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Imaging shallow fault structures by three-dimensional reverse time migration of ground penetration radar data

JOURNAL OF APPLIED GEOPHYSICS 2021年 190卷

作者： Ma, Bowen Zhu, Weiqiang Huang, Qinghua Peking Univ Sch Earth & Space Sci Dept Geophys Beijing 100871 Peoples R China Peking Univ Hebei Hongshan Geophys Natl Observat & Res Stn Beijing 100871 Peoples R China Stanford Univ Sch Earth Energy & Environm Sci Dept Geophys Stanford CA 94305 USA

Ground penetrating radar (GPR) is an effective technology for investigating shallow underground structures using high-frequency electromagnetic waves. Migration is necessary to interpret GPR data because it resolves the true structure from distorted and blurry time-domain profiles. Wave-equation-based reverse time migration (RTM) can provide higher-resolution and more reliable results compared to ray-based migration methods. We have developed a three-dimensional RTM approach based on the finite-difference time-domain algorithm and applied it to field GPR data collected in the northern segment of the Huangzhuang-Gaoliying fault in suburban Beijing. Migrated images clearly show the subsurface structures, with clear indications of underground reflectors in agreement with geological cross-sections proposed in previous studies. Our results demonstrate that GPR is a convenient, non-destructive, and reliable technique that provides a new comprehensive approach to image subsurface conditions, thus allowing effective monitoring of active faults in urban areas. (C) 2021 Elsevier B.V. All rights reserved.

关键词： 3D reverse time migration Ground-penetrating radar Huangzhuang-Gaoliying Fault finite-difference time-domain method

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Band-Gap Tuning in Two-Dimensional Spatiotemporal Phononic Crystals

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Physical Review Applied 2021年第1期15卷 014022-014022页

作者： D. Psiachos M.M. Sigalas Department of Materials Science University of Patras Rio 26504 Greece

We investigate the effect of small spatiotemporal modulations in subwavelength-dimensioned phononic crystals with large band gaps, on the frequency spectrum for elastic waves polarized in the plane of periodicity. When the radius of cylinders periodically placed inside a matrix of highly contrasting elastic properties is time varying, we find that due to the appearance of frequency harmonics throughout the spectrum, the notion of a band gap is destroyed in general, although with the appropriate tuning of parameters, in particular the modulation frequency, it is possible that some band-gap region is retained, making such systems possible candidates for tunable bandpass filters or phononic isolators, accordingly, and for sensor applications.

关键词： Acoustic metamaterials Acoustic phonons Elasticity 2-dimensional systems Diodes Wide band gap systems finite-difference time-domain method

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Selection of Emission Wavelength of Lasing via a Hybrid Microcavity

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Physical Review Applied 2021年第3期16卷 034015-034015页

作者： Hong Yang Hailang Dai Qiheng Wei Hongrui Shan Zhuangqi Cao Xianfeng Chen The State Key Laboratory on Fiber Optic Local Area Communication Networks and Advanced Optical Communication Systems Department of Physics and Astronomy Shanghai Jiao Tong University Shanghai 200240 China Shanghai Research Center for Quantum Science Shanghai 201315 China Jinan Institute of Quantum Technology Jinan 250101 China Collaborative Innovation Center of Light Manipulations and Applications Shandong Normal University Jinan 250358 China

In the applications of optical communication and light-matter interaction manipulation, the capability of on-demand lasing output with programmable and continuous wavelength tunability over a broad spectral range under low threshold is key functionality. However, the ability to control multiwavelength lasing characteristics within a small mode volume with high reconfigurability remains challenging. The number of dyes and the emission wavelengths of existing materials always restrict the color gamut. In this Letter, we introduce a selection of emission wavelength laser by injecting Rhodamine 6G solution mixed with Au nanoparticles in the metal-cladded slab-capillary hybrid microcavity. A mechanism for tuning laser emission wavelengths is designed by manipulating the diameter of Au nanoparticles in Rhodamine 6G solution. Precision control of distinctive lasing wavelengths and a narrower peak are achieved, along with a stable lasing beam output from both ends of the capillary due to coherent superposition. Our findings offer possibilities for realizing a micro selection of emission wavelength laser from a single overall structure.

关键词： Surface plasmons Dye lasers Microcavity & microdisk lasers Nanoparticles Tunable lasers finite-difference time-domain method Fluorescence spectroscopy Resonance techniques

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Femtosecond laser pulse splitting effect in second harmonic generation under Laue diffraction in one-dimensional photonic crystals

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Physical Review B 2021年第23期103卷 235408-235408页

作者： V. B. Novikov T. V. Murzina Department of Physics M. V. Lomonosov Moscow State University Moscow 119991 Russia

The ability to manipulate the frequency of light is a cornerstone of a wide range of applications in photonics expanding spectral ranges of the light sources. To boost the second harmonic generation efficiency, intense efforts toward exploiting artificial microstructures for frequency doubling were carried out. The sought-after approach of utilizing photonic crystals is inspired by their unusual light dispersion. In such structures, the dynamics of the field of femtosecond laser pulses is of paramount importance for frequency conversion. In this work, we investigate the phase-matched second harmonic generation under the effect of diffraction-induced femtosecond laser pulse splitting in one-dimensional photonic crystals at the Bragg diffraction in the Laue geometry. We demonstrate that the interaction of the two pulses at the fundamental frequency that appears in photonic crystals through the dynamical light diffraction leads to a nonmonotonic dependence of the frequency up-conversion efficiency with respect to the laser pulse duration, thus allowing to increase the second harmonic power by tuning the pulse duration.

关键词： Photonic crystals Second order nonlinear optical processes Ultrafast optics Bloch wave theory Electromagnetic wave theory finite-difference time-domain method Optical second-harmonic generation Plane-wave expansion

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A methodology for the SPICE-Compatible modelling of metal-semiconductor-metal photodetectors for nanophotonic interconnects application

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MICROELECTRONICS JOURNAL 2021年 115卷

作者： Qodratnama, Arash Khunjush, Farshad Raji, Mohsen Shiraz Univ Dept Comp Sci & Engn & IT Shiraz Iran Shiraz Univ Sch Elect & Comp Engn Shiraz Iran

On-chip global nanophotonic interconnects are promising alternatives to traditional metallic interconnects in giga-scale integrated circuits. At the very first step, the design and optimization of nanophotonic interconnects require the modelling and characterization of optoelectronic devices with irregular 3D geometries. In this paper, a methodology for the SPICE-compatible modelling of such devices is proposed which does not rely on post-manufacturing data. This methodology couples the optics and electronics domains of such devices in order to improve the model accuracy. The proposed methodology has been applied to the modelling of a waveguide-coupled integrated Metal-Semiconductor-Metal PhotoDetector (MSM PD) with quadratic nanotapers. We have performed optics domain simulation in 3D field-solver MEEP and device simulations using Silvaco Atlas device-TCAD tool. The simulation results agree well with measurement data reported in literature. Agreement with less than 12% error at all bias voltages is observed.

关键词： Nanophotonic interconnect Characterization Metal-semiconductor-metal photodetector Photocurrent finite-difference time-domain method

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Ferroelectric polarization reversal versus pump spot shape

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Physical Review B 2021年第14期104卷 L140102-L140102页

作者： Veniamin A. Abalmasov Institute of Automation and Electrometry SB RAS Novosibirsk 630090 Russian Federation

It has recently been shown that the polarization of a ferroelectric can be strongly affected by light pumping or even transiently reversed by mid-IR pumping within a record short subpicosecond timescale. It was then suggested that the reversal of polarization is most likely prevented by the depolarizing field that appears during the process. To minimize the effect of the depolarizing field, I propose to create an elongated domain by choosing a corresponding pump spot shape. I calculate the polarization dynamics for a particular experimental setup with mid-IR pumping and show that the polarization reversal is possible in this case.

关键词： domains Dynamical phase transitions Ferroelectric domains Ferroelectricity Order parameters Photoinduced effect Ferroelectrics Coherent control Density functional calculations finite-difference time-domain method

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Long-time behavior of a nonlinear electromagnetic wave in vacuum beyond the linear approximation

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Physical Review A 2021年第6期104卷 063513-063513页

作者： Kazunori Shibata Institute of Laser Engineering Osaka University 2-6 Yamada-Oka Suita Osaka 565-0871 Japan

A quantum nature of vacuum is expected to affect electromagnetic fields in vacuum as a nonlinear correction, yielding nonlinear Maxwell's equations. We extend the finite-difference time-domain (FDTD) method in the case that the nonlinear electromagnetic Lagrangian is quartic with respect to the electric field and magnetic flux density. With this extension, the nonlinear Maxwell's equations can be numerically solved without making any assumptions on the electromagnetic field. We demonstrate examples of self-modulations of nonlinear electromagnetic waves in a one-dimensional cavity, in particular, in a timescale beyond an applicable range of linear approximation. A momentarily small nonlinear correction can accumulate and a comparably large self-modulation can be achieved in a long timescale even though the electromagnetic field is not extremely strong. Further, we analytically approximate the nonlinear electromagnetic waves in the cavity and clarify the characteristics, for example, how an external magnetic flux density changes the self-modulations of phase and polarization.

关键词： Classical solutions in field theory Effective field theory Nonlinear optics Nonlinear waves finite-difference time-domain method

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Ultrafast laser-induced guided elastic waves in a freestanding aluminum membrane

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Physical Review B 2021年第6期103卷 064303-064303页

作者： Hao Zhang Alessandro Antoncecchi Stephen Edward Paul Planken Stefan Witte Advanced Research Center for Nanolithography Science Park 106 1098 XG Amsterdam Netherlands Vrije Universiteit Amsterdam De Boelelaan 1105 1081 HV Amsterdam Netherlands Universiteit van Amsterdam Science Park 904 1098 XH Amsterdam Netherlands

Ultrafast laser-induced guided acoustic waves in thin, freely suspended films are important for many applications adopting the laser-ultrasonics technique. These waves show unique dispersion relations, leading to minimal propagation losses and acoustic energy confinement. While this principle has been known, the separation of various physical effects in the formation of measured signals involving these guided acoustic waves has not been clearly elaborated. Here, we present a combined experimental and theoretical study on all-optical excitation and detection of these waves in a thin, freestanding aluminum membrane. The acoustic dynamics is excited and measured by using a femtosecond time-resolved pump-probe technique with controlled probing position, enabling spatially resolved detection. The measured signals are compared with an advanced numerical model that we developed earlier [H. Zhang et al., Phys. Rev. Appl. 13, 014010 (2020)], showing excellent agreement. The combination of experiment and simulation allows us to decode various physical effects in the signal formation, including different acoustic field components. Unknown material properties, such as acoustic attenuation coefficients, and the two complex photoelastic constants are quantitatively retrieved by fitting the measured signals. Furthermore, we provide evidence of nonlinear propagation of the excited guided acoustic waves.

关键词： Acoustic phonons Acoustic wave phenomena Mechanical & acoustical properties Ultrafast phenomena Ultrasonics Thin films Elastic wave theory finite-difference time-domain method Surface acoustic wave Ultrafast pump-probe spectroscopy

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The Modulation Effect on the ELVEs and Sprite Halos by Concentric Gravity Waves Based on the Electromagnetic Pulse Coupled Model

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ATMOSPHERE 2021年第5期12卷

作者： Wang, Chao Wen, Ying Zhang, Jinbo Zhang, Qilin Qiu, Juwei Civil Aviat Flight Univ China Coll Air Traff Management Guanghan 618307 Peoples R China Jiangsu Univ Sch Comp Sci & Commun Engn Zhenjiang 212013 Jiangsu Peoples R China Nanjing Univ Informat Sci & Technol Sch Atmospher Phys Nanjing 210044 Peoples R China Guangdong Ocean Univ Coll Fisheries Zhanjiang 524088 Peoples R China

By employing the finite-difference time-domain method, the processes of electric field variation and morphological development of the optical radiation field of ELVEs and sprite halos were simulated in this article. Simulations of ELVEs show two optical radiation field centers, with a concentrated luminous zone from 85 to 100 km and an inner weaker optical radiation center. The electric field exhibits an obvious sparse and dense ripple pattern induced by the concentric gravity waves (CGWs) at altitudes of 90-100 km, which mainly occurs during the decline period of electric field with a shallow steepness. The alternating distance of the variations in the sparse and dense patterns is about 40 km, which corresponds to the horizontal wavelength of the electric field. The CGWs induce significant deformation of the inner optical radiation field, even splitting into multiple luminous regions. Simulations of sprite halos indicate that the horizontal range of the electrical field generated by lightning current is within 50 km, and a strong local electric field formed in the region right above the lightning channel is due to the small-scale breakdown current. Thus, the increased electron density shields the upper regions and reduces the electrical field's strength. The sprite halos luminous zone is pancake-shaped, and it originates at 85 km along with a downward developing trend. The disturbance of sprite halos' luminescence caused by CGWs mainly occurs at about 80-100 km directly above the lightning channel, and the primary deformation zone is located within 30 km of the lightning channel, which is also the region with the most recognizable electric field disturbance.

关键词： concentric gravity waves transient luminous events finite-difference time-domain method electromagnetic pulse

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Optical Isolation using Compact time-modulated Cavity Array

Optical Isolation using Compact Time-modulated Cavity Array

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International Symposium of Applied-Computational-Electromagnetics-Society (ACES)

作者： Mock, Adam Cent Michigan Univ Sch Engn & Technol Mt Pleasant MI 48859 USA

ISBN: (纸本)9781733509602

It is shown using coupled mode theory and verified using finite-difference time-domain simulations how a time-modulated three-cavity array can be designed to allow transmission from port 1 to port 2 but to prevent transmission from port 2 to port 1 thereby implementing optical isolation. The reciprocity of the system is broken by phase-shifting the modulation signal applied to each cavity by 120 degrees which gives the system a synthetic linear momentum.

关键词： cavity resonators finite-difference time-domain method isolators time-varying circuits

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