A self-oscillating nuclear magnetic resonance gyroscope and a signal measurement method

Abstract

The present invention provides a self-oscillating nuclear magnetic resonance gyroscope and a signal measurement method. A magnetic shielding sleeve is provided with windows in the Y-axis and Z-axis directions for laser incidence or emission. Three groups of Helmholtz coils are arranged in the magnetic shielding sleeve, respectively located in the X, Y, and Z directions, forming a three-dimensional Helmholtz coil; an atomic vapor chamber is placed in the center of the three-dimensional Helmholtz coil; a laser polarization device polarizes the atomic gas in the atomic vapor chamber through the window of the magnetic shielding sleeve; a laser detection device detects atomic spin motion through the window of the magnetic shielding sleeve, and the given electrical signal is amplified and filtered by a circuit device, and finally the NMR frequency is read. The present invention does not rely on external modulation and demodulation, and while suppressing noise and enhancing signals, it also prolongs the decay time, thereby achieving higher-precision inertial sensing measurement.

Description

Technical Field

[0001] The invention belongs to the field of quantum sensing technology, and specifically relates to a nuclear magnetic resonance gyroscope based on an alkali metal electron-inert gas nucleus mixed spin system, which can be used in the field of inertial navigation sensing. Background Art

[0002] The nuclear magnetic resonance gyroscope is an inertial sensor device based on quantum physics effects. Its basic principle is to use inert gas elements with non-zero nuclear spin (such as 129 The Larmor motion of Xe, 131Xe) in a magnetic field B generates a nuclear magnetic resonance (NMR) signal. The frequency of this signal is called the NMR frequency f, which is proportional to the magnetic field: f = gB, where g is the gyromagnetic ratio of the nuclear spin. It is a fixed constant for each specific noble gas element, and g is not equal for different elements. When the gyroscope moves at a rate f relative to the inertial reference frame, the magnetic field is proportional to the magnetic field: f = gB, where g is the gyromagnetic ratio of the nuclear spin. r When rotating, the NMR frequency shifts by an amount equal to the rotation rate f r By measuring the magnitude of the frequency shift, the information about the rotation rate can be obtained, thereby realizing inertial sensing.

[0003] Due to the presence of environmental noise, the magnetic field B is always in a state of random fluctuations, so there is a certain uncertainty in the measurement of NMR frequency, which limits the accuracy of the inertial rotation measurement of the nuclear magnetic resonance gyroscope. Therefore, in practice, two different non-zero nuclear spin noble gas elements are generally used at the same time, such as 3 He and 129 Xe, or 129 Xe and 131 Xe and other combinations, simultaneous measurement of two NMR frequencies, f 1 =g 1 B+f r , f 2 =g 2 B+f r , where g 1 Not equal to g 2 , we can get f through simple calculation r =(f 1 g 2 -f 2 g 1 ) / (g 2 -g 1 ), there is no term for magnetic field B in this formula, and the rotation rate f r The two NMR frequencies f observed experimentally 1 、f 2 and the two nuclear spin spin magnetic ratio constants g 1 , g 2Completely determined, therefore, eliminating the dependence on the magnetic field, thus achieving a more sensitive NMR gyroscope (such as the literature " 3 He- 129 Xe Comagnetometery using 87 Rb Detection and Decoupling,MELimes,D.Sheng,and MVRomalis,Physical Review Letters 120,033401(2018),ASynchronous Spin-Exchange Optically Pumped NMR-Gyroscope SSSorensen,DAThrasher and TGWalker Applied Sciences 10,7099(2020)" documented).

[0004] In the specific practice of nuclear magnetic resonance gyroscopes, precise measurement of NMR frequency is the key to improving the accuracy of inertial measurement. There are two main factors that affect the accuracy of NMR frequency measurement, both of which are related to the NMR signal, which can be approximately expressed as S(t) = A exp(-t / T)cos(ft), that is, an exponentially decaying oscillation signal, where S(t) is a function of the signal changing with time, t is the time independent variable, A is the signal amplitude, T is the characteristic time of exponential decay, and for specific nuclear spin elements, it is generally a constant, and f is the NMR frequency.

[0005] Theoretically, the larger the signal amplitude A, the longer the decay time T, the better the resolution of the frequency f, and the higher the accuracy of the gyroscope. Researchers spend a lot of time and energy on enhancing A and extending T. For example, the commonly used modulation and demodulation technology, while suppressing noise, equivalently improves the relative intensity of A. The commonly used anti-relaxation coating and buffer gas technology are also used to extend the decay characteristic time T of nuclear spins.

[0006] At present, there is a closed-loop nuclear magnetic resonance gyroscope solution that is closest to the solution of the present invention, which uses an external AC magnetic field to drive the nuclear spin Larmor precession (such as the document "Herriott-cavity-assisted closed-loop Xe isotopecomagnetometer, CPHao, QQYu, CQYuan, SQLiu, and D.Sheng, Physical Review A103, 053523 (2021)"). Although the enhancement of the nuclear magnetic resonance signal is achieved, it cannot completely guarantee the complete synchronization of the atomic precession signal and the driving magnetic field in frequency and phase. Another closed-loop nuclear magnetic resonance gyroscope uses an external signal source for modulation and generates a feedback signal through a phase-locked amplifier demodulation technology, which increases the complexity of the system (such as the patent application with publication number CN105258690 A "A closed-loop control method for magnetic resonance excitation magnetic field of a nuclear magnetic resonance gyroscope"). Summary of the invention

[0007] In order to overcome the shortcomings of the prior art, the present invention provides a self-oscillating nuclear magnetic resonance gyroscope, which draws on the self-oscillation technology solution in the magnetometer (such as the document "Self-oscillating rubidium magnetometer using nonlinear magneto-optical rotation, PDD Schwindt, L. Hollberg, and J. Kitching Review of Scientific Instruments 76, 126103 (2005)"), amplifies, filters, and phase-shifts the nuclear spin NMR signal, and in turn applies it to the AC magnetic field coil, thereby realizing a completely self-oscillating nuclear magnetic resonance gyroscope solution that does not rely on external modulation and demodulation, while suppressing noise and improving signals, and also prolonging the decay time, thereby achieving higher-precision inertial sensor measurement.

[0008] The technical solution adopted by the present invention to solve the technical problem is: a self-oscillating nuclear magnetic resonance gyroscope, including an atomic vapor chamber, a magnetic shielding sleeve, a Helmholtz coil, a laser polarization device, a laser detection device and a circuit device.

[0009] The magnetic shielding sleeve is provided with windows in the Y-axis and Z-axis directions for laser incidence or emission, and three groups of Helmholtz coils are arranged in the magnetic shielding sleeve, which are respectively located in the X, Y and Z directions to form a three-dimensional Helmholtz coil; the atomic vapor chamber is placed in the center of the three-dimensional Helmholtz coil; the laser polarization device polarizes the atomic gas in the atomic vapor chamber through the window of the magnetic shielding sleeve; the laser detection device detects the atomic spin motion through the window of the magnetic shielding sleeve, and the given electrical signal is amplified and filtered by the circuit device, and finally the NMR frequency is read.

[0010] The laser polarization device comprises a pumping laser and a quarter wave plate. The linearly polarized laser emitted by the pumping laser is converted into circularly polarized light by the quarter wave plate and then enters the magnetic shielding sleeve.

[0011] The laser detection device comprises a detection laser, a linear polarization prism, a polarization beam splitter prism and a photoelectric detector; the detection laser emitted by the detection laser is incident on a magnetic shielding sleeve after the linear polarization degree of the laser is increased by the linear polarization prism; the detection laser passes through an atomic vapor chamber and is collected by the photoelectric detector through a polarization beam splitter prism to realize photoelectric signal conversion.

[0012] The photoelectric detector is a balanced photoelectric detector.

[0013] The circuit device comprises a primary amplifier, a low-pass filter, a band-pass filter, a secondary amplifier, a phase shifter and a frequency counter; the primary amplifier realizes preliminary amplification of the electrical signal; the low-pass filter removes high-frequency electronic noise and retains the low-frequency signal of the nuclear spin motion; the band-pass filter selectively retains the low-frequency signal of the nuclear spin motion; the secondary amplifier further amplifies the nuclear spin motion NMR signal; the phase shifter arbitrarily adjusts the phase of the nuclear spin motion NMR signal; and the frequency counter reads the frequency of the nuclear spin NMR signal.

[0014] The cut-off frequency of the low-pass filter is not less than 5-10 times the larger value of the nuclear spin NMR frequencies f1 and f2.

[0015] The bandpass filter is a dual-channel bandpass filter, and the passband center frequencies are two nuclear spin NMR frequencies f1 and f2 respectively.

[0016] The present invention also provides a signal measurement method using the self-oscillating nuclear magnetic resonance gyroscope, comprising the following steps:

[0017] Step 1, raising the temperature of the atomic vapor chamber to not less than 100° C., taking the direction of the laser output from the pump laser as the Z axis, opening the Z axis coil magnetic field, adjusting the frequency of the laser output from the pump laser, and resonating the laser with the electric dipole transition of the alkali metal atoms in the atomic vapor chamber to polarize the alkali metal atoms; the alkali metal collides with the inert gas atoms at high temperature, thereby polarizing the nuclear spin of the inert gas element and generating a macroscopic nuclear spin magnetic moment in the Z axis direction;

[0018] Step 2, turn off the Z-axis coil magnetic field, detect the direction of the laser output laser as the Y-axis, turn on the Y-axis coil magnetic field, and keep it for a set time. Under the action of this magnetic field, the nuclear spin magnetic moment deviates from the Z-axis direction; then turn on the Z-axis coil magnetic field and turn off the Y-axis coil magnetic field. At this time, the nuclear spin magnetic moment will undergo Larmor precession under the action of the magnetic torque applied by the Z-axis coil magnetic field;

[0019] Step 3, turn on the detection laser, which is split into two beams of light with different intensities after passing through a polarization beam splitter prism, and irradiates two photoelectric conversion diodes of a balanced photodetector respectively, causing the output of the photodetector to change accordingly, reflecting the change of the nuclear spin magnetic moment over time;

[0020] Step 4: The output signal of the photodetector is sequentially amplified, low-pass filtered, band-pass filtered, secondary amplified and phase shifted, and applied to the X-axis magnetic field coil to achieve synchronous drive of the nuclear spin motion, thereby realizing the self-oscillation function.

[0021] The step 4 adjusts the phase shift from 0° to 180° to achieve the maximum amplitude of the NMR signal.

[0022] The beneficial effects of the present invention are:

[0023] 1) The signal generated by the nuclear spin precession signal itself is fed back to the X-axis magnetic field coil to generate an AC magnetic field that synchronously drives the nuclear spin precession;

[0024] 2) The X-axis magnetic field always maintains the same frequency as the nuclear spin precession, and its physical resonance effect enhances and amplifies the nuclear spin NMR signal, effectively increasing the signal amplitude A;

[0025] 3) Properly adjusting the phase delay of the phase shifter can put the NMR gyroscope in a self-oscillating closed-loop mode, making the oscillation signal more persistent, which is equivalent to extending the decay time T of the NMR signal;

[0026] 4) Therefore, the nuclear magnetic resonance gyroscope can effectively improve the measurement accuracy of the NMR frequency, thereby improving the gyroscope accuracy; at the same time, the closed-loop locking mode can also appropriately improve the dynamic response range of the gyroscope.

[0027] 5) The solution of the present invention does not have additional modulation signal sources and demodulation circuits such as phase-locked amplifiers, and has a simpler structure, which is conducive to the miniaturization of the overall device and reduces the total power consumption of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0029] In the figure, 1- pumping laser; 2- quarter wave plate; 3- atomic gas chamber; 4- y-axis magnetic field coil; 5- z-axis magnetic field coil; 6- x-axis magnetic field coil; 7- detection laser; 8- linear polarization prism; 9- polarization beam splitter prism; 10- balanced photodetector; 11- primary amplifier; 12- low-pass filter; 13- band-pass filter; 14- secondary amplifier; 15- phase shifter; 16- frequency counter. DETAILED DESCRIPTION

[0030] The present invention is further described below in conjunction with the accompanying drawings and embodiments. The present invention includes but is not limited to the following embodiments.

[0031] The technical solution adopted by the present invention to solve its technical problem is:

[0032] A self-oscillating nuclear magnetic resonance gyroscope device comprises an atomic vapor chamber, a magnetic shielding sleeve surrounding the atomic vapor chamber, three groups of Helmholtz coils placed in the magnetic shielding sleeve and located in three directions of X, Y and Z, a laser polarization device for polarizing atomic gas in the atomic vapor chamber, a laser detection device for detecting atomic spin motion, and an electronic circuit device for amplifying and filtering, including a frequency counter for reading NMR frequency.

[0033] The atomic vapor chamber as described above contains a mixture of alkali metals, inert elements and buffer gases (e.g. 100 mg of Rb atoms, 10 torr pressure). 129 Xe, 30torr pressure 131 Xe atomic gas), and includes a corresponding low remanent magnetism heating temperature control device (generally by winding a nickel-chromium-copper alloy heating wire with a certain resistance around the atomic vapor chamber, applying an alternating current of a certain power for heating, the alternating current frequency ranges from tens of kHz to hundreds of kHz, and using a negative feedback control PID algorithm to control the temperature at a certain value, such as 120°C, to ensure that its random fluctuation does not exceed 0.01°C.).

[0034] The laser polarization device as described above comprises a pump laser and a quarter wave plate for converting linearly polarized laser light emitted by the pump laser into circularly polarized light.

[0035] The laser detection device as described above includes a detection laser and a high extinction ratio linear polarization prism for improving the linear polarization degree of the laser.

[0036] The laser detection device as described above includes a polarization beam splitter prism for analyzing a signal of a change in polarization characteristics of the detection laser after passing through the atomic vapor chamber, and a photoelectric detector for realizing photoelectric signal conversion.

[0037] The electronic circuit arrangement as described above comprises a primary amplifier for achieving preliminary electrical signal amplification.

[0038] The electronic circuit device as described above includes a low-pass filter that removes high-frequency electronic noise and retains the low-frequency signal of the nuclear spin motion. The cutoff frequency of the low-pass filter is not less than 5-10 times the larger value of the nuclear spin NMR frequencies f1 and f2 (otherwise the signal is distorted); the low-pass filter here can be an analog filter or a digital filter.

[0039] The electronic circuit device as described above includes a dual-channel bandpass filter that selectively retains low-frequency signals of nuclear spin motion, and the passband center frequencies of the bandpass filter are two nuclear spin NMR frequencies f1 and f2 respectively; the bandpass filter here can be an analog filter or a digital filter.

[0040] The electronic circuit arrangement as described above includes a secondary amplifier for further amplifying the nuclear spin motion NMR signal.

[0041] The electronic circuit device as described above comprises a dual-channel phase shifter which can arbitrarily adjust the phase of the nuclear spin motion NMR signal.

[0042] The electronic circuit arrangement as described above comprises a frequency counter for reading the frequency of the nuclear spin NMR signal.

[0043] The present invention also includes the following self-oscillating nuclear magnetic resonance gyroscope signal measurement method:

[0044] Step 1: First, raise the temperature of the atomic vapor chamber to no less than 100°C (for example, 110°C for Cs atoms and 120°C for Rb atoms), turn on the Z-axis coil magnetic field, adjust the frequency of the pump laser output, resonate with the electric dipole transition of the alkali metal atoms in the atomic vapor chamber, and polarize the alkali metal atoms; the alkali metal collides with the inert gas atoms at high temperature, thereby polarizing the nuclear spin of the inert gas element and generating a macroscopic nuclear spin magnetic moment in the Z-axis direction.

[0045] Step 2: Turn off the Z-axis coil magnetic field and turn on the Y-axis coil magnetic field at the same time, and maintain it for a certain time (about 300 milliseconds). Under the action of this magnetic field, the nuclear spin magnetic moment deviates from the Z-axis direction. Then turn on the Z-axis coil magnetic field and turn off the Y-axis coil magnetic field. At this time, the nuclear spin magnetic moment will undergo Larmor precession under the action of the magnetic torque exerted by the Z-axis coil magnetic field.

[0046] Step 3: Turn on the detection laser. According to the magneto-optical effect in physics, the change of the nuclear spin magnetic moment will cause the polarization direction of the detection laser to rotate. At this time, it passes through the polarization beam splitter prism and is divided into two beams of light with different intensities. They are respectively irradiated on the two photoelectric conversion diodes of the balanced photodetector, causing the output of the photodetector to change accordingly, reflecting the change of the nuclear spin magnetic moment over time.

[0047] Step 4: The output signal of the photodetector is amplified at the primary stage, then low-pass filtered and band-pass filtered, and then secondary amplified and phase shifted (taking into account the phase delay effect of the NMR signal transmitted in the electronic circuit, the range is adjusted from 0° to 180° to achieve the maximum amplitude of the NMR signal), and applied to the X-axis magnetic field coil to achieve synchronous drive of the nuclear spin motion, thereby realizing the self-oscillation function.

[0048] like Figure 1 As shown, an embodiment of the present invention provides a self-oscillating nuclear magnetic resonance gyroscope device, including an atomic vapor chamber 3, a magnetic shielding sleeve 17 surrounding the atomic vapor chamber, three groups of Helmholtz coils 6, 4, and 5 placed in the magnetic shielding sleeve 17 and located in the X, Y, and Z directions respectively, laser polarization devices 1 and 2 for polarizing atomic gas in the atomic vapor chamber 3, laser detection devices 7, 8, 9, and 10 for detecting atomic spin motion, electronic circuit devices 11, 12, 13, 14, and 15 for amplifying and filtering, and a frequency counter 16 for reading NMR frequency.

[0049] The atomic vapor chamber 3 contains a mixture of alkali metals, inert elements and buffer gases (e.g. 100 mg of Rb atoms, 10 torr pressure). 129 Xe, 30torr pressure 131 Xe atomic gas), and includes a corresponding low remanent magnetism heating temperature control device (generally by winding a nickel-chromium-copper alloy heating wire with a certain resistance around the atomic vapor chamber, applying an alternating current of a certain power for heating, the alternating current frequency ranges from tens of kHz to hundreds of kHz, and using a negative feedback control PID algorithm to control the temperature at a certain value, such as 120°C, to ensure that its random fluctuation does not exceed 0.01°C.).

[0050] The laser polarization device comprises a pump laser 1 and a quarter wave plate 2 for converting the linearly polarized laser light emitted by the pump laser into circularly polarized light.

[0051] The laser detection device includes a detection laser 7, a high extinction ratio linear polarization prism 8 for improving the linear polarization degree of the laser, a polarization beam splitter prism 9 for analyzing the polarization characteristic change signal of the detection laser after passing through the atomic vapor chamber 3, and a photoelectric detector 10 for realizing photoelectric signal conversion.

[0052] The electronic circuit device includes a primary amplifier 11 for realizing preliminary electrical signal amplification, a low-pass filter 12 for eliminating high-frequency noise and retaining low-frequency signals of nuclear spin motion, wherein the cut-off frequency of the low-pass filter 12 is not lower than the nuclear spin NMR frequency f1, f2 (for example, according to 129 Xe, 131 The gyromagnetic ratio parameters of Xe atoms are 5-10 times the larger value of f1=11.86Hz, f2=3.52Hz for a magnetic field of B=10mG.

[0053] The electronic circuit device further comprises a dual-channel bandpass filter 13 for retaining low-frequency signals of nuclear spin motion, wherein the passband center frequencies of the bandpass filter 13 are respectively two nuclear spin NMR frequencies f1 and f2.

[0054] The electronic circuit device comprises a secondary amplifier 14 for further amplifying the low-frequency signal of the atomic nuclear spin motion, and a dual-channel phase shifter 15 for arbitrarily adjusting the phase of the atomic nuclear spin motion oscillation signal.

[0055] The electronic circuit arrangement comprises a frequency counter 16 for reading the frequency of the nuclear spin oscillation signal.

[0056] An embodiment of the present invention further provides a method for measuring a self-oscillating nuclear magnetic resonance gyroscope signal, comprising the following steps:

[0057] Step 1: First, the temperature of the atomic vapor chamber 3 is raised to about 120°C, a certain DC current is applied to the z-axis coil 5 to generate a static magnetic field B (generally B=10mG), and the frequency of the laser output by the pump laser 1 is adjusted. The laser is converted into circularly polarized light through the quarter-wave plate 2 and enters the atomic vapor chamber 3, resonating with the electric dipole transition of the alkali metal atoms therein to polarize the alkali metal atoms; the alkali metal collides with the inert gas atoms at high temperature, thereby polarizing the nuclear spin of the inert gas element and generating a macroscopic nuclear spin magnetic moment in the z-axis direction.

[0058] Step 2: Cut off the current of the z-axis coil 5, close the static magnetic field B, and apply a certain DC current (about 2mG) to the y-axis coil 4 to generate a static magnetic field, which lasts for about several hundred milliseconds. Under the action of this magnetic field, the nuclear spin magnetic moment deviates from the z-axis direction, and then turn on the z-axis coil 5 magnetic field B=10mG. At this time, the nuclear spin magnetic moment will undergo Larmor precession under the action of the magnetic torque applied by the magnetic field of the z-axis coil 5.

[0059] Step 3: Turn on the detection laser 7. The laser passes through the linear polarization prism 8 and enters the atomic vapor chamber 3, where it interacts with the nuclear spin magnetic moment that is undergoing Larmor precession. Through the magneto-optical rotation effect, the polarization direction of the detection laser emitted from the atomic vapor chamber 3 will change. By adjusting the relative optical axis angles of the linear polarization prism 8 and the polarization beam splitter prism 9 and by balancing the photodetector 10, the deflection angle of the light polarization direction caused by the change in the nuclear spin magnetic moment can be analyzed.

[0060] Step 4: The output electrical signal of the balanced photodetector 10 passes through the primary amplifier 11, then through the low-pass filter 12 and the band-pass filter 13, and then through the secondary amplifier 14 and the phase shifter 15, and is applied to the x-axis coil 6 to generate an alternating driving magnetic field, synchronously driving the nuclear spin Larmor precession, thereby realizing a self-oscillating nuclear magnetic resonance gyroscope.

Claims

1. A self-oscillating nuclear magnetic resonance gyroscope, comprising an atomic vapor chamber, a magnetic shielding sleeve, a Helmholtz coil, a laser polarization device, a laser detection device and a circuit device, characterized in that: The magnetic shielding sleeve has windows in the Y-axis and Z-axis directions for laser incidence or emission. Three groups of Helmholtz coils are arranged in the magnetic shielding sleeve, respectively located in the X, Y and Z directions, forming a three-dimensional Helmholtz coil; the atomic vapor chamber is placed in the center of the three-dimensional Helmholtz coil; the laser polarization device polarizes the atomic gas in the atomic vapor chamber through the window of the magnetic shielding sleeve; the laser detection device detects the atomic spin motion through the window of the magnetic shielding sleeve, and the given electrical signal is amplified and filtered by the circuit device, and finally the NMR frequency is read; wherein, The laser polarization device comprises a pumping laser and a quarter wave plate. The linearly polarized laser emitted by the pumping laser is converted into circularly polarized light by the quarter wave plate and then enters the magnetic shielding sleeve. The laser detection device comprises a detection laser, a linear polarization prism, a polarization beam splitter prism and a photoelectric detector; the detection laser emitted by the detection laser is incident on the magnetic shielding sleeve after the linear polarization degree of the laser is increased by the linear polarization prism; the detection laser passes through the atomic vapor chamber and is collected by the photoelectric detector through the polarization beam splitter prism to realize photoelectric signal conversion; the photoelectric detector adopts a balanced photoelectric detector; The circuit device comprises a primary amplifier, a low-pass filter, a band-pass filter, a secondary amplifier, a phase shifter and a frequency counter; the primary amplifier realizes preliminary amplification of the electrical signal; the low-pass filter removes high-frequency electronic noise and retains the low-frequency signal of the nuclear spin motion; the band-pass filter selectively retains the low-frequency signal of the nuclear spin motion; the secondary amplifier further amplifies the nuclear spin motion NMR signal; the phase shifter arbitrarily adjusts the phase of the nuclear spin motion NMR signal; the frequency counter reads the frequency of the nuclear spin NMR signal; The cut-off frequency of the low-pass filter is not less than 5-10 times the larger value of the nuclear spin NMR frequencies f1 and f2; The bandpass filter is a dual-channel bandpass filter, and the passband center frequencies are two nuclear spin NMR frequencies f1 and f2 respectively.

2. A signal measurement method using the self-oscillating nuclear magnetic resonance gyroscope according to claim 1, characterized in that: The following steps are involved: Step 1, raising the temperature of the atomic vapor chamber to not less than 100° C., taking the direction of the laser output from the pumping laser as the Z axis, opening the Z axis coil magnetic field, adjusting the frequency of the laser output from the pumping laser, and resonating the laser with the electric dipole transition of the alkali metal atoms in the atomic vapor chamber to polarize the alkali metal atoms; the alkali metal collides with the inert gas atoms at high temperature, thereby polarizing the nuclear spin of the inert gas element and generating a macroscopic nuclear spin magnetic moment in the Z axis direction; Step 2, turn off the Z-axis coil magnetic field, detect the direction of the laser output laser as the Y-axis, turn on the Y-axis coil magnetic field, and keep it for a set time. Under the action of this magnetic field, the nuclear spin magnetic moment deviates from the Z-axis direction; then turn on the Z-axis coil magnetic field and turn off the Y-axis coil magnetic field. At this time, the nuclear spin magnetic moment will undergo Larmor precession under the action of the magnetic torque applied by the Z-axis coil magnetic field; Step 3, turn on the detection laser, which is split into two beams of light with different intensities after passing through a polarization beam splitter prism, and irradiates two photoelectric conversion diodes of a balanced photodetector respectively, causing the output of the photodetector to change accordingly, reflecting the change of the nuclear spin magnetic moment over time; Step 4: The output signal of the photodetector is sequentially amplified, low-pass filtered, band-pass filtered, secondary amplified and phase shifted, and applied to the X-axis magnetic field coil to achieve synchronous drive of the nuclear spin motion, thereby realizing the self-oscillation function.

3. The signal measurement method according to claim 2, characterized in that: The step 4 adjusts the phase shift from 0 degrees to 180 degrees to achieve the maximum amplitude of the NMR signal.

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