Smith-Purcell radiation generating device based on fast electron beam and manufacturing method

Abstract

The application discloses a Smith-Purcell radiation generating device based on a fast electron beam, which comprises a substrate and a non-periodic superstructure grating formed on the substrate; the non-periodic superstructure grating comprises parallel arranged metal nanorods, and the interval of adjacent metal nanorods is not required to be completely consistent; the non-periodic superstructure grating generates Smith-Purcell radiation of a specified wavelength under the induction of the fast electron beam, and the radiation wave front form is determined by the spatial position distribution of the metal nanorods in the non-periodic superstructure grating. Further, the application also provides a manufacturing method of the Smith-Purcell radiation generating device. According to the application, the Smith-Purcell radiation of the specified wavelength can be generated by the non-periodic superstructure grating under the induction of the fast electron beam, and the required Smith-Purcell radiation wave front form can be obtained by adjusting and controlling the spatial position distribution of the metal nanorods in the non-periodic superstructure grating.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optoelectronic functional devices and nanometer light source, and particularly relates to a Smith-Purcell radiation generating device based on a fast electron beam and a manufacturing method. BACKGROUND

[0002] Smith-Purcell radiation is a radiation phenomenon generated by fast-moving charged particles. This radiation is derived from the interaction of the evanescent Coulomb field of the charged particles with the surrounding medium, thereby forming far-field radiation. Since Smith-Purcell radiation can cover a wide spectral range from ultraviolet, visible light, infrared, terahertz to microwave, it is considered an ideal platform for building nanometer-scale light sources. At present, the research on Smith-Purcell radiation covers multiple bands, and its applications include nanostructure light emission, spiral light field generation, and evanescent wave collection and utilization, etc. These researches make Smith-Purcell radiation gradually become an important research platform for integrated photonics.

[0003] The use of Smith-Purcell radiation to manufacture nanometer light sources has significant scientific and technological advantages. In practical applications, the cathodoluminescence spectroscopy system based on a scanning electron microscope provides a convenient and effective method for generating and researching broadband Smith-Purcell radiation. In the traditional electron beam excitation light radiation method, the interaction range of the fast electron beam with the designed excited sample is limited, resulting in weak coupling of electrons and photons. However, in the Smith-Purcell radiation system, the fast-moving electrons can interact with a large number of microstructure units in the excited sample, thereby significantly enhancing the intensity of the generated light radiation. In addition, by adjusting the structural parameters of the microstructure units, various optical functions can be realized. These unique advantages make the light source research based on Smith-Purcell radiation have important value in scientific research and application fields.

[0004] At present, the wavefront control of Smith-Purcell radiation has not yet formed a mature and perfect scientific method. The design method used is relatively single, usually through a periodic artificial structure to generate Smith-Purcell radiation, that is, the wavefront is designed based on the periodic grating theory. Although the design using the periodic grating theory can achieve effective wavefront control, the design based on this theory lacks diversity in function. Moreover, there is no way to integrate multiple optical functions using a single periodic grating structure. SUMMARY

[0005] The application discloses a Smith-Purcell radiation generating device based on a fast electron beam.

[0006] The first aspect of the application discloses a Smith-Purcell radiation generating device based on a fast electron beam, comprising a substrate and a non-periodic superstructure grating formed on the substrate; the non-periodic superstructure grating comprises metal nanorods arranged in parallel, and the intervals of adjacent metal nanorods are not required to be completely consistent; the non-periodic superstructure grating generates Smith-Purcell radiation of a specified wavelength under the induction of a fast electron beam, and the radiation wavefront form is determined by the spatial position distribution of the metal nanorods in the non-periodic superstructure grating.

[0007] As an optional solution, the material of the metal nanorod is any one of gold, silver, platinum and titanium.

[0008] As an optional solution, the width of the metal nanorod is 1 / 5-1 / 30 of the wavelength of the Smith-Purcell radiation, and is not less than 30 nanometers; the thickness of the metal nanorod is 50 nanometers±30 nanometers.

[0009] As an optional solution, the substrate is any one of silicon, silicon dioxide and silicon nitride.

[0010] As an optional solution, the radiation wavefront form comprises any one of focusing, deflection, Bessel beam and Airy beam; the focusing comprises on-axis focusing and off-axis focusing; the angle of the deflection is 0-180 degrees.

[0011] As an optional solution, the specified wavelength range is 200 nanometers to 1550 nanometers.

[0012] As an optional solution, the speed of the fast electron beam is 0.1-0.6 times the speed of light.

[0013] As an optional solution, the non-periodic superstructure grating has at least two groups of superimposed arrangements.

[0014] Each group of non-periodic superstructure gratings generates Smith-Purcell radiation under the induction of a fast electron beam, and the radiation wavefront form is determined by the spatial position distribution of the metal nanorods in each group of non-periodic superstructure gratings.

[0015] A second aspect of the present invention discloses a method for manufacturing a Smith-Purcell radiation generating device, which is used to manufacture the Smith-Purcell radiation generating device based on a fast electron beam as described in the first aspect and any optional solution of the present invention, comprising:

[0016] specifying a wavelength of Smith-Purcell radiation to be generated, wherein the radiation phase generated by the metal nanorod at the specified wavelength is related to the spatial position of the metal nanorod;

[0017] Design the spatial distribution of the metal nanorods in the non-periodic metagrating according to the radiation wavefront of the desired Smith-Purcell radiation;

[0018] Metal nanorods are manufactured on a substrate based on the spatial position distribution, and the Smith-Purcell radiation generating device is obtained after the manufacturing is completed.

[0019] The spatial position distribution of the metal nanorods in the non-periodic metagrating is designed according to the radiation wavefront of the desired Smith-Purcell radiation, specifically including:

[0020] Determine the relationship between the radiation phase φ required to realize the radiation wavefront and the spatial position x, i.e., the φ-x curve, according to optical theory, and limit the phase change of the curve to a range of 0 to 2π;

[0021] Define x as the spatial position of the metal nanorod, and the phase of the emitted radiation at x = 0 is The radiation phase generated when the fast electron beam passes through the metal nanorod The relationship between the spatial position x of the metal nanorod is:

[0022]

[0023] where λ is the specified wavelength of the Smith-Purcell radiation, v is the speed of the fast electron, and c is the speed of light in a vacuum.

[0024] According to the radiation phase generated when the fast electron beam passes through the metal nanorods The relationship between the spatial position x of the metal nanorod is: The curve is constrained to the range 0 to 2π.

[0025] The φ-x curve and The curves are superimposed to obtain a series of intersections, and the spatial position distribution of the intersections is the spatial position distribution of the metal nanorods in the non-periodic metagrating.

[0026] The present invention has the following beneficial effects:

[0027] (1) The present application not only can use non-periodic superlattice grating to generate Smith-Purcell radiation, but also can realize the phase space distribution of any designed Smith-Purcell radiation by accurately regulating the spatial position distribution of metal nanorods in the non-periodic superlattice grating, and further realize various forms of Smith-Purcell radiation wavefront, which has good versatility.

[0028] (2) The present application can realize multiple different Smith-Purcell radiation wavefronts in the same Smith-Purcell radiation generation device by arranging two or more non-periodic superlattice gratings on the same substrate, and can be extended to a wider wavelength range.

[0029] (3) The present application can realize effective specified wavelength Smith-Purcell radiation wavefront design in the wavelength range of 200 nanometers to 1550 nanometers.

[0030] (4) The present application has no special requirements for the material of the metal nanorods in the non-periodic superlattice grating and the material of the substrate, and can use vacuum substrate and common dielectric substrate materials such as silicon, silicon dioxide and silicon nitride.

[0031] (5) The basic structural unit of the non-periodic superlattice grating in the present application is metal nanorod, which has simple structure, high fault tolerance and low manufacturing cost, and is easy to realize.

[0032] (6) The speed and other parameters of the fast electron beam suitable for the Smith-Purcell radiation generation device disclosed by the present application have great selection flexibility, which can cover the range of 0.1-0.6 times the speed of light. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 (a) shows a schematic diagram of Smith-Purcell radiation wavefront regulation using non-periodic superlattice grating, (b) is a side view of non-periodic superlattice grating in x-y plane, (c) shows the phase as a function of wavelength λ and position x, (d) is the relationship between phase and position x for three representative wavelengths of 400 nm, 700 nm and 1000 nm.

[0034] Figure 2 (a) The red solid line in (a) represents the phase φ(x) distribution curve φ-x along the x direction needed to be realized in order to realize the required wavefront; the black solid line represents the relationship curve between the radiation phase φ(x) and the spatial position x of the metal nanorods corresponding to the Smith-Purcell radiation of 700 nm. The blue solid circle represents the intersection point of the two curves obtained by superimposing the φ-x curve on the curve. Both φ and φ x curves are limited in the range of 0 to 2π. (b) is the simulated light intensity distribution for a design with focal length of 25 microns. (c) is the simulated light intensity distribution for a design with off-axis focusing parameters f = 20 microns, x off = -3 microns. off (d) is the simulated light intensity distribution for a design with off-axis focusing parameters f = 30 microns, x

[0035] Figure 3 : (a) The spatial positions of the metal nanorods and the phase distributions provided by the metal nanorods for the design of deflection angles θ = 90° and θ = 60° are represented by the blue circles and red squares, respectively. (b) and (c) are the simulated electromagnetic field H z distributions for θ = 90° and θ = 60°, respectively. (d) To achieve the wavefront of a Bessel beam, the black solid line represents the required conical phase distribution, while the blue circles represent the phase distribution provided by the metal nanorods and the spatial position distribution of the nanorods. (e) The simulated light intensity distribution shows the long-range non-diffracting characteristic of a Bessel beam. (f) The simulated light intensity distribution shows the self-healing property of a Bessel beam. (g) To achieve the wavefront of an Airy beam, the black solid line represents the required Airy beam phase distribution, while the blue circles represent the phase distribution provided by the metal nanorods and the spatial position distribution of the nanorods. (h) The simulated light intensity distribution shows the long-range non-diffracting characteristic of an Airy beam. (i) The simulated light intensity distribution shows the self-healing property of a Bessel beam.

[0036] Figure 4 : (a) Two sets of aperiodic metasurfaces are placed at the same spatial position on the substrate, i.e., the two sets of metasurfaces are superimposed. (b) A design using a single aperiodic metasurface to provide two different Smith-Purcell radiation wavefronts with deflection angles θ1= 90° and θ2= 135°, where the blue circles and red squares represent the spatial positions of the two different sets of metal nanorods and the phase spatial distributions provided by the two different sets of metal nanorods, respectively. (c) shows the simulated electromagnetic field H z distribution. (d) A double-focusing wavefront is achieved using a single aperiodic metasurface, where the blue circles and red squares represent the spatial positions of the metal nanorods and the spatial phase distributions provided by the metal nanorods, respectively. (e) The light intensity distribution of the double-focusing wavefront.

[0037] Figure 5 : (a)-(d) show the intensity distributions of the focusing wavefronts achieved by the aperiodic metasurface method at wavelengths of 200 nm, 550 nm, 800 nm, and 1550 nm, respectively.

[0038] Figure 6 : The Figure 2The parameters of the simulated structure in (b) are modified, wherein (a) is a light intensity distribution simulation result of replacing the material of the aperiodic superstructure grating with silver; (b) is a light intensity distribution simulation result of increasing the width of the metal nanorod to 100 nanometers; (c) is a light intensity distribution simulation result of the aperiodic superstructure grating with the substrate material being silicon; (d) is a light intensity distribution simulation result of adjusting the speed of the fast-moving electron to 0.28c (corresponding to an energy of 20KeV). DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0040] The present application discloses a Smith-Purcell radiation generating device, which can use a fast electron beam to excite an aperiodic superstructure grating to generate Smith-Purcell radiation, and can realize various Smith-Purcell radiation wavefronts (referred to as "radiation wavefronts" or "light wavefronts") by regulating the positions of metal nanorods in the aperiodic superstructure grating. The aperiodic superstructure grating is composed of a group of identical metal nanorods, and the position of each metal nanorod can be accurately adjusted. Through accurate control of the position, the present application can effectively adjust the phase space distribution of Smith-Purcell radiation, thereby realizing various forms of radiation wavefronts, including focusing, deflection, Bessel beams, Airy beams, etc. Further, the present application can also stack two or more aperiodic superstructure gratings on the same substrate to realize various Smith-Purcell radiation wavefronts on the same Smith-Purcell radiation generating device. Moreover, the present application can be used in a super-wide wavelength range of Smith-Purcell radiation from the ultraviolet band to the infrared band to generate Smith-Purcell radiation of a target wavelength. On one hand, the present application can adopt a substrate-free design, and on the other hand, it can also be compatible with various substrate materials such as silicon, silicon dioxide, and silicon nitride. The present application is also compatible with various grating metal materials, and has great compatibility with the width of metal nanorods, thereby providing a broad application prospect for the development of multifunctional nanoscale light sources.

[0041] An embodiment of the present invention provides a Smith-Purcell radiation generating device comprising a substrate and an aperiodic metagrating formed on the substrate. The basic structural unit of the aperiodic metagrating is a metal nanorod with a rectangular cross-section, made of gold. All metal nanorods in the aperiodic metagrating have identical geometric dimensions, with a thickness and width of 50 nanometers. In other embodiments, the thickness of the metal nanorods can be 50 nanometers ± 30 nanometers, and the width is related to the wavelength of the Smith-Purcell radiation being studied, typically ranging from one-fifth to one-thirtieth of the wavelength. Furthermore, due to manufacturing process limitations, the width is typically no less than 30 nanometers. Taking these factors into account, a 50-nanometer width was used when studying Smith-Purcell radiation at 700 nanometers. A 50-nanometer width could also be used when studying wavelengths between 200 nanometers and 1550 nanometers, but this essentially reaches the wavelength limit for which a 50-nanometer width is applicable. The spacing between adjacent metal nanorods in the periodic metagrating does not need to be completely uniform; it is determined by the desired radiation wavefront form, hence the term "aperiodic" in the present invention. For example, when realizing the deflection function, the spacing between adjacent metal nanorods is equal (which can be regarded as a special case of non-periodicity), but when realizing optical wavefronts such as focusing, Bessel beams and Airy beams, the spacing between adjacent metal nanorods is inconsistent or not completely consistent.

[0042] Since the metal nanorods in the non-periodic metagrating are in different positions, the radiation generated when the fast electron beam passes through has a time difference, and this time difference is reflected as the phase difference of the radiation. Therefore, different metal nanorod positions correspond to different radiation phase differences. By regulating the positions of each metal nanorod, the required spatial distribution of the overall Smith-Purcell radiation phase can be obtained. For example, the direction of each metal nanorod extends along the z direction, but their positions in the x direction are different, and the position in the x direction is used to regulate the radiation phase. Since the metal nanorods at different positions have the same structure and material, the radiation generated when the fast electron beam passes through the nanorods at different positions has the same amplitude, and the phase of the radiation is determined by its spatial position. Based on this, the present invention can realize various forms of Smith-Purcell radiation wavefronts by regulating the positions of the metal nanorods in the non-periodic metagrating.

[0043] It can be understood that the excitation mode of Smith-Purcell radiation is that the trajectory of the fast electron beam is perpendicular to the extension direction of the nanorods ( Figure 1In a, along the x direction), the motion trajectory of the fast electron beam is a straight line parallel to the x-z plane where the aperiodic superstructure grating is located, and the distance between the fast electron beam and the grating plane is 50 nanometers. The speed of the fast electrons in the fast electron beam is 0.1-0.6 times the speed of light, and the specific speed is determined by the electron beam energy in the experimental system. The distance between the fast electron beam and the superstructure grating is usually set to 20-80 nanometers, and when the distance exceeds 80 nanometers, the light intensity of the Smith-Purcell radiation generated will be significantly reduced.

[0044] Figure 1 (a) shows a schematic diagram of generating Smith-Purcell radiation and wavefront modulation using an aperiodic superstructure grating. Figure 1 In (a), the aperiodic superstructure grating is composed of a plurality of metal nanorods arranged in parallel along the z direction, so it can also be called a metal nanorod array, and the spatial position distribution of the metal nanorods in the x direction is designed according to the required light wavefront. The fast electron beam moves at high speed along the x direction, and the obtained electron beam motion trajectory is a straight line, and the electron beam trajectory is parallel to the plane where the aperiodic superstructure grating is located. In this embodiment, the distance between the fast electron beam and the aperiodic superstructure grating is 50 nanometers, thereby generating Smith-Purcell radiation.

[0045] The present application uses the finite difference time domain method to simulate the effect of Smith-Purcell radiation generation. In the simulation, the electron beam is represented as a linear current source , where e represents the electronic charge, v is the speed of the fast electron, y0 and z0 represent the position of the electron beam, is the basis vector, which represents the direction of electron motion. In the simulation, the electron speed is set to v=0.34c (c is the speed of light in vacuum), which corresponds to the commonly used 30KeV electron energy in the cathode fluorescent spectrum of the scanning electron microscope. The spatial position of each metal nanorod in the x direction is accurately adjusted according to the wavefront design. Figure 1 (b) is a side view of the aperiodic superstructure grating in the x-y plane, and the phase difference between the radiation generated by the metal nanorods located at positions x and x+Δx can be represented as:

[0046]

[0047] In the formula, λ is the specified wavelength of the Smith-Purcell radiation, v represents the speed of the fast electron, and c is the speed of light in vacuum. The present application defines the phase of the radiation generated by the metal nanorod at position x=0 as Therefore, the phase of the radiation generated by the metal nanorod at position x can be represented as

[0048]

[0049] ​From equation (2), it can be seen that by changing the spatial position of the metal nanorod, the phase of the light radiation generated by the metal nanorod can be changed.

[0050] Figure 1 (c) shows the phase of the radiation generated by the metal nanorod as a function of wavelength λ and the position x of the metal nanorod. The phase varies with x at any given wavelength, and it is notable that the phase varies more rapidly at shorter wavelengths. The present invention has chosen three representative wavelengths, 400 nm, 700 nm and 1000 nm, and the phase Figure 1 is shown in (d) as a function of position x. It is clear that for a given wavelength, the phase of the radiation is determined by the spatial position x of the metal nanorod. It is linearly related to x and exhibits different slopes at different wavelengths, with shorter wavelengths leading to steeper slopes.

[0051] The present invention controls the phase distribution of Smith-Purcell radiation by adjusting the spatial position x of each metal nanorod in the aperiodic superlattice and thereby enables the generation of a variety of Smith-Purcell radiation wavefronts. The embodiments of the present invention first demonstrate a method to achieve a focused wavefront of Smith-Purcell radiation.

[0052] According to the focusing optics formula, in order to achieve the desired focused wavefront, the phase distribution φ(x) along the x direction should satisfy the following equation:

[0053]

[0054] where λ represents the wavelength of the Smith-Purcell radiation and f represents the focal length.

[0055] It can be understood that when the phase distribution φ(x) satisfies equation (3), light focusing, i.e., a focused wavefront, can be achieved. Figure 2 The red solid line in (a) represents the φ-x relationship curve, which has limited the phase change to the range of 0 to 2π (since the period of the trigonometric function is 2π, for the part exceeding 2π, it can be limited to the range of 0-2π by subtracting several 2π). Similarly, the present invention limits the Figure 1 700 nm in (d) to the range of 0 to 2π and plots it as the black solid line in (a). By superimposing the φ-x curve and the Figure 2 curve, the intersection points of the two curves are plotted in (a) and (d). Figure 2 ​(a) is indicated by blue solid circles. The metal nanorods are placed at the positions indicated by these blue intersection points, and the phase of the Smith-Purcell radiation emitted by these metal nanorods can provide the required focusing wavefront phase. Through the above steps, the Smith-Purcell radiation with a wavelength of 700 nm can be focused, and the focal length is designed to be 25 microns. Figure 2 The simulated light field intensity (referred to as "light intensity" for short) distribution in (b) shows that the focusing of the Smith-Purcell radiation can be successfully achieved, and the focal point position and design are consistent. Moreover, the results of the full width at half maximum also confirm that the ideal focusing wavefront is achieved by the present application.

[0056] The design method of the aperiodic superstructure grating can not only achieve on-axis focusing (as shown in Figure b, the focal point position is not offset, on the main optical axis); but also achieve off-axis focusing and control the position of the focal point (as shown in Figures c and d, the focal point position deviates from the main optical axis). For off-axis focusing, the required phase distribution φ(x) is determined by the following equation:

[0057]

[0058] In the formula, x off represents the offset of the intersection point of the off-axis focusing in the x direction.

[0059] The present application designs two kinds of off-axis focusing wavefronts: one is f = 20 microns, x off = -3 microns, and the other is f = 30 microns, x off = 5 microns. Figure 2 The calculated intensity distribution and the full width at half maximum in (c) and Figure 2 (d) show that the off-axis focusing of the effective Smith-Purcell radiation wavefront is achieved.

[0060] In addition to focusing, other forms of Smith-Purcell radiation wavefronts can also be achieved by adjusting the spatial position distribution of the metal nanorods. Subsequently, the present application uses the aperiodic superstructure grating to achieve the beam deflection of the Smith-Purcell radiation. The present application defines the deflection angle θ of the Smith-Purcell radiation as the included angle between the direction of the Smith-Purcell radiation and the x axis. According to the generalized Snell's law, the deflection angle θ and the required phase distribution φ(x) satisfy the following equation:

[0061]

[0062] In Figure 3 (a), the blue circles and the red squares respectively represent the spatial positions of the metal nanorods and the phases that can be provided by them when the design corresponds to θ = 90 degrees and θ = 60 degrees deflection. Figure 3 (b) and Figure 3 (c) are the simulated magnetic field distributions H when the deflection angles are θ = 90 degrees and θ = 60 degrees, respectively.z It can be seen from the simulation results that the deflection of optical radiation at θ = 90 degrees and θ = 60 degrees is successfully achieved, which proves that the method of using aperiodic superlattice grating can achieve the deflection of the Smith-Purcell radiation optical wavefront.

[0063] The present application further demonstrates the generation of Smith-Purcell radiation with Bessel beam and Airy beam wavefronts using aperiodic superlattice gratings. The present application generates a Bessel beam wavefront using a conical phase distribution, the tilt angle θ 0 of which is defined as the angle between the wavefront propagation direction and the y-axis. The conical phase distribution satisfies:

[0064]

[0065] In the example, the present application designs a Bessel beam wavefront with θ 0 = 10°. Figure 3 The black solid line in (d) represents the required conical phase distribution, while the blue circles represent the phase distribution provided by the metal nanorods and the spatial position distribution of the nanorods. In Figure 3 In (e), the typical feature of the Bessel beam, i.e. the long-distance undiffracted beam trajectory, can be clearly observed. In order to verify the self-healing property of the Bessel beam, in the simulation setup, the present application places an obstacle at x = 0 microns, y = 10 microns, which is exactly on the propagation path of the Bessel beam, as shown by the green dot in the figure. Figure 3 (f) clearly shows that the obstacle does not hinder the propagation of the Bessel beam, confirming its self-healing property.

[0066] Further, the present application designs another aperiodic superlattice grating to generate Smith-Purcell radiation with an Airy beam wavefront. The phase distribution of the Airy beam should satisfy:

[0067] φ(x) = arg[Ai(bx)exp(ax)] (7)

[0068] In the formula, Ai(bx) is the Airy function, a is the Airy beam truncation parameter, and b is the transverse scale parameter of the Airy beam. In the example, a = 0.05 and b = 1 are set.

[0069] Since the amplitude of the Airy function rapidly decays to 0 when x > 0. In the simulation setup, the present application only places metal nanorods at x < 0. Figure 3 The black line in (g) is the theoretically required phase to achieve an Airy beam, and the blue circles represent the spatial position of the metal nanorods and the phase distribution they provide. Figure 3(h) shows the simulated light intensity distribution. The result shows that the self-bending Airy beam is successfully achieved. Also to demonstrate the self-healing ability of the Airy beam, an obstacle is introduced in the propagation path of the Airy beam, placed at x = 1 micrometer, y = 20 micrometer. As shown in Figure 3 (i), the Airy beam can continue to propagate without disturbance even when encountering the obstacle, and this self-healing ability of the beam is also a typical feature of the Airy beam.

[0070] In the wavefront shaping design achieved in the foregoing embodiment, each Smith-Purcell radiation generating device contains a single aperiodic superlattice, which is used to generate a specific wavefront. Further, the method of the present application has another great innovation, that is, two or more Smith-Purcell radiation wavefronts are generated by the same Smith-Purcell radiation generating device.

[0071] In another embodiment of the present application, two groups of aperiodic superlattices are placed at the same spatial position of the substrate, that is, the two groups of lattices are superimposed together, which looks similar to a group of lattices, but the two groups of lattices do not interfere with each other in terms of functional implementation, and can achieve two different radiation wavefronts, which are superimposed as shown in Figure 4 (a). The metal nanorods of the two groups of aperiodic superlattices are completely the same, but the spatial positions of the metal nanorods of each group are different according to the radiation wavefronts to be achieved, so that after the superposition of the two groups of aperiodic superlattices, the metal nanorods may overlap or partially overlap. The metal nanorods in the overlapping part are of the same height, but a nanorod with a width wider than the previous single nanorod may be formed.

[0072] Figure 4 (b) shows a design for providing two different Smith-Purcell radiation wavefronts with different deflection angles (θ1= 90° and θ2= 135°) at the same time using a single aperiodic superlattice. The blue circles and red squares represent the spatial positions of the two groups of different metal nanorods and the phase space distributions they provide. Figure 4 (c) shows the simulated magnetic field H z distribution, and it can be observed that the two beams of light radiation propagate along the directions of θ1= 90° and θ2= 135°, respectively.

[0073] Another embodiment of the present application also designs a double-focusing wavefront form, that is, two off-axis foci, and the two foci are at different spatial positions. We place a group of aperiodic superlattices with focusing parameters f1= 22 micrometers, x off,1 = -5 micrometers and another group of superlattices with focusing parameters f2= 17 micrometers, x off,2 = 3 micrometers at the same spatial position to form a new combined lattice. As shown in Figure 4(d) As shown, the combined grating can achieve double focusing, with double focusing parameters f1 = 22 microns, x off,1 = -5 microns and f2 = 17 microns, x off,2 = 3 microns. The blue circles and red squares represent the required phase distribution and the corresponding spatial position of the metal nanorod, respectively. Figure 4 (e) The light intensity distribution of the double focusing wavefront is shown, with the radiation back focused at two pre-designed off-axis focal point positions, effectively realizing the double focusing function. As can be seen, the scheme of the present application can realize the combination of different wavefront functions by using one non-periodic superstructure grating.

[0074] In addition, the theoretical method of the non-periodic superstructure grating proposed in the present application can be applied to a wide range of wavelengths, which can involve a super-wide wavelength range from the ultraviolet band to the infrared band. Figure 5 (a)- Figure 5 (d) The intensity distribution of the focusing wavefront realized by the non-periodic superstructure grating method at wavelengths of 200 nanometers, 550 nanometers, 800 nanometers and 1550 nanometers is shown, and the focal length of each radiation wavefront is designed to be f = 25 microns. These simulation results confirm that the present application can effectively generate a focusing wavefront at these wavelengths. In addition, at these wavelengths, other wavefront forms such as off-axis focusing, deflection, Bessel beams and Airy beams mentioned earlier can also be realized, and the simulation results are not placed here.

[0075] In the foregoing embodiments, the Smith-Purcell radiation generating device uses gold as the material of the non-periodic superstructure grating, and the width of the metal nanorod is set to 50 nanometers for simulation, while assuming that the electron is moving at a speed of 0.34c. However, in fact, these parameters can be flexibly adjusted as needed to meet specific design requirements.

[0076] In order to demonstrate these flexibilities, the present application modifies the parameters in Figure 2 (b) and shows the focusing results after changing the parameters in Figure 6 In Figure 6 (a), the present application replaces the material of the non-periodic superstructure grating with silver; in Figure 6 (b), the present application increases the width of the metal nanorod to 100 nanometers; in Figure 6 (c), the present application selects silicon as the base material of the non-periodic superstructure grating; in Figure 6 (d), the present application adjusts the speed of the fast-moving electron to 0.28c, corresponding to an electron beam energy of 20KeV. Figure 6 (a)- Figure 6All the simulated intensity distributions in (d) successfully achieve the Smith-Purcell radiation focused wavefronts. It is shown that, in addition to gold, other commonly used metal materials such as silver, platinum and titanium can also be used as the material of the aperiodic superlattice for effective wavefront manipulation. Moreover, changing the width of the metal nanorod does not affect the mode of the Smith-Purcell radiation wavefront. And the method of the present application is also effective for different electron velocities.

[0077] In summary, the present application proposes a Smith-Purcell radiation generation device, which can generate different forms of Smith-Purcell radiation wavefronts by exciting aperiodic superlattices with fast electron beams. Unlike traditional methods that rely on the design of precise artificial atoms, the present application mainly realizes various forms of Smith-Purcell radiation wavefronts by regulating the spatial position distribution of metal nanorods in the aperiodic superlattice. Moreover, the present application can effectively regulate the Smith-Purcell radiation wavefront in a wide wavelength range. Further, the present application can also realize multiple wavefront types simultaneously in one Smith-Purcell radiation generation device.

[0078] Finally, it should be noted that although the embodiments of the present application are described above in combination with the drawings, the present application is not limited to the above specific embodiments and application fields. The above specific embodiments are only illustrative and guiding, but not limiting. Those skilled in the art can make many forms under the guidance of the present application without departing from the scope of the claims of the present application, which are all within the protection scope of the present application.

Claims

1. A Smith-Purcell radiation generating device based on a fast electron beam, characterized in that, The non-periodic superlattice includes a substrate and a non-periodic superlattice formed on the substrate; the non-periodic superlattice includes parallelly arranged metal nanorods, and the intervals of adjacent metal nanorods are not required to be completely consistent; The non-periodic superlattice generates Smith-Purcell radiation of a specified wavelength under the induction of a fast electron beam, and the radiation wave front form is determined by the spatial position distribution of the metal nanorods in the non-periodic superlattice; The spatial position distribution of the metal nanorods in the non-periodic superlattice is designed according to the radiation wave front of the Smith-Purcell radiation to be generated, and specifically includes: determining the radiation phase required to achieve the radiation wavefront according to optical theory as a function of spatial position x, i.e. a curve, and limiting the phase variation of the curve to the range 0 to 2π; where x denotes the spatial position of the metal nanorod, the phase of the emitted radiation at the position x = 0 is φ (0) = 0, and the phase of the radiation generated by the fast electron beam passing through the metal nanorod is φ a function of the spatial position x of the metal nanorod: (2) In the formula, λ is the specified wavelength of the Smith-Purcell radiation, v represents the speed of the fast electron, and c is the speed of light in vacuum; Phase of the radiation generated by the passage of the fast electron beam through the metal nanorod φ in relation to the spatial position x of the metal nanorod, obtaining φ the -x curve and limiting it to the range from 0 to 2π; The Curves and φ Superimposing the x-curves results in a series of intersection points, the spatial distribution of which is the spatial distribution of the metal nanorods in the aperiodic superlattice.

2. The Smith-Purcell radiation generating device of claim 1, wherein, The material of the metal nanorod is any one of gold, silver, platinum and titanium.

3. The Smith-Purcell radiation generating device of claim 1, wherein, The width of the metal nanorod is 1 / 5-1 / 30 of the wavelength of the Smith-Purcell radiation, and is not less than 30 nanometers; the thickness of the metal nanorod is 50 nanometers±30 nanometers.

4. The Smith-Purcell radiation generating device of claim 1, wherein, The substrate is any one of silicon, silicon dioxide and silicon nitride.

5. The Smith-Purcell radiation generating device of claim 1, wherein, The radiation wave front form includes any one of focusing, deflection, Bessel beam and Airy beam; the focusing includes on-axis focusing and off-axis focusing; the angle of the deflection is 0-180 degrees.

6. The Smith-Purcell radiation generating device of claim 1, wherein, The specified wavelength range is 200 nanometers to 1550 nanometers.

7. The Smith-Purcell radiation generating device of claim 1, wherein, The speed of the fast electron beam is 0.1-0.6 times the speed of light.

8. A Smith-Purcell radiation generating device as claimed in any one of claims 1 to 7, wherein, The non-periodic superlattice has at least two groups of superimposed arrangements; Each group of non-periodic superlattices generates Smith-Purcell radiation under the induction of a fast electron beam, and the radiation wave front form is determined by the spatial position distribution of the metal nanorods in each group of non-periodic superlattices.

9. A method of fabricating a Smith-Purcell radiation generating device, characterized by, A method for manufacturing a Smith-Purcell radiation generation device based on a fast electron beam according to any one of claims 1 to 8, comprising: specifying the wavelength of the Smith-Purcell radiation to be generated, and the radiation phase generated by the metal nanorod is related to the spatial position of the metal nanorod at the specified wavelength; designing the spatial position distribution of the metal nanorods in the non-periodic superlattice according to the radiation wave front of the Smith-Purcell radiation to be generated; manufacturing the metal nanorods on the substrate based on the spatial position distribution, and obtaining the Smith-Purcell radiation generation device after the manufacturing is completed.

10. The method of claim 9, wherein Designing the spatial position distribution of the metal nanorods in the non-periodic superlattice according to the radiation wave front of the Smith-Purcell radiation to be generated, and specifically includes: determining the radiation phase required to achieve the radiation wavefront according to optical theory as a function of spatial position x, i.e. a curve, and limiting the phase variation of the curve to the range 0 to 2π; where x denotes the spatial position of the metal nanorod, the phase of the emitted radiation at the position x = 0 is φ (0) = 0, the phase of the radiation generated by the fast electron beam passing through the metal nanorod is φ a function of the spatial position x of the metal nanorod: where λ is the specified wavelength of the Smith-Purcell radiation, v denotes the velocity of the fast electron, and c is the speed of light in vacuum; According to the relationship between the radiation phase φ generated by the fast electron beam passing through the metal nanorod and the spatial position x of the metal nanorod, the following is obtained φ - the x curve is limited in the range of 0 to 2π. The Curves and φ Superimposing the -x curves results in a series of intersection points, and the spatial distribution of the intersection points is the spatial distribution of the metal nanorods in the aperiodic superlattice.

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