A method of realizing vector vortex smith-pursell radiation
Patent Information
- Application Number
- CN202311482030.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-11-09
- Publication Date
- 2026-09-08
- Estimated Expiration
- 2043-11-09
AI Technical Summary
然而，史密斯-珀塞尔辐射的自旋和轨道角动量的共调制尚未被揭示
[0033] Compared with the prior art, the advantages of this invention are:
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Figure CN117518300B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of electromagnetics, and more specifically, to a method for realizing vector vortex Smith-Purcell radiation. Background Technology
[0002] The effect of an electron beam moving on a metallic diffraction grating to produce visible light radiation is called Smith-Purcell radiation. Smith-Purcell radiation describes the light emission process when a charged particle moves closely parallel to a periodic structure. Its velocity is slower than the phase velocity of light in the surrounding medium and can be explained by the coupling between the evanescent field of the moving charged particle and the electromagnetic modes of the periodic structure. Due to its unique physical properties, Smith-Purcell radiation has wide applications in many fields. For example, it can be used as an electromagnetic radiation source. Because electron beams carry a wide range of frequency information, and one of the most promising advantages of free electron radiation is its wide tunability and usable wavelength range, electromagnetic radiation from microwaves to X-rays can be realized. Furthermore, it has direct applications in microwave electronics and is considered a promising non-invasive particle beam diagnostic platform. Therefore, research on Smith-Purcell radiation is of great significance.
[0003] Metamaterials, composed of subwavelength structures, exhibit more flexible electromagnetic field manipulation properties than natural materials. These micro / nanostructured artificial media have attracted significant research interest, as well as the ability to achieve intriguing optical phenomena such as negative refraction and perfect imaging through the design of well-designed scattering unit arrays. However, the high losses, strong dispersion associated with resonant responses, and the difficulty in fabricating micro / nanoscale three-dimensional structures of metamaterials hinder their practical applications. Metasurfaces, which are two-dimensional equivalent planes of three-dimensional metamaterials, can significantly suppress unnecessary losses due to their ultrathin thickness along the wave propagation direction. Metasurfaces have garnered increasing attention from researchers due to their efficient light-matter interaction capabilities, excellent electromagnetic properties, simple fabrication processes, multidimensional manipulation of light waves, and ease of integration with functional materials. Over the past decade, metasurfaces have been used in the design and fabrication of optical components and systems, outperforming traditional diffractive optical elements.
[0004] As a type of metasurface, phase-gradient metasurfaces are characterized by phase discontinuities at their interfaces. Currently, phase-gradient metasurfaces have become a research hotspot in electromagnetics, enabling arbitrary beam deflection, broadband achromatic superlenses, arbitrary polarization control, holographic imaging, and other applications. They have also shown a wealth of practical applications in microwave and optical fields (such as antennas).
[0005] The polarization of free electron radiation holds great promise for the development of tunable electromagnetic radiation sources, while orbital angular momentum provides an additional degree of freedom for optical manipulation. More importantly, vortex radiation carrying spin angular momentum offers a new avenue for modern compact wireless communication systems, thereby improving spectral efficiency and channel capacity. However, the co-modulation of spin and orbital angular momentum in Smith-Purcell radiation remains undiscovered. Summary of the Invention
[0006] 1. Technical problems to be solved
[0007] To address the problems existing in the prior art, the present invention aims to provide a method for realizing vector vortex Smith-Purcell radiation, which can realize vortex Smith-Purcell radiation in different polarization states. It utilizes a cascaded system composed of a grating metasurface and a phase gradient metasurface to achieve co-modulation of the spin angular momentum and orbital angular momentum of Smith-Purcell radiation.
[0008] 2. Technical Solution
[0009] To solve the above problems, the present invention adopts the following technical solution.
[0010] A method for realizing vector vortex Smith-Purcell radiation, the method comprising the following steps:
[0011] S1: The polarization vortex Smith-Purcell radiation is set as a structure of dielectric grating, silicon dioxide dielectric plate one, phase gradient metasurface and silicon dioxide dielectric plate two, and the polarization state of free electron radiation is controlled by periodic dielectric grating.
[0012] S2: Using a phase gradient metasurface to modulate the phase of radiated light;
[0013] S3: By adjusting the structure of the dielectric grating according to polarization modulation, electron radiation with different polarizations can be obtained;
[0014] In this process, the electron beam passes through a grating rotated 45° relative to the direction of electron beam propagation to obtain circularly polarized Smith-Purcell radiation.
[0015] When the grating azimuth angle is -45°, left-handed circularly polarized Smith-Purcell radiation is obtained;
[0016] S4: When electric and magnetic dipoles overlap, adjusting the length and width of the structure allows for 2π phase control near the resonant frequency.
[0017] Furthermore, it also includes a dielectric grating, a first silicon dioxide dielectric plate, a phase gradient metasurface, and a second silicon dioxide dielectric plate, wherein the dielectric grating, the first silicon dioxide dielectric plate, the phase gradient metasurface, and the second silicon dioxide dielectric plate are distributed sequentially from top to bottom;
[0018] The polarization state of free electron radiation can be modulated using periodic dielectric gratings;
[0019] The phase of radiated light can be modulated using a phase gradient metasurface.
[0020] Two types of grating structures, a resonant phase-gradient metasurface, and a geometric phase-gradient metasurface were designed to realize linearly polarized and circularly polarized vector vortex electron radiation, respectively. Due to the high transmittance of the all-dielectric metasurface structure, cascading metasurfaces is possible; cascading two metasurfaces can generate vortex electron radiation with arbitrary polarization directions.
[0021] Furthermore, the dielectric grating material is any one of silicon, silicon boride, and zinc sulfide.
[0022] Furthermore, the dielectric grating material used to achieve linear polarization is silicon, with a period of 800 nm, a width of 400 nm, and a height of 291.2 nm. Its optical properties are derived from Palik's experimental data.
[0023] The dielectric grating material used to achieve circular polarization is silicon, with a period of 570 nm, a width of 220 nm, and a height of 320 nm. Its optical properties are derived from Palik's experimental data.
[0024] Furthermore, based on the polarization control requirements, the structure of the dielectric grating can be changed to obtain electron radiation with different polarizations.
[0025] Furthermore, in S1, the orientation angle of the dielectric grating structure is manipulated to control linear polarization or left- or right-hand circular polarization.
[0026] Furthermore, the phase gradient metasurface is based on Huygens' principle and Pancharatnam-Berry's principle to achieve resonant and geometric 2π phase coverage.
[0027] Furthermore, the dielectric grating needs to satisfy 2π phase coverage at the operating wavelength.
[0028] Furthermore, the resonant phase gradient metasurface material is silicon, with a period of 800 nm and a height of 270 nm. Its optical properties are derived from Palik's experimental data. The aim is to achieve 2π phase coverage at the resonant frequency by changing the geometric dimensions using Huygens' principle.
[0029] The geometric phase gradient metasurface material is silicon, with a period of 570 nm, a length of 420 nm, a width of 220 nm, and a height of 1000 nm. Its optical properties are derived from Palik's experimental data, and the aim is to achieve 2π phase coverage using the Pancharatnam-Berry phase.
[0030] The electron beam passes through the grating from above, and the designed operating wavelength is 1550nm.
[0031] Furthermore, the silicon dioxide in the silicon dioxide dielectric plate is 310 mm thick and has a refractive index of 1.46.
[0032] 3. Beneficial effects
[0033] Compared with the prior art, the advantages of this invention are:
[0034] (1) This technical solution realizes the co-modulation of polarization and phase of Smith-Purcell radiation; taking advantage of the high transmittance of the all-dielectric metasurface structure, a four-layer cascade structure is realized to generate vortex electron radiation with arbitrary polarization direction; the whole system forms a compact optical system, providing a simple method to generate electron radiation beams with arbitrary polarization and vortex phase. Attached Figure Description
[0035] Figure 1 This is a schematic diagram of the structure for realizing linearly polarized vortex Smith-Purcell radiation in this invention.
[0036] in, Figure 1 (a) is a schematic diagram of a cascaded metasurface structure;
[0037] Figure 1 (b) is the normalized Stokes polarization parameter S1 distribution of the electron beam passing through the grating in the xy plane;
[0038] Figure 2 This invention achieves x-polarized vortex Smith-Purcell radiation.
[0039] in, Figure 2 (a) shows the phase response curves and transmission coefficients of the four unit structures;
[0040] Figure 2 (b) shows the arrangement of phase gradient metasurface unit structures;
[0041] Figure 2 (c) is the real distribution of Ex on the xy plane at 100 μm below the metasurface;
[0042] Figure 2 (d) represents the phase distribution of Ex;
[0043] Figure 3 This invention achieves y-polarized vortex Smith-Purcell radiation.
[0044] in, Figure 3 (a) shows the phase response curve and transmission coefficient of the metasurface unit structure;
[0045] Figure 3 (b) shows the arrangement of the unit structure;
[0046] Figure 3 (c) is the real distribution of Ex on the xy plane at 100 μm below the metasurface;
[0047] Figure 3 (d) represents the phase distribution of Ex;
[0048] Figure 4 This is a schematic diagram of the structure for realizing circularly polarized vortex Smith-Purcell radiation according to the present invention;
[0049] in Figure 4 (a) is a schematic diagram of the structure when the grating azimuth angle is 45°;
[0050] Figure 4 (b) Normalized Stokes polarization parameter S3 distribution of the electron beam in the xy plane after passing through the grating;
[0051] Figure 5 This invention is a result of realizing circularly polarized vortex Smith-Purcell radiation;
[0052] in, Figure 5 (a) shows the phase response curve and transmission coefficient of the metasurface unit structure;
[0053] Figure 5 (b) shows the arrangement of the unit structure;
[0054] Figure 5 (c) and Figure 5 (d) show the far-field intensity distributions of transmitted right-handed and left-handed circularly polarized light, respectively;
[0055] Figure 5 (e) and Figure 5 (f) shows the phase distributions of right-handed and left-handed circularly polarized light, respectively. Detailed Implementation
[0056] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.
[0057] Example 1:
[0058] Please see Figure 1-5 A method for realizing vector vortex Smith-Purcell radiation.
[0059] The method includes the following steps:
[0060] S1: The polarization state of free electron radiation is controlled by using a periodic dielectric grating;
[0061] S2: Using a phase gradient metasurface to modulate the phase of radiated light;
[0062] S3: By adjusting the structure of the dielectric grating according to polarization modulation, electron radiation with different polarizations can be obtained;
[0063] In this process, the electron beam passes through a grating rotated 45° relative to the direction of electron beam propagation to obtain circularly polarized Smith-Purcell radiation.
[0064] When the grating azimuth angle is -45°, left-handed circularly polarized Smith-Purcell radiation is obtained;
[0065] S4: When electric and magnetic dipoles overlap, adjusting the length and width of the structure allows for 2π phase control near the resonant frequency.
[0066] It also includes a dielectric grating, a first silicon dioxide dielectric plate, a phase gradient metasurface, and a second silicon dioxide dielectric plate, wherein the dielectric grating, the first silicon dioxide dielectric plate, the phase gradient metasurface, and the second silicon dioxide dielectric plate are distributed sequentially from top to bottom;
[0067] The polarization state of free electron radiation can be modulated using periodic dielectric gratings;
[0068] The phase of radiated light can be modulated using a phase gradient metasurface.
[0069] Leveraging the high transmittance of the all-dielectric metasurface structure, a four-layer cascaded structure was achieved, generating vortex electron radiation in arbitrary polarization directions.
[0070] The electron beam passes through the grating from above, parallel to it, as... Figure 1 As shown in (a), for linearly polarized vortex electron radiation, the designed grating, in which the nanograting converts the electron beam radiation into linear polarization in the x-direction. Figure 1 (b) shows the distribution of the normalized Stokes parameter S1 in the xy plane after the electron beam passes through the grating. S1 = 1 indicates x-polarization, and S1 = -1 indicates y-polarization. It is clear that the grating effectively converts the electron beam radiation into x-polarization.
[0071] The dielectric grating material is any one of silicon, silicon boride, and zinc sulfide.
[0072] By changing the structure of the dielectric grating according to the polarization control requirements, electron radiation with different polarizations can be obtained.
[0073] By manipulating the orientation angle of the dielectric grating structure, linear polarization or left- or right-hand circular polarization can be controlled.
[0074] The phase gradient metasurface, based on Huygens' principle and Pancharatnam-Berry's principle, is used to achieve resonant and geometric 2π phase coverage.
[0075] According to Huygens' principle, when an electric dipole and a magnetic dipole overlap, 2π phase control can be achieved near the resonant frequency by adjusting the length and width of the structure. Figure 2 (a) The transmission amplitude and phase response curves of four unit structures of the phase-gradient metasurface are described, where the left y-axis represents the phase and the right y-axis represents the amplitude. The four unit structures achieving π / 2 phase increments cover phase variations from 0 to 2π. Table 1 shows the detailed parameters of the four unit structures (the serial numbers correspond to the position quadrants, the same below). The length and width of the unit structures, as well as the achieved phase and co-polarization transmission coefficients, are shown respectively. The arrangement of the unit structures is as follows... Figure 2 As shown in (b), it divides the plane into four parts to achieve a phase shift of 0-2π. Figure 2 (c) and 2(d) show the real part and phase distribution of Ex in the xy plane 100 μm below the metasurface. The spatial phase diagram exhibits a 2π phase transition around the center, consistent with the theoretical phase of the vortex beam. These results confirm that the aforementioned cascaded metasurface produces x-polarized vortex Smith-Purcell radiation with a topological charge of l = 1.
[0076] Table 1. Detailed parameters for achieving 2π coverage using the unit structure.
[0077]
[0078] Figure 3 The illustration in (a) shows the unit structure for realizing y-polarized vortex Smith-Purcell radiation. The specific parameters of the four unit structures are shown in Table 2. The four unit structures are rotated 45° along the z-axis to achieve 2π phase coverage of cross-polarization. Figure 3 (a) depicts the phase and amplitude of cross-polarization for each unit cell, with the unit cell arrangement of the phase gradient metasurface as shown. Figure 3 As shown in (b). Figure 3 (c) and 3(d) show the real part and phase distribution of Ey in the xy plane 100 μm below the metasurface, demonstrating that the cascaded metasurface produces y-polarized vortex Smith-Purcell radiation with topological charge l = 1.
[0079] Table 2 Detailed parameters for achieving 2π coverage using the unit structure
[0080]
[0081] The dielectric grating must satisfy 2π phase coverage at the operating wavelength.
[0082] The silicon dioxide dielectric plate has a thickness of 310 mm and a refractive index of 1.46.
[0083] Furthermore, in order to achieve vortex radiation carrying circular polarization, the azimuth angle of the grating is adjusted to 45°, where the azimuth angle is the angle between the grating strips and the x-axis. Figure 4 (a) shows a schematic diagram of an electron beam passing through a cascaded metasurface. The S3 parameter distribution on the xy-plane after the electron beam passes through the grating is as follows: Figure 4 As shown in (b), the normalized Stokes parameters S3 = 1 and -1, corresponding to right-circularly polarized light and left-circularly polarized light, respectively. Clearly, circularly polarized Smith-Purcell radiation can be produced when the electron beam passes through a grating rotated 45° relative to the direction of electron beam propagation.
[0084] Based on the design principles of geometric phase gradient metasurfaces, a design was created such as Figure 5 (b) Metasurface structure, the amplitude and phase response of the corresponding unit structure are as follows: Figure 5 As shown in (a), the left y-axis represents the phase, and the right y-axis represents the amplitude. The transmission phase increases linearly with the orientation angle θ, while the transmittance can exceed 90% and is independent of the rotation angle. Figure 5 (c) and 5(e) depict the far-field intensity and phase distribution of the transmitted right-handed circularly polarized light as the electron beam passes through the grating. The electric field exhibits a distribution of a hollow circle with a central defect singularity, and the phase varies by 2π around the center. This demonstrates the generation of right-handed circularly polarized vortex Smith-Purcell radiation at l=1. Similarly, left-handed circularly polarized Smith-Purcell radiation can be realized when the grating azimuth angle is -45°, as shown in Figure 5(e). Figure 5 As shown in (d) and 5(f).
[0085] The above description is merely a preferred embodiment of the present invention; however, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concept, should be covered within the scope of protection of the present invention.
Claims
1. A method for realizing vector vortex Smith-Purcell radiation, characterized in that: The method includes the following steps Suddenly: S1: The vector vortex Smith-Purcell radiation device is configured as a structure of a dielectric grating, a silicon dioxide dielectric plate one, a phase gradient metasurface and a silicon dioxide dielectric plate two, and the polarization state of free electron radiation is controlled by a periodic dielectric grating. S2: The phase of the radiated light is modulated by the phase gradient metasurface to form vortex Smith-Purcell radiation carrying orbital angular momentum; S3: By controlling the polarization state of free electron radiation, the structure of the dielectric grating is changed to obtain electron radiation with different polarizations; S4: When electric and magnetic dipoles overlap, adjusting the length and width of the structure allows for 2π phase control near the resonant frequency. The dielectric grating, silicon dioxide dielectric plate one, phase gradient metasurface, and silicon dioxide dielectric plate two are arranged sequentially from top to bottom.
2. The method for realizing vector vortex Smith-Purcell radiation according to claim 1, characterized in that: In S1, the dielectric grating material is any one of silicon, silicon boride, and zinc sulfide.
3. The method for realizing vector vortex Smith-Purcell radiation according to claim 1, characterized in that: In S1, the orientation angle of the dielectric grating structure is manipulated to control linear polarization or left- or right-hand circular polarization.
4. The method for realizing vector vortex Smith-Purcell radiation according to claim 1, characterized in that: In S3, circularly polarized Smith-Purcell radiation is obtained after the electron beam passes through a grating rotated 45° relative to the direction of electron beam propagation. When the grating azimuth angle is -45°, left-handed circularly polarized Smith-Purcell radiation is obtained.
5. The method for realizing vector vortex Smith-Purcell radiation according to claim 1, characterized in that: The phase gradient metasurface is based on Huygens' principle and the Pancharatnam-Berry phase principle and is used to achieve resonant and geometric 2π phase coverage.
6. The method for realizing vector vortex Smith-Purcell radiation according to claim 1, characterized in that: The silicon dioxide in the silicon dioxide dielectric plate has a refractive index of 1.46.