A method for preparing high-precision complex metal pattern structure on lithium niobate surface

Abstract

The application discloses a method for preparing a high-precision complex metal pattern structure on a lithium niobate surface, and belongs to the technical field of laser micro-nano processing, and comprises the following steps: step one, preparing a sample to be processed; step two, internally modifying the sample to be processed by a femtosecond laser; and step three, mechanically polishing and photoreducing the processed sample. In the method, the femtosecond laser is deeply introduced into the crystal for modification, specifically, photons transfer energy to electrons at a focusing position, the electrons transfer part of the energy to a crystal lattice, and then the crystal lattice vibrates, the temperature at the focusing position is increased, and the crystal material is phase changed. Therefore, the original periodic arrangement of the molecules in the modified area is destroyed, and the original ordered state is changed into a disordered state, and the inner electrons are more easily excited. In this case, the capturing capacity of the modified area exposed by mechanical polishing to metal ions is greatly improved compared with the unirradiated area, and therefore the preparation of a metal pattern can be realized. In the application, various high-precision and complex metal patterns can be prepared by controlling laser pulse energy, pulse number and action path.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of laser micro-nano processing, and particularly relates to a mechanical polishing combined with a photoreduction assisted femtosecond laser internal modification technology, which is used for realizing preparation of a high-precision complex metal pattern structure on a lithium niobate crystal surface. BACKGROUND

[0002] With the development of integrated photonics in recent years, people have shown great interest in realizing the regulation of nonlinear optical phenomena at the micro-nano scale. Lithium niobate, as an excellent optical material, is one of the ideal crystal materials for exciting nonlinear optical effects due to its wide transparent window, good stability and extremely high nonlinear coefficient. However, the problem of low system energy conversion efficiency currently exists. Benefiting from the plasmonic resonance effect between nano structures, the combination of metal nano structures and nonlinear medium is one of the most effective methods to solve this problem. However, how to combine metal nanoparticles with the surface of lithium niobate faces a great challenge.

[0003] Using the ferroelectric properties of lithium niobate crystal, the combination of domain reversal of lithium niobate and ferroelectric lithography by using an applied electric field polarization and electron beam polarization is a common method for combining metal particles with the surface of lithium niobate. The combination principle is to convert the negative domain of lithium niobate into a positive domain, and due to the adsorption of the positive domain to the surface electrons, the electron-reduced metal particles can be deposited on the surface of the positive domain. However, due to the size limitation of the surface electrode, up to now, the applied electric field polarization method can only realize a micron-level metal pattern line width; although the electron beam polarization can achieve a sub-micron level metal pattern line width, the period is still limited to the micron level. More importantly, the basic principle of these two common methods is based on the domain reversal technology of lithium niobate crystal, but the growth and lateral expansion of the domain are difficult to accurately control, which makes it difficult to prepare complex pattern structures. In addition, due to the directionality of the domain, these two methods can only realize the preparation of metal patterns on z-cut lithium niobate.

[0004] Therefore, there is an urgent need for a method for preparing a high-precision complex metal pattern structure on the surface of lithium niobate in any cut direction, so as to further improve the application ability of lithium niobate in nonlinear optics. SUMMARY

[0005] To address the challenge of fabricating high-precision and complex metallic patterns on the surface of lithium niobate crystals with arbitrary tangential orientations in existing technologies, this invention provides a method for fabricating metallic patterns on the surface of lithium niobate crystals using femtosecond laser internal modification combined with mechanical polishing and photoinduced reduction. Unlike traditional methods that use high-energy electron beams to invert ferroelectric domains in crystals, this method modifies the crystal by penetrating the femtosecond laser deep into its interior. Specifically, at the focal point, photons transfer energy to electrons, which in turn transfer some energy to the crystal lattice, causing lattice vibration and a temperature increase at the focal point, resulting in a phase transition in the crystal material. This disrupts the original periodic arrangement of molecules in the modified region, transforming it from an ordered state to a disordered state, making it easier to excite electrons. In this case, the modified region exposed by mechanical polishing has a significantly enhanced ability to capture metal ions compared to the unirradiated region, thus enabling the fabrication of metallic patterns. In this invention, by controlling the laser pulse energy, pulse number, and action path, various high-precision and complex metallic patterns can be fabricated.

[0006] This invention is achieved through the following technical solution:

[0007] A method for preparing high-precision complex metallic pattern structures on the surface of lithium niobate specifically includes the following steps:

[0008] Step 1: Sample preparation;

[0009] First, the sample to be processed is ultrasonically cleaned in acetone, ethanol and deionized water respectively, and then dried with a bulb syringe to obtain a clean crystal surface. The sample preparation is complete.

[0010] Step 2: Femtosecond laser internal modification of the sample to be processed;

[0011] First, the three-dimensional electronic control platform is leveled using a level, and then the sample to be processed is fixed on the processing platform. After the femtosecond laser emitted from the femtosecond laser amplifier enters the micro-nano processing system, it is focused by the objective lens to a position d below the upper surface of the sample to be processed. Then, the laser emission power is adjusted, the pre-designed processing file is imported into the processing program, and the direct writing processing from the inside to near the surface is performed by scanning line by line and layer by layer to obtain the patterned modified area.

[0012] Step 3: Perform mechanical polishing and photo-reduction on the processed sample;

[0013] The specific steps are as follows: first, the sample obtained by the step two is mechanically polished by using a polishing machine to remove a surface layer with a depth of d, so that the modified area is exposed; then, the sample is cleaned in the order of acetone, ethanol and deionized water to clean the polishing debris and residual polishing liquid; then the sample is placed in a silver nitrate solution and heated by using a hot stage; at the same time, the sample is irradiated by using an ultraviolet lamp, so that the electrons in the modified area are excited and adsorb silver ions in the solution to form an in-situ deposition effect; then the deposited sample is taken out of the solution and dried by using an ear cleaning ball; after photoreduction, the metal is deposited on the laser modified area to form a patterned metal structure.

[0014] Further, in step one, the sample to be processed is a transparent lithium niobate crystal sheet with a thickness of 0.3-0.5mm.

[0015] Further, in step two, the laser output power is 100-400mw.

[0016] Further, in step two, the micro-nano processing system comprises a first concave lens L1, a second convex lens L2, a third convex lens L3, an aperture I, a first half mirror M1, a second half mirror M2, an image sensor CCD, an objective lens O and a three-dimensional electric control platform S; the femtosecond laser emitted by the femtosecond laser emits is expanded by the first concave lens L1 and the second convex lens L2 in turn; then the aperture I limits the light beam to a certain extent; then the light beam reaches the objective lens O through the first half mirror M1, and focuses the light beam on the sample placed on the three-dimensional electric control platform S through the objective lens O, wherein the three-dimensional electric control platform S is controlled by a computer; in addition, the mercury lamp light source illuminates the sample on the three-dimensional electric control platform in turn through the second half mirror M2, the first half mirror M1 and the objective lens O, and the reflected light is finally imaged on the image sensor CCD through the second half mirror M2 and the third convex lens L3.

[0017] Further, in step two, the three-dimensional electric control platform is a three-axis electric control platform of X-axis, Y-axis and Z-axis, wherein the moving range of X-axis and Y-axis is 0-5cm, the accuracy is 1-100nm, the moving range of Z-axis is 0-5mm, and the moving accuracy is 1-100nm.

[0018] Further, in step two, the femtosecond laser is an infrared femtosecond laser with a wavelength of 1030nm; the laser repetition frequency is 90-200kHz, the pulse width is 160-280fs; the objective lens used is a 5x-40x lens with a numerical aperture of 0.1-0.75; the depth d is 500nm-3μm; the single pulse energy of laser modification is 50-200nJ; the laser scanning speed is 0.1-2mm / s; the point spacing of the processing data is 100-400nm, the line spacing is 200-1000nm, and the layer spacing is 400-1000nm.

[0019] Further, in step three, the polishing machine rotation speed is 40-100 rpm, and the polishing liquid used is 50-120 nm particle size silica polishing liquid.

[0020] Further, in step three, the molar concentration of the silver nitrate solution used in the photoreduction is 0.01-0.1 mol / L, the hot stage temperature is 300-400 K, the wavelength of the ultraviolet mercury lamp is 254 nm, the power is 20-100 W, and the irradiation time is 10-30 min.

[0021] Compared with the prior art, the application has the following advantages:

[0022] (1) Compared with the external electric field polarization method, the application can prepare a metal pattern with a linewidth and a period in the sub-micron order on the surface of a lithium niobate crystal, and does not need a pre-masking operation; compared with the electron beam writing method, the application can accurately control the shape of the metal pattern, and realize the preparation of an arbitrarily complex metal pattern; more importantly, the application can prepare a metal pattern structure on the surface of a lithium niobate crystal with an arbitrary tangent direction.

[0023] (2) The above two methods are both based on the regulation of the ferroelectric domain inside the lithium niobate crystal, but the growth and lateral expansion of the domain are difficult to accurately control, so that the finally prepared metal pattern is not ideal, and due to the directionality of the positive and negative domains and the optical axis of the crystal, the two methods can only prepare a metal pattern on the surface of a z-cut lithium niobate; the application is based on laser modification to induce phase change of the material, so that the modification region and the laser non-irradiation region form a difference in the capture ability of metal ions, thereby realizing the preparation of a metal pattern, so there is no requirement for the processing crystal face of the lithium niobate, and thanks to the high-precision and high-freedom processing characteristics of the femtosecond laser, the shape of the pattern can be accurately controlled. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the specific embodiments of the application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or the prior art description. In all the drawings, similar elements or parts are generally identified by similar reference signs. In the drawings, the elements or parts are not necessarily drawn according to the actual proportions.

[0025] Figure 1 is a schematic diagram of a method for preparing a high-precision complex metal pattern structure on the surface of a lithium niobate according to the application;

[0026] wherein a is a laser-modified sample diagram, b is an exposed diagram of the modified region after polishing, and c is that the electrons in the modified region are excited and reduce metal ions;

[0027] Figure 2A femtosecond laser processing optical path schematic diagram of a method for preparing a high-precision complex metal pattern structure on a lithium niobate surface;

[0028] Wherein, the first concave lens L1, the second convex lens L2, the third convex lens L3, the diaphragm I, the first half mirror M1, the second half mirror M2, the image sensor CCD, the objective lens O, the three-dimensional electric control platform S;

[0029] Figure 3 A whole flow chart of a method for preparing a high-precision complex metal pattern structure on a lithium niobate surface;

[0030] Figure 4 A flow chart of a method for preparing a high-precision complex metal pattern structure on a lithium niobate surface;

[0031] Figure 5 A Raman intensity distribution diagram of a non-processed area and a laser modified area in a method for preparing a high-precision complex metal pattern structure on a lithium niobate surface;

[0032] Figure 6 A scanning electron microscope diagram and a corresponding scanning electron microscope energy spectrum diagram of a different period high-precision line metal pattern prepared by a method for preparing a high-precision complex metal pattern structure on a lithium niobate surface;

[0033] Wherein, a is a scanning electron microscope diagram of a high-precision line metal pattern, and b is a corresponding scanning electron microscope energy spectrum diagram;

[0034] Figure 7 A scanning electron microscope diagram of a "dragon head" metal pattern prepared on a z-cut and x-cut lithium niobate surface by a method for preparing a high-precision complex metal pattern structure on a lithium niobate surface;

[0035] Wherein, a is a scanning electron microscope diagram of a metal pattern on a z-cut lithium niobate surface, and b is a scanning electron microscope diagram of a metal pattern on an x-cut lithium niobate surface; DETAILED DESCRIPTION

[0036] In order to clearly and completely describe the technical solutions of the present application and the specific working process thereof, in combination with the accompanying drawings of the specification, the specific embodiments of the present application are as follows:

[0037] Example 1

[0038] By mechanical polishing combined with photoreduction assisted femtosecond laser internal modification technology, a different period high-precision line metal pattern structure is prepared on a z-cut lithium niobate surface.

[0039] By Figure 2As shown, the 1030nm femtosecond laser is expanded by the first concave lens L1 and the second convex lens L2 in turn; then the light beam is limited by the diaphragm I; then the light beam reaches the objective lens O through the first half mirror M1, and the light beam is focused on the sample placed on the three-dimensional electric control platform S through the objective lens O, wherein the three-dimensional electric control platform S can be controlled by a computer; in addition, the mercury lamp light source illuminates the sample on the platform in turn through the second half mirror M2, the first half mirror M1 and the objective lens O, and the reflected light is finally imaged on the image sensor CCD through the third convex lens L3 after being reflected by the second half mirror M2.

[0040] Specifically, as shown in Figure 3 Fig. 1 is a schematic diagram of the overall process of a method for preparing a high-precision complex metal pattern structure on the surface of lithium niobate according to the embodiment, and the specific steps of the processing method are as follows:

[0041] Step one: preparation of the sample to be processed;

[0042] First, the z-cut lithium niobate sample with a length of 1cm, a width of 1cm and a thickness of 500μm is ultrasonically cleaned in acetone, ethanol and deionized water for 15min respectively, and is dried with an ear cleaning ball, and the sample preparation is completed;

[0043] Step two: internal modification of the sample to be processed by femtosecond laser;

[0044] First, the three-dimensional electric control platform is leveled by using a level, and then the sample to be processed is fixed on the processing platform; the image sensor and the mercury lamp light source are turned on, the X-axis and Y-axis of the three-dimensional electric control platform are controlled by the computer, the sample is moved to the position directly below the objective lens, then the Z-axis is adjusted to slowly raise the sample, and the upper surface of the sample to be processed is found in the imaging system; the laser output power is adjusted so that the single pulse energy of the laser before focusing by the objective lens is 50nJ, the shutter is opened, the Z-axis is slowly adjusted to the position where the laser can just ablate the upper surface, the shutter is closed, and the three-dimensional electric control platform is raised by 1μm by adjusting the Z-axis, the femtosecond laser is focused inside the crystal, and then the X-axis is adjusted to move away from the laser ablation position; different period line processing programs are imported, wherein the large period is 1μm and the small period is 250nm, the scanning mode is set to gradually scan from the inside to the upper surface, and the scanning layer spacing is set to 800nm for the modification scanning process; the femtosecond laser wavelength is 1030nm, the repetition frequency is 200kHz, the pulse width is 280fs, the laser scanning speed is 0.1mm / s, the acceleration is 1mm / s, the objective lens is a 40x lens, and the numerical aperture is 0.6;

[0045] Step three: mechanical polishing and photoreduction of the processed sample;

[0046] The specific steps are as follows: first, the sample obtained by the step two processing is mechanically polished using a polishing machine, 60nm particle size of silica polishing liquid is used and the polishing machine speed is set to 60rpm, after 40min polishing, the modified area is exposed in the microscope; then clean in the order of acetone, ethanol and deionized water to clean the polishing debris and residual polishing liquid; then the sample is placed in 0.01mol / L silver nitrate solution, and the silver nitrate solution is heated using a hot stage 300K; at the same time, the sample immersed in the silver nitrate solution is irradiated by a ultraviolet mercury lamp with a power of 20W and a wavelength of 254nm, after 20min, the sample after deposition is taken out from the solution with tweezers; finally, the sample is blown dry with an ear bulb. After photoreduction, metal is deposited on the laser modified area, realizing the preparation of high-precision line metal pattern with different periods on the surface of the material.

[0047] Example 2

[0048] A complex "dragon head" metal pattern is prepared on the surface of z-cut and x-cut lithium niobate by mechanical polishing combined with photoreduction assisted femtosecond laser internal modification technology.

[0049] The processing system is shown as Figure 2 The same as example 1.

[0050] The embodiment provides a method for preparing a high-precision complex metal pattern structure on the surface of lithium niobate, and the specific steps are as follows:

[0051] (1) sample preparation;

[0052] First, the z-cut and x-cut lithium niobate samples with a length of 1cm, a width of 1cm and a thickness of 500μm are respectively placed in acetone, ethanol and deionized water for ultrasonic cleaning for 15min, and then dried with an ear bulb, and the sample preparation is completed;

[0053] (2) femtosecond laser internal modification of the sample to be processed;

[0054] First, the 3D electronic control platform was leveled using a level, and then the sample to be processed was fixed on the platform. The image sensor and mercury lamp light source were turned on, and the X and Y axes of the 3D electronic control platform were controlled by a computer to move the sample directly below the objective lens. Then, the Z axis was adjusted to slowly raise the sample, and the upper surface of the sample to be processed was located in the imaging system. The laser output power was adjusted so that the laser single pulse energy before the objective lens was focused was 100nJ. The shutter was opened, and the Z axis was slowly adjusted to a position where the laser could just ablate the upper surface. The shutter was closed, and the Z axis was adjusted to raise the 3D electronic control platform by 1μm, focusing the femtosecond laser into the crystal. Then, the X axis was adjusted to move away from the laser ablation position. The "dragon head" pattern processing program was imported, and the scanning mode was set to scan from the inside to the upper surface, with a scanning layer spacing of 1μm for the modification scanning process. The femtosecond laser wavelength was 1030nm, the repetition frequency was 200kHz, the pulse width was 280fs, the laser scanning speed was 0.3mm / s, the acceleration was 1mm / s, the objective lens was a 40× lens, and the numerical aperture was 0.6.

[0055] (3) Mechanical polishing and photo-reduction of the processed sample;

[0056] First, the sample obtained in step two was mechanically polished using a polishing machine with a 120nm particle size silica polishing slurry and a polishing speed of 65rpm. After 30 minutes of polishing, the modified area was visible under a microscope. Then, the sample was cleaned in the following order: acetone, ethanol, and deionized water, to remove polishing debris and residual polishing slurry. Next, the sample was placed in a 0.01mol / L silver nitrate solution and heated using a 300K hot stage. Simultaneously, a 20W, 254nm ultraviolet mercury lamp was used to irradiate the sample immersed in the silver nitrate solution. After 25 minutes, the deposited sample was removed from the solution with tweezers. Finally, the sample was dried using a syringe. After photoreduction, metal was deposited on the laser-modified area, achieving the fabrication of a "dragon head" metal pattern on the Z-cut and X-cut lithium niobate surfaces.

[0057] Depend on Figure 1 It is known that by using mechanical polishing combined with photoreduction-assisted femtosecond laser internal modification technology, metal patterns can be prepared on the surface of lithium niobate. Specifically, the original periodic arrangement of molecules in the femtosecond laser internal modification region is disrupted, and electrons within it are more easily excited, greatly enhancing the ability to capture metal ions, thereby enabling the preparation of metal pattern structures.

[0058] Depend on Figure 4 It is known that after mechanical polishing exposes the modified region inside the femtosecond laser, selective deposition of metals can be achieved after photo-reduction.

[0059] Depend on Figure 5It can be seen that after femtosecond laser modification, the Raman peak intensity in the modified region decreased, indicating that the crystallization properties of the crystal changed and the vibrational degrees of freedom of the molecules within it were restricted, changing from the original ordered state to a disordered state.

[0060] Depend on Figure 6 As shown in section a, the method of this invention can be used to prepare high-precision linear metal patterns with different periods on the surface of lithium niobate crystals. The linewidth can reach 80 nm, with a large period of 1.5 μm and a small period of 300 nm between lines. This represents a two-order-of-magnitude improvement in linewidth compared to externally polarized electric fields. While electron beam writing can also achieve sub-micron linewidths, the period between lines is limited to 1.5 μm or more. The difference in precision is closely related to their processing mechanisms. The precision of the structure prepared by this invention is mainly determined by the size of the femtosecond laser focusing spot and the scanning trajectory. After focusing by the objective lens, the internal spot size can reach tens of nanometers, thus achieving sub-micron linewidth and period. In contrast, the precision of electron beam writing is limited by the lateral expansion size of the domains in the domain inversion region. Specifically, to achieve good metal deposition, the domain inversion region must penetrate the entire thickness of the crystal. During this process, the lateral expansion of the domains reaches the micrometer level, thus limiting the line period to the micrometer level. Figure 6 As shown in b, the peak position of silver was successfully detected in the energy spectrum, proving that the line is a silver metal line.

[0061] Depend on Figure 7 It is evident that the method of this invention can be used to fabricate complex "dragon head" metal patterns on the surface of z-cut and x-cut lithium niobate crystals. The principle of external electric field polarization and electron beam writing is to induce domain inversion in lithium niobate crystals, but the growth and lateral expansion of domains are difficult to control precisely, making it difficult to fabricate arbitrarily patterned structures. This invention, however, is based on laser modification, which significantly enhances the ability of the modified region to capture metal ions, thereby achieving the fabrication of metal patterns. Furthermore, thanks to the high precision and high degree of freedom of femtosecond laser processing, the shape of the pattern can be precisely controlled. More importantly, due to the directionality of positive and negative domains relative to the crystal's optical axis, the above two methods can only induce changes in the domain polarization direction of the crystal on the surface of z-cut lithium niobate to achieve the fabrication of metal patterns, while this invention, based on the principle of laser modification, does not require specific tangential orientation of the lithium niobate. Figure 7 As can be seen in a and b, complex metal pattern structures can be prepared in both types of tangential lithium niobate crystals, proving that the method proposed in this invention can realize the preparation of complex metal pattern structures on the surface of lithium niobate crystals with arbitrary tangential orientation.

[0062] The preferred embodiments of the present application are described in detail above with reference to the drawings, but the present application is not limited to the specific details of the above-described embodiments. Various simple modifications can be made to the technical solutions of the present application within the technical concept of the present application, and these simple modifications all belong to the protection scope of the present application.

[0063] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, various possible combinations are not described again by the present application.

[0064] In addition, various different embodiments of the present application can also be combined in any appropriate manner, as long as they do not deviate from the idea of the present application, and they should also be considered as disclosed by the present application.

Claims

1. A method for preparing high-precision complex metallic pattern structures on the surface of lithium niobate, characterized in that, Specifically, the steps include the following: Step 1: Sample preparation; First, the sample to be processed is ultrasonically cleaned in acetone, ethanol and deionized water respectively, and then dried with a bulb syringe to obtain a clean crystal surface. The sample preparation is complete. Step 2: Femtosecond laser internal modification of the sample to be processed; First, the three-dimensional electronic control platform is leveled using a level, and then the sample to be processed is fixed on the processing platform. After the femtosecond laser emitted from the femtosecond laser amplifier enters the micro-nano processing system, it is focused by the objective lens to a position d below the upper surface of the sample to be processed. Then, the laser emission power is adjusted, the pre-designed processing file is imported into the processing program, and the direct writing processing from the inside to near the surface is performed by scanning line by line and layer by layer to obtain the patterned modified area. Step 3: Perform mechanical polishing and photo-reduction on the processed sample; The specific steps are as follows: First, the sample obtained in step two is mechanically polished using a polishing machine to remove the surface layer of thickness d, exposing the modified area; then, it is cleaned in the order of acetone, ethanol, and deionized water to remove polishing debris and residual polishing solution; then, the sample is placed in a silver nitrate solution and heated using a hot stage; simultaneously, the sample is irradiated with a UV lamp to excite electrons in the modified area and adsorb silver ions in the solution, forming an in-situ deposition effect; finally, the deposited sample is removed from the solution and dried with a rubber bulb. After photoreduction, the metal is deposited on the laser-modified area to form a patterned metal structure.

2. The method for preparing high-precision complex metallic pattern structures on the surface of lithium niobate as described in claim 1, characterized in that, In step one, the sample to be processed is a transparent lithium niobate crystal sheet with a thickness of 0.3-0.5 mm.

3. The method for preparing high-precision complex metallic pattern structures on the surface of lithium niobate as described in claim 1, characterized in that, In step two, the laser output power is 100-400mw.

4. The method for preparing high-precision complex metallic pattern structures on the surface of lithium niobate as described in claim 1, characterized in that, In step two, the micro / nano fabrication system includes a first concave lens L1, a second convex lens L2, a third convex lens L3, an aperture I, a first semi-reflective lens M1, a second semi-reflective lens M2, an image sensor CCD, an objective lens O, and a three-dimensional electronic control platform S. The femtosecond laser emitted from the femtosecond laser is expanded sequentially by the first concave lens L1 and the second convex lens L2. Then, the aperture I restricts the beam. Afterward, the beam reaches the objective lens O through the first semi-reflective lens M1, and the objective lens O focuses the beam onto the sample placed on the three-dimensional electronic control platform S, which is controlled by a computer. In addition, a mercury lamp light source illuminates the sample on the three-dimensional electronic control platform sequentially through the second semi-reflective lens M2, the first semi-reflective lens M1, and the objective lens O. The reflected light is finally reflected by the second semi-reflective lens M2 and then reaches the image sensor CCD through the third convex lens L3 to form an image.

5. The method for preparing high-precision complex metallic pattern structures on the surface of lithium niobate as described in claim 1, characterized in that, In step two, the three-dimensional electronic control platform is a three-axis electronic control platform with X-axis, Y-axis and Z-axis. The movement range of the X-axis and Y-axis is 0-5cm and the accuracy is 1-100nm. The movement range of the Z-axis is 0-5mm and the movement accuracy is 1-100nm.

6. The method for preparing high-precision complex metallic pattern structures on the surface of lithium niobate as described in claim 1, characterized in that, In step two, the femtosecond laser is an infrared femtosecond laser with a wavelength of 1030nm; the laser repetition frequency is 90-200kHz, and the pulse width is 160-280fs; the objective lens used is a 5×-40× lens with a numerical aperture of 0.1-0.75; the depth d is 500nm-3μm; the single pulse energy for laser modification is 50-200nJ; the laser scanning speed is 0.1-2mm / s; the point spacing of the processing data is 100-400nm, the line spacing is 200-1000nm, and the layer spacing is 400-1000nm.

7. The method for preparing high-precision complex metallic pattern structures on the surface of lithium niobate as described in claim 1, characterized in that, In step three, the polishing machine rotates at 40-100 rpm, and the polishing slurry used is a silica polishing slurry with a particle size of 50-120 nm.

8. The method for preparing high-precision complex metallic pattern structures on the surface of lithium niobate as described in claim 1, characterized in that, In step three, the molar concentration of the silver nitrate solution used for photoreduction is 0.01-0.1 mol / L, the hot stage temperature is 300-400 K, the wavelength of the ultraviolet mercury lamp is 254 nm, the power is 20-100 W, and the irradiation time is 10-30 min.

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