A method and system for measuring the optical axis deviation angle of an electro-optical crystal

Abstract

A method and system for measuring the optical axis deviation angle of an electro-optical crystal, the method comprising: injecting a polarized laser onto a light-transmitting surface of the electro-optical crystal to be measured; causing the electro-optical crystal to be measured to continuously rotate N times along a preset direction around a rotation axis; at each rotation position, imaging a first reflected light using a first imaging device, and obtaining the coordinates of a calibration point; focusing the polarized laser and injecting it again onto the electro-optical crystal to be measured, to obtain a first refracted light and a second refracted light; causing the first refracted light and the second refracted light to interfere with each other, and at each rotation position, imaging the interference light using a second imaging device to obtain an interference image, the interference image including an optical axis exposure point, and obtaining the coordinates of the optical axis exposure point in the interference image; using the coordinates of the calibration point at each rotation position to correct the coordinates of the optical axis exposure point at the rotation position, and obtaining the optical axis deviation angle of the electro-optical crystal based on the coordinates of all corrected optical axis exposure points.

Description

Technical Field

[0001] The present invention relates to the field of measurement technology, and in particular to a method and a system for measuring an optical axis deviation angle of an electro-optical crystal. Background Art

[0002] The Pockels cell is a key component for achieving high-energy, short-pulse laser output. The electro-optical crystal within the device is the primary driver of the Pockels effect. During processing, the crystal is typically cut perpendicular to its optical axis. Design requirements dictate that the optical axis be parallel to the normal to the light-passing surface, making accurate determination of the optical axis orientation crucial. Axis alignment error determines cutting error. As cutting error increases, optical energy loss rapidly increases during use, reducing conversion efficiency.

[0003] To reduce the angular error of electro-optical crystals, accurate measurement is first required, which requires professional measuring instruments. Conventional X-ray crystal axis determination detection equipment is based on the principle of Bragg diffraction, using a standard steel plate as the reference for the light-transmitting surface, and the crystal to be measured needs to be tightly adsorbed on the standard steel plate. Scratches are easily generated when the crystal surface contacts the standard steel plate. In high-power laser systems, scratches can easily cause energy concentration, leading to damage to the electro-optical crystal. Therefore, the X-ray diffraction method is not suitable for optical axis determination detection of electro-optical crystals that have very high requirements for surface defects. In addition, existing X-ray diffraction orientation instruments cannot achieve optical axis orientation of large-aperture crystal components.

[0004] The direction of the optical axis of a crystal can also be determined using the polarization interference pattern of the crystal. By finding the point of emergence of the optical axis (i.e., the black cross intersection) in the interference pattern, the direction of the optical axis can be measured based on the position of the optical axis emergence point relative to the center of the field of view. Polarizing microscopes are commonly used to implement crystal polarization interference. The distance between the optical axis emergence point and the field of view center is measured using the eyepiece graticule and visual inspection. The optical axis deviation angle can be calculated in combination with the numerical aperture of the microscope. However, this method has errors. Summary of the Invention

[0005] In view of this, the present invention provides a method and a system for measuring the optical axis deviation angle of an electro-optical crystal.

[0006] As a first aspect of the present invention, the measurement method comprises:

[0007] injecting polarized laser light onto the light-passing surface of the electro-optical crystal to be measured, wherein the polarized laser light is collimated laser light;

[0008] The electro-optical crystal to be tested is rotated N times continuously around a rotation axis in a preset direction, and the electro-optical crystal to be tested can return to an initial state after rotating N times, and the rotation axis is a straight line where the polarized laser light is located;

[0009] At each rotational position, the first reflected light is imaged using a first imaging device, and the coordinates of the image of the first reflected light on the first imaging device are obtained, i.e., the coordinates of the calibration point; the rotational position is the position reached by the electro-optical crystal to be tested after each rotation, and the first reflected light is the polarized laser reflected by the electro-optical crystal to be tested;

[0010] focusing the polarized laser light and then incident it again on the electro-optical crystal to be tested, wherein the focused polarized laser light undergoes birefringence in the electro-optical crystal to be tested to obtain a first refracted light and a second refracted light;

[0011] causing the first refracted light and the second refracted light to interfere with each other, imaging the interference light at each rotation position using a second imaging device to obtain the interference image, wherein the interference image includes an optical axis exposure point, and obtaining the coordinates of the optical axis exposure point in the interference image;

[0012] The coordinates of the optical axis exposure point at each rotation position are corrected using the coordinates of the calibration point at the rotation position, and the optical axis deviation angle of the electro-optical crystal is obtained according to the coordinates of all corrected optical axis exposure points.

[0013] According to an embodiment of the present invention, using the coordinates of the calibration point at each rotation position to correct the coordinates of the optical axis exposure point at the rotation position includes:

[0014] The coordinates of the optical axis exposure point at each rotation position are corrected according to the offset of the coordinates of the calibration point at each rotation position relative to the coordinates of the calibration point.

[0015] According to an embodiment of the present invention, the method for obtaining the calibration points includes:

[0016] The polarized laser light is made to pass through the position where the electro-optical crystal to be measured is located, and is incident on the plane surface of a plano-convex lens, wherein the plane of the plano-convex lens is parallel to the plane where the electro-optical crystal to be measured is located;

[0017] The second reflected light is imaged by the first imaging device to obtain the coordinates of the image of the second reflected light in the first imaging device, namely the coordinates of the calibration point. The second reflected light is the polarized laser reflected by the plane surface.

[0018] According to an embodiment of the present invention, causing the first refracted light and the second refracted light to interfere includes:

[0019] The target polarization component of the first refracted light and the target polarization component of the second refracted light are caused to interfere with each other, wherein the target polarization components of the first refracted light and the second refracted light have the same polarization direction.

[0020] According to an embodiment of the present invention, the polarization directions of the target polarization component of the first refracted light and the target polarization component of the second refracted light are both opposite to the polarization direction of the polarized laser light.

[0021] According to an embodiment of the present invention, obtaining the optical axis deviation angle of the electro-optical crystal to be tested according to the coordinates of all corrected optical axis exposure points includes:

[0022] Perform circle fitting on the coordinates of all corrected optical axis exposure points to obtain the radius of the fitting circle;

[0023] The optical axis deviation angle of the electro-optical crystal to be measured is obtained according to the fitting circle radius.

[0024] As a second aspect of the present invention, a system for measuring the optical axis deviation angle of an electro-optical crystal is provided, for implementing the above-mentioned measurement method, the measurement system comprising:

[0025] A laser assembly adapted to emit polarized laser light;

[0026] A sample fixing assembly is adapted to cause the electro-optical crystal to be tested to rotate continuously N times along a preset direction around a rotation axis, where the rotation axis is the straight line where the polarized laser light is located;

[0027] a first imaging component adapted to image the first reflected light at each rotational position to obtain coordinates of a calibration point;

[0028] a first lens adapted to focus the polarized laser light and then re-incend it onto the electro-optical crystal to be measured, so that the focused polarized laser light undergoes birefringence in the electro-optical crystal to be measured, thereby obtaining a first refracted light and a second refracted light;

[0029] An interference component, adapted to obtain interference light according to the first refracted light and the second refracted light;

[0030] a second imaging component adapted to image the interference light at each rotational position to obtain an interference image, wherein the interference image includes an optical axis exposure point;

[0031] The processing component is adapted to correct the coordinates of the optical axis exposure point at each rotation position using the coordinates of the calibration point at the rotation position, and is adapted to obtain the optical axis deviation angle of the electro-optical crystal based on the coordinates of all corrected optical axis exposure points.

[0032] According to an embodiment of the present invention, the laser assembly comprises:

[0033] A laser, adapted to emit an initial laser;

[0034] a second lens, adapted to focus the initial laser light;

[0035] A filtering unit, adapted to filter the focused initial laser light to obtain filtered laser light;

[0036] a third lens, adapted to convert the filtered laser light into parallel laser light;

[0037] A polarizer is used to convert the parallel laser light into the polarized laser light.

[0038] According to an embodiment of the present invention, the measurement system further includes:

[0039] a beam splitter, adapted to reflect the first reflected light;

[0040] The fourth lens is arranged between the beam splitter and the first imaging component, and is suitable for focusing the reflected first reflected light onto the first imaging component.

[0041] According to an embodiment of the present invention, the measurement system further includes:

[0042] a motorized aperture, disposed between the first lens and the electro-optical crystal to be measured, and adapted to control the intensity of the polarized laser light incident on the electro-optical crystal to be measured after being focused;

[0043] a fifth lens, adapted to focus the first refracted light and the second refracted light;

[0044] The interference component is an analyzer, and the analyzer and the polarizer form an orthogonal polarization system, which is suitable for obtaining the target polarization component of the first refracted light according to the first refracted light, and obtaining the target polarization component of the second refracted light according to the second refracted light, so as to interfere with the target polarization component of the first refracted light and the target polarization component of the second refracted light to obtain the interference light;

[0045] The sixth lens is adapted to focus the interference light onto the second imaging component.

[0046] According to an embodiment of the present invention, the first image formed by the first reflected light is used to trace the rotational error, and the tracing results of the rotational error of the electro-optical crystal to be tested in each rotational orientation are obtained. The position of the optical axis leakage point located at the same rotational position is corrected using the tracing results, and the coordinates of the optical axis leakage point are corrected to the position of the optical axis exposure point corresponding to the time when the sample surface is parallel to the system optical axis in the rotational orientation, thereby realizing accurate measurement of the optical axis deviation angle of the electro-optical crystal. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0048] Figure 1A flow chart of a method for measuring an optical axis deviation angle of an electro-optical crystal provided by an embodiment of the present invention is shown.

[0049] Figure 2 A system for measuring the optical axis deviation angle of an electro-optical crystal provided according to an embodiment of the present invention is shown.

[0050] Figure 3 The diagram shows images formed by the first reflected light at two different rotational positions of the electro-optical crystal to be measured according to an embodiment of the present invention.

[0051] Figure 4 FIG. 4 shows a first image obtained when the electro-optical crystal to be tested is at a certain rotation position according to an embodiment of the present invention.

[0052] Figure 5 The coordinates of the fixed points and the calibration points when N=4 are provided according to an embodiment of the present invention are shown.

[0053] Figure 6 The figure shows the interference image obtained when the electro-optical crystal to be measured is at a certain rotation position according to an embodiment of the present invention.

[0054] Figure 7 Shown Figure 6 The identification results of the cross intersection in the interference image.

[0055] Figure 8 The figure shows the fitting results of the cross points of all interference images when N=4 according to an embodiment of the present invention.

[0056] Figure 9 yes Figure 8 A partial enlarged view of .

[0057] Figure 10 Schematic diagram of leakage points and correction vectors before and after correction according to an embodiment of the present invention is shown.

[0058] Figure 11 The figure shows the coordinate fitting results of a leakage point on a certain optical axis before and after correction when N=4 according to an embodiment of the present invention.

[0059] Figure 12 FIG2 shows a light path diagram of a light beam after passing through a single refractive surface according to an embodiment of the present invention.

[0060] Figure 13 The figure shows the propagation states of the central light and the edge light in each lens and the sample being tested. Finally, the sixth lens reduces the beam to an appropriate size and the camera completes the collection of the interference pattern.

[0061] Figure 14 for Figure 13The local three-dimensional diagram shows the situation where the interference pattern is collected by the camera after the sixth lens reduces the beam to an appropriate size.

[0062] Reference numerals

[0063] 1 laser assembly; 2 sample fixing assembly; 3 first imaging assembly; 4 first lens;

[0064] 5 eighth lens; 6 second imaging component; 7 processing component; 8 electro-optical crystal to be tested;

[0065] 9 fourth lens; 10 electric aperture; 11 fifth lens; 12 analyzer;

[0066] 13: sixth lens; 14: plano-convex lens; 15: beam splitter;

[0067] 1-1 laser; 1-2 second lens; 1-3 filter unit; 1-4 third lens

[0068] 1-5 polarizers; DETAILED DESCRIPTION

[0069] In the process of implementing the present invention, it was found that there are two main methods for calculating the deviation angle of electro-optical crystals. The first method relies on an image matching algorithm to determine the position of the optical axis exposure point, and combines system parameters (such as lens focal length, beam aperture and number of detector pixels) to calculate the deviation angle. However, this method has significant disadvantages when positioning and testing samples: it requires frequent movement of the focusing lens in and out, and the sample turntable needs to rotate the sample around the system optical axis. The interference fringes on the spectroscopic light path are observed to determine whether the sample surface normal is parallel to the test system optical axis. This operation not only causes the interference pattern to be offset as a whole due to lens movement, introducing errors, but also the interference fringes make it difficult to intuitively and quickly indicate the specific direction and angle of the sample surface normal deviating from the system optical axis, thereby increasing the difficulty of manually correcting the sample posture and complicating the code writing for automatically correcting the sample posture. In addition, this method does not fully consider the impact of sample thickness on the imaging beam.

[0070] Another method uses a digital photoelectric internal focusing autocollimator to calibrate the optical axis direction and calculates the deviation angle by combining the position of the optical axis exposure point of the interference fringes with the position of the crystal surface normal. Although this method excels in ensuring measurement accuracy and repeatability, it requires adapting the measurement to electro-optical crystal samples of varying thickness and refractive index by replacing lenses with different F-numbers, which significantly increases cost and time in practical applications.

[0071] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0072] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprise", "include", etc. used herein indicate the presence of the features, steps, operations and / or components, but do not exclude the presence or addition of one or more other features, steps, operations or components.

[0073] All terms used herein, including technical and scientific terms, have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0074] When expressions such as “at least one of A, B, and C, etc.” are used, they should generally be interpreted in accordance with the meaning commonly understood by those skilled in the art. For example, “a system having at least one of A, B, and C” should include but is not limited to systems having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, and C, etc. When expressions such as “at least one of A, B, or C, etc.” are used, they should generally be interpreted in accordance with the meaning commonly understood by those skilled in the art. For example, “a system having at least one of A, B, or C” should include but is not limited to systems having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, and C, etc.

[0075] It should also be noted that directional terms such as "upper," "lower," "front," "back," "left," and "right" mentioned in the embodiments are merely references to the directions in the accompanying drawings and are not intended to limit the scope of protection of the present invention. Throughout the drawings, identical elements are represented by identical or similar reference numerals. Conventional structures or configurations will be omitted where they may cause confusion in understanding the present invention.

[0076] Figure 1 A flow chart of a method for measuring an optical axis deviation angle of an electro-optical crystal provided by an embodiment of the present invention is shown.

[0077] like Figure 1 As shown, the measurement method includes operations S1 to S6.

[0078] In operation S1 , a polarized laser is incident on a light-transmitting surface of an electro-optical crystal to be tested.

[0079] In operation S2 , the electro-optical crystal to be tested is rotated N times continuously around a rotation axis in a preset direction. After rotating N times, the electro-optical crystal to be tested can return to an initial state. The rotation axis is a straight line where the polarized laser light is located.

[0080] In operation S3, at each rotation position, the first reflected light is imaged by using the first imaging device, and the coordinates of the image of the first reflected light on the first imaging device, i.e., the coordinates of the calibration point, are obtained; the rotation position is the position reached by the electro-optical crystal to be tested after each rotation, and the first reflected light is the polarized laser reflected by the electro-optical crystal to be tested.

[0081] In operation S4, the polarized laser light is focused and incident again on the electro-optical crystal to be tested, wherein the focused polarized laser light undergoes birefringence in the electro-optical crystal to be tested, generating a first refracted light and a second refracted light;

[0082] In operation S5, the first refracted light and the second refracted light are interfered with each other. At each rotation position, the interference light is imaged by a second imaging device to obtain an interference image. The interference image includes an optical axis exposure point. The coordinates of the optical axis exposure point in the interference image (i.e., the coordinates of the cross intersection point) are obtained.

[0083] In operation S6 , the coordinates of the optical axis exposure point at each rotation position are corrected using the coordinates of the calibration point at the rotation position, and the optical axis deviation angle of the electro-optical crystal is obtained according to the coordinates of all the corrected optical axis exposure points.

[0084] According to an embodiment of the present invention, the optical axis deviation angle of the electro-optical crystal is the angle between the optical axis of the electro-optical crystal and the normal line of the light-transmitting surface thereof.

[0085] According to an embodiment of the present invention, the image of the first reflected light is used to trace the rotational error, and the tracing results of the rotational error of the electro-optical crystal 8 to be tested in each rotational orientation are obtained. The tracing results are used to correct the position of the optical axis leakage point located at the same rotational position, and the coordinates of the optical axis leakage point are corrected to the position of the optical axis exposure point corresponding to the sample surface being parallel to the system optical axis in the rotational orientation, thereby realizing accurate measurement of the optical axis deviation angle of the electro-optical crystal.

[0086] According to an embodiment of the present invention, in operation S5, the first refracted light and the second refracted light are caused to interfere, including causing the target polarization component of the first refracted light and the target polarization component of the second refracted light to interfere, wherein the polarization directions of the target polarization component of the first refracted light and the target polarization component of the second refracted light are the same.

[0087] According to the embodiments of the present invention, the polarization directions of the target polarization components of the first and second refracted light are opposite to those of the polarized laser light. This effectively filters out stray light and reduces interference factors during the measurement process, thereby improving measurement precision and accuracy. By precisely controlling the polarization state of light, the reliability and repeatability of measurement results can be ensured.

[0088] According to an embodiment of the present invention, in operation S6, the coordinates of the optical axis exposure point of each rotation position are corrected using the coordinates of the calibration point of that rotation position, including: correcting the coordinates of the optical axis exposure point of that rotation position according to the offset of the coordinates of the calibration point of each rotation position relative to the coordinates of the calibration point.

[0089] According to an embodiment of the present invention, the method for obtaining the calibration points includes operations S61 and S62.

[0090] In operation S61 , a polarized laser is made to pass through the position where the electro-optical crystal to be measured is located, and is incident on the plane surface of a plano-convex lens, wherein the plane of the plano-convex lens is parallel to the plane where the electro-optical crystal to be measured is located.

[0091] In operation S62 , the second reflected light is imaged by a first imaging device to obtain coordinates of the image of the second reflected light in the first imaging device, ie, coordinates of the calibration point. The second reflected light is polarized laser light reflected by a plane surface.

[0092] According to an embodiment of the present invention, obtaining the optical axis deviation angle of the electro-optical crystal to be tested according to the coordinates of all corrected optical axis exposure points includes operations S63 and S64.

[0093] In operation S63 , circle fitting is performed on the coordinates of all corrected optical axis exposure points to obtain a fitting circle radius.

[0094] In operation S64 , the optical axis deviation angle of the electro-optical crystal to be tested is obtained according to the radius of the fitting circle.

[0095] According to an embodiment of the present invention, as a second aspect of the present invention, a system for measuring the optical axis deviation angle of an electro-optical crystal is provided, for implementing the above-mentioned measurement method.

[0096] Figure 2 A system for measuring the optical axis deviation angle of an electro-optical crystal provided according to an embodiment of the present invention is shown.

[0097] like Figure 2 As shown, the measurement system includes: a laser component 1, a sample fixing component 2, a first imaging component 3, a first lens 4, an interference component, a second imaging component 6 and a processing component 7.

[0098] According to an embodiment of the present invention, the laser assembly 1 is suitable for emitting polarized laser light. The sample fixing assembly 2 is suitable for causing the electro-optical crystal 8 to be tested to rotate continuously N times along a preset direction around the rotation axis, where the rotation axis is the straight line where the polarized laser light is located. The first imaging assembly 3 is suitable for imaging the first reflected light at each rotation position to obtain the coordinates of the calibration point. The first lens 4 is suitable for focusing the polarized laser light and then incident it on the electro-optical crystal to be tested, so that the focused polarized laser light undergoes birefringence in the electro-optical crystal to be tested, obtaining a first refracted light and a second refracted light. The interference assembly is suitable for causing the first refracted light and the second refracted light to interfere with each other. The second imaging assembly 6 is suitable for imaging the interference light at each rotation position, and the interference image includes an optical axis exposure point. The processing assembly 7 is suitable for correcting the coordinates of the optical axis exposure point of each rotation position using the coordinates of the calibration point of the rotation position, and is suitable for obtaining the optical axis deviation angle of the electro-optical crystal based on the coordinates of all corrected optical axis exposure points.

[0099] According to an embodiment of the present invention, the first reflected light is imaged by a first imaging component to obtain an image of the first reflected light, the interference image is obtained by a second imaging component, and the rotational error of the electro-optical crystal 8 to be measured at each rotation position is obtained according to the image of the first reflected light by a processing component. The rotational error is used to correct the position of the optical axis leakage point in the interference image at the same rotational position, and the coordinates of the optical axis leakage point are corrected to the position of the optical axis exposure point corresponding to the sample surface being parallel to the system optical axis under the rotation orientation, thereby realizing accurate measurement of the optical axis deviation angle of the electro-optical crystal.

[0100] According to an embodiment of the present invention, the sample fixing component 2 may be, for example, a large six-dimensional adjustment frame, the first imaging component may be a first charge coupled device (CCD1), and the second imaging component may be, for example, a second charge coupled device (CCD2).

[0101] According to an embodiment of the present invention, the laser assembly 1 includes: a laser 1-1, a second lens 1-2, a filter unit 1-3, a third lens 1-4 and a polarizer 1-5.

[0102] The laser 1-1 is adapted to emit an initial laser beam. The second lens 1-2 is adapted to focus the initial laser beam. The filter unit 1-3 is adapted to filter the focused initial laser beam to produce filtered laser beam. The third lens 1-4 is adapted to convert the filtered laser beam into parallel laser beam. The polarizer 1-5 is adapted to convert the parallel laser beam into polarized laser beam.

[0103] According to an embodiment of the present invention, the measurement system further includes a beam splitter 15 and a fourth lens 9. The beam splitter 15 is configured to reflect the first reflected light. The fourth lens 9 is disposed between the beam splitter 8 and the first imaging assembly 3 and is configured to focus the reflected first reflected light onto the first imaging assembly 3. The beam splitter 15 is also configured to transmit the polarized laser light so that the polarized laser light can be incident on the light-transmitting surface of the electro-optical crystal 8 to be measured.

[0104] According to an embodiment of the present invention, the measurement system further comprises: a motorized aperture 10, a fifth lens 11, an analyzer 12, and a sixth lens 13. The motorized aperture 10 is disposed between the first lens 4 and the electro-optical crystal 8 to be measured, and is adapted to control the intensity of light incident on the electro-optical crystal to be measured after the polarized laser is focused. The fifth lens 11 is adapted to focus the first refracted light and the second refracted light. The analyzer 12, together with the polarizers 1-5, forms an orthogonal polarization system, adapted to obtain a target polarization component of the first refracted light based on the first refracted light, and a target polarization component of the second refracted light based on the second refracted light, so as to cause the target polarization component of the first refracted light and the target polarization component of the second refracted light to interfere with each other to obtain interference light. The sixth lens 13 is adapted to focus the interference light onto the second imaging assembly 6.

[0105] Acquire an image of the second reflected light in the first imaging device, namely the calibration point, where the second reflected light is the polarized laser reflected by the plane surface.

[0106] According to an embodiment of the present invention, when the first reflected light is imaged using the first imaging component, the first lens 4 can be removed from the system optical path first, and when the interference image is imaged using the second imaging device, the first lens 4 can be moved into the system optical path so that the polarized laser is focused and incident on the light-transmitting surface of the electro-optical crystal 8 to be tested.

[0107] According to an embodiment of the present invention, the above-mentioned measurement system also includes a plano-convex lens (also called a seventh lens) 14, which is located between the sample fixing assembly 2 and the fifth lens 11. When obtaining the calibration point, it is necessary to remove the sample from the measurement system so that the polarized laser passes through the position where the electro-optical crystal to be measured is located and is incident on the plane surface of the plano-convex lens 14. The polarized laser is reflected on the plane surface of the plano-convex lens 14 to obtain a second reflected light. The image formed by the second reflected light in the first imaging device is the calibration point. According to an embodiment of the present invention, the above-mentioned measurement system also includes an eighth lens 5 arranged between the fifth lens 11 and the analyzer 12, which is used to collimate the focused first refracted light and the second refracted light output by the fifth lens, and transmit the collimated light to the analyzer 12.

[0108] The following lists specific embodiments, and based on the above-mentioned measurement system, the measurement process of the optical axis deviation angle is as follows.

[0109] Step A: After the electro-optical crystal 8 to be measured is clamped on the large six-dimensional adjustment frame, the first lens 4 is moved out of the measurement system through the one-dimensional precision electric translation stage, so that the collimated polarized laser beam is incident on the light-transmitting surface of the electro-optical crystal 8 to be measured, and then is reflected by the electro-optical crystal 8 to be measured, split by the beam splitter 15, and focused by the fourth lens 9 to form an image on the first imaging component 3.

[0110] Figure 3 The diagram shows images formed by the first reflected light at two different rotational positions of the electro-optical crystal to be measured according to an embodiment of the present invention.

[0111] like Figure 3 As shown, after the collimated polarized laser beam is incident on the light-transmitting surface of the electro-optical crystal 8 to be measured, it is reflected by the electro-optical crystal 8 at two different rotation positions, split by the beam splitter 15, and focused by the fourth lens 9 to form an image on the first imaging component 3. That is, the image formed on the first imaging component is the calibration point, which is represented by P1 and P2.

[0112] Figure 4 The figure shows an image formed by the first reflected light when the electro-optical crystal to be tested is at a certain rotation position according to an embodiment of the present invention.

[0113] like Figure 4 As shown, the image obtained when the electro-optical crystal 8 to be tested is at a certain rotation position is a light spot.

[0114] Step B: Use a large six-dimensional adjustment frame to rotate the electro-optical crystal sample 8 to be tested 360°, and collect the image formed by the first reflected light by rotating N times (rotation interval 360° / N).

[0115] Taking N=4 as an example, due to the rotation error of the large six-dimensional adjustment frame, the surface normal of the electro-optical crystal 8 to be measured will deviate from the system optical axis after each rotation. At this time, the offset of the image of the first reflected light on CCD1 (i.e., the calibration point) relative to the calibration point at any rotation position and the angle of the surface normal of the sample at this rotation position deviating from the system optical axis satisfy the relationship in the following formula (1).

[0116] θ = arcsin (S * d / f) (1)

[0117] Among them, θ represents the angle at which the surface normal of the electro-optical crystal 8 to be tested deviates from the optical axis of the system at any rotational position, S represents the offset of the calibration point at the rotational position relative to the calibration point, d represents the length of a single pixel in CCD1, and f represents the focal length of the fourth lens 9. After the electro-optical crystal 8 to be tested completes one rotation, the image of the first reflected light at each rotational position (i.e., the calibration point at each rotational position) is obtained, and the coordinates of the image of the first reflected light on CCD1 (i.e., the coordinates of the calibration point) are obtained after using the binarization, median filtering, contour recognition, and contour center of gravity calculation in the image processing algorithm. These are saved and recorded together with the coordinates of the calibration point, and the vector of each calibration point pointing to the calibration point will be used for subsequent cross leakage point correction calculations. The coordinates of the image of the first reflected light on CCD1 (i.e., the coordinates of the calibration point) and the coordinates of the calibration point obtained are as follows: Figure 5 As shown. Figure 5 The mid-calibration points are represented by P3~P6, and the calibration point is represented by Q.

[0118] Step C: Reset the first lens 4 to the optical path of the measurement system through a one-dimensional precision electric translation stage. At this time, a conoscopic interference pattern can be observed at the CCD2.

[0119] Figure 6 The figure shows the interference image obtained when the electro-optical crystal to be measured is at a certain rotation position according to an embodiment of the present invention.

[0120] like Figure 6 The figure shows the interference image of a cone of light with a deviation angle. A large six-dimensional adjustment mount is used to rotate the sample around the system optical axis. This rotation is repeated N times, corresponding to the number N in the previous step. The interference image is then collected (each rotation position corresponds exactly to the rotation position of the sample during the first reflected light acquisition).

[0121] At this point, the computer system stores N calibration points and N conoscopic interference images. The rotation positions corresponding to the N calibration points correspond to the rotation positions of the N conoscopic interference patterns. The processing component (e.g., computer) uses the method of identifying the edges of the four contours within the interference ring to find the coordinates of the cross intersection (optical axis exposure point) of the N conoscopic interference images and record them. The recognition result is as follows: Figure 7 shown.

[0122] At this point, the data stored by the processing component includes the coordinates of the N images formed by the first reflected light on CCD1 (N calibration point coordinates) and the coordinates of the N black cross intersections (optical axis exit points) of the conoscopic interference patterns. Due to the influence of the rotational error of the large six-dimensional adjustment frame, directly performing a circular fit on the coordinates of the N black cross intersections (optical axis exit points) of the conoscopic interference patterns will reveal that each coordinate has a certain amount of deviation (from the fitting circle), and does not strictly follow a circular motion trajectory.

[0123] Figure 8 The figure shows the fitting results of the cross points of all interference images when N=4 according to an embodiment of the present invention.

[0124] exist Figure 8 The cross intersection points of the interference image in are represented as M1, M2, M3 and M4 respectively.

[0125] Figure 9 yes Figure 8 A partial enlarged view of .

[0126] like Figures 8 and 9 As shown, the fitting result of the optical axis leakage point corresponding to the angle of the surface normal of the electro-optical crystal 8 to be tested deviating from the optical axis of the system by ≈11 mrad (M=2) is locally enlarged. It can be seen that the cross leakage point does not strictly fall on the circular trajectory. This is because when the large six-dimensional adjustment frame rotates the electro-optical crystal 8 to be tested, the surface of the electro-optical crystal 8 to be tested deviates by a small angle due to the inevitable rotation error.

[0127] Step D, calculate the correction vector using the coordinates of the N calibration points and the standard point, and use these correction vectors to correct the coordinates of the optical axis leakage points of the N image processing points with different rotation orientations one by one, so as to obtain the N corrected optical axis leakage points of the sample when the surface normal is perpendicular to the system optical axis and the system optical axis is used as the rotation axis for one rotation. The coordinate comparison of a certain optical axis leakage point before and after correction is as follows: Figure 10 shown.

[0128] Figure 11 The figure shows the coordinate fitting results of all optical axis leakage points before and after correction when N=4 according to an embodiment of the present invention.

[0129] like Figure 11 As shown, the solid line is the corrected fitting circle trajectory, and the dotted line is the corrected fitting circle trajectory. According to the corrected fitting circle radius r0, the optical axis deviation angle of the electro-optical crystal 8 to be tested can be obtained, which is specifically expressed as formula (2).

[0130] α = r0 ÷ R0 × u'' (2)

[0131] Wherein, α represents the optical axis deviation angle of the electro-optical crystal 8 to be tested, r represents the corrected fitting circle radius, R represents the beam half-width of the interference image, and u'' represents the image-side aperture angle after the interference light is emitted from the sixth lens.

[0132] According to an embodiment of the present invention, the following content explains in detail the derivation method of u''.

[0133] Because the initial laser light emitted by laser 1-1 must pass through six lenses in sequence before it is finally imaged on the second imaging device, namely, second lens 1-2, third lens 1-4, first lens 4, plano-convex lens 14, fifth lens 11, and sixth lens 13, the image-side aperture angle of the light beam after passing through the refractive surface of the lens is calculated as follows.

[0134] Figure 12 FIG2 shows a light path diagram of a light beam after passing through a single refractive surface according to an embodiment of the present invention.

[0135] like Figure 12 As shown in the figure, a light beam originates at point A and enters a medium with a refractive index of n at an angle of incidence I. At refraction point E, the light beam is deflected and enters a medium with a refractive index of n' at an angle of refraction T'. The refractive surface has a radius of curvature r. The light beam is incident on the refractive surface from point O at an object-side aperture angle of -U and an incident height of h. After refraction, the light beam continues to travel toward point A' at an image-side aperture angle of U'. The directions of the light beam before and after refraction are labeled U and U', respectively. The distances the light beam travels on the refractive surface are the object-side intercept -L and the image-side intercept L', respectively. This diagram schematically illustrates the path changes of a light beam after passing through a refractive surface, providing a theoretical basis for related optical design. In this figure, the lens refractive surface OE is the interface between the two media with refractive indices of n and n', C is the center of the lens, and OC is the radius of curvature of the sphere, represented by the letter r. The line passing through the center of the sphere is the optical axis, and its intersection with the sphere is called the vertex, represented by the letter O. The distance from vertex O to the intersection of the ray and the optical axis, A, represented by L, is called the object intercept. The angle ∠EAO between the incident ray and the optical axis, represented by U, is called the object aperture angle. After being refracted by the refractive surface, ray AE intersects the optical axis at point A'. The image intercept, L', = OA', and the image aperture angle, U', = ∠EOA'. I is the angle of incidence, and l' is the angle of refraction, with positive values ​​clockwise and negative values ​​counterclockwise.

[0136] According to the triangle theorem, in triangle AEC,

[0137] (3)

[0138] From the law of refraction, we can get

[0139] (4)

[0140] As can be seen in the figure,

[0141] ϕ=U′+I′(5)

[0142] I = −U + ϕ (6)

[0143] The image side aperture angle is expressed as formula (5),

[0144] (7)

[0145] Applying the sine law to triangle A'EC, the square intercept is expressed as (8)

[0146] (8)

[0147] Among them, U, U′ and are the object-side and image-side aperture angles and the object-side and image-side intercepts of the light, and d is the distance between the two refractive surfaces.

[0148] When there are multiple lenses in the system, the above formula needs to be used to calculate the image-side aperture angle of the light emitted from the rear surface of the sixth lens one by one.

[0149] Figure 13 The figure shows the propagation state of the light beam in each lens and the sample being measured. Finally, the sixth lens shrinks the beam to an appropriate size and the camera completes the collection of the interference pattern.

[0150] Figure 14 for Figure 13 The local three-dimensional diagram shows the situation where the interference pattern is collected by the camera after the sixth lens reduces the beam to an appropriate size.

[0151] Combine Figure 13-14 Using the optical path diagram in , as well as the parameters in Equation (8) and Table 1, the u'' of the light emitted from the rear surface of the sixth lens can be calculated lens by lens. Calculating each lens requires transferring the calculation results of the previous refractive surface to the next refractive surface. This can be done using the surface rotation formula. The surface rotation formula involves the parameter changes as light propagates from one surface to another in the optical system. The surface rotation formula is expressed as Equations (9) to (10).

[0152] u m+1 =u m ′(9)

[0153] L m+1 =L m ′−d(10)

[0154] The surface rotation formula reflects how the light parameters are transferred from the mth surface to the m+1th surface under certain conditions. From the surface rotation formula, it can be seen that after the light passes through a refractive surface (or curved surface), its direction will not change before it reaches the next surface position. The image side aperture angle u of the previous refractive surface is m ′ is the object aperture angle u of the next surface m+1. That is, the direction of the light remains unchanged during propagation between the two surfaces. This formula can also express that when the light propagates from the first surface to the second surface, its height (intercept) will change due to the propagation distance d. Through this formula, the object-space intercept of the light exiting the first refractive surface on the second surface can be calculated. The above formula is often used in the linear approximation transfer step in the ray tracing algorithm. Through the above formula, the state of the light can be gradually updated and its behavior in the multi-optical system can be analyzed.

[0155] The parameters of the various components in the embodiment of the present invention are shown in Table 1. u'' can be calculated according to the above formula and the parameters in Table 1.

[0156] Table 1

[0157]

[0158] The measurement method provided by the present invention avoids the need for back-and-forth translation and resetting of the first lens. Instead, it employs a method for identifying rotational errors and correcting the coordinates of the cross-optical axis's leakage point, simplifying the measurement process and achieving a high degree of automation. The deviation angle calculation method considers the influence of the thickness and refractive index of different samples (electro-optical crystals to be tested), enabling the measurement system to accommodate a wider range of electro-optical crystal sample sizes and types (such as lithium niobate and BBO) without requiring lens replacement.

[0159] The above describes embodiments of the present invention. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Although each embodiment has been described separately above, this does not mean that the measures in each embodiment cannot be advantageously used in combination. The scope of the present invention is defined by the appended claims and their equivalents. Without departing from the scope of the present invention, those skilled in the art may make various substitutions and modifications, which are intended to fall within the scope of the present invention.

Claims

1. A method for measuring the optical axis deviation angle of an electro-optical crystal, comprising: injecting polarized laser light onto the light-passing surface of the electro-optical crystal to be measured, wherein the polarized laser light is collimated laser light; The electro-optical crystal to be tested is rotated N times continuously around a rotation axis in a preset direction, and the electro-optical crystal to be tested can return to an initial state after rotating N times, and the rotation axis is a straight line where the polarized laser light is located; At each rotational position, the first reflected light is imaged using a first imaging device, and the coordinates of the image of the first reflected light on the first imaging device are obtained, i.e., the coordinates of the calibration point; the rotational position is the position reached by the electro-optical crystal to be tested after each rotation, and the first reflected light is the polarized laser reflected by the electro-optical crystal to be tested; focusing the polarized laser light and then incident it again on the electro-optical crystal to be tested, wherein the focused polarized laser light undergoes birefringence in the electro-optical crystal to be tested to obtain a first refracted light and a second refracted light; causing the first refracted light and the second refracted light to interfere with each other, imaging the interference light using a second imaging device at each rotation position to obtain an interference image, wherein the interference image includes an optical axis exposure point, and obtaining the coordinates of the optical axis exposure point in the interference image; The coordinates of the optical axis exposure point at each rotation position are corrected using the coordinates of the calibration point at the rotation position, and the optical axis deviation angle of the electro-optical crystal is obtained according to the coordinates of all corrected optical axis exposure points.

2. The measurement method according to claim 1, wherein: Correcting the coordinates of the optical axis exposure point at each rotation position using the coordinates of the calibration point at the rotation position includes: The coordinates of the optical axis exposure point at each rotation position are corrected according to the offset of the coordinates of the calibration point at each rotation position relative to the coordinates of the calibration point.

3. The measurement method according to claim 2, wherein: The method for obtaining the calibration point includes: The polarized laser light is made to pass through the position where the electro-optical crystal to be measured is located, and is incident on the plane surface of a plano-convex lens, wherein the plane of the plano-convex lens is parallel to the plane where the electro-optical crystal to be measured is located; The second reflected light is imaged by the first imaging device to obtain the coordinates of the image of the second reflected light in the first imaging device, namely the coordinates of the calibration point. The second reflected light is the polarized laser reflected by the plane surface.

4. The measurement method according to claim 1, wherein: Causing the first refracted light and the second refracted light to interfere with each other, comprising: The target polarization component of the first refracted light and the target polarization component of the second refracted light are caused to interfere with each other, wherein the target polarization components of the first refracted light and the second refracted light have the same polarization direction.

5. The measurement method according to claim 4, wherein: The polarization directions of the target polarization component of the first refracted light and the target polarization component of the second refracted light are both opposite to the polarization direction of the polarized laser light. The measurement method according to claim 1 , wherein: Obtaining the optical axis deviation angle of the electro-optical crystal to be tested according to the coordinates of all corrected optical axis exposure points includes: Perform circle fitting on the coordinates of all corrected optical axis exposure points to obtain the radius of the fitting circle; The optical axis deviation angle of the electro-optical crystal to be measured is obtained according to the fitting circle radius.

7. A system for measuring the optical axis deviation angle of an electro-optical crystal, for implementing the measurement method according to any one of claims 1 to 6, the measurement system comprising: A laser assembly adapted to emit polarized laser light; A sample fixing assembly is adapted to cause the electro-optical crystal to be tested to rotate continuously N times along a preset direction around a rotation axis, where the rotation axis is the straight line where the polarized laser light is located; a first imaging component adapted to image the first reflected light at each rotational position to obtain coordinates of a calibration point; a first lens adapted to focus the polarized laser light and then re-incend it onto the electro-optical crystal to be measured, so that the focused polarized laser light undergoes birefringence in the electro-optical crystal to be measured, thereby obtaining a first refracted light and a second refracted light; An interference component, adapted to obtain interference light according to the first refracted light and the second refracted light; a second imaging component adapted to image the interference light at each rotational position to obtain an interference image, wherein the interference image includes an optical axis exposure point; The processing component is adapted to correct the coordinates of the optical axis exposure point at each rotation position using the coordinates of the calibration point at the rotation position, and is adapted to obtain the optical axis deviation angle of the electro-optical crystal based on the coordinates of all corrected optical axis exposure points.

8. The measurement system according to claim 7, wherein: The laser assembly comprises: A laser, adapted to emit an initial laser; a second lens, adapted to focus the initial laser light; A filtering unit, adapted to filter the focused initial laser light to obtain filtered laser light; a third lens, adapted to convert the filtered laser light into parallel laser light; A polarizer is used to convert the parallel laser light into the polarized laser light.

9. The measurement system according to claim 7, further comprising: a beam splitter, adapted to reflect the first reflected light; The fourth lens is arranged between the beam splitter and the first imaging component, and is suitable for focusing the reflected first reflected light onto the first imaging component.

10. The measurement system according to claim 7, wherein: The measurement system further comprises: a motorized aperture, disposed between the first lens and the electro-optical crystal to be measured, and adapted to control the intensity of the polarized laser light incident on the electro-optical crystal to be measured after being focused; a fifth lens, adapted to focus the first refracted light and the second refracted light; The interference component is an analyzer, and the analyzer and the polarizer form an orthogonal polarization system, which is suitable for obtaining the target polarization component of the first refracted light according to the first refracted light, and obtaining the target polarization component of the second refracted light according to the second refracted light, so as to cause the target polarization component of the first refracted light and the target polarization component of the second refracted light to interfere with each other to obtain the interference light; The sixth lens is adapted to focus the interference light onto the second imaging component.

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