A surface inspection method for optical components

Abstract

This invention discloses a surface inspection method for optical components. It utilizes an opaque light source to illuminate the surface of the optical component under test in a dark field, and employs a lens and camera operating in the same wavelength band as the light source to acquire a dark field image. Defects on the surface under test are captured on this dark field image, achieving imaging inspection. This method effectively solves the technical problem of the influence of the lower surface during surface inspection of optical components. By utilizing the opacity of the material's wavelength band, the scattering effect of the lower surface is isolated, significantly simplifying surface defect detection and improving accuracy and efficiency. Furthermore, for optical components without opaque light, the lower surface of the sample to be tested is immersed in a liquid with a similar refractive index to suppress strong scattering from the lower surface, reducing interference from lower surface scattering on the upper surface inspection. Illumination and imaging can be completed using conventional visible light wavelengths.

Description

Technical Field

[0001] This invention relates to a surface inspection method for optical components, belonging to the field of surface inspection technology for optical components. Background Technology

[0002] Surface defects in optical components are an important indicator of their surface quality. They can cause scattering and energy loss of light beams incident on the surface of optical components. If the defect size is small, it can also produce more serious diffraction phenomena, such as film damage, diffraction fringes, energy absorption, and defect distortion, which can affect the efficiency and service life of optical components.

[0003] The detection of surface defects in optical components is a long-standing but poorly solved practical engineering problem. Its complexity stems from many factors, such as the depth of scratches, the directionality of scratch edges, and the roughness of defect edges. Another type of component surface defect detection difficulty arises from the surface condition of the component itself, such as complex surface shapes like prisms and the polishing condition of the lower surface.

[0004] There is a class of optical components whose surface defect detection is greatly affected by the lower surface, such as laser cavity mirrors with a frosted lower surface and spherical mirrors with a large curvature. Summary of the Invention

[0005] This invention provides a surface inspection method for optical components to solve the technical problem that the detection of surface defects in optical components with a frosted or similar lower surface is severely affected by the lower surface.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A surface inspection method for optical components involves using an opaque light source to illuminate the surface of the optical component under test in a dark field, and using a lens and camera that operate in the same wavelength band as the light source to acquire dark field images. Defects on the surface under test are captured on the dark field images, thus achieving imaging inspection.

[0008] For example, bright spots or bright stripes in a photo that are significantly brighter than the background indicate pitting or scratches on the surface being tested.

[0009] The above-mentioned method of using an opaque light source to illuminate the surface of the optical component under test in a dark field can limit the light to the surface directly illuminated by the light. The light will not penetrate into the material or reach the lower surface of the optical component, eliminating possible interference from light reflection, refraction, and scattering from outside the directly illuminated surface. This significantly simplifies the detection of surface defects and makes the test accurate and efficient.

[0010] The above method can be used for, but is not limited to, the detection of the following optical components: 1) transparent in the visible and near-infrared bands, but opaque in the ultraviolet band, such as ordinary crown optical glass components; 2) transparent in the visible, ultraviolet and near-infrared bands, but opaque in the mid-infrared and far-infrared bands, such as quartz glass optical components; 3) transparent in the infrared band, but opaque in the visible and ultraviolet bands, such as infrared glass components. Infrared glass is another very important type of glass material, such as various types of chalcogenide glass.

[0011] For optical components that are opaque to ultraviolet light, ultraviolet light sources are used for illumination, along with lenses and cameras that operate in the ultraviolet band, to image and detect defects on the upper surface of the glass. Since the material itself is opaque to ultraviolet light, the ultraviolet light irradiating the upper surface of the glass product will not be able to penetrate the glass material to reach the lower surface of the glass product, thus eliminating scattering interference from the lower surface. In this way, interference from the lower surface of the glass product can be eliminated, allowing focus on the detection of the upper surface of the glass.

[0012] For optical components that are opaque in the mid-infrared and far-infrared bands, mid-infrared or far-infrared light sources are used for illumination, along with lenses and cameras operating in the mid-infrared or far-infrared bands, to image and detect defects on the upper surface of the glass. Similarly, since the material itself is opaque to mid-infrared or far-infrared light, the mid-infrared or far-infrared light irradiating the upper surface of the glass product cannot penetrate the glass material to reach the lower surface of the glass product, thus eliminating scattering interference from the lower surface. In this way, interference from the lower surface of the glass product can be eliminated, allowing focus on the detection of the upper surface of the glass.

[0013] For optical components that are opaque in the visible and ultraviolet light bands, visible or ultraviolet light sources are used for illumination, along with lenses and cameras that operate in the visible or ultraviolet light bands, to image and detect defects on the upper surface of the glass. Similarly, since the material itself is opaque in the ultraviolet or visible light bands, ultraviolet and / or visible light irradiating the upper surface of a glass product will not be able to penetrate the glass material to reach the lower surface of the glass product, thus eliminating scattering interference from the lower surface. In this way, interference from the lower surface of the glass product can be eliminated, allowing focus on the detection of the upper surface of the glass.

[0014] Detection using ultraviolet and infrared light bands is more expensive than detection using visible light bands.

[0015] A detection device for implementing the above-mentioned detection method includes: a support, a sample clamp, a first crossbar, a ring light source, a second crossbar, a camera, and a lens; the support includes a base and a longitudinal support rod vertically disposed on the base; the sample clamp is disposed on the base; the ring light source is connected to the longitudinal support rod via the first crossbar, the lens is connected to the camera, the camera is connected to the longitudinal support rod via the second crossbar and the lens faces downward; the ring light source is located between the sample clamp and the lens.

[0016] To facilitate adjustment of the lateral and longitudinal positions of the ring light source, camera, and lens, both the first and second crossbars are telescopic structures, and their heights on the longitudinal support rods are adjustable.

[0017] The length and height of this application are both adjustable, and existing structures with relevant functions can be directly adopted. For example, it can be a double-layer sleeve structure that is relatively fixed by bolts, or an existing automatic control structure. This application does not have any special improvements compared to the previous one, so it will not be described in detail.

[0018] For easy replacement, the camera is detachably connected to the second crossbar; the ring light source is detachably connected to the first crossbar. The detachable structure can be an existing plug-in structure, a threaded connection structure, or a clamp structure, etc.

[0019] During testing, the optical component is fixed to the sample fixture with the surface to be tested facing upwards. A ring light source illuminates the surface to be tested at an angle of 30 to 75 degrees to provide dark field illumination, meaning that the illumination source will not be directly reflected from the sample surface into the camera lens.

[0020] The aforementioned ring light source, camera, and lens all operate in wavelengths that are opaque to optical components, such as the ultraviolet, infrared, or visible light bands, and the ring light source, camera, and lens operate in the same wavelength band.

[0021] For optical components without opaque light, the side opposite to the surface to be tested is immersed in a liquid with a refractive index difference within ±0.05. A visible light source is used to illuminate the surface under test in a dark field, and a lens and camera that work in the visible light band are used to acquire dark field images. Defects on the surface under test are captured on the dark field images, thus achieving imaging detection.

[0022] This can suppress strong scattering between the opposite surfaces of the test surface, reducing interference between the opposite surfaces of the test surface and the test surface itself; while the light source, camera and lens can still work in the conventional visible light band. Under dark field illumination, the defects on the upper surface of the part are captured in the image, realizing imaging detection.

[0023] Of course, the above liquid immersion method can also be used for optical components that are opaque. The above method is simple, easy to operate, and low in cost.

[0024] If the optical component is polished on one side, with the upper surface being polished and the lower surface being frosted, the frosted surface is immersed in a liquid with a refractive index difference within ±0.05 of the optical component to suppress scattering from the lower surface and reduce the interference of scattering from the lower surface on the detection of the upper surface. The surface to be tested is illuminated in a dark field using a visible light source, and a lens and camera working in the visible light band are used to acquire a dark field image. The defects on the surface to be tested are captured on the dark field image, thus achieving imaging detection.

[0025] The difficulty in detecting surface defects on single-sided polished optical components lies in the fact that the illumination source scatters very strongly on the frosted surface, which greatly increases the background intensity of the image, thus affecting the extraction and interpretation of optical surface defect signals and making defect detection difficult.

[0026] The above method involves immersing the lower surface of the frosted surface in a liquid with a similar refractive index to suppress scattering from the frosted surface, thereby reducing the scattering background, improving the relative signal-to-noise ratio of the target signal, and significantly simplifying the detection of defects on the polished surface.

[0027] A detection device for implementing the above-mentioned detection method includes a support, a liquid collection tray, legs, a sample clamp, a third crossbar, a ring light source, a first crossbar, a camera, a lens, and a second crossbar. The support includes a base and a longitudinal support rod vertically mounted on the base. The liquid collection tray is mounted on the base via the legs. The sample clamp is connected to the longitudinal support rod via the third crossbar. The ring light source is connected to the longitudinal support rod via the first crossbar. The lens is connected to the camera. The camera is connected to the longitudinal support rod via the second crossbar, with the lens pointing downwards. The ring light source is located between the sample clamp and the lens.

[0028] The bottom of the liquid-filled tray is made of the same material as the optical component being tested. The sidewalls of the liquid-filled tray should not affect light scattering. If the diameter of the liquid-filled tray is large enough to not affect the measurement, then the material of the sidewalls is not required.

[0029] To facilitate the adjustment of the lateral and longitudinal positions of optical components, ring light source, camera, and lens, the first, second, and third crossbars are all telescopic structures, and their heights on the longitudinal support rods are all adjustable.

[0030] The aforementioned ring light source, camera, and lens all operate in the visible light band.

[0031] During testing, a liquid with a refractive index within ±0.05 of the optical component is placed in a liquid tray. The optical component is fixed to the sample fixture with the test surface facing upwards. The lower surface of the optical component is completely immersed in the liquid, while the test surface (upper surface) is completely exposed. A ring light source illuminates the test surface at an angle of 30 to 75° for dark field illumination, meaning that the illumination source will not be directly reflected from the sample surface into the camera lens.

[0032] The refractive index of the original liquid used in preparing the soaking solution in this application can be found at: https: / / www.engineeringtoolbox.com / refractive-index-d_1264.html.

[0033] Any techniques not mentioned in this invention are based on existing technologies.

[0034] The surface inspection method for optical components of this invention effectively solves the technical problem of the influence of the lower surface during the surface inspection of optical components. It utilizes the opaque wavelength of the material to isolate the scattering effect of the lower surface, which significantly simplifies the surface defect detection and makes the test accurate and efficient. Furthermore, for optical components without opaque light, the lower surface of the sample to be tested is immersed in a liquid with a similar refractive index to suppress strong scattering from the lower surface, reduce the interference of the lower surface scattering on the detection of the upper surface, and the conventional visible light wavelength can be used for illumination and imaging. Attached Figure Description

[0035] Figure 1 The transparency of crown optical glass components to different light levels;

[0036] Figure 2 The transparency of quartz glass parts to different light levels;

[0037] Figure 3 The transparency of infrared glass components to different light levels;

[0038] Figure 4 A schematic diagram of a detection device that utilizes opaque light;

[0039] Figure 5 A schematic diagram of a liquid detection device;

[0040] Figure 6 This is a dark-field photograph from Example 1;

[0041] Figure 7 This is a dark-field photograph from Example 2;

[0042] Figure 8 This is a dark-field photograph from Example 3;

[0043] In the figure, 1 is an optical component, 2 is a base, 3 is a longitudinal support rod, 4 is a sample clamp, 5 is the first crossbar, 6 is a ring light source, 7 is the second crossbar, 8 is a camera, 9 is a lens, 10 is the third crossbar, 11 is a liquid tray, and 12 is a support leg; a is ultraviolet light, b is visible or infrared light, c is mid-infrared or far-infrared light, d is ultraviolet or visible light, and e is infrared light. Detailed Implementation

[0044] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0045] The directional terms used in this application, such as "vertical," "horizontal," "up," "down," "top," and "bottom," are based on the relative orientation or positional relationship shown in the attached drawings and should not be construed as absolute limitations on this application.

[0046] Example 1

[0047] like Figure 1 As shown, the optical component to be tested is a common crown glass component, which is transparent to visible and near-infrared light, but not transparent to ultraviolet light, and is polished on one side, with the upper surface being polished and the lower surface being frosted.

[0048] like Figure 4 As shown, the detection device includes a support, a sample clamp, a first crossbar, a ring light source, a second crossbar, a camera, and a lens. The support includes a base and a longitudinal support rod vertically mounted on the base. The sample clamp is mounted on the base. The ring light source is detachably connected to the longitudinal support rod via the first crossbar, and can be replaced with a ring light source that meets the requirements. The lens is connected to the camera, which is detachably connected to the longitudinal support rod via the second crossbar with the lens facing downwards. A camera and lens that meet the requirements can be replaced with a camera and lens that meet the requirements. The ring light source is located between the sample clamp and the lens. Both the first and second crossbars are telescopic structures, and their heights on the longitudinal support rod are adjustable, allowing for adjustment of the lateral and longitudinal positions of the ring light source, camera, and lens as needed.

[0049] Crown optical glass components are opaque in the ultraviolet band shorter than 310nm. In this example, a 275nm UVC LED is selected and manufactured into a ring light source. The polished surface of the optical component (the surface to be tested) is fixed upwards on the sample holder. In this example, the sample holder is a groove on the base that conforms to the shape of the optical component. The depth of the groove is less than the thickness of the optical component. During testing, the optical component to be tested is placed in the groove with its side facing upwards. The structure is simple, easy to operate, and has good stability. Then, a 60-degree illumination angle (in practice, 30 degrees, 45 degrees, 75 degrees, etc.) is used to illuminate the surface to be tested in a dark field, meaning that the illumination source will not be directly reflected from the sample surface into the camera lens. Since the light emitted by this ring light source does not pass through this optical component, the illumination light will not reach the lower surface and will not be affected by the scattering effect of the lower surface roughness. The camera and lens used are a Sony XC-EU500 ultraviolet camera operating in the ultraviolet band and a Pinterest UV1628CM quartz lens. Defects such as pits and scratches on the surface being tested scatter the UVC light throughout space, allowing it to enter the lens and be imaged in the camera, forming a dark-field photograph of the surface defects. Figure 6 As shown, the bright spots and bright stripes in the photo that are significantly brighter than the background are the pits and scratches on the tested surface, which fully meet the national standard requirements of 5µm accuracy and 0.1µm precision.

[0050] Example 2

[0051] like Figure 2 As shown, the optical component to be tested is a quartz glass optical component, which is transparent to visible, ultraviolet, and near-infrared light, but opaque to mid-infrared and far-infrared light, and is polished on one side only, with a polished upper surface and a frosted lower surface. The testing device used is the same as in Example 1;

[0052] Quartz glass products are opaque in the infrared band greater than 4.5µm. In this example, a mid-wavelength LED light source with a wavelength longer than 4.5µm is selected: quantum cascaded LEDs are manufactured into a ring light source. Then, a 45-degree illumination angle (in practice, 30 degrees, 60 degrees, 75 degrees, etc.) is used to illuminate the sample in a dark field, meaning the illumination source will not be directly reflected from the sample surface into the camera lens. Since the light emitted by this source does not pass through this optical component, the illumination light will not reach the lower surface and will not be affected by the scattering effect of the lower surface roughness. In this example, the camera that can be selected is the MER2-502-79U3MPOL camera from Daheng Imaging, and the lens is the LeTV LTS-TC08110-5MP lens. Four Xenics models can be used, operating in the mid-infrared band: Tigris 640InSb, Tigris 640InSb BB, Tigris 640MCT, and Tigris 640MCT BB. Three lenses can be used: the RS-L305 / 40MW, RS-L305 / 55MW, and RS-L460IR from Changchun Ruishi. Of course, the choice of camera and lens is not limited to these models; many other combinations can be selected based on cost-effectiveness requirements. Defects such as pitting and scratches on the surface being tested will scatter the illuminated infrared light throughout space, entering the lens and forming an image in the camera, creating a dark-field photograph of the surface defect. Figure 7 The photos were taken with a Tigris 640InSb camera and an RS-L305 / 40MW lens. The bright spots and bright stripes in the photos that are significantly brighter than the background are the pits and scratches on the surface being inspected. The accuracy of the surface is 5µm and the precision is 0.1µm, which fully meet the national standard requirements.

[0053] Example 3

[0054] The optical component to be tested is made of fused silica with a refractive index of 1.46 and is polished on one side only, with the upper surface being polished and the lower surface being frosted.

[0055] like Figure 5As shown, the testing device includes a support, a liquid tray, feet, a sample clamp, a third crossbar, a ring light source, a first crossbar, a camera, a lens, and a second crossbar. The support includes a base and a longitudinal support rod vertically mounted on the base. The liquid tray is supported on the base by the feet, which can be directly positioned around the bottom perimeter of the liquid tray to keep the bottom of the tray away from the base and eliminate interference from light scattering from the base. The bottom of the liquid tray is made of fused silica material, and the inner diameter of the liquid tray is more than 1.5 times that of the optical component under test. During testing, the optical component under test is immersed in the liquid. The liquid-filled tray is positioned at the center, and the sidewalls of the tray do not affect light scattering. The sample holder is connected to the longitudinal support rod via a third crossbar. The ring light source is connected to the longitudinal support rod via a first crossbar. The lens is connected to the camera, which is connected to the longitudinal support rod via a second crossbar with the lens pointing downwards. The ring light source is located between the sample holder and the lens. The first, second, and third crossbars are all telescopic structures, and their heights on the longitudinal support rod are adjustable. This allows for adjustment of the lateral and longitudinal positions of the optical components, ring light source, camera, and lens as needed. The ring light source, camera, and lens all operate in the visible light band. In this example, a LeTV LTS-2HPR250-R / GBW ring light source, a Daheng Imaging MER2-502-79U3M POL camera, and a LeTV LTS-TC08110-5MP lens are used.

[0056] like Figure 5 As shown, the optical component is clamped on the sample holder with the polished surface on top and the frosted surface on the bottom. In this example, the sample holder is a clamp that can stably hold the side of the optical component. The structure is similar to a test tube clamp, except that the diameter that can be clamped is larger than that of a test tube clamp and is adapted to the optical component. Alternatively, a clamp structure can be used. The sample holder is relatively thin, less than 1 / 6 of the thickness of the optical component, so that it does not affect the immersion of the lower surface or the testing of the upper surface. The liquid tray contains carbon tetrachloride (CCl4, refractive index 1.46) to a depth of about 10 mm. The frosted surface of the optical component is immersed in the carbon tetrachloride (CCl4) liquid to a depth of 2-5 mm. The polished surface (upper surface) of the optical component is completely exposed in the liquid. Since the refractive index of the carbon tetrachloride (CCl4) liquid is basically the same as that of the fused silica optical component, the frosted surface (lower surface) immersed in the liquid is basically invisible, that is, there is basically no light scattered from the frosted surface (lower surface). At this point, the part being inspected, the carbon tetrachloride (CCl4) liquid, and the bottom of the container can be treated as a single sample. A ring light source illuminates the surface under test at a 60-degree angle (in practice, 30 degrees, 45 degrees, 75 degrees, etc.) for dark-field illumination. Defects on the surface of the part are captured in dark-field images, such as... Figure 8As shown, the bright spots and bright stripes in the photo that are significantly brighter than the background are the pits and scratches on the tested surface, which fully meet the national standard requirements of 5µm accuracy and 0.1µm precision.

Claims

1. A method for surface inspection of optical components, characterized in that: The optical component is made of fused silica and is polished on one side. The upper surface is polished and the lower surface is frosted. The frosted surface is immersed in a liquid with a refractive index difference of ±0.05 with the optical component to suppress scattering from the lower surface and reduce the interference of scattering from the lower surface on the detection of the upper surface. The surface to be tested is illuminated in the dark field using a light source in the visible light band, and a lens and camera that work in the visible light band are used to acquire dark field images. The defects on the surface to be tested are captured on the dark field images to achieve imaging detection. The detection device includes a support, a liquid collection tray, legs, a sample clamp, a third crossbar, a ring light source, a first crossbar, a camera, a lens, and a second crossbar. The support includes a base and a longitudinal support rod vertically mounted on the base. The liquid collection tray is mounted on the base via the legs. The sample clamp is connected to the longitudinal support rod via the third crossbar. The ring light source is connected to the longitudinal support rod via the first crossbar. The lens is connected to the camera. The camera is connected to the longitudinal support rod via the second crossbar, with the lens pointing downwards. The ring light source is located between the sample clamp and the lens. The support feet are directly placed around the bottom of the liquid tray, keeping the bottom of the liquid tray away from the base to eliminate interference from light scattering from the base; the inner diameter of the liquid tray is more than 1.5 times the size of the optical component under test. During testing, the optical component under test is immersed in the center of the liquid tray, and the sidewalls of the liquid tray will not affect light scattering. The frosted surface of the optical component is immersed in the liquid to a depth of 2-5 mm; the sample clamp is a clamp structure; The bottom of the liquid tray is made of the same material as the optical component under test; the first, second, and third crossbars are all telescopic structures, and their heights on the longitudinal support rods are adjustable; the ring light source, camera, and lens all operate in the visible light band; the liquid tray contains liquid with a refractive index difference of ±0.05 from that of the optical component; the optical component is fixed to the sample fixture with the test surface facing upwards, the lower surface of the optical component is completely immersed in the liquid, and the upper surface of the optical component is completely exposed to the liquid; the ring light source illuminates the test surface at an angle of 30–75° for dark field illumination, and the defects on the upper surface of the component are captured in dark field images.

2. The surface inspection method for optical components as described in claim 1, characterized in that: The ring light source, camera, and lens operate in the visible light band.

Images