A light beat method light speed measuring device and measuring method based on a resonant cavity

Abstract

The application discloses a resonant cavity-based optical beat method light speed measuring device and measuring method, and belongs to the light speed measuring field. The measuring device comprises a laser emitter. One side of the laser emitter comprises, in sequence along the light path direction, an acousto-optic device, two plane mirrors, a half-transmitting and half-reflecting mirror and an illuminance detector. The laser emitter generates monochromatic light. The monochromatic light enters the acousto-optic device to obtain two light waves with a frequency difference, and coupling is performed to obtain one beat wave. The beat wave changes direction after passing through the two plane mirrors and enters the half-transmitting and half-reflecting mirror. The half-transmitting and half-reflecting mirror transmits the beat wave, and at the same time, reflects a part of the beat wave reflected by the illuminance detector, so that the beat wave is reflected back and forth between the half-transmitting and half-reflecting mirror and the illuminance detector. The illuminance detector receives the beat wave on a light-sensitive surface thereof while reflecting a part of the beat wave, so as to measure the illuminance value of the beat wave. The measuring device further comprises a frequency meter, and the frequency meter displays the acoustic frequency of the acousto-optic device. The light speed can be measured by using the measuring device.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of light speed measurement, and particularly relates to a light beat method light speed measurement device and method based on a resonant cavity. BACKGROUND

[0002] Light speed refers to the propagation speed of light waves or electromagnetic waves in vacuum or medium. The light speed in vacuum is the maximum speed of the motion of objects discovered in nature. The light speed in different media is different, and the light speed is about 2.996x10 8 m / s under the condition of 1 standard atmosphere and 25 DEG C. The physical quantity of light speed is closely related to many basic physical theories, such as electromagnetic theory and relativity. Accurate determination of the light speed value can check the accuracy of these theories, and can also help the development of front-end technologies, such as optical fiber communication and satellite navigation technology.

[0003] There are many methods for measuring light speed, mainly including Fresnel interference method, microwave cavity resonance method and light beat method. The Fresnel interference method measures the distance Δx between two interference fringes, the distance D between the virtual light source and the screen, and the distance a between the two virtual light sources, and then calculates the wavelength λ of light through the formula λ=aΔx / D. Finally, the light speed c=λf is calculated by substituting the known light frequency f. The microwave cavity resonance method calculates the wavelength λ of the resonant cavity according to the length of the cavity, and then calculates the light speed c=λf according to the formula c=λf. The traditional light beat method calculates the light beat wavelength λ by measuring the phase difference of the two light beat signals received by the detector, and then calculates the light speed c=λf according to the known light beat frequency f.

[0004] These measurement methods have certain limitations: the Fresnel interference method has a small change period of interference fringes, a large measurement error and low experimental precision; the microwave cavity resonance method has a large experimental operation difficulty due to the invisibility of microwaves;

[0005] The difficulty of the traditional light beat method lies in the adjustment of the optical path and the adjustment and comparison of the waveforms on the oscilloscope. The traditional light beat method measures the wavelength of light according to the optical path difference of two light paths, i.e. the inner and outer double light paths, so as to calculate the light speed. However, in the actual adjustment process, eight or more total reflection mirrors need to be adjusted, and slight deviation of the optical path, such as slight inclination during the adjustment of the optical path or non-incidence to the receiving system, will seriously affect the experimental results. In addition, there is a large measurement error in the specific experimental process. For example, in the area inside each segment of the mirror device, due to the lack of information such as the geometric structure of the mirror and the refractive index of the medium, the optical path of this part is difficult to measure strictly, and can only be estimated, which has a large uncertainty. When comparing whether the phases of the waveforms corresponding to the far and near paths of the two signals on the oscilloscope display screen coincide, there is also a large human error.

[0006] To address the shortcomings of the aforementioned measurement methods, this invention proposes a light speed measurement device and method based on a resonant cavity optical beat method. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a photometric device and method for measuring the speed of light using a resonant cavity, thereby solving the problems in the prior art.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] A resonant cavity-based optical beat speed measurement device includes a laser emitter, and one side of the laser emitter along the optical path includes, in sequence: an acousto-optic device, two plane mirrors, a semi-transparent mirror, and an illuminance detector.

[0010] The laser emitter generates monochromatic light, which enters the acousto-optic device for frequency modulation, resulting in two light waves with a frequency difference. These waves are then coupled in space to form a beat frequency wave. After passing through two plane mirrors, the beat frequency wave changes its propagation direction and enters a semi-transparent mirror. While transmitting the beat frequency wave, the semi-transparent mirror also reflects a portion of the beat frequency wave reflected by the illuminance detector, thus confining the beat frequency wave between the semi-transparent mirror and the illuminance detector and generating back-and-forth reflections to form an interference wave. While the illuminance detector reflects a portion of the beat frequency wave, its photosensitive surface receives the beat frequency wave to measure the illuminance value of the beat frequency wave.

[0011] The measuring device also includes a circuit control box and a frequency meter. The circuit control box is connected to the frequency meter, the laser emitter, and the acousto-optic device via wires. The frequency meter displays the acoustic frequency of the acousto-optic device.

[0012] Furthermore, an optical bench is provided on one side of the illuminance detector, a slider that can be adjusted horizontally is provided on the optical bench, a slide rail that can be adjusted horizontally is provided on the slider, and a connecting plate that can be adjusted vertically is provided on the slide rail, and the connecting plate is fixed to the illuminance detector.

[0013] Furthermore, both the optical bench and the slider are marked with scales. The relative position of the illuminance detector and the slider is read from the scale on the slider. The distance between the slider and the semi-transparent mirror is read from the scale on the optical bench. By combining the readings of the scales on the slider and the optical bench, the distance between the illuminance detector and the semi-transparent mirror can be measured.

[0014] Furthermore, the illuminance detector is equipped with a magnet to fix it to the connecting plate.

[0015] Furthermore, the illuminance detector connects to the illuminance color temperature meter app via Bluetooth on a mobile phone. After successful connection, the illuminance value of the received beat frequency wave can be read by the illuminance color temperature meter app.

[0016] Furthermore, the exit port of the laser emitter that emits light waves is aligned with the entrance port of the acousto-optic device that receives light waves.

[0017] Furthermore, under the directional action of the two plane mirrors, the beat frequency wave passing through the semi-transparent and semi-reflective mirror remains horizontal and can be incident on the photosensitive surface of the illuminance detector.

[0018] A method for measuring the speed of light using a resonant cavity-based optical beat method, employing the aforementioned measuring device, includes the following steps:

[0019] S1, connect the various components of the measuring device and adjust the optical path;

[0020] S2, place the connecting plate at 150mm on the scale of the slider, and align the center of the scale on the slider with 100cm on the optical bench.

[0021] S3, set the measurement distance Δx, first move the slider, measure the illuminance every Δx cm from 100cm on the optical bench to the 0 mark, and record the sum of the scale reading on the optical bench and the scale reading on the slider, as well as the illuminance value.

[0022] S4. Use Origin software to plot the relationship between the sum of the recorded scale readings on the optical bench and the scale readings on the slider and the illuminance value, and find the locations of the maximum and minimum values.

[0023] S5, set the measurement distance Δx', and place the slider and slide rail at the positions of the maximum and minimum illuminance points;

[0024] S6, move the slide rail from the position of the slider scale to both ends of the slider, measure the illuminance every Δx'cm and record the sum of the scale reading on the optical bench and the scale reading on the slider, as well as the illuminance value.

[0025] S7. Use Origin software to plot the relationship between the sum of the recorded scale readings on the optical bench and the scale readings on the slider and the illuminance value, and combine it with the relationship plotted in S4 to find the more accurate locations of the illuminance maximum and minimum points.

[0026] S8, calculate the distance ΔL between the minimum and maximum illuminance points found by drawing the relationship diagram;

[0027] S9, combined with the reading on the frequency meter, reveals ω. 10 -ω 11 We can use this to calculate the speed of light, c.

[0028] Furthermore, in S1, the specific steps for connecting the various components of the measuring device and adjusting the optical path are as follows:

[0029] S11, turn on the power and connect the circuit control box and frequency meter to the power supply;

[0030] S12, connect the circuit control box to the frequency meter, the acousto-optic device, and the laser emitter respectively via wires:

[0031] S13, turn on the circuit control box and frequency meter switch, and adjust the frequency meter knob so that the frequency meter reading is 75.00000MHz±0.02000MHz.

[0032] S14, turn on the illuminance detector switch and the mobile phone Bluetooth, and connect the illuminance detector to the mobile phone illuminance color temperature meter app;

[0033] S15, adjust the relative positions of the laser emitter and the acousto-optic device so that the laser emitted by the laser emitter is accurately incident on the light-receiving port of the acousto-optic device, while keeping the emitted light of the acousto-optic device horizontal.

[0034] S16, Adjust the position of the two plane mirrors to keep the reflected beat frequency light as horizontal as possible;

[0035] S17, adjust the position of the semi-transparent mirror, optical bench, slider and illuminance detector so that the beat frequency light refracted by the semi-transparent mirror is accurately incident on the central photosensitive surface of the illuminance detector.

[0036] S18. Observe the illuminance value of the light received by the illuminance detector through the mobile phone illuminance color temperature meter app. If the illuminance value of the received light is relatively stable, the measurement can begin.

[0037] Furthermore, the formula for calculating the speed of light, c, is:

[0038]

[0039] In the formula, ΔL is the distance between adjacent points of maximum or minimum amplitude, and ω 11 -ω 10 It represents the angular frequency difference between two light waves.

[0040] The beneficial effects of this invention are:

[0041] Compared to the dual-optical-path measurement used in traditional optical imaging methods, this invention greatly simplifies the optical path through its designed single optical path and resonant cavity, making optical path adjustment very convenient. Furthermore, this invention simplifies the measurement device and reduces measurement errors compared to the complex measurement device structure in traditional optical imaging methods through its relatively simple measurement device design. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a schematic diagram of the diffraction of a laser beam after passing through an acousto-optic device;

[0044] Figure 2 This is a typical light-based imaging diagram;

[0045] Figure 3 This is a diagram illustrating the reflection of light between mirror surfaces.

[0046] Figure 4 This is a schematic diagram of the overall structure of the measuring device of the present invention;

[0047] Figure 5 This is the first set of measured illuminance diagrams in Embodiment 3 of the present invention;

[0048] Figure 6 This is the first set of illuminance maps near the maximum measurement point in Embodiment 3 of the present invention;

[0049] Figure 7 This is the first set of illuminance maps near the minimum point measured in Embodiment 3 of the present invention;

[0050] Figure 8 This is the second set of illuminance measurement diagrams in Embodiment 3 of the present invention;

[0051] Figure 9 This is the third set of illuminance measurement diagrams in Embodiment 3 of the present invention;

[0052] Figure 10 This is the fourth set of illuminance measurement diagrams in Embodiment 3 of the present invention;

[0053] Figure 11 This is the fifth set of illuminance measurement diagrams in Embodiment 3 of the present invention;

[0054] Figure 12 This is the sixth set of illuminance measurement diagrams in Embodiment 3 of the present invention.

[0055] In the diagram: 1-Laser emitter, 2-Acousto-optic device, 3-Plane mirror, 4-Semi-transparent mirror, 5-Illumination detector, 6-Slide rail, 7-Slider, 8-Optical bench, 9-Frequency meter, 10-Circuit control box, 11-Wire. Detailed Implementation

[0056] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] In this invention, the principle for calculating the speed of light c is as follows:

[0058] Visible light waves are wavelengths with a frequency of 3.9 × 10⁻⁶. 14 ~7.5×10 14 Electromagnetic waves of Hz and monochromatic visible light waves (632.8 nm) emitted by a laser, after passing through an acousto-optic device, generate two waves with similar frequencies, propagation directions, amplitudes, and polarization directions. These waves superimpose in space, forming an optical beat frequency. When this beat frequency encounters a reflective mirror, it is reflected. After two reflections, the reflected wave and the incident wave propagate in the same direction, and they interfere at the illuminance detector. The different optical path differences between the incident and reflected waves lead to differences in interference intensity, resulting in different detection results. By determining the locations of adjacent detection maximum and minimum values, the speed of light, c, can be calculated.

[0059] The principle, formula, and derivation process for calculating the speed of light, c, are as follows:

[0060] Suppose a laser emits a beam of visible light with a constant angular velocity ω0 and spatial collimation, propagating at a speed of c, with an amplitude of E0 and an initial phase of...

[0061] like Figure 1 As shown, when the laser beam passes through the acousto-optic device, due to the reflection of sound waves on the upper and lower surfaces of the crystal, the laser beam will undergo symmetrical multi-order diffraction in the standing wave field. Each order of diffraction beam is composed of multiple light waves of different frequencies superimposed on each other. The frequency of the light wave contained in the Nth order diffracted beam is:

[0062] ω Nm =ω0+(1+2m)ω (1)

[0063] Where ω is the acoustic angular frequency, corresponding to the acoustic frequency f, and ω and f satisfy the relationship ω=2πf, where f can be controlled by the acousto-optic device, and m=0,1,2…N. If only the first-order diffracted light is selected as the experimental light source, a diffracted beam generated by the superposition of two frequencies E1 and E2, m=0 and m=1, can be obtained, where the angular frequency difference between the two light waves is ω. 11 -ω 10 =2ω.

[0064]

[0065] Since the angular frequency v0 of visible light is much greater than the angular frequency ω of sound, the coupling and superposition of E1 and E2 in space can form a... Figure 2 The beat frequency light E shown:

[0066]

[0067] Slowly changing curves and gradual terms in light-induced shooting Correspondingly, rapidly changing curves and high-frequency terms Correspondingly.

[0068] like Figure 3 As shown, light beat E is passed through a semi-transparent mirror and confined between the illuminance detector and the mirror, reflecting back and forth, achieving an effect similar to a resonant cavity. Different detection values ​​can be obtained by changing the distance between the detector and the mirror; the mathematical derivation is as follows:

[0069] Assuming the distance between the detector and the semi-transparent mirror is L, when the optical beat signal propagates to the detector, the wave equation is:

[0070]

[0071] Part of the light is transmitted into the photosensitive surface of the detector, and the other part is reflected. Since reflection occurs at the detector from a less dense to a denser medium, a half-wave loss occurs, meaning the reflected light travels an additional half-wavelength optical path. The wave equation for the reflected light is:

[0072]

[0073] Where R1 is the reflectivity of the detector. Similarly, half-wave loss also occurs during reflection at the semi-transparent mirror. Therefore, the wave equation for the first-order reflected light E”', which is reflected once at both the detector and the semi-transparent mirror, is:

[0074]

[0075] Where R2 is the reflectivity of the semi-transparent mirror. R1 and R2 are combined and called the attenuation factor.

[0076] In measuring instruments, the working principle of an illuminance detector that receives light signals is to detect the photocurrent i = gE generated within a sampling period T. 2 (g is the photoelectric conversion constant of the illuminance detector). Integrating i over time and taking the average value of the response time t of the illuminance detector, the angular frequency of the high-frequency term is high due to the excessively high frequency of visible light. The frequency is much higher than the sampling frequency, and the photosensitive surface cannot keep up with the real-time changes in light intensity signal. Therefore, the high-frequency terms in the integral... If the value is 0, only the constant E0 and the slowly varying term remain. The actual light intensity signal obtained is:

[0077]

[0078] In equation (8), Δw is for Therefore, the detection results are only related to the slowly varying terms, and not to the high-frequency terms.

[0079] When E′+E”’ produces constructive interference, the detector displays the maximum value. Since the high-frequency term does not affect the detection result, only the slowly varying term affects the result. Therefore, when the phase difference between the slowly varying terms of the incident light E′ and the reflected light E”’ is 2nπ, the constructive interference of the slowly varying term amplitude is the strongest, and the detection intensity is the maximum. This can be obtained from formulas (4) and (8).

[0080]

[0081] By adjusting L, the point of maximum or minimum detection intensity is found. The distance ΔL between adjacent points of maximum or minimum amplitude is:

[0082]

[0083] Furthermore, by measuring ΔL, the speed of light can be calculated:

[0084]

[0085] In the formula, ΔL is the distance between adjacent points of maximum or minimum amplitude, and ω 11 -ω 10 It represents the angular frequency difference between two light waves.

[0086] Example 1

[0087] In this embodiment, a light speed measurement device based on the optical beat method using a resonant cavity is proposed;

[0088] like Figure 4 As shown, a resonant cavity-based optical beat method for measuring the speed of light includes a laser emitter 1. One side of the laser emitter 1, along the optical path direction, includes: an acousto-optic device 2, two plane mirrors 3, a semi-transparent mirror 4, and an illuminance detector 5.

[0089] Laser emitter 1 generates monochromatic light, which enters acousto-optic device 2 for frequency modulation, resulting in two light waves with a frequency difference. These waves are then coupled in space to form a beat frequency wave. After passing through two plane mirrors, the beat frequency wave changes its propagation direction and enters a semi-transparent mirror 4. While transmitting the beat frequency wave, the semi-transparent mirror 4 also reflects a portion of the beat frequency wave reflected by the illuminance detector 5, thus confining the beat frequency wave between the semi-transparent mirror 4 and the illuminance detector 5 and causing back-and-forth reflections to form an interference wave. While the illuminance detector 5 reflects a portion of the beat frequency wave, its photosensitive surface can receive the beat frequency wave to measure the illuminance value of the beat frequency wave.

[0090] An optical bench 8 is provided on one side of the illuminance detector 5. A slider 7 that can be adjusted horizontally is provided on the optical bench 8. A slide rail 6 that can be adjusted horizontally is provided on the slider 7 (the horizontal sliding direction of the slide rail 6 is the same as the horizontal sliding direction of the slider 7, which is used for fine adjustment). A connecting plate that can be adjusted vertically is provided on the slide rail 6 (to align the semi-transparent mirror 4 with the illuminance detector 5 so that the light energy transmitted through the semi-transparent mirror can accurately enter the central photosensitive surface of the detector). The connecting plate is fixed to the illuminance detector 5.

[0091] Both the optical bench 8 and the slider 7 have scales. The relative position of the illuminance detector 5 and the slider 7 can be read from the scale on the slider 7. The distance between the slider 7 and the semi-transparent mirror 4 can be read from the scale on the optical bench 8. By combining the readings of the scales on the slider 7 and the optical bench 8, the distance between the illuminance detector 5 and the semi-transparent mirror 4 can be measured, thereby facilitating the measurement and calculation of the speed of light.

[0092] In this embodiment, the illuminance detector 5 is equipped with a magnet to fix it to the connecting plate.

[0093] The measuring device also includes a circuit control box 10 and a frequency meter 9. The circuit control box 10 is connected to the frequency meter 9, the laser emitter 1 and the acousto-optic device 2 respectively through wires 11, and supplies power to the device. The frequency meter 9 displays the acoustic frequency of the acousto-optic device 2. The acoustic frequency of the acousto-optic device 2 can be changed by rotating the knob on the frequency meter 9, thereby changing the frequency difference of the light wave emitted by the acousto-optic device 2.

[0094] In this embodiment, the illuminance detector 5 can be connected to the illuminance color temperature meter app via Bluetooth on a mobile phone. After successful connection, the illuminance value of the received beat frequency wave can be read by the illuminance color temperature meter app. The illuminance value of the beat frequency wave is monitored in real time.

[0095] Example 2

[0096] This embodiment describes a method for measuring the speed of light using the measuring device described in Embodiment 1 (to avoid the influence of external light on the measurement, the entire measurement process should be carried out in a dark or low-light environment at an indoor temperature of 25°C as much as possible), specifically including the following steps:

[0097] S1, connect the various components of the measuring device and adjust the optical path;

[0098] Specifically:

[0099] S11, turn on the power and connect the circuit control box 10 and frequency meter 9 to the power supply;

[0100] S12, the circuit control box 10 is connected to the frequency meter 9, the acousto-optic device 2, and the laser emitter 1 respectively via the wire 11:

[0101] Use wire 11 to connect the frequency measurement interface on the circuit control box 10 to the corresponding interface on the frequency meter 9, the interface of the acoustic-optical device 2 on the circuit control box 10 to the corresponding interface of the acoustic-optical device 2, and the interface of the laser emitter 1 on the circuit control box 10 to the corresponding interface of the laser emitter 1.

[0102] S13, turn on the circuit control box 10 and the frequency meter 9 switch, and adjust the frequency knob of the frequency meter 9 so that the reading on the frequency meter 9 is 75.00000MHz±0.02000MHz (this frequency is the default sound frequency for measurement, and can be adjusted as needed);

[0103] S14, turn on the switch of illuminance detector 5 and the Bluetooth of the mobile phone, and connect illuminance detector 5 to the mobile phone illuminance color temperature meter app;

[0104] S15, adjust the relative positions of the laser emitter 1 and the acousto-optic device 2 so that the laser emitted by the laser emitter 1 is accurately incident on the light receiving port of the acousto-optic device 2, while keeping the emitted light of the acousto-optic device 2 as horizontal as possible.

[0105] S16, Adjust the position of the two plane mirrors 3 to keep the reflected beat frequency light as horizontal as possible;

[0106] S17, adjust the positions of the semi-transparent mirror 4, optical bench 8, slider 7 and illuminance detector 5 so that the beat frequency light refracted by the semi-transparent mirror 4 can be accurately incident on the central photosensitive surface of the illuminance detector 5. If the incident is successful, a light spot can be seen on the central photosensitive surface of the illuminance detector 5.

[0107] To ensure that interference light waves can be generated, while maintaining a light spot on the central photosensitive surface of the detector, the positions of the semi-transparent mirror 4, the optical bench 8, and the illuminance detector 5 need to be adjusted so that when the slider 7 is moved on the optical bench 8, the light spot always falls on the central photosensitive surface of the detector without changing its position. At this time, the optical bench 8 should be kept parallel to the optical path.

[0108] S18. Observe the illuminance value of the light received by the illuminance detector 5 through the mobile phone illuminance color temperature meter app. If the illuminance value of the received light is relatively stable, it means that the power of the laser emitter 1 is relatively stable at this time (the laser power emitted by the laser emitter 1 is unstable at the beginning, and the laser power emitted will tend to stabilize after a period of time). At this time, the measurement can be started.

[0109] S2, place the connecting plate on one side of the illuminance detector 5 at the 150mm mark on the scale of the slider, aligning the center of the scale on the slider with the 100.0cm mark on the optical bench.

[0110] S3, set the measurement distance Δx. First, move slider 7 and measure the illuminance every Δx cm from 100.0 cm on the optical bench to the 0 mark. Record the sum of the scale reading on the optical bench 8 and the scale reading on slider 7, as well as the illuminance value.

[0111] S4. Use Origin software to plot the relationship between the sum of the scale readings recorded on the optical bench 8 and the scale readings on the slider 7 and the illuminance value, and find the locations of the maximum and minimum values ​​(if the maximum and minimum values ​​are not found, an optical bench with a longer measurement distance can be used for measurement).

[0112] S5, set the measurement distance Δx' (Δx' has a higher measurement accuracy than Δx), and place the slider 7 and slide rail 6 at the approximate positions of the maximum and minimum illuminance points found earlier;

[0113] S6, move slide rail 6 so that slide rail 6 moves from the position of scale on slider 7 to both ends of slider 7. Measure the illuminance every Δx'cm and record the sum of the scale reading on the corresponding optical bench 8 and the scale reading on slider 7, as well as the illuminance value.

[0114] S7. Use Origin software to plot the relationship between the sum of the scale readings recorded on the optical bench 8 and the scale readings on the slider 7 and the illuminance value, and combine it with the relationship plotted in S4 to find the more accurate locations of the illuminance maximum and minimum points.

[0115] S8, using the relationship diagram drawn by S7, calculate the distance between the minimum and maximum illuminance points found, i.e. ΔL in formula (11);

[0116] S9, combined with the reading on the frequency meter 9, we can find that (ω) in formula (11) 10 -ω 11 ), and then by substituting all the known data into formula (11), the speed of light obtained by the entire measuring device after measurement can be obtained.

[0117]

[0118] In the formula, ΔL is the distance between adjacent points of maximum or minimum amplitude, and ω 11 -ω 10 It represents the angular frequency difference between two light waves.

[0119] Example 3

[0120] The effectiveness of the measurement method in Example 2 will be illustrated below through this example.

[0121] In this embodiment, the acoustic frequency f of the acousto-optic device is set to 75.00000MHz ± 0.02000MHz. Formula (1) shows that the frequency difference f1-f2 of the first-order diffracted light generated by the laser after passing through the acousto-optic device is 150.00000MHz. After completing the relevant connections of the experimental instruments, align the scale line of the middle slider with the scale on the optical bench at 87.0cm, then place the detector at 300mm on the slide rail, and wait for the laser power to stabilize before starting the measurement.

[0122] At the start of the measurement, the detector was moved to measure the illuminance every 5 cm from 300 mm to 150 mm on the slider scale, and the corresponding distance and illuminance value were recorded. Next, the slider was moved to measure the illuminance every 5 cm from 87.0 cm to 2.0 cm on the optical bench scale, and the value was recorded. Finally, the slide rail was moved to measure and record the illuminance every 5 cm from 150 mm to 0 mm on the slider scale. A total of 115.0 cm was measured, and 24 measurements were taken.

[0123] Measurements were conducted in air under conditions of no light or low light and a room temperature of 25°C, using the acoustic frequency of the acousto-optic device at f = 75.00000MHz ± 0.02000MHz. For each set of measurements, the acoustic frequency f, the sum of the scale reading and the slider reading L on the optical bench, and the illuminance image received by the illuminance color temperature meter were recorded. The first set of data was selected first. Figure 5 Analysis shows that the sound frequency at this time is f = 75.00000MHz.

[0124] In the first set of data, to roughly locate the illuminance maxima and minima, data was recorded every 5 cm starting from 115.0 cm, down to 0.0 cm. As shown in the graph above, the illuminance maxima occur at L = 110.0 cm, and the illuminance minima occur at L = 10.0 cm. From the data recorded in the Excel chart, the coordinates of the illuminance maxima are (110, 1596), and the coordinates of the illuminance minima are (10, 599). After obtaining the approximate locations of the illuminance maxima and minima, more precise measurements were taken near the maxima and minima based on the first set of data. Therefore, precise measurements were performed near the maxima and minima, resulting in the following image: Figure 6 and Figure 7 As shown;

[0125] from Figure 6 and Figure 7It can be seen that the illuminance maximum occurs at L = 111.0 cm and the illuminance minimum occurs at L = 14.0 cm. From the relevant data recorded in the specific Excel chart, the coordinates of the illuminance maximum point are (111, 1793) and the coordinates of the illuminance minimum point are (14, 638). Therefore, the distance between adjacent amplitude maxima and minima is ΔL / 2 = 111.0 - 14.0 = 97.0 cm, and the distance between adjacent amplitude maxima is ΔL = 2 × 97.0 = 194.0 cm. It is known that the frequency of the diffracted light generated by the laser through the acousto-optic device is f1 - f2 = 150.00000 MHz, so the speed of light c = 194.0 × 10⁻¹⁰ can be calculated by substituting the data into equation (11). -2 ×150.00000×10 6 =2.910×10 8 m / s.

[0126] The measurement result for the first group, calculated above, is 2.910 × 10⁻⁶. 8 m / s. Next, in order to obtain a more accurate measurement of the speed of light, different acoustic frequencies of the acousto-optic devices were set, and the above measurement operation was repeated to obtain the following five sets of measurement data:

[0127] Figures 8-12 The images show the illuminance measurements for groups two through six. The sound frequencies for groups two and six are f = 75.00195 MHz, for groups three and four, f = 74.99834 MHz, f = 74.98931 MHz, f = 75.00437 MHz, and f = 74.99503 MHz, respectively.

[0128] pass Figures 8-12 The coordinates of the adjacent amplitude maxima and minima of each group can be obtained from the Excel table of the five sets of data images. According to the specific situation of each group, repeat the operation of the first group above to measure the positions of the amplitude maxima and minimum points of the other five groups respectively. After obtaining the distance between the adjacent amplitude maxima and minimum points and the initial sound frequency f of the above six groups (the first group to the sixth group), we can substitute the measurement data of each group into equation (11) to obtain the corresponding light speed c of each group, and the average value of the measured light speed. The specific data are shown in Table 1:

[0129] Table 1. Examples of Measurement Data and Calculation Results for the Speed ​​of Light c

[0130]

[0131] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0132] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A resonant cavity-based optical beat-method light speed measurement device, comprising a laser emitter, characterized in that, One side of the laser emitter, along the optical path, includes, in sequence: an acousto-optic device, two plane mirrors, a semi-transparent mirror, and an illuminance detector; The laser emitter generates monochromatic light, which enters the acousto-optic device for frequency modulation, resulting in two light waves with a frequency difference. These waves are then coupled in space to form a beat frequency wave. After passing through two plane mirrors, the beat frequency wave changes its propagation direction and enters a semi-transparent mirror. While transmitting the beat frequency wave, the semi-transparent mirror also reflects a portion of the beat frequency wave reflected by the illuminance detector, thus confining the beat frequency wave between the semi-transparent mirror and the illuminance detector and generating back-and-forth reflections to form an interference wave. While the illuminance detector reflects a portion of the beat frequency wave, its photosensitive surface receives the beat frequency wave to measure the illuminance value of the beat frequency wave. The measuring device also includes a circuit control box and a frequency meter. The circuit control box is connected to the frequency meter, the laser emitter, and the acousto-optic device via wires. The frequency meter displays the acoustic frequency of the acousto-optic device.

2. The optical speed measurement device based on resonant cavity using the optical beat method according to claim 1, characterized in that, An optical bench is provided on one side of the illuminance detector. A slider that can be adjusted horizontally is provided on the optical bench. A slide rail that can be adjusted horizontally is provided on the slider. A connecting plate that can be adjusted vertically is provided on the slide rail. The connecting plate is fixed to the illuminance detector.

3. The optical speed measurement device based on resonant cavity using the optical beat method according to claim 2, characterized in that, Both the optical bench and the slider have scales. The relative position of the illuminance detector and the slider is read from the scale on the slider. The distance between the slider and the semi-transparent mirror is read from the scale on the optical bench. By combining the readings of the scales on the slider and the optical bench, the distance between the illuminance detector and the semi-transparent mirror can be measured.

4. The optical speed measurement device based on resonant cavity using the optical beat method according to claim 2, characterized in that, The illuminance detector is equipped with a magnet to fix it to the connecting plate.

5. The optical speed measurement device based on resonant cavity using the optical beat method according to claim 3, characterized in that, The illuminance detector connects to the illuminance color temperature meter app via Bluetooth on a mobile phone. Once the connection is successful, the illuminance value of the received beat frequency wave can be read by the illuminance color temperature meter app.

6. The optical speed measurement device based on resonant cavity using the optical beat method according to claim 1, characterized in that, The exit port of the laser emitter is aligned with the entrance port of the acousto-optic device for receiving light waves.

7. The optical speed measurement device based on resonant cavity using the optical beat method according to claim 1, characterized in that, Under the directional effect of the two plane mirrors, the beat frequency wave passing through the semi-transparent and semi-reflective mirror remains horizontal and can be incident on the photosensitive surface of the illuminance detector.

8. A method for measuring the speed of light using the optical beat method based on a resonant cavity, employing the measuring device described in claim 5, characterized in that... Includes the following steps: S1, connect the various components of the measuring device and adjust the optical path; S2, place the connecting plate at 150mm on the scale of the slider, and align the center of the scale on the slider with 100cm on the optical bench. S3, set the measurement distance Δx, first move the slider, measure the illuminance every Δx cm from 100cm on the optical bench to the 0 mark, and record the sum of the scale reading on the optical bench and the scale reading on the slider, as well as the illuminance value. S4. Use Origin software to plot the relationship between the sum of the recorded scale readings on the optical bench and the scale readings on the slider and the illuminance value, and find the locations of the maximum and minimum values. S5, set the measurement distance Δx', and place the slider and slide rail at the positions of the maximum and minimum illuminance points; S6, move the slide rail from the position of the slider scale to both ends of the slider, measure the illuminance every Δx'cm and record the sum of the scale reading on the optical bench and the scale reading on the slider, as well as the illuminance value. S7. Use Origin software to plot the relationship between the sum of the recorded scale readings on the optical bench and the scale readings on the slider and the illuminance value, and combine it with the relationship plotted in S4 to find the more precise locations of the illuminance maximum and minimum points. S8. Calculate the distance ΔL between the minimum and maximum illuminance points by drawing the relationship diagram. S9, combined with the reading on the frequency meter, reveals ω. 10 -ω 11 We can use this to calculate the speed of light, c.

9. The method for measuring the speed of light using the optical beat method based on a resonant cavity according to claim 8, characterized in that, In S1, the specific steps for connecting the various components of the measuring device and adjusting the optical path are as follows: S11, turn on the power and connect the circuit control box and frequency meter to the power supply; S12, connect the circuit control box to the frequency meter, the acousto-optic device, and the laser emitter respectively via wires: S13, turn on the circuit control box and frequency meter switch, and adjust the frequency meter frequency knob so that the frequency meter reading is 75.00000MHz±0.02000MHz; S14, turn on the illuminance detector switch and the mobile phone Bluetooth, and connect the illuminance detector to the mobile phone illuminance color temperature meter app; S15, adjust the relative positions of the laser emitter and the acousto-optic device so that the laser emitted by the laser emitter is accurately incident on the light-receiving port of the acousto-optic device, while keeping the emitted light of the acousto-optic device horizontal. S16, Adjust the position of the two plane mirrors to keep the reflected beat frequency light as horizontal as possible; S17, adjust the position of the semi-transparent mirror, optical bench, slider and illuminance detector so that the beat frequency light refracted by the semi-transparent mirror is accurately incident on the central photosensitive surface of the illuminance detector. S18. Observe the illuminance value of the light received by the illuminance detector through the mobile phone illuminance color temperature meter app. If the illuminance value of the received light is relatively stable, the measurement can begin.

10. The method for measuring the speed of light using the optical beat method based on a resonant cavity according to claim 8, characterized in that, The formula for calculating the speed of light, c, is: In the formula, ΔL is the distance between adjacent points of maximum or minimum amplitude, and ω 11 -ω 10 It represents the angular frequency difference between two light waves.

Images