A method for detecting the perpendicularity of a plane to be measured

Abstract

The application discloses a method for detecting the perpendicularity of a to-be-detected plane, which comprises the following steps: adjusting the wave front of an incident light beam through a two-dimensional ultra-thin Fresnel thin film lens to form an axially propagating stable quasi-Bessel light beam; and detecting the normal direction or collimation state of the plane based on the spot pattern evolution characteristics of the quasi-Bessel light beam when the Fresnel thin film lens is tilted, so as to realize the detection stability and engineering applicability of the perpendicularity of the to-be-detected plane without complex refractive optical structures and multi-stage calibration. Furthermore, the structure parameters and diffraction orders of the Fresnel thin film lens can be designed and customized in advance according to the detection requirements of the to-be-detected plane, so as to be applicable to application scenarios with different plane perpendicularity detection precisions.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic detection technology, and in particular to a method for detecting the perpendicularity of a plane to be measured. Background Technology

[0002] The detection of plane perpendicularity and normal direction is a fundamental technical problem in fields such as precision manufacturing, optical system assembly and adjustment, semiconductor packaging and aerospace equipment assembly. Its core lies in accurately obtaining the spatial orientation relationship of the plane to be measured relative to the reference direction. The detection methods are generally based on spatial geometric measurement, displacement (or height) measurement, or beam collimation characteristic measurement to realize the perpendicularity detection of the plane to be measured.

[0003] Among them, the detection method of spatial geometric measurement often uses a laser tracker to obtain the three-dimensional coordinate information of multiple spatial measurement points to realize the verticality measurement of the plane to be measured. However, it is bulky and expensive, and the detection process requires the deployment of measurement base stations outside the plane to be measured, making it difficult to enter narrow spaces or enclosed structures. At the same time, it does not have the ability to attach or conformally measure, and cannot realize in-situ, real-time verticality detection under the operating state of the equipment. Therefore, the engineering application scenarios are limited.

[0004] The detection method for displacement (or height) measurement is to measure the height difference at different positions on the plane to be measured by multiple displacement or height sensors, and to calculate the plane tilt angle and normal direction accordingly. Such as multi-point measurement methods based on spectral confocal displacement meters or capacitive displacement sensors, etc. However, the size and weight of their probes are limited to attachment applications on thin structures or complex surfaces, and the working distance is relatively short, making it difficult to achieve long-distance reference transmission and large-scale detection. Therefore, it is difficult to meet the requirements of non-invasive and in-situ detection.

[0005] The detection method for measuring beam collimation characteristics is based on the Gaussian beam propagation model. Since the Gaussian beam inevitably produces diffraction and divergence during its propagation in free space, its spot size and energy distribution change significantly with the propagation distance. Under the operating environment of vibration, airflow or background light interference, the center position and boundary of its spot are difficult to determine, thus limiting the detection accuracy. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a method for detecting the perpendicularity of a plane to be measured.

[0007] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0008] This invention provides a method for detecting the perpendicularity of a plane to be measured, comprising the following steps: S1, fixing a Fresnel thin-film lens relative to the plane to be measured, setting a light source on the incident side of the Fresnel thin-film lens, and setting a detection unit for acquiring a light spot image on the emitting side of the Fresnel thin-film lens away from the light source; S2, incidenting a laser beam output from the light source onto the Fresnel thin-film lens along a preset reference direction, the incident laser beam undergoing multi-level diffraction through the concentric ring diffraction structure of the Fresnel thin-film lens, and then forming an axially stable quasi-Bessel beam within a preset propagation space; S3, fixing the Fresnel thin-film lens relative to the incident laser beam on the incident laser lens along a preset reference direction; S4, incident a laser beam onto the Fresnel thin-film lens along a preset reference direction; S5, incident a laser beam onto the Fresnel thin-film lens along a preset reference direction; S6, incident a laser beam onto the Fresnel thin-film lens along a preset reference direction; S7, incident a laser beam onto the Fresnel thin-film lens along a preset reference direction; S8, incident a laser beam onto the Fresnel thin-film lens along a preset reference direction; S9, incident a laser beam onto the Fresnel thin-film lens along a preset reference direction; S0, incident a laser beam onto the Fresnel thin-film lens along a preset reference direction; S1, incident a laser beam onto the Fresnel thin-film lens along a preset reference direction; S1, incident a laser beam onto the Fresnel thin-film lens along a preset reference direction; S1, incident a laser beam onto the Fresnel thin-film lens along a preset reference direction; S2 ... The membrane lens is tilted relative to the incident laser beam at different tilt angles, and the resulting quasi-Bessel beam undergoes a beam pattern evolution during propagation; S4, the quasi-Bessel beam beam image under different tilt states acquired by the detection unit is used to form two-dimensional light intensity distribution information; S5, the two-dimensional light intensity distribution information is processed to extract beam feature parameters to characterize the beam pattern change; S6, based on the beam feature parameters and the pre-established correspondence between the beam pattern features and the perpendicularity of the plane to be measured, the perpendicularity of the plane to be measured is calculated, and the detection result is output.

[0009] Furthermore, the light spot characteristic parameters include the distribution variation of the central light spot and / or the side lobe characteristic parameters.

[0010] Furthermore, the sidelobe characteristic parameters include the number of sidelobes, the relative position of the sidelobes, and the symmetry of the sidelobes.

[0011] Furthermore, the change in the distribution of the central light spot includes the intensity distribution of the central light spot and / or the light intensity ratio.

[0012] Furthermore, the laser beam output by the light source is a collimated beam.

[0013] Furthermore, the Fresnel thin-film lens is a thin-film structure, and the concentric ring structure of the Fresnel thin-film lens is used to control the energy ratio of different diffraction order beams; the concentric ring structure of the Fresnel thin-film lens is a binary structure, a ternary structure, or a multi-level structure; or the concentric ring structure of the Fresnel thin-film lens is a continuously gradually changing phase or transmittance distribution; the maximum thickness of the Fresnel thin-film lens is 1 mm.

[0014] Furthermore, the central spot radius of the formed quasi-Bessel beam is determined by the structural parameters of the Fresnel thin-film lens; these parameters include the effective diameter, effective number of rings, radial period of adjacent diffraction rings, ring width, and duty cycle. In addition, the concentric ring structure of the Fresnel thin-film lens can be a binary structure (transmitting / non-transmitting region), a ternary structure (transmitting / semi-transmitting / non-transmitting region), or a multi-level structure. It can also adopt a continuously gradually changing phase or transmittance distribution to achieve control over the energy ratio of beams of different diffraction orders (including second-order, third-order, and higher-order diffraction). This invention does not limit the specific diffraction order implementation method.

[0015] The radial period of adjacent diffraction rings is the main control parameter, related to the equivalent diffraction cone angle of the formed quasi-Bessel beam, thus affecting the size of the central spot and its morphological evolution during propagation. The effective diameter limits the range of effective rings participating in diffraction, thereby affecting the axial propagation stability and non-diffraction propagation distance of the quasi-Bessel beam. Generally, the number of effective rings participating in diffraction increases with the increase of the effective diameter and decreases with the increase of the radial period of adjacent diffraction rings. The ring width and duty cycle are used to control the ratio between the transmission and non-transmission regions, thereby affecting the energy distribution characteristics of beams of different diffraction orders, and thus affecting the energy concentration, sidelobe intensity, and spot morphological stability of the quasi-Bessel beam's central optical axis. When the parameter combination changes, the quasi-Bessel beam may exhibit morphological evolution characteristics such as changes in the central spot size, sidelobe enhancement, or spot splitting during propagation.

[0016] Furthermore, the multi-order diffraction includes a positive-order diffraction beam and a negative-order diffraction beam. The positive-order diffraction beam converges towards the beam axis and forms a quasi-Bessel beam with approximately no diffraction characteristics. The negative-order diffraction beam is divergent, and the intensity of the negative-order diffraction beam is significantly less than the intensity of the positive-order diffraction beam.

[0017] The technical solution provided by this invention has the following beneficial effects:

[0018] 1. This invention utilizes a two-dimensional ultrathin Fresnel thin-film lens to wavefront modulate the incident beam, forming a quasi-Bessel beam with stable axial propagation. Based on the evolution characteristics of the spot shape generated by this quasi-Bessel beam when the Fresnel thin-film lens is tilted, the normal direction or collimation state of the plane is detected. Thus, the stability and engineering applicability of the perpendicularity detection of the plane under test are achieved without the need for complex refractive optical structures and multi-level calibration.

[0019] 2. This invention achieves beam wavefront modulation through a Fresnel thin-film lens to ensure that the formed quasi-Bessel beam maintains stable axial propagation characteristics within a certain propagation distance. This reduces the impact of diffraction divergence and environmental disturbances on the detection results, while improving the repeatability and reliability of collimation detection.

[0020] 3. Since the Fresnel thin film lens does not rely on the refraction and propagation of light in a thick medium, it is less likely to produce the axial displacement problem common to refractive elements when the optical device or the plane under test is tilted. This reduces the sources of system error, reduces the dependence on additional calibration structures, and simplifies system calibration.

[0021] 4. This invention calculates collimation and normal direction based on the overall spot morphology characteristics, enabling non-contact, in-situ detection. It is also applicable to irregular planes and spatially confined scenarios, thus achieving non-invasive detection with strong adaptability.

[0022] 5. Compared with the bulky refractive axial pyramids in the prior art, the Fresnel thin film lens used in this invention is an ultra-thin two-dimensional optical element, which is conducive to system miniaturization, weight reduction and integrated deployment.

[0023] 6. The present invention allows for the pre-design and customization of the structural parameters and diffraction order of the Fresnel thin-film lens according to the detection requirements of the plane to be measured, so as to be suitable for application scenarios with different plane perpendicularity detection accuracies. Therefore, the parameters of the Fresnel thin-film lens are adjustable to ensure engineering flexibility and have good potential for engineering promotion. Attached Figure Description

[0024] Figure 1 The flowchart shown is a method for detecting the perpendicularity of the plane to be tested in Embodiment 1.

[0025] Figure 2 The diagram shown is a schematic diagram of the perpendicularity detection method of the plane to be tested in Embodiment 1.

[0026] Figure 3 The diagram shown is a schematic of the verticality detection system in Embodiment 1;

[0027] Figure 4 The image shown is the center spot of the quasi-Bessel beam in Example 1;

[0028] Figure 5 The image shown is an image of the central spot of the quasi-Bessel beam in Example 1 splitting into two side lobes.

[0029] Figure 6 The diagram shows the structural design of the Fresnel thin-film lens with different parameters in Example 1. Detailed Implementation

[0030] To further illustrate the various embodiments, the present invention provides accompanying drawings. These drawings are part of the disclosure of the present invention and are mainly used to illustrate the embodiments, and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these drawings, those skilled in the art should be able to understand other possible implementations and the advantages of the present invention. Components in the drawings are not drawn to scale, and similar component symbols are generally used to represent similar components.

[0031] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments.

[0032] Example 1

[0033] Reference Figures 1 to 6 Example 1 provides a method for detecting the perpendicularity of a plane to be measured, for quickly and accurately detecting the perpendicularity of the plane 3 to be measured. The plane 3 to be measured can be the surface of an object with a geometric planar structure, including the surface of a mounting plate, the mounting plane of an optical device, the plane of the casing and structural components of a precision instrument, the planar structure of a semiconductor package and substrate, and the positioning plane in industrial equipment or automation devices, etc. Of course, the specific material, size, or application industry of the plane 3 to be measured is not limited.

[0034] In this embodiment, based on the detection requirements of the object being measured (i.e., the plane 3 to be measured), such as the detection distance, accuracy requirements, and installation conditions, a selection or customization is made in advance. Figure 6 The Fresnel thin-film lens 2 with the corresponding structural parameters shown (including effective diameter, radial period of adjacent diffraction rings, ring width, and duty cycle) is used as follows. Figure 2 The perpendicularity detection system shown is used to detect the perpendicularity of the plane 3 to be measured, and specifically includes the following steps:

[0035] Step S1: Fix the Fresnel thin film lens 2, which matches the detection requirements, relative to the plane to be tested 3, and set the light source 1 on the light-incident side of the Fresnel thin film lens 2, and set the detection unit 4 for acquiring light spot images on the light-out side of the Fresnel thin film lens 2 away from the light source 1. The laser beam output by the light source 1 is a collimated beam, and the detection unit 4 includes a CCD sensor or a CMOS sensor.

[0036] In step S2, the laser beam output from light source 1 is incident on Fresnel thin-film lens 2 along a preset reference direction. The incident laser beam undergoes multi-order diffraction through the concentric ring diffraction structure of Fresnel thin-film lens 2, and then forms an axially stable quasi-Bessel beam within a preset propagation space. The multi-order diffraction includes positive-order diffraction beams and negative-order diffraction beams. The positive-order diffraction beams converge towards the beam axis and form a quasi-Bessel beam with approximately no diffraction characteristics. The negative-order diffraction beams are divergent, and the intensity of the negative-order diffraction beams is significantly less than that of the positive-order diffraction beams.

[0037] In step S3, the Fresnel thin-film lens 2 is tilted relative to the incident laser beam at different tilt angles, and the resulting quasi-Bessel beam undergoes a beam pattern evolution during propagation.

[0038] Step S4: The quasi-Bessel beam spot images acquired by the detection unit 4 under different tilt states are used to form two-dimensional light intensity distribution information.

[0039] Step S5: Perform image processing on the two-dimensional light intensity distribution information to extract light spot feature parameters used to characterize the changes in light spot morphology. These light spot feature parameters include only the distribution changes of the central light spot, such as the intensity distribution of the central light spot, in order to calculate the center position of the light spot.

[0040] Step S6: Based on the characteristic parameters of the light spot, and combined with the pre-established correspondence between the light spot morphology and the tilt angle of the plane 3 to be measured, i.e., the light spot morphology change and the tilt angle of the plane 3 to be measured have a stable correspondence, this can be used as the basis for detecting the collimation state or perpendicularity of the plane 3 to be measured, so as to accurately calculate the perpendicularity of the plane 3 to be measured and output the detection result. Of course, according to various detection needs, different tilt states of the Fresnel thin film lens 2 can also be repeatedly detected to verify the stability and repeatability of the detection results.

[0041] In this embodiment, as Figure 6 As shown, the Fresnel thin-film lens 2 is a thin-film structure with a thickness of less than 1 mm, which serves as a diffractive two-dimensional optical element and has a corresponding equivalent diffraction cone angle or non-diffraction propagation distance, thus enabling spatial modulation of the incident beam.

[0042] More specifically, the central spot radius of the formed quasi-Bessel beam is determined by the structural parameters of the Fresnel thin-film lens 2, including the effective diameter, effective number of rings, radial period of adjacent diffraction rings, ring width, and duty cycle. Furthermore, the concentric ring structure of the Fresnel thin-film lens 2 can adopt a binary structure (transmitting / non-transmitting region), a ternary structure (transmitting / semi-transmitting / non-transmitting region), or a multi-level structure. It can also adopt a continuously gradually changing phase or transmittance distribution to achieve the control of beam energy ratios for different diffraction orders (including second-order, third-order, and higher-order diffraction). Of course, this invention does not limit the specific diffraction order implementation method.

[0043] The effective diameter is used to limit the effective number of rings participating in diffraction, thereby affecting the axial stability of the beam and the non-diffraction propagation distance.

[0044] The radial period of adjacent diffraction rings is related to the equivalent diffraction cone angle of the formed quasi-Bessel beam, thus affecting the size of the central spot of the quasi-Bessel beam and its morphological evolution characteristics during propagation.

[0045] The ring width and duty cycle are used to control the ratio between the transmission and non-transmission regions, thereby affecting the energy distribution characteristics of different diffraction order sub-beams, and consequently affecting the energy concentration, side lobe intensity, and spot shape stability of the beam aligned with the central optical axis of the Bessel beam.

[0046] Furthermore, the number of effective rings participating in diffraction increases with the increase of the effective diameter and decreases with the increase of the radial period of adjacent diffraction rings.

[0047] The above structural parameters are not set independently, but are designed collaboratively based on the detection distance, detection sensitivity and stability requirements of the perpendicularity detection of the plane 3 to be measured. By adjusting the combination relationship of each parameter, the quasi-Bessel beam formed produces repeatable and distinguishable changes in the shape of the light spot when it is tilted on the Fresnel thin film lens 2.

[0048] Unlike existing technologies that only utilize the imaging or focusing performance parameters of Fresnel lenses, this invention uses the requirements for the stability and distinguishability of the light spot morphology in the perpendicularity detection of the plane 3 under test as design constraints. Therefore, it performs reverse parameterization design on the various structural parameters of the Fresnel thin-film lens 2. This means that by combining and adjusting the various parameters of the Fresnel thin-film lens 2, it can adapt to different detection distances, different spatial constraints, and different detection sensitivity requirements without changing the overall architecture of the perpendicularity detection system. Specific structural parameters of the Fresnel thin-film lens 2 are as follows: Figure 6 As shown.

[0049] In the embodiment, the central spot radius of the formed quasi-Bessel beam is related to the radial period parameter and diffraction order of the Fresnel thin film lens 2. It typically increases with the increase of the radial period of the adjacent diffraction rings and is adjusted accordingly with the change of the effective diffraction order.

[0050] Since the Fresnel thin-film lens 2 has an ultra-thin structure, it does not introduce a significant optical axis translation effect during tilting. At the same time, the verticality detection method in this embodiment does not rely on the change of the centroid position of the light spot, but uses the overall morphological characteristics of the light spot for judgment, which has higher stability and anti-interference ability. This avoids the need for additional calibration of the incident beam position in the tilt detection of refractive optical elements in the prior art, thus effectively improving the stability and reliability of the detection process.

[0051] In addition, compared to existing millimeter-thick refractive axial pyramid or conical lenses, the ultrathin structure of the Fresnel thin film lens 2 does not introduce a significant optical axis shift effect when tilted, which helps to reduce systematic errors in the collimation detection process.

[0052] When detection requirements change, only the structural parameters of the Fresnel thin-film lens 2 need to be adjusted and remanufactured to obtain detection capabilities that match the new detection scenario, without requiring structural modifications to the overall detection system. This significantly improves the system's engineering applicability, flexibility, and multi-scenario adaptability. In other words, this embodiment adopts a technical approach that combines parametric design and rapid customization. The combination of structural parameters of the Fresnel thin-film lens 2 is determined in reverse based on the size characteristics of the target object, installation conditions, and detection accuracy requirements. Therefore, by combining and adjusting the various parameters of the Fresnel thin-film lens 2, the selected Fresnel thin-film lens 2 can be adapted to detection scenarios with different detection distances, different spatial constraints, and different detection sensitivity requirements without changing the overall architecture of the detection system.

[0053] In summary, based on the size characteristics of the object being measured, the installation space, and the required detection accuracy, a Fresnel thin-film lens 2 with specific diffraction parameters was designed and obtained. This allows the incident beam to form a quasi-Bessel beam with stable axial propagation after passing through the Fresnel thin-film lens 2. Furthermore, when the Fresnel thin-film lens 2 is tilted, the quasi-Bessel beam exhibits repeatable and distinguishable changes in its spot shape during propagation. By collecting and analyzing these changes in spot shape, the perpendicularity or collimation state of the plane can be detected.

[0054] Compared to existing technologies that rely on the propagation characteristics of Gaussian beams, this method is susceptible to diffraction divergence and environmental disturbances, and requires the introduction of heavy refractive devices or complex optical structures to improve stability. This results in problems such as large system size, complex structure, difficult calibration, and difficulty in in-situ application.

[0055] In addition, such as Figure 3 As shown, the beam axis of this embodiment is defined as the Z-axis, and the tilt angle β is the angle between the normal of the Fresnel thin film lens 2 and the Z-axis, so as to characterize the gradual tilt of the normal of the Fresnel thin film lens 2 relative to the Z-axis. Thus, this embodiment can acquire light spot images under different tilt states by gradually changing the tilt angle β of the Fresnel thin film lens 2.

[0056] In practice, the perpendicularity of the plane to be measured 3 is calculated based on the distribution variation of the central spot of the quasi-Bessel beam.

[0057] like Figure 4 and Figure 5 As shown, the detection unit 4 acquires a quasi-Bessel beam spot image at a certain tilt angle β, and the computer processes the quasi-Bessel beam spot image to obtain the corresponding two-dimensional light intensity distribution information.

[0058] By analyzing the two-dimensional light intensity distribution information, the region with the maximum light intensity is identified, and a fixed range is set around it to determine the central light spot region. The light intensity value within the central light spot region is statistically analyzed to obtain the average light intensity I0 of the central light spot region. At the same time, the region with the local maximum light intensity is identified outside the central light spot region, and the side lobe region with the maximum light intensity is selected. The light intensity value of the side lobe region with the maximum light intensity is statistically analyzed to obtain the light intensity I1 of the side lobe region with the maximum light intensity. Then, the light intensity ratio R = I0 / I1 is calculated.

[0059] During the system calibration phase, the light intensity ratio R corresponding to different tilt angles β is pre-acquired, and a correspondence or mapping relationship between the light intensity ratio R and the tilt angle β is established, i.e., a piecewise regression model is built. When a certain light intensity ratio R is obtained during the actual detection process... x At that time, the tilt angle β of the plane to be measured 3 can be determined through the established mapping relationship, thereby determining the perpendicularity of the plane to be measured 3.

[0060] Example 2

[0061] Example 2 provides a method for detecting the perpendicularity of a plane to be measured. The detection methods of Example 2 and Example 1 are largely the same, except that the spot feature parameters of this example only include the side lobe feature parameters.

[0062] Specifically, the light spot image acquired by the detection unit is processed to identify the side lobe regions surrounding the central light spot and extract side lobe feature parameters. These side lobe feature parameters include the number of side lobes, the positional distribution of each side lobe relative to the central light spot, and the symmetry of the side lobe distribution. Specifically, the sum of light intensities of the corresponding side lobe regions on both sides of the central light spot is calculated, and the difference or ratio of their light intensities is used as the symmetry feature parameters of the side lobe distribution.

[0063] During the system calibration phase, sidelobe feature parameters corresponding to different tilt angles are pre-acquired, and a correspondence or mapping relationship is established between the sidelobe feature parameters and the tilt angle of the plane to be measured. When a certain sidelobe feature parameter value is obtained during the actual detection process, the corresponding tilt angle is determined through the established mapping relationship, thereby determining the perpendicularity of the plane to be measured.

[0064] Example 3

[0065] Example 3 provides a method for detecting the perpendicularity of the plane to be measured. The detection method of Example 3 is largely the same as that of Example 1 or Example 2, except that the spot characteristic parameters of this example include both the distribution change of the center spot and the side lobe characteristic parameters, which can further improve the detection accuracy.

[0066] In this embodiment, the intensity distribution features of the central spot and the number, relative position and symmetry features of the side lobes are extracted by image processing of the spot image acquired by the detection unit.

[0067] Based on the intensity ratio characteristics of the central spot and the symmetry characteristics of the side lobes, a weighted analysis or multi-feature fusion method is used to establish the correspondence between the comprehensive spot feature parameters and the tilt angle of the plane under test. Through joint analysis of multiple spot feature parameters, the errors caused by noise or environmental disturbances affecting a single feature can be effectively reduced, thereby further improving the accuracy and stability of verticality detection.

[0068] In the actual detection process, based on the comprehensive spot feature parameters extracted in real time, and based on the mapping relationship between the spot features and the tilt angle of the plane to be measured, a piecewise regression model is established. By inputting relevant feature parameters, the tilt angle of the plane to be measured can be calculated, and the perpendicularity of the plane to be measured can be determined. This enables high-precision plane perpendicularity detection.

[0069] Although the invention has been specifically shown and described in conjunction with preferred embodiments, those skilled in the art should understand that various changes in form and detail may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims, all of which shall be within the scope of protection of the invention.

Claims

1. A method for detecting the perpendicularity of a plane to be measured, characterized in that, Includes the following steps: S1, fix the Fresnel thin film lens relative to the plane to be measured, set a light source on the light-incident side of the Fresnel thin film lens, and set a detection unit for acquiring light spot images on the light-out side of the Fresnel thin film lens away from the light source; S2, the laser beam output from the light source is incident on the Fresnel thin film lens along the preset reference direction. The incident laser beam undergoes multi-level diffraction through the concentric ring diffraction structure of the Fresnel thin film lens, and then forms an axially stable quasi-Bessel beam within the preset propagation space. S3, the Fresnel thin film lens is tilted relative to the incident laser beam at different tilt angles, and the quasi-Bessel beam formed by it produces a beam pattern evolution during propagation; S4, the quasi-Bessel beam spot images under different tilt states acquired by the detection unit are used to form two-dimensional light intensity distribution information; S5, the two-dimensional light intensity distribution information obtained in S4 is processed to extract the light spot feature parameters used to characterize the changes in light spot morphology; S6. Based on the spot feature parameters obtained in S5, and combined with the pre-established correspondence between the spot morphology features and the perpendicularity of the plane to be measured, calculate the perpendicularity of the plane to be measured and output the detection result. The maximum thickness of the Fresnel thin-film lens is 1 mm; The radius of the central spot of the formed quasi-Bessel beam is determined by the structural parameters of the Fresnel thin-film lens. These parameters include the effective diameter, the number of effective rings, the radial period of adjacent diffraction rings, the ring width, and the duty cycle. The effective diameter limits the number of effective rings participating in diffraction, thus affecting the axial stability of the beam and the non-diffraction propagation distance. The radial period of adjacent diffraction rings adjusts the equivalent diffraction cone angle of the formed quasi-Bessel beam, thereby adjusting the size of the central spot of the quasi-Bessel beam and its morphological evolution characteristics during propagation. The ring width and duty cycle are used to control the ratio between the transmission and non-transmission regions, thereby adjusting the energy distribution of different diffraction order beams, and further adjusting the energy concentration of the central optical axis, side lobe intensity, and beam pattern stability of the quasi-Bessel beam. Moreover, the number of effective rings participating in diffraction increases with the increase of the effective diameter and decreases with the increase of the radial period of adjacent diffraction rings.

2. The method for detecting the perpendicularity of the plane to be measured according to claim 1, characterized in that: The light spot characteristic parameters include the distribution variation of the central light spot and / or the side lobe characteristic parameters.

3. The method for detecting the perpendicularity of the plane to be measured according to claim 2, characterized in that: The sidelobe characteristic parameters include the number of sidelobes, the relative position of the sidelobes, and the symmetry of the sidelobes.

4. The method for detecting the perpendicularity of the plane to be measured according to claim 2, characterized in that: The changes in the distribution of the central light spot include the intensity distribution of the central light spot and / or the light intensity ratio.

5. The method for detecting the perpendicularity of the plane to be measured according to claim 1, characterized in that: The laser beam output by the light source is a collimated beam.

6. The method for detecting the perpendicularity of the plane to be measured according to any one of claims 1-5, characterized in that: The Fresnel thin-film lens is a thin-film structure, and the concentric ring structure of the Fresnel thin-film lens is used to control the energy ratio of different diffraction order sub-beams. The concentric ring structure of the Fresnel thin-film lens is a binary structure, a ternary structure, or a multi-level structure; or the concentric ring structure of the Fresnel thin-film lens is a continuously gradually changing phase or transmittance distribution.

7. The method for detecting the perpendicularity of the plane to be measured according to claim 6, characterized in that: The binary structure includes a transmissive region and a non-transmissive region; the ternary structure includes a transmissive region, a semi-transmissive region, and a non-transmissive region.

8. The method for detecting the perpendicularity of the plane to be measured according to claim 1, characterized in that: The multi-order diffraction includes a positive-order diffraction beam and a negative-order diffraction beam. The positive-order diffraction beam converges towards the beam axis and forms a quasi-Bessel beam with approximately no diffraction characteristics. The negative-order diffraction beam is divergent, and the intensity of the negative-order diffraction beam is significantly less than that of the positive-order diffraction beam.

Images