Device and method for measuring longitudinal relaxation time of miniaturized atomic air chamber

Abstract

The invention belongs to the technical field of nuclear magnetic resonance gyroscopes, and relates to a device and a method for measuring longitudinal relaxation time of a miniaturized atomic air chamber. The measuring device comprises: a miniaturized atomic gas cell; the pumping light and light path structure comprises a pumping light laser, a pumping light polarizer, a quarter-wave plate and a light absorption black body which are sequentially arranged along the Z axis; the detection light and light path structure comprises a detection light laser, a detection light polarizer, a half-wave plate, a first right-angle prism reflector, a second right-angle prism reflector, a polarization splitting prism, a first photoelectric detector and a second photoelectric detector which are sequentially arranged along a detection light path; the temperature control system comprises non-magnetic heating devices arranged on the two sides of the miniaturized atomic gas chamber and a temperature control circuit; the magnetic field control system comprises a double-layer magnetic shielding cover, a three-axis magnetic field coil arranged on the outer side of the miniaturized atomic gas chamber, and a magnetic field control circuit; and the signal processing system performs fitting calculation on the longitudinal relaxation time.

Description

Technical Field

[0001] This invention belongs to the field of nuclear magnetic resonance gyroscope technology, specifically relating to a device and method for measuring the longitudinal relaxation time of a miniaturized atomic gas cell. Background Technology

[0002] The core sensing unit of a nuclear magnetic resonance gyroscope (NMR gyroscope) is the atomic gas cell. The carrier angular rate is measured by measuring the resonant frequency drift of inert gas atoms in a magnetic field. The longitudinal relaxation time of the inert gas describes the time required for the longitudinal magnetization of the spin system to return to equilibrium after excitation. It reflects the spin polarization of the inert gas and is related to the signal-to-noise ratio of the NMR gyroscope. Therefore, the longitudinal relaxation time is a crucial parameter for miniaturized atomic gas cells, and measuring it helps evaluate cell performance and gyroscope operating status.

[0003] Common methods for measuring longitudinal relaxation time include the saturation recovery method and the inversion recovery method. The saturation recovery method uses multiple π / 2 pulses to saturate the longitudinal magnetization, acquires signals after different recovery times, and fits the longitudinal relaxation time using an exponential curve of signal intensity recovery over time. The saturation recovery method is fast but sensitive to transverse relaxation time and has a low signal-to-noise ratio. The inversion recovery method applies a π pulse, followed by an inversion time and then another π / 2 pulse, fitting the longitudinal relaxation time by changing the inversion time and signal intensity variation. The inversion recovery method is highly accurate but requires a longer time than the saturation recovery method and is sensitive to the non-uniformity of the radio frequency field. For nuclear magnetic resonance gyroscopes, although magnetic shielding and active magnetic compensation are used to suppress stray magnetic fields, due to their miniaturized design and high integration, a small amount of randomly pointing residual magnetism still exists at the atomic gas cell location, making the spin precession axis uncertain and resulting in inaccurate measurements. Another method involves providing a static magnetic field along the pump light direction as a defined precession axis, and providing a pulsed magnetic field perpendicular to the pump light direction to induce the nuclear spin to precess around the main magnetic field. However, this method has a smaller transverse component and requires more sophisticated detection equipment. Summary of the Invention

[0004] This invention provides a device and method for measuring the longitudinal relaxation time of a miniaturized atomic gas cell, solving the problems of low measurement accuracy, uncertain nuclear spin precession axis orientation, and small detection signal in existing methods.

[0005] Technical solution: A measuring device for the longitudinal relaxation time of a miniaturized atomic gas cell, comprising: Miniaturized atomic gas chamber; The pump light and optical path structure includes a pump laser, a pump polarizer, a quarter-wave plate, and a blackbody arranged sequentially along the Z-axis. The probe light and optical path structure includes a probe light laser, a probe light polarizer, a half-wave plate, a first right-angle prism reflector, a second right-angle prism reflector, a polarizing beam splitter, a first photodetector, and a second photodetector arranged sequentially along the probe light path. The temperature control system includes a non-magnetic heating device installed on both sides of the miniaturized atomic gas chamber and a temperature control circuit. The magnetic field control system includes a double-layer magnetic shield, a triaxial magnetic field coil installed outside the miniaturized atomic gas chamber, and a magnetic field control circuit. The signal processing system is used to block, differentiate, and amplify the output signal of the photodetector, realize the precession signal detection based on the Faraday rotation effect, and complete the fitting calculation of the longitudinal relaxation time.

[0006] Furthermore, the output laser frequencies of the pump laser and the probe laser are the transition frequencies of alkali metal atoms. After the pump light is output from the laser, it is converted into left-handed circularly polarized light by a polarizer and a quarter-wave plate, and then incident on the atomic gas cell along the z-axis to achieve the polarization preparation of alkali metal atoms. The outgoing light is absorbed by a blackbody to avoid stray light interference. After the probe light is output from the laser, it is converted into linearly polarized light by a polarizer and a half-wave plate, and then incident on the atomic gas cell along the y-axis after passing through a right-angle prism reflector to achieve the detection of the spin magnetic moment of the inert gas. The outgoing light is differentially detected by a photodetector after passing through a right-angle prism reflector and a polarizing beam splitter.

[0007] Furthermore, the non-magnetic heating device is connected in series with the temperature control circuit to achieve low electromagnetic noise and high-precision closed-loop temperature control of the atomic gas chamber.

[0008] Furthermore, the double-layer magnetic shield isolates the external magnetic field; the triaxial magnetic field coil compensates for the remaining internal magnetic field and provides a uniform magnetic field at the atomic gas chamber; and the magnetic field control circuit achieves high-precision synchronous control of the triaxial magnetic field coil through a high-precision clock.

[0009] A method for measuring the longitudinal relaxation time of a miniaturized atomic gas chamber, the method being performed using the aforementioned measuring device for the longitudinal relaxation time of a miniaturized atomic gas chamber, the method comprising: S1, the temperature control system prepares the atomic gas cell to the working temperature, adjusts the temperature and current of the pump laser and the probe laser to align them with the D2 and D1 transition frequencies of the alkali metal atoms, and realizes the preparation of alkali metal polarization and the detection of inert gas magnetic moments. S2, after the working temperature and laser stabilize, set the static magnetic field strength along the z-axis to provide the nuclear spin precession axis along the z-axis direction; S3. After the spin magnetic moment returns to the equilibrium state, turn off the z-axis static magnetic field and at the same time provide a pulsed magnetic field along the x-axis to make the spin magnetic moment rotate around the x-axis by a certain angle. After the pulsed magnetic field ends, turn on the z-axis static magnetic field again. S4. After waiting for the first given time, the static magnetic field along the z-axis is turned off, while a static magnetic field is provided along the x-axis to cause the spin magnetic moment that is precessing along the z-axis to precess along the x-axis, forming a transverse projection of the magnetic moment in the y-axis direction. The precession is detected by the probe light through balanced differential detection. The precession signal with a length of the second given time is recorded, and the precession signal is fitted by the free induction decay curve to obtain the initial amplitude and transverse relaxation time of the inert gas. S5, record the first given time and the initial amplitude as a sample pair, turn on the static magnetic field in the z-axis, turn off the static magnetic field in the x-axis direction, adjust the first given time with the first given time step, and return to S3 and S4 to record new sample pairs until the number of sample pairs reaches 100 pairs. Fit the sample pair group in an exponential form to obtain the longitudinal relaxation time of the inert gas.

[0010] Furthermore, in S1, the operating temperature of the air chamber is 120°C~130°C.

[0011] Furthermore, in S2, the static magnetic field strength along the z-axis is 20µT; in S3, the pulsed magnetic field along the x-axis is a π-pulse magnetic field with a magnetic field strength of 10µT; and in S4, the static magnetic field strength along the x-axis is 10µT.

[0012] Furthermore, in S4, the first given time is a variable with an initial value of 500ms, which is subsequently adjusted according to the first given time step, and the second given time is 20s; in S5, the first given time step is 500ms.

[0013] Furthermore, the initial amplitude and transverse relaxation time of the inert gas can be obtained by fitting the free induction decay curve:

[0014] In the formula, M y ( t ) represents the transverse y-axis component of the spin magnetic moment of the inert gas, i.e., the detected precession signal; M z ( τ ) represents the initial amplitude of the precession about the x-axis, which is the longitudinal component of the spin magnetic moment of the inert gas along the z-axis. τ Give a time for number one; T 2 represents the lateral relaxation time; f The precession frequency; φ This is the initial phase; t For time.

[0015] Furthermore, the longitudinal relaxation time of the inert gas can be obtained by fitting an exponential relationship to the sample pairs:

[0016] In the formula, M 0 represents the equilibrium value; T 1 represents the longitudinal relaxation time.

[0017] Beneficial effects: This invention provides a method for measuring the longitudinal relaxation time of a miniaturized atomic gas chamber. The method uses a z-axis static magnetic field to provide a defined initial precession axis for the nuclear spin of an inert gas, and applies a pulsed magnetic field with a fixed pulse width to reverse the nuclear spin. During the longitudinal relaxation of the nuclear spin, the nuclear spin precession axis is shifted from the z-axis to the x-axis by synchronously controlling the z-axis and x-axis static magnetic fields at given time intervals, forming a spin magnetic moment projection in the y-axis direction. The nuclear spin precession signal is detected using a probe light based on the Faraday rotation effect. By fitting a free-induction decay curve, the initial amplitude of the precession signal around the x-axis static magnetic field, i.e., the longitudinal magnetic moment intensity after a given time interval, can be obtained. Based on the exponential relationship between the longitudinal magnetic moment intensity and the given time interval, the longitudinal relaxation time can be fitted. Compared with existing methods, the longitudinal relaxation time measurement method provided by this invention uses high-precision synchronous control of the magnetic fields of the z-axis and x-axis to make the spin magnetic moment of the inert gas nucleus precess along a given precession axis. The motion trajectory is clear, the projection in the direction of the probe light is large, the signal-to-noise ratio is high, and the measurement accuracy is high, making it suitable for miniaturized atomic gas chambers. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart illustrating the specific method for measuring the longitudinal relaxation time of a miniaturized atomic gas chamber. Figure 2 This is a schematic diagram of the synchronous control of the z-axis magnetic field and x-axis magnetic field in a method for measuring the longitudinal relaxation time of a miniaturized atomic gas cell. Figure 3 This is a schematic diagram of a device for measuring the longitudinal relaxation time of a miniaturized atomic gas chamber.

[0020] The reference numerals in the above figures have the following meanings: Figure 2 In this context, τ represents the given time; π represents the width of the x-axis pulse magnetic field, which is half the precession period of the inert gas.

[0021] Figure 3 In this system, 1- Miniaturized atomic gas cell; 2- Pump laser; 3- Pump polarizer; 4- Quarter-wave plate; 5- Absorbing blackbody; 6- Probe laser; 7- Probe polarizer; 8- Half-wave plate; 9- Right-angle prism reflector (number one); 10- Right-angle prism reflector (number two); 11- Polarizing beam splitter; 12- Photodetector (number one); 13- Photodetector (number two); 14- Non-magnetic heating device; 15- Temperature control circuit; 16- Double-layer magnetic shield; 17- Triaxial magnetic field coil; 18- Magnetic field control circuit; 19- Signal processing system. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] The features and illustrative embodiments of various aspects of the present invention will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific setups and methods set forth below, but covers any improvements, substitutions, and modifications to structures, methods, and devices without departing from the spirit of the invention. Well-known structures and techniques are not shown in the drawings and the following description to avoid unnecessarily obscuring the invention.

[0024] In the description of this invention, it should be noted that the directions or positional relationships indicated by terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing and simplifying the invention, and should not be construed as limiting the invention. Furthermore, the use of ordinal numbers (e.g., "first and second," etc.) is for distinguishing objects and is not limited to this order, and should not be construed as indicating or implying relative importance.

[0025] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly, encompassing both direct connection and indirect connection via an intermediate medium. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0026] It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other, and the various embodiments can be referenced and cited in each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0027] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0028] This invention provides a device for measuring the longitudinal relaxation time of a miniaturized atomic gas cell, comprising: a miniaturized atomic gas cell; a pump beam and optical path structure, including a pump laser, a pump polarizer, a quarter-wave plate, and a blackbody; a probe beam and optical path structure, including a probe laser, a probe polarizer, a half-wave plate, a first right-angle prism reflector, a second right-angle prism reflector, a polarizing beam splitter, a first photodetector, and a second photodetector; a temperature control system, including a non-magnetic heating device and a temperature control circuit; a magnetic field control system, including a double-layer magnetic shield, a triaxial magnetic field coil, and a magnetic field control circuit; and a signal processing system for blocking, differentially dividing, and amplifying the output signal of the photodetectors, detecting precession signals based on the Faraday rotation effect, and performing fitting calculations of the longitudinal relaxation time using a computational algorithm.

[0029] Furthermore, the miniaturized atomic gas chamber is mainly used in nuclear magnetic resonance gyroscopes, and its interior is filled with alkali metal vapor, inert gas, and buffer gas. Alkali metal atoms transfer their polarization state to inert gas atoms through spin exchange collisions and are sensitive to the macroscopic magnetic moment of the inert gas; inert gas atoms are the main working atoms, the detection signal of the device is the inert gas magnetic moment precession signal, and the longitudinal relaxation time is the longitudinal relaxation time of the inert gas atoms.

[0030] Furthermore, the output laser frequencies of the pump laser and probe laser are the transition frequencies of alkali metal atoms. The pump light, after being output from the laser, is converted into left-handed circularly polarized light by a polarizer and a quarter-wave plate, and then incident along the z-axis into the atomic gas cell to achieve polarization preparation of alkali metal atoms. The outgoing light is absorbed by a blackbody to avoid stray light interference. The probe light, after being output from the laser, is converted into linearly polarized light by a polarizer and a half-wave plate, and then incident along the y-axis into the atomic gas cell after passing through a right-angle prism reflector to detect the spin magnetic moment of the inert gas. The outgoing light, after passing through a right-angle prism reflector and a polarizing beam splitter, is differentially detected by a photodetector.

[0031] Furthermore, the non-magnetic heating device is connected in series with the temperature control circuit to achieve low electromagnetic noise and high-precision closed-loop temperature control of the atomic gas chamber.

[0032] Furthermore, the double-layer magnetic shield isolates the external magnetic field; the triaxial magnetic field coil compensates for the remaining internal magnetic field and provides a uniform magnetic field at the atomic gas chamber; and the magnetic field control circuit achieves high-precision synchronous control of the triaxial magnetic field coil through a high-precision clock.

[0033] This invention also provides a method for measuring the longitudinal relaxation time of a miniaturized atomic gas cell. The method is executed using the aforementioned measuring device for the longitudinal relaxation time of a miniaturized atomic gas cell. The method includes: S1, a temperature control system prepares the atomic gas cell to the operating temperature, and adjusts the temperature and current of the pump laser and probe laser to align them with the D2 and D1 transition frequencies of alkali metal atoms, thereby achieving alkali metal polarization preparation and inert gas magnetic moment detection; S2, after the operating temperature and laser stabilize, the z-axis static magnetic field strength is set, providing a nuclear spin precession axis along the z-axis direction; S3, after the spin magnetic moment returns to equilibrium, the z-axis static magnetic field is turned off, and simultaneously a pulsed magnetic field is provided along the x-axis direction, causing the spin magnetic moment to rotate around the x-axis by a certain angle. After the pulsed magnetic field ends... Reactivate the z-axis static magnetic field; S4, after waiting for the first given time, deactivate the z-axis static magnetic field, and simultaneously provide a static magnetic field along the x-axis to redirect the spin magnetic moment precessing along the z-axis to precessing along the x-axis, forming a transverse projection of the magnetic moment in the y-axis direction. Precession is detected by the probe light through balanced differential detection, and a precession signal of length two given time is recorded. The precession signal is fitted by the free induction decay curve to obtain the initial amplitude and transverse relaxation time of the inert gas; S5, record the first given time and the initial amplitude as a sample pair, adjust the first given time step by the first given time, and repeat S3 and S4 to record new sample pairs until the number of sample pairs reaches 100 pairs. The longitudinal relaxation time of the inert gas is obtained by fitting the sample pair group in an exponential form.

[0034] Furthermore, in S1, the operating temperature of the air chamber is 120°C~130°C.

[0035] Furthermore, in S2, the static magnetic field strength along the z-axis is 20µT; in S3, the pulsed magnetic field along the x-axis is a π-pulse magnetic field with a magnetic field strength of 10µT; and in S4, the static magnetic field strength along the x-axis is 10µT.

[0036] Furthermore, in S4, the first given time is a variable with an initial value of 500ms, which is subsequently adjusted according to the first given time step, and the second given time is 20s; in S5, the first given time step is 500ms.

[0037] Furthermore, the initial amplitude and transverse relaxation time of the inert gas can be obtained by fitting the free induction decay curve:

[0038] In the formula, M y ( t ) represents the transverse y-axis component of the spin magnetic moment of the inert gas, i.e., the detected precession signal; M z ( τ ) represents the initial amplitude of the precession about the x-axis, which is the longitudinal component of the spin magnetic moment of the inert gas along the z-axis. τ Give a time for number one; T 2 represents the lateral relaxation time; f The precession frequency; φ This is the initial phase; t For time.

[0039] Furthermore, the longitudinal relaxation time of the inert gas can be obtained by fitting an exponential relationship to the sample pairs:

[0040] In the formula, M 0 represents the equilibrium value; T 1 represents the longitudinal relaxation time.

[0041] Example: like Figure 1 As shown, according to a specific embodiment of the present invention, a method for measuring the longitudinal relaxation time of a miniaturized atomic gas chamber is provided. The specific steps of the method are as follows: (1) The temperature control system prepares the atomic gas cell to the working temperature, adjusts the temperature and current of the pump laser and the probe laser to align them with the transition frequency of alkali metal atoms, and realizes the preparation of alkali metal polarization and the detection of inert gas magnetic moment. (2) After the working temperature and laser stabilize, set the static magnetic field strength along the z-axis to provide the nuclear spin precession axis; (3) After the spin magnetic moment returns to the equilibrium state, the z-axis static magnetic field is turned off, and a pulsed magnetic field is provided along the x-axis to make the spin magnetic moment rotate around the x-axis by a certain angle. After the pulsed magnetic field ends, the z-axis static magnetic field is turned on again. (4) After waiting for the given time, the static magnetic field along the z-axis is turned off, and a static magnetic field is provided along the x-axis to cause the spin magnetic moment that is precessing along the z-axis to precess along the x-axis, forming a transverse projection of the magnetic moment in the y-axis direction. The precession is detected by the probe light through balanced differential detection, and a precession signal with a length of 20s is recorded. The precession signal is fitted by the free induction decay curve to obtain the initial amplitude and transverse relaxation time of the inert gas. (5) Record the first given time and the initial amplitude as a sample pair, adjust the first given time step with the first given time step, and repeat S3 and S4 to record new sample pairs until the number of sample pairs reaches 100 pairs. Fit the sample pair group in exponential form to obtain the longitudinal relaxation time of the inert gas.

[0042] Specifically, in this invention, the working temperature of the gas chamber is 120°C~130°C; the z-axis static magnetic field strength is 20µT; in step (3), the x-axis pulse magnetic field is a π-pulse magnetic field with a magnetic field strength of 10µT; in step (4), the x-axis static magnetic field strength is 10µT. A schematic diagram of the synchronous control of the z-axis magnetic field and the x-axis magnetic field is shown below. Figure 2 As shown.

[0043] Furthermore, to ensure fitting accuracy, the first given time step is a variable, with an initial value of 500ms, and subsequent steps are adjusted according to the first given time step of 500ms.

[0044] In this invention, M y ( t ) represents the transverse y-axis component of the spin magnetic moment of the inert gas, i.e., the detected precession signal; M z ( τ ) represents the initial amplitude of the precession about the x-axis, which is the longitudinal component of the spin magnetic moment of the inert gas along the z-axis. τ Give a time for number one; T 2 represents the lateral relaxation time; f The precession frequency; φ This is the initial phase; t Let be the time. The initial amplitude can be obtained by fitting the detected precession signal to the free induction decay curve as shown in the following formula.

[0045]

[0046] Furthermore, M 0 represents the equilibrium value; T 1 represents the longitudinal relaxation time. The longitudinal relaxation time can be obtained by fitting a sample pair according to the exponential relationship between the initial amplitude and the given time as shown in the following formula.

[0047]

[0048] like Figure 3 As shown, according to a specific embodiment of the present invention, a measuring device for the longitudinal relaxation time of a miniaturized atomic gas chamber is provided. The device uses the method described above for measuring the longitudinal relaxation time of a miniaturized atomic gas chamber to measure the longitudinal relaxation time of an inert gas. The device includes: (1) Miniaturized atomic gas chamber 1: mainly used in nuclear magnetic resonance gyroscopes, its interior is filled with alkali metal vapor. 87 Rb, inert gas isotopes 131 Xe / 129 Xe and the buffer gas N2. Alkali metal atoms 87 Rb transfers the polarization state to Rb through spin-exchange collisions. 131 Xe / 129 Xe, and sensitive 131 Xe / 129 The macroscopic magnetic moment of Xe; 131 Xe / 129 Xe is the primary working atom, and the detection signal of the device is... 131 Xe / 129 Xe magnetic moment precession signal, longitudinal relaxation time 131 Xe / 129 The longitudinal relaxation time of Xe.

[0049] (2) The pump beam and optical path structure include a pump laser 2, a pump polarizer 3, a quarter-wave plate 4, and a blackbody 5; the probe beam and optical path structure include a probe laser 6, a probe polarizer 7, a half-wave plate 8, a first right-angle prism reflector 9, a second right-angle prism reflector 10, a polarizing beam splitter 11, a first photodetector 12, and a second photodetector 13. The output laser frequency of the pump laser 2 is... 87 The D1 line of Rb is 794.98nm, and the output laser frequency of the probe laser 6 is... 87 The D2 line of Rb is 780.24 nm. The pump light, output from laser 2, is converted into left-handed circularly polarized light by polarizer 3 and quarter-wave plate 4, and then incident along the z-axis into atomic gas cell 1, achieving [the desired effect]. 87 The polarization preparation of Rb involves the output light being absorbed by a blackbody 5 to avoid stray light interference. The probe light, output from a laser 6, is converted into linearly polarized light by a polarizer 7 and a half-wave plate 8. After passing through a right-angle prism reflector 9, it enters the atomic gas cell along the y-axis, achieving the polarization of Rb. 131 Xe / 129 The Xe spin magnetic moment is detected by the outgoing light passing through the right-angle prism reflector 10 and the polarizing beam splitter 11, and then by the photodetectors 12 and 13 for differential detection.

[0050] (3) Temperature control system, including non-magnetic heating device 14 and temperature control circuit 15. Non-magnetic heating device 14 uses two non-magnetic heating resistors, one of which is equipped with a PT1000 thermistor. The non-magnetic heating resistors are symmetrically distributed on both sides of atomic gas chamber 1 along the x-axis and connected in series with temperature control circuit 15 to realize low electromagnetic noise and high-precision closed-loop temperature control of atomic gas chamber 1.

[0051] (4) Magnetic field control system, including a double-layer magnetic shield 16, a three-axis magnetic field coil 17 and a magnetic field control circuit 18. The double-layer magnetic shield 16 is made of permalloy to isolate the magnetic field from the external environment; the three-axis magnetic field coil 17 is a non-uniform solenoid to compensate for the residual magnetic field inside and to provide a uniform magnetic field at the atomic gas chamber 1; the magnetic field control circuit 18 achieves high-precision synchronous control of the three-axis magnetic field coil 17 through a high-precision clock.

[0052] (5) Signal processing system, used to block, differentiate and amplify the output signals of photodetectors 12 and 13, realize the precession signal detection based on Faraday rotation effect, and complete the fitting calculation of longitudinal relaxation time by calculation algorithm.

[0053] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A device for measuring the longitudinal relaxation time of a miniaturized atomic gas cell, characterized in that, include: Miniaturized atomic gas chamber; The pump light and optical path structure includes a pump laser, a pump polarizer, a quarter-wave plate, and a blackbody arranged sequentially along the Z-axis. The probe light and optical path structure includes a probe light laser, a probe light polarizer, a half-wave plate, a first right-angle prism reflector, a second right-angle prism reflector, a polarizing beam splitter, a first photodetector, and a second photodetector arranged sequentially along the probe light path. The temperature control system includes a non-magnetic heating device installed on both sides of the miniaturized atomic gas chamber and a temperature control circuit. The magnetic field control system includes a double-layer magnetic shield, a triaxial magnetic field coil installed outside the miniaturized atomic gas chamber, and a magnetic field control circuit. The signal processing system is used to block, differentiate, and amplify the output signal of the photodetector, realize the precession signal detection based on the Faraday rotation effect, and complete the fitting calculation of the longitudinal relaxation time.

2. The measuring device for longitudinal relaxation time of a miniaturized atomic gas cell according to claim 1, characterized in that, The output laser frequencies of the pump laser and probe laser are the transition frequencies of alkali metal atoms. After being output from the laser, the pump light is converted into left-handed circularly polarized light by a polarizer and a quarter-wave plate, and then incident on the atomic gas cell along the z-axis to achieve the polarization preparation of alkali metal atoms. The outgoing light is absorbed by a blackbody to avoid stray light interference. After being output from the laser, the probe light is converted into linearly polarized light by a polarizer and a half-wave plate, and then incident on the atomic gas cell along the y-axis after passing through a right-angle prism reflector to achieve the detection of the spin magnetic moment of the inert gas. The outgoing light is differentially detected by a photodetector after passing through a right-angle prism reflector and a polarizing beam splitter.

3. The measuring device for longitudinal relaxation time of a miniaturized atomic gas cell according to claim 2, characterized in that, The non-magnetic heating device is connected in series with the temperature control circuit to achieve low electromagnetic noise and high-precision closed-loop temperature control of the atomic gas chamber.

4. The measuring device for longitudinal relaxation time of a miniaturized atomic gas cell according to claim 3, characterized in that, The double-layer magnetic shield isolates the magnetic field from the external environment; the triaxial magnetic field coil compensates for the residual magnetic field inside and provides a uniform magnetic field at the atomic gas chamber; the magnetic field control circuit achieves high-precision synchronous control of the triaxial magnetic field coil through a high-precision clock.

5. A method for measuring the longitudinal relaxation time of a miniaturized atomic gas chamber, said method being performed by means of the measuring device for measuring the longitudinal relaxation time of a miniaturized atomic gas chamber according to any one of claims 1-4, said method comprising: S1, the temperature control system prepares the atomic gas cell to the working temperature, adjusts the temperature and current of the pump laser and the probe laser to align them with the D2 and D1 transition frequencies of the alkali metal atoms, and realizes the preparation of alkali metal polarization and the detection of inert gas magnetic moments. S2, after the working temperature and laser stabilize, set the static magnetic field strength along the z-axis to provide the nuclear spin precession axis along the z-axis direction; S3. After the spin magnetic moment returns to the equilibrium state, turn off the z-axis static magnetic field and at the same time provide a pulsed magnetic field along the x-axis to make the spin magnetic moment rotate around the x-axis by a certain angle. After the pulsed magnetic field ends, turn on the z-axis static magnetic field again. S4. After waiting for the first given time, the static magnetic field along the z-axis is turned off, while a static magnetic field is provided along the x-axis to cause the spin magnetic moment that is precessing along the z-axis to precess along the x-axis, forming a transverse projection of the magnetic moment in the y-axis direction. The precession is detected by the probe light through balanced differential detection. The precession signal with a length of the second given time is recorded, and the precession signal is fitted by the free induction decay curve to obtain the initial amplitude and transverse relaxation time of the inert gas. S5, record the first given time and the initial amplitude as a sample pair, turn on the static magnetic field in the z-axis, turn off the static magnetic field in the x-axis direction, adjust the first given time with the first given time step, and return to S3 and S4 to record new sample pairs until the number of sample pairs reaches 100 pairs. Fit the sample pair group in an exponential form to obtain the longitudinal relaxation time of the inert gas.

6. The method according to claim 5, characterized in that, In S1, the working temperature of the air chamber is 120°C~130°C.

7. The method according to claim 5, characterized in that, In S2, the static magnetic field strength along the z-axis is 20µT; in S3, the pulsed magnetic field along the x-axis is a π-pulse magnetic field with a strength of 10µT; in S4, the static magnetic field strength along the x-axis is 10µT.

8. The method according to claim 5, characterized in that, In S4, the first given time is a variable, with an initial value of 500ms, and is subsequently adjusted according to the first given time step. The second given time is 20s. In S5, the first given time step is 500ms.

9. The method according to claim 5, characterized in that, The initial amplitude and transverse relaxation time of the inert gas can be obtained by fitting the free induction decay curve. In the formula, M y ( t ) represents the transverse y-axis component of the spin magnetic moment of the inert gas, i.e., the detected precession signal; M z ( τ ) represents the initial amplitude of the precession about the x-axis, which is the longitudinal component of the spin magnetic moment of the inert gas along the z-axis. τ Give a time for number one; T 2 represents the lateral relaxation time; f The precession frequency; φ This is the initial phase; t For time.

10. The method according to claim 6, characterized in that, The longitudinal relaxation time of the inert gas can be obtained by fitting an exponential relationship to the sample pairs: In the formula, M 0 represents the equilibrium value; T 1 represents the longitudinal relaxation time.

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