetry of the system can lead to strong molecular frame dependence in the resulting photoemission time delays at low energies. |
Tuesday, June 6, 2023 11:15AM - 11:27AM |
C04.00002: Resolving Molecular Electron Dynamics with Attosecond Spectroscopy Using Visible Light Zifan Wang, Daniel R Tuthill, Louis F DiMauro, Mette B Gaarde, Robert R Jones, Francois Mauger, Kenneth Lopata, Kenneth J Schafer Photoionization is a fundamental process in the interaction between light and matter. Our work aims to study ultrafast electron dynamics through photoionization of molecules and resolve the resulting multielectron dynamics. In attosecond spectroscopy of molecules, ionization by a high-harmonic generation (HHG) source using a conventional near-infrared (NIR) laser produces electrons from different energy states that overlap with each other, which makes it difficult to resolve each state. The overlap is due to the close spacing of high-harmonics produced from a NIR laser, and the complex structure of molecules which creates closely spaced ionization potentials for different states. In our work, we generate attosecond pulses using visible light with the wavelength of 400nm. With this wavelength, we have greater spectral separation between neighboring high harmonics as well as adequate high-harmonic flux. By using the reconstruction of attosecond beating by interference of two-photon transitions (RABBITT) method, we can retrieve the photoionization delay in the target molecule. The outgoing electron can also experience an effective potential by multielectron dynamics, modifying the photoionization delay. By measuring both the amplitude and phase of photoionization, we can resolve dynamic processes in molecules such as shape resonances. Here we present photoionization measurements in CO2 using attosecond pulses generated by visible light. |
Tuesday, June 6, 2023 11:27AM - 11:39AM |
C04.00003: Theoretical calculations of RABBIT spectra and associated photoionization time delays in polyatomic molecules Celso Manuel Gonzalez Collado, Etienne Plésiat, Piero Decleva, Alicia Palacios, Fernando Martín In the RABBIT (Reconstruction of Attosecond Beating By Interference of Two-photon Transitions), the photoelectrons produced by ionization of a target gas by a train of XUV attosecond pulses are measured in the presence of the IR laser field used to generate that train as a function of the XUV-IR delay. The photoelectron spectrum produced by the XUV pulse train is a replica of the harmonic spectrum with discrete peaks separated by twice the frequency of the driving field. When the IR field is added, additional peaks are produced in the photoelectron spectrum, which appear as sidebands of the former peaks and are due to the absorption or emission of one IR photon (for weak IR intensities). These two paths are indistinguishable, so they interfere, and as a result of this, the amplitude of the sidebands exhibits a periodic modulation with respect to the time delay between the XUV and the IR pulses. This allows one to extract the intrinsic phase difference of the matrix elements corresponding to photoionization from consecutive harmonics. |
Tuesday, June 6, 2023 11:39AM - 11:51AM |
C04.00004: Evolving ultrafast electron dynamics in C60 from relaxation to ionization Himadri Chakraborty, Maia Magrakvelidze, Esam Ali, Ruma De, Mohamed El-Amine Madjet Investigation of ultrafast dynamics of photoinduced processes in fullerene materials are valuable in applications from photovoltaics and photothermal therapy to quantum plasmonics. For the fundamental science, fullerenes are eminent “laboratory” to probe femtosecond electron relaxation upon a mid-UV photon absorption as well as plasmonic electron emission in attoseconds driven by an extreme-UV radiation. Recent results [1, 2] of our computational studies of these processes for C60 will be covered in the talk. The plasmonic emission delay results are found in excellent conformity [2] with attosecond photoemission streaking measurements and probed the energy-differential plasmon dephasing mechanism. The relaxation results, on the other hand, should inspire ultrafast transient absorption or time-resolved photoelectron experiments. [1] Madjet et al., Phys. Rev. Lett. 126, 183002, (2021); [2] Biswas et al., (in review) preprint arXiv:2111.14464 [physics.atom-ph] https://arxiv.org/abs/2111.14464 |
Tuesday, June 6, 2023 11:51AM - 12:21PM |
C04.00005: Coherence Survival in Resonant Attosecond Ionization Processes Invited Speaker: Luca Argenti This talk explores through examples the control of coherence in the ionization of atomic and molecular systems by attosecond light pulses. The first example concerns the creation and reconstruction of the electronic coherence of a He+ ion following XUV-pump IR-probe ionization of He above the N=2 and N=3 thresholds, where autoionizing states play a prominent role [1,2]. The second example considers the apparent decoherence in integral multiphoton ionization cross sections, when the presence of resonant states cause the radial and angular photoelectron degrees of freedom to be entangled [3]. The third discusses the entanglement between light and matter in the metastable Autler-Townes multiplets that emerge from the interaction between the 3s-14p and several light-induced states in argon [3,4], which can stabilize resonances against autoionization. A forth example shows how the nuclear recoil due to C-1s photoemission and intramolecular scattering in the CO molecule [5] results in a residual coherence of the ionic vibrational state that can be reconstructed with photoelectron interferometry. This work is supported by the DOE CAREER grant DE-SC0020311 and NSF grant No.1912507. |
Tuesday, June 6, 2023 12:21PM - 12:33PM |
C04.00006: Probing the amplitudes and phases of quantum beats in spin-orbit split continua James K Wood, Miguel Alarcon, Alexander C Plunkett, Dipayan Biswas, Chris H Greene, Arvinder S Sandhu Electron ion core interactions influence wavepacket dynamics of excited states and manifest in the photoionization to spin-orbit slit ionization thresholds. We used an XUV pulse to excite a 2[P1/2]o5s-3d Rydberg wavepacket in Argon atom, which is then ionized with an IR pulse in a two-photon process leaving the core in either J=1/2 and J=3/2 state, where the interaction of the outgoing electron with the ion core alters the angular momentum for one of the channels. We analyze the photoelectron spectra and angular distributions as a function of XUV-IR delay. We observe a strong quantum beat corresponding to the 2[P1/2]o5s-3d energy gap in both ionization channels. Interestingly, the beats in two channels are out-of-phase, and the results also exhibit beats at unexpected photoelectron energies. The phase difference potentially contains information on the relative photoionization delays into two channels. Theoretical analysis of the two-color ionization shows remarkable agreement with the observed experimental amplitude and phases. In addition, we present angular distribution analysis which points to the small role of higher order Raman-like processes in photoionization signal. Our experimental and theoretical results offer a platform to study electron-ion core interactions in this and other systems. |
Tuesday, June 6, 2023 12:33PM - 12:45PM |
C04.00007: A finite-pulse virtual-sequential model for the two-photon double ionization of Ne and Ar. Siddhartha Chattopadhyay, Carlos A Marante Valdes, Jeppe Olsen, Barry I Schneider, Luca Argenti The pump-probe experiments enabled by XFELs [1,2] will allow us to directly observe correlated electronic motion with attosecond time resolution by detecting photoelectron pairs in coincidence. In helium, the transition between the non-sequential and sequential regime in two-photon double ionization (TPDI) is well explained by a virtual-sequential model (VS) [3]. Much less is known, however, about TPDI in more complex atoms. Recently, we have extended the VS model to arbitrary light pulses [4], using multi-channel scattering states for the single ionization of both the neutral and the ionized target [5]. This finite-pulse virtual-sequential model (FPVSM) reproduces all the qualitative features of ab-initio angularly integrated observables [6,7]. As a step towards the description of TPDI in polyelectronic atoms, we used the FPVSM to calculate the joint photoelectron energy distribution and sharing in neon and argon. Our simulations reveal two-particle interferences and the signature of autoionizing states, which should be observable with current experimental technologies [2]. |
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