High-speed detection imaging system and method for large-aperture optical mirror surface defects

Abstract

The invention provides a high-speed detection imaging system and method for large-aperture optical mirror defects, and belongs to the technical field of high-speed imaging detection. The system mainly comprises a detection light source unit, a phase imaging unit and a signal processing unit, the detection light source unit is used for generating a time domain stretching ultrafast laser pulse, the phase imaging unit is used for scanning and detecting an optical mirror surface, and the signal processing unit is used for recovering an acquired signal, so that the intensity and phase image reconstruction of the optical mirror surface is realized. According to the invention, the imaging speed limitation of traditional camera detection can be broken through, the megahertz imaging detection frame rate of the optical mirror surface is achieved, and meanwhile, the strength and phase images are combined, so that the online continuous high-precision and high-sensitivity detection of the defects of the optical mirror surface is realized.

Description

Technical Field

[0001] This invention belongs to the field of high-speed imaging detection technology, and in particular relates to a high-speed detection imaging system and method for defects in large-aperture optical mirrors. Background Technology

[0002] With the rapid development of modern industry and optical technology, large-aperture optical components have been widely used in high-tech fields such as laser processing, astronomical observation, and laser inertial confinement fusion. In these fields, the quality of optical components directly affects the stable operation of the entire precision system. Especially in the field of high-power lasers, under high-intensity laser radiation, defects on the surface of optical components are prone to thermal effects, which significantly lowers the laser damage threshold of the components, potentially leading to breakage or localized melting of the optical components, or even serious safety accidents. Therefore, defect detection of large-aperture optical mirrors is crucial.

[0003] Currently, the main detection methods used both domestically and internationally include imaging detection and energy dispersive scattering (EDS). EDS can determine the severity of defects, but it cannot accurately and intuitively determine the specific location and shape of the defects. Imaging detection methods mainly include visual inspection and detection methods based on optical sensor arrays. Visual inspection relies on the experience of the inspector for damage assessment, and cannot provide objective, quantitative detection results, nor can it perform in-situ observation of the optical components inside the device. Detection methods based on optical sensors can intuitively and quantitatively display the detection results of the mirror surface, but their detection accuracy and speed are limited by the resolution and sampling frequency of the optical sensor array, resulting in low overall detection efficiency and difficulty in effectively meeting large-scale detection needs. Furthermore, current imaging detection methods can only acquire intensity information from the lens surface, and cannot accurately capture changes in defect depth, nor can they timely and accurately assess the state of defects, affecting timely control over the performance of the entire precision system. Summary of the Invention

[0004] This invention addresses the problems of low detection efficiency and insufficient detection information in existing large-aperture optical mirror defect detection methods by providing a high-speed detection imaging system and method for large-aperture optical mirror defects.

[0005] A first aspect of this invention provides a high-speed detection imaging system for defects in large-aperture optical mirrors. The high-speed detection imaging system includes: a femtosecond laser for generating high-frequency pulses as an imaging light source; a first beam splitter for dividing the imaging light source into a detection optical path and a reference optical path, the detection optical path being directed towards the large-aperture optical mirror, and the large-aperture optical mirror reflecting the light to form a reflected optical path; a second beam splitter for changing the direction of the reflected optical path; an optical fiber coupler for receiving the reflected optical path and the reference optical path output from the second beam splitter, and causing the reflected optical path and the reference optical path to spatially interfere to form an interference optical field; a high-speed photodetector for acquiring the interference optical field and converting it into an interference signal; and a signal processor for acquiring the interference signal and rapidly reconstructing an image of the large-aperture optical mirror based on the interference signal, thereby achieving rapid detection of defects in the large-aperture optical mirror.

[0006] In some embodiments, the high-speed detection imaging system further includes a time-domain dispersion unit located between the femtosecond laser and the first beam splitter, used to perform a time-domain dispersive Fourier transform on the imaging light source of the high-frequency pulses to stretch the imaging light source into a one-dimensional sequence of pulses.

[0007] In some embodiments, the high-speed detection imaging system further includes a high-speed acousto-optic deflector located between the first beam splitter and the second beam splitter, for deflecting the detection optical path so that the one-dimensional sequence pulses perform two-dimensional scanning on the surface of the large-aperture optical mirror.

[0008] In some embodiments, the high-speed detection imaging system further includes a diffraction grating located between the second beam splitter and the large-aperture optical mirror, used to spatially disperse the detection optical path and to spatially combine the reflected optical path.

[0009] In some embodiments, the high-speed detection imaging system further includes a lens assembly located between the diffraction grating and the large-aperture optical mirror, for focusing the spatially scattered detection light path onto the large-aperture optical mirror and converging the reflected light path onto the second beam splitter.

[0010] In some embodiments, the high-speed detection imaging system further includes a delay component located between the first beam splitter and the fiber coupler, for adjusting the optical path difference between the reference optical path and the reflected optical path.

[0011] In some embodiments, the delay component includes: a mirror group comprising a plurality of mirrors, each mirror being used to reflect the reference optical path and direct the reference optical path toward the fiber coupler; and a displacement stage connected to at least a portion of the mirrors for adjusting the optical path of the reference optical path between the first beam splitter and the fiber coupler.

[0012] In some embodiments, the high-speed detection imaging system further includes: a first collimator located between the delay component and the fiber coupler; and a second collimator located between the second beam splitter and the fiber coupler.

[0013] A second aspect of this invention provides a high-speed detection and imaging method for defects in large-aperture optical mirrors, implemented using the high-speed detection and imaging system for defects in large-aperture optical mirrors provided in the first aspect of this invention. The high-speed detection and imaging method includes: controlling a femtosecond laser to generate high-frequency pulses as an imaging light source; controlling a signal processor to acquire the interference signal from the high-speed photodetector; rapidly reconstructing an image of the large-aperture optical mirror based on the interference signal; and identifying defects in the large-aperture optical mirror based on the image.

[0014] In some embodiments, the high-speed detection imaging system further includes a time delay component, and the high-speed detection imaging method further includes: controlling the time delay component to adjust the optical path of the reference optical path so that the reference optical path and the reflected optical path can spatially interfere.

[0015] Compared with existing technologies, the high-speed imaging detection system proposed in this invention differs from traditional detection technologies. By using high-speed photoelectric signal detection equipment to replace traditional imaging elements such as CCD and CMOS, it breaks through the limitations of imaging speed and can achieve megahertz-level online detection of large optical mirror defects. Based on high-speed imaging, this invention can simultaneously acquire intensity and phase signals, increasing the dimensions of imaging detection information for large optical mirror defects, and effectively improving the accuracy and sensitivity of defect detection. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of a rapid detection imaging system for defects in large-aperture optical mirrors provided in an embodiment of the present invention; Figure 2 This is a flowchart illustrating a rapid detection and imaging method for defects in large-aperture optical mirrors, provided as an embodiment of the present invention.

[0017] Explanation of reference numerals in the attached figures 101. Femtosecond laser; 102. Time-domain dispersion unit; 103. First beam splitter; 104. High-speed acousto-optic deflector; 105. Second beam splitter; 106. Diffraction grating; 107. First lens; 108. Second lens; 109. Third lens; 110. Large-aperture optical mirror; 111. Delay assembly; 112. Fiber optic coupler; 113. High-speed photodetector; 114. Signal processor. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0020] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0021] In some embodiments, such as Figure 1 As shown, the high-speed detection imaging system includes: a femtosecond laser 101, a first beam splitter 103, a second beam splitter 105, an optical fiber coupler 112, a high-speed photodetector 113, and a signal processor 114. A femtosecond laser 101 is used to generate high-frequency pulses as an imaging light source. A first beam splitter 103 is used to receive the imaging light source and separate the imaging light source into a detection optical path and a reference optical path. The detection optical path passes through a second beam splitter 105 and is directed towards the large-aperture optical mirror 110 to be detected. The large-aperture optical mirror 110 reflects the detection optical path in its original path to form a reflected optical path. The reflected optical path returns to the second beam splitter 105 and is reflected by the second beam splitter to the fiber coupler 112, thereby enabling the reflected optical path and the reference optical path to generate a spatial interferometer within the fiber coupler 112 to generate an interference signal. A high-speed photodetector 113 is used to collect the interference signal and convert it into an electrical signal that can be processed by a computer through photoelectric conversion. The signal processor 114 obtains the electrical signal from the high-speed photodetector 113, samples and modulates the continuous electrical signal, converts it into a discrete signal, and quickly reconstructs the image of the large-aperture optical mirror based on the discrete signal to achieve rapid detection of defects in the large-aperture optical mirror.

[0022] It should be noted that typical objects being detected usually have complex-shaped surfaces that are generally diffuse reflective. The reflected light typically does not form a uniformly oriented light field, making it impossible for the reflected light to stably interfere with the detection light source. Even if some reflected light does interfere with the detection light source, the resulting light field may not be stably and regularly arranged. Therefore, it is impossible to quickly reconstruct the surface image of the object being detected based on a stable and regularly arranged interference light field. Consequently, various complex algorithms are needed to process the acquired image signals with a large computational load, hindering rapid detection. The applicant, realizing this... Unlike typical test surfaces, large-aperture optical mirrors have a simple emitting surface shape and are specular reflective. This allows the detection light path to be reflected back along its original path in defect-free areas, enabling spatial interference between the reflected light and the detection light source. The resulting interference light field is relatively stable and regularly arranged, allowing for rapid and simple reconstruction of the image from the large-aperture optical mirror. Furthermore, the distortion or brightness distortion within the interference light field can quickly identify defects in the large-aperture optical mirror, achieving high-speed defect detection.

[0023] This invention provides a high-speed detection imaging system for defects in large-aperture optical mirrors. The system includes a femtosecond laser for generating high-frequency pulses as an imaging light source, a first beam splitter for dividing the imaging light source into a detection optical path and a reference optical path, wherein the detection optical path is directed towards the large-aperture optical mirror, and the large-aperture optical mirror emits a reflected optical path. The system also includes a second beam splitter for changing the direction of the reflected optical path, receiving the reflected and reference optical paths output by the second beam splitter, and causing the reflected and reference optical paths to spatially interfere to form an interference light field. And it is used to acquire interference signals and quickly reconstruct images of large-aperture optical mirrors based on the interference signals, so as to realize the rapid detection of defects in large-aperture optical mirrors. Since large-aperture optical mirrors can return the detection optical path along the original path, the returned reflected signal contains the image information of the large-aperture mirror. The reflected signal can interfere with the reference optical path in space and form an interference light field. Compared with the complex reflected signals of general object surfaces, the arrangement of the interference light field has a more stable arrangement pattern. Through this interference light field with a regular arrangement pattern, the image of the large-aperture optical mirror can be quickly reconstructed and rapid defect detection is realized.

[0024] In some embodiments, such as Figure 1As shown, the high-speed detection imaging system also includes a time-domain dispersion unit 102, used to perform a dispersive Fourier transform on the imaging light source in the time domain, so as to stretch the imaging light source into a one-dimensional sequence of pulses. This can be understood as the time-domain dispersion unit 102 converting the light source into a scan line in a plane. By causing relative motion between the large-aperture optical mirror to be detected and this scan line, the imaging light source can scan the large-aperture optical mirror. Optionally, the relative motion between the scan line and the large-aperture optical mirror can be achieved by translating the large-aperture optical mirror. Alternatively, as... Figure 1 As shown, the high-speed detection imaging system also includes a high-speed acousto-optic deflector 104, which is located between the first beam splitter 103 and the second beam splitter 105, and is used to deflect the detection optical path so that the one-dimensional sequence pulses can perform two-dimensional scanning on the surface of the large-aperture optical mirror.

[0025] In some embodiments, such as Figure 1 As shown, the high-speed detection imaging system also includes a diffraction grating 106, which is located between the second beam splitter 105 and the large-aperture optical mirror 110. The diffraction grating 106 is used to spatially disperse the detection light path. The dispersed detection light path is directed towards the large-aperture optical mirror and the reflected light path is reflected back to the diffraction grating 106. The diffraction grating 106 can spatially combine the dispersed reflected light path.

[0026] In some embodiments, such as Figure 1 As shown, the high-speed detection imaging system also includes a lens assembly, which includes multiple lenses. The lens assembly is located between the diffraction grating 106 and the large-aperture optical mirror 110. The multiple lenses can focus the dispersed light onto the large-aperture optical mirror 110, and the reflected light path reflected from the large-aperture optical mirror 110 can also be focused by the lens assembly onto the second beam splitter 105. Optionally, the lens assembly includes a first lens 107, a second lens 108, and a third lens 109.

[0027] In some embodiments, such as Figure 1 As shown, the high-speed detection imaging system also includes a delay component 111, located between the first beam splitter 103 and the fiber coupler 112, used to adjust the optical path difference between the reference optical path and the reflected optical path. By making the optical path difference between the reference optical path and the reflected optical path an integer multiple of the period of the high-frequency pulse, the reference optical path and the reflected optical path can perform spatial interference. It should be noted that the delay component 111 can adjust the optical path length of the reference optical path from the first beam splitter 103 to the fiber coupler 112 through refraction or reflection.

[0028] Optionally, the delay component 111 includes a mirror group and a displacement stage. The mirror group includes multiple mirrors, each mirror reflecting a reference optical path, and the reflected optical path emitted from the last mirror can be directed toward the fiber coupler 112. The displacement stage is connected to at least a portion of the mirror group. By sliding a portion of the mirrors, the optical path of the reference optical path can be changed while ensuring that the reference optical path emitted from the mirror group can still be directed toward the fiber coupler 112, thereby adjusting the optical path difference between the reflected optical path and the reference optical path.

[0029] In some embodiments, the high-speed detection imaging system further includes a first collimator and a second collimator. The first collimator is located between the delay component and the fiber coupler and is used to direct the reference optical path into the fiber coupler in a direction facing the fiber coupler. The second collimator is located between the second beam splitter and the fiber coupler and is used to direct the reflected optical path into the fiber coupler in a direction facing the fiber coupler, thereby enabling better spatial interference between the reference optical path and the reflected optical path.

[0030] In some embodiments, the high-speed detection light source is used to generate time-stretched ultrafast laser pulses; the phase imaging unit is used to perform high-speed scanning detection on the optical mirror to capture the intensity and phase information of the optical mirror; and the signal processing unit is used to perform recovery processing on the acquired signal to realize the reconstruction of the intensity and phase image of the optical mirror.

[0031] Specifically, the high-speed detection light source is implemented as follows: a high repetition rate femtosecond pulse laser is used as the imaging light source, and a section of dispersive fiber is used to stretch the ultrashort pulse into a one-dimensional time-series pulse in the time domain.

[0032] like Figure 1 As shown, the phase imaging process is as follows: the stretched one-dimensional time-series pulse is split into two paths by the first beam splitter, one is the detection optical path and the other is the reference optical path. The detection optical path pulse is transmitted to the diffraction grating through the high-speed acousto-optic deflector and the second beam splitter, and is projected onto the optical mirror through the lens group. The mirror information is encoded in the detection optical path pulse. Then, the optical pulse containing the mirror information is reflected back to the second beam splitter along the original optical path. By adjusting the optical path of the reference optical path, the detection optical path and the reference optical path are spatially interfered, and the signal is acquired by the high-speed photodetector.

[0033] The optical path of the imaging system is as follows: a femtosecond laser 101 generates femtosecond pulses, which are then stretched in the time domain by a dispersive fiber 102 and transmitted through a collimator. A first beam splitter 103 is placed in front of the collimator, splitting the stretched pulses into two paths: one as a detection optical path and the other as a reference optical path. The detection optical path is incident on a high-speed acousto-optic deflector 104, which deflects the pulse. The pulse then passes through a second beam splitter 105 and is transmitted to a diffraction grating 106, where it is spatially dispersed. After passing through lenses 107 and 108 of a 4f system, the pulse is shaped and focused by a third lens 109 onto the surface of a large-aperture optical mirror 110 to collect sample information. The detection pulse containing the sample information returns along the original optical path, passes through the third lens 109, the second lens 108, and the first lens 107, and is then spatially combined by the diffraction grating 106 before being transmitted to the second beam splitter 105. The reflected detection optical path passes through a collimator and is incident on a coupler 112. The reference optical path signal, after being adjusted by the delay component 111 to reduce the optical path difference with the detection optical path, passes through the collimator and is incident on the fiber coupler 112, interfering with the detection optical path signal. The interference signal is acquired by the photodetector 113, and the signal processor 114 stores and calculates the signal to recover the sample intensity and phase information.

[0034] The femtosecond laser is connected to the dispersive fiber and collimator. A first beam splitter is positioned in front of the collimator at a distance (e.g., d1=10mm) and an angle (e.g., 45°). A high-speed acousto-optic deflector is positioned in front of the first beam splitter at a distance (e.g., d2=100mm). A second beam splitter is positioned in front of the high-speed acousto-optic deflector at a distance (e.g., d3=105mm). A diffraction grating is positioned in front of the second beam splitter at a distance (e.g., d4=50mm) and an angle (e.g., 45°). The lens is positioned in front of the diffraction grating at a distance (e.g., a distance meeting the lens focal length requirement) and an angle (e.g., 90°). The optical mirror under test is positioned at the focal plane in front of the lens. The delay component is positioned in front of the reflected optical path of the first beam splitter at a distance (e.g., a distance meeting the two-pathway difference requirement) and an angle (e.g., 90°). The reflected detection optical path signal and the reference optical path signal are connected to the collimator and fiber coupler, respectively. The fiber coupler is connected to the photodetector and the signal processor.

[0035] This invention also provides a high-speed detection and imaging method for defects in large-aperture optical mirrors. This high-speed detection and imaging method utilizes, as described in... Figure 1 The high-speed detection and imaging system shown is implemented.

[0036] In some embodiments, such as Figure 2 As shown, high-speed detection and imaging methods for defects in large-aperture optical mirrors include: Step S101: Control the femtosecond laser to generate high-frequency pulses as the imaging light source.

[0037] This can be understood as follows: the femtosecond laser is controlled to turn on and output a high-frequency pulsed laser as an imaging light source. The pulsed laser is injected into the first beam splitter and split into a detection optical path and a reference optical path. The reference optical path is injected into the fiber coupler. The detection optical path is injected into the large-aperture optical mirror and is reflected to form a reflected optical path that includes the image information of the optical mirror. The reflected optical path is reflected to the second beam splitter and its direction is changed by the second beam splitter before being injected into the fiber coupler. The reference optical path and the reflected optical path generate spatial interference within the fiber coupler to form an interference optical field.

[0038] Step S102: The control signal processor acquires the interference signal from the high-speed photodetector and quickly reconstructs the image of the large-aperture optical mirror based on the interference signal, and identifies the defects of the large-aperture optical mirror based on the image.

[0039] This can be understood as follows: the photodetector acquires the interference light field through the fiber optic coupler and converts the interference light field into an interference signal in the form of an electrical signal through photoelectric conversion. After the signal processor acquires the interference signal, it quickly reconstructs the image of the large-aperture optical mirror based on the arrangement pattern of the interference signal. Since most of the interference signal is a regularly arranged signal, if there is a defect in the large-aperture optical mirror, it will produce local distortion in the interference signal. Through these local distortions, the location and degree of the defect can be quickly located. The remaining areas without distortion can be considered as having no distortion. When reconstructing the image of the large-aperture optical mirror, it can be easily reconstructed as a defect-free mirror. The amount of computation required for reconstruction is very small, so fast reconstruction can be achieved.

[0040] For example, the interference signal is represented as a matrix, where each element corresponds to the pixel brightness of a corresponding position on a large-aperture optical mirror. The regions in the regularly arranged matrix are quickly reconstructed as mirrors. If there are regions in the matrix that are arranged differently from other regions, it is considered that there is distortion in that region. If the brightness of the corresponding position on the large-aperture optical mirror is distorted, and if the brightness of the region decreases overall, it indicates that the distortion in that region is mirror wear. If the arrangement of the region is represented by some elements being zero and the brightness of some elements being abnormally increased, it indicates that the defect type of that region is fragmentation.

[0041] Optionally, the high-speed detection imaging system also includes a time delay component, and the high-speed detection imaging method further includes: controlling the time delay component to adjust the optical path of the reference optical path so that the reference optical path and the reflected optical path can perform spatial interference, so that the optical path difference between the reference optical path and the reflected optical path is an integer multiple of the wavelength of the imaging light source.

[0042] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A high-speed detection imaging system for defects in large-aperture optical mirrors, characterized in that, The high-speed detection imaging system includes: Femtosecond lasers are used to generate high-frequency pulses as imaging light sources; The first beam splitter is used to divide the imaging light source into a detection optical path and a reference optical path. The detection optical path is used to direct the light onto the large-aperture optical mirror, and the large-aperture optical mirror reflects the light to form a reflection optical path. The second beam splitter is used to change the direction of the reflected light path; An optical fiber coupler is used to receive the reflected optical path and the reference optical path output by the second beam splitter, and to make the reflected optical path and the reference optical path spatially interfere to form an interference optical field; A high-speed photodetector is used to collect the interference light field and convert it into an interference signal; A signal processor is used to acquire the interference signal and quickly reconstruct an image of the large-aperture optical mirror based on the interference signal, so as to achieve rapid detection of defects in the large-aperture optical mirror.

2. The high-speed detection imaging system according to claim 1, characterized in that, The high-speed detection imaging system also includes: The time-domain dispersion unit, located between the femtosecond laser and the first beam splitter, is used to perform a time-domain dispersive Fourier transform on the imaging light source of the high-frequency pulses, so as to stretch the imaging light source into a one-dimensional sequence of pulses.

3. The high-speed detection imaging system according to claim 2, characterized in that, The high-speed detection imaging system also includes: A high-speed acousto-optic deflector, located between the first beam splitter and the second beam splitter, is used to deflect the detection optical path so that the one-dimensional sequence pulses can perform a two-dimensional scan on the surface of the large-aperture optical mirror.

4. The high-speed detection imaging system according to claim 1, characterized in that, The high-speed detection imaging system also includes: A diffraction grating, located between the second beam splitter and the large-aperture optical mirror, is used to spatially disperse the detection light path and to spatially combine the reflected light path.

5. The high-speed detection imaging system according to claim 4, characterized in that, The high-speed detection imaging system also includes: The lens assembly, located between the diffraction grating and the large-aperture optical mirror, is used to focus the detection light path after spatial scattering onto the large-aperture optical mirror and to converge the reflected light path to the second beam splitter.

6. The high-speed detection imaging system according to claim 1, characterized in that, The high-speed detection imaging system also includes: A delay component, located between the first beam splitter and the fiber coupler, is used to adjust the optical path difference between the reference optical path and the reflected optical path.

7. The high-speed detection imaging system according to claim 6, characterized in that, The delay component includes: A mirror assembly includes multiple mirrors, each of which is used to reflect the reference optical path and direct the reference optical path toward the fiber coupler; A displacement stage, connected to at least a portion of the reflector, is used to adjust the reference optical path between the first beam splitter and the fiber coupler.

8. The high-speed detection imaging system according to claim 6, characterized in that, The high-speed detection imaging system also includes: A first collimator is located between the delay component and the fiber coupler; The second collimator is located between the second beam splitter and the fiber coupler.

9. A high-speed detection and imaging method for defects in large-aperture optical mirrors, characterized in that, The high-speed detection imaging method is implemented using the high-speed detection imaging system as described in any one of claims 1 to 8, and the high-speed detection imaging method includes: The femtosecond laser is controlled to generate high-frequency pulses as an imaging light source; The signal processor is controlled to acquire the interference signal from the high-speed photodetector, and to quickly reconstruct the image of the large-aperture optical mirror based on the interference signal, and to identify the defects of the large-aperture optical mirror based on the image.

10. The high-speed detection imaging method according to claim 9, characterized in that, The high-speed detection imaging system further includes a time delay component, and the high-speed detection imaging method further includes: The delay component is controlled to adjust the optical path of the reference optical path so that the reference optical path and the reflected optical path can spatially interfere.

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