A test device and test method for optical uniformity of biaxial crystal principal axis direction

Abstract

The present invention discloses a testing device and a testing method for the optical uniformity of the main axis direction of a biaxial crystal. The testing device comprises a light source, a focusing lens, a collimating lens, a polarizer, a phase compensator, an analyzer, an imaging lens and a camera arranged in sequence along the optical axis direction. The crystal to be tested is placed between the phase compensator and the analyzer. The phase compensator is composed of two optical wedges. The phase delay amount is adjusted by adjusting the relative positions of the two optical wedges. The material of the optical wedge is a crystal with the same composition as the crystal to be tested and good optical uniformity. The device of the present invention has a simple structure, low cost and is easy to maintain. Compared with the traditional testing method, the method of the present invention does not need to repeatedly test the background interference and the interference pattern formed by lasers in different polarization states passing through the crystal, is less affected by the environment, has high testing efficiency, and is suitable for mass production testing; and the method of the present invention is simple to operate, has low processing requirements for the test crystal, and is easy to promote and use.

Description

Technical Field

[0001] The invention relates to the detection of crystal optical uniformity, and in particular to a testing device and a testing method for the optical uniformity in the main axis direction of a biaxial crystal. Background Art

[0002] Crystal materials are widely used in modern laser systems for frequency conversion and phase modulation. The uniformity of the crystal directly determines the performance of the laser system. It can be seen that optical uniformity is an important indicator for evaluating crystal quality. In the process of crystal growth, it is inevitable that due to the influence of gravity, temperature, impurities and other factors, structural defects will appear in the crystal and the optical uniformity will decrease. Therefore, an essential step in making optical devices using crystal materials is to test the optical uniformity of the material and select the reasonably usable area for processing.

[0003] At present, the main method for testing the optical uniformity of crystals is to use a large laser interferometer to obtain the interference fringes of the plane wave of the transmitted crystal, and calculate the phase of different positions of the crystal by the wavefront reconstruction method to obtain the crystal refractive index distribution (i.e., optical uniformity). Although this method has high test accuracy, there are many inconveniences in using this test method in the production of crystal optical devices: first, this test method requires expensive equipment, which directly leads to an increase in the test cost; second, it places extremely high requirements on sample processing, environmental vibration, and the quality of operators, and the test conditions are relatively harsh; third, the test steps are cumbersome, and before the test, it is necessary to test the interference generated by the reflection of the cavity and the front and back surfaces of the crystal in turn to eliminate background interference. In the actual production process, test efficiency and accuracy are equally important. It is often necessary to quickly and accurately judge the optical uniformity of the crystal before arranging the subsequent processes. Therefore, a simple and practical device and method are needed to improve the test efficiency. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a testing device and a testing method for the optical uniformity of the main axis direction of a biaxial crystal with a simple structure, low cost and easy operation in view of the deficiencies in the prior art.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A device for testing the optical uniformity of a biaxial crystal in the main axis direction comprises a light source, a condenser lens, a collimating lens, a polarizer, a phase compensator, an analyzer, an imaging lens and a camera which are sequentially arranged along the optical axis direction. The crystal to be tested is placed between the phase compensator and the analyzer. The phase compensator is composed of two optical wedges. The phase delay amount is adjusted by adjusting the relative positions of the two optical wedges. The material of the optical wedge is a crystal with the same composition as that of the crystal to be tested and good optical uniformity.

[0007] In the above test device, the light source is a white point light source, preferably an LED lamp or a fiber optic halogen lamp, more preferably an LED lamp or a fiber optic halogen lamp with a color temperature range of 3000-6000K. The diameter of the light source is preferably controlled at 5-10mm.

[0008] In the above-mentioned test device, the function of the focusing lens and the collimating lens is to expand and collimate the point light source to form a uniform parallel light field as the detection light, and the focusing lens and the collimating lens adopt achromatic cemented lenses. The polarizer is used to convert the incoherent detection light into linearly polarized light. The function of the analyzer is to make the two beams of linearly polarized light after passing through the crystal to be tested interfere in the analysis direction to form colorful interference colors. The imaging lens preferably adopts an object-side telecentric lens, which has the advantage of only receiving the main light parallel to the optical axis during imaging and shielding the influence of stray light in other directions on interference. At the same time, the object-side telecentric lens can obtain the undistorted outline of the crystal to be tested, so that the optical uniformity of different areas of the crystal to be tested can be accurately judged. The camera is preferably a color CCD camera or a color CMOS camera, which is used to receive the image formed by the imaging lens.

[0009] The crystal to be tested needs to undergo conventional test polishing. It is usually required to control the parallelism of the light-transmitting surface of the crystal to be tested to be ≥20 arc seconds and the flatness to be ≥λ / 4. The length of the crystal to be tested should be within the compensation range of the phase compensator.

[0010] In order to work in a wide spectral range, the optical components involved in the above device are not coated.

[0011] The present invention also provides a method for testing the optical uniformity of a crystal using the above-mentioned device for testing the optical uniformity of the biaxial crystal in the main axis direction, comprising the following steps:

[0012] a. Focus, expand, collimate and polarize the selected light source to obtain parallel linear polarized light as the detection light;

[0013] b. Adjust the angle of the crystal to be tested so that the detection light is incident on the light-transmitting surface of the crystal to be tested, and set the angle between the polarization direction of the detection light and the fast axis of the crystal to be tested and the angle between the polarization direction of the detection light and the slow axis of the crystal to be tested to 45°;

[0014] c. Adjust the phase compensator to offset the phase difference between the two linearly polarized lights passing through the crystal to be tested;

[0015] d. Set the polarization state of the analyzer to be perpendicular to the polarizer, and two linearly polarized beams form polarization interference along the direction of the analyzer;

[0016] e. The polarization interference image is captured by the imaging lens and camera, and the optical uniformity of the main axis direction of the crystal to be tested is determined based on the interference color.

[0017] The selection and functions of the light source, imaging lens, camera, etc. involved in the above method are the same as described above.

[0018] In the above method, a precision micrometer is usually used to adjust the relative position of two optical wedges constituting the phase compensator to adjust the phase delay.

[0019] Compared with the prior art, the present invention is characterized in that:

[0020] 1. The device of the present invention has a simple structure, low cost and is easy to maintain.

[0021] 2. Compared with the traditional testing method, the method of the present invention does not need to repeatedly test the background interference and the interference pattern formed by lasers of different polarization states passing through the crystal, is less affected by the environment, has high testing efficiency, and is suitable for mass production testing.

[0022] 3. The method of the present invention is simple to operate, has low processing requirements for the test crystal, is easy to train operators, and is suitable for popularization and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The figure is a schematic structural diagram of an embodiment of a testing device for optical uniformity in the main axis direction of a biaxial crystal according to the present invention.

[0024] The numbers in the figure are:

[0025] 1. Light source, 2. Focusing lens, 3. Collimating lens, 4. Polarizer, 5. Phase compensator, 6. Crystal to be tested, 7. Analyzer, 8. Imaging lens, 9. Camera. DETAILED DESCRIPTION

[0026] The optical uniformity test device for the biaxial crystal main axis direction of the present invention is based on the following principles:

[0027] The parallel light emitted by the white point light source after focusing and collimation is converted into linear polarized light through the polarizer. When the angle between the polarization direction of the incident light and the fast axis of the crystal to be tested and the angle between the polarization direction of the incident light and the slow axis of the crystal to be tested are both 45°, the incident light is decomposed into two linear polarized lights with the same intensity and vertical vibration directions but different propagation speeds inside the crystal due to the birefringence effect. These two polarized lights produce a certain phase difference δ after passing through the crystal to be tested. 1 The function of the phase compensator is to generate a reverse phase difference δ 2 =-δ 1 , so that the total phase difference (δ = δ 1 +δ 2 ) is zero. The polarization direction of the analyzer is perpendicular to the polarizer. According to the polarization interference formula When the optical path difference generated by two beams of monochromatic polarized light is an even multiple of half the wavelength, the intensity of the emitted light is zero. White light is composed of seven monochromatic lights of different wavelengths. Except for the optical path difference being zero, any optical path difference cannot be simultaneously equal to an even multiple of half the wavelength of each monochromatic wave, and it is impossible to make the seven monochromatic lights cancel each other out and become extinguished. When the refractive index of the crystal to be tested is uneven, there will be slight deviations in the optical path difference generated in each area, which is reflected in the different colors of the transmitted light. As the optical path difference gradually increases from zero, the interference color starts from black and gray-black, and the order of the change of various interference colors appears in sequence. The optical uniformity of different areas of the crystal to be tested can be characterized according to the color difference, forming the test method for the optical uniformity of the crystal provided by the present invention.

[0028] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] Embodiment 1: Device for testing optical uniformity of the biaxial crystal principal axis direction of the present invention

[0030] like Figure 1 As shown, the testing device for the optical uniformity of the biaxial crystal in the main axis direction of the present invention comprises a light source 1, a focusing lens 2, a collimating lens 3, a polarizer 4, a phase compensator 5, an analyzer 7, an imaging lens 8 and a camera 9 which are sequentially arranged along the optical axis direction, and the crystal 6 to be tested is placed between the phase compensator 5 and the analyzer 7, and the phase compensator 5 is composed of two optical wedges, and the phase delay amount is adjusted by adjusting the relative positions of the two optical wedges, wherein the material of the optical wedge is a crystal with the same composition as that of the crystal to be tested and good optical uniformity.

[0031] In this embodiment, the light source 1 is a white point light source, more specifically an LED lamp or a fiber optic halogen lamp with a color temperature of 3000k-6000k, and the diameter of the light source is controlled within the range of 5-10mm to improve the parallelism of the detection light.

[0032] The condenser lens 2 and the collimator lens 3 are mainly used to expand and collimate the light emitted by the light source 1 to obtain a homogenized parallel light beam, thereby enhancing the detection capability of crystals with different apertures to be tested and improving the contrast of the detection light interference imaging.

[0033] The polarizer 4 makes the parallel light emitted from the collimating lens 3 become completely linearly polarized light to meet the conditions of polarization interference.

[0034] The phase compensator 5 is composed of two crystal wedges with the same composition as the crystal 6 to be measured and good optical uniformity. The three main axes of the two wedges are completely overlapped in structure. A precision micrometer is used to push the relative position of the two wedges constituting the phase compensator 5 to adjust the phase delay. The function of the phase compensator 5 is to generate a reverse phase difference to offset the phase difference caused by the double refraction of the crystal to be measured.

[0035] The light transmission direction of the crystal 6 to be tested is parallel to the detection light, the angle between the polarization direction of the polarizer 4 and the fast axis of the crystal 6 to be tested is 45°, and the angle between the polarization direction of the polarizer 4 and the slow axis of the crystal 6 to be tested is also 45°. In this embodiment, the light transmission direction of the crystal 6 to be tested is the crystal x-axis direction, the fast axis is the crystal y-axis, and the slow axis is the crystal z-axis.

[0036] It should be noted that the light transmission directions of the crystal to be tested 6 and the phase compensator 5 are along the same main axis direction, and it should be ensured that the fast axis of the crystal to be tested 6 coincides with the slow axis of the phase compensator 5, and the slow axis of the crystal to be tested 6 coincides with the fast axis of the phase compensator 5. In this embodiment, the light transmission main axis directions of the crystal to be tested 6 and the phase compensator 5 are both x-axis, the slow axis z-axis of the crystal to be tested 6 coincides with the fast axis y-axis of the phase compensator 5, and the fast axis y-axis of the crystal to be tested 6 coincides with the slow axis z-axis of the phase compensator 5.

[0037] The function of the analyzer 7 is to make the two linearly polarized lights after the crystal 6 to be tested interfere in the analysis direction to form colored interference colors. It should be noted here that the polarizer 4 and the analyzer 7 should be in the extinction position, that is, the polarization states of the two are perpendicular to each other.

[0038] The imaging lens 8 is used to image the parallel light passing through the crystal to be tested and filter out the stray light from other directions. The imaging lens 8 adopts an object-side telecentric lens, which has the advantage of only receiving the main light parallel to the optical axis during imaging and shielding the interference effect of stray light from other directions. At the same time, the object-side telecentric lens can obtain the outline of the crystal to be tested 6 without distortion, so that the optical uniformity of different areas of the crystal to be tested 6 can be accurately determined.

[0039] The camera 9 is a color CMOS camera or a color CCD camera, and is used to capture the image formed by the imaging lens 8 .

[0040] Example 2: Using Figure 1 Method for testing crystal optical uniformity in the embodiment

[0041] 1) Adjust the relative positions of the light source 1, the focusing lens 2, and the collimating lens 3 so that the expanded detection light is emitted in parallel in the horizontal direction;

[0042] 2) Adjust the positions and angles of the polarizer 4, analyzer 7, imaging lens 8, and camera 9 so that the incident parallel light is incident on the center of the above optical elements; set the reference polarization direction of the polarizer 4 to the horizontal direction or the vertical direction, and the polarization directions of the analyzer 4 and the polarizer 7 are perpendicular to each other. At this time, the picture taken by the camera 9 should be a uniform black background;

[0043] 3) Insert the crystal 6 to be tested, ensure that the detection light can completely cover the crystal aperture, the light transmission direction is the main axis direction of the crystal to be tested, adjust the polarization state of the polarizer 4 so that the angle between the polarization direction of the detection light and the fast axis of the crystal 6 to be tested is 45°, and the angle between the polarization direction of the polarizer 4 and the slow axis of the crystal 6 to be tested is also 45°;

[0044] 4) inserting the phase compensator 5, and rotating the phase compensator 5 along the optical axis so that the fast axis of the phase compensator 5 coincides with the slow axis of the crystal 6 to be measured, and the slow axis of the phase compensator 5 coincides with the fast axis of the crystal 6 to be measured;

[0045] 5) Use a precision micrometer to move the relative positions of the two optical wedges constituting the phase compensator 5 until the color within the crystal outline in the image of the crystal 6 to be tested taken by the camera 9 changes from all white to a gray-black area, and judge the optical uniformity of the crystal in the main axis direction based on the color comparison of the image of the crystal 6 to be tested taken by the camera 9 and the interference color sequence table.

[0046] The above embodiments are only specific examples for further illustrating the purpose, technical solutions and beneficial effects of the present invention, and the present invention is not limited thereto. Any modification, equivalent replacement, improvement, etc. made within the scope of the disclosure of the present invention are included in the protection scope of the present invention.

Claims

1. A test device for the optical uniformity of a biaxial crystal in the main axis direction, characterized in that: The invention comprises a light source (1), a focusing lens (2), a collimating lens (3), a polarizer (4), a phase compensator (5), an analyzer (7), an imaging lens (8) and a camera (9) which are sequentially arranged along the optical axis direction; the crystal (6) to be measured is placed between the phase compensator (5) and the analyzer (7); the phase compensator (5) is composed of two optical wedges; the phase delay amount is adjusted by adjusting the relative position of the two optical wedges; the material of the optical wedges is a crystal with the same composition as the crystal (6) to be measured and good optical uniformity; the light source (1) is a white point light source; the polarizer (4) and the analyzer (7) are in an extinction position.

2. The device for testing optical uniformity of biaxial crystal principal axis direction according to claim 1, characterized in that: The light source (1) is an LED lamp or an optical fiber halogen lamp.

3. The device for testing optical uniformity of biaxial crystal principal axis direction according to claim 1, characterized in that: The imaging lens (8) is an object-side telecentric lens.

4. The device for testing optical uniformity of biaxial crystal principal axis direction according to claim 1, characterized in that: The camera (9) is a color CCD camera or a color CMOS camera.

5. A method for testing the optical uniformity of a crystal using the apparatus for testing the optical uniformity of the biaxial crystal in the main axis direction according to claim 1, comprising the following steps: a. focusing, expanding, collimating and polarizing the selected light source (1) to obtain parallel linearly polarized light as the detection light; b. Adjust the angle of the crystal (6) to be tested so that the detection light is incident on the light-transmitting surface of the crystal (6) to be tested, and set the angle between the polarization direction of the detection light and the fast axis of the crystal (6) to be tested and the angle between the polarization direction of the detection light and the slow axis of the crystal (6) to be tested to be 45 ; c. Adjusting the phase compensator (5) to offset the phase difference between the two linearly polarized beams passing through the crystal to be tested (6); d. The polarization state of the analyzer (7) is set perpendicular to that of the polarizer (4), and two linearly polarized light beams along the direction of the analyzer (7) form polarization interference; e. The polarization interference image is captured by the imaging lens (8) and the camera (9), and the optical uniformity of the main axis direction of the crystal (6) to be tested is determined based on the interference color.

6. The method according to claim 5, characterized in that: The phase delay amount is adjusted by adjusting the relative position of two optical wedges constituting the phase compensator (5) using a precision micrometer.

7. The method according to claim 5, characterized in that: The imaging lens (8) is an object-side telecentric lens.

8. The method according to claim 5, characterized in that: The camera (9) is a color CCD camera or a color CMOS camera.

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