CN117331135A - Absolute gravimeter device and method for free falling of microspheres in optical standing wave - Google Patents
Absolute gravimeter device and method for free falling of microspheres in optical standing wave Download PDFInfo
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Abstract
The invention discloses an absolute gravimeter device and method based on free falling of transparent medium microspheres in optical standing waves. The invention utilizes laser to build a standing wave light path along the vertical direction, wherein a light beam at one end of the standing wave is incident to a light intensity detector. Suspending the transparent medium microsphere in a potential well, closing the potential well to enable the microsphere to freely fall in the standing wave. When the microsphere passes through the node position repeatedly, the light intensity detector receives the periodical change signal, so that the displacement of the microsphere is measured in real time, the falling acceleration value is calculated, and then a potential well is started to pull the microsphere back to the original release point to fall repeatedly. Compared with the prism falling body in the traditional gravimeter, the microsphere falling body in the invention has short time consumption for pulling back the release point and high measurement bandwidth. And no collision loss exists in the deceleration process, and the measurement service life is long. The microsphere can be manufactured in batches, and has small volume and relatively low processing difficulty. In summary, the present invention provides a high measurement bandwidth, miniaturized and low cost absolute gravimetric method and apparatus.
Description
Technical Field
The invention relates to an absolute gravimeter, in particular to an absolute gravimeter device and method based on free falling of transparent medium microspheres in optical standing waves.
Background
Absolute gravimeter refers to an instrument that directly measures the gravitational acceleration value of the earth's surface, and its measurement of the amount of space and/or time can be directly traced to a defined reference of international standard units such as atomic clocks. The absolute gravimeter is widely applied to engineering application fields such as metering science, geodetic measurement, geophysical and other basic researches, vibration prevention and disaster reduction, ocean exploration, resource exploration, inertial navigation and the like. The principle scheme of the absolute gravimeter mainly comprises two kinds of free falling prisms and Raman laser action.
The prism fall time in the prism freefall scheme does not exceed 1s, but to prevent chipping, it takes tens of seconds for the prism to slow down and lift to the release point with the tray, so the scheme measures the bandwidth of the gravity signal to be typically less than 0.05Hz. And because of the slight collision caused by the residual relative speed between the prism and the tray, the prism has a certain loss every time it falls, which limits the service life of the prism, so that the absolute gravimeter based on the free falling body of the prism cannot continuously measure for a long period of time at high frequency. The prism is in the shape of a pyramid prism, so that the directions of incident light beams and emergent light beams of the prism are completely opposite, and therefore, the processing precision requirements on the included angle and the flatness of the reflecting surface of the prism are higher.
In the raman laser action scheme, a two-dimensional magneto-optical trap formed by two groups of two-to-two orthogonal correlation beams is generally used for precooling the mass center motion equivalent temperature of an atomic group, then three groups of three-dimensional magneto-optical traps of two-to-two orthogonal correlation beams are used for deep cooling, and in addition, a group of correlation raman laser beams and a group of detection beams for measuring the atomic transition probability between two ground states are also needed in the falling process of the atomic group. Therefore, the absolute gravimeter based on the Raman laser action needs ten laser beams which are finely designed and regulated to participate in the action, and not only has a complex optical path structure, is inconvenient to install and adjust, but also has higher manufacturing and maintenance costs.
In summary, compared with the absolute gravimeter based on the raman laser effect, the absolute gravimeter based on the prism free falling body has the advantages of relatively simple optical path structure and design and manufacturing cost, but the high-precision processing requirement and the fragile characteristic of the prism per se limit the bandwidth and the service life of the prism per se for measuring the gravity signal.
Disclosure of Invention
The invention provides an absolute gravimeter device and method based on free falling of transparent medium microspheres in optical standing waves, aiming at the problems that an absolute gravimeter based on free falling of a prism in the prior art is relatively simple in optical path structure and has advantages in design and manufacturing cost, but the high-precision processing requirement and the fragile characteristic of the prism limit the bandwidth and the service life of the measurement gravity signal of the prism. The invention utilizes laser to build a standing wave light path along the vertical direction, wherein a light beam at one end of the standing wave is incident to a light intensity detector. Suspending transparent medium microsphere in optical, electric or magnetic potential well, closing the potential well to make microsphere fall freely in standing wave. When the microsphere passes through the node position repeatedly, the light intensity detector receives the periodical change signal, so that the displacement of the microsphere is measured in real time, the falling acceleration value is calculated, and then a potential well is started to pull the microsphere back to the original release point to fall repeatedly.
The specific technical scheme of the invention is as follows:
1. absolute gravimeter device for free falling of microsphere in optical standing wave
The absolute gravimeter device comprises transparent medium microspheres, a laser beam, a beam splitter, a light intensity detector, a potential well generator, a potential well driver, a timing module and a resolving module;
the timing module is connected with the potential well driver and the resolving module, the potential well driver is connected with the potential well generator, and the potential well driver is used for controlling the potential well generator to generate or not generate a potential well force field. The side of the potential well generator is provided with a beam splitter, laser beams are reflected and transmitted after passing through the beam splitter, reflected light of the beam splitter is incident into a light intensity detector, the light intensity detector is connected with a resolving module, the transmission direction of transmitted light of the beam splitter is vertical downward, reverse laser is arranged below the beam splitter, the transmission direction of the reverse laser is vertical upward, the transmitted light of 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 of the wavelength of the laser beams, transparent medium microspheres are arranged in the optical standing wave, and potential wells generated by the potential well generator act on the transparent medium microspheres, so that the transparent medium microspheres move up and down along the axial direction of the optical standing wave. The light intensity detector converts a light intensity signal of the laser into a voltage signal for output, and when the transparent medium microsphere vertically falls along the optical standing wave optical axis, the light intensity of the laser received by the light intensity detector periodically changes, wherein when the spherical center of the transparent medium microsphere is overlapped with the optical standing wave node, the light intensity of the laser received by the light intensity detector is minimum.
The reverse laser is a laser coaxial with the transmitted light of the beam splitter, which is the same frequency, the same phase and the same polarization direction as the laser beam, but whose propagation direction is vertically upward.
The reverse laser is generated by arranging a plane reflector below the beam splitter, wherein the plane reflector is horizontally arranged, and the transmitted light of the beam splitter is reflected by the plane reflector, or the reverse laser beam with the vertical upward propagation direction is directly arranged below the beam splitter.
The diameter of the transparent medium microsphere is between tens of nanometers and tens of micrometers, and the transparent medium microsphere is made of a solid material transparent to visible light and near infrared light bands, and specifically comprises silicon dioxide, polystyrene, polymethyl methacrylate and the like.
The wavelength of the laser beam is between hundreds of nanometers and a few micrometers, the laser beam is a Gaussian fundamental mode beam with single mode and narrow line width, the laser beam is a collimated parallel beam, and the beam waist diameter is between hundreds of micrometers and a few millimeters.
The potential well force field type generated by the potential well generator comprises an optical radiation force field, an electric field and a magnetic field, and the transparent medium microspheres are always in the potential well force field range generated by the potential well generator, namely the potential field range covers the release point and the dropping end point of the transparent medium microspheres.
The timing module outputs a periodic clock signal to the potential well driver, when the potential well driver receives a low level, the potential well driver controls the potential well generator not to generate a potential well force field, the transparent medium microspheres are released and fall freely, when the potential well driver receives a high level, the potential well driver controls the potential well generator to generate a potential well force field, the transparent medium microspheres are pulled back to a release point from a falling end point and stably suspend, the release point is positioned at a node of the optical standing wave, and the falling end point is not overlapped with the node position of the optical standing wave.
2. Gravity acceleration measurement method utilizing free falling of microspheres in optical standing wave
The method adopts the absolute gravimeter device with the microsphere freely falling in the optical standing wave, and comprises the following steps:
1) Transferring transparent medium microspheres from a container to a potential well force field of a potential well generator, controlling the potential well generator to generate potential field force by adjusting a potential well driver, and enabling the transparent medium microspheres to stably suspend on wave nodes of a light beam standing wave and be marked as release points;
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, the transparent medium microspheres are released and freely fall, and the time when the transparent medium microspheres are released is recorded as the zero time of a clock signal;
3) When the sphere center of the transparent medium microsphere is overlapped with each node of the optical standing wave, the laser intensity received by the light intensity detector is minimum, and the calculation module records all clock signals with minimum laser intensity received by the light intensity detector in the falling process of the transparent medium microsphere from the zero moment of the clock signals to obtain a falling time sequence, { t } k }，t k Clock signal for minimizing k-th laser light intensityK=1,..n, N represents the total number of times;
4) When the transparent medium microspheres reach the dropping end point, the timing module sends high level to the potential well driver, and the potential well driver controls the potential well generator to generate a potential well force field so as to pull the transparent medium microspheres back to the release point;
5) Calculating according to the falling time sequence to obtain a time square sequence and a displacement sequence, and performing linear fitting on the time square sequence and the displacement sequence to obtain the gravity acceleration under the current signal wave; wherein the slope obtained after linear fittingAs a single measurement of gravitational acceleration.
6) The timing module outputs periodic clock signals (consisting of M rectangular waves) to the potential well driver, and the steps 2) -5) are repeated to obtain the gravity acceleration under the corresponding signal wave, and the gravity acceleration is averaged to be used as a final gravity acceleration measurement value.
In the step 1), when the laser light intensity received by the light intensity detector reaches the 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 microspheres are stably suspended on the wave nodes of the light beam standing wave.
In said 5), the time squared sequence { x } k Meeting x k ＝t k 2 2, the displacement sequence { y } k } satisfy y k =k×λ/2, where t k For the clock signal for which the kth laser light intensity reaches the minimum, k=1, N represents the total number of times, x k Represents the kth time squared value, y k And the displacement of the transparent medium microsphere when the laser intensity of the kth time reaches the minimum is shown, and lambda is the laser wavelength.
The distance between the release point and the drop end point of the transparent medium microsphere is between a few millimeters and hundreds of millimeters.
The clock signal output by the timing module is a square wave signal or a sine signal with high frequency stability, and the frequency is between a few megahertz and hundreds of megahertz. The calculating module is used for continuously counting the number of clock signal cycles to obtain the current time value.
The invention pulls back the suspension and the deceleration to the release point through the potential well in a non-contact way, has no collision loss, high pulling speed, high measurement bandwidth and long service life. The invention provides a miniaturized, low-cost and high-measurement-bandwidth absolute gravimeter method and device by free falling of microspheres in an optical standing wave.
Compared with the prior art, the invention has the beneficial effects that:
compared with the falling body of a centimeter-scale prism in the traditional free falling body absolute gravimeter, the falling body, namely the transparent medium microsphere, has the diameter of only tens of nanometers to tens of micrometers and the mass of not more than 1 microgram. The transparent medium microspheres are suspended in an optical, electrical or magnetic potential well and pulled back to the initial release point by optical radiation force, electric field force or magnetic force. The suspension and the deceleration pull-back are both non-contact processes, so that no collision loss exists, the pull-up speed is high, the measurement bandwidth is high, and the service life is long. On the other hand, compared with the prism which needs a precise optical processing technology, the transparent medium microsphere can be manufactured in batches by a microemulsion method, flame forming and other methods, and the characteristics of the microsphere such as density uniformity, smoothness, sphericity and the like are easy to control and ensure quality. In summary, the present invention provides a miniaturized, low cost and high measurement bandwidth absolute gravimetric method and apparatus by free fall of microspheres in an optical standing wave.
Drawings
Fig. 1 is a schematic view of the device connection according to the present invention.
FIG. 2 is a schematic flow chart of the method of the present invention.
Fig. 3 is a schematic view of a device structure according to a first embodiment of the present invention.
Fig. 4 is a graph showing the light intensity variation on the photosensitive surface of the light intensity detector 5 in the first embodiment.
Fig. 5 is a schematic diagram of a device structure according to a second embodiment.
In fig. 1, transparent medium microsphere 1, laser beam 2, plane mirror 3, beam splitter 4, light intensity detector 5, potential well generator 6, potential well driver 7, timing module 8, resolving module 9, and reverse laser beam 10.
Detailed Description
The invention will be described in detail below with respect to certain specific embodiments thereof in order to better understand the invention and thereby to more clearly define the scope of the invention as claimed. It should be noted that the following description is only some embodiments of the inventive concept and is only a part of examples of the present invention, wherein the specific direct description of the related structures is only for the convenience of understanding the present invention, and the specific features do not naturally and directly limit the implementation scope of the present invention. Conventional selections and substitutions made by those skilled in the art under the guidance of the present inventive concept, and reasonable arrangement and combination of several technical features under the guidance of the present inventive concept should be regarded as being within the scope of the present invention claimed.
Example 1
An absolute gravimeter device based on free falling of transparent medium microspheres in an optical standing wave comprises transparent medium microspheres 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 resolving module 9; the timing module 8 is connected with the potential well driver 7 and the resolving module 9, the potential well driver 7 is connected with the potential well generator 6, and the potential well driver 7 is used for controlling the potential well generator 6 to generate or not generate a potential well force field. The side of the potential well generator 6 is provided with a beam splitter 4, the laser beam 2 is reflected and transmitted after passing through the beam splitter 4, the reflected light of the beam splitter 4 is incident into a light intensity detector 5, the light intensity detector 5 is connected with a resolving module 9, the transmission direction of the transmitted light of the beam splitter 4 is vertical downward, reverse laser is arranged below the beam splitter 4, the transmission direction of the reverse laser is vertical upward, the transmitted light of the beam splitter 4 and the reverse laser form an optical standing wave, as shown by a dotted line in fig. 1, the distance between two adjacent wave nodes in the optical standing wave is half of the wavelength of the laser beam 2, transparent medium microspheres 1 are arranged in the optical standing wave, and a potential well generated by the potential well generator 6 acts on the transparent medium microspheres 1, so that the transparent medium microspheres 1 move up and down along the axial direction of the optical standing wave. The light intensity detector 5 converts the light intensity signal of the laser into a voltage signal for output, when the transparent medium microsphere 1 vertically falls along the optical standing wave optical axis, the light intensity of the laser received by the light intensity detector 5 periodically changes, wherein when the spherical center of the transparent medium microsphere 1 is overlapped with the optical standing wave node, the light intensity of the laser received by the light intensity detector 5 is minimum.
The wavelength of the laser beam 2 is between hundreds of nanometers and a few micrometers, the laser beam 2 is a Gaussian fundamental mode beam with single mode and narrow line width, and is a collimated parallel beam, and the beam waist diameter is between hundreds of micrometers and a few millimeters.
The reverse laser is a laser light coaxial with the transmitted light of the beam splitter 4, which is the same frequency, the same phase and the same polarization direction as the laser beam 2, but whose propagation direction is vertically upward. As shown in fig. 1 and 3, the reverse laser is generated by arranging a plane mirror 3 below a beam splitter 4, the plane mirror 3 being horizontally placed, and the transmitted light of the beam splitter 4 being reflected by the plane mirror 3, or by arranging a reverse laser beam 10 having a propagation direction vertically upward directly below the beam splitter 4, the reverse laser beam 10 and the laser beam 2 being split by the same laser.
The diameter of the transparent medium microsphere 1 is between tens of nanometers and tens of micrometers, and the transparent medium microsphere 1 is made of a solid material transparent to visible light and near infrared light bands, and specifically comprises silicon dioxide, polystyrene, polymethyl methacrylate and the like.
The type of the potential well force field generated by the potential well generator 6 comprises an optical radiation force field, an electric field and a magnetic field, and the transparent medium microsphere 1 is always in the range of the potential well force field generated by the potential well generator 6, namely the range of the potential field covers the release point and the dropping end point of the transparent medium microsphere 1.
The timing module 8 outputs a periodic clock signal to the well driver 7, when the well driver 7 receives a low level, the well driver 7 controls the well generator 6 not to generate a well force field, the transparent medium microsphere 1 is released and falls freely, when the well driver 7 receives a high level, the well driver 7 controls the well generator 6 to generate a well force field, the transparent medium microsphere 1 is pulled back to a release point from a falling end point and stably floats, the release point is located at a node of an optical standing wave, and the falling end point is not overlapped with the node position of the optical standing wave.
The timing module 8 outputs a clock signal synchronous with the rising edge and the falling edge of the periodic clock signal to the resolving module 9, the light intensity detector 5 outputs a voltage signal to the resolving module 9, and the resolving module 9 measures a gravity acceleration value once according to the clock signal and the voltage signal each time the transparent medium microsphere 1 falls.
Example two
An absolute gravimeter device based on free falling of transparent medium microspheres in an optical standing wave comprises transparent medium microspheres 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 resolving module 9; the timing module 8 is connected with the potential well driver 7 and the resolving module 9, the potential well driver 7 is connected with the potential well generator 6, and the potential well driver 7 is used for controlling the potential well generator 6 to generate or not generate a potential well force field. The side of the potential well generator 6 is provided with a beam splitter 4, the laser beam 2 is reflected and transmitted after passing through the beam splitter 4, the reflected light of the beam splitter 4 is incident into a light intensity detector 5, the light intensity detector 5 is connected with a resolving module 9, the transmission direction of the transmitted light of the beam splitter 4 is vertical downward, reverse laser is arranged below the beam splitter 4, the transmission direction of the reverse laser is vertical upward, the transmitted light of the beam splitter 4 and the reverse laser form an optical standing wave, the distance between two adjacent wave nodes in the optical standing wave is half of the wavelength of the laser beam 2, transparent medium microspheres 1 are arranged in the optical standing wave, and a potential well generated by the potential well generator 6 acts on the transparent medium microspheres 1, so that the transparent medium microspheres 1 move up and down along the axial direction of the optical standing wave. The light intensity detector 5 converts the light intensity signal of the laser into a voltage signal for output, when the transparent medium microsphere 1 vertically falls along the optical standing wave optical axis, the light intensity of the laser received by the light intensity detector 5 periodically changes, wherein when the spherical center of the transparent medium microsphere 1 is overlapped with the optical standing wave node, the light intensity of the laser received by the light intensity detector 5 is minimum.
The wavelength of the laser beam 2 is between hundreds of nanometers and a few micrometers, the laser beam 2 is a Gaussian fundamental mode beam with single mode and narrow line width, and is a collimated parallel beam, and the beam waist diameter is between hundreds of micrometers and a few millimeters.
The reverse laser is a laser light coaxial with the transmitted light of the beam splitter 4, which is the same frequency, the same phase and the same polarization direction as the laser beam 2, but whose propagation direction is vertically upward. As shown in fig. 4, the reverse laser is a reverse laser beam 10 having a propagation direction vertically upward is disposed directly below the beam splitter 4, and the reverse laser beam 10 and the laser beam 2 are split by the same laser.
The diameter of the transparent medium microsphere 1 is between tens of nanometers and tens of micrometers, and the transparent medium microsphere 1 is made of a solid material transparent to visible light and near infrared light bands, and specifically comprises silicon dioxide, polystyrene, polymethyl methacrylate and the like.
The type of the potential well force field generated by the potential well generator 6 comprises an optical radiation force field, an electric field and a magnetic field, and the transparent medium microsphere 1 is always in the range of the potential well force field generated by the potential well generator 6, namely the range of the potential field covers the release point and the dropping end point of the transparent medium microsphere 1.
The timing module 8 outputs a periodic clock signal to the well driver 7, when the well driver 7 receives a low level, the well driver 7 controls the well generator 6 not to generate a well force field, the transparent medium microsphere 1 is released and falls freely, when the well driver 7 receives a high level, the well driver 7 controls the well generator 6 to generate a well force field, the transparent medium microsphere 1 is pulled back to a release point from a falling end point and stably floats, the release point is located at a node of an optical standing wave, and the falling end point is not overlapped with the node position of the optical standing wave.
The timing module 8 outputs a clock signal synchronous with the rising edge and the falling edge of the periodic clock signal to the resolving module 9, the light intensity detector 5 outputs a voltage signal to the resolving module 9, and the resolving module 9 measures a gravity acceleration value once according to the clock signal and the voltage signal each time the transparent medium microsphere 1 falls.
A method for measuring gravitational acceleration by using free falling transparent medium microspheres in an optical standing wave, which adopts an absolute gravimeter device based on free falling transparent medium microspheres in the optical standing wave, as shown in fig. 2, and comprises the following steps:
1) Transferring the transparent medium microspheres 1 from the container to a potential well force field of the potential well generator 6, controlling the potential well generator 6 to generate potential field force by adjusting the potential well driver 7, and enabling the transparent medium microspheres 1 to stably suspend on a wave node of a light beam standing wave to be marked as a release point;
in the step 1, when the laser light intensity received by the light intensity detector 5 reaches the 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 light beam standing wave.
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, the transparent medium microsphere 1 is released and falls freely, and the time when the transparent medium microsphere 1 is released is recorded as the zero time of a clock signal;
3) When the sphere center of the transparent medium microsphere 1 is coincident with each node of the optical standing wave, the laser intensity received by the light intensity detector 5 is minimum, and the calculation module 9 records all clock signals with minimum laser intensity received by the light intensity detector 5 in the falling process of the transparent medium microsphere 1 from the zero moment of the clock signal, so as to obtain a falling time sequence { t } k }，t k For the clock signal with the laser intensity reaching the minimum at the kth time, k=1, …, N represents the total number of times;
4) When the transparent medium microsphere 1 reaches the dropping 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 so as to pull the transparent medium microsphere 1 back to the release point; the distance between the release point and the drop end point of the transparent medium microsphere 1 is between several millimeters and hundreds of millimeters.
5) Calculating according to the falling time sequence to obtain a time square sequence and a displacement sequence, and performing linear fitting on the time square sequence and the displacement sequence to obtain the gravitational acceleration under the current rectangular wave; wherein the slope obtained after linear fittingAs a single measurement of gravitational acceleration.
Wherein the time squared sequence { x } k Meeting x k ＝t k 2 2, the displacement sequence { y } k } satisfy y k =k×λ/2, where t k For the clock signal for which the kth laser light intensity reaches the minimum, k=1,..n, N representsTotal times, x k Represents the kth time squared value, y k The displacement of the transparent medium microsphere 1 when the laser intensity of the kth time reaches the minimum is shown, and lambda is the laser wavelength.
6) The timing module 8 outputs a periodic clock signal (e.g. consisting of M rectangular waves) to the potential well driver 7, repeats 2) -5), obtains the gravitational acceleration under the corresponding rectangular wave, and averages all gravitational accelerations to obtain a final gravitational acceleration measurement value. The clock signal output by the timing module 8 is a square wave signal or a sine signal with high frequency stability, and the frequency is between several megahertz and hundreds of megahertz. The calculation module 9 counts the number of clock signal cycles continuously to obtain the current time value.
Application example one
A specific embodiment is given below for describing an optical path structure configuration of the present invention for forming an optical standing wave and magnetic trap floating pull-up by using two opposite beams.
As shown in the schematic device structure of fig. 3, the fiber laser S1 emits near infrared laser with a wavelength of 1064nm and a line width of 10kHz (coherence length of about 30 km), which is expanded to a beam waist diameter of 3mm by the lenses L1 and L2 and collimated into parallel beams, and then split into two beams by the polarization independent beam splitter BS1, the laser beam 10 propagates vertically upward after being directed by the mirrors M1, M2 and M3 in sequence, and the laser beam 2 propagates vertically downward after being directed by the mirrors M4 and M5 in sequence. The two lasers are transmitted in opposite directions along the vertical direction, and interfere to form an optical standing wave with the node spacing of 532nm (shown by dotted lines in fig. 3). The intensity of each laser beam was 50. Mu.W.
The transparent silicon dioxide medium microsphere 1 with the diameter of 10 micrometers is released after being stably suspended in the quadrupole-shaped 1J50 iron-nickel magnetically soft alloy magnetic trap generator 6. The resonance frequency corresponding to the suspension elastic restoring force in the vertical direction is about 21Hz. The generation and recovery of the magnetic trap potential field is controlled by the power-off and power-on of the copper coils wound on the magnetic trap, and the potential trap controller 7 outputs a certain current to the magnetic trap generator 6 to control the magnitude of the magnetic force for suspending the microspheres. The action of the timing module 8, the light intensity detector 5 and the resolving module 9 in fig. 3 and the process of measuring the gravitational acceleration value by repeated dropping of the microspheres have been described previously. Fig. 4 shows a light intensity variation curve on the photosensitive surface of the light intensity detector 5 in the process of calculating the distance of 3 wavelengths of the free falling of the transparent medium microsphere 1 along the optical standing wave optical axis by using the electromagnetic simulation software COMSOL, and it can be known that the light intensity of the laser received by the light intensity detector 5 is minimum when the center of the sphere of the transparent medium microsphere 1 falls to the node when the light intensity variation curve takes half wavelength as a period.
The potential well equilibrium position (i.e., stable suspension and initial release position) is within the potential well range at 320 μm down in the vertical direction (i.e., the drop end position, at the lower end of the arrow near the transparent medium microsphere 1 in fig. 3), and the transparent medium microsphere 1 can be pulled back to the release point as long as within the potential well range. The sphere center of the microsphere falls through 600 nodes, namely the length N of the time and displacement data sequence is 600, and the fitting error of the acceleration measurement value obtained by linear fitting is small. The single motion period of the microsphere from the release point and the release point which is pulled back is 9.6ms, so that the measurement bandwidth of the absolute gravimeter can reach about 104Hz, which is far higher than that of the traditional absolute gravimeter based on prism free falling body by about 0.05Hz. The microsphere is in a high vacuum environment in the falling and pulling processes and does not touch the magnetic poles, so that the microsphere has no collision loss and can work for a long time.
Application example II
A specific example will be given below for an optical path structure configuration in which a single beam forms an optical standing wave and an optical trap is suspended by a mirror in the present invention.
As shown in the schematic device structure of fig. 5, the semiconductor laser S2 emits near infrared laser with wavelength 980nm and line width about 500kHz (coherence length about 600M), after the near infrared laser is expanded to beam waist diameter 3mm by lenses L1 and L2 and collimated into parallel beams, the directions of the near infrared laser are adjusted by mirrors M4 and M5 in sequence, the laser beam 2 vertically propagates downwards to the horizontally placed mirrors, and the incident beam 2 and the reflected beam 10 interfere to form an optical standing wave with node spacing of 490nm (as shown by dotted lines in fig. 4), and the light intensity of each laser beam is 50 μw.
After the solid laser S1 emits green laser with the wavelength of 532nm, the beam is expanded to the beam waist diameter of 3mm through the lenses L3 and L4 and collimated into parallel beams, the parallel beams are sequentially regulated by the reflectors M1, M2 and M3 to be directed back and vertically upwards to propagate, and the beams are weakly focused through the lens L5 with the focal length of 100mm to form an optical radiation force potential well (shown by a dotted line in fig. 4), so that the optical axis of the green laser beam and the optical axis of the near infrared laser beam 2 are completely overlapped. The light intensity of the green laser beam was 200mW. The green laser beam generates upward optical radiation thrust near the focusing point in the axial direction of the beam and generates optical radiation restoring force always pointing to the optical axis in the radial direction of the beam, so that the gravity of the microsphere can be overcome, and the microsphere can be stably suspended at the position 30 mu m above the focusing point. The resonance frequency corresponding to the suspension elastic restoring force in the vertical direction is about 46Hz. The generation and recovery of the optical radiation force potential field is controlled by controlling the light intensity of the green laser beam by an acousto-optic modulator, i.e. a potential well controller 7. The action of the timing module 8, the light intensity detector 5 and the resolving module 9 in fig. 4 and the process of measuring the gravitational acceleration value by repeated dropping of the microspheres have been described previously.
The potential well equilibrium position (i.e., stable levitation and initial release positions) is within the potential well range up to 2.3mm down in the vertical direction, so long as the release point can be pulled back within the potential well range. The sphere center of the microsphere falls through 4694 nodes, namely the length N of the time and displacement data sequence is 4694, and the fitting error of the acceleration measurement value obtained by linear fitting is small. The single motion period of the microsphere from the release point and the release point which is pulled back is 46.2ms, so that the measurement bandwidth of the absolute gravimeter can reach about 21.6Hz, which is far higher than that of the traditional absolute gravimeter based on prism free falling body by about 0.05Hz. The microsphere is in a high vacuum environment in the falling and pulling processes and does not touch the magnetic poles, so that the microsphere has no collision loss and can work for a long time.
Finally, it should be noted that the above-mentioned embodiments and descriptions are only illustrative of the technical solution of the present invention and are not limiting. It will be understood by those skilled in the art that various modifications and equivalent substitutions may be made to the present invention without departing from the spirit and scope of the present invention as defined in the appended claims.
Claims (10)
1. An absolute gravimeter device for free falling of microspheres in an optical standing wave is characterized by comprising transparent medium microspheres (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 decoding module (9);
the timing module (8) is connected with the potential well driver (7) and the resolving module (9), the potential well driver (7) is connected with the potential well generator (6), the laser beam (2) is reflected and transmitted after passing through the beam splitter (4), reflected light of the beam splitter (4) is incident into the light intensity detector (5), the light intensity detector (5) is connected with the resolving module (9), the transmission direction of the transmitted light of the beam splitter (4) is vertical downward, reverse laser is arranged below the beam splitter (4), the transmission direction of the reverse laser is vertical upward, the transmitted light of the beam splitter (4) and the reverse laser form an optical standing wave, transparent medium microspheres (1) are arranged in the optical standing wave, and the potential well generated by the potential well generator (6) acts on the transparent medium microspheres (1) to enable the transparent medium microspheres (1) to move up and down along the axial direction of the optical standing wave.
2. An absolute gravimeter device according to claim 1 in which said counter-laser is a laser coaxial with the transmitted light of the beam splitter (4) but with a propagation direction vertically upwards, of the same frequency, in phase and in the same polarization as the laser beam (2).
3. An absolute gravimeter device according to claim 1 or 2 in which the microspheres are free falling in an optical standing wave, characterized in that the reverse laser is produced by arranging a plane mirror (3) under the beam splitter (4), the plane mirror (3) being placed horizontally, the transmitted light of the beam splitter (4) being reflected by the plane mirror (3), or by arranging a reverse laser beam (10) with a propagation direction directed vertically upwards under the beam splitter (4).
4. An absolute gravimeter device according to claim 1 in which the microspheres fall freely in an optical standing wave, characterized in that the transparent medium microspheres (1) have a diameter between tens of nanometers and tens of micrometers, the transparent medium microspheres (1) being of a solid material transparent to the visible and near infrared bands.
5. An absolute gravimeter device according to claim 1 in which the microspheres are free-falling in an optical standing wave, characterized in that the wavelength of the laser beam (2) is between a few hundred nanometers and a few micrometers, the laser beam (2) being a gaussian fundamental mode beam of single mode narrow linewidth.
6. An absolute gravimeter device according to claim 1 in which the microspheres are free falling in an optical standing wave, characterized in that the type of well force field generated by the well generator (6) comprises the optical radiation force field, the electric field and the magnetic field, the transparent medium microspheres (1) being always in the range of the well force field generated by the well generator (6).
7. An absolute gravimeter device according to claim 1 in which the microspheres are free falling in an optical standing wave, characterized in that the timing module (8) outputs a periodic clock signal to the well driver (7), when the well driver (7) receives a low level, the well driver (7) controls the well generator (6) not to generate a well force field, the transparent medium microspheres (1) are released and free falling, when the well driver (7) receives a high level, the well driver (7) controls the well generator (6) to generate a well force field, the transparent medium microspheres (1) are pulled back from the end point of the falling to the release point and stably suspended.
8. A method for measuring gravitational acceleration by free fall of microspheres in an optical standing wave, characterized in that the method employs an absolute gravimeter device according to any one of claims 1-7, the method comprising the steps of:
1) Transferring the transparent medium microspheres (1) from the container to a potential well force field of a potential well generator (6), controlling the potential well generator (6) to generate potential field force by adjusting a potential well driver (7), and enabling the transparent medium microspheres (1) to be stably suspended on a wave node of a light beam standing wave and marked as a 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, the transparent medium microspheres (1) are released and freely fall, and the time when the transparent medium microspheres (1) are released is recorded as the zero time of a clock signal;
3) The calculating module (9) records all clock signals with the minimum laser light intensity received by the light intensity detector (5) in the falling process of the transparent medium microsphere (1) from the zero moment of the clock signal, and obtains a falling time sequence;
4) When the transparent medium microsphere (1) reaches the dropping 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 so as to pull the transparent medium microsphere (1) back to the release point;
5) Calculating according to the falling time sequence to obtain a time square sequence and a displacement sequence, and performing linear fitting on the time square sequence and the displacement sequence to obtain the gravity acceleration under the current signal wave;
6) The timing module (8) outputs a periodic clock signal to the potential well driver (7), and the steps of 2) -5 are repeated to obtain the gravity acceleration under the corresponding signal wave, and the gravity acceleration is averaged to be used as a final gravity acceleration measurement value.
9. The method for measuring the gravitational acceleration by utilizing the free falling of the microspheres in the optical standing wave according to claim 8, wherein in the step 5), the time square sequence { x } k Meeting x k ＝t k 2 2, the displacement sequence { y } k } satisfy y k =k×λ/2, where t k For the clock signal for which the kth laser light intensity reaches the minimum, k=1, N represents the total number of times, x k Represents the kth time squared value, y k The displacement of the transparent medium microsphere (1) when the laser intensity of the kth time reaches the minimum is shown, and lambda is the laser wavelength.
10. The method for measuring the gravitational acceleration by utilizing the free falling of the microspheres in the optical standing wave according to claim 8, wherein in the step 1), when the light intensity of the laser received by the light intensity detector (5) is 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 microspheres (1) are stably suspended on the wave node of the optical beam standing wave.
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