A digital holographic deformation detection method

Abstract

This invention relates to a digital holographic deformation detection method, belonging to the field of optoelectronic detection technology. The invention includes the following steps: performing a Michelson interferometry experiment on the emitted light from different types of semiconductor lasers to collect coherent fringes; calculating the coherence length and selecting a suitable object plane size; forming a rectangular uniform light field through a square waveguide cavity superimposed imager using the emitted laser light; acquiring the same object plane information by adjusting the position information of the CMOS, obtaining the non-coplanar phase information before and after the object plane displacement; performing image processing on the laser holograms obtained before and after the object plane displacement, extracting the corresponding phase information; constructing a three-dimensional relationship using the position information between the CMOS and the object plane; and performing three-dimensional reconstruction processing on the phase information to obtain the three-dimensional displacement components. This invention achieves industrial-precision deformation detection at low cost and without destructive testing.

Description

Technical Field

[0001] This invention relates to a digital holographic deformation detection method, belonging to the field of optoelectronic detection technology. Background Technology

[0002] Semiconductor lasers possess advantages such as low cost, low power consumption, good monochromaticity, small size, and ease of modulation, making them widely used in fields such as fiber optic communication, laser processing, medicine, and the military. However, semiconductor lasers suffer from poor beam quality and large beam divergence angles. The different divergence angles of two perpendicular beams result in an uneven optical field distribution, preventing their direct application to high-precision optical measurements. However, this improved method allows for their application in industrial measurements.

[0003] Compared with traditional holography, digital holographic reconstruction has the advantages of lower production cost, faster imaging speed, and obvious imaging effect. Furthermore, the digital holographic optical path built using optical instruments is more flexible, allowing for changes in the wavelength of light, a larger optical path between the object beam and the reference beam, or changes in the laser model to adjust the measurement range, resulting in greater coordination. Summary of the Invention

[0004] This invention provides a digital holographic deformation detection method for displacement detection to reduce costs. This invention uses a low-cost semiconductor laser and CMOS to replace high-power lasers and CCDs. It applies CMOS multi-directional acquisition to collect phase information of non-coplanar components. Through a series of image processing steps, it realizes the detection of three-dimensional deformation of the object surface, thus laying the foundation for the industrialization of digital holography.

[0005] The technical solution of this invention is: a digital holographic deformation detection method, which involves performing a Michelson interferometry experiment on the emitted light of different types of semiconductor lasers to collect coherent fringes; calculating the coherence length and selecting a suitable object plane size; forming a rectangular uniform light field by passing the emitted light of the laser through a square waveguide cavity superimposed imager; collecting the same object plane information by adjusting the position information of the CMOS to obtain the non-coplanar phase information before and after the object plane displacement; performing image processing on the laser holograms obtained before and after the object plane displacement by superimposing the object light and the reference light to extract the corresponding phase information; constructing a three-dimensional relationship through the position information between the CMOS and the object plane; and performing three-dimensional reconstruction processing on the phase information to obtain the three-dimensional displacement components.

[0006] As a further aspect of the present invention, the specific steps of the digital holographic deformation detection method are as follows:

[0007] Step 1: Construct a Michelson interferometer optical path for the laser emitted by the semiconductor laser, and use the Michelson interferometer optical path to measure the wavelength and diffraction angle of the semiconductor laser.

[0008] First, a laser beam emitted from the semiconductor laser is split into two beams by a polarizing beam splitter (PBS1). One beam is transmitted and split by a distance L1, is reflected by a mirror (M1), and then reflected by the polarizing beam splitter (PBS1) to illuminate the screen (P). The other beam is reflected by a mirror (M2) by a distance L2, and then transmitted through the polarizing beam splitter (PBS1) to illuminate the screen (P).

[0009] Adjust the reflection angles of mirrors (CL1) and (CL2) so that the images of the two beams on the screen completely overlap. Add a small hole in the optical path after beam merging to retain only the information of complete overlap. By adjusting the optical paths L1 and L2 of the two beams, analyze the coherence information of the screen (P) in Step 2, calculate the coherence length using the equal inclination formula, and select an appropriate object plane size.

[0010] Step 2: After selecting a suitable object plane size, construct the digital holographic interference optical path: Construct the measurement optical path, and adjust the output light of the semiconductor laser Laser with a wavelength of λ = 632nm using a square waveguide cavity stacker. Adjust the appropriate distance so that the output light field is a rectangular uniform spot. The uniform output light is split into two beams by a polarizing beam splitter (PBS2). One beam serves as a reference beam, which is reflected by a mirror (CL1), expanded by a beam expander (SF1), collimated by a collimating lens (L1), and then reflected by a mirror (CL3) into the polarizing beam splitter (PBS3). The other beam serves as the probe object light, which is expanded and collimated by a beam expander (SF2) and a collimating lens (L2), reflected by a mirror (CL2), and then illuminates the surface of the test piece (S). The light reflected from the test piece surface enters the polarizing beam splitter (PBS3). The information obtained by fitting the two beams after passing through the polarizing beam splitter (PBS3) is received by the image acquisition system.

[0011] Step 3: Image processing is performed on the phase holograms acquired by the image acquisition system. The laser holograms obtained before and after the object plane displacement, which are superimposed with the reference light, are subjected to neighborhood averaging to eliminate minor noise. The extracted object plane information is processed by a first-order fast Fourier transform (1-FFT) of Fresnel diffraction and image plane filtering to extract the complete object image. Then, through the inverse Fourier operation of Fresnel diffraction, the object field light before and after deformation without interference is extracted, and angular spectrum diffraction reconstruction is performed on it. Fourier transform filtering is used to reduce noise. Finally, iterative unwrapping is performed based on the least squares algorithm to extract the corresponding phase information.

[0012] Step 4: Perform three-dimensional reconstruction processing on the extracted phase information; using the angle between the object reference light and the object plane reflected light, the angle between the object plane reflected light and the three directions V1, V2, V3 of the image acquisition system and their position information, build a mathematical relationship model, and reconstruct the acquired phase information in three dimensions to obtain the corresponding displacement components in the x, y, and z directions.

[0013] As a further aspect of the present invention, the image acquisition system in Step 2 includes:

[0014] An electric displacement platform was built to enable precise movement of the CMOS sensor in the x, y, and z directions.

[0015] An electric displacement platform was used to enable the CMOS to collect phase information of the object plane and the reference light fitted at the beam splitter (PBS3) at three non-collinear but coplanar positions (V1, V2, V3).

[0016] The beneficial effects of this invention are:

[0017] 1. This invention utilizes a low-cost semiconductor laser to achieve the acquisition of phase information of the object plane by measuring the coherence length and improving beam shaping. By building an electric displacement platform, it not only achieves the measurement of three-dimensional deformation at the micrometer level, but also saves the cost of multi-directional information measurement.

[0018] 2. Because it adopts a digital holographic acquisition scheme, it achieves contactless acquisition, which is non-destructive acquisition, and the information obtained is more comprehensive. The acquisition accuracy has also reached the micron level, which can be widely used in the industrial field.

[0019] 3. By using an electric displacement platform and a semiconductor laser, data can be networked to enable remote control of experimental instruments. Attached Figure Description

[0020] Figure 1 The Michelson optical path designed for this invention;

[0021] Figure 2 This is the measurement optical path of the present invention;

[0022] Figure 3 This is a schematic diagram of the image acquisition system of the present invention;

[0023] Figure 4 This is a schematic diagram illustrating the data processing flow obtained by the image acquisition system according to the present invention;

[0024] Figure 5 This is a schematic diagram illustrating the implementation process of the present invention. Detailed Implementation

[0025] Example 1: As Figures 1-5As shown, a digital holographic deformation detection method improves the beam quality of a low-cost semiconductor laser and uses an electric displacement platform to achieve multi-directional acquisition of the object plane, that is, to acquire laser holograms of the object beam and reference beam before and after displacement or deformation of the object plane; the invention is applicable to low-cost semiconductor lasers with different divergence angles in the horizontal and vertical directions, and the two output light sources after beam splitting are also different.

[0026] This invention performs Michelson interferometry experiments on the output light of different types of semiconductor lasers to collect coherent fringes; calculates the coherence length and selects an appropriate object plane size; the output light of the laser forms a rectangular uniform light field through a square waveguide cavity superimposed imager; by adjusting the position information of the CMOS, the same object plane information is collected to obtain the non-coplanar phase information before and after the object plane displacement; the corresponding phase information is extracted by image processing of the laser holograms obtained before and after the object plane displacement, the three-dimensional relationship is constructed by the position information between the CMOS and the object plane, and the phase information is reconstructed in three dimensions to obtain the three-dimensional displacement components.

[0027] As a further aspect of the present invention, the specific steps of the digital holographic deformation detection method are as follows:

[0028] Step 1: Construct a Michelson interferometer optical path for the laser emitted by the semiconductor laser, and use the Michelson interferometer to measure the wavelength and diffraction angle of the semiconductor laser; refer to... Figure 1 The schematic diagram of the Michelson interferometer experiment is used to measure the relevant parameters of the semiconductor laser, which is to determine the relevant parameters of the optical path for the subsequent construction of the digital holographic image.

[0029] First, a laser beam emitted from the semiconductor laser is split into two beams by a polarizing beam splitter (PBS1). One beam is transmitted and split by a distance L1, is reflected by a mirror (M1), and then reflected by the polarizing beam splitter (PBS1) to illuminate the screen (P). The other beam is reflected by a mirror (M2) by a distance L2, and then transmitted through the polarizing beam splitter (PBS1) to illuminate the screen (P).

[0030] Adjust the reflection angles of mirrors (CL1) and (CL2) to ensure that the images of the two beams on the screen are completely superimposed. Because the divergence angle and light output effect of the semiconductor laser are different in the horizontal and vertical directions, the output light effect is different. By adding a small hole in the optical path after beam combining, only the information of complete superposition is retained. By adjusting the optical paths L1 and L2 of the two beams, the coherence information of the screen (P) in Step 2 is analyzed. The coherence length is calculated to be 5cm using the equal inclination formula. The object plane is selected as a circular deformation standard part.

[0031] Step 2: After selecting a suitable object plane size, construct the digital holographic interference optical path: construct the measurement optical path, apply an electric displacement platform to move the CMOS in multiple directions, and collect the corresponding phase information. Phase information before and after displacement is acquired from the obtained phase hologram. The output light of the semiconductor laser Laser with a wavelength of λ = 632 nm is adjusted using a square waveguide cavity stacker to make the output light field a rectangular uniform spot. The uniform output light is split into two beams by a polarizing beam splitter (PBS2). One beam serves as a reference beam, which is reflected by a mirror (CL1), expanded by a beam expander (SF1), collimated by a collimating lens (L1), and then reflected by a mirror (CL3) into the polarizing beam splitter (PBS3). The other beam serves as the probe beam, which is expanded and collimated by a beam expander (SF2) and a collimating lens (L2), reflected by a mirror (CL2), and then illuminates the surface of the test piece (S). The light reflected from the test piece surface enters the polarizing beam splitter (PBS3). The information from the two beams fitted by the polarizing beam splitter (PBS3) is received by the image acquisition system.

[0032] Step 3: Utilize, for example, the phase hologram acquired by the image acquisition system... Figure 4 The digital image processing method shown performs image processing. The laser hologram of the object light and reference light superimposed before and after the object plane displacement is obtained, and the neighborhood averaging is performed on it. The phase difference subtraction algorithm is performed on the images before and after deformation to retain only the phase information generated by deformation and eliminate irrelevant environmental noise. The extracted object plane information is processed by Fresnel diffraction with a first fast Fourier transform (1-FFT) and image plane filtering to extract the complete object image. Then, through the inverse Fourier operation of Fresnel diffraction, the object field light before and after deformation without interference is extracted, and angular spectrum diffraction reconstruction is performed on it. Fourier transform filtering is used for noise reduction. Finally, iterative unwrapping is performed based on the least squares algorithm to extract the corresponding phase information.

[0033] Step 4: Perform three-dimensional reconstruction processing on the extracted phase information; using the angle between the object reference light and the object plane reflected light, the angle between the object plane reflected light and the three directions V1, V2, V3 of the image acquisition system and their position information, build a mathematical relationship model, and reconstruct the acquired phase information in three dimensions to obtain the corresponding displacement components in the x, y, and z directions.

[0034] As a further aspect of the present invention, the image acquisition system in Step 2 includes:

[0035] An electric displacement platform was built to enable precise movement of the CMOS sensor in the x, y, and z directions.

[0036] An electric displacement platform was used to enable the CMOS to collect phase information of the object plane and the reference light fitted at the beam splitter (PBS3) at three non-collinear but coplanar positions (V1, V2, V3).

[0037] This invention uses a low-cost semiconductor to illuminate an object plane, applies the Michelson interferometry principle to utilize relevant parameters of the semiconductor laser, and uses a square waveguide cavity and beam expander to shape the outgoing light with different divergence angles and beam qualities in the horizontal and vertical directions. This enables the acquisition of holograms of the object plane before and after deformation. An electric displacement platform is used to achieve multi-directional image acquisition, reducing the cost of multiple cameras. Multiple deformation fields of the object plane are acquired, and digital image processing methods are used to analyze the acquired images. This invention achieves industrial-precision deformation detection at a low cost and without destructive testing.

[0038] The specific embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A digital holographic deformation detection method, characterized in that: The coherent length is obtained by calculation, and a proper object plane size is selected; the laser light emitted by the laser is formed into a rectangular uniform light field by a square waveguide cavity imager, the same object plane information is collected by adjusting the position information of the CMOS, and the phase information of the object planes before and after the displacement is obtained; the laser hologram obtained by superimposing the object light and the reference light before and after the displacement of the object plane is subjected to image processing to extract the corresponding phase information, a three-dimensional relationship is established between the CMOS and the object plane based on the position information, the phase information is subjected to three-dimensional reconstruction processing, and the three-dimensional displacement component is obtained; The specific steps of the digital holographic deformation detection method are as follows: Step 1: build a Michelson interference optical path for the laser emitted by the semiconductor laser, and measure the wavelength and diffraction angle of the semiconductor laser by using the Michelson interference optical path; Firstly, a laser beam emitted from a semiconductor laser is split into two beams by a polarizing beam splitter (PBS1), one of which is transmitted and the other of which is reflected l The transmitted beam is reflected by a mirror (M1) and then reflected by the polarizing beam splitter (PBS1) to illuminate a screen (P) after a light path of 1. The reflected beam is reflected by a mirror (M2) and then transmitted by the polarizing beam splitter (PBS1) to illuminate the screen (P) after a light path of 2. l The transmitted beam is reflected by a mirror (M1) and then reflected by the polarizing beam splitter (PBS1) to illuminate a screen (P) after a light path of 1. The reflected beam is reflected by a mirror (M2) and then transmitted by the polarizing beam splitter (PBS1) to illuminate the screen (P) after a light path of 2. Adjust the reflecting angle of the reflecting mirror (CL1) and the reflecting mirror (CL2) so that the imaging of the two beams of light on the light screen completely coincides, add a small hole in the light path after the combination, and only keep the completely coincided information; adjust the passing of the two beams of light l 1 and l 2 optical paths, analyze the coherent information of the light screen (P) in Step 2, calculate the coherent length through the isocline formula, and select a suitable object plane size; Step 2: after selecting a proper object plane size, build a digital holographic interference optical path: build a measurement optical path, adjust the emitted light of the semiconductor laser Laser with a wavelength of 632 nm by using a square waveguide cavity imager, adjust the appropriate distance, and make the emitted light field present a rectangular uniform spot; the uniform emitted light is divided into two beams by a polarization beam splitter (PBS2); one of the two beams is reflected by a reflecting mirror (CL1), expanded by an expansion lens (SF1), collimated by a collimating lens (L1), reflected by a reflecting mirror (CL3), and then incident into a polarization beam splitter (PBS3); the other beam is reflected by a reflecting mirror (CL2) after being expanded by an expansion lens (SF2) and collimated by a collimating lens (L2), and then irradiated onto the surface of the tested object (S), and the light reflected by the surface of the tested object is incident into the polarization beam splitter (PBS3); the information of the two beams fitted by the polarization beam splitter (PBS3) is received by an image acquisition system; Step 3: perform image processing on the phase hologram collected by the image acquisition system, perform field average processing on the laser hologram obtained by superimposing the object light and the reference light before and after the displacement of the object plane, eliminate small noise, perform 1-FFT processing on the extracted object plane information, extract the complete object image through image plane filtering, then extract the interference-free object field light before and after the deformation through inverse Fourier operation of Fresnel diffraction, perform angular spectrum diffraction reconstruction, perform Fourier transform filtering and noise reduction, and finally perform iterative unwrapping based on the least square algorithm to extract the corresponding phase information; Step 4: perform three-dimensional reconstruction processing on the extracted phase information; build a mathematical relationship model based on the included angle between the object light and the reference light and the included angle and position information of the object plane reflected light to the positions V1, V2 and V3 of the image acquisition system, reconstruct the collected phase information in three directions, and obtain the displacement components in the x, y and z directions.

2. The digital holographic deformation detection method of claim 1, wherein: The image acquisition system in Step 2 includes: Build an electric displacement platform to realize the accurate movement of CMOS in x, y, z three directions; Use the electric displacement platform to make CMOS collect the phase information of the fitting of the object plane and the reference light at the polarization beam splitter (PBS3) at three non-collinear but coplanar positions (V1, V2, V3).

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