Multi-view-field imaging synthesis scattering type light beam analyzer

Abstract

The invention discloses a multi-view-field imaging synthesis scattering type light beam analyzer which comprises a first camera, a first plane mirror and a second plane mirror, the first plane mirror and the second plane mirror are used for segmenting view fields, and scattered light of a laser beam in a medium is connected with an incident end of the second plane mirror through a transmitting end of the first plane mirror. The reflecting end of the second plane mirror is provided with a second camera used for collecting the full light beam range between the incident aperture and the emergent aperture, and the first camera is arranged behind the first plane mirror and used for collecting scattered light for imaging the laser beam. And splicing the first camera and the second camera to obtain a complete light beam image for detecting the light beam quality of the detected laser beam. According to the invention, the light beam information of a large field of view is obtained by adopting a mode of splicing and imaging lenses with different multiplying powers, the high-resolution measurement of the beam waist position is ensured, the precision of laser beam quality parameter measurement is obviously improved, and the measurable range of the scattering type light beam analyzer is expanded.

Description

Technical Field

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

[0002] Lasers are widely used in many fields such as machining and additive manufacturing. As a key indicator for measuring the performance of lasers, the beam quality plays a decisive role in the processing effect. At present, laser beam analyzers are commonly used tools for measuring beam quality. However, with the continuous increase in laser power density, direct-irradiation measurement-type analyzers are difficult to meet the requirements for beam analysis of high-power lasers due to the risk of being damaged by high-power lasers.

[0003] In this context, scattering beam analyzers that obtain beam quality information based on measuring the Rayleigh scattering image of a laser beam have emerged. However, such existing technologies have obvious defects. According to the ISO test standard, to accurately fit the beam, at least the beam information at three Rayleigh lengths starting from the beam waist position needs to be measured. 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 imaging with a large field of view. However, a single lens cannot balance high resolution and a large imaging field of view during imaging. If a large imaging field of view is selected, the resolution of beam waist measurement will decrease, and it is difficult to balance the two, resulting in the existing scattering beam analyzers being only able to measure laser beams with a relatively large beam waist and a large M 2 as well, and unable to meet diverse measurement requirements. Therefore, a multi-field-of-view imaging synthetic scattering beam analyzer is needed. Summary of the Invention

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

[0005] To achieve the above object, the present invention is implemented according to the following technical solution: The present invention includes a first camera, a first plane mirror and a second plane mirror for dividing the field of view. The scattered light of the laser beam is connected through the emitting end of the first plane mirror and the incident end of the second plane mirror. A second camera is provided at the reflecting end of the second plane mirror for collecting the full beam range between the incident and exit apertures. The first camera is arranged behind the first plane mirror for imaging the scattered light of the 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.

[0006] Further, the size of the first plane mirror matches the imaging field of view of the second camera, and the reflected part of the first plane mirror meets the imaging requirements of the second camera.

[0007] Further, 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 to the second camera is 1:5-25.

[0008] Further, the method for obtaining a complete beam image by splicing the first camera and the second camera includes the first camera collecting and identifying the imaging dark area image formed by the occlusion of the first plane mirror. The dark field center of the imaging dark area image coincides with the imaging center of the second camera. Taking the image center point as the splicing coincidence point, and synchronously imaging according to the magnification ratios of the two lenses of the first camera and the second camera, and processing and splicing the image data to obtain a complete beam image.

[0009] Further, the field of view range of the lens of the first camera is larger than the field of view range of the lens of the second camera.

[0010] Further, the first plane mirror is coaxial with the lens of the first camera. The first plane mirror forms a uniform occlusion at the center of the field of view of the lens of the first camera, and a black background is formed after the occlusion imaging, which is the recognition feature for the field of view splicing.

[0011] Further, the first mirror is a plane mirror, a right-angle prism or a transmissive-reflective mirror.

[0012] On the other hand, a multi-field imaging synthesis scattered beam analysis method for realizing the function of the multi-field imaging synthesis scattered beam analyzer includes: Align the optical path of the laser beam through the incident aperture and the exit aperture so that the beam center is located at the center of the camera field of view; Adopt a dual-lens imaging system. The first lens is used to collect the scattered light image of the full beam range that is not blocked by the mirror 1 between the incident and exit apertures; the second lens is used to collect the scattered light image of the beam center position after being reflected twice by the mirror.

[0013] Splice the images collected by the first lens and the second lens. Taking the dark field center formed by the occlusion of the mirror in the first lens image as the splicing coincidence point with the image center of the second lens, and combining the lens magnification to process and synchronously image to obtain a complete beam image; Use the Canny operator to identify the gradient maximum points as boundary points, determine the two sides of the beam boundary, calculate the boundary spacing, and the position with the minimum spacing is the estimated position of the beam waist.

[0014] Further, perform Gaussian smoothing processing on the spliced image. Based on the characteristic that the gray values of adjacent pixels conform to the Gaussian distribution, calculate the new pixel gray value to reduce noise.

[0015] The beneficial effects of the present invention are: The present invention is a multi-field imaging synthetic scattering beam analyzer. Compared with the prior art, the present invention has the following technical effects: By adopting the method of stitching images with lenses of different magnifications, the low-magnification telecentric lens of the present invention can achieve a complete image of the beam in the entire field of view, while the high-magnification telecentric lens can provide a micron-level spatial resolution for the laser beam waist. This design enables the acquisition of beam information in a large field of view during the measurement process and ensures high-resolution measurement of the beam waist position. Compared with the prior art, the accuracy of measuring the laser beam quality parameters is significantly improved. Especially in the measurement of the beam waist size and position, it can more accurately reflect the actual characteristics of the beam, greatly expanding the measurable range of the scattering beam analyzer and meeting the needs of laser beam quality analysis in more scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a structural diagram of a multi-field imaging synthetic scattering beam analyzer of the present invention; Figure 2 It is a structural diagram of a partial transmission lens of a multi-field imaging synthetic scattering beam analyzer of the present invention; Figure 3 It is a schematic diagram of a right-angle prism reflection structure in an embodiment of a multi-field imaging synthetic scattering beam analyzer of the present invention; Figure 4 It is a schematic diagram of a structure in which a mirror is placed at an angle other than 45° in an embodiment of a multi-field imaging synthetic scattering beam analyzer of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be further described below through specific embodiments. The schematic embodiments and descriptions herein are used to explain the present invention, but not to limit the present invention.

[0018] It should be explained that high-power laser refers to a laser with an output power above 1 kW. Laser beam quality refers to an evaluation index of laser transmission characteristics. The beam parameter product refers to the product of the laser beam waist and the divergence angle, which is used to characterize the laser beam quality. M 2 represents the ratio of the optical parameter product of the actual beam to the optical parameter product of the ideal fundamental mode Gaussian beam, and is often used to characterize the laser beam quality.

[0019] As Figure 1 and 2 shown. The present invention includes a first plane mirror, a second plane mirror, 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, and 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.

[0020] The imaging dark area image formed by the mirror occlusion at the acquisition and recognition center position of the first camera. The center of the image in the dark field coincides with the center of the second camera's imaging. Taking the image center point as the stitching coincidence point, a complete beam image is obtained after processing and stitching the image data according to the magnification ratios of the two lenses of the first camera and the second camera. Before the device is used, the laser beam is aligned through the incident aperture and the exit aperture to ensure that the beam center is located at the middle position of the entire device. During measurement, the laser beam passes through the device, generating a scattering signal. The scattered light at the center position of the laser beam is reflected twice by mirror 1 and mirror 2 and enters lens 2, where it is collected and imaged in camera 2. The part of the scattered light that is not blocked by mirror 1 within the full beam range between the incident and exit apertures of the laser beam is collected by lens 1 and imaged in camera 1. Lens 1 uses a low magnification telecentric lens, such as a 0.3X or 0.1X magnification, to achieve complete imaging of the beam in the entire field of view. When selecting the type, calculate according to the required field of view width in combination with the camera detector size. Assuming the maximum field of view width is HOF and the detector width is HOC, the magnification X of lens 1 1 The calculation is as follows: Lens 2 uses a high magnification telecentric lens, such as a 1X or 2X magnification, to achieve a micron-level spatial resolution at the laser beam waist position. When selecting the type, calculate according to the required spatial resolution. Assuming the maximum spatial resolution is ROF and the detector pixel size is SOC, the magnification X of lens 2 2 The calculation is as follows: Data acquisition is controlled by the host computer. The host computer software performs stitching processing on the acquired images. During image stitching, for the image captured by camera 1, identify the imaging dark area at the center position. This dark area is formed by the mirror occlusion, and its dark field center coincides with the center of camera 2's imaging. Taking the image center point as the stitching coincidence point, a complete beam image is obtained after processing and stitching the image data according to the magnification ratios of the two lenses. This image has a high resolution at the beam waist position and a large imaging field of view in the beam propagation direction, expanding the measurable range of the scattering beam analyzer.

[0021] When selecting a lens, the main factor to consider is the magnification, and the secondary factor is the resolution that the lens can achieve. The imaging resolution of the selected lens should match the detector. The lens resolution standard refers to the test results of the resolution target board, with the MTF curve at 40% as the criterion. For a lens, its minimum imaging should be at least twice the pixel size of the detector. At this time, the imaging is at the Rayleigh limit, and the camera can just resolve the lens imaging. For a lens with a lower resolution, its imaging should preferably not exceed 5 times the pixel size of the detector to avoid insufficient resolution. For example, if the detector of the camera is the IMX183 detector produced by SONY, with a pixel size of 2.4 microns, it can be known that the optimal resolution of the camera should meet 4.8 microns. At this time, the test result of the lens corresponding to the camera resolution target board is Group 6, No. 5. Relax the lens resolution requirement to 5 times the pixel size. At this time, the test result of the lens corresponding to the camera resolution target board is Group 5, No. 5. After selecting the camera detector and the lens magnification, the imaging field width is already determined and does not need to be used as a separate selection index. The imaging range of the lens only needs to cover the entire target surface of the detector. For example, for the IMX183, the output picture size is 15.86 mm in diagonal length, and the picture ratio is 3:2. Selecting a 1x lens can obtain an imaging field of 13.19 mm × 8.79 mm. When selecting a 0.3x lens, this field of view is enlarged 3 times. For a CMOS chip with a fixed ratio of 4:3, its field of view range is shown in Table 1: Table 1 Comparison of the field of view ranges of different lenses for CMOS sizes

[0022] It can be seen from this that with the change of the lens magnification, the corresponding change relationship of its field of view. For a lens with a higher magnification, its field of view is always smaller, and for a lens with a lower magnification, a larger field of view can always be obtained.

[0023] Since the resolutions of lenses are different at the same magnification, here, for the case where the lens is theoretically of high resolution at each magnification, the influence of lens resolution on imaging resolution is discussed. Assume that Lens 1 is 0.3x high definition and Lens 2 is 1x high definition. Usually, a 0.3x high definition resolution lens on the market can resolve a standard target board of 5 / 2, that is, a line width of 13.92 microns. A 1x high definition resolution lens on the market can resolve a standard target board of 7 / 1, that is, 3.91 microns. When shooting the laser beam waist, due to problems such as diffraction effects, its actual resolution is about 1 / 4 of this resolution. It can be seen that for the laser beam waist, a high-magnification lens has a better resolution advantage.

[0024] After the reflector is placed, there will be an unilluminated black area in the image. Calculate the center position of the black area. When the center position of the black area coincides with the center position of the detector itself, it means that the spatial positioning of the occlusion is accurate. Calculate the grayscale value of the black occluded area. When the grayscale of the boundary of the occluded area is close and the deviation does not exceed 5%, it means that the occlusion is uniform and no adjustment is required. If the local deviation is large, it is necessary to fine-tune the mirror angle to achieve more uniform occlusion.

[0025] 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 their boundaries are close, so stitching is performed based on this.

[0026] The laser wavelength is mainly within the visible light range, which is related to the lens coating and camera response. If the camera is replaced with an infrared response camera and the lens is an infrared lens, the quality of the infrared laser beam can be detected. The humidity is 10%~20% and the temperature is 20 degrees Celsius to 25 degrees Celsius. The test results are similar. In theory, the temperature has a smaller impact and the humidity has a greater impact. For a more humid environment, the scattering signal is stronger and it is easier to measure the signal.

[0027] 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.

[0028] Perform Gaussian smoothing on the collected images; 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.

[0029] For the smoothed image, calculate its grayscale gradient: perform calculation and detection on each pixel, and select the point with the maximum gradient as the boundary point. After obtaining the two boundaries of the light beam, calculate the boundary spacing, and the position with the smallest spacing is the location of the beam waist.

[0030] Take a column of pixels from the image, construct the propagation parameter expression, and calculate the accurate Rayleigh length and divergence angle of the beam by fitting multiple beam cross sections.

[0031] 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. For a point in the image, its gray value can be expressed as a function of the coordinates of the point , take the neighboring 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: For the smoothed image, calculate its grayscale gradient, amplitude and direction using the following relationship: The magnitude of the gray gradient G is determined by the horizontal gradient G x and the vertical gradient G y The amplitude of is found: The gradient direction of the grayscale gradient is θ G We can also obtain: 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 light beam are obtained, the boundary spacing is calculated, and the position with the smallest spacing is the location of the beam waist.

[0032] Take a column of pixels from the image, whose horizontal coordinate is z, and the beam diameter obtained by Gaussian fitting is d. The two can be expressed by the propagation parameters a, b, and c as follows: Through fitting of 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, c, and then the accurate Rayleigh length and M can be calculated. 2 for: For a laser with a certain output line width, here The value is based on the central wavelength. , the divergence angle of the beam for: Considering that the existing scattered beam analyzer has two types of single-axis measurement and dual-axis measurement, the present invention is equally applicable to both. This solution can be adopted simultaneously when dual-axis measurement is selected to improve the resolution of the beam waist. For a beam with high symmetry, this solution can also be considered to be selected only in one axial direction, while the other axial direction remains unchanged.

[0033] When making measurements, first place this device on a horizontal workbench and perform a rough alignment according to the path through which the laser will pass. Turn on the laser indicating light and perform a detailed alignment to ensure that the laser passes through the center of the light inlet and outlet holes of this device, and place a beam blocker or perform other treatments on the emitted laser to ensure safety. For lasers whose beam waist can be measured, the position of the beam waist should be adjusted to be near the center of the camera's field of view. For those whose beam waist is difficult to adjust to the center of the camera's field of view, a focusing lens should be added before the light enters, and an appropriate focal length should be selected so that the focused beam waist is located at the center of the camera's field of view. After adjusting the optical path, turn on the camera and enter the measurement state. Turn on the laser and adjust its output power so that the output power is within the measurement range. Confirm that the beam coincides with the field of view and is well focused on the camera acquisition interface before data acquisition can be carried out. After the image data is acquired, corresponding processing will be performed by the software to obtain information such as the beam quality of the measured laser beam.

[0034] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A multi-field imaging synthetic scattered beam analyzer, characterized in that: The invention comprises a first camera, a first plane reflector and a second plane reflector for dividing a field of view, the scattered light of a laser beam in a medium is connected to the incident end of the second plane reflector through the emitting end of the first plane reflector, the reflecting 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, and the first camera and the second camera are spliced ​​to obtain a complete beam image for detecting the beam quality of the measured laser beam.

2. The multi-field imaging synthetic scattered beam profiler according to claim 1, characterized in that: 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.

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 method of obtaining a complete light beam image by splicing the first camera and the second camera includes collecting, by the first camera, identifying an imaging dark area image formed by 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, taking the image center point as the splicing coincidence point, and obtaining a complete light beam image by processing and stitching image data through synchronous imaging based on the magnification of the two lenses of the first camera and the second camera.

5. The multi-field imaging synthetic scattered beam profiler according to claim 4, 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.

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

7. 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.

8. A method for analyzing a multi-field imaging synthetic scattered beam, for realizing the function of the multi-field imaging synthetic scattered beam analyzer as claimed in any one of claims 1 to 7, 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 full 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 of the center position of the beam reflected twice by the reflector; The images captured by the first lens and the second lens are stitched together, and the center of the dark field formed by the reflector occlusion in the image of the first lens coincides with the center of the image of the second lens as the stitching coincidence 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.

9. The method for analyzing a multi-field imaging synthetic scattered light beam according to claim 8, 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 grayscale values ​​of new pixels are calculated to reduce noise.

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