Device and method for synchronously measuring refractive index and thickness of transparent material

Abstract

The invention discloses a device and a method for synchronously measuring the refractive index and the thickness of a transparent material, a Michelson interferometer is improved on the basis of the Michelson interference principle, and a reflecting mirror, an attenuation sheet with known refractive index and thickness and an optical screen are utilized after multiple light splitting designs. Three groups of interference fringes of different surfaces of the transparent material and the reflecting mirror are obtained, and the surface appearance and the refractive index of the transparent material are measured at the same time by combining the fringe radius.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical measurement, and can be widely applied to the fields of optical device manufacturing, materials science, criminal investigation, military, astronomical equipment, etc. Specifically, it relates to a device and a measurement method for synchronously measuring the refractive index and thickness of a transparent material. Background Art

[0002] The geometric thickness and refractive index of optical materials are important parameters in material engineering applications and scientific research. There are currently various methods for measuring these parameters. However, some methods can only measure one parameter at a time, such as only measuring thickness or only measuring refractive index. There are also many methods in the prior art that can measure geometric thickness and refractive index simultaneously, but different methods have their own advantages and disadvantages. Traditional methods (such as photometric method, ellipsometry) need to measure the thickness and refractive index of the transparent material separately, with low efficiency and large errors. The traditional Michelson interferometer can only indirectly calculate another parameter through known parameters (such as calculating thickness or refractive index through optical path difference), and cannot achieve synchronous measurement. At the same time, when the external environment (external force, temperature, etc.) changes, the refractive index n and thickness l of the material will change accordingly. The prior art has insufficient ability to dynamically analyze the refractive index n and thickness l of the material affected by external fields (such as stress, temperature), and it is difficult to meet the requirements of precision measurement.

[0003] Patent application document CN101614526A also discloses a method and a device for simultaneously measuring the geometric thickness and refractive index of a transparent material. After building the optical path, the coincident foci on both sides are defined as the so-called standard points. After putting the material in, by moving the optical paths on the left and right sides, using the principle of the maximum response value of the photodetector, the front focus and the rear focus are respectively made to hit the front and rear surfaces of the material. The thickness of the material is obtained from the simple geometric shift of moving left and right, and then the refractive index is further calculated. However, it uses the method of manually moving the confocal filter group to change the response value of the photodetector, which requires high operation accuracy for the moving stage and also requires fine operation during the manual moving process. Patent application document CN103983609A discloses a device and a measurement method for measuring the refractive index and thickness of a transparent material based on spectral interference. It abandons the reference arm of the Michelson interferometer and builds a single optical path system. Although the operation is simple, it depends on the data processing of the spectrometer and Fourier transform, and the measurement accuracy is affected.

[0004] With the development of optical device manufacturing and materials science, the requirements for the measurement accuracy of the thickness and refractive index of transparent materials are getting higher and higher. Traditional methods cannot meet the requirements of synchronous measurement and high-precision measurement. There is an urgent need for a device and a method that can simultaneously measure thickness and refractive index and can analyze their influence by external fields. Summary of the Invention

[0005] Based on the above technical status quo, the present invention improves the Michelson interferometer on the basis of the Michelson interference principle. After multiple beam splitting designs, using a mirror, an attenuation sheet with a known refractive index and thickness, and a light screen, three groups of interference fringes of different surfaces of the transparent material and the mirror are obtained, and the surface topography and refractive index of the transparent material are measured simultaneously by combining the fringe radius.

[0006] The technical solution adopted by the present invention is as follows: A device for synchronously measuring the refractive index and thickness of a transparent material, comprising an optical path system and an image acquisition module;

[0007] The optical path system includes a light source, a beam splitter assembly, a mirror assembly, a light screen assembly, and a clamping bracket for the object to be measured. The beam splitter assembly includes a first beam splitter, a second beam splitter, a third beam splitter, and a circular beam splitter. The mirror assembly includes a first mirror, a second mirror, a third mirror, a fourth mirror, a fifth mirror, a sixth mirror, and a seventh mirror. The light screen assembly includes a first screen and a second screen for receiving interference fringes. The clamping bracket for the object to be measured is used to clamp the transparent material;

[0008] The light source, the third beam splitter, and the second mirror are arranged coaxially along a first axis. A first mirror is arranged on one side of the third beam splitter, and a seventh mirror is arranged on one side of the second mirror, and the first mirror and the seventh mirror are distributed on different sides of the first axis; The third mirror, the first beam splitter, the second beam splitter, and the sixth mirror are arranged coaxially in sequence along a second axis, and the second axis is perpendicular to the first axis; The clamping bracket for the object to be measured is arranged coaxially with the second axis between the first beam splitter and the second beam splitter; The first mirror and the third mirror are coaxial along a third axis, the seventh mirror and the sixth mirror are coaxial along a fourth axis, and both the third axis and the fourth axis are parallel to the first axis; The fourth mirror, the first beam splitter, and the second screen are arranged coaxially in sequence along a fifth axis; The fifth mirror, the circular beam splitter, the second beam splitter, and the first screen are arranged coaxially in sequence along a sixth axis;

[0009] The image acquisition module is arranged corresponding to the first screen and the second screen for acquiring the interference fringes on the two light screens.

[0010] Further, the optical path system further includes a first attenuation sheet and a second attenuation sheet. The first attenuation sheet is arranged between the first beam splitter and the clamping bracket for the object to be measured; The second attenuation sheet is arranged between the fourth mirror and the first beam splitter. The setting of the two attenuation sheets can optimize the contrast of the interference fringes and suppress stray light.

[0011] Preferably, a first calibration plate is arranged on the first screen, and a second calibration plate is arranged on the second screen to assist in visually obtaining the size data of the interference fringes on the light screen.

[0012] The light source can be a laser. In actual experiments, a 532 nm laser was used, and the image acquisition module used a camera to acquire interference fringe images.

[0013] The present invention also claims a method for synchronously measuring the refractive index and thickness of a transparent material. Based on the device described above, it includes the following steps:

[0014] Step 1: Place the components of the device on a horizontal tabletop, turn on the light source, and check whether the light source is working properly.

[0015] Step 2: Place the transparent material to be measured, such as K9 optical glass, sapphire, quartz, acrylic plate, etc., into the sample clamping area of the sample clamping bracket for the object to be measured.

[0016] Step 3: Adjust the position of the transparent material to be measured so that two light spots formed by the reflected light from its left surface and the reflected light from the fourth mirror appear at appropriate positions on the second screen, and two light spots formed by the reflected light from its right surface and the reflected light from the fifth mirror, and two light spots formed by the light transmitted through the transparent material to be measured and the reflected light from the circular beam splitter, a total of four light spots, appear at appropriate positions on the first screen.

[0017] Step 4: Adjust the adjustment knob behind the fourth mirror (the knob for adjusting the pitch angle and tilt angle that comes with the existing mirror) to change the pitch angle and tilt angle of the mirror, so that two light spots formed by the reflected light from the left surface of the transparent material to be measured and the reflected light from the fourth mirror form clear interference fringes M1 at appropriate positions on the second light screen.

[0018] Step 5: Adjust the adjustment knobs behind the fifth mirror and the circular beam splitter so that two light spots formed by the reflected light from the right surface of the transparent material to be measured and the reflected light from the fifth mirror form clear interference fringes M2 on the first light screen; two light spots formed by the light transmitted through the transparent material to be measured and the reflected light from the circular beam splitter form clear interference fringes M3 at appropriate positions on the right first light screen.

[0019] Step 6: Place the camera on the one-dimensional slide rail in front of the two light screens, make it face the interference fringes M1, M2, M3 and the two calibration plates, record the obtained interference images, upload the images to the computer program terminal, and perform subsequent image processing and numerical calculations based on software such as Matlab.

[0020] Step 7: Measure the radius of the first ring of the interference fringes, including the radius r1 of the first ring of the interference fringes M1, the radius r2 of the first ring of the interference fringes M2, and the radius r3 of the first ring of the interference fringes M3.

[0021] Step 8: Calculate the optical path difference according to the measured radius of the first ring.

[0022] The optical path difference of the interference fringes M1 is:

[0023] The optical path difference of the interference fringe M2 is:

[0024] The optical path difference of the interference fringe M3 is:

[0025] In each formula of this step: N represents the Nth bright ring of the equal inclination interference fringe, λ is the optical wavelength, r1 is the radius of the first ring of the interference fringe M1, r2 is the radius of the first ring of the interference fringe M2, r3 is the radius of the first ring of the interference fringe M3, L1 represents the total optical path from the light source forming the interference fringe M1 to the light screen, L2 represents the total optical path from the light source forming the interference fringe M2 to the light screen, and L3 represents the total optical path from the light source forming the interference fringe M3 to the light screen;

[0026] Step 9: Interfere the light reflected back from the left surface of the transparent material to be measured with the light reflected by the reflector four to obtain the distance l from the left surface of the transparent material to be measured to the first spectroscope 10 ,

[0027] In the formula, l7 is the distance between the reflector four and the first spectroscope;

[0028] Interfere the light reflected back from the right surface of the transparent material to be measured with the light reflected by the reflector five to obtain the distance l from the right surface of the transparent material to be measured to the second spectroscope 11 ,

[0029] In the formula, l’5 is the distance between the reflector five and the second spectroscope;

[0030] Step 10: Calculate the thickness l8 of the transparent material to be measured:

[0031] l8 = l9 - (l4 + l 11 ) - (l6 + l 10 ); In the formula, l9 is the distance between the reflector three and the reflector six; l4 is the distance between the second spectroscope and the reflector six; l6 is the distance between the reflector three and the first spectroscope;

[0032] Based on the interference between the light transmitted through the transparent material to be measured and the light reflected by the circular spectroscope, calculate the refractive index n of the transparent material to be measured according to the following formula:

[0033] l6 + l 10 + n l8 + l 11 - (l4 + 2l5) = θl3, where l5 is the distance between the circular spectroscope and the second spectroscope. Given the optical path difference, finally, the refractive index n of the transparent material to be measured can be obtained.

[0034] The measurement method provided by the present invention has the following advantages:

[0035] 1. The Michelson interferometer is improved. By combining two sets of Michelson interferometers, the refractive index n and thickness l are measured simultaneously and in real time. They compensate for each other, enabling precise measurement of n and l and dynamic analysis thereof, breaking through the limitations of traditional measurement and making the measurement more accurate.

[0036] 2. Through optical path analysis, a new calculation formula for calculating the optical path difference based on measuring the fringe radius is independently designed, and then the thickness and refractive index of the material are obtained, breaking through the traditional method of calculating the optical path difference by counting the number of fringes, making the algorithm simpler and less time-consuming. Description of the Drawings

[0037] Figure 1 is the design diagram of the optical path system of the present invention;

[0038] Figure 2 is the schematic diagram of the principle of the measurement method of the present invention;

[0039] Figure 3 is the schematic diagram of the overall structure of the device of the present invention;

[0040] In the figure: 1. Camera, 2. Laser, 3-1. First convex lens, 3-2. Second convex lens, 4-1. First mirror, 4-2. Second mirror, 4-3. Third mirror, 4-4. Fourth mirror, 4-5. Fifth mirror, 4-6. Sixth mirror, 4-7. Seventh mirror, 5-1. First beam splitter, 5-2. Second beam splitter, 5-3. Third beam splitter, 6. Attenuator, 7. Clamping bracket for the object to be measured, 8. Circular beam splitter, 9-1. First calibration plate, 9-2. Second calibration plate. Detailed Embodiment

[0041] See Figure 1 , which is the design diagram of the optical path system of the present invention. All components are integrally built on the measurement platform. Among them, the third mirror, the first beam splitter, the second beam splitter, and the sixth mirror are coaxially placed in sequence. The object to be measured, that is, the transparent material to be measured, is placed between the first beam splitter and the second beam splitter and adjusted to be coaxial with the above-mentioned coaxial axis to form the first coaxial axis. The laser emitted by the light source is split into two by the third beam splitter. The first light path enters the third mirror after being reflected by the first mirror, and then propagates along the first coaxial axis. The second light path is reflected by the second mirror to the seventh mirror, then reflected by the seventh mirror to the sixth mirror, and then reflected by the sixth mirror to the second beam splitter, and then also propagates along the coaxial axis.

[0042] Place mirror four on one side of a spectroscope and screen two on the other side. Moreover, mirror four, spectroscope one, and screen two also form a coaxial axis for the light path propagation, serving as the second coaxial axis, which is perpendicular to the first coaxial axis; place mirror five and a circular spectroscope on one side of spectroscope two and screen one on the other side. Mirror five, the circular spectroscope, spectroscope two, and screen one constitute a coaxial axis for the light path propagation, serving as the third coaxial axis, which is also perpendicular to the first coaxial axis and parallel to the second coaxial axis.

[0043] Figure 2 is a schematic diagram of the principle of the measurement method of the present invention. The following combines Figure 1 and Figure 2 to clearly explain the light path design concept and working principle of the present invention first.

[0044] Specifically, multiple guide rails or guide grooves extending along the x-axis and y-axis can be set on the measurement platform. Each component is installed along the guide rail or guide groove at the corresponding position, and the positions of each component are fixed and adjusted through structures such as short screws that can be tightened and loosened on the guide rail or guide groove. Refer to Figure 1 , set the optical path distance between the light source and spectroscope three as l0, set the optical path distance between the first path of light split from the light source between spectroscope three and mirror one as l2, set the optical path distance between the second path of light split between spectroscope three and mirror two as l1, and also set the optical path distance between mirror two and mirror seven as l2. Both sections of the optical path l2 are parallel to the first coaxial axis; the optical path between mirror seven and mirror six is l3. Since mirror six and mirror three are coaxial, the optical path distance between mirror one and mirror three is (l1 + l3), that is, the optical path l2 and the optical path (l1 + l3) are perpendicularly arranged with respect to the first coaxial axis; set the optical path distance between mirror three and spectroscope one as l6, set the optical path distance between spectroscope two and mirror six as l4, and set the total optical path distance between mirror three and mirror six as l9. Set the optical path distance between spectroscope one and screen two as l 12 , set the optical path distance between spectroscope two and screen one as l 13 , adjust the preset positions of each component along the guide rail or guide groove, then the optical path distances l0, l1, l2, l3, l4, l6, l9, l 12 , l 13 are all adjustable known values.

[0045] Refer to Figure 1 for the illustration: It is the design diagram of the optical path system of the present invention. Based on Figure 1 , the measurement principle of the present invention is:

[0046] By improving the Michelson interferometer and combining two sets of Michelson interferometers, three sets of interference fringes are obtained, and then the material thickness l and refractive index n are calculated;

[0047] The first set of interference fringes: The light reflected from the left surface of the material to be measured interferes with the light reflected back by the fourth mirror, obtaining: l 10 ;

[0048] The second set of interference fringes: The light reflected from the right surface of the material to be measured interferes with the light reflected back by the fifth mirror, obtaining: l 11 ;

[0049] From Figure 1 The geometric relationship in it easily obtains the material thickness l8:

[0050] l8 = l9 - (l4 + l 11 ) - (l6 + l 10 )

[0051] The third set of interference fringes: The light transmitted through the material to be measured interferes with the light reflected back by the circular beam splitter, obtaining the optical path difference Δl3 between the optical path of the light transmitted through the material and its standard surface;

[0052] From its optical path difference, it can be obtained:

[0053] l6 + l 10 + nl8 + l 11 - (l4 + 2l5) = Δl3

[0054] Obtain: The refractive index n of the material to be measured.

[0055] See Figure 2 The illustration of: It is an equivalent optical path diagram obtained by symmetrically transforming the optical path of the basic principle. Based on Figure 2 , the data processing principle of the present invention is: Based on the optical path of the Michelson interferometer, after the parameters of the device are fixed, the optical path difference of the two coherent lights is fixed, and the radius of its interference fringes is related to k (standard surface), that is, the present invention utilizes this corresponding relationship, and the corresponding optical path difference can be calculated through the measured radius of the interference fringes, and finally the material thickness l and refractive index n are calculated:

[0056] Deduction:

[0057] The equal inclination interference generated by the beam reflected by the mirror and the upper surface of the material:

[0058] 2n0hcosi = kλ

[0059] The equal inclination interference generated by the beam reflected by the mirror and the lower surface of the material:

[0060]

[0061] When the light is incident perpendicularly, i = 0, the central order k:

[0062]

[0063] The Nth bright fringe of equal inclination interference corresponds to i N :

[0064]

[0065] The optical path difference corresponds one-to-one with the radius of the bright fringe:

[0066]

[0067] Let

[0068] H = h1 + h2 + 2h’

[0069] From Figure 2 The geometric relationship gives:

[0070]

[0071] Then the optical path difference for generating the standard ring interference fringe ④ is:

[0072] H1 - H2 = k1λ

[0073] Also

[0074]

[0075] Then the optical path difference for generating the interference fringe ⑤ is:

[0076] H’1 - H’2 = k2λ

[0077] Let

[0078] k1 = k2

[0079] We get

[0080] H1 - H2 = H’1 - H’2

[0081] Substituting the above equations, we can obtain:

[0082]

[0083] That is: The distance (i.e., the optical path difference) Δ between the surface of the material and its standard surface has a quartic equation relationship with the radius R2 of the interference fringe.

[0084] Based on this design principle, the device for synchronously measuring the refractive index and thickness of a transparent material of the present invention is as Figure 3 shown, which includes an optical path system and an image acquisition module;

[0085] The optical path system includes a light source, a beam splitter assembly, a mirror assembly, a light screen assembly, and a clamping bracket for the object to be measured. The beam splitter assembly includes a first beam splitter 5-1, a second beam splitter 5-2, a third beam splitter 5-3, and a circular beam splitter 8. The mirror assembly includes a first mirror 4-1, a second mirror 4-2, a third mirror 4-3, a fourth mirror 4-4, a fifth mirror 4-5, a sixth mirror 4-6, and a seventh mirror 4-7. The light screen assembly includes a first screen and a second screen for receiving interference fringes.

[0086] The light source can be a laser 2, such as a 532 nm laser. The laser 2, the third beam splitter 5-3, and the second mirror 4-2 are arranged coaxially along a first axis. The first mirror 4-1 is arranged on one side of the third beam splitter 5-3, and the seventh mirror 4-7 is arranged on one side of the second mirror 4-2. The first mirror 4-1 and the seventh mirror 4-7 are distributed on different sides of the first axis. The third mirror 4-3, the first beam splitter 5-1, the second beam splitter 5-2, and the sixth mirror 4-6 are arranged coaxially in sequence along a second axis, and the second axis is perpendicular to the first axis. The clamping bracket 7 for the object to be measured is arranged coaxially with the second axis between the first beam splitter 5-1 and the second beam splitter 5-2. The first mirror 4-1 and the third mirror 4-3 are coaxial along a third axis, and the seventh mirror 4-7 and the sixth mirror 4-6 are coaxial along a fourth axis. Both the third axis and the fourth axis are parallel to the first axis. Correspondingly, both the third axis and the fourth axis are perpendicular to the second axis. The fourth mirror 4-4, the first beam splitter 5-1, and the second screen are arranged coaxially in sequence along a fifth axis, that is, the first beam splitter 5-1 is located between the fourth mirror 4-4 and the second screen, and the fifth axis is parallel to the first axis. The fifth mirror 4-5, the circular beam splitter 8, the second beam splitter 5-2, and the first screen are arranged coaxially in sequence along a sixth axis, that is, the second beam splitter 5-2 is located between the circular beam splitter 8 and the first screen, and the sixth axis is also parallel to the first axis.

[0087] The image acquisition module includes a camera 1. The camera 1 is arranged corresponding to the first screen and the second screen for acquiring the interference fringes on the two light screens.

[0088] After acquiring the interference fringes, the radius of the interference fringes is measured, and the optical path difference can be calculated using it, and then the refractive index n and thickness l of the material can be calculated.

[0089] Furthermore, a first calibration plate 9-1 is arranged on the first screen, and a second calibration plate 9-2 is arranged on the second screen, which can assist in visually obtaining the size data of the interference fringes on the light screen.

[0090] During the measurement experiment of a small part of the samples, we found that speckles would be generated and the interference fringe phenomenon was not good. Therefore, based on the contrast principle, on the basis that the previous beam splitters all split the light by five to five, we calculated the energy. Then we optimized the designed optical path and added two attenuation filters to the optical path, effectively overcoming the speckle phenomenon and obtaining better interference patterns. For details, see Figure 3 The transparent material to be measured is clamped on the object clamping bracket 7, and the object clamping bracket 7 provides a two-dimensional adjustment range; an attenuation filter 6 is arranged between the first beam splitter 5-1 and the transparent material to be measured, and at the same time, another attenuation filter (not shown in the figure) is arranged between the fourth mirror 4-4 and the first beam splitter 5-1. Adding two attenuation filters can optimize the interference fringe contrast and suppress stray light.

[0091] Based on the device for synchronously measuring the refractive index and thickness of a transparent material, the measurement method specifically adopted by the present invention is as follows:

[0092] Step 1: Place the components of the device on a horizontal tabletop, turn on the laser 2, and check whether the laser 2 is working properly;

[0093] Step 2: Place the transparent material to be measured, such as K9 optical glass, sapphire, quartz, acrylic plate, etc., into the sample clamping area of the object clamping bracket 7;

[0094] Step 3: Adjust the position of the transparent material to be measured so that two light spots formed by the reflected light from the left surface of the transparent material and the reflected light from the fourth mirror 4-4 appear at appropriate positions on the second screen, and two light spots formed by the reflected light from the right surface of the transparent material and the reflected light from the fifth mirror 4-5, and two light spots formed by the light transmitted through the transparent material and the reflected light from the circular beam splitter 8, a total of four light spots appear at appropriate positions on the first screen;

[0095] Step 4: Adjust the adjustment knob behind the fourth mirror 4-4 (the existing mirror comes with a knob for adjusting the pitch angle and tilt angle) to change the pitch angle and tilt angle of the mirror, so that two light spots formed by the reflected light from the left surface of the transparent material to be measured and the reflected light from the fourth mirror 4-4 form clear interference fringes M1 at appropriate positions on the second light screen;

[0096] Step 5: Adjust the adjustment knobs behind the fifth mirror 4-5 and the circular beam splitter 8 so that two light spots formed by the reflected light from the right surface of the transparent material to be measured and the reflected light from the fifth mirror 4-5 form clear interference fringes M2 on the first screen; two light spots formed by the light transmitted through the transparent material to be measured and the reflected light from the circular beam splitter 8 form clear interference fringes M3 at appropriate positions on the right first screen;

[0097] Step 6: Place the camera 1 on the one-dimensional slide rail in front of the two light screens, making it face the interference fringes M1, M2, M3 and the two calibration plates. Record the obtained interference images, upload the images to the computer program terminal, and obtain the radius after fitting the interference fringes into a circle based on the built-in source program of Matlab software.

[0098] Step 7: Measure the radius of the first ring of the interference fringes, including the radius r1 of the first ring of the interference fringe M1, the radius r2 of the first ring of the interference fringe M2, and the radius r3 of the first ring of the interference fringe M3.

[0099] Step 8: Substitute the measured radius of the first ring into the above formula (1) for the relationship between the radius of the ring and the optical path difference to calculate the required optical path difference; the optical path difference of the interference fringe M1 where N represents the Nth bright ring of the equal-inclination interference fringes. Select the first ring, i.e., N is 1, λ is the light wavelength, L1 represents the total optical path from the light source that forms the interference fringe M1 to the light screen. The interference fringe M1 is formed on the light screen by the interference of the reflected light from the left surface of the object to be measured and the reflected light from the mirror four. Therefore, referring to Figure 1 , L1 represents that the light travels from the light source through the beam splitter three, the mirror one, the mirror three, the beam splitter one, the mirror four in sequence, and then after being reflected by the mirror four, it is projected onto the screen two after passing through the beam splitter one. Combining with the appendix Figure 1 can be expressed as L1 = l0 + l2 + l1 + l3 + l6 + 2l7 + l 12 , which is only related to the placement distances between the optical components and can be obtained through actual measurement.

[0100] The optical path difference of the interference fringe M2 In the formula, L2 represents the total optical path from the light source that forms the interference fringe M2 to the light screen. The interference fringe M2 is formed on the light screen by the interference of the reflected light from the right surface of the object to be measured and the reflected light from the mirror five. Similarly, combining with the appendix Figure 1 can be expressed as L2 = l0 + l1 + l2 + l3 + l4 + 2l'5 + l 13 , l’5 is the distance between the mirror five and the beam splitter two, which is also a set value that has been determined.

[0101] The optical path difference of the interference fringe M3 In the formula, L3 represents the total optical path from the light source that forms the interference fringe M3 to the light screen. The interference fringe M3 is the interference fringe on the light screen one formed by the light passing through the object to be measured and the reflected light from the circular beam splitter. Similarly, combining with the appendix Figure 1 can be expressed as L3 = l0 + l1 + l2 + l3 + l4 + 2l5 + l 13 .

[0102] By using the interference of the light reflected back from the left surface of the transparent material to be measured and the light reflected by the mirror four 4-4, the distance l from the left surface of the transparent material to be measured to the beam splitter one 5-1 can be obtained 10, l7 is the distance between the mirror four 4-4 and the beam splitter one 5-1;

[0103] By using the interference between the light reflected from the right surface of the transparent material to be measured and the light reflected by the mirror five 4-5, the distance l from the right surface of the transparent material to be measured to the beam splitter two 5-2 can be obtained. 11 , l’5 is the distance between the mirror five 4-5 and the beam splitter two 5-2;

[0104] Furthermore, from Figure 1 the geometric relationship in it, the thickness l8 of the material can be easily obtained: l8 = l9 - (l4 + l 11 ) - (l6 + l 10 ); Then, by using the interference between the light transmitted through the transparent material to be measured and the light reflected by the circular beam splitter 8, from Figure 1 , the distance Δl3 between the optical path of the light transmitted through the material and its standard surface can be obtained. From its optical path difference, it can be obtained that: l6 + l 10 + nl8 + l 11 - (l4 + 2l5) = Δl3. Finally, the refractive index n of the transparent material to be measured can be obtained.

[0105] If measurements of different sample thicknesses and refractive indices are to be carried out, only the sample on the clamping bracket 7 of the object to be measured needs to be replaced, and the remaining steps remain unchanged.

[0106] In actual experiments, we measured sapphire as the sample. The interference fringe patterns obtained were processed, and the numerical values of the radius of the first ring were as follows: (In the table, R1 is the corresponding value obtained from the interference between the light transmitted through the sample and the light reflected by the circular beam splitter, R2 is the corresponding value obtained from the interference between the light reflected from the left surface of the sample and the light reflected by the mirror four, and R3 is the corresponding value obtained from the interference between the light reflected from the right surface of the sample and the light reflected by the mirror five).

[0107] Table 1 Measurement data of the radius of the first ring of the interference fringes of the sapphire sample

[0108]

[0109] Substitute the average value of the measured ring radius into the formula (1) for the relationship between the radius of the first ring of the interference fringes and the optical path difference. The thickness and refractive index of the sapphire sample calculated are as follows:

[0110] Table 2 Measurement data of the thickness and refractive index of the sapphire sample

[0111]

[0112] Based on the above data analysis, especially Table 1, the error of the measurement method designed by the present invention mainly lies in the measurement of the radius of the interference fringe rings. Taking the average value of multiple measurements will also bring certain errors. In addition, when using a camera to capture the interference image, the resolution of the camera will introduce uncertainty. Therefore, we carried out a measurement based on the Michelson white light interference principle as a comparative experiment. The results are shown in Table 3. The measurement method designed by the present invention has more accurate advantages in the measurement accuracy of thickness and refractive index compared with the traditional Michelson interference measurement method.

[0113] Table 3 Relative error of the measurement results of sapphire samples

[0114]

[0115] Although the specific implementation manners of the present invention have been described above in conjunction with the accompanying drawings, it is not a limitation on the protection scope of the present invention. Those skilled in the art should understand that, based on the technical solution of the present invention, various equivalent structural or equivalent process modifications or deformations that can be made by those skilled in the art without creative efforts, or directly or indirectly applied to other related technical fields, are still within the protection scope of the present invention.

Claims

1. A device for synchronously measuring the refractive index and thickness of a transparent material, characterized in that: Including optical path system and image acquisition module; The optical path system includes a light source, a beam splitter assembly, a reflector assembly, a light screen assembly and a clamping bracket for the object to be measured. The beam splitter assembly includes a beam splitter 1, a beam splitter 2, a beam splitter 3 and a circular beam splitter. The reflector assembly includes a reflector 1, a reflector 2, a reflector 3, a reflector 4, a reflector 5, a reflector 6 and a reflector 7. The light screen assembly includes a screen 1 and a screen 2 for receiving interference fringes. The clamping bracket for the object to be measured is used to clamp a transparent material. The light source is arranged coaxially with the beam splitter three and the reflector two according to the first axis, the reflector one is arranged on one side of the beam splitter three, the reflector seven is arranged on one side of the reflector two, and the reflector one and the reflector seven are distributed on different sides of the first axis; the reflector three, the beam splitter one, the beam splitter two, and the reflector six are arranged coaxially in sequence according to the second axis, and the second axis is perpendicular to the first axis; the clamping bracket of the object to be measured is arranged coaxially with the second axis between the beam splitter one and the beam splitter two; the reflector one and the reflector three are coaxially according to the third axis, the reflector seven and the reflector six are coaxially according to the fourth axis, and the third axis and the fourth axis are both parallel to the first axis; the reflector four, the beam splitter one, and the screen two are arranged coaxially according to the fifth axis in sequence; the reflector five, the circular beam splitter, the beam splitter two, and the screen one are arranged coaxially according to the sixth axis in sequence; The image acquisition module is arranged corresponding to screen one and screen two, and is used for acquiring interference fringes on the two light screens.

2. The device for synchronously measuring the refractive index and thickness of a transparent material according to claim 1, further characterized in that: The optical path system also includes a first attenuation plate and a second attenuation plate, wherein the first attenuation plate is arranged between the first beam splitter and the clamping bracket of the object to be measured; and the second attenuation plate is arranged between the fourth reflector and the first beam splitter.

3. The device for synchronously measuring the refractive index and thickness of a transparent material according to claim 1, further characterized in that: A calibration plate 1 is arranged on the screen 1, and a calibration plate 2 is arranged on the screen 2.

4. The device for synchronously measuring the refractive index and thickness of a transparent material according to claim 1, further characterized in that: The light source is a laser.

5. The device for synchronously measuring the refractive index and thickness of a transparent material according to claim 1, further characterized by: The image acquisition module uses a camera to acquire interference fringe images.

6. A method for synchronously measuring the refractive index and thickness of a transparent material, based on the device according to any one of claims 1 to 5, comprising the following steps: Step 1: Place the components of the device on a horizontal table, turn on the light source, and check whether the light source is working properly; Step 2: Place the transparent material to be tested into the sample clamping area of ​​the test object clamping bracket; Step 3: Adjust the position of the transparent material to be tested so that two light spots formed by the reflected light from its left surface and the reflected light from the reflector 4 appear at the appropriate position on the screen 2, and two light spots formed by the reflected light from its right surface and the reflected light from the reflector 5, and two light spots formed by the light passing through the transparent material to be tested and the reflected light from the circular beam splitter appear at the appropriate position on the screen 1; Step 4: Adjust the pitch angle and tilt angle of the reflector 4 so that the two light spots formed by the reflected light from the left surface of the transparent material to be measured and the reflected light from the reflector 4 form clear interference fringes M1 at appropriate positions on the light screen 2; Step 5: Adjust the angles of the reflector 5 and the circular beam splitter so that the two light spots formed by the reflected light from the right surface of the transparent material to be tested and the reflected light from the reflector 5 form clear interference fringes M2 on the light screen 1; at the same time, the two light spots formed by the light passing through the transparent material to be tested and the reflected light from the circular beam splitter form clear interference fringes M3 at appropriate positions on the light screen 1 on the right side; Step 6: Record the images of interference fringes M1, M2, and M3 based on the image acquisition module, and upload the images to the computer program terminal; Step 7: Based on the image collected in step 6, the first ring radius of the interference fringe is measured, including the first ring radius r1 of the interference fringe M1, the first ring radius r2 of the interference fringe M2, and the first ring radius r3 of the interference fringe M3; Step 8: Calculate the optical path difference according to the measured radius of the first circular ring; Optical path difference of interference fringe M1 Optical path difference of interference fringe M2 Optical path difference of interference fringe M3 In the formulas of this step: N represents the Nth bright ring of the equally inclined interference fringe, λ is the wavelength of light, r1 is the radius of the first ring of the interference fringe M1, r2 is the radius of the first ring of the interference fringe M2, r3 is the radius of the first ring of the interference fringe M3, L1 represents the total optical path from the light source forming the interference fringe M1 to the light screen, L2 represents the total optical path from the light source forming the interference fringe M2 to the light screen, and L3 represents the total optical path from the light source forming the interference fringe M3 to the light screen; Step 9: Use the light reflected from the left surface of the transparent material to be tested to interfere with the light reflected from the fourth reflector to obtain the distance l from the left surface of the transparent material to be tested to the first beam splitter 10 , Where l7 is the distance between reflector 4 and beam splitter 1; The distance l from the right surface of the transparent material to be tested to the beam splitter 2 is obtained by using the interference between the light reflected from the right surface of the transparent material to be tested and the light reflected from the reflector 5. 11 , Where, l'5 is the distance between reflector 5 and beam splitter 2; Step 10: Calculate the thickness of the transparent material to be tested l8 = l9-(l4+l 11 )-(l6+l 10 );wherein, l8 represents the thickness of the transparent material to be measured, l9 is the distance between the reflector 3 and the reflector 6; l4 is the distance between the reflector 2 and the reflector 6; l6 is the distance between the reflector 3 and the reflector 1; Based on the interference between the light passing through the transparent material to be tested and the light reflected by the circular beam splitter, the refractive index n of the transparent material to be tested is calculated based on the following formula: l6+l 10 +nl8+l 11 -(l4+2l5)=Δl3, where l5 is the distance between the circular beam splitter and the second beam splitter.

7. The method for synchronously measuring the refractive index and thickness of a transparent material according to claim 6, further characterized by: The transparent material is suitable for K9 optical glass, sapphire, quartz or acrylic plate.

8. The method for synchronously measuring the refractive index and thickness of a transparent material according to claim 6, further characterized by: In step 6, the camera is placed on a one-dimensional slide rail in front of two light screens, and the camera position is adjusted by sliding so that it faces the interference fringes M1, M2, M3 and the two calibration plates, and the resulting image is recorded.

Images