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Wong LWW, Shi X, Karnieli A, Lim J, Kumar S, Carbajo S, Kaminer I, Wong LJ. Free-electron crystals for enhanced X-ray radiation. LIGHT, SCIENCE & APPLICATIONS 2024; 13:29. [PMID: 38267427 PMCID: PMC10808554 DOI: 10.1038/s41377-023-01363-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2023] [Revised: 10/26/2023] [Accepted: 12/18/2023] [Indexed: 01/26/2024]
Abstract
Bremsstrahlung-the spontaneous emission of broadband radiation from free electrons that are deflected by atomic nuclei-contributes to the majority of X-rays emitted from X-ray tubes and used in applications ranging from medical imaging to semiconductor chip inspection. Here, we show that the bremsstrahlung intensity can be enhanced significantly-by more than three orders of magnitude-through shaping the electron wavefunction to periodically overlap with atoms in crystalline materials. Furthermore, we show how to shape the bremsstrahlung X-ray emission pattern into arbitrary angular emission profiles for purposes such as unidirectionality and multi-directionality. Importantly, we find that these enhancements and shaped emission profiles cannot be attributed solely to the spatial overlap between the electron probability distribution and the atomic centers, as predicted by the paraxial and non-recoil theory for free electron light emission. Our work highlights an unprecedented regime of free electron light emission where electron waveshaping provides multi-dimensional control over practical radiation processes like bremsstrahlung. Our results pave the way towards greater versatility in table-top X-ray sources and improved fundamental understanding of quantum electron-light interactions.
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Affiliation(s)
- Lee Wei Wesley Wong
- School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore
| | - Xihang Shi
- Solid State Institute and Faculty of Electrical and Computer Engineering, Technion - Israel Institute of Technology, Haifa, 3200003, Israel
| | - Aviv Karnieli
- School of Electrical Engineering, Fleischman Faculty of Engineering, Tel Aviv University, Tel Aviv, 69978, Israel
- Department of Applied Physics, Stanford University, Stanford, CA, 94305, USA
| | - Jeremy Lim
- Science, Mathematics and Technology, Singapore University of Technology and Design, 8 Somapah Road, Singapore, 487372, Singapore
| | - Suraj Kumar
- School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore
| | - Sergio Carbajo
- Electrical and Computer Engineering Department, UCLA, 420 Westwood, Los Angeles, CA, 90095, USA
- Physics and Astronomy Department, UCLA, 475 Portola Plaza, Los Angeles, CA, 90095, USA
- SLAC National Accelerator Laboratory, Stanford University, 2575 Sand Hill Road, Menlo Park, CA, 94025, USA
| | - Ido Kaminer
- Solid State Institute and Faculty of Electrical and Computer Engineering, Technion - Israel Institute of Technology, Haifa, 3200003, Israel
| | - Liang Jie Wong
- School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore.
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Fu T, Wang D, Yang Z, Deng ZL, Liu W. Steering Smith-Purcell radiation angle in a fixed frequency by the Fano-resonant metasurface. OPTICS EXPRESS 2021; 29:26983-26994. [PMID: 34615121 DOI: 10.1364/oe.434580] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Accepted: 07/24/2021] [Indexed: 06/13/2023]
Abstract
Smith-Purcell radiation (SPR) is a kind of electromagnetic wave radiation that happens when an energetic beam of electrons passes very closely parallel to the surface of a ruled optical diffraction grating. The frequency of radiation waves varies in the upper and lower space of the grating for different electron velocity, satisfying the SPR relationship. In this study, a Fano-resonant metasurface was proposed to steer the direction of the SPR waves at the fixed resonant frequency by changing the velocity of the electron beam without varying the geometric parameters or adding extra coupling structure. The maximum emission power always locates at the resonant frequency by utilizing the integration of the Poynting vector. The relative radiated efficiency can reach to a maximum value of 91% at the frequency of 441 GHz and the efficiency curve has a dip when the direction of SPR is nearly vertical due to the high transmission. There is a great consistence of steering radiation angle from 65 degrees to 107 degrees by altering the velocity of electron beam from 0.6c to 0.95c both in analytical calculation and PIC (particle-in-cell of CST) simulation at terahertz frequencies, where c is the speed of light in vacuum. Furthermore, the destructive interference of Fano resonance between the magnetic mode and the toroidal mode shows the underlying physics of steering SPR in a fixed frequency. Our study indicates that the proposed structure can produce direction-tunable THz radiation waves at resonant frequency by varying the velocity of the electron beam, which is promising for various applications in a compact, tunable, high power millimeter wave and THz wave radiation sources.
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Wong LJ, Rivera N, Murdia C, Christensen T, Joannopoulos JD, Soljačić M, Kaminer I. Control of quantum electrodynamical processes by shaping electron wavepackets. Nat Commun 2021; 12:1700. [PMID: 33731697 PMCID: PMC7969958 DOI: 10.1038/s41467-021-21367-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2016] [Accepted: 01/14/2021] [Indexed: 01/31/2023] Open
Abstract
Fundamental quantum electrodynamical (QED) processes, such as spontaneous emission and electron-photon scattering, encompass phenomena that underlie much of modern science and technology. Conventionally, calculations in QED and other field theories treat incoming particles as single-momentum states, omitting the possibility that coherent superposition states, i.e., shaped wavepackets, can alter fundamental scattering processes. Here, we show that free electron waveshaping can be used to design interferences between two or more pathways in a QED process, enabling precise control over the rate of that process. As an example, we show that free electron waveshaping modifies both spatial and spectral characteristics of bremsstrahlung emission, leading for instance to enhancements in directionality and monochromaticity. The ability to tailor general QED processes opens up additional avenues of control in phenomena ranging from optical excitation (e.g., plasmon and phonon emission) in electron microscopy to free electron lasing in the quantum regime.
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Affiliation(s)
- Liang Jie Wong
- School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, Singapore.
| | - Nicholas Rivera
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Chitraang Murdia
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Thomas Christensen
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - John D Joannopoulos
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Marin Soljačić
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Ido Kaminer
- Department of Electrical Engineering, Technion, Haifa, Israel.
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Liu Y, Liu W, Liang L, Jia Q, Wang L, Lu Y. Threshold-less and focused Cherenkov radiations using sheet electron-beams to drive sub-wavelength hole arrays. OPTICS EXPRESS 2018; 26:34994-35002. [PMID: 30650914 DOI: 10.1364/oe.26.034994] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2018] [Accepted: 12/12/2018] [Indexed: 06/09/2023]
Abstract
Cherenkov radiation (CR) was one of the most famous discoveries in the last century and still has broad applications in modern physics. Recently, threshold-less and reversed CRs have attracted even more attention thanks to their unique characteristics and application prospects. Here we illustrated a threshold-less CR in vacuo by using a sheet free-electron beam (FEB) to excite an oblique-lined sub-wavelength hole array. It is achieved by setting the effective velocity of emitters-resonant modes successively excited by the sheet FEB-to be greater than the speed of light in vacuo. By letting the sub-wavelength holes line up along a designed curve, we further demonstrated a focused CR with radiation being convergent to specific focusing spots, which can be located at any designed positions in space, achieving backward (reversed) as well as forward (normal) CRs in effect. This focused CR does not have the conventional Cherenkov cone, and its intensity at the focusing spot is greatly enhanced. These newly revealed threshold-less and focused CRs may lead to broad interest and attractive applications, especially for developing integrated and focused light sources in the terahertz region.
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Shu GX, Liu G, Qian ZF. Simulation study of a high-order mode terahertz radiation source based on an orthogonal grating waveguide and multiple sheet electron beams. OPTICS EXPRESS 2018; 26:8040-8048. [PMID: 29715777 DOI: 10.1364/oe.26.008040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2018] [Accepted: 03/16/2018] [Indexed: 06/08/2023]
Abstract
Generally, it is difficult for the common backward wave oscillator (BWO) to produce powerful THz radiation when the operating frequency increases to a high level such as over 1 THz due to the very small structural dimensions. The concept of generating powerful THz radiation from the interaction between high-order mode THz wave and multiple sheet electron beams is a promising solution to address the issue. For the high-order mode operation, a novel orthogonal grating waveguide is proposed, which is relatively ease of fabrication compared with the overmoded structure based on the double staggered grating waveguide. A high-order mode BWO based on the orthogonal grating waveguide and multiple sheet electron beams is studied by simulations. Particle-in-cell simulations show that the BWO can provide over 1.08 W power in the frequency range of 1.18-1.30 THz. Such a methodology opens up a new way to extend the BWO's operating frequency to a higher level and provides a potential solution for developing compact powerful THz radiation sources with wide tunable bandwidth.
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