Background point preparation method for high-precision background schlieren measurement experiment and background point

Abstract

The invention provides a background point preparation method for a high-precision background schlieren measurement experiment and a background point, and belongs to the technical field of optical measurement. The preparation method comprises the following steps: performing dust-free pretreatment on the surface of the reflecting mirror serving as a background; background point distribution data is generated by applying a Poisson disk sampling algorithm, and the data is imported into laser equipment; under the protection of an inert gas atmosphere, laser engraving is carried out by using laser equipment, and a base material of the reflector is exposed by removing a surface layer of a local area of the reflector, so that a background point is prepared; and after-treatment is conducted on the engraved surface, machining residues are removed, and surface cleaning is completed. According to the method, high-precision and non-destructive processing of the base material is realized by innovatively utilizing the selective absorption characteristic difference of the metal coating surface layer and the inorganic non-metal material base material on the infrared laser; the prepared background point structure has the excellent characteristics of clear boundary, high contrast ratio, no thermal stress and the like.

Description

Technical Field

[0001] This invention belongs to the field of optical measurement technology, specifically relating to a method for preparing background points and background points for high-precision background schlieren measurement experiments. Background Technology

[0002] Background schlieren is an optical measurement method for visualizing flow fields based on the principle of light refraction in media of different densities. It is widely used in research fields such as fluid mechanics, aerodynamics, and heat transfer. In traditional background schlieren systems, a high-contrast background dot pattern is typically prepared on a background plate to identify pattern displacement caused by density changes in the flow field. To improve the spatial resolution of the measurement system, some high-precision systems use concave mirrors as reflective backgrounds. In this case, the background dots need to be prepared directly on the mirror surface, which places higher demands on the accuracy, stability, and durability of the pattern.

[0003] Currently, the preparation of background dots on the surface of mirrors mainly relies on spraying, deposition, and chemical etching methods, but all of these have limitations:

[0004] (1) The spraying method uses ink to form background dots on the surface, but it has problems such as weak adhesion and poor uniformity. It is easy to fall off on the surface of optical components, which affects the measurement stability.

[0005] (2) The deposition method generates background points through colloidal deposition, but the pattern accuracy is low, the distribution is difficult to control on complex curved surfaces, and the adhesion is insufficient, and it is prone to degradation after long-term use.

[0006] (3) Chemical etching uses etching solution to corrode the coating to form background dots. Although it can obtain high contrast patterns, it generates chemical waste liquid, requires additional treatment equipment, increases costs and is not environmentally friendly.

[0007] The aforementioned methods suffer from low precision, poor adhesion, insufficient uniformity, and environmental pollution, making them unsuitable for high-precision background schlieren systems. Therefore, a novel background dot preparation technology that is high-precision, has high adhesion, is non-destructive to the substrate, and is environmentally friendly is urgently needed. Summary of the Invention

[0008] This invention addresses the problems of low precision, poor adhesion, insufficient uniformity, and environmental pollution in existing background point preparation techniques for reflective surfaces. It provides a method and a set of background points for high-precision background schlieren measurement experiments. By precisely matching the laser wavelength with the material absorption characteristics, it removes only the coating without damaging the inorganic non-metallic substrate, overcoming the shortcomings of traditional techniques and providing a reliable solution for high-precision optical measurement. Specifically, the laser engraving machine in this invention uses a 1064 nm infrared wavelength laser source. This is because common reflective coating materials (such as aluminum, silver, etc.) have extremely high absorption rates (>90%) for 1064 nm lasers, enabling efficient energy coupling and material removal. Furthermore, the inorganic non-metallic substrate has extremely low absorption rates (<5%) at this wavelength, ensuring that the laser energy is almost completely absorbed by the coating layer without causing thermal damage to the substrate. In addition, the 1064 nm wavelength belongs to the near-infrared band, which has better penetration and a smaller heat-affected zone compared to shorter wavelengths, minimizing the impact of thermal stress on optical components while ensuring processing efficiency. This wavelength selection based on the intrinsic absorption characteristics of materials is key to achieving high-precision engraving.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] In a first aspect, a method for preparing background points for high-precision background schlieren measurement experiments includes the following steps:

[0011] The surface of the background mirror is pretreated to be dust-free;

[0012] Background point distribution data is generated using the Poisson disk sampling algorithm and then imported into the laser device.

[0013] Under the protection of an inert gas atmosphere, laser engraving is performed using laser equipment. By removing the surface layer of a local area of ​​the reflector, the substrate of the reflector is exposed, thereby creating background dots.

[0014] Post-processing is performed on the engraved surface to remove processing residues and complete surface cleaning.

[0015] Optionally, the substrate of the reflector is an inorganic non-metallic material, and the surface is coated with an aluminum film or a silver film with a coating thickness of 0.5 to 5 micrometers.

[0016] Optionally, the background point satisfies:

[0017] The background dot size is 0.1–50 mm;

[0018] The minimum spacing between adjacent background points is 0.1 to 10 millimeters.

[0019] Optionally, the laser engraving parameters of the laser device include:

[0020] The laser power is 10–50 watts;

[0021] The pulse frequency is 20–100 kHz;

[0022] The scanning speed is 100–9000 mm / s.

[0023] Optionally, the laser device uses a laser source with an infrared wavelength of 1064 nanometers, which can be a solid-state laser, a fiber laser, or a carbon dioxide laser.

[0024] Optionally, the depth of a single background point formed by laser engraving is 0.5 to 5 micrometers.

[0025] Optionally, the background dots are formed by local engraving of the coating on the surface of the mirror, the engraved area exposes the substrate, and the steepness of the engraved edge is not less than 80 degrees.

[0026] Optionally, the inert gas is helium, and the gas flow rate is 5 to 20 liters per minute.

[0027] Optionally, the post-processing includes:

[0028] Use helium gas to blow away the molten slag from the surface of the mirror;

[0029] Clean with isopropanol for 5-10 minutes;

[0030] After cleaning, use compressed air to dry it.

[0031] In a second aspect, the present invention provides a background point for a high-precision background schlieren measurement experiment, which is prepared by the method described in the first aspect.

[0032] The beneficial effects of this invention are:

[0033] (1) High-precision control: This invention uses laser engraving technology, which can precisely control the size, density and morphology of the background dot pattern. The parameters in the laser engraving process (such as laser power, pulse frequency, scanning speed, etc.) can be finely adjusted to ensure that the size and distribution of the background dots meet the predetermined design requirements and satisfy the high requirements of measurement for the accuracy of the background dots.

[0034] (2) Excellent contrast and uniformity: The background dot pattern generated on the surface of the mirror by laser engraving has extremely high contrast and uniformity. This background dot pattern can significantly improve measurement accuracy, especially in optical measurement applications that require high contrast and consistency, and can provide stable test data.

[0035] (3) Strong adhesion and good stability: This invention exposes the substrate by partially engraving the coating on the surface of the reflector, forming a solid background dot structure. Compared with traditional spraying or deposition methods, the background dot pattern produced by laser engraving has stronger adhesion, ensuring that it is not easy to fall off or deform during long-term use.

[0036] (4) Green and environmentally friendly: Compared with chemical etching, the laser engraving method used in this invention does not involve the use of harmful chemicals or waste liquids, thus avoiding the pollution to the environment caused by chemical etching. In addition, the laser engraving process generates no pollutants, which meets the requirements of green and environmental protection.

[0037] (5) Wide applicability: This invention is applicable to a variety of mirror substrates, whether plane mirrors or curved mirrors, and can accurately prepare background dot patterns. Its wide applicability means that this method can not only be used in the field of background schlieren technology, but also extended to other high-precision optical measurement or surface dot pattern preparation applications. Attached Figure Description

[0038] Figure 1 This is an overall flowchart of a method for preparing background points for high-precision background schlieren measurement experiments according to the present invention.

[0039] Figure 2 This is a schematic diagram of the reflective surface of a concave mirror coated with an aluminum film.

[0040] Figure 3 This is a schematic diagram of the reverse side of a concave reflector.

[0041] Figure 4 The background point pattern generated by the Poisson disk sampling method.

[0042] Figure 5 The image shows the finished product and a magnified view of the background dot pattern after laser engraving.

[0043] Figure 6 This is a comparison chart of flame imaging results measured based on traditional background schlieren methods and high-precision background schlieren imaging results based on the concave reflector of this invention.

[0044] Figure 7 This is a comparison chart of flame displacement measured using the traditional background schlieren method and high-precision background schlieren displacement measured using the concave reflector of this invention. Detailed Implementation

[0045] The invention will now be described in further detail with reference to the accompanying drawings.

[0046] like Figure 1 As shown, this invention proposes a method for preparing background points and background points for high-precision background schlieren measurement experiments. The preparation method includes the following steps:

[0047] Step S1: Perform a dust-free pretreatment on the surface of the reflector used as the background.

[0048] First, based on the background schlieren experiment requirements, a concave mirror with a focal length of 750 mm and a diameter of 203 mm was prepared. The mirror is made of glass substrate with an aluminum film coating on its surface, the coating thickness being 2 micrometers. The reflective surface of the concave mirror coating is shown below. Figure 2 See the other side Figure 3 Place the concave mirror in a dust-free environment and clean it with isopropyl alcohol for 8 minutes. After cleaning, dry it with compressed air to ensure the mirror surface is free of dust and oil.

[0049] Step S2: Use the Poisson disk sampling algorithm to generate background point distribution data and import the data into the laser device.

[0050] Background point distribution data were generated using the Poisson disk sampling method. The diameter of the background points was 0.4 mm, and the average spacing between the background points was 0.1 mm (e.g., ...). Figure 4 (As shown). The generated data file is imported into the laser engraving system via computer, ready for engraving. The Poisson disk sampling method used here ensures the uniformity of the background point distribution while meeting the requirements of high-precision optical measurement.

[0051] Step S3: Under the protection of an inert gas atmosphere, laser engraving is performed using laser equipment. By removing the surface layer of a local area of ​​the reflector, the substrate of the reflector is exposed, thereby creating background dots.

[0052] Under an inert helium atmosphere, an infrared fiber laser with a wavelength of 1064 nm was used to engrave the surface of the mirror. The laser engraving parameters were set as follows:

[0053] Laser power: 30 watts;

[0054] Pulse frequency: 50 kHz;

[0055] Scanning speed: 3000 mm / s.

[0056] The laser beam is focused onto the surface of the mirror to form a fine background dot pattern. The laser engraving depth is about 2 micrometers, and a high-precision laser positioning system ensures that the engraved pattern is consistent with the predetermined design pattern.

[0057] In step S3, a 1064 nm infrared wavelength laser source is selected for the laser equipment. This is because common mirror coating materials (such as aluminum, silver, and other metals) have extremely high absorption rates (>90%) for 1064 nm wavelength lasers, enabling efficient energy coupling and material removal. Furthermore, the inorganic non-metallic substrate has extremely low absorption rates (<5%) at this wavelength, ensuring that the laser energy is almost completely absorbed by the coating layer without causing thermal damage to the substrate. In addition, the 1064 nm wavelength belongs to the near-infrared band, which has better penetration and a smaller heat-affected zone compared to shorter wavelengths, minimizing the impact of thermal stress on optical components while ensuring processing efficiency. This wavelength selection based on the intrinsic absorption characteristics of the material is key to achieving selective engraving.

[0058] Step S4: Perform post-processing on the engraved surface to remove processing residues and complete surface cleaning.

[0059] After laser engraving, a small amount of slag may remain on the surface of the mirror. Remove the slag using helium gas, then clean with isopropanol for 8 minutes. After cleaning, dry the mirror surface with compressed air to ensure it is clean and free of contaminants. At this point, a background dot pattern with high contrast and good uniformity has been successfully created on the mirror surface (see finished product and magnified view). Figure 5 The background point is formed by local engraving of the coating on the surface of the mirror, with the engraved area exposing the substrate and the steepness of the engraved edge not less than 80 degrees.

[0060] In the background schlieren experiment, the traditional background schlieren method was studied and compared. Figure 6 (a) and the concave reflector based on the present invention ( Figure 6 The imaging effect of (b)).

[0061] Will Figure 6 The displacement data in the image was calculated using the optical flow method to obtain... Figure 7 Displacement data. Figure 7 The results show that, compared to traditional background shading methods ( Figure 7 In (a)), the concave reflector of the present invention is used. Figure 7 (b) can more clearly display the flow structure and significantly improve measurement accuracy, fully verifying the practical value of the present invention.

[0062] This invention, by precisely matching the laser wavelength with the material absorption characteristics, ensures efficient removal of metal coatings while maintaining the inorganic non-metallic substrate without damage, solving the industry challenge of balancing processing precision and substrate protection using traditional methods. The background dot pattern prepared by this invention possesses excellent characteristics such as clear boundaries, high contrast, and no thermal stress, making it particularly suitable for high-precision optical measurement technology. This invention not only improves the quality of background dot pattern preparation but also significantly optimizes the environmental friendliness and applicability of the process, making it suitable for various complex optical components, including mirrors.

[0063] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A background point preparation method for high-precision background schlieren measurement experiments, characterized in that, The method comprises the following steps: applying a dust-free pretreatment to the mirror surface as a background; generating background point distribution data by using a Poisson disk sampling algorithm and importing the data into a laser device; under the protection of an inert gas atmosphere, performing laser engraving by using the laser device to remove the surface layer of the mirror in a local area, thereby exposing the base material of the mirror to prepare the background points; performing post-treatment on the engraved surface to remove processing residues and complete surface cleaning.

2. The method for preparing background points for high-precision background schlieren measurement experiments according to claim 1, characterized in that: The base material of the mirror is an inorganic non-metallic material, and the surface is plated with an aluminum film or a silver film, with a film thickness of 0.5-5 microns.

3. The method for preparing background points for high-precision background schlieren measurement experiments according to claim 1, characterized in that: The background points satisfy: the size of the background points is 0.1-50 mm; the minimum distance between adjacent background points is 0.1-10 mm.

4. The method for preparing background points for high-precision background schlieren measurement experiments according to claim 1, characterized in that: The laser engraving parameters of the laser device include: the laser power is 10-50 W; the pulse frequency is 20-100 kHz; the scanning speed is 100-9000 mm / s.

5. The method for preparing background points for high-precision background schlieren measurement experiments according to claim 1, characterized in that: The laser device uses a 1064 nm infrared wavelength laser source, which is a solid-state laser, a fiber laser or a carbon dioxide laser.

6. The method for preparing background points for high-precision background schlieren measurement experiments according to claim 1, characterized in that: The depth of a single background point formed by laser engraving is 0.5-5 microns.

7. The method for preparing background points for high-precision background schlieren measurement experiments according to claim 1, characterized in that: The formed background points are formed by local engraving of the mirror surface film, the engraved area exposes the base material, and the steepness of the engraved edge is not less than 80 degrees.

8. The method for preparing background points for high-precision background schlieren measurement experiments according to claim 1, characterized in that: The inert gas is helium, and the gas flow rate is 5-20 L / min.

9. The method for preparing background points for high-precision background schlieren measurement experiments according to claim 1, characterized in that: The post-treatment includes: blowing off the mirror surface slag using helium; cleaning with isopropyl alcohol, with a cleaning time of 5-10 min; blowing dry with compressed air after cleaning.

10. A background spot for high precision background schlieren measurement experiments, characterized in that Prepared by the method of any one of claims 1-9.

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