CN104237989A - Large-area optical grating manufacturing method based on ultrashort-pulse laser-induction self-assembly feature - Google Patents

Abstract

A large-area grating fabrication method based on ultrashort pulse laser-induced self-assembly characteristics, including substrate preparation, multi-beam pulse laser parallel processing and surface grating structure transfer to a quartz glass substrate. This method will spontaneously form a grating structure with high period precision within the diameter range of laser spot irradiation, and its grating structure can seamlessly and neatly follow the movement and scanning of the laser spot for large-area spontaneous growth; this method has the advantages of grating The characteristics of high fabrication speed, large grating area, high quality and laser-induced self-assembly.

Description

Ultrashort-pulse laser-induced self-assembly properties for large-area grating fabrication

technical field

The invention relates to the production of gratings, in particular to a method for producing large-area gratings with ultrashort pulse laser-induced self-assembly characteristics.

Background technique

In 1965, M. Birnbaum first reported the phenomenon of grating-like (with obvious stripe features) damage pattern on the surface of semiconductor materials under the action of pulsed ruby laser, which was later called laser-induced periodic surface structure (Laser Induce Periodic) Surface Structure, the English abbreviation is LIPSS). Since then, a large number of experiments have been carried out on a variety of materials such as semiconductors, metals, dielectrics and polymers, and the results have shown that laser-induced grating-like patterns are a universal class of physical phenomena. However, after nearly 50 years of development, there has been no progress in the quality control of grating structures. Therefore, except for applications in material modification, coloring, etc., LIPSS still cannot be used as a fabrication method for grating devices.

At the same time, the fabrication technology of large-scale, especially meter-scale optical gratings has always been a technical challenge. There are two ways to increase the raster size:

1) Use the splicing method to splice several small gratings into a large grating, that is, the mechanical splicing method;

2) Fabricate a larger monolithic grating with an optical method

At present, the manufacturing methods of large-scale holographic gratings mainly include single exposure method represented by LLNL (Lawrence Livermore National Laboratory, Lawrence Livermore National Laboratory, USA), scanning exposure (Scanning Beam Interference Lithography) of PGL (Plymouth Grating Laboratory), scanning beam interference lithography) and exposure stitching methods.

From the current manufacturing method of large-aperture gratings, a single exposure needs to produce large-aperture, high-quality aspheric collimator mirrors. The main problems are difficult processing techniques and unknown time costs; while scanning exposure and exposure splicing Although the above-mentioned problems are avoided by making a large grating by the method, very high requirements are put forward for the control of the relative position of the substrate and the exposure beam. Any unstable factors in the exposure and measurement system will introduce stitching errors and affect the diffraction wavefront of the large grating. Although the exposure splicing method has been experimentally verified on a small scale, it still needs to overcome problems such as the deflection of the exposure wavefront, the surface shape of the substrate, exposure aberrations, and seams in order to expand to the production of large-scale gratings. Therefore, carrying out research on new manufacturing technologies for large-area gratings is of positive significance for promoting the development of large-area gratings in my country, especially the manufacturing technology including laser fusion pulse pressure gratings.

Contents of the invention

The purpose of the present invention is to provide a large-area grating fabrication method based on ultrashort pulse laser-induced self-assembly characteristics. The method carefully designs functional thin film materials and laser processing methods, so that within the diameter range of laser spot irradiation, there will be Spontaneously form a grating structure with high periodic precision, and its grating structure can seamlessly and neatly follow the moving scanning of the laser spot for large-area spontaneous growth;

A method of parallel processing of multi-beam pulsed lasers is designed to increase the production speed of gratings; chemical methods and ion etching methods are used to transfer the grating structure to the quartz glass substrate to form high-quality optical gratings. This method can be used to fabricate diffraction gratings with high optical quality and large area, even meter-scale gratings. The above aspects are closely related; there is also a close relationship between each step and the speed and quality of grating production:

1) Different material compositions and film structures have different LIPSS formation mechanisms; in turn, different LIPSS mechanisms can guide material design, preparation methods, and pulsed laser treatment of materials;

2) The difference in material composition, film layer structure and film forming process, as well as the different processing methods of pulsed laser on materials, will affect the surface grating quality and grating manufacturing speed;

3) Different material composition, film structure and film forming process, the transfer method of the grating structure to the quartz glass substrate is not exactly the same;

4) When the grating structure is transferred to the quartz glass substrate, the optical quality, diffraction efficiency and laser damage threshold of the grating will be significantly improved;

5) On the basis of the research on the processing method of ultrashort pulse laser on thin film materials, the oblique multi-beam parallel material processing method is adopted to further increase the grating manufacturing speed.

Technical solution of the present invention is as follows:

A method for fabricating large-area gratings with ultrashort pulse laser-induced self-assembly characteristics, characterized in that the method

The method includes the following steps:

①Substrate preparation: select titanium, tungsten, germanium, antimony, tellurium or their mixtures as functional materials for preparation, and prepare reflective film, heat insulation film and functional film in turn on the quartz glass substrate by vacuum coating method; The hot film adopts ZnS, AlN or _SiO2 film, and the reflective film adopts the multilayer dielectric film of the current pulse compression grating;

②Pulse laser treatment of the film to form a surface grating structure;

③Using multiple beams in parallel to process grating materials;

④The surface grating structure is transferred to the quartz glass substrate.

The step ②:

1) The laser must be linearly polarized light, and the polarization plane remains unchanged during scanning; the wave vector direction of the grating period is parallel to the electric field direction of the polarized light;

2) The peak intensity of the incident pulsed laser is close to but lower than the ablation threshold of the functional thin film;

3) The grating period is controlled according to the composition and film thickness of the functional film, the angle and wavelength of the incident laser light;

4) The groove width and groove depth of the grating are adjusted according to actual requirements;

5) Under the condition that the peak intensity of the incident pulsed laser is close to but lower than the ablation threshold of the functional film, the laser power is increased to 2 to 3 times, the area of the large laser spot is increased, the diameter is not less than 10 microns, and the frequency of the laser pulse is increased To 2 times, realize the improvement of laser scanning speed to 2 to 3 times;

6) The control principle of the laser scanning speed is that the number of pulsed laser irradiations in each area is more than 1000 times.

Step ③ as described:

1) Using multi-beam pulsed lasers for parallel processing, on the XY plane, there are n beams of laser spots arranged obliquely in a straight line, scanning along the Y-axis direction, and the wave vector direction of the grating is parallel to the X-axis; The distance between them should be at least greater than the spot diameter d to ensure that the spots do not interfere with each other; at the same time, the distance between the projections of the center points of adjacent spots on the X axis should be smaller than the spot diameter d, so that the edge of the next spot can be scanned during the scanning process. Contact the grating formed by the previous spot along the Y axis; the grating structure induced by the first spot (L1) becomes the scattering center within the range of the second spot (L2), further inducing a seamlessly connected periodic grating structure ;Similarly, the grating structure induced by the second light spot (L2) becomes the scattering center within the scope of the third light spot (L3); ;

2) Using a binary grating element to perform n-fold splitting on a high-energy laser beam.

The step ④:

1) The functional film not covered by the grating structure is etched away by chemical etching, and on this basis, the surface grating pattern is transferred to the glass substrate material by ion beam etching;

2) After corrosion cleaning, remove the residual functional film.

Compared with the prior art, the present invention has the following advantages:

1) Extend the ultra-short laser-induced periodic surface structure fabrication method from the application of material surface treatment and coloring to the research on the fabrication of diffraction grating devices;

2) Drawing lessons from the current holographic grating manufacturing process, transferring the ultrashort pulse laser-induced grating structure to the quartz glass substrate is another feature of the present invention, which will greatly improve the optical quality and life of the grating;

3) Using the multi-beam oblique follow-up scanning method may greatly increase the production speed of the grating.

4) Since the grating is formed by self-feedback and has extremely high periodic accuracy, it does not need to precisely control the relative position of the substrate and the exposure beam like the scanning beam interference lithography method, and also requires the substrate surface shape, exposure Problems such as aberrations and seams need to be overcome, not to mention the need to produce large-aperture, high-quality aspheric collimating mirrors like the single-exposure method. Therefore, the optical path for large-area grating fabrication using ultrashort pulse laser-induced self-assembly is extremely simple, which can greatly save the development cycle and cost.

Description of drawings

Fig. 1 is a schematic diagram of the multi-beam parallel laser processing method of the present invention

Fig. 2 is a multi-beam parallel laser processing optical path diagram of the present invention

Fig. 3 is the basic process flow diagram of the transfer of the grating structure of the present invention to the quartz glass substrate

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention should not be limited thereby.

A method for fabricating large-area gratings with ultrashort-pulse laser-induced self-assembly characteristics, comprising the following steps:

①Substrate preparation, selection of functional materials, thin film structure design and thin film preparation;

②Pulse laser to process the surface of the material to form a surface grating structure;

③In order to speed up the production speed, multiple beams are used to process the grating production materials in parallel;

④Transfer of surface grating structure to quartz glass substrate.

The selection of functional materials, film structure design and film preparation in the step ①:

1) The selected functional materials can be various materials such as semiconductors and metals. These materials can undergo laser ablation or oxidation reaction characteristics under the action of ultrashort pulse laser. Materials can be selected from metal titanium (Ti), tungsten (W) or semiconductor germanium (Ge), antimony (Sb), tellurium (Te) and their mixtures.

2) The designed multi-layer structure is as follows: functional film, heat insulation film, reflective film, and quartz glass substrate. The heat insulation film can use ZnS, AlN, SiO ₂ film and other films with good optical quality and low thermal conductivity. The reflective film can adopt the multilayer dielectric film structure of the currently used pulse compression grating, such as the multilayer film system of HfO ₂ and SiO ₂ film with high and low refractive index ratio.

3) The film preparation method adopts a vacuum coating method, and the defects of the film should be as low as possible, and the thickness of each film layer should be strictly controlled. After the coating is completed, the thickness of the film can be measured with an ellipsometer.

4) The principle of optimizing the functional film material composition, film layer structure, and film formation process is to make the laser threshold of the functional film as low as possible.

The step ② pulse laser to process the surface of the material:

1) Carefully select laser wavelength, polarization, power, spot size, pulse length, repetition period, duty cycle, moving speed, and moving direction. Different ultra-short pulse laser sources can be used for material processing. These laser sources can output different pulse widths (from <130fs to 35ps), different repetition rates (1KHz, 10KHz, 200KHz to 80MHz), different pulse energies, and different wavelengths (can be Femtosecond laser light sources with tuning wavelengths of 240nm-2600nm and picosecond laser light sources with wavelengths of 1064nm, 532nm, 355nm, and 266nm respectively).

2) The laser must be linearly polarized light, and the polarization plane remains unchanged during scanning. The wave vector direction of the grating period is parallel to the electric field direction of the polarized light.

3) The peak intensity of the incident pulsed laser is close to but lower than the ablation threshold of the functional thin film. Such incident pulsed laser light is scattered by existing nanostructures or surface defects. The interference of scattered and incident light results in an immediate change in the intensity of light adjacent to the scattered point. When the light intensity exceeds the ablation threshold, the functional film (such as Ti film) will ablate or react rapidly with O ₂ in the air to form oxides (such as TiO ₂ ). This creates a laser-induced periodic surface structure (LIPSS). And this is a positive feedback self-assembly process. At the same time, as the nanostructure grows, its range of scattering of incident light gradually expands. As the oxide layer (such as _TiO2 layer) thickens, the _O2 index that can penetrate the oxide layer decreases, so that the reaction of metal or semiconductor functional materials with _O2 decreases and the growth stops, which is another negative feedback process.

4) The grating period is controllable and can be changed with the composition and film thickness of the functional film, the angle and wavelength of the incident laser light. Ideally, the accuracy of the grating period can be less than 1nm, which is much smaller than that achieved by any other fabrication method.

5) The grating groove width and groove depth are also controllable, which can be changed with the composition and film thickness of the functional film, the angle of incident laser light, wavelength, power, power, and scanning speed.

6) The surface defects of the functional film should be as few as possible, so that the number of defects within the diameter of the laser spot is less than 2. In this way, since the peak intensity of the incident pulsed laser is close to but lower than the ablation threshold of the functional film, and there is only one defect in the functional film within the range of the laser spot, the first periodic grating structure caused by the defect is within the range of the laser spot. High precision and high quality. After the grating structure is formed in the range of the first spot, as the laser spot scans, the subsequent gratings are self-assembled from the previously formed gratings. At this time, even if there is a defect, a grating formation center that can compete with the previous grating will not be formed. In this way, with the scanning of the laser light speed, the grating structure can seamlessly and neatly follow the movement and scanning of the laser spot for large-area spontaneous growth. The period accuracy of this grating is very high. At the same time, as few surface defects as possible will also make the quality of the grating better. Use electron microscope or atomic force microscope to characterize the surface morphology of materials before and after laser treatment; use laser Raman spectrometer and laser ablation inductively coupled plasma yard emission spectroscopy analysis technology to analyze the micro-area chemical composition of the material surface medium before and after laser treatment, The phase composition of the micro-area was analyzed. Through morphology analysis and composition analysis, the preparation conditions of materials and laser treatment methods are further controlled, so that the grating not only has a high period, but also has better optical quality.

7) Under the condition that the peak intensity of the incident pulsed laser is close to but lower than the ablation threshold of the functional film, try to increase the laser power, increase the large laser spot area (not less than 10 microns in diameter), and increase the repetition rate of the laser pulse (more than 1MHz repetition rate), so as to maximize the laser scanning speed.

8) The control principle of the laser scanning speed is that the number of pulse laser irradiation in each area is more than 1000 times, but try not to exceed 1000 times too much, so as not to reduce the scanning speed.

The step ③ multi-beam processing grating production materials in parallel:

1) Using multi-beam pulsed lasers for parallel processing, on the XY plane, there are n beams of laser spots arranged obliquely on a straight line, scanning along the Y-axis direction, and the wave vector direction of the grating is parallel to the X-axis (see Figure 1 ). The distance between the laser beams should be at least greater than the spot diameter d (ie (s ² +h ² ) ^1/2 >d) to ensure that the spots do not interfere with each other; at the same time, the center points of adjacent spots on the X-axis The projection s should be smaller than the spot diameter d, so that the edge of the latter spot can touch the grating formed by the previous spot along the Y-axis direction. In this way, the grating structure induced by the spot L1 becomes the scattering center within the range of the spot L2, and further induces a seamlessly connected periodic grating structure; similarly, the grating structure induced by the spot L2 becomes the scattering center within the range of the spot L3 . By analogy, until the light spot Ln induces a seamlessly connected periodic grating structure. Using this parallel scanning method, the grating production speed can be increased by n times without problems such as seams.

2) Use a precisely designed binary grating element to split a high-energy laser beam by n times.

3) Since the grating is formed by self-feedback, it has extremely high periodic accuracy. In addition to the need to ensure that the linear polarization plane of the laser maintains a stable direction and has few surface defects, it does not need to do the substrate and exposure beam as in the scanning beam interference lithography method. Precise control of the relative position also needs to overcome the problems of substrate surface shape, exposure aberration and seam like the exposure splicing method, not to mention the need to produce large-diameter, high-quality aspheric collimator mirrors like the single exposure method. Therefore, the optical path diagram of large-area grating fabrication using ultrashort pulse laser-induced self-assembly characteristics is extremely simple in comparison. As shown in Fig. A binary Damman grating 3 forms n beams of the same linearly polarized light; after passing through the mirror 4, a grating is formed on the large-area sample 6 through the lens 5; the sample is placed on the sample stage 7, and the X-axis translation stage 8 and The Y-axis translation stage 9 is driven to scan.

For the transfer of the grating structure to the quartz glass substrate in the above step (4) (taking the functional film as an example of a Ti film), it is necessary to:

1) The functional film not covered by the grating structure (such as the Ti film not covered by TiO2) is etched away by chemical etching, and on this basis, the surface grating pattern is transferred to the glass substrate material by ion beam etching;

2) After chemical cleaning, the residual functional film (such as Ti film) is etched away to obtain a grating close to the design target.

The basic process flow chart of the above-mentioned grating transfer is shown in Figure 3 (including steps ① selection of functional materials, film structure design and film preparation; ② pulse laser treatment of the surface of the material to form a surface grating structure).

A method for producing large-area gratings with ultrashort pulse laser-induced self-assembly characteristics, characterized in that: through the careful design of functional thin film materials and laser processing methods, within the diameter range of laser spot irradiation, periodic precision will be formed spontaneously The grating structure is very high, and its grating structure can seamlessly and neatly follow the movement and scanning of the laser spot for large-area spontaneous growth; a parallel processing method for multi-beam pulsed lasers is designed to improve the production speed of the grating; using chemical The method and the ion etching method transfer the grating structure to the quartz glass substrate to form a high-quality optical grating. This method can be used to fabricate diffraction gratings with high optical quality and large area, even meter-scale gratings.

Example:

The technical solution of the present embodiment is as follows:

A method for fabricating a large-area grating with ultrashort pulse laser-induced self-assembly characteristics, comprising the following steps:

①Substrate preparation, selection of functional materials, thin film structure design and thin film preparation;

②Pulse laser to process the surface of the material to form a surface grating structure;

③In order to speed up the production speed, multiple beams are used to process the grating production materials in parallel;

④Transfer of surface grating structure to quartz glass substrate.

For the selection of functional materials, film structure design and film preparation in the above step ①:

1) The selected functional material is metal titanium (Ti);

2) The multi-layer structure is as follows: functional film, heat insulation film, reflective film, and quartz glass substrate; the heat insulation film can use _SiO2 film, which has good optical quality and low thermal conductivity. The reflective film adopts the multilayer dielectric film structure of the current pulse compression grating, and adopts the multilayer film system of HfO ₂ and SiO ₂ film with high and low refractive index ratio.

3) The film preparation method adopts the vacuum sputtering coating method, the defects of the film should be as low as possible, and the thickness of each film layer should be strictly controlled. After the coating is completed, use an ellipsometer to measure the thickness of the film layer;

4) The thickness of the functional film Ti is 180 nm.

For the above-mentioned step ② multi-beam parallel pulse laser to process the surface of the material:

1) A Ti:Sapphire femtosecond pulsed laser source is used for material processing. The output pulse width of the laser source is 120fs, the repetition frequency is 10MHz, the single pulse energy is 50μJ, and the wavelength is 800nm.

2) The laser must be linearly polarized light, the polarization direction remains unchanged during scanning, and the wave vector direction of the grating period to be formed is parallel to the electric field direction of the polarized light.

3) The optical path diagram of large-area grating fabrication using ultrashort pulse laser-induced self-assembly characteristics is extremely simple in comparison. As shown in Figure 2, the pulsed laser starts from laser 1, first passes through a polarizing polarizer 2, and then After passing through a binary Damman grating 3, 200 beams of the same linearly polarized light are formed; after passing through the mirror 4, a grating is formed on the large-area sample 6 through the lens 5; the sample is placed on the sample stage 7, and the X-axis translation stage 8 and The Y-axis translation table 9 is driven to scan;

4) The diameter of each laser spot is 25 μm, and the energy of each pulse is 250nJ, so that the peak intensity of the incident pulsed laser is close to but lower than the ablation threshold of the functional film (about 5x10 ¹¹ w cm ^-2 );

5) The surface defects of the functional film should be as few as possible, so that the number of defects within the diameter of each laser spot is less than 2;

6) Multi-beam pulsed lasers are used for parallel processing. On the XY plane, 200 laser spots are arranged obliquely on a straight line, scanning along the Y-axis direction, and the wave vector direction of the grating is parallel to the X-axis. The distance between the laser beams is 30 μm, which is greater than the spot diameter d, so as to ensure that the spots do not interfere with each other; at the same time, the projection s of the center point of the adjacent spot on the X axis is 21.2 μm, which is smaller than the spot diameter d, so that the latter spot The edge of can touch the grating formed by the previous spot along the Y-axis direction. In this way, the grating structure induced by the first light spot L1 becomes the scattering center within the range of the second light spot L2, and further induces a seamlessly connected periodic grating structure; similarly, the grating structure induced by the second light spot L2 becomes the second light spot L2. Scattering center within the range of three spots L3. By analogy, until the 200th light spot L ₂₀₀ is induced to generate a seamlessly connected periodic grating structure. Using this parallel scanning method, the raster production speed can be increased by 200 times without problems such as seams.

7) When the laser scanning speed is 50mm/s, the number of pulsed laser irradiation for each area is more than 5000 times; the grating area of parallel recording per second is about 200mm ² . It only takes about 3 hours to burn a meter-level grating with an area of 2 square meters.

8) The period of the grating on the surface is 680nm, which is controllable and can change with the film thickness of the functional film and the angle of the incident laser light. The accuracy of the grating period in this experiment can be less than 1nm, which is far less than the accuracy that can be achieved by any other fabrication method.

9) The groove width of the grating is 350nm and the groove depth is 80nm, which are also controllable, and can be changed with the film thickness of the functional film, the angle of incident laser light, wavelength, power, and scanning speed.

For the transfer of the grating structure to the quartz glass substrate in the above step ③, it is necessary to:

1) Use chemical etching to etch away the functional film not covered by the grating structure (such as the Ti film not covered by TiO ₂ ), on this basis, use the ion beam etching method to transfer the surface grating pattern to the glass substrate material;

2) After chemical cleaning, the residual functional film (such as Ti film) is etched away to obtain a grating close to the design target.

The basic process flow chart of the above-mentioned grating transfer is shown in Figure 3 (including steps ① selection of functional materials, film structure design and film preparation; ② pulse laser treatment of the surface of the material to form a surface grating structure).

Compared with the prior art, the present invention has the following advantages:

1) Extend the ultra-short laser-induced periodic surface structure fabrication method from the application of material surface treatment and coloring to the research on the fabrication of diffraction grating devices;

2) Drawing lessons from the current holographic grating manufacturing process, transferring the ultrashort pulse laser-induced grating structure to the quartz glass substrate is another feature of the present invention, which will greatly improve the optical quality and life of the grating;

3) Using the multi-beam oblique follow-up scanning method may greatly increase the production speed of the grating.

4) Since the grating is formed by self-feedback and has extremely high periodic accuracy, it does not need to precisely control the relative position of the substrate and the exposure beam like the scanning beam interference lithography method, and also requires the substrate surface shape, exposure Problems such as aberrations and seams need to be overcome, not to mention the need to produce large-aperture, high-quality aspheric collimating mirrors like the single-exposure method. Therefore, the optical path diagram of large-area grating fabrication using ultrashort pulse laser-induced self-assembly characteristics is extremely simple in comparison, which can greatly save the development cycle and cost.

Claims (4)

1. an ultrashort pulse laser-induced self-assembly characteristic is carried out large-area grating manufacturing method, it is characterized in that the method comprises the steps: ①Substrate preparation: select titanium, tungsten, germanium, antimony, tellurium or their mixtures as functional materials for preparation, and prepare reflective film, heat insulation film and functional film in turn on the quartz glass substrate by vacuum coating method; The hot film adopts ZnS, AlN or _SiO2 film, and the reflective film adopts the multilayer dielectric film of the current pulse compression grating; ②Pulse laser treatment of the film to form a surface grating structure; ③Using multiple beams in parallel to process grating materials; ④The surface grating structure is transferred to the quartz glass substrate. 2. The method according to claim 1, characterized in that said step ②: 1) The laser must be linearly polarized light, and the polarization plane remains unchanged during scanning; the wave vector direction of the grating period is parallel to the electric field direction of the polarized light; 2) The peak intensity of the incident pulsed laser is close to but lower than the ablation threshold of the functional thin film; 3) The grating period is controlled according to the composition and film thickness of the functional film, the angle and wavelength of the incident laser light; 4) The groove width and groove depth of the grating are adjusted according to actual requirements; 5) Under the condition that the peak intensity of the incident pulsed laser is close to but lower than the ablation threshold of the functional film, the laser power is increased to 2 to 3 times, the area of the large laser spot is increased, the diameter is not less than 10 microns, and the frequency of the laser pulse is increased To 2 times, realize the improvement of laser scanning speed to 2 to 3 times; 6) The control principle of the laser scanning speed is that the number of pulsed laser irradiations in each area is more than 1000 times. 3. The method according to claim 1, characterized in that said step ③: 1) Using multi-beam pulsed lasers for parallel processing, on the XY plane, there are n beams of laser spots arranged obliquely in a straight line, scanning along the Y-axis direction, and the wave vector direction of the grating is parallel to the X-axis; The distance between them should be at least greater than the spot diameter d to ensure that the spots do not interfere with each other; at the same time, the distance between the projections of the center points of adjacent spots on the X axis should be smaller than the spot diameter d, so that the edge of the next spot can be scanned during the scanning process. Contact the grating formed by the previous spot along the Y axis; the grating structure induced by the first spot (L1) becomes the scattering center within the range of the second spot (L2), further inducing a seamlessly connected periodic grating structure ;Similarly, the grating structure induced by the second light spot (L2) becomes the scattering center within the scope of the third light spot (L3); ; 2) Using a binary grating element to perform n-fold splitting on a high-energy laser beam. 4. The method according to claim 1, characterized in that said step ④: 1) The functional film not covered by the grating structure is etched away by chemical etching, and on this basis, the surface grating pattern is transferred to the glass substrate material by ion beam etching; 2) After corrosion cleaning, remove the residual functional film.