Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session M27: Ultrafast Dynamics and Control of Quantum Materials IIRecordings Available
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Sponsoring Units: DLS Chair: Emroz Khan, Purdue University Room: McCormick Place W-187C |
Wednesday, March 16, 2022 8:00AM - 8:12AM |
M27.00001: Photoelectron vortices in strong-field ionization of chiral molecules with linearly polarized light Andres F Ordonez Lasso, Andrew Maxwell, Xavier Barcons, Maciej Lewenstein Similarly to optical vortices, electron vortices – electron waves with orbital angular momentum – have revealed a new set of possibilities out of reach for regular plane waves. Among their applications, electron vortices could be used to probe the chirality of nanoclusters and macromolecules in inelastic electron scattering. Here, we propose to use electron vortices as the fingerprint of molecular chirality in photoionization. We analyzed the orbital angular momentum (OAM) of photoelectrons emitted by a chiral target when subjected to an ultrashort intense IR field, linearly polarized along z . For an achiral target there is no correlation between the photoelectron direction p_z and its OAM. For a chiral target we found a strong correlation between p_z and the OAM. For a given enantiomer, photoelectrons with positive p_z have positive OAM and photoelectrons with negative p_z have negative OAM. For the opposite enantiomer the correlation is reversed, i.e. photoelectrons with positive (negative) p_z have negative (positive) OAM. This effect is robust across a wide range of photoelectron momenta and since it occurs within the electric-dipole approximation, it yields enantiomeric discrimination on par with the most powerful techniques, such as photoelectron circular dichroism (PECD). |
Wednesday, March 16, 2022 8:12AM - 8:24AM |
M27.00002: Temporally Flattop Picosecond Pulses through Nonlinear Conversion and Phase Manipulation Randy A Lemons, Sergio Carbajo, Charles G Durfee, Joe Duris, Nicole Neveu, Agostino Marinelli Generating temporally flat-top picosecond UV laser pulses for reducing electron emittance from photocathodes driving high repetition rate x-ray free electron lasers (XFELs), such as LCLS-II, is challenged by shape distortions and material damage. One promising avenue towards this end is laser pulse shaping through non-colinear sum-frequency generation (SFG) between pulses with opposite spectral phase in a few dispersion order terms [1]. With this method, the SFG pulse is simultaneously generated, shaped, and spectrally compressed. Additionally, the narrowband pulses have near-flat phase such that they are resistant to shape distortions once generated. We present an experimental demonstration of this principle and generation of shaped narrowband picosecond shaped pulses from chirped femtosecond pulses. Additionally, we discuss how this principle may be applied to generate pulses with non-flattop shape. |
Wednesday, March 16, 2022 8:24AM - 8:36AM |
M27.00003: Opportunities for imaging chiral nuclear dynamics on ultrafast timescales with synthetic chiral light David Ayuso, Misha Ivanov, Olga Smirnova Chiral molecules appear in pairs of left- and right-handed enantiomers. These “mirror twins” behave identically, unless they interact with another chiral “object”. Distinguishing them is vital, but also hard [1]. Traditional optical methods rely on the helical structure that circularly polarized light draws in space. However, the pitch of this helix is too large, which leads to weak enantio-sensitivity (usually below 0.1%) and poses major challenges for imaging chiral dynamics, especially on ultrafast time scales. |
Wednesday, March 16, 2022 8:36AM - 8:48AM |
M27.00004: Distinguishing Intrinsic from Extrinsic Effects in Time-resolved Photoemission Patrick S Kirchmann, Heike Pfau, Jonathan A Sobota, Hadas Soifer, Nicolas Gauthier, Kejun Xu, Shujie Tang, Costel R Rotundu, Zhi-Xun Shen Time- and angle-resolved photoemission is a powerful tool for the study of electron dynamics in condensed matter. Ultrafast excitation results in changes of binding energies and line shapes but not all effects are intrinsic or report on the physics inside the sample. We discuss how apparent binding energy shifts due to surface photovoltage can be distinguished from shifts and broadening due to pump-induced vacuum space charge. We will share strategies to mitigate pump-induced space charge. |
Wednesday, March 16, 2022 8:48AM - 9:00AM |
M27.00005: Measurements of strong coupling between metamaterials and superconducting Josephson plasmons in La2-xSrxCuO4 at terahertz frequencies Kelson Kaj, Ian N Hammock, Chunxu Chen, Xiaoguang Zhao, Kevin A Cremin, Jacob S Schalch, Yuwei Huang, Michael M Fogler, Dmitri N Basov, Xin Zhang, Richard D Averitt We experimentally investigate the coupling between an array of metamaterial (MM) resonators and the Josephson Plasma Resonance (JPR) in superconducting La2-xSrxCuO4 using terahertz (THz) time domain spectroscopy. The MM can be placed within ~1μm of the LSCO surface (the c-axis lies in the sample plane) by fabricating the MM/polyimide films that can be adhered and detached from the surface, allowing for the possibility of measuring different MM resonators and variations in the MM-LSCO-surface spacing. The electrodynamic response is characterized by a plasma-edge-like feature that is highly renormalized compared to the bare crystal JPR. Measurements as a function of temperature and THz field strength demonstrate how the renormalized response reports strong coupling between the MM resonance and the JPR. Theoretical models provide insight into the observed response, indicating that the edge-like feature is due to splitting of the JPR response from longitudinal coupling with the resonators. Our analysis further elucidates how the upper polariton is not seen in the measured reflectivity, consistent with previously published results [1]. |
Wednesday, March 16, 2022 9:00AM - 9:12AM |
M27.00006: Observation of white-light continuum generation and ions emission lines spectra from the plasma generated from laser ablation from the surfaces of the metals, insulators, and semiconductors using high-intensity femtosecond laser pulses Shah Faisal Mazhar, Sandra Mamani, Robert Alfano Observation of white-light continuum and emission from ions' spectra from the plasma generated from laser ablation is reported and studied. The emitted spectra arise from the surfaces of different materials such as metals like copper, Al; insulators like glass, calcite; and semiconductors like Silicon, GaAs using focused high power > 1 mJ laser with 90 femtosecond pulses at 800 nm wavelength. The intense femtosecond light-matter interaction at 800 nm on the surface of different condensed matters has produced plasma which has created a white light supercontinuum spanning from 380 nm to 700 nm with the sharp emission peak lines rising from the characteristics of ions of the material for example ionization lines of +1 and +2 as well as Second Harmonic Generation (SHG) lines. The images of laser ablations on the surface have also been studied and a model will be presented to explain the interactions. |
Wednesday, March 16, 2022 9:12AM - 9:24AM |
M27.00007: About group velocity of electromagnetic wave in linear isotropic non-homogeneous medium Michael Galinsky, Vladimir Rumyantsev, Stanislav Fedorov Researches of spatial distribution of group velocity of different laser beams are of high actuality for the last years. These researches are important for developing of information technologies, especially for laser communication systems. The most of these works are applicable for particular cases of laser beams in homogeneous medium [1,2]. In the new work the theoretical model is presented, which allows not only to find spatial distribution of group velocity of beams (direct problem), but also to find spatial structure of beams with necessary group velocity (inverse problem). This model is applicable to any type of laser beams and for any linear isotropic inhomogeneous medium. No additional approximations, like paraxial one, are used. Solutions of the final system of equations are always satisfy energy conservation law, because the system includes it in explicit form. It is also shown condition, where evanescent wave appears and beam with necessary group velocity is spatially limited. This model is of high generality and prospective for applications for information technologies, like laser communications in atmosphere, free space and developing of photonic integrated circuits. [1] D. Giovannini et al., Science. 347, 857 (2015). [2] F. Bouchard et al., Optica. 3, 351 (2016) |
Wednesday, March 16, 2022 9:24AM - 9:36AM |
M27.00008: THz pump-probe spectroscopy: instantaneous response and coherent oscillations Mattia Udina The latest advances in time-resolved spectroscopic techniques, based on the generation of intense ultra-short light pulses, have paved new intriguing ways for the investigation of collective phenomena in many complex systems. In spite of this huge experimental progress, an exhaustive theoretical framework able to connect the measured quantity to the microscopic properties of the material under study is still lacking. With the aim to fill in part this knowledge gap, we provide a general scheme shedding light on some of the most relevant features observed in the experiments, such as the instantaneous response following the squared pump field in wide band insulators, also referred to as THz Kerr effect, and the appearance of time-resolved oscillations at the typical frequencies of different collective modes. We will show how the first aspect can be related to the off-resonant excitation of the electronic population as well as to absorption effects due to the lattice, while the latter is associated with a Raman-like excitation process, explaining both the generation of coherent optical phonons and electronic collective modes, such as charge, amplitude (Higgs) and phase fluctuations in a superconductor. |
Wednesday, March 16, 2022 9:36AM - 9:48AM |
M27.00009: Ultrafast coherent spectroscopy of photocatalytic TiO2 surfaces Namitha A James, Hrvoje Petek Understanding the photoexcited electron dynamics in TiO2 is vital to extend its applications in photocatalysis through a thorough understanding of its electronic structure. In our previous study of reduced TiO2 by two-photon photoemission using UV excitation, we found a pair of nearly degenerate unoccupied states, which we attributed to transitions between Ti-3d bands of t2g and eg symmetry. We extended our study to multiphoton photoemission(mPP) spectroscopy in the near-IR-VIS spectral region. I will report on the dynamics of electrons excited from defect states of reduced TiO2(110) and Au/TiO2 through its conduction band by mPP with a tunable ultrashort(~20 fs) laser pulses. mPP spectra reveal resonances where TiO2 defect state electrons absorb energy to reveal new electronic energy levels. We performed interferometric time resolved-mPP experiments on these resonances to study the photoinduced polarization and electron relaxation dynamics. Surprisingly, the experiment reveals measurable coherent polarization and population relaxation dynamics on tens of femtosecond time scales. Decoration of the surfaces with Au overlayer introduces new resonances. Our study contributes to a comprehensive knowledge of these transitions relevant to the photocatalytic processes on TiO2. |
Wednesday, March 16, 2022 9:48AM - 10:00AM |
M27.00010: Microring resonator laser using bound states in the continuum to create a widely tunable output frequency Matthew Bandy Lasers have had a significant impact within many fields of physics and have developed immensely in recent times. Particularly, lasers created using bound states in the continuum (BICs), which are also known as dark states, have recently become a more prominent area of study within quantum mechanics. Dark states are waves that remain localized to a specified region regardless of the flow of other waves through the system. These states are much more susceptible to manipulations of frequencies while having very little loss of energy. We created mathematical models to numerically simulate possible systems containing dark states; to obtain dark states, we added a single ring resonator to a waveguide and manipulated multiple points of connection between them. This ring interacts with the waveguide to cause interference between the connection regions. We can currently control this interference by adjusting the strength of the couplings between the waveguide and the impurity or by altering the location of the ring. These manipulations let us easily vary the dark state frequencies which allows for a continuous adjustment of the output frequency of the laser through a wide range to create a system that can be used throughout many different fields. |
Wednesday, March 16, 2022 10:00AM - 10:12AM |
M27.00011: Molecular Raman in KXe Kavita Desai, Stephen Messing, Andrey Mironov, J. Gary Eden Stimulated electronic Raman scattering has been observed in the transient molecule, KXe, by optically exciting ground state K-Xe pairs. Stimulated emission with a linewidth of 2 cm-1 on the B2Σ+1/2→X2Σ+1/2 transition of the molecule has also been observed despite the dissociative nature of the B2Σ+1/2 potential in the interval 769.6‑770.6 nm. Additional wavelengths can be generated through stimulated emission by detuning the pump wavelength away from the resonance line, a phenomena previously not observed in other alkali rare gas systems. |
Wednesday, March 16, 2022 10:12AM - 10:24AM |
M27.00012: Multi-dimensional high harmonic spectroscopy of ultrafast phonon dynamics in hBN Ofer Neufeld, Jin Zhang, Umberto De Giovannini, Hannes Huebener, Angel Rubio High harmonic spectroscopy has recently been pioneered as a promising method for probing ultrafast electron dynamics in solids. However, its possible applications for tracking structural changes and phonon dynamics are not yet clear. We explore here pump-probe high harmonic generation (HHG) from monolayer hexagonal-Boron-Nitride, where a terahertz pump excites optical phonons that are subsequently probed with intense laser pulses that drive HHG. Through state-of-the-art ab-initio calculations, we show that the structure of the HHG spectrum is attenuated by the phonons and comprises a continuous emission in the plateau region. The HHG yield strongly oscillates with the pump-probe delay, corresponding to femtosecond-scale changes in the lattice such as bond compression or stretching. Remarkably, we show that the HHG process can become sensitive to the carrier-envelope-phase (CEP) of the driving laser, even when the pulse duration is long. We find that the degree of CEP sensitivity vs. pump-probe delay is a highly selective measure for instantaneous structural changes in the lattice, providing a new approach for ultrafast multi-dimensional HHG-spectroscopy. Our work shows new routes for probing ultrafast structural changes and provides a mechanism for controlling solid HHG emission. |
Wednesday, March 16, 2022 10:24AM - 10:36AM |
M27.00013: Observation of a High Magnetic Field-Induced Phase Transition in Frustrated Magnet Gadolinium Gallium Garnet Junzhe Bao, Nicolas Marquez Peraca, Fuyang Tay, Timothy E Kritzell, Xinwei Li, Gary T Noe, Ikufumi Katayama, Jun Takeda, Hiroyuki Nojiri, Hiroyasu Yamahara, Hitoshi Tabata, Andrey Baydin, Junichiro Kono Gadolinium gallium garnet (Gd3Ga5O12), or GGG, is a frustrated magnet in which antiferromagnetic exchange interactions exist among Gd3+ ions located on two triangular sublattices. The geometric frustration prevents ordering, and the system is best described as a spin liquid at low temperatures. It has been shown that an applied magnetic field of ~1 T produces an antiferromagnetic phase below ~0.4 K, but properties of GGG in higher magnetic fields remain unexplored. Here, we have carried out terahertz magnetospectroscopy measurements on GGG in fields up to 25 T using a table-top pulsed magnet. We performed magnetic field- and temperature-dependent THz transmission measurements and observed a splitting of the electron paramagnetic resonance (EPR) peak for Ga3+ ions. Our results indicate that, at high enough magnetic fields and low enough temperatures, there exists a new phase where EPR exhibits two peaks. By taking the 1-peak-to-2-peak transition point as the critical field/temperature, we constructed a phase diagram, which shows a critical magnetic field of ~17 T (~23 T) at 10 K (250 K). We will present a model that takes into account the effect of a strong magnetic field on the antiferromagnetic Gd-Gd exchange interactions on a triangular lattice. |
Wednesday, March 16, 2022 10:36AM - 10:48AM |
M27.00014: Leaky modes in multilayer InSe flakes Yinxiao Xiang Periodic fringes of both the second and third harmonic generations are observed near the edge of multilayer InSe flakes exfoliated on PMMA/Si substrates. Combined experimental and theoretical investigations show that these fringes are induced by the propagation of in-plane leaky modes of the fundamental wave launched by the flake edges. The leaky mode becomes fully guided as the InSe flakes are transferred on a free-standing 30 nm SiN membrane. Using multiphoton microscopy, the propagation of leaky- or guided-mode in 2D materials can be mapped in a fast and non-perturbative manner, demonstrating an effective approach in probing the optical and electronic properties of van der Waals structures. Since InSe is associated with an ultra-high second-order nonlinear susceptibility, a nanophotonic InSe rib waveguide is numerically proposed based on our findings to realize highly-efficient second harmonic generation with perfect phase-matching. We will also discuss how the exfoliated InSe flakes can be tailored to form nanoantennas or metasurfaces in sensing and optoelectronic applications. |
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