An absolute gravimeter device and method in which microspheres are free-falling in an optical standing wave

Abstract

The application discloses a kind of absolute gravimeter device and method based on transparent medium microsphere free falling in optical standing wave.The application uses laser to build standing wave optical path along vertical direction, wherein standing wave one end beam is incident to light intensity detector.Then transparent medium microsphere is suspended in potential well, and microsphere is free falling in standing wave when potential well is closed.Light intensity detector receives periodic variation signal when microsphere repeatedly passes through wave node position, thereby real-time measurement microsphere displacement, and the acceleration value of falling is calculated, then potential well is opened to pull microsphere up to original release point and repeat falling.Compared with prism falling body in traditional gravimeter, microsphere falling body in the application is pulled back to release point in short time, and measurement bandwidth is high.There is no collision loss in deceleration process, and measurement life is long.Microsphere can be mass-produced, and volume is small and processing difficulty is relatively low.In short, the application provides a kind of absolute gravimeter method and device with high measurement bandwidth, miniaturization and low cost.

Description

Technical Field

[0001] This invention relates to an absolute gravimeter, specifically to an absolute gravimeter device and method based on the free fall of transparent medium microspheres in optical standing waves. Background Technology

[0002] An absolute gravimeter is an instrument that directly measures the acceleration due to gravity at the Earth's surface. Its measurements of spatial and / or temporal quantities are directly traceable to the definitions of international standard units such as atomic clocks. Absolute gravimeters are widely used in basic research fields such as metrology, geodesy, and geophysics, as well as in engineering applications such as earthquake disaster prevention and mitigation, marine exploration, resource exploration, and inertial navigation. Currently, the main principles of absolute gravimeters include prism free-fall and Raman laser manipulation.

[0003] In the prism free-fall scheme, the prism's fall time is less than 1 second. However, to prevent breakage, a tray is used to slowly decelerate and lift the prism to the release point over several seconds. Therefore, the bandwidth of the gravity signal measured in this scheme is generally less than 0.05 Hz. Furthermore, due to the slight collisions caused by the residual relative velocity between the prism and the tray, the prism suffers some wear with each fall, limiting its lifespan and preventing high-frequency, long-term continuous measurements from being performed by an absolute gravimeter based on prism free-fall. The prism is a pyramidal prism to ensure that the incident and outgoing beams are in completely opposite directions, thus requiring high precision in the machining of the prism's reflecting surface angle and flatness.

[0004] In Raman laser-based methods, a two-dimensional magneto-optical trap consisting of two sets of pairwise orthogonal opposing beams is typically used to pre-cool the atomic cluster's center of mass to its equivalent temperature. Then, a three-dimensional magneto-optical trap consisting of three sets of pairwise orthogonal opposing beams is used for deep cooling. Additionally, during the cluster's descent, a set of opposing Raman laser beams and a set of probe beams are needed to measure the probability of atomic transitions between the two ground states. Therefore, an absolute gravimeter based on Raman laser-based methods requires dozens of precisely designed and adjusted laser beams, resulting in a complex optical path structure, inconvenient installation and adjustment, and high manufacturing and maintenance costs.

[0005] In summary, absolute gravimeters based on free fall of prisms have a simpler optical path structure and are more cost-effective than those based on Raman lasers. However, the high precision requirements and fragility of the prisms themselves limit the bandwidth and lifespan of their gravity measurement signals. Summary of the Invention

[0006] To address the limitations of existing absolute gravimeters based on prism free-fall, which have a simpler optical path structure and lower design and manufacturing costs compared to Raman laser-based absolute gravimeters, the high precision requirements and fragility of the prism itself restrict the bandwidth and lifespan of the gravity signal measurement. This invention proposes an absolute gravimeter device and method based on the free fall of a transparent medium microsphere in an optical standing wave. The invention utilizes a laser to construct a vertically oriented standing wave optical path, with one end of the beam incident on a light intensity detector. The transparent medium microsphere is then suspended in an optical, electrical, or magnetic potential well. The potential well is closed, allowing the microsphere to fall freely within the standing wave. As the microsphere repeatedly passes through nodes, the light intensity detector receives periodically changing signals, thereby measuring the microsphere's displacement in real time and calculating the acceleration value. The potential well is then opened to pull the microsphere back to its original release point for repeated falls.

[0007] The specific technical solution of the present invention is as follows:

[0008] I. An absolute gravimeter device for free fall of microspheres in optical standing waves

[0009] The absolute gravimeter device includes a transparent medium microsphere, a laser beam, a beam splitter, a light intensity detector, a potential well generator, a potential well driver, a timing module, and a calculation module;

[0010] The timing module is connected to both the potential well driver and the solution module. The potential well driver is connected to the potential well generator and is used to control whether the potential well generator generates a potential well force field. A beam splitter is located to the side of the potential well generator. After the laser beam passes through the beam splitter, it is reflected and transmitted. The reflected light from the beam splitter is incident on a light intensity detector, which is connected to the solution module. The transmitted light from the beam splitter propagates vertically downwards. A reverse laser is located below the beam splitter, and its propagation direction is vertically upwards. The transmitted light from the beam splitter and the reverse laser form an optical standing wave. The distance between two adjacent wave nodes in the optical standing wave is half the wavelength of the laser beam. A transparent dielectric microsphere is placed in the optical standing wave. The potential well generated by the potential well generator acts on the transparent dielectric microsphere, causing the transparent dielectric microsphere to move up and down along the axis of the optical standing wave. The light intensity detector converts the light intensity signal of the laser into a voltage signal output. When the transparent medium microsphere falls vertically along the optical standing wave axis, the laser light intensity received by the light intensity detector changes periodically. The laser light intensity received by the light intensity detector is the minimum when the center of the transparent medium microsphere coincides with the optical standing wave node.

[0011] The reverse laser is a laser with the same frequency, phase, and polarization direction as the laser beam, coaxial with the transmitted light of the beam splitter, but propagating vertically upwards.

[0012] The reverse laser is generated by placing a horizontal plane mirror below the beam splitter, and the transmitted light from the beam splitter is reflected by the plane mirror, or by directly placing a reverse laser beam with a vertically upward propagation direction below the beam splitter.

[0013] The diameter of the transparent medium microspheres is between tens of nanometers and tens of micrometers. The transparent medium microspheres are made of solid materials that are transparent to visible and near-infrared light bands, specifically including silicon dioxide, polystyrene, and polymethyl methacrylate.

[0014] The wavelength of the laser beam is between hundreds of nanometers and several micrometers. The laser beam is a single-mode narrow-linewidth Gaussian mode beam, which is a collimated parallel beam with a beam waist diameter between hundreds of micrometers and several millimeters.

[0015] The potential well generator produces potential well force fields of various types, including optical radiation force fields, electric fields, and magnetic fields. The transparent medium microsphere is always within the range of the potential well force field generated by the potential well generator, that is, the potential field range covers the release point and the falling endpoint of the transparent medium microsphere.

[0016] The timing module outputs a periodic clock signal to the potential well driver. When the potential well driver receives a low level, it controls the potential well generator not to generate a potential well force field, and the transparent dielectric microsphere is released and falls freely. When the potential well driver receives a high level, it controls the potential well generator to generate a potential well force field, and the transparent dielectric microsphere is pulled back from the falling endpoint to the release point and floats stably. The release point is located at the node of the optical standing wave, and the falling endpoint does not coincide with the node position of the optical standing wave.

[0017] II. A method for measuring gravitational acceleration using microspheres freely falling in optical standing waves.

[0018] The method employs an absolute gravimeter device that allows microspheres to fall freely in an optical standing wave, and includes the following steps:

[0019] 1) Transfer the transparent dielectric microsphere from the container to the potential field of the potential field generator. Control the magnitude of the potential field force generated by the potential field generator by adjusting the potential field driver, so that the transparent dielectric microsphere is stably suspended at the wave node of the beam standing wave, which is recorded as the release point.

[0020] 2) When the timing module sends a low level to the potential well driver, the potential well driver controls the potential well generator not to generate a potential well force field, and the transparent medium microsphere is released and falls freely. The moment when the transparent medium microsphere is released is recorded as the zero moment of the clock signal.

[0021] 3) When the center of the transparent dielectric microsphere coincides with each node of the optical standing wave, the laser intensity received by the light intensity detector is at its minimum. The calculation module records all clock signals with the minimum laser intensity received by the light intensity detector during the fall of the transparent dielectric microsphere, starting from the zero time of the clock signal, to obtain the fall time series, {t k}, t k The clock signal for the k-th laser beam intensity to reach its minimum is given, where k = 1, ..., N, and N represents the total number of times.

[0022] 4) When the transparent medium microsphere reaches the falling endpoint, the timing module sends a high level to the potential well driver. The potential well driver controls the potential well generator to generate a potential well force field, which pulls the transparent medium microsphere back to the release point.

[0023] 5) Calculate the time square sequence and displacement sequence based on the fall time sequence. After linear fitting of the time square sequence and displacement sequence, obtain the gravitational acceleration under the current signal wave; whereby the slope obtained after linear fitting is... As a single measurement of gravitational acceleration.

[0024] 6) The timing module outputs a periodic clock signal (composed of M rectangular waves) to the potential well driver, repeating 2)-5) to obtain the gravitational acceleration under the corresponding signal wave. The average value of all gravitational accelerations is taken as the final gravitational acceleration measurement value.

[0025] In step 1), when the laser light intensity received by the light intensity detector reaches its minimum, the adjustment of the potential field force of the potential well generator is stopped and the potential field force is fixed so that the transparent medium microsphere is stably suspended on the wave node of the standing wave of the beam.

[0026] In 5), the time squared sequence {x} k}, satisfying x k =t k 2 / 2, the displacement sequence {y k}, satisfying y k = k*λ / 2, where t k Let x be the clock signal at which the laser intensity reaches its minimum during the k-th iteration, where k = 1, ..., N, and N represents the total number of iterations. k Let y represent the squared value at the k-th time. k Let λ represent the displacement of the transparent medium microsphere when the intensity of the laser light reaches its minimum during the k-th laser pulse, and λ be the laser wavelength.

[0027] The distance between the release point and the fall endpoint of the transparent medium microsphere is between several millimeters and several hundred millimeters.

[0028] The timing module outputs a clock signal that is a high-frequency stable square wave or sine wave, with a frequency between several megahertz and hundreds of megahertz. The calculation module continuously counts the number of clock signal cycles to obtain the current time value.

[0029] This invention utilizes a potential well to non-contactly pull the suspended and decelerated particles back to the release point, eliminating collision losses, achieving rapid lifting speed, high measurement bandwidth, and long service life. Furthermore, this invention provides a miniaturized, low-cost, and high-bandwidth absolute gravimeter method and apparatus by allowing microspheres to fall freely within an optical standing wave.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] Compared to the centimeter-scale prism falling body in traditional free-fall absolute gravimeters, the falling body in this invention is a transparent dielectric microsphere, with a diameter ranging from tens of nanometers to tens of micrometers and a mass of no more than 1 microgram. The transparent dielectric microsphere is suspended in an optical, electric, or magnetic potential trap and pulled back to its initial release point by optical radiation force, electric field force, or magnetic force. Both suspension and deceleration pull-back are non-contact processes, thus eliminating collision losses, resulting in rapid lifting speed, high measurement bandwidth, and long service life. Furthermore, compared to prisms requiring precise optical processing, transparent dielectric microspheres can be mass-produced using methods such as microemulsion methods and flame forming. The density uniformity, smoothness, and sphericity of the microspheres are easily controlled and their quality guaranteed. In summary, this invention provides a miniaturized, low-cost, and high-bandwidth absolute gravimeter method and apparatus by allowing microspheres to fall freely in an optical standing wave. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the connection of the device described in this invention.

[0033] Figure 2 This is a schematic diagram of the method described in this invention.

[0034] Figure 3 This is a schematic diagram of the device structure in Application Embodiment 1.

[0035] Figure 4 This is a graph showing the change in light intensity on the photosensitive surface of the light intensity detector 5 in Application Example 1.

[0036] Figure 5 This is a schematic diagram of the device structure in Application Embodiment 2.

[0037] Figure 1 In the diagram, there are 1 transparent medium microspheres, 2 laser beams, 3 plane mirrors, 4 beam splitters, 5 light intensity detectors, 6 potential well generators, 7 potential well drivers, 8 timing modules, 9 calculation modules, and 10 reverse laser beams. Detailed Implementation

[0038] To enable those skilled in the art to better understand the present invention and to more clearly define the scope of protection of the present invention, the present invention will be described in detail below with reference to certain specific embodiments. It should be noted that the following are only some specific embodiments of the present invention, and are merely a part of the embodiments of the present invention. The specific and direct descriptions of related structures are only for the convenience of understanding the present invention, and the specific features do not necessarily or directly limit the scope of the present invention. Conventional selections and substitutions made by those skilled in the art under the guidance of the present invention, as well as reasonable arrangements and combinations of several technical features under the guidance of the present invention, should all be considered within the scope of protection of the present invention.

[0039] Example 1

[0040] An absolute gravimeter device based on the free fall of transparent dielectric microspheres in an optical standing wave includes a transparent dielectric microsphere 1, a laser beam 2, a beam splitter 4, a light intensity detector 5, a potential well generator 6, a potential well driver 7, a timing module 8, and a calculation module 9. The timing module 8 is connected to both the potential well driver 7 and the calculation module 9. The potential well driver 7 is connected to the potential well generator 6 and controls whether the potential well generator 6 generates a potential well force field. A beam splitter 4 is positioned to the side of the potential well generator 6. The laser beam 2 is reflected and transmitted after passing through the beam splitter 4. The reflected light from the beam splitter 4 is incident on the light intensity detector 5, which is connected to the calculation module 9. The transmitted light from the beam splitter 4 propagates vertically downwards. A reverse laser is positioned below the beam splitter 4, propagating vertically upwards. The transmitted light from the beam splitter 4 and the reverse laser form an optical standing wave, such as... Figure 1 As shown by the midpoint line, the distance between two adjacent nodes in the optical standing wave is half the wavelength of the laser beam 2. A transparent dielectric microsphere 1 is placed in the optical standing wave. The potential well generated by the potential well generator 6 acts on the transparent dielectric microsphere 1, causing it to move up and down along the axis of the optical standing wave. The light intensity detector 5 converts the laser intensity signal into a voltage signal output. When the transparent dielectric microsphere 1 falls vertically along the optical axis of the optical standing wave, the laser intensity received by the light intensity detector 5 changes periodically. The laser intensity received by the light intensity detector 5 is minimum when the center of the transparent dielectric microsphere 1 coincides with a node of the optical standing wave.

[0041] The wavelength of laser beam 2 is between hundreds of nanometers and several micrometers. Laser beam 2 is a single-mode narrow-linewidth Gaussian mode beam, which is a collimated parallel beam with a beam waist diameter between hundreds of micrometers and several millimeters.

[0042] The reverse laser is a laser beam with the same frequency, phase, and polarization direction as laser beam 2, coaxial with the transmitted light from beam splitter 4, but propagating vertically upwards. For example... Figure 1 and Figure 3As shown, the reverse laser is generated by placing a plane mirror 3 below the beam splitter 4. The plane mirror 3 is placed horizontally, and the transmitted light from the beam splitter 4 is reflected by the plane mirror 3. Alternatively, a reverse laser beam 10 with a vertically upward propagation direction is directly placed below the beam splitter 4. The reverse laser beam 10 and the laser beam 2 are split from the same laser.

[0043] The diameter of the transparent medium microsphere 1 is between tens of nanometers and tens of micrometers. The transparent medium microsphere 1 is made of a solid material that is transparent to visible and near-infrared light bands, specifically including silica, polystyrene and polymethyl methacrylate.

[0044] The potential field generated by the potential well generator 6 includes optical radiation force field, electric field and magnetic field. The transparent medium microsphere 1 is always within the range of the potential field generated by the potential well generator 6, that is, the potential field range covers the release point and the falling end point of the transparent medium microsphere 1.

[0045] The timing module 8 outputs a periodic clock signal to the potential well driver 7. When the potential well driver 7 receives a low level, it controls the potential well generator 6 to not generate a potential well force field, and the transparent medium microsphere 1 is released and falls freely. When the potential well driver 7 receives a high level, it controls the potential well generator 6 to generate a potential well force field, and the transparent medium microsphere 1 is pulled back from the falling endpoint to the release point and floats stably. The release point is located at the node of the optical standing wave, and the falling endpoint does not coincide with the node position of the optical standing wave.

[0046] The timing module 8 outputs a clock signal synchronized with the rising and falling edges of the periodic clock signal to the calculation module 9. The light intensity detector 5 outputs a voltage signal to the calculation module 9. Each time the transparent medium microsphere 1 falls, the calculation module 9 measures the gravitational acceleration value based on the clock signal and the voltage signal.

[0047] Example 2

[0048] An absolute gravimeter device based on the free fall of transparent medium microspheres in optical standing waves, the device includes transparent medium microspheres 1, laser beam 2, beam splitter 4, light intensity detector 5, potential well generator 6, potential well driver 7, timing module 8 and calculation module 9; timing module 8 is connected to potential well driver 7 and calculation module 9, potential well driver 7 is connected to potential well generator 6, and potential well driver 7 is used to control potential well generator 6 to generate or not generate potential well force field. A beam splitter 4 is positioned to the side of the potential well generator 6. The laser beam 2 is reflected and transmitted after passing through the beam splitter 4. The reflected light from the beam splitter 4 is incident on the intensity detector 5, which is connected to the solution module 9. The transmitted light from the beam splitter 4 propagates vertically downwards. A reverse laser is positioned below the beam splitter 4, propagating vertically upwards. The transmitted light from the beam splitter 4 and the reverse laser form an optical standing wave. The distance between two adjacent nodes in the optical standing wave is half the wavelength of the laser beam 2. A transparent dielectric microsphere 1 is placed within the optical standing wave. The potential well generated by the potential well generator 6 acts on the transparent dielectric microsphere 1, causing it to move up and down along the axis of the optical standing wave. The intensity detector 5 converts the laser intensity signal into a voltage signal output. As the transparent dielectric microsphere 1 falls vertically along the optical axis of the optical standing wave, the laser intensity received by the intensity detector 5 changes periodically. The intensity of the laser received by the intensity detector 5 is minimum when the center of the transparent dielectric microsphere 1 coincides with a node of the optical standing wave.

[0049] The wavelength of laser beam 2 is between hundreds of nanometers and several micrometers. Laser beam 2 is a single-mode narrow-linewidth Gaussian mode beam, which is a collimated parallel beam with a beam waist diameter between hundreds of micrometers and several millimeters.

[0050] The reverse laser is a laser beam with the same frequency, phase, and polarization direction as laser beam 2, coaxial with the transmitted light from beam splitter 4, but propagating vertically upwards. For example... Figure 4 As shown, the reverse laser is a reverse laser beam 10 with a vertically upward propagation direction directly below the beam splitter 4. The reverse laser beam 10 and the laser beam 2 are split from the same laser.

[0051] The diameter of the transparent medium microsphere 1 is between tens of nanometers and tens of micrometers. The transparent medium microsphere 1 is made of a solid material that is transparent to visible and near-infrared light bands, specifically including silica, polystyrene and polymethyl methacrylate.

[0052] The potential field generated by the potential well generator 6 includes optical radiation force field, electric field and magnetic field. The transparent medium microsphere 1 is always within the range of the potential field generated by the potential well generator 6, that is, the potential field range covers the release point and the falling end point of the transparent medium microsphere 1.

[0053] The timing module 8 outputs a periodic clock signal to the potential well driver 7. When the potential well driver 7 receives a low level, it controls the potential well generator 6 to not generate a potential well force field, and the transparent medium microsphere 1 is released and falls freely. When the potential well driver 7 receives a high level, it controls the potential well generator 6 to generate a potential well force field, and the transparent medium microsphere 1 is pulled back from the falling endpoint to the release point and floats stably. The release point is located at the node of the optical standing wave, and the falling endpoint does not coincide with the node position of the optical standing wave.

[0054] The timing module 8 outputs a clock signal synchronized with the rising and falling edges of the periodic clock signal to the calculation module 9. The light intensity detector 5 outputs a voltage signal to the calculation module 9. Each time the transparent medium microsphere 1 falls, the calculation module 9 measures the gravitational acceleration value based on the clock signal and the voltage signal.

[0055] A method for measuring gravitational acceleration using transparent dielectric microspheres in free fall within an optical standing wave, employing an absolute gravimeter device based on the free fall of transparent dielectric microspheres in an optical standing wave, such as... Figure 2 As shown, the method includes the following steps:

[0056] 1) Transfer the transparent medium microsphere 1 from the container to the potential field of the potential field generator 6. Control the magnitude of the potential field force generated by the potential field generator 6 by adjusting the potential field driver 7, so that the transparent medium microsphere 1 is stably suspended on the wave node of the beam standing wave, which is recorded as the release point.

[0057] In step 1, when the laser light intensity received by the light intensity detector 5 reaches its minimum, the adjustment of the potential field force of the potential well generator 6 is stopped and the potential field force is fixed, so that the transparent medium microsphere 1 is stably suspended on the wave node of the standing wave of the beam.

[0058] 2) When the timing module 8 sends a low level to the potential well driver 7, the potential well driver 7 controls the potential well generator 6 not to generate a potential well force field, and the transparent medium microsphere 1 is released and falls freely. The moment when the transparent medium microsphere 1 is released is recorded as the zero moment of the clock signal.

[0059] 3) When the center of the transparent dielectric microsphere 1 coincides with each node of the optical standing wave, the laser intensity received by the light intensity detector 5 is at its minimum. The calculation module 9 records all clock signals with the minimum laser intensity received by the light intensity detector 5 during the falling process of the transparent dielectric microsphere 1, starting from clock signal zero, to obtain the falling time sequence {t}. k}, t k The clock signal for the k-th laser beam intensity to reach its minimum is given, where k = 1, ..., N, and N represents the total number of times.

[0060] 4) When the transparent medium microsphere 1 reaches the falling endpoint, the timing module 8 sends a high level to the potential well driver 7. The potential well driver 7 controls the potential well generator 6 to generate a potential well force field, which pulls the transparent medium microsphere 1 back to the release point. The distance between the release point and the falling endpoint of the transparent medium microsphere 1 is between several millimeters and several hundred millimeters.

[0061] 5) Calculate the time square sequence and displacement sequence based on the fall time sequence. After linear fitting of the time square sequence and displacement sequence, obtain the gravitational acceleration under the current rectangular wave; where the slope obtained after linear fitting is... As a single measurement of gravitational acceleration.

[0062] Among them, the time square sequence {x k}, satisfying x k =t k 2 / 2, the displacement sequence {y k}, satisfying y k = k*λ / 2, where t k Let x be the clock signal at which the laser intensity reaches its minimum during the k-th iteration, where k = 1, ..., N, and N represents the total number of iterations. k Let y represent the squared value at the k-th time. k Let λ represent the displacement of the transparent medium microsphere 1 when the intensity of the laser light reaches its minimum during the k-th laser pulse, and λ be the laser wavelength.

[0063] 6) Timing module 8 outputs a periodic clock signal (e.g., composed of M rectangular waves) to potential well driver 7, repeating steps 2)-5) to obtain the gravitational acceleration under the corresponding rectangular waves. The average of all gravitational accelerations is taken as the final gravitational acceleration measurement value. The clock signal output by timing module 8 is a high-frequency stable square wave or sine wave signal with a frequency between several megahertz and hundreds of megahertz. Calculation module 9 continuously counts the number of clock signal periods to obtain the current value.

[0064] Application Example 1

[0065] The following is a specific embodiment illustrating an optical path structure configuration for forming optical standing waves and magnetic trap levitation and lifting in this invention.

[0066] like Figure 3As shown in the schematic diagram of the device, the fiber laser S1 emits a near-infrared laser with a wavelength of 1064nm and a linewidth of 10kHz (coherence length approximately 30km). After being expanded by lenses L1 and L2 to a beam waist diameter of 3mm and collimated into a parallel beam, it is split into two laser beams by the polarization-independent beam splitter BS1. Laser beam 10 propagates vertically upward after being oriented by mirrors M1, M2, and M3 in sequence, while laser beam 2 propagates vertically downward after being oriented by mirrors M4 and M5 in sequence. The two laser beams propagate in opposite directions along a vertical direction, interfering to form an optical standing wave with a node spacing of 532nm (e.g., ...). Figure 3 (As shown by the midpoint line). The intensity of each laser beam is 50 μW.

[0067] A 10-micrometer diameter silica transparent dielectric microsphere 1 is released after being stably suspended in a quadrupole 1J50 iron-nickel soft magnetic alloy magnetic trap generator 6. The resonant frequency corresponding to the vertical levitation elastic restoring force is approximately 21 Hz. The generation and restoration of the magnetic trap potential field are controlled by the de-energization and energization of a copper coil wound on the magnetic trap. The potential trap controller 7 outputs a certain current to the magnetic trap generator 6 to control the magnitude of the magnetic force used to levitate the microsphere. Figure 3 The functions of timing module 8, light intensity detector 5, and calculation module 9, as well as the process of repeatedly dropping the microsphere to measure the gravitational acceleration value, have been explained previously. Figure 4 The graph shows the light intensity change curve on the photosensitive surface of the light intensity detector 5 during the process of the transparent medium microsphere 1 falling freely along the optical standing wave axis for 3 wavelengths, calculated using the electromagnetic simulation software COMSOL. It can be seen that the light intensity change curve has a period of half a wavelength, and the laser light intensity received by the light intensity detector 5 is the minimum when the center of the transparent medium microsphere 1 falls to the node.

[0068] The potential well equilibrium position (i.e., the stable suspension and initial release position) is 320 μm downwards along the vertical direction (i.e., the final position of the fall). Figure 3 The area near the lower end of the arrow (near the transparent medium microsphere 1) is within the potential well range, and as long as it is within the potential well range, the transparent medium microsphere 1 can be pulled back to the release point. During the fall of the microsphere, its center passes through approximately 600 nodes, meaning the length N of the time and displacement data sequence is 600, resulting in a small fitting error for the acceleration measurement value obtained through linear fitting. The calculated single motion period of the microsphere from release to being pulled back to the release point is 9.6 ms. Therefore, the measurement bandwidth of this absolute gravimeter can reach approximately 104 Hz, which is much higher than the approximately 0.05 Hz measurement bandwidth of traditional absolute gravimeters based on prism free fall. The microsphere is in a high vacuum environment during both the fall and the pull-back process and does not come into contact with magnetic poles, so there is no collision loss and it can work for a long time.

[0069] Application Example 2

[0070] The following is a specific embodiment illustrating the optical path structure configuration of the present invention, in which a single beam forms an optical standing wave through a reflector and is suspended and pulled up by an optical trap.

[0071] like Figure 5 As shown in the schematic diagram of the device structure, the semiconductor laser S2 emits a near-infrared laser with a wavelength of 980nm and a linewidth of approximately 500kHz (coherence length of approximately 600m). After being expanded to a beam waist diameter of 3mm by lenses L1 and L2 and collimated into a parallel beam, it passes through mirrors M4 and M5 in sequence to adjust its direction. The laser beam 2 propagates vertically downwards to a horizontally placed mirror. The incident beam 2 and the reflected beam 10 interfere to form an optical standing wave with a node spacing of 490nm (e.g., ...). Figure 4 (As shown by the midpoint line), the intensity of each laser beam is 50μW.

[0072] Solid-state laser S1 emits a 532nm green laser beam, which is expanded to a beam waist diameter of 3mm by lenses L3 and L4 and collimated into a parallel beam. After being directed by mirrors M1, M2, and M3, the beam propagates vertically upwards. This beam is then weakly focused by lens L5 (100mm focal length) to form an optical radiation potential well (e.g., ...). Figure 4 As shown by the dotted line, the optical axes of the green laser beam and the near-infrared laser beam 2 are completely coincident. The intensity of the green laser beam is 200mW. Near the focal point, the green laser beam generates an upward optical radiation thrust along the beam axis and a restoring force in the beam radial direction that always points towards the optical axis. Therefore, it can overcome the gravity of the microsphere and stably suspend the microsphere at a position 30μm above the focal point. The resonant frequency corresponding to the vertical suspending elastic restoring force is approximately 46Hz. The generation and restoration of the optical radiation force potential field are controlled by controlling the intensity of the green laser beam through an acousto-optic modulator, i.e., a potential well controller 7. Figure 4 The functions of timing module 8, light intensity detector 5, and calculation module 9, as well as the process of repeatedly dropping the microsphere to measure the gravitational acceleration value, have been explained previously.

[0073] The potential well equilibrium position (i.e., the stable suspension and initial release position) is within the potential well range for a maximum downward distance of 2.3 mm along the vertical direction. As long as it is within the potential well range, it can be pulled back to the release point. During the microsphere's descent, its center passes through approximately 4694 nodes, meaning the length N of the time and displacement data sequence is 4694. Linear fitting yields a small fitting error for the acceleration measurements. The calculated single motion period of the microsphere from release to pull-back to the release point is 46.2 ms. Therefore, the measurement bandwidth of this absolute gravimeter can reach approximately 21.6 Hz, far exceeding the approximately 0.05 Hz measurement bandwidth of traditional prism-based free-fall absolute gravimeters. The microsphere operates in a high vacuum environment during both descent and pull-back and does not come into contact with magnetic poles, thus experiencing no collision damage and allowing for long-term operation.

[0074] Finally, it should be noted that the above embodiments and descriptions are only used to illustrate the technical solutions of the present invention and not to limit it. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the disclosure of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the protection scope of the claims of the present invention.

Claims

1. An absolute gravimeter device for free-falling microspheres in optical standing waves, characterized in that, It includes transparent dielectric microspheres (1), laser beam (2), beam splitter (4), light intensity detector (5), potential well generator (6), potential well driver (7), timing module (8) and calculation module (9); The timing module (8) is connected to the potential well driver (7) and the calculation module (9). The potential well driver (7) is connected to the potential well generator (6). The laser beam (2) is reflected and transmitted after passing through the beam splitter (4). The reflected light from the beam splitter (4) is incident into the light intensity detector (5). The light intensity detector (5) is connected to the calculation module (9). The propagation direction of the transmitted light from the beam splitter (4) is vertically downward. A reverse laser is set below the beam splitter (4). The reverse laser is a laser with the same frequency, phase and polarization direction as the laser beam (2), coaxial with the transmitted light from the beam splitter (4), but with a propagation direction vertically upward. The transmitted light from the beam splitter (4) and the reverse laser form an optical standing wave. A transparent medium microsphere (1) is set in the optical standing wave. The potential well generated by the potential well generator (6) acts on the transparent medium microsphere (1), causing the transparent medium microsphere (1) to move up and down along the axis of the optical standing wave. The timing module (8) outputs a periodic clock signal to the potential well driver (7). When the potential well driver (7) receives a low level, the potential well driver (7) controls the potential well generator (6) not to generate a potential well force field, and the transparent medium microsphere (1) is released and falls freely. When the potential well driver (7) receives a high level, the potential well driver (7) controls the potential well generator (6) to generate a potential well force field, and the transparent medium microsphere (1) is pulled back from the fall endpoint to the release point and floats stably.

2. The absolute gravimeter device for free fall of microspheres in optical standing waves according to claim 1, characterized in that, The reverse laser is generated by setting a plane mirror (3) below the beam splitter (4), with the plane mirror (3) placed horizontally, and the transmitted light from the beam splitter (4) is reflected by the plane mirror (3), or by setting a reverse laser beam (10) with a vertical upward propagation direction directly below the beam splitter (4).

3. The absolute gravimeter device for free fall of microspheres in optical standing waves according to claim 1, characterized in that, The diameter of the transparent medium microsphere (1) is between tens of nanometers and tens of micrometers, and the material of the transparent medium microsphere (1) is a solid material that is transparent to the visible and near-infrared light bands.

4. The absolute gravimeter device for free fall of microspheres in optical standing waves according to claim 1, characterized in that, The wavelength of the laser beam (2) is between hundreds of nanometers and several micrometers, and the laser beam (2) is a single-mode narrow-linewidth Gaussian mode beam.

5. The absolute gravimeter device for free fall of microspheres in optical standing waves according to claim 1, characterized in that, The potential well force field generated by the potential well generator (6) includes optical radiation force field, electric field and magnetic field, and the transparent medium microsphere (1) is always within the range of the potential well force field generated by the potential well generator (6).

6. A method for measuring gravitational acceleration using microspheres freely falling in an optical standing wave, characterized in that, The method employs the absolute gravimeter device for free fall of microspheres in optical standing waves as described in any one of claims 1-5, and the method includes the following steps: 1) Transfer the transparent medium microsphere (1) from the container to the potential field of the potential field generator (6). Control the magnitude of the potential field force generated by the potential field generator (6) by adjusting the potential field driver (7) so that the transparent medium microsphere (1) is stably suspended on the wave node of the beam standing wave, which is recorded as the release point. 2) When the timing module (8) sends a low level to the potential well driver (7), the potential well driver (7) controls the potential well generator (6) not to generate a potential well force field, and the transparent medium microsphere (1) is released and falls freely. The moment when the transparent medium microsphere (1) is released is recorded as the zero moment of the clock signal. 3) The calculation module (9) records all the clock signals with the minimum laser light intensity received by the light intensity detector (5) during the falling process of the transparent medium microsphere (1) starting from the zero time of the clock signal, and obtains the falling time sequence; 4) When the transparent medium microsphere (1) reaches the falling end point, the timing module (8) sends a high level to the potential well driver (7), and the potential well driver (7) controls the potential well generator (6) to generate a potential well force field, which pulls the transparent medium microsphere (1) back to the release point. 5) Calculate the time square sequence and displacement sequence based on the falling time sequence, and obtain the gravitational acceleration under the current signal wave by linear fitting the time square sequence and displacement sequence. 6) The timing module (8) outputs a periodic clock signal to the potential well driver (7) and repeats 2)-5) to obtain the gravitational acceleration under the corresponding signal wave. The average value of all gravitational accelerations is taken as the final gravitational acceleration measurement value.

7. The method for measuring gravitational acceleration using microspheres freely falling in optical standing waves according to claim 6, characterized in that, In section 5), the time squared sequence { x k },satisfy x k =t k 2 / 2, the displacement sequence { y k },satisfy y k =k* λ / 2, where, t k For the first k The clock signal at which the laser intensity reaches its minimum. k =1,2,3,... N , N Indicates the total number of times. x k Indicates the first k The squared value of time, y k Indicates the first k Displacement of transparent dielectric microsphere (1) when the laser intensity reaches its minimum. λ is the laser wavelength.

8. The method for measuring gravitational acceleration using microspheres freely falling in optical standing waves according to claim 6, characterized in that, In step 1), when the laser light intensity received by the light intensity detector (5) reaches the minimum, the magnitude of the potential field force of the potential well generator (6) is stopped and the potential field force is fixed so that the transparent medium microsphere (1) is stably suspended on the wave node of the standing wave of the beam.

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