Mohamed A. K. Othman

SLAC National Accelerator Laboratory

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Trends

Author Order

Document Type

Co-Authors

Filippo Capolino

University of California, Irvine

Emilio A. Nanni

SLAC National Accelerator Laboratory

Matthias C. Hoffmann

SLAC National Accelerator Laboratory

Sami Tantawi

SLAC National Accelerator Laboratory

Xijie Wang

Zhejiang University

Emma Snively

SLAC National Accelerator Laboratory

Annika E. Gabriel

SLAC National Accelerator Laboratory

Samantha M. Lewis

Fermi National Accelerator Laboratory

Stephen Weathersby

SLAC National Accelerator Laboratory

M. Kozina

Linac Coherent Light Source

Cooperative Institutions

SLAC National Accelerator Laboratory

Stanford University

Menlo School

Stanford Synchrotron Radiation Lightsource

Linac Coherent Light Source

University of California, Irvine

Argonne National Laboratory

Fermi National Accelerator Laboratory

University of California, Los Angeles

Lawrence Berkeley National Laboratory

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Field

Parallel-plate waveguides for terahertz-driven MeV electron bunch compression

Optics Express (2019)

Mohamed A. K. Othman Matthias C. Hoffmann M. Kozina Xijie Wang Renkai Li

We demonstrate the electromagnetic performance of waveguides for femtosecond electron beam bunch manipulation and compression with strong-field terahertz (THz) pulses. The compressor structure is a dispersion-free exponentially-tapered parallel-plate waveguide (PPWG) that can focus single-cycle THz pulses along one dimension. We show test results of the tapered PPWG structure using electro-optic sampling (EOS) at the interaction region with peak fields of at least 300 kV/cm, given 0.9 µJ of incoming THz energy. We also present a modified shorted design of the tapered PPWG for better beam manipulation and reduced magnetic field as an alternative to a dual-feed approach. As an example, we demonstrate that with 5 µJ of THz energy, the PPWG compresses a 2.5 MeV electron bunch by a compression factor of more than 4, achieving a bunch length of about 18 fs.

10.1364/oe.27.023791

Cite

Citations (17)

Graphene-based tunable hyperbolic metamaterials and enhanced near-field absorption

Optics Express (2013)

Mohamed A. K. Othman Caner Guclu Filippo Capolino

We investigate a novel implementation of hyperbolic metamaterial (HM) at far-infrared frequencies composed of stacked graphene sheets separated by thin dielectric layers. Using the surface conductivity model of graphene, we derive the homogenization formula for the multilayer structure by treating graphene sheets as lumped layers with complex admittances. Homogenization results and limits are investigated by comparison with a transfer matrix formulation for the HM constituent layers. We show that infrared iso-frequency wavevector dispersion characteristics of the proposed HM can be tuned by varying the chemical potential of the graphene sheets via electrostatic biasing. Accordingly, reflection and transmission properties for a film made of graphene-dielectric multilayer are tunable at terahertz frequencies, and we investigate the limits in using the homogenized model compared to the more accurate transfer matrix model. We also propose to use graphene-based HM as a super absorber for near-fields generated at its surface. The power emitted by a dipole near the surface of a graphene-based HM is increased dramatically (up to 5 × 10(2) at 2 THz), furthermore we show that most of the scattered power is directed into the HM. The validity and limits of the homogenized HM model are assessed also for near-fields and show that in certain conditions it overestimates the dipole radiated power into the HM.

Split-ring resonator

Transformation Optics

Negative Refraction

10.1364/oe.21.007614

Cite

Citations (273)

Oscillator Based on Lumped Double Ladder Circuit with Band Edge Degeneracy

arXiv (Cornell University) (2016)

Dmitry Oshmarin Farshad Yazdi Mohamed A. K. Othman Jeff Sloan Mohammad Hadi Radfar

An oscillator design based on a periodic, double ladder resonant circuit is proposed. The circuit exhibits a degenerate band edge (DBE) in the dispersion diagram of its phase-frequency eigenstates, and possesses unique resonance features associated with a high Q-factor resonance, compared to a single ladder or a conventional LC tank circuit. This oscillator is shown to have an oscillation threshold that is half that of a single LC ladder circuit having the same total quality factor, and thus is more robust than an LC oscillator in the presence of losses. It is also shown that the output and amplitude of the double-ladder oscillator is much less sensitive to the output loading compared to single-ladder oscillators. We show the analysis and design of such oscillators that potentially lead to enhancing the efficiency of RF components and sources.

LC circuit

Oscillation (cell signaling)

Pierce oscillator

Degeneracy (biology)

Parametric oscillator

Electronic oscillator

10.48550/arxiv.1610.00415

Cite

Citations (8)

Terahertz Driven Compression and Time-Stamping Technique for Single-Shot Ultrafast Electron Diffraction

12th International Particle Accelerator Conference (IPAC'21), Campinas, SP, Brazil, 24-28 May 2021 (2021)

Mohamed A. K. Othman Annika E. Gabriel Matthias C. Hoffmann Fuhao Ji Emilio A. Nanni

Ultrafast electron diffraction

Single shot

10.18429/jacow-ipac2021-mopab141

Cite

Citations (1)

Design of A Low Magnetic Field Coupler For Output Structure of The SLAC 75XP4 Klystron

Mohamed A. K. Othman Valery Dolgashev E. Jongewaard Brandon Weatherford

Klystron

Electromagnet

10.1109/ivecivesc60838.2024.10694890

Cite

Citations (0)

Parallel-Plate THz Waveguides for Relativistic Electron Bunch Compression

Conference on Lasers and Electro-Optics (2019)

Mohamed A. K. Othman Matthias C. Hoffmann Renkai Li Emilio A. Nanni X. J. Wang

We present results from testing a new dispersion-free THz parallel-plate-based tapered structure optimized for focusing single-cycle THz pulses, producing high fields and with the potential for electron bunch compression to a few femtoseconds.

Pulse compression

10.1364/cleo_si.2019.sth3f.2

Cite

Citations (1)

Design, fabrication, and tuning of a THz-driven electron gun

arXiv (Cornell University) (2022)

Samantha M. Lewis Julian Merrick Mohamed A. K. Othman Andrew Haase Sami Tantawi

We present the design, fabrication, and low power testing of a THz-driven field emission electron gun. The two cell standing-wave gun is designed to be powered by a 110 GHz gyrotron and produce 360 keV electrons with 500 kW of input power. Several gun structures were fabricated using a high precision diamond turned mandrel and copper electroforming. The field emission source is a copper tip with a 50 $μ$m radius inserted halfway into first cell. The frequencies of the cavity resonances were mechanically tuned using azimuthal compression. This work presents electromagnetic and particle simulations of the design and cold test measurements of the fabricated structures.

Electron gun

10.48550/arxiv.2203.15939

Cite

Citations (0)

Graphene-based hyperbolic metamaterial

Mohamed A. K. Othman Caner Guclu Filippo Capolino

We introduce a graphene-based composite multilayer structure that exhibits hyperbolic-like wavevector dispersion at terahertz and mid-infrared frequencies. The multilayer structure comprises graphene sheets separated by dielectric layers. We formulate the effective permittivity tensor of the multilayer using a simple homogenization scheme. In addition, we employ Bloch theory for evaluating the wavevector dispersion for a propagation mode inside the HM, and show that the homogenization scheme is in good agreement with Bloch theory in a very wide spatial spectrum. We report the tunability of transition from elliptic to hyperbolic iso-frequency wavevector dispersion by varying the chemical potential of graphene sheets.

Wave vector

Homogenization

Bloch wave

Spatial dispersion

Dispersion relation

10.1109/aps.2013.6710903

Cite

Citations (1)

Third order modal degeneracy in waveguids: Features and application in amplifiers

Farshad Yazdi Mohamed A. K. Othman Mehdi Veysi Filippo Capolino Alexander Figotin

We investigate a particular degeneracy condition in the dispersion of coupled periodic structures causing three eigenmodes to coalesce under proper coupling between eigenmodes supported by the system. This condition is referred to as a stationary inflection point (SIP) which is a third order degeneracy. We also show that by tuning the coupling parameters in the coupled periodic structure, the dispersion can be engineered to exhibit a slight positive or negative group velocity around the SIP frequency rather than zero group velocity. In particular, such regime provides a three-mode synchronous operation with an electron beam which is potentially beneficial for enhancing the efficiency of the traveling wave tubes (TWTs). Therefore, we use the proposed regime to design a SIP-based TWT where we show a gigantic gain enhancement compared to conventional single-mode Pierce-like TWTs.

Degeneracy (biology)

Inflection point

Group velocity

Mode (computer interface)

Traveling-wave tube

10.1109/usnc-ursi.2017.8074921

Cite

Citations (2)

Giant Resonance and Anomalous Quality Factor Scaling in Degenerate Band Edge Coupled Resonator Optical Waveguides

Journal of Lightwave Technology (2018)

Mohamed Y. Nada Mohamed A. K. Othman Ozdal Boyraz Filippo Capolino

We propose a novel scheme for enhancing the quality factor (Q factor) of coupled resonators optical waveguides (CROWs) side coupled to a straight waveguide when operating near a degenerate band edge (DBE). The DBE is an exceptional point of degeneracy occurring without the need of loss or gain when four Bloch eigenwaves coalesce, providing a resonance condition with field enhancement and other unique properties associated with such frozen mode. We derive an analytic expression that describes the flatness of the dispersion diagram at the DBE and show how this is related to engineering the quality factor. We report an anomalous scaling law of the quality factor for a cavity made of the DBE-CROW with the fifth power of the number of rings when operating at the resonance frequency closest to the DBE frequency, even in the presence of losses and structural perturbations. Remarkably, the Q factor of the proposed DBE-CROW can be engineered to exceed that of a single ring resonator having a diameter equal to the total DBE-CROW length; hence, the DBE leads to an overall huge area reduction. We also demonstrate the robustness of the DBE-CROW's Q factor scaling near the DBE against perturbations and disorders that could arise from tolerances in fabrication. The findings reported in this paper are critical for enhancing field's amplitudes to giant levels and the Q factor of ring resonators, and are very beneficial for various applications including four-wave mixing, Q switching, lasers, and highly sensitive sensors.

Q factor

Degeneracy (biology)

Flatness (cosmology)

Waveguide

Optical ring resonators

10.1109/jlt.2018.2822600

Cite

Citations (31)