Liquid refractive index measuring method and system based on Michelson interferometer

Abstract

The invention relates to the technical field of optical measurement, in particular to a liquid refractive index measuring method and system based on a Michelson interferometer, and the system comprises the Michelson interferometer, a cuvette, a digital display angle gauge, a spiral micrometer, a smart phone and a support. The cuvette is introduced to contain liquid to be measured, the digital display angle gauge accurately measures the deflection angle, the spiral micrometer drives the angle to change, and the smart phone records the interference fringe change and automatically counts. The liquid refractive index is calculated by utilizing the change relation between the optical path difference and the interference fringes and combining a formula, and meanwhile the method can be expanded to be used for measuring the air refractive index and the transparent sheet thickness. The device can improve the measurement precision and objectivity, reduces the personal error, is convenient to operate, is low in cost, and is suitable for teaching and scientific research popularization.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optical measurement technology, and specifically relates to a liquid refractive index measurement method and system based on a Michelson interferometer. BACKGROUND

[0002] In the field of optical measurement technology, accurate measurement of liquid refractive index is of great significance in university physics experiment teaching and scientific research. Although the traditional measurement method such as Abbe refractometer can provide a certain measurement accuracy, its application range is limited, only suitable for solutions with refractive index between 1.3 and 1.7, and cannot be used for the measurement of acid and alkali solutions, which is difficult to meet the diversified experimental needs. In addition, in the Michelson interference experiment, the traditional way of observing and recording the change of interference fringes by human eyes not only easily leads to eye fatigue, but also may affect the accuracy of experimental results due to human error. At the same time, the existing liquid parameter measurement device has relatively single function, and can usually only focus on the measurement of a certain specific parameter, and it is difficult to realize the synchronous detection of multiple parameters, which limits its application in complex experimental scenes. Therefore, developing a liquid refractive index measurement method and system which can overcome the above limitations and has high precision and multi-functionality has become a problem to be solved in the current field of optical measurement technology. The present application aims to improve the measurement accuracy, expand the measurement range, and realize the optimization of operation convenience and cost-effectiveness by introducing the technical scheme of Michelson interferometer combined with modern intelligent devices. SUMMARY

[0003] The present application proposes a liquid refractive index measurement method and system based on Michelson interferometer to overcome the defects of existing liquid refractive index measurement technology. The system realizes accurate measurement of refractive index of various liquids by introducing cuvettes, digital angle meters, screw micrometers and smart phones, and expands the functionality and application range of the device.

[0004] The present application provides a liquid refractive index measurement system based on Michelson interferometer, which comprises a Michelson interferometer, a cuvette, a digital angle meter and a screw micrometer are sequentially arranged in one light path of the Michelson interferometer. The cuvette is used to hold the liquid to be measured, and the inner diameter length is a fixed value. The digital angle meter is used to measure the deflection angle of the cuvette in real time. The screw micrometer is connected to one side of the digital angle meter, and drives the cuvette to change the angle by precise rotation, so as to change the optical path difference and cause the change of interference pattern. Further, the system also comprises a smart phone and its bracket, and the smart phone is installed with an application program calling optical sensor, which is used to record the change of bright and dark stripes of interference pattern.

[0005] In particular, the design of the cuvette must meet the optical path requirements, and its material must have high transparency and low optical absorption properties to reduce the impact of light loss on the measurement results. The accuracy of the digital display angle meter is not less than 0.01° to ensure the accuracy of angle measurement. The pitch design of the micrometer screw must be adapted to the experimental requirements to ensure that each rotation can produce a detectable change in the optical path difference. The smartphone collects interference fringe change data through its optical sensor and transmits the data to the application for processing, replacing the traditional human eye observation and recording method.

[0006] The detection principle of the present invention is based on the interference phenomenon of the Michelson interferometer, and the refractive index of the liquid is calculated by the relationship between the optical path difference and the change of the interference fringes. Specifically, the system uses the formula

[0007]

[0008] Calculate the refractive index of the liquid, where (t) is the inner diameter of the cuvette, (θ) is the deflection angle of the cuvette, (λ) is the wavelength of the light source, (ΔN = n1 - n2), (n1) represents the effect on the optical path when the cuvette is full, and (n2) represents the effect on the optical path when the cuvette is empty.

[0009] Furthermore, the wavelength of the light source must be determined based on experimental requirements. Typically, a laser light source with good monochromaticity and wavelength stability within ±0.1 nm is selected. The deflection angle of the cuvette is set between 0° and 30° to ensure that the amplitude of the interference pattern changes is suitable for the detection capabilities of the optical sensor. The smartphone application must have real-time data acquisition and processing capabilities, capable of automatically counting interference fringe changes and generating corresponding data curves.

[0010] During the experiment, the cuvette is first placed in an empty state. The micrometer screw is adjusted to change the angle between the cuvette and the optical path, while the interference fringe changes are recorded. The cuvette is then filled with ultrapure water, and the above steps are repeated. The experimental results are compared with the standard refractive index of ultrapure water to determine the optimal operating angle of the system. At this optimal operating angle, the test liquid is measured at different concentration gradients, and the interference fringe changes are recorded and substituted into the formula to calculate the liquid's refractive index.

[0011] The system's versatility is particularly evident in its ability to be modified to measure the refractive index of air or the thickness of a transparent sheet. For example, by removing the cuvette and inserting a transparent sheet into the optical path, the actual thickness can be calculated using the interference fringe data combined with the sheet thickness formula. Furthermore, the system can be used to study how the refractive index of liquids changes under different temperature conditions. By adding a thermostat to the cuvette, the liquid temperature can be adjusted while simultaneously recording the refractive index data.

[0012] The present invention has significant technical benefits. By incorporating smartphone optical sensors, the human error associated with traditional visual observation and recording methods is eliminated, improving the objectivity and accuracy of measurements. Experimental verification demonstrates that, using ultrapure water as a standard material, at an optimal working angle of 12°, the percentage deviation in the refractive index of ultrapure water is only 0.07%. For salt solutions and sucrose solutions with varying concentration gradients, the percentage deviations in refractive index measurements are controlled within 3% and 2%, respectively, meeting the precision requirements for liquid refractive index measurement in teaching and scientific research.

[0013] Furthermore, the system significantly enhances operational convenience. The smartphone app is free of charge and offers a user-friendly interface, making it easy for students and researchers to quickly get started. The overall cost of the device is only one-tenth that of a fully automated Abbe refractometer, while offering high measurement accuracy and a wide range of applications, making it suitable for widespread use in university physics experimental teaching and related scientific research.

[0014] In particular, the system's modular design enhances its scalability. For example, polarizers or filters can be added to the optical path to study the effects of polarized light on interference phenomena. Alternatively, by switching to a different wavelength light source, the influence of wavelength on refractive index measurements can be explored. This flexibility makes the system suitable not only for teaching basic physics experiments but also as a research tool for in-depth study of optical phenomena.

[0015] In summary, this invention achieves precise measurement of liquid refractive index through the innovative integration of a Michelson interferometer, a cuvette, a digital goniometer, a micrometer screw, and a smartphone, while simultaneously expanding the system's functionality and application scenarios. This technical solution boasts a clear structure, simple operation, and low cost, providing a novel solution for liquid parameter measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the overall structure of the liquid refractive index measurement system based on the Michelson interferometer;

[0017] Figure 2 It is a partial enlarged schematic diagram of the cuvette, digital display goniometer and micrometer screw;

[0018] Figure 3 Schematic diagram of the smartphone, its bracket and the optical path.

[0019] The accompanying drawings are numbered as follows:

[0020] 1. Michelson interferometer; 2. Cuvette; 3. Digital goniometer; 4. Micrometer screw; 5. Smartphone; 6. Smartphone holder; 7. Light source; 8. Optical sensor; 9. Liquid to be measured; 10. Optical path. DETAILED DESCRIPTION

[0021] The present application provides a liquid refractive index measurement system based on Michelson interferometer and a method thereof, which will be described below in combination with the accompanying Figure 1 to the accompanying Figure 3 The specific embodiments of the present application are described in detail. The system realizes accurate measurement of liquid refractive index by introducing cuvette, digital angle gauge and screw micrometer into one light path of Michelson interferometer, and cooperating with smart phone and its support. The overall structure of the experimental device is shown in Figure 1 , wherein the functions and connection relationships of each component will be described one by one in the following.

[0022] Firstly, when building the experimental device, it is necessary to ensure that all components are installed firmly and accurately positioned. As shown in Figure 1 , the Michelson interferometer 1 as the core optical equipment is placed on a stable experiment table, and a cuvette 2, a digital angle gauge 3 and a screw micrometer 4 are sequentially installed in one light path thereof. The cuvette 2 is used to hold the liquid to be measured 9, and the material thereof is selected to be high-transparency quartz glass to reduce the influence of light loss on the measurement results. The inner diameter length of the cuvette 2 is a fixed value t, which will be used in the subsequent calculation of the liquid refractive index. The digital angle gauge 3 is connected to the cuvette 2, which is used to measure the deflection angle θ of the cuvette 2 in real time, and the accuracy thereof is not less than 0.01°, so as to ensure the accuracy of angle measurement. The screw micrometer 4 is connected to one side of the digital angle gauge 3, which drives the cuvette 2 to change the angle through precise rotation, thereby changing the optical path difference and causing the change of interference pattern. In addition, the smart phone 5 and its support 6 are arranged at the end of the light path of the interferometer, the smart phone 5 is installed with an application program calling the optical sensor 8, which is used to record the change of bright and dark stripes of the interference pattern.

[0023] S1: After the device is built, the selection and calibration of the light source 7 are needed. The light source 7 selects a laser with good monochromaticity, and the stability of the wavelength λ needs to reach within ±0.1 nm. The light beam emitted by the light source 7 is introduced into the beam splitter of the Michelson interferometer 1, so that the light beam is divided into two beams which propagate along two light paths respectively. Among them, one light returns through the fixed mirror, and the other light returns through the cuvette 2 and is adjusted by the digital angle gauge 3 and the screw micrometer 4. The two beams recombine at the beam splitter to form an interference pattern. At this time, the optical sensor 8 of the smart phone 5 needs to be adjusted to a position where it can accurately receive the interference pattern.

[0024] S2: After completing the setup, enter the experimental preparation phase. Install and launch the Phyphox app on smartphone 5. Select the "Light" sensor in the "Raw Sensors" menu and ensure that the optical sensor 8 is active. Next, use a volumetric flask to prepare the test liquid 9 with varying concentration gradients, such as salt solution or sucrose solution, and prepare ultrapure water to determine the optimal operating angle of the device. The standard refractive index of ultrapure water is known and can be used as a calibration reference.

[0025] S3: While the cuvette 2 is unloaded, use the micrometer screw 4 to adjust the angle between the cuvette 2 and the optical path while observing the changes in the interference fringes recorded by the smartphone 5. By slowly rotating the micrometer screw 4, the angle of the cuvette 2 changes, thereby changing the optical path difference and causing changes in the interference pattern. The smartphone 5 app automatically records the data of the changes in the brightness of the interference fringes and generates a corresponding curve. This step aims to obtain the change pattern of the interference pattern when the cuvette 2 is unloaded, and the data is recorded and stored as n2.

[0026] S4: Repeat the above steps with cuvette 2 filled with ultrapure water. Compare the experimental results with the standard refractive index of ultrapure water to determine the optimal operating angle for the system. In this embodiment, the optimal operating angle is 12°. Specifically, when the cuvette 2 is deflected by an angle θ of 12°, the change in the interference pattern is most significant and easily detected. At this angle, the percentage deviation of the refractive index of ultrapure water is only 0.07%, demonstrating the system's high measurement accuracy.

[0027] S5: After determining the optimal working angle, fill the cuvette 2 with the test liquid 9 of different concentration gradients, such as salt solution or sucrose solution, and record the corresponding interference fringes changes. For each test liquid 9, the experiment needs to be repeated multiple times to ensure the reliability of the data. The application of the smartphone 5 automatically records the interference fringes change data and transmits it to the calculation module for processing. According to the formula

[0028]

[0029] Calculate the refractive index of the liquid, where (t) is the inner diameter of cuvette 2, (θ) is the deflection angle of cuvette 2, (λ) is the wavelength of light source 7, and (ΔN) is the change in the optical path difference between when the cuvette 2 is full and when it is empty, i.e., (ΔN = n1 - n2). By substituting the experimental data into the refractive index of the test liquid 9 at different concentration gradients, the refractive index can be obtained.

[0030] S6: To further verify the system's performance, the measured results were compared with theoretical values ​​or values ​​obtained using other standard measurement methods. The experimental results showed that for salt solutions with varying concentration gradients, the percent deviation of the refractive index measurements was within 3%; for sucrose solutions, the percent deviation was within 2%. These data demonstrate that the system has sufficient measurement accuracy for teaching and scientific research.

[0031] S7: In addition to measuring the refractive index of liquids, this system is also versatile. With appropriate modifications, it can be used to measure the refractive index of air or the thickness of transparent sheets. For example, by removing cuvette 2 and inserting a transparent sheet into the optical path, the actual thickness can be calculated using the interference fringe data combined with the sheet thickness formula. Furthermore, a thermostat can be added to the outside of cuvette 2 to regulate the liquid temperature while simultaneously recording the refractive index data, allowing for the study of how the liquid's refractive index changes under different temperature conditions.

[0032] S8: In terms of user convenience, the smartphone 5 app offers a user-friendly interface and is free of charge, making it easy for students and researchers to quickly get started. The app features real-time data acquisition and processing, automatically counting interference fringe changes and generating corresponding data curves. This eliminates the human error associated with traditional visual observation and recording, improving the objectivity and accuracy of measurements.

[0033] S9: This system offers significant cost advantages, costing only one-tenth of a fully automated Abbe refractometer. This makes it suitable for use in university physics experimental teaching and related scientific research. Furthermore, the system's modular design enhances its scalability. For example, polarizers or filters can be added to the optical path to study the effects of polarized light on interference phenomena. Alternatively, by replacing light sources with different wavelengths, the influence of wavelength on refractive index measurements can be explored. This flexibility makes this system suitable not only for teaching basic physics experiments, but also for use as a scientific research tool for in-depth study of optical phenomena.

[0034] S10: Finally, combine Figure 2 and Figure 3 Provide additional explanation of local details. Figure 2 A partial enlarged schematic diagram of the cuvette 2, digital goniometer 3, and micrometer screw 4 is shown, clearly illustrating the connections and operating principles of each component. The pitch of micrometer screw 4 is designed to adapt to experimental requirements, ensuring that each rotation produces a detectable change in optical path difference. Figure 3 A schematic diagram of the cooperation between the smartphone 5 and its bracket 6 and the optical path is shown. The optical sensor 8 of the smartphone 5 needs to be adjusted to a position where it can accurately receive the interference pattern to ensure the accuracy of data collection.

[0035] In summary, the present invention achieves precise measurement of the refractive index of liquids by incorporating a cuvette 2, a digital goniometer 3, a micrometer screw 4, and a smartphone 5. The system design fully considers measurement accuracy, ease of use, and cost advantages, providing a novel solution for liquid parameter measurement.

Claims

1. A liquid refractive index measurement system based on Michelson interferometer, characterized in that The invention comprises a Michelson interferometer (1), wherein a cuvette (2), a digital display goniometer (3) and a micrometer screw (4) are sequentially arranged in an optical path of the Michelson interferometer (1), and further comprises a smart phone (5) and a bracket (6) thereof, wherein the cuvette (2) is used to hold a liquid to be measured (9), the digital display goniometer (3) is used to measure the deflection angle of the cuvette (2) in real time, the micrometer screw (4) is connected to one side of the digital display goniometer (3) to drive the cuvette (2) to change its angle, and the smart phone (5) is installed with an application for calling an optical sensor (8) to record changes in light and dark fringes of an interference pattern.

2. The liquid refractive index measuring system according to claim 1, wherein The material of the cuvette (2) is high-transparency quartz glass, and its inner diameter is a fixed value.

3. The liquid refractive index measuring system according to claim 2, wherein The measurement accuracy of the digital display inclinometer (3) is not less than 0.01°.

4. The liquid refractive index measuring system according to claim 1, wherein The pitch design of the micrometer screw (4) is adapted to the experimental requirements, and each rotation can produce a detectable change in the optical path difference.

5. The liquid refractive index measuring system according to claim 1, wherein The light source (7) is a monochromatic laser, and its wavelength stability is within ±0.1nm.

6. The liquid refractive index measuring system according to claim 1, wherein The application program of the smart phone (5) has the function of real-time data acquisition and processing, and can automatically count the changes of interference fringes and generate corresponding data curves.

7. The liquid refractive index measuring system according to claim 1, wherein The deflection angle range of the cuvette (2) is set between 0° and 30°.

8. The liquid refractive index measuring system according to claim 1, wherein The system also includes a constant temperature control device for adjusting the external temperature of the cuvette (2) and synchronously recording the refractive index data.

9. The liquid refractive index measuring system according to claim 1, wherein The system removes the cuvette (2) and inserts a transparent sheet into the light path, and calculates the sheet thickness using the interference fringe change data combined with the sheet thickness formula.

Images