Device for measuring the angle between the normal to the light passing surface of an electro-optic crystal and the optical axis of the crystal

Abstract

The disclosure provides an electric-optical crystal light passing surface normal and crystal optical axis angle measuring device, comprising: a laser (1) for generating a test light beam; an optical shaping module for shaping and expanding the test light beam; a conic interference module for adjusting the polarization degree of the shaped and expanded test light beam, and adjusting the test light beam into a conic light beam acting on the measured electric-optical crystal; a sample posture adjusting assembly (8) for setting the measured electric-optical crystal, and adjusting the rotation angle of the measured electric-optical crystal in three-dimensional space; a collimation imaging module for focusing the test light beam emitted after passing through the measured electric-optical crystal; a first detection module (11) for receiving the test light beam emitted after passing through the measured electric-optical crystal to obtain the optical axis exposure point; and a measurement and calculation module for calculating the angle between the light passing surface normal of the measured electric-optical crystal and the crystal optical axis.

Description

Technical Field

[0001] This disclosure relates to the field of measurement technology, and in particular to a device for measuring the angle between the normal of the light-transmitting surface of an electro-optic crystal and the optical axis of the crystal. Background Technology

[0002] The Pockel cell is a key component for achieving high-energy, short-pulse laser output, with the electro-optic crystal inside the device being the primary agent of its Pockel effect. During crystal fabrication, the crystal is typically cut along a direction perpendicular to its optical axis. The design requires that the optical axis be parallel to the normal direction of the light-transmitting surface, making the determination of its optical axis particularly crucial; the axis-fixing error determines the cutting error. As the cutting error increases, the optical energy loss of the electro-optic crystal increases rapidly during use, resulting in a decrease in conversion efficiency.

[0003] To reduce the angular error of electro-optic crystals, accurate measurement is essential, requiring specialized measuring instruments. Conventional X-ray crystal alignment equipment, based on the Bragg diffraction principle, uses a standard steel plate as the reference for the light transmission surface, and the crystal under test must be firmly adhered to the standard steel plate. Scratches are easily generated when the crystal surface contacts the standard steel plate. In high-power laser systems, these scratches can easily cause energy concentration, leading to damage to the electro-optic crystal. Therefore, X-ray diffraction is not suitable for Z-axis alignment of electro-optic crystals, which have very high requirements for surface imperfection control. Furthermore, existing X-ray diffraction orientation instruments cannot achieve optical axis orientation for large-aperture crystal elements.

[0004] The optical axis direction of a crystal can also be determined using its polarized light interferogram. This is achieved by locating the point where the optical axis emerges (the intersection of the black crosses) in the interferogram, and then measuring the direction of the optical axis based on the position of this point relative to the center of the field of view. A polarizing microscope is commonly used to perform crystal polarized light interferometry. The distance between the optical axis emergence point and the center of the field of view is measured using the reticle of the eyepiece and visual estimation. The optical axis deviation angle can then be calculated by combining this with the numerical aperture of the microscope. However, this method has a relatively large error, ranging from 3° to 5°. Summary of the Invention

[0005] In view of the above problems, the present invention provides a device for measuring the angle between the normal of the light transmission surface of an electro-optic crystal and the optical axis of the crystal.

[0006] One aspect of this disclosure provides a device for measuring the angle between the normal of the light-transmitting surface of an electro-optic crystal and the optical axis of the crystal, comprising: a laser for generating a test beam; an optical shaping module for shaping and expanding the test beam; a conical interferometry module for adjusting the polarization degree of the shaped and expanded test beam and adjusting the test beam into a conical beam to act on the electro-optic crystal under test; a sample attitude adjustment component for setting the electro-optic crystal under test and adjusting the rotation angle of the electro-optic crystal under test in three-dimensional space; a collimation imaging module for focusing the test beam emitted through the electro-optic crystal under test; a first detection module for receiving the test beam emitted through the electro-optic crystal under test and obtaining its optical axis exposure point; and a measurement calculation module for calculating the angle between the normal of the light-transmitting surface of the electro-optic crystal under test and the optical axis of the crystal based on the optical axis exposure point of the electro-optic crystal under test in different rotation attitudes; wherein the laser, the optical shaping module, the conical interferometry module, the electro-optic crystal under test, the collimation imaging module, and the first detection module are arranged in a straight line along the optical axis of the crystal.

[0007] Optionally, the light shaping module includes: a first lens for focusing the test beam into a filter aperture; a filter aperture for improving the uniformity of the intensity distribution of the test beam spot; and a second lens for collimating and expanding the test beam after passing through the filter aperture.

[0008] Optionally, the conical interferometer module includes: a polarizer for adjusting the polarization degree of the test beam to cause interference; and a first lens group disposed after the polarizer for adjusting the interfering test beam into a conical beam.

[0009] Optionally, the conical interferometer module further includes a magneto-optical device for applying a sinusoidal modulation signal to adjust the position and angle of the polarizer and improve the polarization degree of the test beam.

[0010] Optionally, the conical interferometer module further includes an electric aperture, disposed after the first lens group, for matching the spot size of the test beam to the size of the electro-optic crystal under test.

[0011] Optionally, the collimation imaging module includes: a second lens group for collimating and narrowing the test beam passing through the electro-optic crystal under test; and an analyzer for converting the test beam into linearly polarized light to form an interference pattern on the first detection module.

[0012] Optionally, the sample attitude adjustment assembly includes a two-dimensional translation adjustment mechanism, a rotation adjustment mechanism, and a three-dimensional attitude adjustment mechanism.

[0013] Optionally, the device further includes a sample positioning component, used to detect the change in the orientation of the far field of the surface reflected light of the electro-optic crystal under test in a rotating state based on the centering principle, so as to ensure the attitude positioning accuracy of the electro-optic crystal under test.

[0014] Optionally, the sample positioning component includes: a beam splitter, disposed between the polarizer and the first lens group, for transmitting the test beam and redirecting the far-field reflected light from the electro-optic crystal under test by a 90° angle; a third lens group, disposed in the redirection direction of the surface reflected light, for focusing the surface reflected light from the electro-optic crystal under test; and a second detection module, for detecting the surface reflected light, wherein when the spot of the surface reflected light is aligned with the center of the second detection module, the plane of the electro-optic crystal under test is perpendicular to the test beam.

[0015] Optionally, the sample positioning component further includes a corner cube prism, which is placed on the sample attitude adjustment component before the test begins to reflect the test beam along its original path, and works with the beam splitter, the third lens group and the second detection module to determine the reference plane of the electro-optic crystal under test.

[0016] The above-described at least one technical solution adopted in the embodiments of this disclosure can achieve the following beneficial effects:

[0017] The device for measuring the angle between the normal of the light-transmitting surface of an electro-optic crystal and the optical axis of the crystal disclosed herein is based on the sample attitude positioning technology of a centering instrument. It detects the change in the direction of the far field of the surface reflected light under sample rotation, ensuring attitude positioning accuracy without the need to move the lens. The device uses the crystal normal as a measurement reference and a corner cube prism as a reflector to achieve high-precision reference positioning with an error of less than 2°. Attached Figure Description

[0018] To gain a more complete understanding of this disclosure and its advantages, reference will now be made to the following description taken in conjunction with the accompanying drawings, wherein:

[0019] Figure 1 This schematically illustrates a measurement of the angle between the normal to the light-transmitting surface of an electro-optic crystal and the optical axis of the crystal, according to an embodiment of this disclosure.

[0020] Figure 2 This illustration schematically shows a diagram illustrating the establishment of a crystal optical axis reference according to an embodiment of the present disclosure;

[0021] Figure 3 The illustration shows a schematic diagram of the principle of a cornerstone prism provided in an embodiment of the present disclosure.

[0022] Figure label:

[0023] 1-Laser; 2-First lens; 3-Filter aperture; 4-Second lens; 5-Polarizer; 6-First lens group; 7-Electrically operated aperture; 8-Sample attitude adjustment assembly; 9-Second lens group; 10-Analyzer; 11-First detection module; 12-Beam splitter; 13-Third lens group; 14-Second detection module; 15-Corner prism. Detailed Implementation

[0024] The embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0025] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0026] 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 are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0027] Figure 1 The illustration shows a schematic diagram of the angle measurement between the normal of the light-transmitting surface of an electro-optic crystal and the optical axis of the crystal, according to an embodiment of the present disclosure.

[0028] like Figure 1 As shown in the figure, an embodiment of this disclosure provides a device for measuring the angle between the normal of the light-transmitting surface of an electro-optic crystal and the optical axis of the crystal, comprising: a laser 1, an optical shaping module, a conical interferometry module, a sample posture adjustment component 8, a collimation imaging module, a first detection module 11, and a measurement calculation module. The laser 1, the optical shaping module, the conical interferometry module, the electro-optic crystal under test, the collimation imaging module, and the first detection module 11 are arranged in a straight line along the optical axis of the crystal.

[0029] Laser 1 is used to generate the test beam. Laser 1 is selected as the test light source due to its good beam quality, fundamental mode output, and stable performance. Its maximum output power is >5mW. The wavelength can be visible light, or a light source similar to the one used in the specific application of the crystal, or a tunable light source, allowing adjustment of the output wavelength as needed. Laser 1 operates in continuous, linearly polarized output mode. Typical output parameters of laser 1 are as follows: output spot diameter ~1mm, divergence angle <1.2mrad, pointing stability <0.02mrad, tube length <700mm, and power consumption <20mW after stable operation.

[0030] The optical shaping module is used to shape and expand the test beam, and includes a first lens 2, a filter aperture 3, and a second lens 4. The first lens 2 focuses the test beam into the filter aperture 3; the filter aperture 3 improves the uniformity of the intensity distribution of the test beam; the second lens 4 collimates and expands the test beam after passing through the filter aperture 3. Furthermore, the optical shaping module can be fine-tuned to achieve laser output with higher collimation.

[0031] The conical interferometer module is used to adjust the polarization degree of the test beam after shaping and expanding, and to adjust the test beam into a conical beam that acts on the electro-optic crystal under test. The conical interferometer module includes a polarizer 5 and a first lens group. The polarizer 5 is used to adjust the polarization degree of the test beam to cause interference; the first lens group is located after the polarizer 5 and is used to adjust the interfering test beam into a conical beam. By designing a conical beam adjustment unit with a dual-lens combination, the lens distance can be adjusted to achieve a large divergence angle beam output. High extinction ratio Glan prisms or polarizers can be selected as polarization devices. Using magneto-optical devices, a sinusoidal modulation signal is applied to adjust the position and angle of the polarizer 5, achieving high-precision adjustment of the orthogonal state of the two Glan prisms, improving the polarization degree of the test beam, and ensuring a high extinction state at the center of the interferogram. The conical interferometer module may also include an electric aperture 7, located after the first lens group, used to match the spot size of the test beam to the size of the electro-optic crystal under test.

[0032] The sample attitude adjustment component 8 is used to position the electro-optic crystal under test and adjust its rotation angle in three-dimensional space. The sample attitude adjustment component 8 includes a two-dimensional translation adjustment mechanism, a rotation adjustment mechanism, and a three-dimensional attitude adjustment mechanism.

[0033] The collimation imaging module is used to focus the test beam emitted through the electro-optic crystal under test. The collimation imaging module includes a second lens group 9 and an analyzer 10. The second lens group 9 is used to collimate and narrow the test beam emitted through the electro-optic crystal under test; the analyzer 10 is used to convert the test beam into linearly polarized light, forming an interference pattern on the first detection module 11.

[0034] The first detection module 11 is used to receive the test beam emitted through the electro-optic crystal under test and obtain its optical axis emergence point. In this embodiment, the first detection module 11 is a CCD.

[0035] During the process, the sample under test is controlled to rotate along the optical axis of the system. The measurement and calculation module is used to calculate the angle between the normal of the light transmission surface of the electro-optic crystal under test and the optical axis of the crystal based on the optical axis exposure point of the electro-optic crystal under test in different rotation postures.

[0036] The device for measuring the angle between the normal of the light transmission surface of an electro-optic crystal and the optical axis of the crystal provided in this disclosure also includes a sample positioning component, which is used to detect the change in the direction of the far field of the surface reflected light of the electro-optic crystal under test in a rotating state based on the principle of a centering instrument, so as to ensure the attitude positioning accuracy of the electro-optic crystal under test.

[0037] Figure 2 The schematic diagram illustrates the establishment of a crystal optical axis reference provided in an embodiment of this disclosure.

[0038] like Figure 2 As shown, the sample positioning assembly includes a beam splitter 12, a third lens group 13, and a second detection module 14. The beam splitter 12 is positioned between the polarizer 5 and the first lens group, used to transmit the test beam and redirect the surface-reflected light from the electro-optic crystal under test at a 90° angle to the far field. The third lens group 13 is positioned in the redirection direction of the surface-reflected light, used to focus the surface-reflected light from the electro-optic crystal under test. The second detection module 14 detects the surface-reflected light; when the spot of the surface-reflected light is aligned with the center of the second detection module 14, the plane of the electro-optic crystal under test is perpendicular to the test beam. In this embodiment, the second detection module 14 is an imaging device such as a CMOS or CCD.

[0039] Specifically, before the measuring device starts operating, the electro-optic crystal is rotated, and the far-field direction of the reflected light is monitored in real time by a camera. When the far-field spot of the reflected light points to the center of the camera, the plane of the electro-optic crystal is perpendicular to the test light source. After the measuring system starts operating, by monitoring the deviation of the far-field direction of the reflected light from the camera center in real time, the vertical positioning accuracy of the plane of the crystal can be determined online during the operation of the measuring system. Finally, the impact of factors such as the instability of the rotating mechanism's shaft on the system's measurement uncertainty can be evaluated. Alternatively, the lens and camera combination can be replaced with an autocollimator, utilizing the accuracy of the autocollimator to improve the positioning accuracy of the reference and plane.

[0040] If the size of the conic interferogram is too large, it can also be imaged onto the camera using a lens. This can be achieved by adding an imaging lens after the analyzer 10.

[0041] In this embodiment, the sample positioning component further includes a corner cube prism 15.

[0042] Figure 3 The illustration shows a schematic diagram of the principle of a cornerstone prism provided in an embodiment of the present disclosure.

[0043] like Figure 3 As shown, the corner cube prism 15 is a prism that acts as a corner reflector, and is a type of rear-facing reflector. It consists of three mutually perpendicular right-angled facets. Incident light rays undergo total internal reflection at the three right angles and return along their original path. The direction of the reflected beam is nominally parallel to the direction of the incident beam, and its accuracy is limited only by the accuracy of the direction of the reflecting surface; the beam parallelism error is <2°.

[0044] refer to Figure 2 Before the test begins, the corner cube prism 15 is placed on the sample attitude adjustment assembly 8 to reflect the test beam along its original path. This, together with the beam splitter 12, the third lens group 13, and the second detection module 14, determines the reference plane of the electro-optic crystal under test.

[0045] This disclosure provides a device for measuring the angle between the normal of the optical transmission surface of an electro-optic crystal and the optical axis of the crystal. A laser beam output from a laser 1 is expanded and filtered by a beam expander system and then passed through polarizers 5 to achieve high polarization. The beam is then formed into a conical beam by a lens group. A test beam matching the sample size is selected by an aperture and applied to the sample. After collimation and focusing by lenses, the test beam passes through an analyzer 10 to form an interference pattern, which is recorded by a first detection module 11. During the test, the sample is first rotated, and positioning and monitoring are performed using a third lens group 13 and a second detection module 14. The test is then conducted after positioning is completed.

[0046] The device for measuring the angle between the normal of the light-transmitting surface of an electro-optic crystal and the optical axis of the crystal provided in this embodiment adopts the principle of a centering device to detect the change in the direction of the far field of the surface reflected light under the sample rotation state, ensuring planar positioning accuracy without the need to move the lens; the crystal normal measurement reference uses a corner cube prism 15 as a reflector to achieve high-precision reference positioning of <2°; the crystal under test is placed on a 5-dimensional adjustment mechanism, and the sample normal positioning can be achieved by adjusting the pitch and tilt; for large-diameter samples, scanning tests are achieved through a two-dimensional platform mechanism, which can also be achieved by adjusting the position of the test beam.

[0047] Those skilled in the art will understand that the features described in the various embodiments and / or claims of this disclosure can be combined or combined in various ways, even if such combinations or combinations are not explicitly described in this disclosure. In particular, the features described in the various embodiments and / or claims of this disclosure can be combined or combined in various ways without departing from the spirit and teachings of this disclosure. All such combinations and / or combinations fall within the scope of this disclosure.

[0048] Although this disclosure has been shown and described with reference to specific exemplary embodiments thereof, those skilled in the art will understand that various changes in form and detail may be made to this disclosure without departing from the spirit and scope of the disclosure as defined by the appended claims and their equivalents. Therefore, the scope of this disclosure should not be limited to the above embodiments, but should be defined not only by the appended claims, but also by their equivalents.

Claims

1. A device for measuring the angle between the normal to the light-transmitting surface of an electro-optic crystal and the optical axis of the crystal, characterized in that, include: Laser (1) is used to generate a test beam; A beam shaping module is used to shape and expand the test beam; The conical interferometer module includes a polarizer (5) and a first lens group (6). The polarizer (5) is used to adjust the polarization degree of the test beam after shaping and expanding, so that the test beam interferes. The first lens group (6) is located after the polarizer (5) and is used to adjust the interfering test beam into a conical beam to act on the electro-optic crystal under test. The sample attitude adjustment component (8) is used to set the electro-optic crystal under test and adjust the rotation angle of the electro-optic crystal under test in three-dimensional space. A collimation imaging module is used to focus the test beam emitted through the electro-optic crystal under test; The first detection module (11) is used to receive the test beam emitted through the electro-optic crystal under test and obtain its optical axis exposure point; The measurement and calculation module is used to calculate the angle between the normal of the light transmission surface of the electro-optic crystal under test and the optical axis of the crystal; The laser (1), the optical shaping module, the conical interferometer module, the electro-optic crystal under test, the collimation imaging module, and the first detection module (11) are arranged in a straight line along the optical axis of the crystal. The sample positioning component is used to detect the change in the orientation of the far field of the surface reflected light of the electro-optic crystal under test in a rotating state, based on the principle of a centering instrument, so as to ensure the attitude positioning accuracy of the electro-optic crystal under test. The sample positioning component includes: A beam splitter (12) is disposed between the polarizer (5) and the first lens group (6) for transmitting the test beam and directing the surface reflected light of the electro-optic crystal under test to a far-field angle of 90°. The third lens group (13) is located in the turning direction of the surface reflected light and is used to focus the surface reflected light of the electro-optic crystal under test. The second detection module (14) is used to detect the surface reflected light. When the spot of the surface reflected light is aligned with the center of the second detection module (14), the plane where the electro-optic crystal under test is located is perpendicular to the test beam. A corner prism (15) is placed on the sample attitude adjustment assembly (8) before the test begins to reflect the test beam along its original path, and works with the beam splitter (12), the third lens group (13), and the second detection module (14) to determine the reference plane of the electro-optic crystal under test.

2. The included angle measuring device according to claim 1, characterized in that, The optical shaping module includes: The first lens (2) is located after the laser (1) and is used to focus the test beam into the filter aperture (3); A filter aperture (3) is located after the first lens (2) to improve the uniformity of the intensity distribution of the test beam. The second lens (4) is located after the filter aperture (3) and is used to collimate and expand the test beam after passing through the filter aperture (3).

3. The included angle measuring device according to claim 1, characterized in that, The conical interferometer module also includes: The magneto-optical device adjusts the position and angle of the polarizer (5) by applying a sinusoidal modulation signal, thereby increasing the polarization degree of the test beam.

4. The included angle measuring device according to claim 1, characterized in that, The conical interferometer module also includes: An electric aperture (7) is provided after the first lens group (6) to make the spot size of the test beam match the size of the electro-optic crystal under test.

5. The included angle measuring device according to claim 1, characterized in that, The collimation imaging module includes: The second lens group (9) is used to collimate and reduce the test beam passing through the electro-optic crystal under test; The analyzer (10), located after the second lens group (9), is used to convert the test beam into linearly polarized light and form an interference pattern on the first detection module (11).

6. The included angle measuring device according to claim 1, characterized in that, The sample attitude adjustment component (8) includes a two-dimensional translation adjustment mechanism, a rotation adjustment mechanism and a three-dimensional attitude adjustment mechanism.

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