Voltage-controlled directional terahertz radiation source based on Smith-Purcell effect

Abstract

The present invention discloses a voltage-controlled direction-adjustable terahertz radiation source based on the Smith-Purcell effect, wherein the active plane is arranged parallel to the metasurface and located above the metasurface, and the electron beam is arranged on the active plane and moves at a uniform speed along the X direction. Through the interaction of the electron beam when passing at a uniform speed above the metasurface where the structural units are periodically arranged, a reflection field is generated in the upper half space of the metasurface, and a radiation wave is generated in the process of energy exchange. By adjusting the electron beam speed, that is, the voltage or the electron beam energy, the frequency is determined, and the radiation direction of the terahertz radiation wave can be adjusted within a certain angle. The problem that it is difficult to achieve the adjustability of the radiation wave direction in Smith-Purcell radiation in the prior art without changing the structural parameters is solved.

Description

Technical Field

[0001] The invention relates to the technical field of vacuum electronics, and in particular to a voltage-controlled direction-adjustable terahertz radiation source based on the Smith-Purcell effect. Background Art

[0002] Terahertz waves refer to electromagnetic waves with a frequency between 0.1-10THz, which are located between microwaves and infrared light in the electromagnetic spectrum. They are the only band in the electromagnetic spectrum that has not yet been fully developed. Due to the particularity of the position of terahertz waves in the electromagnetic spectrum, terahertz waves also have many unique properties: terahertz spectroscopy is of great help in the physical processes in condensed materials; the photon energy of terahertz rays is relatively low compared to other rays, so terahertz rays have a relatively small impact on biological cells, so using terahertz rays to examine the human body or other organisms is undoubtedly more popular; according to the high-frequency characteristics of terahertz waves themselves, they can also be used to suppress the interference caused by background radiation noise. Therefore, the development of terahertz sources is the foundation for the development of terahertz science and technology, and it is also the main bottleneck restricting the development of terahertz science and technology.

[0003] At present, the research on terahertz sources in the world is mainly divided into the following categories: ultrafast laser technology, laser optical technology, and vacuum electronic technology. As a special Smith-Purcell effect in vacuum electronic technology, the emitter emits a continuous electron beam, which passes through the surface of the periodic structure and excites the slow-wave structure to produce surface waves of a certain frequency. The surface wave then interacts with the electron beam to cause clustering. In this process, the energy exchange caused by the interaction between the slow wave and the electron beam will cause the terahertz wave to radiate. Traditional Smith-Purcell radiation is incoherent, with low radiation intensity and efficiency, and the radiation direction includes all directions in the upper half space of the structure. Further research shows that superradiance can produce terahertz radiation waves in a fixed direction, but if this unidirectional radiation needs to adjust the radiation direction, it is necessary to change the direction of the structure, and it is difficult to achieve directional adjustability, which greatly limits the development and application of terahertz radiation sources. Summary of the invention

[0004] The purpose of the present invention is to provide a voltage-controlled direction-adjustable terahertz radiation source based on the Smith-Purcell effect, aiming to solve the technical problem in the prior art that it is difficult to achieve the adjustability of the radiation wave direction without changing the structural parameters of the Smith-Purcell radiation.

[0005] To achieve the above object, the present invention adopts a voltage-controlled direction-adjustable terahertz radiation source based on the Smith-Purcell effect, comprising a metasurface, an active plane and an electron beam, wherein the active plane is arranged parallel to the metasurface and located above the metasurface, and the electron beam is arranged on the active plane and moves at a uniform speed along the X direction;

[0006] The metasurface is composed of a plurality of groups of structural units, and the structural units are periodically arranged along the X direction and the Y direction. The arrangement periods of the structural units along the X direction and the Y direction are equal and are fixed values.

[0007] Among them, three gaps are arranged in the structural unit, and the gaps are arranged in parallel along the Y direction. The center distance d between two groups of the gaps is equal to 100um. The range value of the width w of the gap is 2um to 300um, and the range value of the height h is 15um to 950um.

[0008] The range value of the arrangement period parameter p of the structural unit along the X direction and the Y direction is 30um to 1000um, and the structural unit is a conductor.

[0009] The distance z0 between the active plane and the hypersurface is an adjustable value, which is usually set to 0.2 times of the p value.

[0010] Wherein, the arrangement period parameter p is 500um, the width w of the gap is 60um, and the height h is 300um.

[0011] The voltage-controlled direction-adjustable terahertz radiation source based on the Smith-Purcell effect of the present invention generates a reflection field in the upper half space of the metasurface through the interaction of the electron beam when it passes over the metasurface with periodic arrangement of the structural units at a uniform speed, generates radiation waves in the process of energy exchange, and obtains a terahertz radiation wave whose frequency is determined by adjusting the electron beam speed, that is, the voltage or the electron beam energy, and whose radiation direction can be adjusted within a certain angle. The problem in the prior art that it is difficult to achieve the adjustability of the radiation wave direction without changing the structural parameters of Smith-Purcell radiation is solved. The structure of the present invention is compact and easy to implement, and the structural dimensions meet the requirements of existing process standards, and can achieve miniaturization and integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0013] Figure 1 It is a schematic diagram of the principle of the voltage-controlled direction-adjustable terahertz radiation source based on the Smith-Purcell effect of the present invention.

[0014] Figure 2 It is a schematic diagram of the structure of the structural unit of the present invention.

[0015] Figure 3 It is the transmission and reflection spectrum obtained by simulation calculation of the present invention.

[0016] Figure 4 It is a curve fitting diagram of the radiation direction calculated by simulation of the present invention and the radiation direction calculated by theoretical formula.

[0017] 1-metasurface, 11-structural unit, 12-slit, 2-active plane, 3-electron beam, 4-radiation wave. DETAILED DESCRIPTION

[0018] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0019] In the description of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, in the description of the present invention, "multiple" means two or more, unless otherwise clearly and specifically defined.

[0020] See also Figures 1 to 4 The present invention provides a voltage-controlled direction-adjustable terahertz radiation source based on the Smith-Purcell effect, comprising a metasurface 1, an active plane 2 and an electron beam 3, wherein the active plane 2 is arranged parallel to the metasurface 1 and is located above the metasurface 1, and the electron beam 3 is arranged on the active plane 2 and moves at a uniform speed along the X direction;

[0021] The metasurface 1 is composed of a plurality of groups of structural units 11, and the structural units 11 are periodically arranged along the X direction and the Y direction. The arrangement periods of the structural units 11 along the X direction and the Y direction are equal and are fixed values.

[0022] Three slits 12 are arranged in the structural unit 11. The slits 12 are arranged in parallel along the Y direction. The center distance d between two groups of the slits 12 is equal to 100um. The width w of the slit 12 ranges from 2um to 300um, and the height h ranges from 15um to 950um.

[0023] The range value of the arrangement period parameter p of the structural unit 11 along the X direction and the Y direction is 30um-1000um, and the structural unit 11 is a conductor.

[0024] The distance z0 between the active plane 2 and the metasurface 1 is an adjustable value, which is usually set to 0.2 times of the p value.

[0025] The arrangement period parameter p is 500um, the width w of the gap is 60um, and the height h is 300um.

[0026] In this embodiment, the metasurface 1 has periodicity in the X direction and the Y direction, the active plane 2 at a distance z0 above the metasurface 1 is the plane where the electron beam 3 is located, and the electron beam 3 moves at a uniform speed along the X direction. When the electron beam 3 passes over the metasurface 1 at a uniform speed, an evanescent wave is excited in the space between the electron beam 3 and the metasurface 1, and the evanescent wave in turn interacts with the metasurface 1, generating a reflection field in the upper half space of the metasurface 1, and the reflection field can be expressed by the Floquet module as shown in Formula 1:

[0027]

[0028] Among them, H r represents the reflected field above the metasurface due to the interaction between the evanescent wave and the metasurface, m, n are both integers, k xmn , k ymn , k zmn Represents the wave number in the x, y, and z directions respectively

[0029] The energy exchange in this process will generate Smith-Purcell radiation to the upper half space. The Smith-Purcell radiation is generated by the interaction between uniformly charged particles and the wave beam of the metasurface 1. The radiation frequency is fixed, but the radiation direction can be controlled by the speed of the electron beam 3.

[0030] Furthermore, the radiation frequency of the Smith-Purcell radiation is related to the structural parameters of the metasurface 1, especially the parameters of the three gaps 12. The metasurface structure has the characteristic that the resonant frequency basically does not change as the period changes within a certain range. Based on this characteristic, the relationship between the structural period, the electron beam velocity, and the structural resonant frequency is established. The resonant frequency can be kept unchanged when the electron beam velocity changes within a certain range, that is, the frequency of the radiation wave remains unchanged. Combined with the Floquet boundary condition, a radiation wave with a frequency of 0.44 THz can be generated, and the direction of the radiation wave can be adjusted by the electron beam velocity.

[0031] Furthermore, the spatial wave vector of the radiation wave 4 satisfies the relationship shown in Formula 2:

[0032]

[0033] where k xmn =k x +2mπ / p,k ymn =2nπ / p

[0034] By introducing the electric vector Based on far-field radiation, m = -1, n = 0, then the spatial wave vector will become k, f, p and v e There are only three variables f, p and v in this relationship. e , combined with the Smith-Purcell radiation frequency relationship, it can be seen that as long as two of the three variables remain unchanged, the direction of the radiation wave 4 can be controlled by the other variable. In the present invention, the period of the structural unit 11 remains unchanged, and the frequency of the radiation wave 4 can also be kept unchanged by the characteristics of the structure. Then, the direction of the radiation wave 4 can be adjusted within a certain range by regulating the speed of the electron beam 3 (i.e., the voltage or the energy of the electron beam 3). This method does not require adjusting the geometric parameters of the structure, nor does it require changing the orientation of the structure.

[0035] Furthermore, the radiation wave frequency formula 3 of the Smith-Purcell radiation is as follows:

[0036]

[0037] Among them, θ is the angle between the radiation direction and the direction of movement of the electron beam 3, f is the frequency of the radiation wave 4, and v e is the speed of the electron beam 3, p is the period of the metasurface 1 structure, c is the speed of light in a vacuum, and m is the diffraction order (usually an integer).

[0038] Since the structure of the metasurface 1 is periodic in the X and Y directions, one of the structural units 11 can be intercepted and simulated in combination with the above-mentioned Floquet periodic boundary conditions. In the simulation, the surface current density is used to approximate the electron beam 3, and a perfect matching layer is used in the far-field region to absorb waves to prevent the reflected waves from affecting the radiation characteristics of the structure.

[0039] Preferably, adjusting the geometric parameters of the structure of the metasurface 1 within a specified range will not affect the radiation characteristics.

[0040] What is disclosed above is only a preferred embodiment of the present invention, and it certainly cannot be used to limit the scope of rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiment and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A voltage-controlled direction-adjustable terahertz radiation source based on the Smith-Purcell effect, characterized in that: It comprises a metasurface, an active plane and an electron beam, wherein the active plane is arranged parallel to the metasurface and located above the metasurface, and the electron beam is arranged on the active plane and moves at a uniform speed along the X direction; The metasurface is composed of a plurality of groups of structural units, the structural units are periodically arranged along the X direction and the Y direction, and the arrangement periods of the structural units along the X direction and the Y direction are equal and are fixed values; Three gaps are arranged in the structural unit, and the gaps are arranged in parallel along the Y direction. The center distance d between two groups of the gaps is equal to 100um. The range value of the width w of the gap is 2um to 300um, and the range value of the height h is 15um to 950um. The range value of the arrangement period parameter p of the structural unit along the X direction and the Y direction is 30um to 1000um, and the structural unit is a conductor.

2. The voltage-controlled direction-adjustable terahertz radiation source based on the Smith-Purcell effect according to claim 1, characterized in that: The distance z0 between the active plane and the metasurface is an adjustable value.

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