Device and method for detecting transmittance of thin film polarizer

Abstract

A detection device for the transmittance of a thin-film polarizer, belonging to the field of laser technology. The specific solution is as follows: A detection device for the transmittance of a thin-film polarizer includes a test light source, a polarization cube, a rotating table, a mounting seat, a convex lens, and a power meter. The mounting seat is fixedly arranged on the rotating table and their centers coincide. The thin-film polarizer to be tested is arranged on the mounting seat and their centers coincide. The light emitted by the test light source passes through the polarization cube and is incident on the center of the thin-film polarizer to be tested, reflected by the thin-film polarizer to be tested and reaches the center of the convex lens, and then reaches the power meter. The distances between the center of the convex lens and the center of the rotating table and between the center of the convex lens and the power meter are both 2f. This detection device can ensure that when the thin-film polarizer is rotated near the Brewster angle, the reflected light will always stably enter the center of the power meter probe, avoiding the test error caused by the repeated movement of the power meter position during the test, and thus ensuring accurate measurement.

Description

Technical Field

[0001] The present invention belongs to the field of laser technology, and particularly relates to a detection device and method for the transmittance of a thin-film polarizer. Background Art

[0002] The thin-film polarizer is a kind of optical polarizer, which obtains polarized light by using the interference effect of multi-layer dielectric films. An optical thin film is deposited on materials such as glass. When incident at certain specific angles, the thin-film polarizer will allow s-polarized light to be reflected and p-polarized light to be transmitted. Usually, the incident angle is designed as the Brewster angle, so as to avoid the reflection loss of the backward transmitted light. The thin-film polarizer is a commonly used optical element in Q-switched Nd:YAG lasers. Its transmittance of p-polarized light is an important parameter to be considered when designing a Q-switched laser. Therefore, it is very crucial to accurately obtain the transmittance of p-light of the thin-film polarizer. Although the manufacturer will provide a detection report when the polarizer leaves the factory, it is still very necessary for users to re-measure it or test it again before use.

[0003] The transmittance test of the thin-film polarizer usually adopts the "light transmission method", that is, the incident light is incident on the polarizer at an approximate Brewster angle, and then a power meter is used to record the p-light transmission power and the incident power value respectively, and their ratio is considered to be the transmittance of the polarizer. Although the above method is simple and direct, since the transmission power is very close to the incident light power, and coupled with the reading fluctuation during the measurement by the power meter, the transmittance test result will be very inaccurate. Although the transmittance can also be obtained by measuring the reflectivity, since the reflected power is related to the incident angle of the incident light, different incident angles will cause a large difference in the reflected power; in addition, while adjusting the incident angle, the reflection direction of the reflected light will also change, which requires constantly adjusting the position of the power meter probe, bringing inconvenience to the test and introducing additional measurement errors, resulting in inaccurate test results. The present invention provides a detection device and method for the transmittance of a thin-film polarizer, which obtains the transmittance of the polarizer by measuring the reflectivity, and at the same time, during the process of adjusting the incident angle, the reflected light can always stably enter the power meter probe, ensuring the accuracy of the test result. Summary of the Invention

[0004] The first object of the present invention is to solve the problem that the transmittance of the thin-film polarizer in the prior art cannot be accurately measured, and provides a detection device for the transmittance of the thin-film polarizer.

[0005] The second object of the present invention is to provide a detection method for the transmittance of the thin-film polarizer.

[0006] In order to achieve the above objects, the present invention adopts the following technical solutions:

[0007] A detection device for the transmittance of a thin-film polarizer, comprising a test light source, a polarization cube, a rotating table, a mounting seat, a convex lens and a power meter. The mounting seat is fixedly arranged on the rotating table and their centers coincide. The thin-film polarizer to be tested is arranged on the mounting seat and their centers coincide. The light emitted by the test light source passes through the polarization cube, is incident on the center of the thin-film polarizer to be tested, is reflected by the thin-film polarizer to be tested to the center of the convex lens, and then reaches the power meter. The angle α between the light emitted by the test light source and the plane where the thin-film polarizer to be tested is located is 33±1°. The focal length of the convex lens is f, and the distances between the center of the convex lens and the center of the rotating table and between the center of the convex lens and the power meter are both 2f.

[0008] Further, the light-transmitting aperture of the convex lens is not less than 4f*tanθ, where θ is the angle between the line connecting the center of the rotating table and the center of the convex lens and the line connecting the center of the rotating table and the edge point of the convex lens.

[0009] Further, both surfaces of the convex lens are coated with an antireflection film corresponding to the working wavelength of the thin-film polarizer to be tested.

[0010] Further, the transmittance of the antireflection film is greater than 99.9%.

[0011] Further, the inner wall of the probe of the power meter is an integrating sphere coated with a white diffuse reflection material.

[0012] Further, the angular resolution of the rotating table is greater than 0.1°.

[0013] A method for detecting the transmittance of a thin-film polarizer by using the above detection device, comprising the following steps:

[0014] Step 1: Fix the mounting seat at the rotation center of the rotating table, and then place the thin-film polarizer to be tested at the center of the mounting seat;

[0015] Step 2: Place the test light source so that the light emitted by it is incident on the center of the thin-film polarizer to be tested, and rotate the rotating table so that the angle α between the light emitted by the test light source and the plane where the thin-film polarizer to be tested is located is 33±1°;

[0016] Step 3: Place the polarization cube and the convex lens so that the light emitted by the test light source passes through the polarization cube, the thin-film polarizer to be tested and the center of the convex lens in sequence;

[0017] Step 4: Adjust the position of the convex lens so that the distance between the center of the convex lens and the center of the rotating table is 2f;

[0018] Step 5: First, use a power meter to measure the optical power P1 after passing through the polarization cube. Then, move the power meter to a distance of 2f from the center of the convex lens so that the light passing through the convex lens is incident on the center of the probe of the power meter.

[0019] Step 6: Rotate the turntable clockwise and counterclockwise respectively, with the rotation angle less than ±10°, and record the minimum power value P2 collected by the power meter during the rotation process.

[0020] Step 7: The p-light transmittance of the thin-film polarizer to be measured can be calculated using the formula T = 1 - P2 / P1.

[0021] Further, in Step 5, before using the power meter to measure the optical power P1, adjust the current of the test light source so that its output power is 1 - 1.2 W.

[0022] Further, in Step 5, after using the power meter to measure the optical power P1, adjust the measurement range of the power meter to the mW range.

[0023] Further, the output wavelength of the test light source is the working wavelength of the thin-film polarizer to be measured, and its beam quality is less than 2.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] Using the detection device of the present invention to measure the reflection power of the thin-film polarizer to obtain the transmittance of the polarizer. Compared with the existing method of measuring the transmitted light power, the measurement accuracy of the transmittance of the polarizer is greatly improved. At the same time, in this detection device, the distance between the center of the convex lens and the center of the turntable and the distance between the center of the convex lens and the power meter are both 2f, which can ensure that when the thin-film polarizer is rotated near the Brewster angle, the reflected light will always be stably incident on the center of the probe of the power meter, and there is no need to constantly adjust the position of the probe of the power meter, avoiding additional measurement errors, thereby improving the measurement accuracy again. The present invention has the advantages of simple test device and accurate test results, and can be used for accurate detection of the transmittance of thin-film polarizers. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a detection device for the transmittance of the thin-film polarizer of the present invention.

[0027] In the figure, 1 is a test light source, 2 is a polarization cube, 3 is a turntable, 4 is a mounting seat, 5 is a convex lens, and 6 is a power meter. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] The technical solution of the present invention will be further described below in conjunction with the drawings, but it is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention shall be covered by the protection scope of the present invention. Specific Embodiment 1

[0030] A detection device for the transmittance of a thin - film polarizer, comprising a test light source 1, a polarization cube 2, a rotating table 3, a mounting base 4, a convex lens 5 and a power meter 6. The mounting base 4 is fixedly arranged on the rotating table 3 and their centers coincide. The thin - film polarizer to be measured is arranged on the mounting base 4 and their centers coincide. The light emitted by the test light source 1 passes through the polarization cube 2, is incident on the thin - film polarizer to be measured, is reflected by the thin - film polarizer to the center of the convex lens 5, and then reaches the power meter 6. The angle α between the light emitted by the test light source 1 and the plane where the thin - film polarizer to be measured is located is 33 ± 1°. The focal length of the convex lens 5 is f, and the distance between the center of the convex lens 5 and the center of the rotating table 3 and the distance between the center of the convex lens 5 and the power meter 6 are both 2f. The specific arrangement of each component is as Figure 1 shown. The polarization cube is used to obtain the p - polarized light of the test light source 1. The specific outer shape structure of the mounting base 4 is designed according to the shape of the thin - film polarizer to be measured.

[0031] Further, the clear aperture of the convex lens 5 is not less than 4f*tanθ, to prevent the reflected light from hitting the outside of the convex lens 5 when the thin - film polarizer to be measured rotates, where θ is the angle between the line connecting the rotation center O point of the rotating table 3 and the center of the convex lens 5 and the line connecting the rotation center O point of the rotating table 3 and the edge point of the convex lens 5.

[0032] Further, both surfaces of the convex lens 5 are coated with an antireflection film corresponding to the working wavelength of the thin - film polarizer to be measured. The transmittance of the antireflection film is greater than 99.9%, and the antireflection film is used to reduce the power loss of the convex lens 5 for reflection.

[0033] Further, the inner wall of the probe of the power meter 6 is an integrating sphere coated with white diffuse - reflection material, and the measuring range of the meter head is selected as mW.

[0034] Further, the angular resolution of the rotating table 3 is greater than 0.1°, and it can be rotated in an electric or manual manner. Specific Embodiment 2

[0036] A method for detecting the transmittance of a thin - film polarizer by using the detection device described in Specific Embodiment 1, comprising the following steps:

[0037] Step 1: Fix the mounting base 4 at the rotation center O point of the rotating table 3, and then set the thin - film polarizer to be measured at the center of the mounting base 4;

[0038] Step 2: Place the test light source 1 and turn it on so that the light emitted by it is incident on the center of the thin-film polarizer to be tested. Rotate the turntable 3 so that the angle α between the light emitted by the test light source 1 and the plane where the thin-film polarizer to be tested is located is 33 ± 1°;

[0039] Step 3: Place the polarization cube 2 and the convex lens 5 so that the light emitted by the test light source 1 passes through the centers of the polarization cube 2, the thin-film polarizer to be tested, and the convex lens 5 in sequence;

[0040] Step 4: Adjust the position of the convex lens 5 so that the distance between the center of the convex lens 5 and the center of the turntable 3 is 2f;

[0041] Step 5: Set the measurement range of the power meter 6 to the 10W range, adjust the current of the test light source 1 so that its output power is 1 - 1.2W. First, use the power meter 6 to measure the optical power P1 (unit: milliwatt) after passing through the polarization cube 2, then set the measurement range of the power meter 6 to the mW range and move it to a distance of 2f from the center of the convex lens 5 so that the light passing through the convex lens 5 is incident on the center of the probe of the power meter 6;

[0042] Step 6: Rotate the turntable 3 clockwise and counterclockwise respectively, with the rotation angle less than ±10°, and record the minimum power value P2 (unit: milliwatt) collected by the power meter 6 during the rotation process;

[0043] Step 7: Using the formula T = 1 - P2 / P1, the p-light transmittance of the thin-film polarizer to be tested can be calculated.

[0044] Furthermore, the output wavelength of the test light source 1 is the working wavelength of the thin-film polarizer to be tested, and its beam quality is less than 2.

[0045] The core innovation of the present invention is:

[0046] 1. Adopt the method of measuring the reflection power to test the transmittance of the thin-film polarizer. Since the reflection power is relatively small, the present invention uses a power meter with a milliwatt range, which can accurately measure the reflection power. Compared with the method of directly testing the passing power, the accuracy is greatly improved.

[0047] Second, when measuring the reflected power, since the polarizer needs to continuously rotate the angle to find the accurate Brewster angle, during this rotation process, the reflected light will move, which requires the power meter to be moved continuously. The back-and-forth movement measurement of the power meter is bound to bring additional errors. Since the power measured by the present invention is in the milliwatt level, the errors brought by the back-and-forth movement of the power meter are very large. To solve the above problems, the present invention introduces a convex lens, and the distance between the center of the convex lens and the center of the rotating table and the distance between the center of the convex lens and the power meter are limited to 2f, so as to ensure that during the movement of the polarizer, the reflected light always remains stationary. Therefore, the power meter can always be placed in one position, and the reflected light will almost always hit the same position of the power meter, thereby greatly improving the measurement accuracy.

Claims

1. A method for detecting the transmittance of a thin-film polarizer. The detection device used in the detection method includes a power meter (6), a test light source (1), a polarization cube (2), a rotating table (3), a mounting base (4), and a convex lens (5). The mounting base (4) is fixedly arranged on the rotating table (3) and their centers coincide. The thin-film polarizer to be tested is arranged on the mounting base (4) and their centers coincide. The light emitted by the test light source (1) passes through the polarization cube (2), enters the center of the thin-film polarizer to be tested, is reflected by the thin-film polarizer to be tested to the center of the convex lens (5), and then reaches the power meter (6). The angle α between the light emitted by the test light source (1) and the plane where the thin-film polarizer to be tested is located is 33 ± 1°. The focal length of the convex lens (5) is f. The distance between the center of the convex lens (5) and the center of the rotating table (3) and the distance between the center of the convex lens (5) and the power meter (6) are both 2f; The detection method comprises the following steps: Step 1: Fix the mounting base (4) at the rotation center of the rotating table (3), and then place the thin-film polarizer to be tested at the center of the mounting base (4); Step 2: Place the test light source (1) so that the light it emits enters the center of the thin-film polarizer to be tested, and rotate the rotating table (3) so that the angle α between the light emitted by the test light source (1) and the plane where the thin-film polarizer to be tested is located is 33 ± 1°; Step 3: Place the polarization cube (2) and the convex lens (5) so that the light emitted by the test light source (1) passes through the centers of the polarization cube (2), the thin-film polarizer to be tested, and the convex lens (5) in sequence; Step 4: Adjust the position of the convex lens (5) so that the distance between the center of the convex lens (5) and the center of the rotating table (3) is 2f; Step 5: First, use the power meter (6) to measure the optical power P1 after passing through the polarization cube (2), and then move the power meter (6) to a distance of 2f from the center of the convex lens (5) so that the light passing through the convex lens (5) enters the center of the probe of the power meter (6); Step 6: Rotate the rotating table (3) clockwise and counterclockwise respectively, with the rotation angle less than ±10°, and record the minimum power value P2 collected by the power meter (6) during the rotation process; Step 7: Use the formula T = 1 - P2 / P1 to calculate the p-light transmittance of the thin-film polarizer to be tested.

2. The method for detecting the transmittance of a thin-film polarizer according to claim 1, characterized in that: The light passing aperture of the convex lens (5) is not less than 4f * tanθ, where θ is the included angle between the line connecting the center of the rotating table (3) and the center of the convex lens (5) and the line connecting the center of the rotating table (3) and the edge point of the convex lens (5).

3. The method for detecting the transmittance of a thin-film polarizer according to claim 1, characterized in that: Both surfaces of the convex lens (5) are coated with an antireflection film corresponding to the working wavelength of the thin-film polarizer to be tested.

4. The method for detecting the transmittance of a thin-film polarizer according to claim 3, characterized in that: The transmittance of the antireflection film is greater than 99.9%.

5. The method for detecting the transmittance of a thin-film polarizer according to claim 1, characterized in that: The inner wall of the probe of the power meter (6) is an integrating sphere coated with a white diffuse reflection material.

6. The method for detecting the transmittance of a thin-film polarizer according to claim 1, characterized in that: The angular resolution of the rotating table (3) is greater than 0.1°.

7. The method according to claim 1, characterized in that: In step five, before using the power meter (6) to measure the optical power P1, adjust the current of the test light source (1) so that its output power is 1 - 1.2 W.

8. The method according to claim 1, characterized in that: In step five, after using the power meter (6) to measure the optical power P1, adjust the measurement range of the power meter (6) to the mW range.

9. The method according to claim 1, characterized in that: The output wavelength of the test light source (1) is the working wavelength of the thin film polarizer to be measured, and its beam quality is less than 2.

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