A cold atom interferometer gravity meter using a laser interferometer to monitor vibration noise and a method of gravity measurement thereof

Abstract

This invention addresses the technical problems of insufficient vibration noise suppression and limited measurement accuracy in existing cold atom interferometric gravimeters by proposing a cold atom interferometric gravimeter and its gravity measurement method that uses a laser interferometer to monitor vibration noise. The invention includes a laser interferometer system, a Raman laser system, a cold atom interferometer physical system, and a vibration isolation platform. The laser interferometer system is mounted on the vibration isolation platform, and the cold atom interferometer physical system is positioned above the laser interferometer system with their gravity sensing axes aligned. The Raman laser output from the Raman laser system enters the laser interferometer system as its working light source. This invention utilizes a dual-frequency laser interferometer to directly monitor the vertical displacement of the Raman laser reflector, achieving precise filtering of vibration noise across a wide frequency range, improving the measurement accuracy of the cold atom interferometric gravimeter, reducing accuracy drift, and expanding the applicable frequency range.

Description

Technical Field

[0001] This invention relates to the field of neutral cold atom interferometry precision measurement technology, specifically to a cold atom interferometer gravimeter that uses a laser interferometer to monitor vibration noise and its gravity measurement method. Background Technology

[0002] In a cold atom interferometer gravimeter, as cold atom clusters rise and fall, the atoms are successively subjected to three Raman laser beams, creating atomic interference. For example... Figure 1 As shown, the Raman laser 10 consists of two laser beams with different frequencies. They are reflected from the same mirror (Raman laser mirror 40) and act together on the cold atom 50. Therefore, the phase stability of the Raman laser directly determines the measurement accuracy. Ideally, if the mirror is absolutely stationary, the wavefront phase of the Raman laser is extremely stable, and the phase of its interference fringes only reflects the change in gravitational acceleration. However, in actual working environments, various vibrations cause the Raman laser mirror to vibrate accordingly, and the mirror moves along the optical axis (vertical direction). This will introduce an additional phase shift into the laser light reflected from its surface. The relationship is as follows: in That's the laser wavelength. It can be seen that even a tiny displacement change can lead to a large phase change. This directly modulates the phase of the Raman laser, severely interfering with or even completely drowning out the gravitational signal.

[0003] To eliminate vibration noise, existing cold atom interferometric gravimeter systems typically mount a Raman laser mirror 40 onto a seismograph 30. The seismograph 30 is used to measure the minute vertical vibration displacement of the Raman laser mirror 40 itself in real time with high precision. The measured vibration signal The feedback is sent in real time to an active vibration isolation table to compensate for the displacement caused by vibration, thereby keeping the Raman laser reflector 40 relatively stationary, or calculating... The phase noise introduced by the seismograph 30 is subtracted from the calculated vibration phase noise in the electronic software after acquiring the final phase signal from the cold atom interferometer. This yields a phase signal caused solely by gravity, resulting in a more accurate absolute gravity value. However, seismographs (including mechanical and electromagnetic types) generally suffer from large accuracy drift, limited dynamic range, and frequency response limitations, making their ability to filter vibration noise relatively limited. Furthermore, the background noise of existing seismographs rises sharply in the extremely low frequency band (<0.01Hz), severely interfering with gravity measurement results, especially since the seismograph outputs an acceleration signal. It needs to go through Only a quadratic integral transform can be used for phase calculation. The integration process amplifies low-frequency noise and DC drift, requiring complex filtering and processing, which increases the system delay time, making it difficult to suppress phase noise during gravity measurement and increasing the uncertainty of the measurement results. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problems of insufficient vibration noise suppression and limited measurement accuracy of existing cold atom interferometric gravimeters. It proposes a cold atom interferometric gravimeter and its gravity measurement method that uses a laser interferometer to monitor vibration noise. The invention uses a dual-frequency laser interferometer to directly monitor the vertical displacement of the Raman laser mirror, thereby achieving accurate filtering of vibration noise over a wide frequency range, improving the measurement accuracy of the cold atom interferometric gravimeter, reducing accuracy drift, and expanding the applicable frequency range.

[0005] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0006] A cold atom interferometric gravimeter that uses a laser interferometer to monitor vibration noise is unique in that:

[0007] This includes laser interferometer systems, Raman laser systems, cold atom interferometer physical systems, and vibration isolation platforms;

[0008] The laser interferometer system is mounted on the vibration isolation platform, and the cold atom interferometer physical system is positioned above the laser interferometer system with their gravity sensing axes aligned. The output of the Raman laser system is connected to the laser interferometer system and the cold atom interferometer physical system via optical fibers.

[0009] The laser interferometer system includes a laser interferometer cavity, a main polarizing beam splitter disposed within the laser interferometer cavity, a Raman laser reflector embedded on the top surface of the laser interferometer cavity and located above the main polarizing beam splitter, a reference reflector vertically disposed on the inner side of the laser interferometer cavity and located on one side of the main polarizing beam splitter, a first polarizing beam splitter and a second polarizing beam splitter disposed side by side on the other side of the main polarizing beam splitter, a quarter-wave plate located on the emitting surface of the reference reflector, and a first photodetector disposed on the bottom surface of the laser interferometer cavity below the second polarizing beam splitter and a second photodetector located below the main polarizing beam splitter.

[0010] The Raman laser system outputs two Raman laser beams, which are transmitted to the first polarizing beam splitter and the second polarizing beam splitter, respectively. The reflected light from both beams is reflected to the first photodetector. The transmitted light from the second polarizing beam splitter is reflected by the main polarizing beam splitter prism to the Raman laser mirror. After being reflected twice by the Raman laser mirror to change its path, it is transmitted through the main polarizing beam splitter prism and then output to the second photodetector. The transmitted light from the first polarizing beam splitter is transmitted through the main polarizing beam splitter prism and the quarter-wave plate, reflected along the original path by the reference mirror, transmitted through the quarter-wave plate, reflected by the main polarizing beam splitter prism, and then output to the second photodetector.

[0011] Furthermore, the Raman laser reflector consists of a plane reflector with its reflecting surface facing upward and two isosceles right-angle reflectors respectively connected to the bottom surface of the plane reflector. The inclined surfaces of the two isosceles right-angle reflectors are arranged opposite each other to reflect the reflected light from the main polarizing beam splitter, and their reflection direction is parallel to the direction of gravity.

[0012] Furthermore, the laser interferometer system also includes a laser interferometer base disposed at the bottom of the laser interferometer cavity, a main polarization beam splitter base disposed on the laser interferometer base and located within the laser interferometer cavity, a reference laser collimator disposed on the side wall of the laser interferometer cavity, and a Raman master beam collimator; the polarization beam splitter base is used to support the main polarization beam splitter, the output end of the reference laser collimator corresponds to the first polarization beam splitter, and its input end is connected to the first output end of the Raman laser system through an optical fiber; the output end of the Raman master beam collimator corresponds to the second polarization beam splitter, and its input end is connected to the second output end of the Raman laser system through an optical fiber.

[0013] Furthermore, a half-wave plate is disposed between the second polarizing beam splitter and the main polarizing beam splitter prism; the half-wave plate is used to adjust the polarization state of the Raman laser.

[0014] Furthermore, the upper end of the cold atom interferometer physical system is connected to the third output end of the Raman laser system via an optical fiber. The Raman pulse emitted by the Raman laser system enters the cold atom interferometer physical system from above, is transmitted downwards to the reflecting surface of the Raman laser mirror, and is reflected. The cold atom interferometer physical system is used for cold atom preparation, interference, and providing the ultra-high vacuum space required for interference information acquisition.

[0015] Furthermore, the reflective surface of the Raman laser mirror is coated with a total laser reflection film.

[0016] A gravity measurement method using a cold atom interferometer gravimeter that employs a laser interferometer to monitor vibration noise is characterized by the following steps:

[0017] Step S1: The two Raman laser beams generated by the Raman laser system are used as the reference beam and the main beam, respectively, and are horizontally transmitted to the laser interferometer system.

[0018] In step S2, the reference beam and the main beam are respectively input to the first polarization beam splitter and the second polarization beam splitter of the laser interferometer system, and each beam is split into a sub-beam that is collinearly guided into the first photodetector; the frequency of the electrical signal output by the first photodetector is: The initial heterodyne frequency; where f0 and f1 are the beam frequencies of the reference beam and the principal beam, respectively;

[0019] In step S3, the main polarization beam splitter separates the reference light and the main light according to their polarization states. The main light is reflected into the measurement optical path, and its polarization state and frequency change. The reference light is transmitted into the reference optical path, and its polarization state changes, while its frequency remains unchanged. Both the main light and the reference light are eventually output to the second photodetector.

[0020] Step S4: Three Raman pulses are emitted to the cold atom interferometer physical system through the Raman laser system. The position change error of the Raman mirror when the three Raman pulses interact with the cold atoms of the cold atom interferometer physical system is calculated based on the main light and the reference light, and the measurement vibration error of the laser interferometer is obtained. Then, the measurement vibration error is differentially divided with the measurement value of the cold atom interferometer to obtain the gravity value.

[0021] Furthermore, the specific steps of step S4 are as follows:

[0022] Step S4.1, let the frequency of the main light that meets the second photodetector be... With polarization S and the reference light having frequency f0 and polarization P, the frequency of the electrical signal output by the second photodetector is obtained. for:

[0023]

[0024] in, It is the Doppler frequency shift value of the Raman laser mirror when it vibrates;

[0025] Step S4.2: Calculate the Doppler frequency shift value of the Raman laser mirror. The displacement of the Raman laser mirror is obtained. :

[0026]

[0027] in, t is the vacuum wavelength of the main light, n is the refractive index of the medium, and t is the duration of each Raman pulse.

[0028] Step S4.3: Three Raman pulses are emitted to the cold atom interferometer physical system via the Raman laser system. The position change error of the Raman mirror caused by the interaction between the Raman pulse and the cold atom at the three time points, t1, t2, and t3, is obtained respectively. The measurement vibration error caused by the vibration was calculated. :

[0029]

[0030] Where T is the interval between the three Raman pulses;

[0031] Step S4.4, measure the vibration error Measurements with cold atom interferometer By performing the difference, the value of gravity g can be obtained.

[0032] Compared with the prior art, the present invention has the following beneficial technical effects:

[0033] 1. This invention employs a cold atom interferometric gravimeter with laser interferometer to monitor vibration noise and its gravity measurement method. The laser interferometer system directly outputs the displacement signal of the Raman laser reflector. With no integration error, phase change data can be obtained directly with almost no delay and no distortion, significantly reducing phase error and improving the accuracy of cold atom interferometric gravity measurement; the resolution of the laser interferometer system for measuring the vibration displacement of Raman laser mirrors can reach nanometer, picometer or even higher, making the measurement of the mirror's vibration trajectory more accurate and the phase compensation more precise, which can significantly improve the sensitivity of the cold atom interferometric gravimeter.

[0034] 2. This invention employs a cold atom interferometric gravimeter and its gravity measurement method to monitor vibration noise using a laser interferometer. The measurement accuracy of the laser interferometer system is directly determined by the wavelength of the laser and the timing accuracy of the signal processor, eliminating the need for calibration with other vibration sensors. Therefore, using a laser interferometer system to monitor the vibration displacement of a Raman laser mirror eliminates the need for frequent calibration, significantly reducing the accuracy drift of the cold atom interferometer.

[0035] 3. The present invention employs a cold atom interferometric gravimeter and its gravity measurement method for monitoring vibration noise using a laser interferometer. The laser interferometer can measure vibrations from DC to GHz, greatly increasing the upper limit of the measurement frequency and expanding the applicable frequency range of the cold atom interferometric measurement system. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the existing cold atom interferometric gravimeter system of the present invention;

[0037] Figure 2 This is a schematic diagram of an embodiment of the cold atom interferometric gravimeter for monitoring vibration noise using a laser interferometer, as described in this invention.

[0038] Figure 3This is a schematic diagram of the structure and optical path of the laser interferometer system in the embodiment of the cold atom interferometer gravimeter for monitoring vibration noise using a laser interferometer according to the present invention;

[0039] The annotations in the attached figures are explained as follows:

[0040] 100 - Laser interferometer system; 200 - Raman laser system; 300 - Cold atom interferometer physical system; 400 - Vibration isolation platform; 101 - Raman laser reflector; 102 - Reference reflector; 103 - Quarter-wave plate; 104 - Main polarizing beam splitter; 105 - Laser interferometer cavity; 106 - First polarizing beam splitter; 107 - Second polarizing beam splitter; 110 - Main polarizing beam splitter base; 108 - First photodetector; 109 - Second photodetector; 110 - Main polarizing beam splitter base; 111 - Laser interferometer base; 112 - Half-wave plate; 113 - Reference laser collimator; 114 - Raman main beam collimator; 201 - Reference light; 202 - Main light; 203 - Follower light. Detailed Implementation

[0041] To make the objectives, advantages, and features of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that these embodiments are merely used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0042] Example 1

[0043] This embodiment provides a cold atom interferometric gravimeter that uses a laser interferometer to monitor vibration noise. Its working principle is as follows:

[0044] Two collinear Raman laser beams (frequency f1 and f2) are used to drive transitions between two energy levels in atoms. One beam (frequency f2) is typically reflected by a mirror to form a configuration that propagates in the opposite direction to the other beam (frequency f1), thus providing the momentum change required for atomic interferometry. The reflector is fixed on a vibration isolation platform 400 connected to the ground, serving as the phase reference for the Raman laser. Therefore, the vibration of the vibration isolation platform 400 directly causes the Raman laser reflector 101 to shift, changing the optical path of the reflected light and thus modulating the phase of the reflected Raman laser. This modulated phase is imprinted on the atomic interference fringes, coupling the vibration acceleration error into the measured gravity value.

[0045] like Figure 2 , Figure 3As shown, the present invention employs a laser interferometer to monitor vibration noise in a cold atom interferometer gravimeter, comprising a laser interferometer system 100, a Raman laser system 200, a cold atom interferometer physical system 300, and a vibration isolation platform 400. The laser interferometer system 100 is used to monitor vertical vibrations, and the vibration measurement mirror therein also serves as a Raman light mirror 101 during the cold atom interferometry process. The Raman laser system 200 is used to provide the Raman pulses for the cold atom interferometer and the working light for the laser interferometer system 100. The cold atom interferometer physical system 300 is used to provide the ultra-high vacuum space required for cold atom preparation, interference, and acquisition of interference information. The vibration isolation platform 400 is located below the cold atom interferometer physical system 300, providing physical support for the cold atom interferometer physical system 300 and filtering out atomic interferometric measurement noise caused by environmental vibrations above 1 Hz.

[0046] The laser interferometer system 100 includes a Raman laser reflector 101, a reference reflector 102, a quarter-wave plate 103, a main polarizing beam splitter 104, a laser interferometer cavity 105, a first polarizing beam splitter 106, a second polarizing beam splitter 107, a first photodetector 108, a second photodetector 109, a main polarizing beam splitter base 110, a laser interferometer base 111, a half-wave plate 112, a reference laser collimator 113, and a Raman main beam collimator 114. The polarizing beam splitter base 110 supports the main polarizing beam splitter 104 and is mounted on the laser interferometer base 111. The reference laser collimator 113 and the Raman master beam collimator 114 are both fixed on the laser interferometer cavity 105. The reference laser collimator 113 is located between the first polarizing beam splitter 106 and the Raman laser system 200. The Raman master beam collimator 114 is located between the second polarizing beam splitter 107 and the Raman laser system 200. The half-wave plate 112 is located between the second polarizing beam splitter 107 and the main polarizing beam splitter 104. The function of the half-wave plate 112 is to adjust the polarization state of the beam. After the linearly polarized light emitted by the Raman principal collimator 114 passes through the second polarizing beam splitter 107, its polarization direction is parallel to the transmission polarization direction of the principal polarizing beam splitter 104. The half-wave plate 112 is used to adjust its polarization to be orthogonal to the transmission polarization direction of the principal polarizing beam splitter 104, so that the beam is reflected by the principal polarizing beam splitter 104.

[0047] The Raman laser system 200 outputs two Raman laser beams: a reference beam 201 inputs to the first polarizing beam splitter 106, and a main beam 202 inputs to the second polarizing beam splitter 107. The reflected light from both beams is input to the first photodetector 108. The transmitted light from the second polarizing beam splitter 107 is input to the main polarizing beam splitter prism 104, then reflected to the Raman laser reflector 101. After being reflected again by the Raman laser reflector 101 and changing its path, the light is output to the second photodetector 109. The transmitted light from the first polarizing beam splitter 106 is input to the main polarizing beam splitter prism 104, then passes sequentially through the main polarizing beam splitter prism 104 and the quarter-wave plate 103, and is reflected along its original path by the reference reflector 102. The reflected light then re-enters the main polarizing beam splitter prism 104 and is output to the second photodetector 109.

[0048] The upper surface of the Raman laser reflector 101 is a reflective plane, with its normal parallel to the direction of gravity, used to reflect the Raman laser beam from the cold atom interferometer gravimeter; the lower reflective surface of the Raman laser reflector 101 is an isosceles right-angled reflective surface with a right apex angle, used to reflect the working laser of the laser interferometer system 100, with its reflection direction parallel to the direction of gravity; the reference reflector 102 is a plane reflector, with its normal perpendicular to the direction of gravity; in the laser interferometer system 100 of this invention, the coating on the light-transmitting surfaces of all transmission optical elements is an anti-reflection coating for 780nm wavelength lasers; both the upper and lower reflective surfaces of the Raman laser reflector 101 are coated with a total laser reflection coating; all glass elements are integrally fabricated using low-expansion-coefficient glass or microcrystalline glass or bonded together by adhesive bonding; all metal elements are made of non-magnetic materials, such as titanium alloys. When vibration acts on reference mirror 101, the positional change of reference mirror 102 in the Z direction due to the vibration does not affect the length of the reference arm during laser interferometry. Therefore, only the positional change of the measuring mirror 101 (i.e., the Raman laser reflection from the cold atom interferometer gravimeter) in the Z direction is considered. Reference light 201

[0049] After passing through a single-mode polarization-maintaining fiber, the main beam 202 reaches the reference laser collimator 113 and the Raman main beam collimator 114 respectively. After collimation, it becomes a parallel Raman laser beam with a circular cross-section. The cross-sectional intensity distribution of the Raman laser beam is Gaussian and the beam diameter is 18mm.

[0050] After receiving the light 203, the cold atom interferometer physical system 300 propagates downward through the cold atom interferometer physical system 300, reaches the upper reflecting surface of the Raman laser mirror 101 in the laser interferometer system 100, and is then reflected back into the cold atom interferometer physical system 300. The main light 202 received by the laser interferometer system 100 is reflected upward by the main polarization beam splitter 104 to the lower reflecting surface of the Raman laser mirror 101. After reflection, it forms a collinearity with the reference light 201 and enters the second photodetector 109 to form optical interference for measuring the vertical position change of the Raman laser mirror 101.

[0051] In this embodiment, the working substance selected in the cold atom interferometer physical system 300 is... 87 The wavelength of the laser used to cool and trap Rb atoms is approximately 780.24 nm. The laser used for cooling and trapping the atoms consists of a superposition of cooling and repumping light, with the frequency of the cooling laser beam relative to |5... 2 S 1 / 2 F=3>→|5 2 P 3 / 2 The red detuning of the F′=3> transition is 10–20 MHz, with a total power greater than 160 mW. The frequency of the re-pumped laser is related to |5 2 S 1 / 2 F=1>→|5 2 P 3 / 2 The transition resonance of F′=2> has a power greater than 6mW.

[0052] The reference light 201 (frequency f0) of the Raman laser system 200 is locked to the modulated transfer spectrum. 87 |5 of Rb atoms 2 S 1 / 2 F=1>→|5 2 P 3 / 2 At the transition peak of F′=0>, the main Raman laser 202 (frequency f1) is detuned by 700MHz relative to the reference Raman laser 201, the slave Raman laser 203 (frequency f2) has a frequency difference of 6.834GHz with the main Raman laser 201, and the slave Raman laser 203 is phase locked with the main Raman laser 201.

[0053] The output power of the reference beam 201 of the Raman laser system 200 is divided into two parts: one part (10mW) is used for modulation and transfer spectrum frequency locking, and the other part (20mW) is used for laser interferometry. The output power of the master beam 202 of the Raman laser system 200 is also divided into two parts: one part (60mW) is used for cold atom interferometry, and the other part (20mW) is used for laser interferometry. The slave beam 203 has an output power of 35mW and is used only for cold atom interferometry.

[0054] The total power of the Raman laser used for cold atom interferometry is 95mW. The duration of the π / 2 pulse (π / 2, π, π / 2 pulses) used to manipulate the cold atom cluster 301 is set to 20μs, and the time interval between the three Raman pulses is set to T=50ms. The total power of the light output from the reference light 201 and the main light 202 of the Raman laser system 200 for laser interferometry is 40mW, which is output to the laser interferometer system 100 through polarization-maintaining fibers as the working light source of the laser interferometer system 100.

[0055] This invention also proposes a gravity measurement method using a cold atom interferometer gravimeter, the specific steps of which are as follows:

[0056] 1. The two Raman laser beams generated by the Raman laser system 200 are converted into parallel beams that propagate in the horizontal direction by the reference laser collimator 113 and the Raman principal beam collimator 114, respectively, and then transmitted to the laser interferometer system 100. The beam that passes through the reference laser collimator 113 is the reference beam 201; the beam that passes through the Raman principal beam collimator 114 is the principal beam 202.

[0057] 2. After the reference beam 201 and the main beam 202 are respectively input to the first polarizing beam splitter 106 and the second polarizing beam splitter 107 of the laser interferometer system 100, each beam is split into a sub-beam and collinearly introduced into the first photodetector 108; the electrical signal output by the first photodetector 108 is an AC signal with a frequency equal to the difference between the frequencies of the reference beam 201 and the main beam 202, and its frequency is: , is the initial heterodyne frequency (a known constant); where f0 and f1 are the beam frequencies of the reference beam 201 and the main beam 202, respectively;

[0058] 3. The reference light 201 and the main light 202 beams are each split into a sub-beam by the first polarizing beam splitter 106 and the second polarizing beam splitter 107, respectively, and collinearly guided into the first photodetector 108; the main polarizing beam splitter prism 104 separates the reference light 201 and the main light 202 beams according to their polarization states: the main light 202 (S polarization) is reflected and enters the measurement optical path; the reference light 201 (P polarization) is transmitted and enters the reference optical path;

[0059] In the reference optical path, the reference light 201 passes through the main polarizing beam splitter 104 and the quarter-wave plate 103 in sequence, and is reflected by the reference mirror 102 along the original path. After passing through the quarter-wave plate 103 again, its polarization becomes S-polarization, and it is reflected vertically downward by the main polarizing beam splitter 104. Since the reference mirror 102 is fixed, its reflecting surface does not move in the horizontal direction under the action of low-frequency vibration in the vertical direction of propagation. The frequency of the reflected light of the reference light 201 remains unchanged, and the velocity frequency shift is still f0.

[0060] In the measurement optical path, the main beam 202 is reflected vertically to the lower reflecting surface of the Raman laser mirror 101. When there is vibration, the position of the Raman laser mirror 101 in the Z direction changes randomly, and the frequency of the reflected main beam 202 shifts due to the Doppler effect. If the Raman laser reflector 101 is located further away from the main polarizing beam splitter 104 in the Z direction, the frequency decreases to If it is close, then increase to The main light 202, reflected by the lower reflective surface of the Raman laser mirror 101, carries a frequency shift and is transmitted collinearly with the reference light 201 through the returning main polarization beam splitter 104 to the second photodetector 109.

[0061] 4. By calculating the positional change error of the Raman mirror 101 when the three Raman pulses interact with the cold atoms of the cold atom interferometer physical system 300 through the data processing circuit of the laser interferometer system 100, the measurement vibration error of the laser interferometer 100 is obtained.

[0062] Two beams of light meet at the second photodetector 109: one from the measurement optical path, with a frequency of... The polarization is S. From the reference optical path: frequency f0, polarization P. These two beams undergo optical heterodyne interference, and the electrical signal output by the second photodetector 109 is an AC signal with a frequency equal to the difference between the two optical frequencies. Its frequency is:

[0063]

[0064] The Doppler frequency shift value of the Raman laser mirror 101 can be calculated through the data processing circuit of the laser interferometer (100). , The following relationship exists between the displacement of the Raman laser mirror 101 and the displacement of the Raman laser mirror 101:

[0065]

[0066] The vacuum wavelength of the main light 202 is n, the refractive index of the medium is n, and the integration time t is the duration of each Raman pulse.

[0067] 5. Three Raman pulses are emitted to the cold atom interferometer physical system via a Raman laser system. The position change error of the Raman mirror caused by the interaction between the Raman pulse and the cold atom at the three time points, t1, t2, and t3, is obtained respectively. The measurement vibration error caused by the vibration was calculated. :

[0068]

[0069] Where T is the interval between the three Raman pulses;

[0070] The specific method for deriving the above formula is as follows:

[0071] When there is vibration: Raman laser mirror 101 produces Z-axis displacement. At this point, the optical path length of the reflected Raman laser beam from a certain reference surface to the reflecting mirror and back becomes... Changes in optical path difference directly lead to phase changes, with the following relationship: ,in That is the laser wavelength. Therefore, it is caused by the vibration of the mirror. The resulting additional phase of the reflected light is:

[0072] (1)

[0073] in It is the wavenumber of the laser.

[0074] As can be seen, the vibration of the mirror introduces an additional noise term into the phase difference of the Raman laser sensed by the atoms: .

[0075] In a cold atom interferometric gravimeter with three Raman laser pulses (π / 2-π-π / 2), cold atom wave packets interact with Raman light sequentially at times t0, t0+T, and t0+2T (i.e., t1, t2, and t3), where T is the pulse interval. The total phase difference experienced by the atom during the three pulse interactions (t1, t2, t3) is... The phase noise caused by vibration is introduced into the final interference phase according to the weighted combination of this formula. Therefore, the total laser phase noise term caused by vibration is:

[0076] (2)

[0077] Total phase difference of cold atom interferometer It consists of a signal term and a noise term:

[0078] (3)

[0079] When considering only vibration and noise, the following relationship holds:

[0080] (4)

[0081] The relationship between the signal term in the total phase difference and gravity is as follows:

[0082] (5)

[0083] Cold atom interferometers will convert the total phase difference Interpreted as gravitational acceleration The change in phase difference, therefore the total phase difference of the cold atom interferometer Actual measured value of gravity The relationship is:

[0084] (6)

[0085] in, It is the effective wave vector (because the atom absorbs one photon and is stimulated to emit another photon, the net change in momentum is (k1−k2)≈2hk (h is Planck's constant, h = 6.62607015×10). ⁻34 J·s), along the Z direction).

[0086] Measurement of gravity Includes actual gravity values Measurement errors caused by vibration due to gravity The two parts have the following relationship:

[0087] (7)

[0088] Therefore, from equations (3) to (7), we know that the gravity measurement error caused by vibration is known. satisfy:

[0089] (8)

[0090] Will and Substituting the expression into the above equation, the relationship between vibration noise and gravity error is as follows:

[0091]

[0092] 6. Measure the vibration error using the laser interferometer system 100. Measurements with cold atom interferometer By performing a difference operation, the gravity value can be obtained. .

[0093] The measurement method of the present invention uses a Raman light reflector as a vibration displacement measuring element, and forms a laser interferometer with another reflector whose normal to the reflection surface is orthogonal to the direction of gravity. This allows for the real-time acquisition of the vertical displacement of the Raman light reflector caused by vibration, thereby calculating the acceleration caused by vibration. The true value of gravity can then be obtained by differentiating the laser interferometric measurement results with the cold atom interferometric measurement results.

[0094] Example 2

[0095] The difference between this embodiment and Embodiment 1 is that a portion of the reference light 201 (frequency f0) of the Raman laser system 200 passes through a path with a center frequency of f. AOM The frequency-shifted beam (frequency: f0±f) produced by the acousto-optic modulator (AOM) AOM It replaces the main light as the working light of one frequency of the laser interferometer system 100.

[0096] The specific implementation method is as follows:

[0097] The reference light 201 (frequency f0) of the Raman laser system 200 is locked to the modulated transfer spectrum. 87 |5 of Rb atoms 2 S 1 / 2 F=1>→|5 2 P 3 / 2 At the transition peak where F′=0>, a portion of the reference beam 201 (frequency f0) passes through a center frequency f once. AOM An 80MHz AOM (Area-of-Mechanism) is used, and the diffraction efficiency of the AOM is adjusted to 50%, generating a positive or negative first-order diffracted frequency-shifted beam 204 (frequency: f0+80MHz, or f0-80MHz). In this embodiment, the frequency-shifted beam 204 is set as a negative first-order diffracted beam. The frequency difference between the reference beam 201 and the frequency-shifted beam 204 is 80MHz. Both beams are transmitted through optical fibers and pass through the reference laser collimator 113 and the Raman master beam collimator 114 before entering the laser interferometer 100. The subsequent operating modes of the laser interferometer system 100 in this embodiment are the same as in Embodiment 1.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present invention.

Claims

1. A cold atom interferometric gravimeter for monitoring vibration noise using a laser interferometer, characterized in that: Includes a laser interferometer system (100), a Raman laser system (200), a cold atom interferometer physical system (300), and a vibration isolation platform (400). The laser interferometer system (100) is mounted on the vibration isolation platform (400), and the cold atom interferometer physical system (300) is mounted above the laser interferometer system (100) with their gravity sensing axes coinciding. The output of the Raman laser system (200) is connected to the laser interferometer system (100) and the cold atom interferometer physical system (300) via optical fibers. The laser interferometer system (100) includes a laser interferometer cavity (105), a main polarizing beam splitter (104) disposed in the laser interferometer cavity (105), a Raman laser reflector (101) embedded on the top surface of the laser interferometer cavity (105) and located above the main polarizing beam splitter (104), a reference reflector (102) vertically disposed on the inner side of the laser interferometer cavity (105) and located on one side of the main polarizing beam splitter (104), a first polarizing beam splitter (106) and a second polarizing beam splitter (107) disposed side by side on the other side of the main polarizing beam splitter (104), a quarter-wave plate (103) located on the emitting surface of the reference reflector (102), and a first photodetector (108) disposed on the bottom surface of the laser interferometer cavity (105) below the second polarizing beam splitter (107) and a second photodetector (109) located below the main polarizing beam splitter (104). The Raman laser system (200) outputs two Raman laser beams, which are transmitted to the first polarizing beam splitter (106) and the second polarizing beam splitter (107) respectively. The reflected light is reflected to the first photodetector (108). The transmitted light through the second polarizing beam splitter (107) is reflected by the main polarizing beam splitter (104) to the Raman laser mirror (101). After being reflected twice by the Raman laser mirror (101) to change its path, it is transmitted through the main polarizing beam splitter (104) and then output to the second photodetector (109). The transmitted light through the first polarizing beam splitter (106) is transmitted through the main polarizing beam splitter (104) and the quarter-wave plate (103) in sequence. The reference mirror (102) reflects along the original path, and then is transmitted through the quarter-wave plate (103) and reflected by the main polarizing beam splitter (104) before being output to the second photodetector (109).

2. The cold atom interferometer gravimeter employing a laser interferometer to monitor vibrational noise according to claim 1, wherein: The Raman laser reflector (101) consists of a plane reflector with its reflecting surface facing upward and two isosceles right-angle reflectors connected to the bottom surfaces of the plane reflector. The inclined surfaces of the two isosceles right-angle reflectors are arranged opposite each other to reflect the reflected light from the main polarizing beam splitter (104), and their reflection direction is parallel to the direction of gravity.

3. The cold atom interferometer gravimeter employing a laser interferometer to monitor vibrational noise according to claim 2, wherein: The laser interferometer system (100) further includes a laser interferometer base (111) disposed at the bottom of the laser interferometer cavity (105), a main polarization beam splitter base (110) disposed on the laser interferometer base (111) and located inside the laser interferometer cavity (105), a reference laser collimator (113) disposed on the side wall of the laser interferometer cavity (105), and a Raman main beam collimator (114); the polarization beam splitter base (110) is used to support the main polarization beam splitter (104), the output end of the reference laser collimator (113) corresponds to the first polarization beam splitter (106), and its input end is connected to the first output end of the Raman laser system (200) through an optical fiber; the output end of the Raman main beam collimator (114) corresponds to the second polarization beam splitter (107), and its input end is connected to the second output end of the Raman laser system (200) through an optical fiber.

4. The cold atom interferometer gravimeter employing a laser interferometer to monitor vibrational noise according to claim 3, wherein: A half-wave plate (112) is disposed between the second polarizing beam splitter (107) and the main polarizing beam splitter (104); the half-wave plate (112) is used to adjust the polarization state of the Raman laser.

5. The cold atom interferometer gravimeter employing a laser interferometer to monitor vibrational noise according to claim 4, wherein: The upper end of the cold atom interferometer physical system (300) is connected to the third output end of the Raman laser system (200) via optical fiber. The Raman pulse emitted by the Raman laser system (200) enters the cold atom interferometer physical system (300) from above, is transmitted downwards to the reflecting surface of the Raman laser mirror (101), and is reflected. The cold atom interferometer physical system (300) is used for cold atom preparation, interference, and providing the ultra-high vacuum space required for interference information acquisition.

6. The cold atom interferometer gravimeter employing a laser interferometer to monitor vibrational noise according to claim 5, wherein: The reflective surface of the Raman laser mirror (101) is coated with a total laser reflection film.

7. A method of gravity measurement using a cold atom interferometer gravimeter of any one of claims 1-6 to monitor vibration noise, characterized in that, Includes the following steps: Step S1: The two Raman laser beams generated by the Raman laser system (200) are used as reference light (201) and main light (202) respectively, and are horizontally transmitted to the laser interferometer system (100). Step S2, the reference light (201) and the main light (202) are respectively input to the first polarizing beam splitter (106) and the second polarizing beam splitter (107) of the laser interferometer system (100), and each divides a beam of sub-beam to be collinearly introduced into the first photoelectric detector (108); the frequency of the electrical signal output by the first photoelectric detector (108) is: The initial heterodyne frequency; wherein f0 and f1 are the beam frequencies of the reference light (201) and the main light (202) respectively; In step S3, the main polarization beam splitter (104) separates the reference light (201) and the main light (202) according to their polarization states. The main light (202) is reflected into the measurement optical path, and its polarization state and frequency change. The reference light (201) is transmitted into the reference optical path, and its polarization state changes, while its frequency remains unchanged. Both the main light (202) and the reference light (201) are eventually output to the second photodetector (109). Step S4: Three Raman pulses are emitted to the cold atom interferometer physical system (300) through the Raman laser system (200). The position change error of the Raman mirror (101) when the three Raman pulses interact with the cold atoms of the cold atom interferometer physical system (300) is calculated based on the main light (202) and the reference light (201), and the measurement vibration error of the laser interferometer (100) is obtained. Then, the measurement vibration error is differentially divided with the measurement value of the cold atom interferometer to obtain the gravity value.

8. The method of claim 7, wherein the method further comprises: determining a frequency of the laser interferometer; and determining a frequency of the cold atom interferometer. The specific steps of step S4 are as follows: Step S4.1, set the frequency of the main light (202) that meets the second photodetector (109) is f1, the polarization is S; the frequency of the reference light (201) is f0, the polarization is P, the frequency of the electrical signal output by the second photodetector (109) is: f1-f0. ​ ； wherein is the Doppler shift value of the Raman laser mirror when vibrating; Step S4.2, the Doppler shift value of the Raman laser mirror (101) is calculated , and the displacement amount of the Raman laser mirror (101) is obtained : ； wherein, is the vacuum wavelength of the primary light (202), n is the refractive index of the medium, and t is the duration of each Raman pulse. Step S4.3, three Raman pulses are sent to the cold atom interferometer physical system (300) by the Raman laser system (200), and the position change errors of the Raman mirror (101) generated by the interaction of the Raman pulses with the cold atoms at three time points t1, t2, t3 are obtained respectively , and the vibration-induced measurement vibration error is calculated ； Where T is the interval between the three Raman pulses; Step S4.4, measure the vibration error Measurements with cold atom interferometer By performing the difference, the value of gravity g can be obtained.

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