A method and apparatus for measuring small-angle deflection accuracy based on conical interferometry

Abstract

This invention discloses a method and apparatus for measuring the accuracy of small-angle deflection based on conical interferometry. The method includes: a laser emitted from a laser source sequentially passes through a deflector under test and a polarizer to obtain linearly polarized light; the linearly polarized light is incident on an electro-optic crystal at a preset angle, decomposing into o-ray and e-ray, and generating a phase delay; the o-ray and e-ray interfere after passing through an analyzer, and the generated interference light is received by a photodetector; the electro-optic crystal is rotated until the spot intensity is maximum, and the first incident field angle is recorded; the deflector under test is scanned with a scanning step size until the spot intensity is 0, and the second incident field angle is recorded; the number of resolvable spots received by the photodetector during the change in spot intensity from maximum to 0 is counted, and the scanning accuracy of the deflector under test is calculated by dividing the difference between the first and second incident field angles by the number of spots. This method achieves a simple measurement method and apparatus with high measurement accuracy.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronics and laser technology, and more specifically, relates to a method and apparatus for measuring the accuracy of small-angle deflection based on conical interferometry. Background Technology

[0002] High-speed laser scanning systems have been widely used in laser engraving, imaging, and photolithography. Currently, the main high-speed laser scanning methods can be divided into two categories: one is mechanical scanners based on mirrors, mainly including galvo scanners and piezo scanners; the other is optical solid-state deflectors based on optical systems, mainly including acousto-optic deflectors (AOD) and electro-optic deflectors (EOD).

[0003] Traditional mirror-based mechanical scanning methods suffer from the mechanical movement and hysteresis errors of the mirrors, affecting the accuracy and repeatability of beam positioning in high-precision manufacturing. Therefore, their deflection angular velocity is essentially limited by the inertia related to the mass of the rotating mirror and other moving parts. In contrast, acousto-optic deflectors and electro-optic deflectors contain no moving mechanical parts, thus avoiding the wear, mechanical noise, and drift associated with mechanical scanners. They can deflect the laser beam with high precision unaffected by mechanical inertia, offering advantages such as fast scanning speed, high accuracy, short response time, and random access scanning, and are widely used in laser direct-write systems.

[0004] In order to effectively evaluate the scanning accuracy of acousto-optic deflectors (AOD) and electro-optic deflectors (EOD), it is necessary to use precise small-angle measurement methods to quantify them. With the rapid development of laser industrial processing and photonic imaging, the requirements for the scanning accuracy of acousto-optic deflectors (AOD) and electro-optic deflectors (EOD) are increasing. Therefore, traditional precise measurement methods for beam deflection angle, such as CCD-based direct measurement method, autocollimation method and dual-mirror reflection method, have the following problems: (1) CCD-based direct measurement method is complicated to operate, has high measurement cost, is easily affected by ambient stray light, and its accuracy is limited by pixel size and camera lens focal length. Therefore, it has limitations and is difficult to achieve high precision for acousto-optic deflectors (AOD) and electro-optic deflectors (EOD). (1) The accuracy requirements of the scanning device; (2) The imaging optical path of the autocollimation method is relatively complex and difficult to adjust, and the measurement distance is generally short. In addition, the autocollimation method usually requires precise calibration and adjustment in advance, so it is difficult to adapt to the dynamically changing measurement scenario; (3) The dual-mirror reflection method has high requirements for the surface quality of the mirror, so the manufacturing cost is high. In addition, the dual-mirror reflection method requires precise installation and debugging of the mirror to ensure that the position and angle of the mirror and the light source are precisely aligned. Therefore, the installation and debugging process is relatively difficult. The accuracy of this method is also limited by the measurement distance and angle range, so its practicality is not high. (4) The measurement resolution is insufficient (>2μrad), which cannot match the high scanning accuracy (≤0.2μrad) of the acousto-optic deflector (AOD) and electro-optic deflector (EOD).

[0005] Therefore, existing methods for measuring small angles of deflectors suffer from problems such as complex operation, high cost, and low accuracy. Summary of the Invention

[0006] In view of the shortcomings of related technologies, the purpose of this invention is to provide a method and apparatus for measuring the accuracy of small-angle deflection based on conical interferometry, which aims to solve the problems of complex operation, high measurement cost and low measurement accuracy of existing small-angle measurement methods for deflectors.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a method for measuring small-angle deflection accuracy based on conical interferometry, comprising:

[0008] The laser light emitted from the laser source passes sequentially through the deflector under test and the polarizer to obtain linearly polarized light;

[0009] The linearly polarized light is incident on the electro-optic crystal at a preset angle, decomposed into o-ray and e-ray, and a phase delay is generated;

[0010] The o-ray and e-ray obtained from the decomposition interfere after passing through the analyzer, and the resulting interference light is received by the photodetector.

[0011] Rotate the electro-optic crystal until the light spot intensity received by the photodetector is at its maximum, and record the first incident field angle.

[0012] The deflector under test is scanned in a scanning step until the intensity of the light spot received by the photodetector is 0, and the second incident field angle is recorded.

[0013] The scanning accuracy of the deflection device under test is calculated by counting the number of resolvable light spots received by the photodetector as the light spot intensity changes from maximum to 0, and dividing the difference between the first incident field of view and the second incident field of view by the number of light spots.

[0014] Optionally, before the laser emitted from the laser source passes sequentially through the deflector under test and the polarizer, the following method is further included:

[0015] The laser emitted from the laser source is collimated by a collimating lens to obtain a reference beam.

[0016] Optionally, the preset angle is the angle between the incident linearly polarized light and the optical axis of the electro-optic crystal, and the preset angle is 5°.

[0017] Optionally, the phase delay is:

[0018]

[0019] Where L is the thickness of the electro-optic crystal. n o n e ω represents the principal refractive indices of the o-ray and e-ray, respectively, and ω is a preset angle.

[0020] Optionally, the intensity of the interference light is:

[0021]

[0022] Where A1 is the amplitude of the incident linearly polarized light, θ is the angle between the projection direction De of the electric displacement direction of the e-ray in the xy plane and the polarization direction P1 of the polarizer, and A o2 and A e2 These are the amplitudes of the o-ray and e-ray after passing through the analyzer, respectively.

[0023] Optionally, when δ = 2kπ, the interference fringes are bright fringes, and the intensity of the light spot received on the photodetector is the maximum.

[0024] When δ=(2k+1)π, the interference fringes are dark fringes, and the intensity of the light spot received on the photodetector is 0; where k represents the interference order, k=0,1,2,3,4,…….

[0025] Optionally, the deflector under test is an acousto-optic deflector or an electro-optic deflector. If it is an acousto-optic deflector, the reference beam coincides with the zero-order diffraction direction of the acousto-optic deflector.

[0026] In a second aspect, the present invention also provides a device for measuring the small-angle deflection accuracy based on conical interferometry, for performing the method described in any of the first aspects, comprising: a laser source, a collimating lens, a deflector to be measured, a polarizer, an electro-optic crystal, an analyzer, and a photodetector arranged sequentially along the optical path;

[0027] The collimating lens is used to collimate the laser emitted by the laser source to obtain a reference beam;

[0028] The deflector under test is used to deflect the reference beam at a small angle;

[0029] The polarizer is used to convert the incident light beam into linearly polarized light;

[0030] The electro-optic crystal is used to decompose incident linearly polarized light into o-ray and e-ray, and to generate phase delay;

[0031] The analyzer is used to generate interference light by transmitting o-light and e-light in a preset direction;

[0032] The photodetector is used to receive the light spot generated by interference light.

[0033] Compared with the prior art, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0034] 1. The present invention provides a method for measuring the accuracy of small-angle deflection based on conical interferometry. The optical path of the measuring device is simple and easy to adjust, which is beneficial for practical applications. It utilizes the birefringence characteristics of electro-optic crystals to allow deflection light to be incident on the electro-optic crystal at different angles, generating phase differences of different magnitudes. This allows the photodetector to receive high-contrast light intensity, thereby measuring the accuracy of the deflection device. The measurement accuracy is not affected by the measurement range and the pixel resolution of the photodetector, thus ensuring high resolution even with a large measurement range.

[0035] 2. The present invention provides a method for measuring the small-angle deflection accuracy based on conical interferometry. The measurement accuracy of the system can be adjusted according to the scanning accuracy of the deflection device under test, so that the measurement accuracy of the system matches the scanning accuracy of the deflection device under test, thereby increasing practical feasibility. The deflection device to be measured is an acousto-optic deflector or an electro-optic deflector, which has a wide range of applications.

[0036] 3. The present invention provides a method for measuring the accuracy of small-angle deflection based on conical interferometry. The accuracy of this method is not limited by the measurement distance and angle range. Therefore, no precise installation and debugging are required. It is only necessary to adjust the angle of the electro-optic crystal to change the initial field of view of the deflected light entering the electro-optic crystal. Therefore, the operation is simple and the practicality is strong. Attached Figure Description

[0037] Figure 1 This is a flowchart illustrating a method for measuring small-angle deflection accuracy based on conical interferometry, provided in an embodiment of the present invention.

[0038] Figure 2 This is a diagram of a device for interfering two beams of light in an embodiment of the present invention;

[0039] Figure 3 This is a schematic diagram of the structure of a device for measuring small-angle deflection accuracy based on conical interferometry provided in an embodiment of the present invention;

[0040] Figure 4 This is a diagram showing the conical interference pattern of incident light when it is incident on an electro-optic crystal at different field angles, and the corresponding light intensity variation curves received by the photodetector.

[0041] Figure 5 This is a diagram showing the relationship between the angular spacing between adjacent bright and dark fringes and the field of view of the incident light entering the electro-optic crystal, provided in an embodiment of the present invention.

[0042] Figure 6 This is a schematic diagram illustrating the relationship between ultrasonic frequency and relative light intensity provided in an embodiment of the present invention;

[0043] Figure 7 This is a schematic diagram of another device for measuring small-angle deflection accuracy based on conical interferometry provided in an embodiment of the present invention;

[0044] Figure 8 This is a schematic diagram illustrating the relationship between electric field strength and relative light intensity provided in an embodiment of the present invention.

[0045] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1 is a laser source; 2 is a collimating lens; 3 is an acousto-optic deflector (AOD); 4 is an electro-optic deflector (EOD); 5 is a polarizer; 6 is an electro-optic crystal; 7 is an analyzer; 8 is a photodetector; 9 is o-light; 10 is e-light. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0047] The following description, in conjunction with a preferred embodiment, illustrates the content involved in the above embodiments.

[0048] Example 1

[0049] like Figure 1 As shown, a method for measuring small-angle deflection accuracy based on conical interferometry includes:

[0050] S1. The laser light emitted from the laser source passes sequentially through the deflector to be tested and the polarizer to obtain linearly polarized light;

[0051] S2. The linearly polarized light enters the electro-optic crystal at a preset angle, decomposes into o-light and e-light, and generates a phase delay;

[0052] S3. The o-ray and e-ray obtained from the decomposition interfere after passing through the analyzer, and the resulting interference light is received by the photodetector.

[0053] S4. Rotate the electro-optic crystal until the light spot intensity received by the photodetector is at its maximum, and record the first incident field angle.

[0054] S5. The deflector under test is scanned with a scanning step size until the light spot intensity received by the photodetector is 0, and the second incident field angle is recorded.

[0055] S6. During the process of the light spot intensity changing from the maximum to 0, the number of resolvable light spots received by the photodetector is counted. The scanning accuracy of the deflection device under test is calculated by dividing the difference between the first incident field of view and the second incident field of view by the number of light spots.

[0056] This invention provides a method for measuring the accuracy of small-angle deflection based on conical interferometry, which is applied to a device for measuring the accuracy of small-angle deflection based on conical interferometry. For example... Figure 2As shown, the specific implementation device includes: a polarizer 5, an electro-optic crystal 6, and an analyzer 7 arranged along the optical path. First, the relevant reference coordinate system and directions are defined in this embodiment: the crystal principal axis direction of the electro-optic crystal 6 is the x and y directions. Taking the crystal principal axis direction x and y of the electro-optic crystal 6 as the reference coordinate system, the transmission directions of the polarizer 5 and the analyzer 7 are defined as P1 and P2, respectively. P1 and P2 are orthogonal to each other, and the angle between them and the crystal principal axis direction x and y of the electro-optic crystal 6 is 45°. The angle between the polarization direction P1 of the polarizer 5 and the projection direction De of the electric displacement direction of the e-beam 7 in the xy plane is θ. The field of view angle between the optical axis direction of the electro-optic crystal 6 and the laser incident direction is ω.

[0057] The basic working principle is described as follows: Normally, two linearly polarized beams with mutually perpendicular vibration directions cannot interfere when superimposed, even if they have the same frequency and a fixed phase difference. However, if these two beams of light are passed through a polarizer, their vibrational components along the transmission axis of the polarizer will be in the same direction, and the two beams of light can then interfere. Figure 2 This is a diagram of a device used to achieve interference between two beams of light. (See diagram for example.) Figure 2 As shown, the incident light becomes linearly polarized after passing through polarizer 5, and then strikes the electro-optic crystal 6 at a field of view angle ω. The principal axes of electro-optic crystal 6 are in the x and y directions. Taking the x and y directions of the principal axes of electro-optic crystal 6 as the reference coordinate system, the incident linearly polarized light will be decomposed into o-light 9 and e-light 10 within electro-optic crystal 6. The projections of the electric displacement directions of o-light 9 and e-light 10 onto the xy plane are Do and De. After exiting electro-optic crystal 6, o-light 9 and e-light 10 are combined into elliptically polarized light, which can also be regarded as two linearly polarized beams with a certain phase difference. When these beams are then struck by analyzer 7, only the vibration component in the transmission direction P2 of analyzer 7 can pass through. Therefore, the vibrations of the two outgoing beams are in the same direction, and interference can occur. Figure 3 As shown, the device for measuring the accuracy of small-angle deflection includes a laser source 1, a collimating lens 2, a deflector under test 3, a polarizer 5, an electro-optic crystal 6, an analyzer 7, and a photodetector 8 arranged sequentially along the optical path. The optical axis of the laser source 1 coincides with the optical axis of the lens and also with the output light direction of the deflector under test 3. The interference light generated by the analyzer 7 is received by the photodetector 8.

[0058] According to the interference conditions, when δ = 2kπ, the interference fringes are bright fringes, that is, the intensity of the light spot received on the photodetector 8 is the maximum; when δ = (2k+1)π, the interference fringes are dark fringes, that is, the incident light is completely lost after passing through the measuring device, and the intensity of the light spot received on the photodetector 8 is 0; where k = 0, 1, 2, 3, 4, ..., represents the interference order.

[0059] like Figure 3As shown, based on the light spot displayed by photodetector 8, rotate electro-optic crystal 6 until the intensity of the light spot received by photodetector 8 is at its maximum. At this point, the interference fringes are bright fringes, and the first incident field of view angle is recorded. Keeping electro-optic crystal 6 stationary, start the deflector under test 3 to scan in scanning steps. During the process of the deflector under test 3 stepping one scanning step, observe the intensity of the light spot received on photodetector 8 until the light spot intensity is 0. At this point, the interference fringes are dark fringes, and the second incident field of view angle is recorded. As the deflector under test 3 continues to scan, the pattern of the light spot received by photodetector 8 is as follows: Figure 4 As shown, the diagram shows the conical interference patterns of incident light incident on the electro-optic crystal at different field angles and the corresponding light intensity variation curves received by the photodetector.

[0060] Specifically, it can be seen that when the incident light enters the electro-optic crystal 6 at different field of view angles, the conical interference pattern consists of periodic alternating bright and dark fringes. The brightness of the fringes represents the intensity loss of the incident light after passing through the conical interferometry system composed of polarizer 5, electro-optic crystal 6, and analyzer 7. The maximum value of the bright fringes indicates that there is no loss of the incident light after passing through the conical interferometry system composed of polarizer 5, electro-optic crystal 6, and analyzer 7. Therefore, the light spot intensity received on the photodetector 8 is the maximum. The minimum value of the dark fringes indicates that the incident light is completely lost after passing through the conical interferometry system composed of polarizer 5, electro-optic crystal 6, and analyzer 7. Therefore, the light spot intensity received on the photodetector 8 is 0. Figure 4 The diagram shows that as the incident field of view changes, the bright and dark fringes will exhibit periodic changes, and therefore the intensity of the light spot received on the photodetector 8 will also change periodically. To obtain a sufficiently high measurement resolution, the difference in the incident field of view corresponding to the maximum and minimum values ​​of the bright and dark fringes within the same period must be selected as the measurement range of the method of this invention. Therefore, the angular spacing between adjacent bright and dark fringes characterizes the measurement range of the method of this invention. Furthermore, to obtain the angular spacing between adjacent bright and dark fringes under different periods, the relationship between the angular spacing between adjacent bright and dark fringes and the size of the field of view of the incident light entering the electro-optic crystal 6 needs to be studied.

[0061] In this embodiment, P1 and P2 represent the transmission axis directions of polarizer 5 and analyzer 7, respectively, and A1 is the amplitude of the incident linearly polarized light. The angle between the projection direction De of the electric displacement direction of e-ray 10 in the xy plane and the polarization direction P1 of polarizer 5 is θ. Therefore, the amplitudes of o-ray 9 and e-ray 10 in electro-optic crystal 6 are A1, A2, and P2, respectively. o =A1sinθ, A e =A1cosθ. When the o-ray 9 and e-ray 10 pass through the electro-optic crystal 6 and then through the transmission direction P2 of the analyzer 7, only the components whose vibration direction is parallel to the transmission direction P2 of the analyzer 7 can interfere, and their amplitudes are equal.

[0062] A O2 =A O cosθ=A1 sinθcosθ

[0063] A e2 =A e sinθ=A1 sinθcosθ

[0064] According to the intensity formula for two-beam interference, the intensity of the interference light between the o-beam and e-beam is:

[0065]

[0066] Where A1 is the amplitude of the incident linearly polarized light, θ is the angle between the projection direction De of the electric displacement direction of the e-ray in the xy plane and the polarization direction P1 of the polarizer, and A o2 and A e2 These are the amplitudes of the o-ray and e-ray after passing through the analyzer, respectively.

[0067] δ represents the phase difference between the o-ray and e-ray after passing through the electro-optic crystal 6, and the phase delay is:

[0068]

[0069] In the formula, L is the thickness of the electro-optic crystal. n o n e These are the principal refractive indices of o-ray 9 and e-ray 10, respectively, and ω is the angle between the incident light and the optical axis of the electro-optic crystal 6, i.e., the preset angle at which the light enters the electro-optic crystal 6.

[0070] From the above equation, we can see that the angular distance between adjacent bright and dark fringes can be written as:

[0071]

[0072] As can be seen from the above equations, the angular distance between adjacent bright and dark fringes is related to the wavelength of the laser source 1, the length of the electro-optic crystal 6, the crystal type, and the order of the interference fringes. The interference order is related to the field of view of the output light incident on the electro-optic crystal. Therefore, the measurement range of the method of the invention is related to the wavelength of the laser source 1, the length of the electro-optic crystal 6, the crystal type, and the field of view of the light incident on the electro-optic crystal 6.

[0073] like Figure 5 As shown, the relationship between the angular spacing between adjacent bright and dark fringes and the field of view of the incident light entering the electro-optic crystal 6 is presented. It can be seen that the angular spacing between adjacent bright and dark fringes decreases as the incident field of view increases. Furthermore, in order to match the high scanning accuracy of the deflection device under test, adjacent bright and dark fringes of a specific interference order need to be selected to obtain a sufficiently large measurement resolution. Therefore, Figure 5 The paper also presents the intensity variation curves of the light spot detected by the photodetector 8 when the incident field of view of the electro-optic crystal 6 is 5°, under the interference order corresponding to this field of view, and when the incident field of view varies between the field of view corresponding to the maxima of adjacent bright fringes and the minima of dark fringes. It can be seen that when the incident field of view is 87.3 mrad (5°), it corresponds to the maxima of the bright fringes; when the incident field of view is 87.2982 mrad, it corresponds to the minima of the dark fringes. Therefore, when the preset incident angle is 5°, the measurement range achievable by the method of this invention is 1.7952 urad. Based on the above embodiment, before testing the deflector 3 under test, a preset angle of 5° is set, where the preset angle is the angle between the incident linearly polarized light and the optical axis of the electro-optic crystal.

[0074] Based on the above embodiments, further, before step S1, the laser emitted by the laser source is collimated by a collimating lens to obtain a reference beam.

[0075] Collimating lenses are used to reduce the divergence angle of laser light and obtain a parallel light path.

[0076] In this embodiment of the invention, linearly polarized light is decomposed into o-ray and e-ray by an electro-optic crystal, and a phase delay is generated. The o-ray and e-ray interfere after passing through an analyzer, and the generated interference light is received by a photodetector. The electro-optic crystal is rotated until the light spot intensity is at its maximum, and the first incident field of view angle is recorded. The deflector under test is scanned with a scanning step size until the light spot intensity is 0, and the second incident field of view angle is recorded. The number of light spots received by the photodetector during the change in intensity between the bright and dark fringes from maximum to 0 is counted. The scanning accuracy of the deflector under test is calculated by dividing the difference in incident field of view angles by the number of light spots. By utilizing the birefringence characteristics of the electro-optic crystal, the deflected light is incident on the electro-optic crystal at different angles to generate different phase differences, so that the photodetector receives high-contrast light intensity, achieving the effect of the present invention. This solves the technical problems of complex operation, high measurement cost, and low measurement accuracy in the existing small-angle measurement methods for deflectors, and achieves the beneficial effects of simple optical path, wide applicability, stable measurement accuracy, and high resolution.

[0077] Based on the above embodiments, the deflector under test is an acousto-optic deflector or an electro-optic deflector. Specific embodiments are given below to illustrate how the method of the present invention is used to measure the scanning accuracy of an acousto-optic deflector (AOD) and an electro-optic deflector (EOD).

[0078] If the deflector under test 3 is an acousto-optic deflector, then the reference beam coincides with the zero-order diffraction direction of the acousto-optic deflector.

[0079] like Figure 3As shown, a device for measuring the scanning accuracy of an acousto-optic deflector includes the following specific parameters: a laser source 1 with a wavelength of 355 nm, a collimating lens 2, an acousto-optic deflector (AOD) 3, a polarizer 5 including a radio frequency drive power supply, an LN crystal as a piezoelectric transducer, a quartz crystal as the acousto-optic interaction medium coated with an antireflection film that highly enhances the laser wavelength, an electro-optic crystal 6 being a uniaxial crystal with a crystal aperture of 3 mm and a crystal length of 20 mm, an analyzer 7, and a photodetector 8. The optical axis of the laser source 1 coincides with the optical axis 2 of the collimating lens and also coincides with the direction of the zero-order diffraction output light of the acousto-optic deflector 3. The principal axes of the electro-optic crystal 6 are in the x and y directions. Using the x and y directions of the principal axes of the electro-optic crystal 6 as a reference coordinate system, the transmission directions of the polarizer 5 and analyzer 7 are defined as P1 and P2, respectively. P1 and P2 are orthogonal to each other and form an angle of 45° with the x and y directions of the principal axes of the electro-optic crystal 6. Based on these parameters, the equations above can be used to calculate that when the positive first-order Bragg diffraction output light enters the electro-optic crystal 6 at a field of view of 5°, the measurement range achievable by this measuring device is 1.7952 urad.

[0080] like Figure 3 As shown, when the acousto-optic deflector 3 is added to the sound field, the angle of the electro-optic crystal 6 is adjusted so that the field of view of the positive first-order Bragg diffraction output light entering the electro-optic crystal 6 is 5°. Furthermore, considering potential errors in the fabrication and assembly of the electro-optic crystal, the angle of the electro-optic crystal 6 needs to be finely adjusted until the light intensity of the spot detected by the photodetector 8 reaches its maximum. When the sound field frequency is changed, if the change in sound frequency is... The corresponding change in beam deflection is:

[0081]

[0082] In the formula, λ is the laser wavelength, n is the refractive index of the quartz crystal, and ν is the refractive index of the quartz crystal. s The speed of sound. At this moment, the field of view of the positive first-order Bragg diffraction output light entering the electro-optic crystal 6 is (5° - Δθ). B This will cause a change in the phase difference between the o-ray (9) and the e-ray (10), resulting in a decrease in the intensity of the output light spot. The frequency of the sound is continuously changed by step size. When the cumulative change in frequency is Δω, the intensity of the output light spot becomes 0. During this process, light spots of different intensities will be detected at different positions on the photodetector 8. Assuming the number of light spots is N, the scanning accuracy of the acousto-optic deflector 4 is... Specific implementation results are as follows: Figure 6 As shown.

[0083] When the acousto-optic deflector 4 is not working, the relative intensity received by the photodetector 8 is 1, that is, the light intensity is at its maximum; when the relative intensity is... When the frequency amplitude is changed by step size, the corresponding change in beam deflection is Δθ. B At this time, the field of view of the first-order Bragg diffraction output light entering the electro-optic crystal 6 will also change, which will lead to a decrease in the intensity of the output light spot. As the number of step sizes increases, the intensity of the output light spot will decrease sequentially. Therefore, different intensity light spots will be received at different positions of the photodetector 8. By counting the number of light spots with different intensities received, the scanning accuracy of the acousto-optic deflector 4 can be calculated.

[0084] Furthermore, to further improve the measurement accuracy of the system while keeping the laser source 1 and electro-optic crystal 6 unchanged, such as... Figure 5 As shown, the field of view of the positive first-order Bragg diffraction output light entering the electro-optic crystal 6 can be increased, and the theoretical measurement accuracy can reach nrad.

[0085] like Figure 7 As shown, a device for measuring the scanning accuracy of an electro-optic deflector includes the following specific parameters: a laser source 1 with a wavelength of 355 nm, a collimating lens 2, an electro-optic deflector (EOD) 4, a polarizer 5, an electro-optic crystal 6 (a uniaxial crystal with a 3 mm aperture and a 20 mm length), an analyzer 7, and a photodetector 8. The optical axis of the laser source 1 coincides with the optical axis of the collimating lens 2 and the optical axis of the electro-optic deflector 4. The principal axis of the electro-optic crystal 6 is in the x and y directions. Using the x and y directions of the principal axis of the electro-optic crystal 6 as a reference coordinate system, the transmission directions of the polarizer 5 and the analyzer 7 are defined as P1 and P2, respectively. P1 and P2 are orthogonal to each other and form an angle of 45° with the x and y directions of the principal axis of the electro-optic crystal 6. Based on the above parameters, the above equation can be used to calculate that when the output light after passing through the electro-optic deflector 4 enters the electro-optic crystal 6 at a field of view of 5°, the measurement range that this measuring device can achieve is 1.7952 urad.

[0086] like Figure 7 As shown, when an electric field is applied to the electro-optic deflector 4, the angle of the electro-optic crystal 6 is adjusted so that the field of view of the output light after passing through the electro-optic deflector 4 entering the electro-optic crystal 6 is 5°. Furthermore, considering potential errors in the fabrication and assembly of the electro-optic crystal, the angle of the electro-optic crystal 6 needs to be finely adjusted until the light intensity of the spot detected by the photodetector 8 reaches its maximum. When the electric field strength is changed, if the change in the electric field is Δ... E The corresponding change in beam deflection is:

[0087]

[0088] In the formula, L is the length of the electro-optic deflector 4, d is the thickness of the electro-optic deflector 4, and n o γ is the principal refractive index of the electro-optic crystal used in electro-optic deflector 4.63 Here is the electro-optic coefficient of the electro-optic crystal used in electro-optic deflector 4. Similar to the acousto-optic deflector principle described in Example 1, the field of view of the output light after passing through electro-optic deflector 4 entering electro-optic crystal 6 is (5° - Δθ). E This will cause a change in the phase difference between o-ray 9 and e-ray 10, resulting in a decrease in the intensity of the output light spot. (Using Δ...) E The electric field strength is continuously changed by step size. When the cumulative change in electric field strength is Δv, the intensity of the output light spot becomes 0. During this process, light spots of different intensities will be detected at different positions on the photodetector 8. Assuming the number of light spots is N, the scanning accuracy of the electro-optic deflector 4 is... Specific implementation results are as follows: Figure 8 As shown.

[0089] Furthermore, to further improve the measurement accuracy of the system while keeping the laser source 1 and electro-optic crystal 6 unchanged, such as... Figure 5 As shown, the same idea of ​​increasing the field of view of the output light entering the electro-optic crystal 6 can be adopted, and the theoretical measurement accuracy can reach nrad.

[0090] Example 2

[0091] like Figure 3 As shown, a device for measuring the small-angle deflection accuracy based on conical interferometry is used to perform the method described in any of the embodiments, comprising: a laser source 1, a collimating lens 2, a deflector to be measured 3, a polarizer 5, an electro-optic crystal 6, an analyzer 7, and a photoelectric sensor 87 arranged sequentially along the optical path;

[0092] The collimating lens 2 is used to collimate the laser emitted by the laser source 1 to obtain a reference beam;

[0093] The deflector 3 under test is used to deflect the reference beam at a small angle;

[0094] The polarizer 5 is used to convert the incident light beam into linearly polarized light;

[0095] The electro-optic crystal 6 is used to decompose the incident linearly polarized light into o-light and e-light, and to generate a phase delay;

[0096] The analyzer 7 is used to generate interference light by transmitting o-light and e-light in a preset direction;

[0097] The photodetector 8 is used to receive the light spot generated by interference light.

[0098] The device for measuring small-angle deflection accuracy based on conical interferometry provided in the embodiments of the present invention executes the method for measuring small-angle deflection accuracy based on conical interferometry provided in any embodiment of the present invention. The device has the corresponding functional modules and beneficial effects for executing the method.

[0099] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for measuring the accuracy of small-angle deflection based on conical interferometry, characterized in that, include: The laser light emitted from the laser source passes sequentially through the deflector under test and the polarizer to obtain linearly polarized light; The linearly polarized light is incident on the electro-optic crystal at a preset angle, decomposed into o-ray and e-ray, and a phase delay is generated; The o-ray and e-ray obtained from the decomposition interfere after passing through the analyzer, and the resulting interference light is received by the photodetector. Rotate the electro-optic crystal until the light spot intensity received by the photodetector is at its maximum, and record the first incident field angle. The deflector under test is scanned in a scanning step until the intensity of the light spot received by the photodetector is 0, and the second incident field angle is recorded. The scanning accuracy of the deflector under test is calculated by counting the number of resolvable light spots received by the photodetector as the light spot intensity changes from maximum to 0, and by dividing the difference between the first incident field of view and the second incident field of view by the number of light spots.

2. The method as described in claim 1, characterized in that, Before the laser emitted from the laser source passes sequentially through the deflector under test and the polarizer, the following is also included: The laser emitted from the laser source is collimated by a collimating lens to obtain a reference beam.

3. The method as described in claim 1, characterized in that, The preset angle is the angle between the incident linearly polarized light and the optical axis of the electro-optic crystal, and the preset angle is 5°.

4. The method as described in claim 3, characterized in that, The phase delay is: Where L is the thickness of the electro-optic crystal. n o n e ω represents the principal refractive indices of the o-ray and e-ray, respectively, and ω is a preset angle.

5. The method as described in claim 4, characterized in that, The intensity of the interference light is: Where A1 is the amplitude of the incident linearly polarized light, θ is the angle between the projection direction De of the electric displacement direction of the e-ray in the xy plane and the polarization direction P1 of the polarizer, and A o2 and A e2 These are the amplitudes of the o-ray and e-ray after passing through the analyzer, respectively.

6. The method as described in claim 5, characterized in that, When δ = 2kπ, the interference fringes are bright fringes, and the intensity of the light spot received on the photodetector is the maximum. When δ=(2k+1)π, the interference fringes are dark fringes, and the intensity of the light spot received on the photodetector is 0; where k represents the interference order, k=0,1,2,3,4,…….

7. The method as described in claim 1, characterized in that, The deflector under test is an acousto-optic deflector or an electro-optic deflector. If it is an acousto-optic deflector, the reference beam coincides with the zero-order diffraction direction of the acousto-optic deflector.

8. A device for measuring small-angle deflection accuracy based on conical interferometry, used to perform the method as described in any one of claims 1-7, characterized in that, include: The laser source, collimating lens, deflector under test, polarizer, electro-optic crystal, analyzer and photodetector are arranged sequentially along the optical path. The collimating lens is used to collimate the laser emitted by the laser source to obtain a reference beam; The deflector under test is used to deflect the reference beam at a small angle; The polarizer is used to convert the incident light beam into linearly polarized light; The electro-optic crystal is used to decompose incident linearly polarized light into o-ray and e-ray, and to generate phase delay; The analyzer is used to generate interference light by transmitting o-light and e-light in a preset direction; The photodetector is used to receive the light spot generated by interference light.

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