KOOI AWAVE STUDIO VERIFICATION
Subsequently, a circular waveguide filling with dielectric is designed to model moving electrons, which enables the verification of the spiral field generation in Smith-Purcell radiation in the microwave regime.
Here, the angular momentum l is an integer of two possible values (☑). The intrinsically nonradiative energy bound at the source current sheet is coupled to an electric dipole with an azimuthal phase factor when swift electrons pass through the helical metagrating. Semitheoretical analysis of the spiral field generation in Smith-Purcell radiation from a helical metagrating is performed.
In this letter, we propose a new method to generate angular momentum in Smith-Purcell radiation when a swift electron passes through a helical metagrating.
KOOI AWAVE STUDIO HOW TO
However, to the best of our knowledge, few works discuss how to introduce angular momentum into the Smith-Purcell radiation so far. Recently, the study of Smith-Purcell radiation was extended beyond the simple periodic structure, into aperiodic arrays, disordered plasmonic arrays, and Babinet metasurfaces for manipulation on the Smith-Purcell radiation polarization, beyond the simple periodic structure. Unlike Cherenkov radiation, Smith-Purcell radiation is generated from the induced current varying in space and time when charges moving near the periodically deformed surface. Especially, due to the emergence of negative-index metamaterials, reversed Cherenkov radiation has been proposed and experimentally observed. For example, Cherenkov radiation is emitted when the speed of an electron is greater than that of light in the background medium. In particular, swift electrons carry the evanescent field, which can generate far-field radiation when the electrons interact with materials. Common schemes of electron vortex beams use spiral phase plates or interaction of the e-beam in free-electron lasers (FELs) to the magnetic field of the helical undulator Įlectron plays a significant role in physics. Electron vortices have also been explored as detectors of chirality in crystals and molecules. Recently, a new approach which is able to produce vortices based on radiation emission in extreme ultraviolet (XUV) even X-ray from electron vortex beams has developed rapidly. Owing to the fascinating properties and wide applications, generating optical vortices has been under intense study and various schemes have been proposed such as spiral phase plate, computer generated holograms (CGH), metamaterials/metasurfaces, and spoof plasmonics. Special characteristics of optical vortices have attracted plenty of interests from many communities, such as optical tweezers, optical communications, biology microscopy, and so forth. Since then, various studies on optical vortices have been reported. The spin angular momentum of light is associated with light polarization, experimentally demonstrated by Beth in 1935, while, until 1992, light carrying orbital angular momentum called optical vortices was firstly investigated by Allen and soon verified experimentally. IntroductionĪngular momentum including spin and orbital angular momentum is a fundamental physical quantity in both classical and quantum physics. Our findings not only pave a way for design of orbital angular momentum free-electron lasers but also provide a platform to study the interplay between swift electrons with chiral objects. The angular momentum of the radiated wave is determined solely by the handedness of the helical structure, and it thus serves as a potential candidate for the detection of chiral objects.
Experimental measurements show efficient control over angular momentum of the radiated field at microwave regime, utilizing a phased electromagnetic dipole array to mimic moving charged particles.
Spiral field patterns can be generated while introducing a gradient azimuthal phase distribution to the induced electric dipole array at the cylindrical interface. In this letter, we investigate the Smith-Purcell radiation from helical metagratings, chiral structures similar to deoxyribonucleic acid (DNA), in order to understand the interplay between electrons, photons, and object chirality. Moving electrons interacting with media can give rise to electromagnetic radiations and has been emerged as a promising platform for particle detection, spectroscopies, and free-electron lasers.
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