Blackbody surface structure based on micro blackbody cavity and laser preparation method thereof

Abstract

The application discloses a blackbody surface structure based on a micro blackbody cavity and a laser preparation method thereof, and belongs to the technical field of material preparation. The micro blackbody cavity is a blind hole structure, the blackbody surface structure is composed of a blind hole structure array arranged periodically or non-periodically on the surface of a metal material, the blind hole structure is prepared by a laser processing method, two adjacent blind holes are not overlapped, the absorption bandwidth of the blackbody surface structure is controlled by adjusting the diameter of the blind hole, the cut-off wavelength of the blackbody surface structure is twice the diameter of the blind hole, and light smaller than or equal to the cut-off wavelength is fully absorbed. The laser processing technology can be used to prepare a large-area uniform wideband high-emissivity blackbody surface, and the emissivity in the infrared wave band is required to be above 0.95. The application is suitable for processing scenes such as large-area preparation and free curved surface processing, and has the prospect of industrial application.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of material preparation, and particularly relates to a blackbody surface structure based on a micro blackbody cavity and a laser preparation method thereof. BACKGROUND

[0002] With the continuous progress of infrared measurement equipment and technology in recent years, infrared detection, sensing and ranging technologies have been widely used in military, environmental monitoring and energy fields. The surface blackbody source is a key device for infrared calibration of infrared remote sensing detectors. Generally speaking, the higher the emissivity of the surface blackbody source, the higher the accuracy of calibrating infrared detection instruments. Currently, the aperture of the surface blackbody source is generally required to be more than 100 mm, and the temperature uniformity and the emissivity uniformity are the key indicators of infrared calibration test.

[0003] The traditional blackbody radiation source is a spherical cavity blackbody, however, the equivalent emissivity of the cavity blackbody mainly depends on the influence of factors such as the opening size of the blackbody cavity, the shape of the blackbody cavity, the emissivity of the surface material in the blackbody cavity, and the isothermal degree in the cavity. In addition, the structure size of the cavity blackbody is large, the larger the aperture of the blackbody cavity, the lower the emissivity, and the worse the temperature uniformity. On the other hand, the common blackbody paint is carbon nanomaterial coating. Carbon nanomaterials include carbon nanotubes, porous graphene, carbon nanospheres, etc. The preparation methods of carbon nanomaterials mainly include chemical synthesis method, chemical vapor deposition method, graphite oxide reduction method, laser-induced carbonization, etc. Among them, the chemical vapor deposition method is the most commonly used method, however, the equipment and process cost is high, and a complex transfer process is needed to obtain high-purity carbon nanomaterials. The current commercial surface blackbody source is coated with a carbon nanomaterial coating on the metal surface, and the emissivity is about 0.95, however, due to the insufficient adhesion and poor high-temperature resistance of the coating, it is easy to fall off and be worn out.

[0004] In addition, the use of ultrafast laser processing to prepare a blackbody metal surface that absorbs sunlight is also a method for preparing a surface blackbody source. The Chunlei Guo group at the University of Rochester in the United States has been studying the technology of laser processing blackbody metal surfaces. In 2020, the group used femtosecond lasers to prepare a porous blackbody aluminum surface for use in photothermal conversion and seawater purification. The surface has a sunlight absorption rate of 0.92 (300-2500nm) and an emissivity of more than 0.75 in the far infrared (8-14μm) band. (Singh, SC, ElKabbash, M., Li, Z., Li, X., Regmi, B., Madsen, M., Sohail AJ, Zhibing Z., Jihua Z. & Guo, C. (2020). Nature Sustainability, 3(11), 938-946). In the same year, the group also studied the use of femtosecond laser processing of blackbody surfaces on aluminum, iron, copper and tungsten surfaces, and successfully prepared a selective solar absorption surface on the tungsten surface, with a solar absorption rate of 0.92, but an emissivity of only 0.18 in the far infrared band. (Jalil, SA, Lai, B., ElKabbash, M., Zhang, J., Garcell, EM, Singh, S., & Guo, C. (2020). Light: Science & Applications, 9(1), 14). However, in current research, the blackbody metal surface processed by ultrafast laser has achieved a high solar absorption rate (α = 0.92), but the emissivity in the infrared band is far less than 0.90, which cannot meet the emissivity index requirement of the surface blackbody source (ε>0.95).

[0005] In summary, existing blackbody surfaces have their own shortcomings, mainly reflected in the large size of cavity blackbodies, the poor high temperature resistance and wear resistance of carbon nanomaterial coatings, and the insufficient infrared emissivity of blackbody metal surfaces based on laser processing. How to manufacture a blackbody surface with a wide spectrum and high emissivity has become a key technical issue. Summary of the Invention

[0006] To address the low infrared emissivity, complex processing, and difficulty in large-scale fabrication of existing surface blackbody sources, this paper proposes a blackbody surface structure based on a micro-blackbody cavity and a laser fabrication method. This method produces a large-area, uniform, broadband, high-emissivity blackbody surface with an infrared emissivity exceeding 0.95. This method is suitable for large-area fabrication and freeform surface processing, and has the potential for industrial application.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A blackbody surface structure based on a micro blackbody cavity, the micro blackbody cavity is a blind hole structure, the blackbody surface structure is composed of an array of blind hole structures arranged periodically or non-periodically on a metal material surface, the blind hole structure is prepared by a laser processing method, two adjacent blind holes do not overlap, the absorption bandwidth of the blackbody surface structure is controlled by adjusting the blind hole diameter, the cutoff wavelength of the blackbody surface structure is 2 times the diameter of the blind hole, and light less than or equal to the cutoff wavelength is completely absorbed.

[0009] Further, the metal material surface is a plane or a free-form surface.

[0010] Further, the design method of the array of blind hole structures is:

[0011] Divide the region to be processed of the metal material surface into periodic or non-periodic grids, and take the geometric center of each grid as the blind hole processing position;

[0012] Take the geometric center of each grid as the center and the maximum inscribed circle diameter of the grid as the blind hole diameter, establish a simulation model of equivalent thermal emissivity and blind hole depth according to the ratio of blind hole diameter to blind hole period, obtain a relationship curve of equivalent thermal emissivity and blind hole depth, and take the blind hole depth range when the equivalent thermal emissivity is greater than 0.95 as the design depth range, the blind hole depth range does not exceed the thickness of the metal material processing surface.

[0013] The blind hole processing position, diameter and depth are the design results of the array of blind hole structures.

[0014] Further, the grid division strategy adopts adaptive division based on curvature, specifically: according to the curvature and local geometric features of the metal material surface, smaller polygonal grid units are divided in regions with higher curvature, and larger polygonal grid units are divided in regions with lower curvature, and the polygonal grid units cover the region to be processed of the metal material surface.

[0015] Further, the blind hole depth is selected from the lowest value of the design depth range.

[0016] Further, the metal material surface is a plane or a free-form surface, the metal material surface of the plane structure adopts periodic grid division, and the metal material surface of the free-form surface structure adopts non-periodic grid division.

[0017] Further, the blind hole period refers to the size of the grid in the periodic grid or the average size of all grids in a certain region, when the blind hole depth is constant, the closer the ratio of blind hole diameter to blind hole period is to 1, the higher the equivalent thermal emissivity is.

[0018] Furthermore, laser processing technology is used to directly fabricate a micro blackbody cavity with high emissivity on the surface of a metal material in a single step based on the design results of the blind hole structure array, and a large-area blackbody surface based on the micro blackbody cavity is obtained by combining in a "point-to-surface" manner;

[0019] The laser processing technology includes: confocal in-situ measurement laser processing technology, multi-focus laser processing technology based on spatial light modulator, and multi-focus laser processing technology based on super lens; for the surface of metal materials with planar structure, multi-focus laser processing technology based on spatial light modulator or multi-focus laser processing technology based on super lens is adopted, and multi-focus is quickly processed to obtain black body surface structure; for the surface of metal materials with curved structure, confocal in-situ measurement laser processing technology is adopted, and single focus is processed one by one to obtain black body surface structure.

[0020] The above-mentioned application of the blackbody surface structure based on the micro blackbody cavity in the surface blackbody source has an emissivity of more than 0.95 in the infrared band.

[0021] The beneficial effects of the present invention are:

[0022] 1. The blackbody surface structure design of the micro blackbody cavity of the present invention is highly versatile and applicable to all metal materials, not limited to the surface of metal materials. It is a high-temperature resistant ultra-thin blackbody surface structure, which is more conducive to application in the aerospace field.

[0023] 2. The inner surface of the micro blackbody cavity based on laser processing proposed in the present invention utilizes the laser roughening effect, without the need to apply blackbody paint, and directly obtains a higher emissivity (the emissivity in the infrared band is above 0.95), which significantly increases the specific surface area of ​​the material and has a wider absorption and radiation bandwidth. The preparation method is simple, environmentally friendly and low-cost, keeps the original material of the metal surface unchanged, and has stronger high temperature resistance, wear resistance and durability.

[0024] 3. The confocal in-situ measurement laser processing system used in the present invention has strong adaptability and can be customized according to actual needs. It is suitable for curved surfaces. The multi-focus laser processing optical path based on spatial light modulator and super lens has high processing efficiency and is suitable for large-area planar surfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the blackbody surface structure of the micro blackbody cavity and the cross-sectional view and top view of each metasurface unit;

[0026] Figure 2 Periodic and non-periodic filled grids, where a micro blackbody cavity is filled in the geometric center of each grid;

[0027] Figure 3 It is a confocal in-situ measurement laser processing optical path, which can be applied to flat or curved workpieces;

[0028] Figure 4 It is a multi-focus laser processing optical path based on spatial light modulator, which can be applied to large-area and efficient preparation.

[0029] Figure 5 It is a multi-focus laser processing optical path based on a superlens, which can be applied to large-area and efficient preparation;

[0030] Figure 6 is the finite element calculation result of the equivalent radiation rate of the metasurface unit, where (a) the equivalent radiation rate ε under different duty cycles (D / P = 0.25, 0.50, 0.76) is meta Relationship with hole depth z; (b) Equivalent emissivity ε under different hole depths (z = 10, 100 μm) meta Relationship with duty cycle D / P;

[0031] Figure 7 Full-wave simulation results of long-wave infrared light incident on blind holes of different diameters, including the electric field diagrams of light with wavelengths of (a) λ = 8 μm and (b) λ = 14 μm coupled into a blind hole with D = 8 μm, and the electric field diagrams of light with wavelengths of (c) λ = 8 μm and (d) λ = 14 μm coupled into a blind hole with D = 4 μm.

[0032] Figure 8 The experimental results are shown in Figure 1, where (a) a photo of the blackbody surface structure samples (Pattern 1 and Pattern 2) based on the micro blackbody cavity and the blackbody paint; (b) an enlarged image of Pattern 1 and Pattern 2. Pattern 1 has a period of 200 μm and a diameter of 180 μm, while Pattern 2 has a period of 100 μm and a diameter of 90 μm.

[0033] Figure: 1. Blackbody surface structure based on micro blackbody cavity, 2. Cross-sectional view of metasurface unit, 3. Top view of metasurface unit, 4. Periodic rectangular grid, 5. Periodic regular hexagonal (honeycomb) grid, 6. Non-periodic hexagonal grid, 7. Non-periodic triangular grid, 8. Polarizer, 9. Half-wave plate, 10. Quarter-wave plate, 11. Laser light path, 12. Galvanometer U axis and its reflector, 13. Galvanometer V axis and its reflector, 14. Focusing lens, 15. Planar workpiece, 16. Three-axis translation stage, 17. High-pressure air jet Mouth, 18, curved workpiece, 100, dichroic beam splitter, 101, continuous laser, 102, concave lens, 103, convex lens 1, 104, polarizer, 105, photodiode, 106, pinhole light bar, 107, convex lens 2, 108, narrow-band filter, 109, polarizing prism, 110, continuous laser light path, 111, 1 / 4 wave plate, 201, spatial light modulator, 202, lens, 203, light bar, 204, lens, 301, objective lens 1, 302, holographic super lens, 303, objective lens 2. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0035] The present invention proposes a blackbody surface structure based on a micro blackbody cavity and a laser preparation method thereof. The blackbody surface structure based on the micro blackbody cavity is composed of a series of blind hole structure arrays prepared on the surface of a metal material by a high-precision laser processing method. Based on the theory of thermal radiation, the blind hole structure can be equivalent to a micro blackbody cavity. According to the size requirements of the actual workpiece, the micro blackbody cavity is filled with the entire surface or a specified area, thereby obtaining the blackbody surface structure based on the micro blackbody cavity. The metasurface unit containing the micro blackbody cavity can be periodically or non-periodically distributed. The present invention is prepared by using a laser processing method, and a blind hole with high emissivity is directly prepared on the metal surface in a single step to obtain a blackbody surface structure based on the micro blackbody cavity. This is a cross-scale micro-nano surface structure that can achieve broadband high emissivity.

[0036] In the present invention, the design of the blackbody surface structure based on the micro blackbody cavity includes the following steps:

[0037] Step 1: If Figure 1 As shown in , multiple micro blackbody cavities are filled on the metal surface according to a certain distribution. The filling method can be based on a periodic or non-periodic grid, such as Figure 2As shown in FIG, the metal surface is divided into periodic or non-periodic grids, and a micro blackbody cavity is processed at the geometric center of each grid. The micro blackbody cavity is a blind hole structure, and a large-area blackbody surface structure is combined using the "point-to-surface" method. In the present invention, the grid division strategy is an adaptive division based on curvature, that is, according to the curvature and local geometric characteristics of the surface, smaller polygonal grid units are used in areas with higher curvature, and larger polygonal grid units are used in areas with lower curvature. Generally, a periodic grid is used for a planar workpiece, such as Figure 2-4 and 2-5; the surface workpiece uses a non-periodic grid, such as Figure 2-6 and 2-7.

[0038] Step 2: Define each grid cell with a blackbody cavity as a metasurface. As the roughness of the laser-processed cavity surface increases, the emissivity ε1 of the cavity surface naturally increases. Therefore, the emissivity ε1 of the cavity surface is greater than the emissivity ε0 of the cavity surface.

[0039] Step 3: Based on the thermal radiation theory, the emissivity ε1 of the cavity surface and the emissivity ε0 of the cavity surface are considered respectively, and the geometric dimensions of the metasurface (including period, blind hole diameter and depth) are calculated and optimized. Finally, the overall processing dimensions of the blackbody surface structure based on the micro blackbody cavity are determined.

[0040] Based on the design of a classic blackbody radiation cavity, light reflects back and forth on the inner surface of the blackbody cavity. Assuming the absorptivity of the blackbody cavity inner surface is not zero, the light will eventually be completely absorbed, that is, the absorptivity α = 1. According to Kirchhoff's law of thermal radiation (reciprocity theorem), the absorptivity is equal to the emissivity. For an ideal blackbody, α = ε = 1.

[0041] Based on the principle of thermal radiation of a blackbody cavity, assuming that the opening diameter of the blind hole is much larger than the wavelength, when the aspect ratio of the blind hole reaches a certain level, the light entering the blind hole will be completely absorbed, and the emissivity can be close to 1. In this case, the blind hole can also be equivalent to a miniature blackbody cavity.

[0042] Based on the classical thermal radiation theory, assuming that the interior of the micro blackbody cavity is adiabatic, the equivalent thermal radiation rate ε at the opening of the micro blackbody cavity is a It can be expressed as Where F represents the angular coefficient of the inner surface of the micro blackbody cavity to the outside world. The angular coefficient F is determined by the geometric dimensions of the structure, and ε0 represents the thermal emissivity of the inner surface of the micro blackbody cavity. Then, the equivalent thermal emissivity of the entire metasurface unit is ε meta =fε a+(1-f)ε0, where f = D / P is the ratio of the blind hole diameter D to the average period P of the metasurface unit, also known as the duty cycle. In a periodic grid, the average period P is equivalent to the size of the grid. In a non-periodic grid, the average period P is defined as the average size of all grid cells within a certain area (for example, a 1mm×1mm area).

[0043] Therefore, as long as the dimensions (diameter and depth) of the micro-blackbody cavity are controlled to minimize the angular coefficient F, the equivalent thermal emissivity of the micro-blackbody cavity can be close to 1. Furthermore, to achieve high emissivity over a large area, the ratio f of the blind hole diameter to the average period of the metasurface unit must also be as large as possible. However, to ensure the integrity of each blind hole structure, blind holes cannot overlap. Therefore, the blind hole diameter D must be smaller than the average period P of the metasurface unit, that is, the duty cycle f = D / P < 1.

[0044] Based on the above theory, the equivalent thermal emissivity ε of the blackbody surface structure of the micro blackbody cavity is meta It is related to the depth z and the duty cycle f. Figure 6 As shown in (a), when the duty cycle f is constant, the increase of depth z will cause ε meta Tends to saturation. When the depth z is constant, the equivalent thermal radiation rate ε of the metasurface meta The relationship with the duty cycle f is as follows: Figure 6 (b) In theory, in order to achieve high emissivity ε meta >0.95, then the duty cycle f>0.95 and the depth z>200μm are required.

[0045] Absorption bandwidth and cut-off wavelength: The size of the aperture is directly related to the absorption bandwidth of the blackbody surface structure, such as Figure 7 As shown in (a) to (d) in the figure, the electric field diagrams of apertures D = 8 μm and D = 4 μm are analyzed through full-wave simulation. Figure 7 (a) and (b) show that when D = 8 μm, light with λ = 8 μm and λ = 14 μm can be coupled into the blind hole; Figure 7 From (c) and (d), we can see that when the diameter is as small as sub-wavelength, such as D = 4μm, the light with λ = 8μm can just be coupled into the blind hole, but the light with λ = 14μm cannot enter the blind hole and is totally reflected. Near the critical wavelength λ = 8μm, the electric field energy of the light with λ = 8.1μm, λ = 8.2μm, and λ = 8.3μm coupled into the hole with D = 4μm gradually decreases, as shown in Figure 2. Figure 7 (e)-(f) Therefore, it can be concluded that the cutoff wavelength of the micro blackbody cavity is λ≈2D, and light less than or equal to the cutoff wavelength will be completely absorbed, otherwise it will be totally reflected.

[0046] To achieve the blackbody characteristic of broadband absorption, the necessary condition is that the diameter of the blind hole be no less than half a wavelength, preferably D>λ / 2. Therefore, by varying the size of the aperture D, the blackbody surface structure based on the micro-blackbody cavity can achieve controllable absorption bandwidth, allowing it to be manufactured into photothermal conversion devices such as "selective solar absorbers."

[0047] This invention uses metal materials as processing samples and selects high-power pulsed lasers for subtractive processing, including but not limited to femtosecond or picosecond pulsed lasers. To achieve high-aspect-ratio hole structures, an axial feed laser processing method is employed. The specific process for the laser printing method of producing blackbody material on a metal substrate is as follows:

[0048] Step 1: After the processing laser is expanded and collimated, it passes through a series of polarization elements to adjust the polarization state of the laser. Then, the processing laser passes through the galvanometer and focusing lens and is focused on the surface of the sample to be processed.

[0049] Step 2: Fix the sample on the stage and perform laser focusing; open the high-pressure air valve.

[0050] Step 3: Achieve fast and efficient laser scanning through the movement of the galvanometer, and optimize the laser scanning processing parameter group based on experimental design and empirical methods.

[0051] Step 4: According to the morphology of the micro blackbody cavity, adjust and select the appropriate laser scanning processing parameter group; start cyclic processing. After the laser scans one layer, the laser focus moves a certain distance along the optical axis to move the focus downward; the general requirement is that the feed amount is equal to the processing depth of each layer to keep the laser focus always on the material surface.

[0052] Step 5: After processing is completed, close the high-pressure air valve and take out the sample.

[0053] Step 6: Clean the sample and complete the preparation process.

[0054] The micro blackbody cavity prepared by laser processing has a high emissivity on the surface of the cavity itself. The reason is the laser roughening effect. The surface processed by the laser becomes rough, thereby increasing the emissivity of the surface of the cavity.

[0055] Typically, the inner surface of a cavity-type blackbody requires blackbody paint to ensure that the blackbody cavity perfectly absorbs all wavelengths of light, achieving high emissivity. In contrast, the laser-processed micro-blackbody cavity surface of the present invention utilizes laser roughening, eliminating the need for blackbody paint and directly achieving a higher emissivity. Therefore, the laser processing method of the present invention is simpler and more environmentally friendly.

[0056] Furthermore, the processing system for the aforementioned laser printing method for producing blackbody material on a metal substrate can integrate multiple optical modules to address engineering challenges such as curved surface processing and large-scale batch processing. The present invention also provides three laser processing examples: a confocal in-situ measurement module, a multi-focus module based on a spatial light modulator, and a multi-focus module based on a superlens. Finally, an application example of the described blackbody surface structure based on a micro-blackbody cavity in a surface blackbody source is demonstrated.

[0057] Example 1: Laser preparation method for high degree of freedom and customizable patterning

[0058] In this embodiment, the processing laser is selected as a femtosecond pulse laser (wavelength of 1030nm), and the measurement laser is selected as a continuous laser (wavelength of 632nm). The processed sample is a titanium alloy material (curved workpiece 18). Using the confocal in-situ measurement laser processing system, as shown in FIG. Figure 3 As shown, a blackbody surface structure with high degree of freedom and customizable patterning is prepared, which is suitable for preparation on curved surfaces and patterning. The specific steps are as follows:

[0059] Step 1: Adjust the processing laser light path. After the processing laser is expanded and collimated, it passes through the polarizer 8, half-wave plate 9, and quarter-wave plate 10 to adjust the polarization state of the laser. Preferably, the laser polarization state is set to circular polarization to eliminate the anisotropy of the laser-ablated material. Then, after passing through the dichroic beam splitter 100 in the confocal measurement module, the processing laser passes through the galvanometer (galvanometer U axis and its reflector 12, galvanometer V axis and its reflector 13) and focusing lens 14, and is focused on the surface of the sample material.

[0060] Step 2: Adjust the confocal measurement laser optical path. A continuous laser 101 emits the measurement laser, which is expanded and collimated by a lens assembly (concave lens 102, convex lens 103). The polarization state is then adjusted by a polarizer 104. The incident light enters the polarization prism 109, passes through the quarter-wave plate 111 and the dichroic beam splitter 100, and is coupled into the processing optical path, becoming coaxial with the processing laser. The light focused on the sample surface is then reflected back to the confocal measurement module, passing through the dichroic beam splitter 100, quarter-wave plate 111, polarization prism 109, narrowband filter 108, convex lens 107, and pinhole aperture 106 before reaching the photodiode 105. Calibrate the confocal measurement to establish a curve showing the relationship between the photocurrent and the Z-axis position of the photodiode.

[0061] Step 3: Open the high-pressure air valve and adjust the laser processing parameters. Through the movement of the galvanometer, fast and efficient laser scanning processing is carried out. Based on experimental design and empirical methods, the laser scanning processing parameter set is optimized.

[0062] Step 4: Use the co-convergence measurement module to autofocus the laser. Adjust and select the appropriate laser scanning processing parameter set. Cyclic processing begins. After scanning one layer, the material removal depth is measured. The laser focus is moved a certain distance along the optical axis, and laser autofocus is performed again to maintain the laser focus on the material surface.

[0063] Step 5: After processing a small area, move the sample horizontally and repeat step 4 to process the next area. Repeat this cycle to form a large-area blackbody surface structure.

[0064] Step 6: After processing is completed, close the high-pressure air valve and take out the sample.

[0065] Step 7: Clean the sample and complete the preparation process.

[0066] Example 2: Large-area laser preparation method based on laser multi-focus

[0067] In this embodiment, the processing laser is a femtosecond pulse laser (wavelength of 1030nm), and the sample to be processed is an aluminum alloy flat plate (flat workpiece 15). The optional multi-focus laser optical paths are multi-focus laser processing optical paths based on spatial light modulators ( Figure 4 ) and multi-focus laser processing optical path based on superlens ( Figure 5 The specific steps are as follows:

[0068] Step 1: Adjust the processing laser light path. After the processing laser is expanded and collimated, it passes through the polarizer 8, half-wave plate 9, and quarter-wave plate 10 to adjust the polarization state of the laser.

[0069] Step 2: For the multi-focus laser processing optical path based on spatial light modulator ( Figure 4 ), the laser polarization state must be set to linear polarization. After the laser is obliquely incident on the spatial light modulator module, it undergoes amplitude and phase modulation by the spatial light modulator 201. The zero-order light and higher-order diffracted light are then filtered by a 4f system consisting of two lenses 202 and 204 and a light barrier 203. The processing laser then passes through the galvanometer mirrors (galvanometer U axis and its reflector 12, galvanometer V axis and its reflector 13) and focusing lens 14, where multiple focal points are focused on the sample material surface. The advantage of a spatial light modulator is that it can flexibly change the distribution of multiple focal points and the spatial morphology of the laser.

[0070] Similarly, for the multi-focus laser processing optical path based on the metalens ( Figure 5) and adjust the laser polarization state according to the design of the metalens. The laser passes through objective lens 1 301 and is focused onto the holographic metalens 302. The metalens changes the spatial distribution of the laser into a multi-focal image. This is then amplified by objective lens 2 303 and coupled into the galvanometer system. After the processing laser passes through the galvanometers (galvanometer U-axis and its reflector 12, galvanometer V-axis and its reflector 13) and focusing lens 14, the multi-focal laser light is focused on the sample surface. Compared to a spatial light modulator, a metalens not only performs all the functions of a spatial light modulator, but also makes the laser optical path more compact and simple, thereby increasing efficiency.

[0071] Step 3: Fix the sample on the three-axis translation stage, adjust the Z-axis position and perform manual laser focus.

[0072] Step 4: Open the high-pressure air valve and test the laser processing parameters. The movement of the galvanometer allows for fast and efficient laser scanning. Based on experimental design and empirical methods, the laser scanning processing parameter set is optimized, and the processing depth for each scan is pre-calibrated.

[0073] Step 5: Adjust and select the appropriate laser scanning processing parameter group. Start cyclic processing. After the laser scans one layer, the laser focus moves a certain distance along the optical axis. The distance moved is equal to the processing depth of each scan to keep the laser focus on the material surface.

[0074] Step 6: After processing a small area, move the sample horizontally and repeat step 5 to process the next area. Repeat this cycle to form a large-area blackbody surface structure.

[0075] Step 7: After processing is completed, close the high-pressure air valve and take out the sample.

[0076] Step 8: Clean the sample and complete the preparation process.

[0077] Compared with the single-focus laser processing method, if N focuses are used for parallel scanning, assuming that the energy density of the N focuses is the same as that of the single focus, the average power of the laser processing will increase N times, and the processing time will be reduced N times, which exponentially increases the processing efficiency and is suitable for large-area and high-efficiency preparation.

[0078] Example 3: Application of a blackbody surface structure based on a micro blackbody cavity as a surface blackbody source

[0079] The sample material is titanium alloy. According to the laser processing method of Example 1 or Example 2, the blackbody surface structure based on the micro blackbody cavity is prepared, such as Figure 8(b) This embodiment shows two structures of different sizes. The left pattern 1 has a period of 200μm and a blind hole diameter of 180μm; the right pattern 2 has a period of 100μm and a blind hole diameter of 90μm. The hole depths of both pattern 1 and pattern 2 are 250μm. The infrared radiation temperature of the blackbody surface structure based on the micro blackbody cavity is compared with that of commercial blackbody paint (emissivity ε = 0.95). Their actual photos are shown in the figure. Figure 8 Hereinafter, the blackbody surface structure based on the micro blackbody cavity is referred to as the sample, and the commercial blackbody paint is referred to as the blackbody paint.

[0080] Experimental results: Under normal temperature conditions, in the mid-wave infrared band (3-5μm), the radiation temperature of the sample is 23.3±0.46°C, while the radiation temperature of blackbody paint is 22.2±0.06°C. On the other hand, when both are placed on the same hot plate and heated to 100°C, in the long-wave infrared band (8-14μm), the radiation temperature of the sample is 123±0.4°C, and the radiation temperature of blackbody paint is 104±0.7°C. In addition, the temperature difference between pattern 1 and pattern 2 of the sample is not large, and the temperature error is less than 2%. Because the radiation temperature of the sample is higher than that of the blackbody paint, it can be inferred that the emissivity of the sample ε>0.95.

[0081] Therefore, compared to commercial blackbody paint, the blackbody surface structure based on the micro-blackbody cavity of the present invention has a higher infrared radiation temperature in the mid-wave infrared and long-wave infrared bands, that is, a higher infrared emissivity, and better temperature uniformity. In summary, the blackbody surface structure based on the micro-blackbody cavity proposed in the present invention is a surface structure that is closer to an ideal blackbody, with a wide spectrum of extremely high emissivity (ε>0.95).

[0082] The above examples are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above examples, and many variations are possible. All variations that can be directly derived or imagined by a person skilled in the art from the disclosure of the present invention should be considered to be within the scope of protection of the present invention.

Claims

1. A blackbody surface structure based on a micro blackbody cavity, characterized in that: The micro blackbody cavity is a blind hole structure. The blackbody surface structure is composed of an array of blind hole structures arranged periodically or non-periodically on the surface of a metal material. The blind hole structure is prepared by a laser processing method. Due to the laser roughening effect, the emissivity of the cavity surface is improved. There is no overlap between two adjacent blind holes. The absorption bandwidth of the blackbody surface structure is controlled by adjusting the blind hole diameter. The cutoff wavelength of the blackbody surface structure is twice the blind hole diameter. Light less than or equal to the cutoff wavelength will be completely absorbed, and the duty cycle is satisfied. f >0.95, blind hole depth z > 200 μm, blind hole diameter D Smaller than the average period of the metasurface unit P ; The duty cycle is the blind hole diameter D Average period of metasurface unit P ratio.

2. The blackbody surface structure based on a micro blackbody cavity according to claim 1, characterized in that: The design method of the blind hole structure array is: The area to be processed on the surface of the metal material is divided into periodic or non-periodic grids, and the geometric center of each grid is used as the blind hole processing position; Taking the geometric center of each grid as the center of the circle and the diameter of the largest inscribed circle of the grid as the blind hole diameter, a simulation model of equivalent thermal emissivity and blind hole depth is established according to the blind hole diameter and blind hole period ratio, and a relationship curve between equivalent thermal emissivity and blind hole depth is obtained. According to the relationship curve, the blind hole depth range when the equivalent thermal emissivity is greater than 0.95 is taken as the design depth range, and the blind hole depth range does not exceed the thickness of the metal material processing surface; The blind hole processing position, diameter and depth are the design results of the blind hole structure array.

3. The blackbody surface structure based on a micro blackbody cavity according to claim 2, characterized in that: The mesh division strategy adopts curvature-based adaptive division, specifically: according to the curvature and local geometric characteristics of the metal material surface, smaller polygonal mesh units are divided in the area with higher curvature, and larger polygonal mesh units are divided in the area with lower curvature. The polygonal mesh units cover the area to be processed on the surface of the metal material.

4. The blackbody surface structure based on a micro blackbody cavity according to claim 2, characterized in that: The blind hole depth is selected from the lowest value of the designed depth range.

5. The blackbody surface structure based on a micro blackbody cavity according to claim 2, characterized in that: The surface of the metal material is a plane or a free-form surface. The surface of the metal material with a plane structure is divided into periodic grids, and the surface of the metal material with a free-form surface structure is divided into non-periodic grids.

6. The blackbody surface structure based on a micro blackbody cavity according to claim 2, characterized in that: The blind hole period refers to the grid size in the periodic grid or the average size of all grids in a certain area. When the blind hole depth is constant, the closer the ratio of the blind hole diameter to the blind hole period is to 1, the higher the equivalent thermal radiation rate is.

7. The laser processing method of the blackbody surface structure based on the micro blackbody cavity according to claim 2, characterized in that: Using laser processing technology, a micro blackbody cavity with high emissivity is directly fabricated on the surface of a metal material in a single step based on the design results of the blind hole structure array. A large-area blackbody surface based on the micro blackbody cavity is obtained through a "point-to-surface" combination method. The laser processing technology includes: confocal in-situ measurement laser processing technology, multi-focus laser processing technology based on spatial light modulator, and multi-focus laser processing technology based on super lens; for the surface of metal materials with planar structure, multi-focus laser processing technology based on spatial light modulator or multi-focus laser processing technology based on super lens is adopted, and multi-focus is quickly processed to obtain black body surface structure; for the surface of metal materials with curved structure, confocal in-situ measurement laser processing technology is adopted, and single focus is processed one by one to obtain black body surface structure.

8. Use of a blackbody surface structure based on a micro blackbody cavity according to any one of claims 1 to 6 in a surface blackbody source, wherein the blackbody surface structure based on a micro blackbody cavity has an emissivity of greater than 0.95 in the infrared band.

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