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 Q03: Focus Session: Attosecond Multi-wave-mixing and Nonlinear SpectroscopyFocus Live Streamed
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Chair: Alicia Palacios, Universidad Autonoma de Madrid Room: Ballroom 111 B |
Thursday, June 8, 2023 8:00AM - 8:30AM |
Q03.00001: Quantum control of electron dynamics in the continuum Invited Speaker: Arvinder S Sandhu The entangled light-matter character of autoionizing states in the presence of laser fields, which makes them polaritons, forms a relatively unexplored topic. We report the study of multiple radiatively coupled autoionizing light-induced states in argon, as well as evidence of their stabilization, thus confirming a long standing prediction. XUV absorption measurements were conducted in the presence of a tunable light fields and the non-linear light-matter interactions were interepreted with ab initio simulations. We demonstrated optical control over the formation of autoionizing polaritons and their decay rate into different channels. This is achieved by arranging destructive interferences between the interfering Auger decay and radiative ionization paths, which leads to the stabilization of the system against the ionization. We also investigated the avoided crossings between the bright states and light induced autoionizing states. The application of tunable attosecond transient absorption and multi-wave-mixing between XUV and IR fields offers new insights into the properties of autoionizing states, and provides tools for the control of polyelectronic metastable systems, opening the doors for implementation of quantum control protocols in the continuum. |
Thursday, June 8, 2023 8:30AM - 8:42AM |
Q03.00002: Phase-shift control of the Rabi sideband emission from excitation gratings in cross-beam filament wake channels in a dense argon gas* Suyash Bajpai, Dmitri A Romanov, Robert J Levis When femtosecond laser filamentation happens in a dense gas at the crossing of two laser beams, the intensity modulation in the crossing area leads to the formation of finite density gratings of ions and excited atoms. The resulting excitation grating can be controlled by the parameters of the crossing laser pulses, specifically, by the crossing angle and the inter-beam phase delay. The variation in the latter parameter has a prominent effect on the grating structure, which is especially pronounced when the crossing angle is small. Addressing the case of high-pressure argon gas, we explore theoretically the excitation grating formation and show the quantitative relation between the positions of the grating maxima and the inter-beam phase delay. If a picosecond probe pulse is incident normally on thus produced excitation gratings, the electric field of the probe pulse couples the excited state manifolds, resulting in Rabi sideband emission at frequencies red-shifted and blue-shifted about the probe carrier frequency. This emitted radiation participates in spatial and temporal interference and generates complicated spatial-spectral interference patterns on a remote screen. We investigate how these patterns are considerably modified in response to variations in the phase delay between the grating-generating crossing beams. |
Thursday, June 8, 2023 8:42AM - 8:54AM |
Q03.00003: Attosecond control in solids with high-order wavemixing David N Purschke, Álvaro Jiménez-Galán, Thomas Brabec, Andrei Y Naumov, David M Villeneuve, Giulio Vampa Recently, many of the tools from strong-field physics have been adpated to study solids with great success, however, there remains an unexplored potential for using two-color fields to control attosecond processes in condensed matter. Here, we use the gas-phase technique of two-color non-collinear high-harmonic generation (HHG) to isolate the high-order wavemixing pathways in solids. A strong ultrashort pulse and its weak second harmonic are coincident with a small separation angle on an MgO surface. The resulting HHG consists of a series of angularly dispersed beams, where the angle and energy of each harmonic can be used to index the underlying photon mixing pathway. We observe bright extreme-ultraviolet wavemixing peaks with generation efficiencies that can exceed that of the single-color HHG, showing that high-order wavemixing is an excellent control mechanism for solid-state HHG. To gain further insight, we develop a quantum theory within the strong-field approximation that explains how the different pathways are isolated in the far field, demonstrates the origin of their perturbative scaling, and outlines the selection rules governing the diffraction pattern. In this theory, the full HHG dipole arises from the quantum interference of the different pathways, suggesting that two-color HHG can be generally framed as coherent control of high-order wavemixing. Our work shows how high-order wavemixing will be a useful tool to probe and control attosecond processes in condensed matter. For example, we discuss how non-collinear HHG can provide a new window into dephasing or enable all-optical solid-state XUV optics. |
Thursday, June 8, 2023 8:54AM - 9:06AM |
Q03.00004: Probing ultrafast excited-state dynamics using EUV-IR six-wave-mixing emission spectroscopy Islam S Shalaby, Nisnat Chakraborty, Sergio Yanez-Pagans, James K Wood, Dipayan Biswas, Arvinder S Sandhu We demonstrate application of six-wave-mixing (SWM) spectroscopy in the study of excited states of neon. By combining extreme ultraviolet (EUV) excitation with multi-color near-infrared (NIR) and mid-infrared (MIR) laser fields, we obtained strong emission signals from several channels. Specifically, the EUV pulse excites the system to a 3d state, while the synchronous NIR pulse transfers the electronic population to neighboring dark states. The delayed MIR pulse probes the dynamics of these states, and we observe quantum beats stemming from the interferences between two pathways separated by the spin-orbit splitting. The non-commensurate photon energies of light pulses results in background-free spectral emission that can be isolated from the main EUV spectrum. The multi-color excitation provides access to the optically dark states which cannot be accessed by a one-photon transition from the ground state. Finally, the tunability of the MIR photon energy allows us to control the electronic couplings between states. The SWM spectroscopy thus offers a powerful tool to probe the excited states wave packet dynamics in atomic and molecular systems. |
Thursday, June 8, 2023 9:06AM - 9:36AM |
Q03.00005: Novel Ultrafast X-ray Probes of Elementary Molecular Events Invited Speaker: Shaul Mukamel Novel X-ray pulse sources from free-electron lasers and high-harmonic generation setups enable the monitoring of molecular events on unprecedented temporal, spatial and energetic scales. The attosecond duration of X-ray pulses, their large bandwidth over a large tunable energy range, and the atomic selectivity of core X-ray excitations offer a uniquely high spatial and temporal selectivity for non-linear spectroscopies. In this talk, we survey recent theoretical developments that design, simulate, and predict spectroscopic signals revealing detailed information about ultrafast molecular dynamics. A special focus lies on the chirality of molecules and light. Resonant attosecond X-ray probes allow to monitor the dissociation of a single iodine atom from a chiral center. The loss of chiral information is distinctly visible in the transient signal, giving information about the timescale and distance across which chirality is experienced. From the light perspective, sophisticated spatio-temporal polarization profiles known from optical pulses is translated to X-ray wavelengths. We show how the Orbital Angular Momentum of X-ray light fields can be leveraged to detect coherences emerging at conical intersections due to the bifurcation of molecular wavepackets. |
Thursday, June 8, 2023 9:36AM - 9:48AM |
Q03.00006: Resonant Perfect Absorption and Autoionization Dynamics Revealed by Attosecond Transient Absorption Spectroscopy Yu He, Shuyuan Hu, Gergana Borisova, Zuoye Liu, Shaohua Sun, Bitao Hu, Adrian N Pfeiffer, Mette B Gaarde, Christian Ott, Thomas Pfeifer We introduce a general approach to manipulate and substantially enhance the resonant absorption property of a macroscopic medium. By emptying the population of the excited state after its excitation, the polarization decay of the target system is temporally reshaped and confined. The tunable temporal gate between excitation and termination allows us to tailor the tail of the excitation pulse developed during propagation, which thus interferes controllably with the original pulse. Numerical and analytical results on an ensemble of two-level systems demonstrate that the resonant absorption of light can be reduced or significantly enhanced by more than 5 orders of magnitude relative to that without laser manipulation, and resonant “perfect absorption” can be achieved at certain conditions. These results are further supported by large-scale calculations of the coupled time-dependent Schrödinger and Maxwell wave equations in helium. Experimentally, we report the transient-absorption measurement of sp2,n± autoionization states in helium gas. The spectral signature of sp2,4- shows up in the presence of a moderately intense visible pulse, which is otherwise suppressed due to its low dipole coupling to the ground state. The different temporal dynamics of these states are analyzed, and the roles of propagation effects in the line-shape manipulation are discussed. |
Thursday, June 8, 2023 9:48AM - 10:00AM |
Q03.00007: Circular dichroism in attosecond transient absorption spectroscopy of isotropic media Lorenz B Drescher, Nicola Mayer, Jonah Adelman, Kylie Gannan, Stephen R Leone Circular polarized light offers opportunities to probe symmetry-dependent properties of matter such as chirality, inversion-symmetry and spin. However, circular dichroism measurements typically require further intrinsic or extrinsic breaking of symmetry by e.g. enantiomeric excess, orientation, magnetic fields or direction-sensitive detectors. Here we introduce circular-dichroic attosecond transient absorption spectroscopy by leveraging the spin-selectivity of two circular-polarized pulses, both pump and probe, in an isotropic medium, breaking the symmetry by preparing spin-specific excited states. As a proof-of-principle we demonstrate a circular-dichroic measurement of the attosecond transient absorption of He Rydberg states: By limiting the allowed coupling pathways due to magnetic quantum number selection rules for co- and counter-rotating circular polarized NIR and XUV pulses, different spectral reshaping of the XUV absorption due to the AC Stark effect is observed. Paired with time-dependent Schrödinger equation calculations, our results allow for an in-situ determination of the XUV ellipticity in an absorption experiment. Our results open up new opportunities to study coupling pathways of excited states as well as spin-dependent dynamics.
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