A multi-field imaging synthetic scattered beam profiler

Abstract

The present invention discloses a multi-field imaging synthetic scattered beam profiler, comprising a first camera, a first plane reflector for dividing the field of view, and a second plane reflector. The scattered light of a laser beam in a medium is connected to the incident end of the second plane reflector via the emitting end of the first plane reflector. The reflecting end of the second plane reflector is provided with a second camera for capturing the full beam range between the incident and exit apertures. The first camera is disposed behind the first plane reflector for capturing the scattered light of the imaged laser beam. The first and second cameras are spliced ​​together to obtain a complete beam image for detecting the beam quality of the measured laser beam. By employing a splicing imaging method using lenses of different magnifications, the present invention obtains beam information over a large field of view, ensuring high-resolution measurement of the beam waist position, significantly improving the accuracy of laser beam quality parameter measurements and expanding the measurable range of the scattered beam profiler.

Description

Technical Field

[0001] The present invention relates to the technical field of imaging synthesis scattering analysis, and in particular to a multi-field imaging synthesis scattering beam analyzer. Background Art

[0002] Lasers are widely used in numerous fields, including machining and additive manufacturing. Laser beam quality, a key indicator of laser performance, plays a decisive role in determining processing results. Currently, laser beam profilers are a common tool for measuring beam quality. However, as laser power density continues to increase, direct-irradiation measurement analyzers are unable to meet the demands of high-power laser beam analysis due to the risk of damage from high-power lasers.

[0003] In this context, a scattering beam profiler that measures the Rayleigh scattering image of the laser beam to obtain beam quality information has emerged. However, this type of existing technology has obvious defects. According to the ISO test standard, to accurately fit the beam, it is necessary to measure the beam information of at least three Rayleigh lengths from the beam waist position. The Rayleigh length is proportional to the square of the beam waist radius. As the beam waist increases, the Rayleigh length will increase rapidly, which requires the imaging to have a large field of view. However, a single lens cannot take into account both high resolution and a large imaging field of view when imaging. If a large imaging field of view is selected, the resolution of the beam waist measurement will be reduced. It is difficult to balance the two, resulting in the existing scattering beam profiler being able to only measure beams with a large waist and M 2 The large laser beam cannot meet the diverse measurement requirements. Therefore, a multi-field imaging synthetic scattered beam profiler is needed. Summary of the Invention

[0004] The object of the present invention is to provide a multi-field imaging synthetic scattered light beam analyzer.

[0005] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0006] The present invention includes a first camera, a first plane reflector and a second plane reflector for dividing the field of view. The scattered light of the laser beam is connected to the incident end of the second plane reflector through the emission end of the first plane reflector. The reflection end of the second plane reflector is provided with a second camera for collecting the full beam range between the incident and exit apertures. The first camera is arranged behind the first plane reflector for collecting the scattered light of the imaging laser beam. After splicing the first camera and the second camera, a complete beam image is obtained to detect the beam quality of the measured laser beam.

[0007] Furthermore, the size of the first plane reflector matches the imaging field of view of the second camera, and the reflected portion of the first plane reflector meets the imaging requirement of the second camera.

[0008] Furthermore, the lens of the first camera is a low-magnification telecentric lens, the lens of the second camera is a high-magnification telecentric lens, and the lens magnification ratio of the first camera and the second camera is 1:5-25.

[0009] Furthermore, the method of obtaining a complete light beam image by splicing the first camera and the second camera includes collecting, by the first camera, an imaging dark area image formed by the occlusion of the first plane reflector, the dark field center of the imaging dark area image coincides with the imaging center of the second camera, and the image center point is used as the splicing coincidence point. The complete light beam image is obtained by processing and stitching the image data according to the magnification of the two lenses of the first camera and the second camera through synchronous imaging.

[0010] Furthermore, the field of view of the lens of the first camera is greater than the field of view of the lens of the second camera.

[0011] Furthermore, the first plane reflector is coaxial with the lens of the first camera, and the first plane reflector forms a uniform occlusion at the center of the lens field of view of the first camera. After the occlusion imaging, a black background is formed as an identification feature of the field of view stitching.

[0012] Furthermore, the first reflector is a plane reflector, a right-angle prism or a transflective mirror.

[0013] On the other hand, a multi-field imaging synthetic scattered beam analysis method is used to realize the functions of the multi-field imaging synthetic scattered beam analyzer, comprising:

[0014] Align the laser beam through the incident aperture and the exit aperture so that the center of the beam is located at the center of the camera's field of view;

[0015] A dual-lens imaging system is used. The first lens is used to collect the scattered light image of the entire beam range between the incident and exit apertures that is not blocked by the reflector 1; the second lens is used to collect the scattered light image at the center of the beam that is reflected twice by the reflector.

[0016] The images captured by the first lens and the second lens are stitched together, with the center of the dark field formed by the reflector occlusion in the first lens image and the center of the image of the second lens being the overlapped point, and the complete beam image is obtained by synchronous imaging combined with the lens magnification processing;

[0017] The Canny operator is used to identify the maximum gradient point as the boundary point, determine the boundaries on both sides of the beam, calculate the boundary spacing, and the point with the minimum spacing is the estimated position of the beam waist.

[0018] Furthermore, Gaussian smoothing is performed on the spliced ​​image, and based on the grayscale values ​​of adjacent pixels conforming to the Gaussian distribution characteristics, new pixel grayscale values ​​are calculated to reduce noise.

[0019] The beneficial effects of the present invention are:

[0020] The present invention is a multi-field imaging synthetic scattered beam profiler. Compared with the prior art, the present invention has the following technical effects:

[0021] The present invention utilizes a stitched imaging method using lenses of different magnifications. A low-magnification telecentric lens can fully image the beam across the entire field of view, while a high-magnification telecentric lens can provide micron-level spatial resolution at the laser beam waist. This design enables the acquisition of beam information across a large field of view while ensuring high-resolution measurement of the beam waist position. Compared to existing technologies, this significantly improves the accuracy of laser beam quality parameter measurements, particularly in the measurement of beam waist size and position. This more accurately reflects the actual characteristics of the beam, significantly expanding the measurable range of scattered beam profilers and meeting the needs of laser beam quality analysis in a wider range of scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a structural diagram of a multi-field imaging synthetic scattered beam profiler of the present invention;

[0023] Figure 2 This is a structural diagram of a partially transmissive lens of a multi-field imaging synthetic scattered beam profiler of the present invention;

[0024] Figure 3 This is a schematic diagram of a right-angle prism reflection structure of an embodiment of a multi-field imaging synthetic scattered beam profiler of the present invention;

[0025] Figure 4 This is a schematic diagram of a structure in which a reflector is placed at a non-45° angle, according to an embodiment of the present invention, in which a multi-field imaging synthetic scattered light beam profiler is used. DETAILED DESCRIPTION

[0026] The present invention will be further described below through specific examples. The illustrative examples and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0027] It should be explained that high-power laser refers to lasers with an output power of more than 1 kW, laser beam quality is an evaluation index of laser transmission characteristics, and beam parameter product is the product of the laser beam waist and the divergence angle, which is used to characterize the laser beam quality. 2 It is expressed as the ratio of the product of the optical parameters of the actual beam to the product of the optical parameters of the ideal fundamental mode Gaussian beam, and is often used to characterize laser beam quality.

[0028] like Figure 1 and 2The present invention includes a first plane reflector, a second plane reflector, a first imaging lens, a second imaging lens, a first imaging camera, and a second imaging camera for dividing the field of view; the first imaging lens is a low-magnification lens, the second imaging lens is a high-magnification lens, the lens of the first camera is a low-magnification telecentric lens, and the lens of the second camera is a high-magnification telecentric lens.

[0029] The first camera captures and identifies the dark area image formed by the reflector obstruction at the center. This dark area image is aligned with the center of the second camera image. Using the image center as the overlap point, the first and second cameras simultaneously image and process the image data to obtain a complete beam image.

[0030] Before the device is used, the laser beam is aligned through the incident aperture and the exit aperture to ensure that the center of the beam is located in the middle of the entire device. When measuring, the laser beam passes through the device and generates a scattered signal. The scattered light at the center of the laser beam is reflected twice by reflector 1 and reflector 2 and enters lens 2, and is captured and imaged in camera 2. The scattered light of the laser beam in the full beam range between the incident and exit apertures, which is not blocked by reflector 1, is collected by lens 1 and imaged in camera 1. Lens 1 uses a low-magnification telecentric lens, such as 0.3X or 0.1X magnification, to achieve complete imaging of the light beam in the entire field of view. When selecting, the required field of view width is calculated in combination with the camera detector size. Assuming that the maximum field of view width is HOF and the detector width is HOC, the magnification X1 of lens 1 is calculated as follows:

[0031]

[0032] Lens 2 uses a high-magnification telecentric lens, such as 1X or 2X magnification, to achieve micron-level spatial resolution at the laser beam waist. When selecting, calculate based on the required spatial resolution. Assuming the maximum spatial resolution is ROF and the detector pixel size is SOC, the magnification of Lens 2, X2, is calculated as follows:

[0033]

[0034] Data acquisition is controlled by a host computer. The host computer software stitches the captured images. During image stitching, the dark area at the center of the image captured by camera 1 is identified. This dark area is obscured by the reflector, and its center coincides with the center of the image captured by camera 2. Using the image center as the stitching overlap point, the image data is processed and stitched based on the magnification of the two lenses to obtain a complete beam image. This image has high resolution at the beam waist and a large imaging field of view in the beam propagation direction, expanding the measurable range of the scattered beam profiler.

[0035] When selecting a lens, the primary consideration is magnification, with achievable resolution being a secondary factor. The lens's imaging resolution should be aligned with the detector. Lens resolution is measured using the resolution target test results, with an MTF curve of 40% being the standard. The minimum imaging width of a lens should be at least twice the detector pixel size. At this point, the image reaches the Rayleigh limit, and the camera can just resolve the lens image. For lower-resolution lenses, the imaging width should ideally not exceed five times the detector pixel size to avoid insufficient resolution. For example, if the camera's detector is a Sony IMX183 with a 2.4-micron pixel size, the optimal resolution should be 4.8 microns. In this case, the lens's corresponding resolution target test result is 6 groups, number 5. Relaxing the lens's resolution requirement to five times the pixel size results in a 5-group, number 5 result. The imaging field width is already determined once the camera detector and lens magnification are selected and does not need to be a separate selection criterion. It suffices for the lens's imaging range to cover the entire detector surface. For example, the IMX183 outputs an image with a diagonal length of 15.86 mm and a 3:2 image ratio. Selecting a 1x lens yields an imaging field of view of 13.19 mm × 8.79 mm. Selecting a 0.3x lens expands the field of view by a factor of three. For a CMOS chip with a fixed 4:3 ratio, the field of view is shown in Table 1:

[0036] Table 1 Comparison of CMOS field of view for different lens sizes

[0037]

[0038] From this, we can see that as the lens magnification changes, its field of view changes accordingly. For a lens with a higher magnification, its field of view is always smaller, and for a lens with a lower magnification, a large field of view can always be obtained.

[0039] Because lens resolution varies at the same magnification, this article discusses the impact of lens resolution on image resolution, focusing on the theoretically high-resolution lens at each magnification. Assuming that lens 1 is a 0.3x HD lens and lens 2 is a 1x HD lens, a commercially available 0.3x HD lens can typically resolve a standard target line width of 5 / 2, or 13.92 microns. A commercially available 1x HD lens can resolve a standard target line width of 7 / 1, or 3.91 microns. When imaging the laser beam waist, the actual resolution is approximately 1 / 4 of this resolution due to diffraction effects and other issues. This shows that high-magnification lenses offer superior resolution advantages for the laser beam waist.

[0040] After the reflector is placed, an unilluminated black area will appear in the image. Calculate the center of this black area. If the center of the black area coincides with the center of the detector itself, the spatial positioning of the occlusion is accurate. Calculate the grayscale value of the black occluded area. If the grayscale of the occluded area borders is close, with a deviation of no more than 5%, the occlusion is uniform and no adjustment is required. If there is a large local deviation, fine-tune the mirror angle to achieve more uniform occlusion.

[0041] The shape of the dark area is the projection shape of the reflector, and the image taken by the other camera matches the reflector. The centers of the two coincide and the boundaries are close, so stitching is performed based on this.

[0042] Laser wavelengths primarily fall within the visible light range and are related to lens coatings and camera response. Replacing the camera with an infrared-responsive camera and lens with an infrared lens can detect infrared laser beam quality. Tests were conducted at humidity levels of 10% to 20% and temperatures between 20°C and 25°C, yielding similar results. Theoretically, temperature has a smaller impact, while humidity has a greater influence. In more humid environments, the scattering signal is stronger, making it easier to detect.

[0043] like Figure 3 As shown, the first reflector uses a right-angle prism to divide the field of view, replacing the original total reflection plane mirror. Other similar prisms with reflection functions can also be considered as this type of alternative solution. Figure 4 As shown, the reflected light path is tilted to adjust the field of view of the reflection system.

[0044] Perform Gaussian smoothing on the collected images;

[0045] The Canny operator is used to identify the beam boundary, and then the narrowest position of the boundary is obtained to obtain the estimated position of the beam waist.

[0046] For the smoothed image, calculate its grayscale gradient: perform a calculation test on each pixel and select the point with the maximum gradient as the boundary point. After obtaining the two boundaries of the beam, calculate the distance between the boundaries. The location with the minimum distance between the boundaries is the beam waist.

[0047] Take a column of pixels from the image, construct a propagation parameter expression, and calculate the accurate Rayleigh length and beam divergence angle by fitting multiple beam cross sections.

[0048] For the beam image of the scattering measurement using dual-axis measurement, the Canny operator will identify the beam boundary, and then find the narrowest position of the boundary to obtain the estimated position of the beam waist. Before the calculation, considering that the image has a certain amount of noise, it needs to be Gaussian smoothed. The gray value of a point in the image can be expressed as a function of the coordinates of the point , take the adjacent pixels for each pixel, assuming that the grayscale values ​​of adjacent pixels should meet the standard deviation Gaussian distribution, then the image can be Gaussian smoothed, and the newly obtained pixel gray value for:

[0049]

[0050] For the smoothed image, its grayscale gradient is calculated. The amplitude and direction are obtained from the following relationship:

[0051] The magnitude of the grayscale gradient G is determined by the horizontal gradient G x and vertical gradient G y The amplitude of is found:

[0052]

[0053] The gradient direction of the grayscale gradient θ G We can also obtain:

[0054]

[0055] Each pixel is calculated and tested, and the point with the maximum gradient is selected as the boundary point. After the two boundaries of the beam are obtained, the distance between the boundaries is calculated. The position with the smallest distance between the boundaries is the location of the beam waist.

[0056] Take a column of pixels from the image, whose horizontal coordinate is z, and the beam diameter obtained by Gaussian fitting is d. Then the two can be expressed by the propagation parameters a, b, and c as follows:

[0057]

[0058] By fitting multiple beam cross sections, the horizontal coordinate z and its corresponding beam diameter d are obtained respectively. At least 5 sets of data points are taken within 1 Rayleigh length on both sides of the beam waist, and at least 5 sets of data points are taken within 2 to 3 Rayleigh lengths on both sides of the beam waist. These data are fitted with the formula to obtain the propagation parameters a, b, and c, and then the accurate Rayleigh length and M can be calculated. 2 for:

[0059]

[0060]

[0061] For a laser with a certain output linewidth, here The value is based on the central wavelength. , the divergence angle of the beam for:

[0062]

[0063]

[0064] Considering that existing scattered beam profilers offer both single-axis and dual-axis measurement options, the present invention is equally applicable to both. This solution can be employed simultaneously with dual-axis measurement to improve beam waist resolution. For highly symmetric beams, this solution can also be employed for only one axis, while the other axis remains unchanged.

[0065] To perform a measurement, first place the device on a level work surface and perform a rough alignment based on the laser's intended path. Turn on the laser indicator light and perform detailed alignment to ensure the laser passes through the center of the device's entry and exit apertures. Place a beam stop or perform other safety measures on the outgoing laser. For lasers with a measurable beam waist, adjust the beam waist to be near the center of the camera's field of view. If the beam waist is difficult to adjust to the center of the camera's field of view, add a focusing lens before the light enters the device and select an appropriate focal length so that the focused beam waist is centered in the camera's field of view. After adjusting the optical path, turn on the camera and enter measurement mode. Turn on the laser and adjust its output power so that it is within the measurement range. Verify on the camera acquisition interface that the beam aligns with the field of view and is well focused before data acquisition can begin. After image data acquisition, the software performs appropriate processing to determine information such as the beam quality of the measured laser beam.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A multi-field imaging synthetic scattered beam profiler, characterized in that: The invention comprises a first camera, a first reflector and a second plane reflector for dividing the field of view, the scattered light of the laser beam in the medium is connected to the incident end of the second plane reflector through the emitting end of the first reflector, the reflecting end of the second plane reflector is provided with a second camera for collecting the scattered light of the imaging laser beam, the first camera is arranged behind the first reflector for collecting the full beam range between the incident and exit apertures, the first camera and the second camera are spliced ​​together to obtain a complete beam image for detecting the beam quality of the measured laser beam, and the method for obtaining the complete beam image by splicing the first camera and the second camera comprises the following steps: the first camera collects and identifies the imaging dark area image formed by the occlusion of the first reflector, the dark field center of the imaging dark area image coincides with the imaging center of the second camera, the image center point is used as the splicing coincidence point, and the image data is processed and spliced ​​according to the magnification of the two lenses of the first camera and the second camera to obtain a complete beam image.

2. The multi-field imaging synthetic scattered beam profiler according to claim 1, characterized in that: The size of the first reflector matches the imaging field of view of the second camera, and the reflected portion of the first reflector meets the imaging requirements of the second camera.

3. The multi-field imaging synthetic scattered beam profiler according to claim 1, characterized in that: The lens of the first camera is a low-magnification telecentric lens, the lens of the second camera is a high-magnification telecentric lens, and the lens magnification ratio of the first camera and the second camera is 1:5-25.

4. The multi-field imaging synthetic scattered beam profiler according to claim 1, characterized in that: The field of view of the lens of the first camera is greater than the field of view of the lens of the second camera.

5. The multi-field imaging synthetic scattered beam profiler according to claim 1, characterized in that: The first reflector is coaxial with the lens of the first camera. The first reflector forms a uniform occlusion at the center of the lens field of view of the first camera. After the occlusion imaging, a black background is formed as an identification feature of the field of view stitching.

6. The multi-field imaging synthetic scattered beam profiler according to claim 1, characterized in that: The first reflector is a plane reflector, a right-angle prism or a transflective mirror.

7. A multi-field imaging synthetic scattered beam analysis method, used to realize the function of the multi-field imaging synthetic scattered beam profiler according to any one of claims 1 to 6, characterized in that: include: Align the laser beam through the incident aperture and the exit aperture so that the center of the beam is located at the center of the camera's field of view; A dual-lens imaging system is used. The first lens is used to collect the scattered light image of the entire beam range between the incident and exit apertures that is not blocked by the reflector; the second lens is used to collect the scattered light image at the center of the beam that is reflected twice by the reflector. The images captured by the first lens and the second lens are stitched together, with the center of the dark field formed by the reflector occlusion in the first lens image and the center of the image of the second lens being the overlapped point, and the complete beam image is obtained by synchronous imaging combined with the lens magnification processing; The Canny operator is used to identify the maximum gradient point as the boundary point, determine the boundaries on both sides of the beam, calculate the boundary spacing, and the point with the minimum spacing is the estimated position of the beam waist.

8. The multi-field imaging synthetic scattered beam analysis method according to claim 7, characterized in that: Gaussian smoothing is performed on the stitched image. Based on the fact that the grayscale values ​​of adjacent pixels conform to the Gaussian distribution characteristics, the new pixel grayscale value is calculated to reduce noise.

Images