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

Abstract

The invention discloses a Smith-Purse radiation generating device based on fast electron beams. The Smith-Purse radiation generating device comprises a substrate and a non-periodic super-structure grating formed on the substrate. The non-periodic super-structure grating comprises metal nanorods which are arranged in parallel, and the distances between the adjacent metal nanorods are not required to be completely consistent; the aperiodic super-structure grating generates Smith-Purse radiation with 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 aperiodic super-structure grating. Furthermore, the invention also provides a manufacturing method of the Smith-Purse radiation generating device. According to the invention, not only can the fast electron beam be utilized to induce the aperiodic super-structure grating to generate Smith-Purse radiation with a specified wavelength, but also the required Smith-Purse radiation wavefront form can be obtained by regulating and controlling the spatial position distribution of the metal nanorods in the aperiodic super-structure grating.

Description

Technical Field

[0001] The present invention belongs to the technical field of optoelectronic functional devices and nano light sources, and in particular relates to a Smith-Purcell radiation generating device based on a fast electron beam and a manufacturing method thereof. Background Art

[0002] Smith-Purcell radiation is a radiation phenomenon generated by fast-moving charged particles. This radiation originates from the interaction between the evanescent Coulomb field of the charged particles and the surrounding medium, thus forming far-field radiation. Since Smith-Purcell radiation can cover a wide spectral range including ultraviolet, visible light, infrared, terahertz and even microwaves, it is considered to be an ideal platform for building nanoscale light sources. At present, the research on Smith-Purcell radiation covers multiple bands, and its applications include nanostructure luminescence, spiral light field generation, and evanescent wave collection and utilization. These studies have made Smith-Purcell radiation gradually become an important research platform for integrated photonics.

[0003] There are significant scientific and technological advantages in using Smith-Purcell radiation to manufacture nano-light sources. In practical applications, the cathode fluorescence spectroscopy system based on a scanning electron microscope provides a convenient and effective method for generating and studying broadband Smith-Purcell radiation. In the traditional electron beam excitation light radiation method, the interaction range of the fast electron beam and the designed excited sample is limited, resulting in weak coupling between electrons and photons. However, in the Smith-Purcell radiation system, 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, a variety of optical functions can be achieved by adjusting the structural parameters of the microstructure units. These unique advantages make the research on light sources based on Smith-Purcell radiation of great value in scientific research and application fields.

[0004] At present, there is no mature and complete scientific method for the control of Smith-Purcell radiation wavefront. The design method used is relatively simple, usually using periodic artificial structures to generate Smith-Purcell radiation, that is, designing the wavefront based on periodic grating theory. Although the design based on periodic grating theory can achieve effective wavefront control, the design based on this theory lacks in functional diversity. In addition, there is currently no way to use a single periodic grating structure to achieve the integration of multiple optical functions. Summary of the invention

[0005] In order to solve the above problems, the present invention proposes a Smith-Purcell radiation generating device based on a fast electron beam, which can not only use the fast electron beam to induce a non-periodic metagrating to generate Smith-Purcell radiation of a specified wavelength, but also obtain the desired Smith-Purcell radiation wavefront form by regulating the spatial position distribution of metal nanorods in the non-periodic metagrating. Furthermore, the present invention also provides a method for manufacturing the above Smith-Purcell radiation generating device.

[0006] The first aspect of the present invention discloses a Smith-Purcell radiation generating device based on a fast electron beam, comprising a substrate and a non-periodic metagrating formed on the substrate; the non-periodic metagrating comprises metal nanorods arranged in parallel, and the spacing between adjacent metal nanorods is not required to be completely consistent; the non-periodic metagrating 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 metagrating.

[0007] As an optional solution, the material of the metal nanorods 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 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 includes any one of focusing, deflection, Bessel beam and Airy beam; the focusing includes on-axis focusing and off-axis focusing; the deflection angle 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 metagrating has at least two groups arranged in a superimposed manner;

[0014] Each group of non-periodic metagratings 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 metagratings.

[0015] The 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 the wavelength of the 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 position distribution of 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 Smith-Purcell radiation to be generated, specifically including:

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

[0021] Define x to represent 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 invention can not only utilize a non-periodic metagrating to generate Smith-Purcell radiation, but also realize arbitrarily designed Smith-Purcell radiation phase spatial distribution by precisely controlling the spatial position distribution of metal nanorods in the non-periodic metagrating, thereby realizing a variety of different forms of Smith-Purcell radiation wavefronts, and has good versatility.

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

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

[0030] (4) The present invention has no special requirements on the material of the metal nanorods and the substrate in the non-periodic metagrating. A vacuum substrate and common dielectric substrate materials such as silicon, silicon dioxide, and silicon nitride can be used.

[0031] (5) The basic structural unit of the non-periodic metagrating in the present invention is a metal nanorod, which has a simple structure, is not strict with its size, has high fault tolerance, low manufacturing cost, and is easy to implement.

[0032] (6) The parameters such as the speed of the fast electron beam applicable to the Smith-Purcell radiation generating device disclosed in the present invention have great flexibility in selection and can cover the range of 0.1-0.6 times the speed of light. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 :(a) shows the schematic diagram of Smith-Purcell radiation wavefront control using non-periodic metagrating. (b) is the side view of the non-periodic metagrating in the xy plane. (c) shows the phase Variation with wavelength λ and position x. (d) is the phase at three representative wavelengths of 400 nm, 700 nm and 1000 nm. Relationship with position x.

[0034] Figure 2 :(a) The red solid line represents the phase φ(x) distribution curve φ-x along the x direction that needs to be achieved in order to achieve the desired wavefront; the black solid line represents the radiation phase corresponding to the Smith-Purcell radiation of 700 nanometers The relationship curve between the spatial position x of the metal nanorod The blue solid circle indicates the superposition of the φ-x curve on The intersection of the two curves obtained on the curve. The φ-x curve is limited to the range of 0 to 2π. (b) is the simulation result of the light intensity distribution when the designed focal length is 25 microns. (c) is the designed off-axis focusing parameter f = 20 microns, x off = -3 microns, the light intensity distribution simulation results. (d) is the designed off-axis focusing parameter f = 30 microns, x off =5 microns, light intensity distribution simulation results.

[0035] Figure 3 :(a) The blue circles and red squares represent the spatial position of the metal nanorods and the phase distribution provided when the deflection design is θ=90 degrees and θ=60 degrees respectively. (b) and (c) are the simulated electromagnetic field distribution H when θ=90 degrees and θ=60 degrees respectively. z . (d) To realize the Bessel beam wavefront, the black solid line represents the required conical phase distribution, and 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-distance non-diffraction characteristics of the Bessel beam. (f) The simulated light intensity distribution shows the self-healing properties of the Bessel beam. (g) The design realizes the Airy beam wavefront. The black solid line represents the required Airy beam phase distribution, and 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-distance non-diffraction characteristics of the Airy beam. (i) The simulated light intensity distribution shows the self-healing properties of the Bessel beam.

[0036] Figure 4 :(a) Placing two sets of non-periodic metagratings at the same spatial position on the substrate, that is, superimposing the two sets of gratings together. (b) Using a single non-periodic metagrating to provide two different deflection angles (θ 1 =90° and θ 2 =135°), where the blue circles and red squares represent the spatial positions of two different sets of metal nanorods and the phase spatial distribution provided. (c) shows the simulated electromagnetic field H z (d) Double-focused wavefront using a non-periodic grating, where the blue circles and red squares represent the spatial positions of the metal nanorods and the spatial phase distribution provided, respectively. (e) Light intensity distribution of the double-focused wavefront.

[0037] Figure 5 : (a)-(d) show the intensity distribution of the focused wavefront achieved by the non-periodic metagrating method at wavelengths of 200nm, 550nm, 800nm ​​and 1550nm, respectively.

[0038] Figure 6 :Will Figure 2The parameters of the simulation structure in (b) have been modified, among which (a) is the light intensity distribution simulation result when the material of the non-periodic metagrating is replaced with silver; (b) is the light intensity distribution simulation result when the width of the metal nanorods is increased to 100 nanometers; (c) is the light intensity distribution simulation result of the non-periodic metagrating with silicon as the substrate material; (d) is the light intensity distribution simulation result when the speed of fast-moving electrons is adjusted to 0.28c (corresponding to an energy of 20KeV). DETAILED DESCRIPTION

[0039] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] The present invention discloses a Smith-Purcell radiation generating device, which can generate Smith-Purcell radiation by exciting a non-periodic metagrating with a fast electron beam, and realize a variety of Smith-Purcell radiation wavefronts (referred to as "radiation wavefronts" or "light wavefronts") by adjusting the positions of metal nanorods in the non-periodic metagrating. Among them, the non-periodic metagrating is composed of a group of completely identical metal nanorods, and the position of each metal nanorod can be precisely adjusted. Through the precise control of this position, the present invention can effectively adjust the phase space distribution of Smith-Purcell radiation, thereby realizing various forms of radiation wavefronts, including focusing, deflection, Bessel beams and Airy beams. Further, the present invention can also superimpose more than two groups of non-periodic metagratings on the same substrate to realize a variety of Smith-Purcell radiation wavefronts through the same Smith-Purcell radiation generating device. In addition, the present invention can be used in the ultra-wide wavelength range of Smith-Purcell radiation from the ultraviolet band to the infrared band to generate Smith-Purcell radiation of the target wavelength. On the one hand, the present invention can adopt a substrate-free design, and on the other hand, it can be compatible with a variety of substrate materials such as silicon, silicon dioxide, silicon nitride, etc. The invention is also compatible with a variety of grating metal materials and has great compatibility with the width of metal nanorods, thereby providing broad application prospects for the development of multifunctional nanoscale light sources.

[0041] The embodiment of the present invention provides a Smith-Purcell radiation generating device, including a substrate and a non-periodic metagrating formed on the substrate, wherein the basic structural unit of the non-periodic metagrating is a metal nanorod with a rectangular cross section, and the material of the metal nanorod is gold. All metal nanorods in the non-periodic metagrating have the same geometric dimensions, wherein the thickness and width are both 50 nanometers. In other embodiments, the thickness of the metal nanorod can be 50 nanometers ± 30 nanometers, and the width is related to the wavelength of the Smith-Purcell radiation being studied, usually between one-fifth and one-thirtieth of the wavelength. On the other hand, considering the limitations of the manufacturing process, the width is usually not less than 30 nanometers. Therefore, considering these points, we use a width of 50 nanometers when studying 700 nanometer Smith-Purcell radiation, and when studying 200 nanometers to 1550 nanometers, we can also choose a width of 50 nanometers, but basically we have reached the limit wavelength that the 50 nanometer width can be applied to. The spacing between adjacent metal nanorods in the periodic metagrating is not required to be completely consistent, and is specifically determined by the radiation wavefront form to be achieved, so the present invention is called "non-periodic". 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 in different positions have the same structure and material, the radiation generated when the fast electron beam passes through the nanorods in 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 motion trajectory of the fast electron beam is perpendicular to the extension direction of the nanorods ( Figure 1a), along the x direction), the trajectory of the fast electron beam is a straight line parallel to the xz plane where the non-periodic metagrating 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 metagrating is usually set to 20-80 nanometers. When the distance exceeds 80 nanometers, the light intensity of the generated Smith-Purcell radiation will be significantly reduced.

[0044] Figure 1 (a) Schematic diagram showing the use of a non-periodic metagrating to generate Smith-Purcell radiation and perform wavefront control. Figure 1 The non-periodic metagrating in (a) is composed of a plurality of metal nanorods extending in the z direction arranged in parallel, so it can also be called a metal nanorod array. The spatial position distribution of the metal nanorods in the x direction is designed according to the light wavefront to be realized. The fast electron beam moves at high speed in the x direction, and the resulting electron beam motion trajectory is a straight line. The electron beam trajectory is parallel to the plane where the non-periodic metagrating is located. In this embodiment, the distance between the fast electron beam and the non-periodic metagrating is 50 nanometers, thereby generating Smith-Purcell radiation.

[0045] The present invention uses the finite difference time domain method to simulate the effect of Smith-Purcell radiation. In the simulation, the electron beam is represented as The line current source is, where e represents the electron charge, v is the speed of the fast electron, and y is 0 and z 0 represents the position of the electron beam, is the basis vector, indicating the direction of electron motion. In the simulation, the electron velocity is set to v = 0.34c (c is the speed of light in a vacuum), which is equivalent to the 30KeV electron energy commonly used in cathode fluorescence spectroscopy of scanning electron microscopes. The spatial position of each metal nanorod in the x direction is precisely adjusted according to the wavefront design. Figure 1 (b) is a side view of the non-periodic metagrating in the xy plane. The phase difference between the radiation generated by the metal nanorods at positions x and x+Δx can be expressed as:

[0046]

[0047] Where λ is the specified wavelength of Smith-Purcell radiation, v represents the speed of fast electrons, and c is the speed of light in a vacuum. The present invention defines the radiation phase generated by the metal nanorod at the position x=0 as Therefore, the radiation phase generated by the metal nanorod at position x is It can be expressed as:

[0048]

[0049] It can be seen from formula (2) that by changing the spatial position of the metal nanorods, the phase of the light radiation generated by them can be changed.

[0050] Figure 1 (c) shows the radiation phase generated by the metal nanorods The phase changes with the wavelength λ and the position x of the metal nanorod. At any given wavelength, the phase changes with x. It is worth noting that the phase changes more rapidly at shorter wavelengths. The present invention selects three representative wavelengths, 400 nanometers, 700 nanometers and 1000 nanometers, and Figure 1 (d) shows the phase The relationship between the position x and the wavelength is obvious. 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 resulting in steeper slopes.

[0051] The present invention controls the phase of Smith-Purcell radiation by adjusting the spatial position x of each metal nanorod in the non-periodic metagrating The distribution of the Smith-Purcell radiation wavefronts can be realized, thereby realizing the generation of multiple Smith-Purcell radiation wavefronts. The embodiment of the present invention firstly shows a method for realizing the Smith-Purcell radiation focusing wavefront.

[0052] According to the focusing optical 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 is the wavelength of the Smith-Purcell radiation and f is the focal length.

[0055] It can be understood that when the phase distribution φ(x) satisfies formula (3), light focusing, that is, focusing the 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 (because the period of the trigonometric function is 2π, so for the part exceeding 2π, it can be limited to the range of 0-2π by subtracting several 2π). Figure 1 (d) 700 nm The curve is also constrained to the range 0 to 2π and is plotted as Figure 2 The black solid line in (a). By combining the φ-x curve and The curves are superimposed together, and the intersection of these two curves is Figure 2(a) is indicated by a blue solid circle. Metal nanorods are placed at the positions indicated by these blue intersections, and the Smith-Purcell radiation phase emitted by these metal nanorods can provide the required focusing wavefront phase. Through the above steps, the present invention can focus the Smith-Purcell radiation with a wavelength of 700 nanometers, and the focal length is designed to be 25 microns. Figure 2 The simulated light field intensity (abbreviated as “light intensity”) distribution in (b) shows that the Smith-Purcell radiation can be focused successfully, and the focal position is consistent with the design. Moreover, the full half-width results also confirm that the present invention achieves an ideal focused wavefront.

[0056] The design method of the non-periodic metagrating can not only achieve on-axis focusing (as shown in Figure b, the focus position is not offset and is on the main optical axis); it can also achieve off-axis focusing and control the focus position (as shown in Figure c and Figure d, the focus 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 Indicates the offset of the intersection point of off-axis focusing in the x direction.

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

[0060] In addition to focusing, other Smith-Purcell radiation wavefront forms can be achieved by adjusting the spatial position distribution of the metal nanorods. Subsequently, the present invention uses a non-periodic metagrating to achieve beam deflection of Smith-Purcell radiation. The present invention defines the Smith-Purcell radiation deflection angle θ as the angle between the Smith-Purcell radiation direction 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] exist Figure 3 In (a), the blue circles and red squares represent the spatial positions of the metal nanorods and the phases they can provide when the deflection is θ = 90 degrees and θ = 60 degrees, respectively. Figure 3 (b) and Figure 3 (c) The simulated magnetic field distribution H when the deflection is θ = 90 degrees and θ = 60 degrees respectivelyz It can be seen that the simulation results successfully achieved the deflected light radiation of θ = 90 degrees and θ = 60 degrees, proving that the deflected light wavefront of Smith-Purcell radiation can be achieved using the method of using non-periodic metagratings.

[0063] The present invention further demonstrates the use of a non-periodic metagrating to generate Smith-Purcell radiation with Bessel beam and Airy beam wavefronts. The present invention uses a conical phase distribution to generate a Bessel beam wavefront, and the inclination angle θ of the conical distribution is 0 , defined as the angle between the wavefront propagation direction and the y-axis. The conical phase distribution satisfies:

[0064]

[0065] The present invention designs a θ 0 =10° Bessel beam wavefront. Figure 3 The black solid line in (d) represents the desired conical phase distribution, while the blue circles represent the phase distribution provided by the metal nanorods and the spatial position distribution of the nanorods. Figure 3 In (e), the typical characteristics of the Bessel beam, i.e., the long-distance non-diffraction beam trajectory, can be clearly observed. In order to verify the self-healing properties of the Bessel beam, in the simulation setting, the present invention places an obstacle at x = 0 microns, y = 10 microns, and the obstacle is exactly located 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] Furthermore, the present invention designs a non-periodic metagrating 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] Wherein, Ai(bx) is the Airy function, a is the Airy beam cutoff parameter, and b is the transverse scale parameter of the Airy beam. In the embodiment, a=0.05 and b=1 are set.

[0069] Since the amplitude of the Airy function decays rapidly to 0 when x>0, in the simulation setting, the present invention only places metal nanorods at x<0. Figure 3 The black line in (g) is the phase of the theoretically required Airy beam, and the blue circle represents the spatial position of the metal nanorod and the phase distribution it provides. Figure 3(h) shows the simulated light intensity distribution. The results show that the self-bending Airy beam was successfully realized. In order to demonstrate the self-healing ability of the Airy beam, the present invention introduces an obstacle in the propagation path of the Airy beam, which is placed at x = 1 micron and y = 20 microns. Figure 3 As shown by the green dots in (i), the Airy beam can continue to propagate without interference even if it encounters an obstacle. This beam self-healing ability is also a typical feature of the Airy beam.

[0070] In the wavefront shaping design implemented in the aforementioned embodiment, each Smith-Purcell radiation generating device includes a separate non-periodic metagrating for generating a specific wavefront. Furthermore, the method of the present invention has another major innovation, that is, more than two Smith-Purcell radiation wavefronts are generated by the same Smith-Purcell radiation generating device.

[0071] In another embodiment of the present invention, two groups of non-periodic metagratings are placed at the same spatial position of the substrate, that is, the two groups of gratings are superimposed together. The appearance is similar to a group of gratings, but the two groups of gratings do not interfere with each other in terms of function realization, and two different radiation wavefronts can be realized. The superposition method is as follows: Figure 4 (a) shows that the metal nanorods of the two groups of non-periodic metagratings are exactly the same, but the spatial positions of the metal nanorods of each group are different according to the radiation wavefront to be realized. Therefore, after the two groups of non-periodic metagratings are superimposed, the metal nanorods may overlap or partially overlap. The metal nanorods in the overlapping part have the same height, but may form a nanorod with a wider width than the previous single nanorod.

[0072] Figure 4 (b) Demonstrates the use of a single non-periodic metagrating to provide two different deflection angles (θ 1 =90° and θ 2 =135°). The blue circles and red squares indicate the spatial positions of two different groups of metal nanorods and the phase spatial distributions they provide. Figure 4 (c) shows the simulated magnetic field H z Distribution, it can be observed that the two beams of light radiate along θ 1 =90° and θ 2 =135°.

[0073] Another embodiment of the present invention also designs a double-focused wavefront form, that is, two off-axis focuses, and the two foci are at different positions in space. Our set of focusing parameters is f 1 =22 microns, x off,1 = -5 micron non-periodic metagrating and another set of focusing parameters f 2 =17 microns, xoff,2 =3 micron super-gratings are placed in the same spatial position to form a new combined grating. Figure 4 As shown in (d), the combined grating can achieve double focusing, and the double focusing parameters are f 1 =22 microns, x off,1 = -5 microns and f 2 =17 microns, x off,2 = 3 μm. The blue circles and red squares represent the desired phase distribution and the spatial positions of the corresponding metal nanorods, respectively. Figure 4 (e) shows the light intensity distribution of the dual-focus wavefront, where the radiation is focused at two pre-designed off-axis focal positions, effectively achieving the dual-focusing function. It can be seen that the solution of the present invention can use a non-periodic metagrating to achieve a combination of different wavefront functions.

[0074] In addition, the theoretical method of the non-periodic metagrating proposed in the present invention can be applied to a wide wavelength range, involving an ultra-wide wavelength range from the ultraviolet band to the infrared band. Figure 5 (a)- Figure 5 (d) shows the intensity distribution of the focused wavefront achieved by the non-periodic metagrating method at wavelengths of 200 nm, 550 nm, 800 nm and 1550 nm, and the focal length of each radiation wavefront is designed to be f = 25 μm. These simulation results confirm that the present invention can effectively generate focused wavefronts at these wavelengths. In addition, at these wavelengths, other wavefront forms can also be achieved, such as the off-axis focusing, deflection, Bessel beam and Airy beam mentioned above, but the simulation results are not placed here.

[0075] In the above embodiment, the Smith-Purcell radiation generating device uses gold as the material of the non-periodic metagrating, and sets the width of the metal nanorod to 50 nanometers for simulation, and assumes that there is no substrate and the electrons move at a speed of 0.34c. However, in fact, these parameters can be flexibly adjusted as needed to meet specific design requirements.

[0076] To demonstrate these flexibilities, the present invention will Figure 2 The parameters in (b) are modified, and the focusing results after the parameters are changed are shown in Figure 6 In. Figure 6 In (a), the present invention replaces the material of the non-periodic metagrating with silver; Figure 6 In (b), the present invention increases the width of the metal nanorods to 100 nanometers; Figure 6 In (c), the present invention uses silicon as the substrate material for the non-periodic metagrating; Figure 6 In (d), the present invention adjusts the speed of the fast-moving electrons to 0.28c, corresponding to an electron beam energy of 20KeV. Figure 6(a)- Figure 6 All simulated intensity distributions in (d) successfully achieve the Smith-Purcell radiation focusing wavefront. This shows that in addition to gold, other commonly used metal materials such as silver, platinum and titanium can also be used as materials for non-periodic metagratings for effective wavefront manipulation. Moreover, changing the width of the metal nanorods will not affect the pattern of the Smith-Purcell radiation wavefront. And the method of the present invention is also effective for different electron speeds.

[0077] In summary, the present invention proposes a Smith-Purcell radiation generating device, which can generate different forms of Smith-Purcell radiation wavefronts by exciting a non-periodic metagrating with a fast electron beam. Unlike the traditional method that relies on precise artificial atom design, the present invention mainly realizes various forms of Smith-Purcell radiation wavefronts by regulating the spatial position distribution of metal nanorods in the non-periodic metagrating. Moreover, the present invention can effectively regulate the Smith-Purcell radiation wavefront over a wide wavelength range. Furthermore, the present invention can also realize multiple wavefront types simultaneously in a Smith-Purcell radiation generating device.

[0078] Finally, it should be noted that although the embodiments of the present invention are described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments and application fields, and the above-mentioned specific embodiments are only illustrative and instructive, rather than restrictive. Under the guidance of this specification, a person of ordinary skill in the art can also make many forms without departing from the scope of protection of the claims of the present invention, all of which belong to the scope of protection of the present invention.

Claims

1. A Smith-Purcell radiation generating device based on a fast electron beam, characterized in that: The invention comprises a substrate and a non-periodic meta-grating formed on the substrate; the non-periodic meta-grating comprises metal nano-rods arranged in parallel, and the spacing between adjacent metal nano-rods is not required to be completely consistent; The non-periodic meta-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 metal nanorods in the non-periodic meta-grating.

2. The Smith-Purcell radiation generating device according to claim 1, characterized in that: The material of the metal nanorods is any one of gold, silver, platinum and titanium.

3. The Smith-Purcell radiation generating device according to claim 1, characterized in that: The width of the metal nanorod is 1 / 5-1 / 30 of the wavelength of 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 according to claim 1, characterized in that: The substrate is any one of silicon, silicon dioxide and silicon nitride.

5. The Smith-Purcell radiation generating device according to claim 1, characterized in that: The radiation wavefront form includes any one of focusing, deflection, Bessel beam and Airy beam; the focusing includes on-axis focusing and off-axis focusing; the deflection angle is 0-180 degrees.

6. The Smith-Purcell radiation generating device according to claim 1, characterized in that: The specified wavelength range is 200 nanometers to 1550 nanometers.

7. The Smith-Purcell radiation generating device according to claim 1, characterized in that: The speed of the fast electron beam is 0.1-0.6 times the speed of light.

8. The Smith-Purcell radiation generating device according to any one of claims 1 to 7, characterized in that: The non-periodic metagrating has at least two groups arranged in a superimposed manner; Each group of non-periodic metagratings 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 metagratings.

9. A method for manufacturing a Smith-Purcell radiation generating device, characterized in that: A Smith-Purcell radiation generating device based on a fast electron beam as claimed in any one of claims 1 to 8, comprising: Specifying the wavelength of the 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; Design the spatial position distribution of metal nanorods in the non-periodic metagrating according to the radiation wavefront of the desired Smith-Purcell radiation; 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.

10. The manufacturing method according to claim 9, characterized in that: The spatial position distribution of the metal nanorods in the non-periodic metagrating is designed according to the radiation wavefront of the Smith-Purcell radiation to be generated, specifically including: Determine the relationship between the radiation phase φ required to realize the radiation wavefront and the spatial position x according to optical theory, that is, the φ-x curve, and limit the phase change of the curve to a range of 0 to 2π; Define x to represent 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: Where λ is the specified wavelength of Smith-Purcell radiation, v represents the speed of fast electrons, and c is the speed of light in a vacuum; 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. 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.

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