Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session G52: Ultrafast Spectroscopy and Optical Techniques |
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Sponsoring Units: DLS Chair: David Reis, Stanford PULSE Institute Room: Room 308 |
Tuesday, March 7, 2023 11:30AM - 11:42AM |
G52.00001: Light-field-driven electron dynamics in topologically protected materials Christian Heide The prediction and realization of topological insulators have sparked great interest in experimental approaches to material classification [1]. The phase transition between a non-trivial and trivial topological state is important not only for basic materials science but also for next-generation technology, such as dissipation-free electronics with ramifications in coherent light-wave electronics [2, 3]. Therefore it is crucial to develop advanced probes suitable for a wide range of samples and environments. Here, we demonstrate that circularly-polarized laser-field-driven high-harmonic generation is distinctly sensitive to the non-trivial and trivial topological phases in the prototypical three-dimensional topological insulator bismuth selenide [4,5]. The phase transition is chemically initiated by reducing the spin-orbit interaction strength through the substitution of bismuth with indium atoms. We find strikingly different high-harmonic responses of trivial and non-trivial topological surface states that manifest themselves as a conversion efficiency and elliptical dichroism that depend both on the driving laser ellipticity and crystal orientation [5]. The origins of the anomalous high-harmonic response are corroborated by calculations using the semiconductor optical Bloch equations with pairs of surface and bulk bands. As a purely optical approach, this method offers sensitivity to the electronic structure of the material, including their nonlinear response, and is compatible with a wide range of samples and sample environments. |
Tuesday, March 7, 2023 11:42AM - 11:54AM |
G52.00002: Momentum-resolved spectroscopy based on time-reversed light pulses emitted from optically driven quasiparticles Shohei Imai, Atsushi Ono, Sumio Ishihara High harmonic generation has been observed in various crystalline solids and has recently been used to reconstruct the energy band structure of electrons in an all-optical manner. In this study, we investigate the real-time quasiparticle dynamics induced by an optical excitation pulse and a subsequent few-cycle pulse [1]. We show the appearance of echoes with the time-reversed waveform of the excitation pulse when the quasiparticle wavepackets recombine and that the frequency of the echoes reflects the dispersion relation of the quasiparticles. Furthermore, the echoes can be observed even in correlated insulators such as a Mott insulator and a charge-ordered insulator. These results provide a framework of momentum-resolved spectroscopy of quasiparticles in a wide variety of crystalline solids. |
Tuesday, March 7, 2023 11:54AM - 12:06PM |
G52.00003: Theoretical study of the THz induced high-order harmonic generation and nonlinear transport in graphene Wenwen Mao, Angel Rubio, Shunsuke A Sato We theoretically study the microscopic mechanism of THz-induced HHG in graphene with the quantum master equation. By changing chemical potential, the enhancement of emitted harmonics is observed, consistently with the recent experimental observation. We find that the THz-induced electron dynamics are well described by a nonequilibrium steady-state at each instance under quasi-static approximation. Additionally, we compared our nonequilibrium model with the previously developed thermodynamic model and clarified that the nonequilibrium nature is indispensable to properly describe the THz-induced HHG and nonlinear charge transport in graphene in the strong field regime. Furthermore, we discuss a method to enhance or suppress the MIR laser-induced HHG in graphene coupled with few-cycle THz pulses, opening paths toward achieving ultrafast control of charge transport by light through non-equilibrium and nonlinear electron dynamics in matter. |
Tuesday, March 7, 2023 12:06PM - 12:18PM |
G52.00004: Higher Harmonic and Supercontinuum Generation from the Response Time of the Kerr Effect using Intense Femtosecond and Picosecond Laser Pulses in Different States of Matter Shah Faisal Mazhar, Robert R Alfano, Mikhail Sharonov Based on electromagnetic theory, odd Higher Harmonic Generation (HHG) and Supercontinuum (SC) generation from intense femtosecond and picosecond pulses for visible and NIR lasers are simulated based on the parameters from experimental observation. HHG depends critically on different Kerr material response times τ from the ultrafast on the order of 100 attoseconds for electronic cloud distortion to fast 10 femtoseconds processes. The effect of Kerr nonlinear response time on HHG and SC generation explains the effect of underlying instantaneous electronic cloud distortion, fast plasma molecular redistribution, and other slower Molecular mechanisms in different states of matter. HHG and SC generation is simulated in different states of matter from noble gas Argon to condensed matter ZnO and LBG. This effect of Kerr response time on HHG and SC generation supports the ESPM model from nonlinear Kerr index n2 which will impact the development of new attosecond lasers. Additionally, it shows how HHG and SC generation is possible in different states of matter using laser pulses with <100 fs pulse width in visible and IR ranges. Only the ultrafast mechanism Kerr response times below 1fs give rise to HHG for optical and NIR laser pulses. |
Tuesday, March 7, 2023 12:18PM - 12:30PM |
G52.00005: Measurement of Higher Order X-ray Optical Mixing Chance Ornelas-Skarin, David A Reis, Jerome B Hastings, Mariano Trigo, Shambhu Ghimire, Daria Gorelova, Matthias Fuchs, Sharon Shwartz, Diling Zhu, Takahiro Sato, Quynh L Nguyen, Tatiana Bezriadina, Henrik Lemke, Roman Mankowsky, Mathias Sander, Nelson Hua, Ludmila Diniz Leroy, Gilberto De La Pena X-ray optical wave mixing is a nonlinear diffraction method that gives direct information about the Ångstrom and femtosecond-scale structure of the local optically-induced charge density in bulk solids, information unavailable to purely optical methods. The first measurements of wave mixing between x rays and optical photons were reported for single crystal diamond [Glover et al., Nature 488, 603 (2012)]. Here we report x-ray optical wave mixing experiments using the Swiss-FEL and LCLS hard x-ray free-electron lasers. To measure the wave-mixing signal we use silicon crystal optics to monochromate the free-electron laser output and analyze the energy-angle dependent wave-mixing signal while rejecting the elastic background. The results include the first measurements from silicon and the first measurement of the higher-order wave-mixing process generating the sum frequency of two optical and one x-ray photon. The latter gives access to the lowest-order local nonlinear electronic response to strong optical fields. Here we observe a nontrivial laser-polarization dependence which we compare to theoretical predictions from first-principles electronic structure calculations using a Bloch-Floquet formalism. Preliminary analysis of these results is presented here. |
Tuesday, March 7, 2023 12:30PM - 12:42PM |
G52.00006: Phonon-Polaritons in Hexagonal Boron Nitride Induced by Evanescent Radiative Coupling William D Hutchins
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Tuesday, March 7, 2023 12:42PM - 12:54PM |
G52.00007: Ultrafast electron diffuse scattering in superionic conductor AgCrSe2 Yusuke Chiashi, Asuka Nakamura, Junpei Koga, Takahiro Shimojima, Rikizo Yano, Takao Sasagawa, Kyoko Ishizaka AgCrSe2 is a layered material that exhibits superionic conductivity at high temperature (> 460 K). It has been recently attracting much attention for the study of transverse acoustic phonon and the emergence of ultra-low thermal conductivity in the “liquid state”, which is advantageous for thermoelectric functions [1]. In AgCrSe2 crystals, there are two sites where Ag ions intercalated between CrSe2 layers can reside. At low temperatures, all Ag ions occupy one of them to form a 2-dimensional triangular network, while in the superionic conducting state at high temperature, the occupancy becomes completely random between these two sites, i.e. order-disorder phase transition. In this study, we investigate the phononic dynamics in AgCrSe2 by ultrafast electron diffraction method utilizing an ultrafast transmission electron microscope [2,3]. We discuss the phonon excitation and disorder effect by comparing the diffuse scattering in the picosecond to nanosecond range with the numerical simulations. |
Tuesday, March 7, 2023 12:54PM - 1:06PM |
G52.00008: Vibronic coherences in semiconductor quantum dots with organic surface-capping ligands Nila Mohan T. M., Ryan W Tilluck, P. Gregory Van Patten, Mengliang Zhang, Warren F Beck Exciton relaxation in semiconductor quantum dots (QDs) is strongly dependent on the nature and extent of passivation of the surface by organic ligands. To determine how the ligands participate in nonradiative decay mechanisms, we characterized preparations of CdSe QDs capped with hexadecylamine or oleate ligands using broadband multidimensional spectroscopy with 6.7-fs laser pulses. Population transfer to the band edge and then to the photoluminescent state after optical preparation of the X3 exciton (1Pe state) is revealed in two-dimensional electronic spectra (2DES) by the time evolution of an off-diagonal cross peak. This process involves excited-state coherent wavepacket motions through a cascade of conical intersections between exciton potential-energy surfaces. Time-windowed oscillation maps allow us to distinguish between excited-state and ground-state (stimulated Raman) wavepacket motions at frequencies matching the vibrational modes of the organic ligands. These observations indicate that the ligand vibrations are quantum coherently mixed with the core electronic states of the QDs. These results raise new opportunities for engineering photoinduced electron transfer processes in QDs through control of electronic-vibrational coupling with organic ligands. |
Tuesday, March 7, 2023 1:06PM - 1:18PM |
G52.00009: Computational Toolbox for Modeling Nonlinear Optical Coherence Phenomena Matthew T Larson, Carsten A Ullrich, Hans-Peter Wagner We present a simple and versatile computational approach for simulating ultrafast nonlinear optical processes in coupled systems. This approach is based on the numerical time propagation of the density-matrix equations of motion describing interacting optical two-level systems. This method bridges the gap between the high-speed dynamics of decay modes and oscillation frequencies and the low-speed modulation of heterodyned optical mixing. Through the use of a pulse train, modes of interest such as four-wave or three-wave mixing signals can be selected and isolated, allowing for the robust simulation of realistic practical systems such as coupled excitons and plasmons. Applications of this process are then discussed and compared with existing low order models traditionally used to describe nonlinear optical processes. |
Tuesday, March 7, 2023 1:18PM - 1:30PM |
G52.00010: Terahertz spectroscopy of bulk InSb and SrTiO3 in reflection geometry Kasturie Jatkar Terahertz time-domain spectroscopy (THz-TDS) is a reliable technique for studying the complex optical properties of materials. Its energy range makes it suitable for detecting low energy collective excitations such as phonons, magnons, and plasmons. The technique for THz-TDS in transmission geometry has gained much attention over the years. However, despite the need for exploring reflective samples, the advancement of THz-TDS in reflection geometry has faced several obstacles, mainly due to its strict requirement for high precision in the placement of the sample and reference. |
Tuesday, March 7, 2023 1:30PM - 1:42PM |
G52.00011: On-chip time domain terahertz spectrometer with rapid sample exchange Alex Potts, Abhay K Nayak, Michael Nagel, Kelson Kaj, Biljana Stamenic, Richard D Averitt, Andrea Young Free-space time domain THz spectroscopy is a powerful technique that struggles to measure samples physically smaller than the diffraction limit (~0.3 mm), such as van der Waals materials and heterostructures. We present an on-chip, time-domain THz spectrometer based on photoconductive Auston switches. Our spectrometer features an interchangeable sample architecture with a usable bandwidth of 100 GHz to 800 GHz. We qualify our spectrometer using the superconducting transition in 6-um wide superconducting NbN films, ~40 times smaller than the wavelength at 800 GHz. |
Tuesday, March 7, 2023 1:42PM - 1:54PM |
G52.00012: 3D Direct Laser Writing without Femtosecond Lasers sinan gundogdu, Tim Schroeder, Sofia Pazzagli Direct laser writing is a common technique for generating 3-dimensional (3D) refractive index modification in materials. It relies on a two-photon absorption mechanism and to date requires high-power femtosecond lasers. We demonstrate a method that uses a low-power quasi-CW laser to write 3D, sub-wavelength features in a transparent material. To achieve this, we exploit the time-dependent changes in the linear absorption coefficient of the material to generate a localized modification of the refractive index, up to 12%. We present an analytical model for material modification, simulation results, and experimental results, as well as a technique for in-situ characterization of the material modification. |
Tuesday, March 7, 2023 1:54PM - 2:06PM |
G52.00013: Modeling of lasing threshold in GeSn waveguides on silicon Jay A Mathews, Zairui Li, Imad Agha Silicon photonic integrated circuits (PICs) could be used for many applications such as increasing internet routing bandwidth, enabling LIDAR for self-driving vehicles, and lab-on-a-chip biological and chemical sensors, but the creation of a Si-based laser has yet to be achieved. Si has an indirect band gap, so it cannot be used as a laser gain medium due to inefficient optical emission. GeSn alloys are grown on Si substrates, and GeSn has a band structure that allows for efficient optical emission in the infrared. Waveguides fabricated from GeSn allows have demonstrated lasing at cryogenic temperatures, but room temperature lasing has yet to be achieved in such devices. |
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