Methods and systems for measuring nuclear spin relaxation time in spin-exchange optically pumped systems

Abstract

This invention discloses a method and system for measuring the nuclear spin relaxation time of a spin-exchange light-pumped system. The method includes: applying a static magnetic field to an atomic gas cell and emitting circularly polarized light until a time threshold is reached; stopping the emission of circularly polarized light to allow the alkali metal atoms to spin polarize along with the spin polarization of the inert gas atoms; when applying an alternating magnetic field and a modulation magnetic field to the atomic gas cell, emitting linearly polarized light and converting the first outgoing polarized light passing through the atomic gas cell into a first electrical signal and demodulating it; obtaining the longitudinal relaxation time of the nuclear spin by fitting the amplitude of the demodulated first spin polarization component signal using an exponential function; and when applying a pulsed magnetic field and a modulation magnetic field to the atomic gas cell, emitting linearly polarized light and converting the second outgoing polarized light passing through the atomic gas cell into a second electrical signal and demodulating it; obtaining the transverse relaxation time of the nuclear spin by fitting the amplitude of the demodulated second spin polarization component signal using an exponential function. This invention can eliminate measurement errors caused by the non-uniform distribution of pump light.

Description

Technical Field

[0001] This invention relates to the field of atomic sensor technology, and in particular to a method and system for measuring nuclear spin relaxation time in a spin-exchange optically pumped system. Background Technology

[0002] Spin-exchange optically pumped systems typically refer to mixed systems containing alkali metal vapor and inert gases with non-zero nuclear spin magnetic moments. The alkali metal vapor possesses electron spin, while the inert gas possesses nuclear spin. Spin-exchange optically pumped systems can achieve polarization of electron and nuclear spins through spin-exchange optical pumping. These systems have significant applications in fields such as spin gyroscopes, spin magnetometers, fundamental physics detection devices, and magnetic resonance imaging.

[0003] In gaseous spin atomic sensors based on alkali metal atom-inert gas atom coupled spin systems, a transparent atomic chamber is typically used to seal a certain amount of alkali metal and inert gas. As the core component of the atomic sensor, the performance of the atomic chamber is a decisive factor in the limiting performance of the atomic sensor. The characterization of nuclear spin relaxation time plays a key role in the fabrication and development of the atomic chamber. Nuclear spin relaxation time includes nuclear spin longitudinal relaxation time and nuclear spin transverse relaxation time, which are related to factors such as the microscopic properties of the inner wall of the atomic chamber, magnetic field gradient, alkali metal vapor density, and pump light gradient.

[0004] In existing technologies, methods for measuring nuclear spin longitudinal relaxation time typically include the inversion recovery method and the piecewise Fourier transform method, while methods for measuring nuclear spin transverse relaxation time typically include the free induction decay method and the amplitude fitting method. Both existing methods require continuous pumping of alkali metal atoms with pump light. However, in actual measurements, the pump light cannot maintain a uniform distribution within the atomic gas cell. This is partly because the pump light typically exhibits a Gaussian distribution across its cross-section, and partly because it gradually attenuates due to absorption by the alkali metal vapor during propagation. This non-uniform distribution of the pump light leads to non-uniform polarization of the alkali metal atoms, resulting in significant measurement errors and making it impossible to accurately measure the nuclear spin relaxation time of spin-exchange-pumped systems. Summary of the Invention

[0005] This invention provides a method and system for measuring the nuclear spin relaxation time of a spin-exchange optically pumped system, thereby solving the technical problem that existing technologies cannot accurately measure the nuclear spin relaxation time of a spin-exchange optically pumped system. By measuring the nuclear spin relaxation time of the spin-exchange optically pumped system after stopping the emission of circularly polarized light into the atomic gas cell, the measurement error caused by the non-uniform distribution of the pump light can be eliminated, thus enabling accurate measurement of the nuclear spin relaxation time of the spin-exchange optically pumped system.

[0006] To address the aforementioned technical problems, the first aspect of this invention provides a method for measuring the nuclear spin relaxation time of a spin-exchange optically pumped system, comprising the following steps:

[0007] Based on a preset input DC current value, a static magnetic field is applied to the atomic gas cell, and circularly polarized light in the same direction as the static magnetic field is emitted into the atomic gas cell to spin polarize the alkali metal atoms and inert gas atoms in the atomic gas cell.

[0008] When the irradiation time of the circularly polarized light reaches a preset time threshold, the emission of the circularly polarized light into the atomic gas cell is stopped, so that the alkali metal atoms are spin polarized along with the spin polarization of the inert gas atoms;

[0009] When an alternating magnetic field is applied to the atomic gas cell to induce nuclear magnetic resonance in the spin-polarized inert gas atoms, and a modulation magnetic field that resonates with the alkali metal atoms is applied to the atomic gas cell, linearly polarized light in the same direction as the alternating magnetic field is emitted into the atomic gas cell, and the first outgoing polarized light passing through the atomic gas cell is obtained; wherein, the direction of applying the alternating magnetic field is different from the direction of applying the static magnetic field;

[0010] The first emitted polarized light is converted into a first electrical signal, and the first electrical signal is demodulated according to the preset static magnetic field strength component value, the gyromagnetic ratio of the alkali metal atom nucleus spin, the modulation magnetic field strength, the modulation magnetic field frequency, the spin exchange rate between the alkali metal atom and the inert gas atom, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the first spin polarization component signal of the alkali metal atom.

[0011] The longitudinal relaxation time of the nuclear spin is obtained by fitting the amplitude of the first spin polarization component signal with a preset first exponential function.

[0012] When a pulsed magnetic field and a modulated magnetic field that resonates with the alkali metal atoms are applied to the atomic gas cell, linearly polarized light in the same direction as the pulsed magnetic field is emitted into the atomic gas cell to obtain a second outgoing polarized light that has passed through the atomic gas cell; wherein, the direction of the applied pulsed magnetic field is different from the direction of the applied static magnetic field;

[0013] The second emitted polarized light is converted into a second electrical signal, and the second electrical signal is demodulated according to the preset pump rate, the intensity of the modulation magnetic field, the frequency of the modulation magnetic field, the gyromagnetic ratio of the spin of the alkali metal atom nucleus, and the initial magnetization vector of the spin of the inert gas atom when the circularly polarized light stops, to obtain the amplitude of the second spin polarization component signal of the alkali metal atom.

[0014] The nuclear spin transverse relaxation time is obtained by fitting the amplitude of the second spin polarization component signal to a preset second exponential function.

[0015] As a preferred embodiment, the step of converting the first emitted polarized light into a first electrical signal, and demodulating the first electrical signal according to a preset static magnetic field strength component value, the gyromagnetic ratio of the alkali metal atom nuclei, the modulation magnetic field strength, the modulation magnetic field frequency, the spin exchange rate between the alkali metal atom and the inert gas atom, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the first spin polarization component signal of the alkali metal atom, specifically includes the following steps:

[0016] The first emitted polarized light is transmitted to a balanced photodetector via a polarizer and a Wollaston prism.

[0017] The first emitted polarized light is converted into a first electrical signal by the balanced photodetector and transmitted to the signal processing module.

[0018] The signal processing module demodulates the first electrical signal based on preset static magnetic field strength component values, the gyromagnetic ratio of the alkali metal atom nuclei, the modulation magnetic field strength, the modulation magnetic field frequency, the spin exchange rate between the alkali metal atom and the inert gas atom, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the first spin polarization component signal of the alkali metal atom.

[0019] As a preferred embodiment, the step of demodulating the first electrical signal based on preset static magnetic field strength component values, the gyromagnetic ratio of the alkali metal atom nuclei, the modulation magnetic field strength, the modulation magnetic field frequency, the spin exchange rate between the alkali metal atom and the inert gas atom, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the first spin polarization component signal of the alkali metal atom, specifically includes the following steps:

[0020] Based on the preset static magnetic field strength component value, the gyromagnetic ratio of the alkali metal atom nuclei, the modulation magnetic field strength, the modulation magnetic field frequency, the spin exchange rate between the alkali metal atom and the inert gas atom, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, the first electrical signal is demodulated using the following expression to obtain the amplitude of the first spin polarization component signal of the alkali metal atom:

[0021]

[0022] in, B represents the amplitude of the first spin polarization component signal; yIndicates the value of the static magnetic field strength component; γ Rb J1 represents the first-order Bessel function; J2 represents the second-order Bessel function; J0 represents the zeroth-order Bessel function; R represents the gyromagnetic ratio of the alkali metal nuclei; J1 represents the first-order Bessel function; J2 represents the second-order Bessel function; J0 represents the zeroth-order Bessel function; R represents the first-order Bessel function. se T1 represents the spin exchange rate between the alkali metal atoms and the inert gas atoms; M represents the longitudinal relaxation time of the nuclear spin; Xe0 The vector represents the initial magnetization of the spins of the inert gas atoms when the circularly polarized light stops; t represents any moment after the circularly polarized light stops.

[0023] The independent variables of the zeroth-order Bessel function, the first-order Bessel function, and the second-order Bessel function are all: B c ω represents the intensity of the modulated magnetic field; c This indicates the frequency of the modulated magnetic field.

[0024] As a preferred embodiment, the step of fitting the amplitude of the first spin polarization component signal using a preset first exponential function to obtain the nuclear spin longitudinal relaxation time specifically includes the following steps:

[0025] Through the preset first exponential function: The amplitude of the first spin polarization component signal is fitted to obtain the nuclear spin longitudinal relaxation time; where a0 and a1 represent the first fitting parameter and the second fitting parameter, respectively.

[0026] As a preferred embodiment, the step of converting the second emitted polarized light into a second electrical signal, and demodulating the second electrical signal according to a preset pump rate, the modulation magnetic field strength, the modulation magnetic field frequency, the gyromagnetism ratio of the alkali metal atom nuclei, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the second spin polarization component signal of the alkali metal atom, specifically includes the following steps:

[0027] The second outgoing polarized light is transmitted to a balanced photodetector via a polarizer and a Wollaston prism.

[0028] The second emitted polarized light is converted into a second electrical signal by the balanced photodetector and transmitted to the signal processing module.

[0029] The signal processing module demodulates the second electrical signal based on the preset pump rate, the modulation magnetic field strength, the modulation magnetic field frequency, the gyromagnetic ratio of the alkali metal nuclei spin, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the second spin polarization component signal of the alkali metal atom.

[0030] As a preferred embodiment, the step of demodulating the second electrical signal based on a preset pump rate, the modulation magnetic field strength, the modulation magnetic field frequency, the gyromagnetism ratio of the alkali metal atom nuclei, and the initial magnetization vector of the inert gas atom spins when the circularly polarized light stops, to obtain the amplitude of the second spin polarization component signal of the alkali metal atom, specifically includes the following steps:

[0031] Based on the preset pump rate, the modulation magnetic field strength, the modulation magnetic field frequency, the gyromagnetism ratio of the alkali metal atom nuclei, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, the second electrical signal is demodulated using the following expression to obtain the amplitude of the second spin polarization component signal of the alkali metal atom:

[0032]

[0033] in, R represents the amplitude of the second spin polarization component signal; P J1 represents the pump rate; J0 represents the first-order Bessel function; T2 represents the nuclear spin transverse relaxation time; M represents the pump rate; J1 represents the first-order Bessel function; J0 represents the zero-order Bessel function; T2 represents the nuclear spin transverse relaxation time; M represents the nuclear spin transverse relaxation time; M represents the nuclear spin transverse relaxation time; T2 ... Xe0 The vector represents the initial magnetization of the inert gas atoms' spins when the circularly polarized light stops; t represents any moment after the circularly polarized light stops; i represents the imaginary unit; ω Xe This represents the spin magnetic resonance frequency of inert gas atoms;

[0034] The independent variables of the zeroth-order Bessel function and the first-order Bessel function are both: γ Rb B represents the gyromagnetic ratio of the nuclei of the alkali metal atoms. c ω represents the intensity of the modulated magnetic field; c This indicates the frequency of the modulated magnetic field.

[0035] As a preferred embodiment, the step of fitting the amplitude of the second spin polarization component signal using a preset second exponential function to obtain the nuclear spin transverse relaxation time specifically includes the following steps:

[0036] Through a preset second exponential function: The nuclear spin transverse relaxation time is obtained by fitting the amplitude of the second spin polarization component signal; where b0 and b1 represent the third and fourth fitting parameters, respectively.

[0037] As a preferred embodiment, before inputting a DC current into the static magnetic field coils located on both sides of the atomic gas chamber according to a preset current value, the method further includes the following steps:

[0038] The atomic gas chamber is heated to a preset target temperature by a preset heating module.

[0039] As a preferred embodiment, the direction in which the alternating magnetic field is applied is perpendicular to the direction in which the static magnetic field is applied; the direction in which the pulsed magnetic field is applied is perpendicular to the direction in which the static magnetic field is applied.

[0040] The second aspect of the present invention provides a nuclear spin relaxation time measurement system for a spin-switched optical pumping system, which applies the nuclear spin relaxation time measurement method for a spin-switched optical pumping system as described in any of the first aspects, including an atomic gas cell, a first coil, a circularly polarized light emission module, a second coil, a linearly polarized light emission module, and a signal processing component;

[0041] The first coil is located on both sides of the atomic gas cell and is used to apply a static magnetic field to the atomic gas cell based on a preset input DC current value. The circularly polarized light emission module is used to emit circularly polarized light in the same direction as the static magnetic field into the atomic gas cell so as to spin polarize the alkali metal atoms and inert gas atoms in the atomic gas cell.

[0042] The circularly polarized light emission module is also used to stop emitting the circularly polarized light into the atomic gas cell when the irradiation time of the circularly polarized light reaches a preset time threshold, so that the alkali metal atoms are spin polarized along with the spin polarization of the inert gas atoms;

[0043] When the second coil is used to apply an alternating magnetic field to the atomic gas cell to induce nuclear magnetic resonance in the spin-polarized inert gas atoms, and the first coil is used to apply a modulated magnetic field that resonates with the alkali metal atoms to the atomic gas cell, the linearly polarized light emission module is used to emit linearly polarized light in the same direction as the alternating magnetic field into the atomic gas cell; wherein, the direction of applying the alternating magnetic field is different from the direction of applying the static magnetic field;

[0044] The signal processing component is used to acquire the first emitted polarized light passing through the atomic gas cell; convert the first emitted polarized light into a first electrical signal, and demodulate the first electrical signal according to a preset static magnetic field strength component value, the gyromagnetic ratio of the alkali metal atom nucleus spin, the modulation magnetic field strength, the modulation magnetic field frequency, the spin exchange rate between the alkali metal atom and the inert gas atom, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the first spin polarization component signal of the alkali metal atom; fit the amplitude of the first spin polarization component signal using a preset first exponential function to obtain the nuclear spin longitudinal relaxation time;

[0045] When the second coil is used to apply a pulsed magnetic field to the atomic gas cell, and the first coil is used to apply a modulated magnetic field that resonates with the alkali metal atoms to the atomic gas cell, the linearly polarized light emission module is used to emit linearly polarized light in the same direction as the alternating magnetic field into the atomic gas cell; wherein, the direction of applying the pulsed magnetic field is different from the direction of applying the static magnetic field;

[0046] The signal processing component is used to acquire the second emitted polarized light passing through the atomic gas cell; convert the second emitted polarized light into a second electrical signal, and demodulate the second electrical signal according to a preset pump rate, the intensity of the modulation magnetic field, the frequency of the modulation magnetic field, the gyromagnetic ratio of the alkali metal atom nucleus spin, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the second spin polarization component signal of the alkali metal atom; and fit the amplitude of the second spin polarization component signal using a preset second exponential function to obtain the nuclear spin transverse relaxation time.

[0047] Compared with the prior art, the beneficial effect of the embodiments of the present invention is that by measuring the nuclear spin relaxation time of the spin-exchange light-pumped system after stopping the emission of circularly polarized light into the atomic gas cell, the measurement error caused by the non-uniform distribution of the pump light can be eliminated, thereby enabling accurate measurement of the nuclear spin relaxation time of the spin-exchange light-pumped system. Attached Figure Description

[0048] Figure 1 This is a flowchart illustrating the method for measuring the nuclear spin relaxation time of the spin-exchange optical pumping system in an embodiment of the present invention.

[0049] Figure 2 This is a schematic diagram comparing the measurement results of nuclear spin transverse relaxation time in an embodiment of the present invention;

[0050] Figure 3 This is a schematic diagram of the nuclear spin relaxation time measurement system of the spin-exchange optical pumping system in an embodiment of the present invention;

[0051] Among them, 301 is the pump laser; 302 is the beam expander prism; 303 is the second polarizer; 304 is the first half-wave plate; 305 is the quarter-wave plate; 306 is the first coil; 307 is the second coil; 308 is the probe laser; 309 is the third polarizer; 310 is the second half-wave plate; 311 is the atomic gas cell; 312 is the first polarizer; 313 is the Wollaston prism; 314 is the balanced photodetector; 315 is the signal processing module; 316 is the heating module; 317 is the multi-layer magnetic shielding barrel; and 318 is the spare coil. Detailed Implementation

[0052] 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, and 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.

[0053] See Figure 1 The first aspect of this invention provides a method for measuring the nuclear spin relaxation time of a spin-exchange optically pumped system, comprising the following steps S1 to S8:

[0054] Step S1: Based on a preset input DC current value, a static magnetic field is applied to the atomic gas cell, and circularly polarized light in the same direction as the static magnetic field is emitted into the atomic gas cell to spin polarize the alkali metal atoms and inert gas atoms in the atomic gas cell.

[0055] Step S2: When the irradiation time of the circularly polarized light reaches a preset time threshold, stop emitting the circularly polarized light into the atomic gas cell so that the alkali metal atoms spin polarize along with the spin polarization of the inert gas atoms.

[0056] Step S3: When an alternating magnetic field is applied to the atomic gas cell to induce nuclear magnetic resonance in the spin-polarized inert gas atoms, and a modulation magnetic field that resonates with the alkali metal atoms is applied to the atomic gas cell, linearly polarized light in the same direction as the alternating magnetic field is emitted into the atomic gas cell to obtain the first outgoing polarized light passing through the atomic gas cell; wherein, the direction of applying the alternating magnetic field is different from the direction of applying the static magnetic field;

[0057] Step S4: Convert the first emitted polarized light into a first electrical signal, and demodulate the first electrical signal according to the preset static magnetic field strength component value, the gyromagnetic ratio of the alkali metal atom nucleus spin, the modulation magnetic field strength, the modulation magnetic field frequency, the spin exchange rate between the alkali metal atom and the inert gas atom, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the first spin polarization component signal of the alkali metal atom;

[0058] Step S5: Fit the amplitude of the first spin polarization component signal using a preset first exponential function to obtain the nuclear spin longitudinal relaxation time.

[0059] Step S6: When a pulsed magnetic field and a modulated magnetic field that resonates with the alkali metal atoms are applied to the atomic gas cell, linearly polarized light in the same direction as the pulsed magnetic field is emitted into the atomic gas cell to obtain a second outgoing polarized light that has passed through the atomic gas cell; wherein, the direction of applying the pulsed magnetic field is different from the direction of applying the static magnetic field;

[0060] Step S7: Convert the second emitted polarized light into a second electrical signal, and demodulate the second electrical signal according to the preset pump rate, the intensity of the modulation magnetic field, the frequency of the modulation magnetic field, the gyromagnetic ratio of the spin of the alkali metal atom nucleus, and the initial magnetization vector of the spin of the inert gas atom when the circularly polarized light stops, to obtain the amplitude of the second spin polarization component signal of the alkali metal atom.

[0061] Step S8: Fit the amplitude of the second spin polarization component signal using a preset second exponential function to obtain the nuclear spin transverse relaxation time.

[0062] In step S1, a static magnetic field is applied to the atomic gas cell based on a preset input DC current value. Pump light is emitted into the atomic gas cell via a pump laser. In the optical path of the pump light, the pump light is expanded by a beam-expanding prism, and then adjusted to linearly polarized light by a polarizer. The polarization direction of the linearly polarized light is changed to the target polarization direction by a half-wave plate, and finally adjusted to circularly polarized light by a quarter-wave plate. This achieves the emission of circularly polarized light in the same direction as the static magnetic field into the atomic gas cell, so that the alkali metal atoms in the atomic gas cell undergo spin polarization under the action of the circularly polarized light, with the polarization direction consistent with the direction of the static magnetic field. At the same time, spin exchange occurs between the polarized alkali metal atoms and the inert gas atoms in the gas cell, ultimately polarizing the nuclear spin of the inert gas atoms as well.

[0063] In step S2, when the irradiation time of circularly polarized light reaches a preset time threshold, the spin-exchange optical pumping system tends to a steady state. The alkali metal atoms and inert gas atoms in the atomic gas cell are fully polarized, and the relaxation mechanism is still in effect. At this time, the emission of circularly polarized light into the atomic gas cell is stopped to break the equilibrium state of the spin-exchange optical pumping system and induce the relaxation process. Under the action of the relaxation mechanism, the nuclear spins undergo depolarization or decoherence, and thus the macroscopic magnetic moment of the spin-exchange optical pumping system changes. The polarization of alkali metal atoms is entirely provided by nuclear spin polarization and changes with the nuclear spin polarization rate.

[0064] In step S3, when an alternating magnetic field with the same Larmor precession frequency as the inert gas atoms is applied to the atomic gas cell to induce nuclear magnetic resonance (NMR) in the spin-polarized inert gas atoms, and a modulation magnetic field resonating with the alkali metal atoms is simultaneously applied to the atomic gas cell, linearly polarized light in the same direction as the alternating magnetic field is emitted into the atomic gas cell, and the first outgoing polarized light passing through the atomic gas cell is obtained. The direction of the applied alternating magnetic field differs from the direction of the applied static magnetic field. It is worth noting that the NMR of the inert gas atoms causes a continuous change in their spin polarization direction, which in turn affects the spin polarization of the alkali metal atoms. The spin polarization of the alkali metal atoms affects the polarization state of the linearly polarized light. By monitoring the polarization state of the linearly polarized light, the NMR signal of the inert gas atoms can be monitored. The intensity of the NMR signal of the inert gas atoms under alternating magnetic fields of different frequencies is measured, and the frequency of the alternating magnetic field that produces the maximum value of the NMR signal intensity of the inert gas atoms is considered the measured value of the Larmor precession frequency of the inert gas atoms.

[0065] In step S4, the first emitted polarized light is converted into a first electrical signal. Based on preset static magnetic field strength component values, the gyromagnetic ratio of alkali metal atom nuclei, the modulation magnetic field strength, the modulation magnetic field frequency, the spin exchange rate between alkali metal atoms and inert gas atoms, and the initial magnetization vector of the inert gas atom spins when the circularly polarized light stops, the first electrical signal amplitude of the first spin polarization component of the alkali metal atom is obtained. For example, the amplitude of the first spin polarization component signal of the alkali metal atom is the amplitude of the alkali metal atom spin polarization x component.

[0066] In step S5, the amplitude of the first spin polarization component signal is fitted using a preset first exponential function to obtain the nuclear spin longitudinal relaxation time. It is worth noting that the amplitude of the first spin polarization component signal of the alkali metal atom obtained by demodulation exhibits an exponential variation with the magnetization vector of the inert gas atom spin. Therefore, the change process of the first spin polarization component signal amplitude over time can be fitted using an exponential function, thereby enabling the measurement of the nuclear spin longitudinal relaxation time.

[0067] In step S6, when a pulsed magnetic field and a modulated magnetic field that resonates with alkali metal atoms are applied to the atomic gas cell, based on longitudinal polarization, a π / 2 pulsed magnetic field is used to deflect the inert gas atoms from the direction of the static magnetic field to a plane perpendicular to the direction of the static magnetic field. Then, the spin of the inert gas atom nuclei will precess around the direction of the static magnetic field. At this time, linearly polarized light in the same direction as the pulsed magnetic field is emitted into the atomic gas cell, and a second outgoing polarized light passing through the atomic gas cell is obtained. The direction of the applied pulsed magnetic field is different from the direction of the applied static magnetic field.

[0068] In step S7, the second emitted polarized light is converted into a second electrical signal. Based on preset pump rate, modulation magnetic field strength, modulation magnetic field frequency, gyromagnetism ratio of alkali metal nuclei, and the initial magnetization vector of the inert gas atoms' spins when the circularly polarized light stops, the second electrical signal is demodulated to obtain the amplitude of the second spin polarization component signal of the alkali metal atoms. For example, the amplitude of the second spin polarization component signal of the alkali metal atoms is the amplitude of the x-component of the alkali metal atom's spin polarization.

[0069] In step S8, the amplitude of the second spin polarization component signal is fitted using a preset second exponential function to obtain the nuclear spin transverse relaxation time. It is worth noting that the amplitude of the second spin polarization component signal of the alkali metal atoms obtained by demodulation exhibits an exponential variation with the magnetization vector of the inert gas atom spin. Therefore, the change process of the second spin polarization component signal amplitude over time can be fitted using an exponential function, thereby enabling the measurement of the nuclear spin transverse relaxation time. Since applying alternating magnetic fields and pulsed magnetic fields to the atomic gas cell results in different motion characteristics of the spin-exchange optical pumping system, signals corresponding to the longitudinal and transverse relaxation times can be obtained from the signal.

[0070] It is worth noting that in this embodiment, a probe laser is used to emit probe light into the atomic gas cell. In the optical path of the probe light, a polarizer and a half-wave plate are used to adjust the probe light into linearly polarized light, thereby realizing the emission of linearly polarized light into the atomic gas cell that is in the same direction as the alternating magnetic field / pulse magnetic field.

[0071] As a preferred embodiment, the step of converting the first emitted polarized light into a first electrical signal, and demodulating the first electrical signal according to a preset static magnetic field strength component value, the gyromagnetic ratio of the alkali metal atom nuclei, the modulation magnetic field strength, the modulation magnetic field frequency, the spin exchange rate between the alkali metal atom and the inert gas atom, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the first spin polarization component signal of the alkali metal atom, specifically includes the following steps:

[0072] The first emitted polarized light is transmitted to a balanced photodetector via a polarizer and a Wollaston prism.

[0073] The first emitted polarized light is converted into a first electrical signal by the balanced photodetector and transmitted to the signal processing module.

[0074] The signal processing module demodulates the first electrical signal based on preset static magnetic field strength component values, the gyromagnetic ratio of the alkali metal atom nuclei, the modulation magnetic field strength, the modulation magnetic field frequency, the spin exchange rate between the alkali metal atom and the inert gas atom, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the first spin polarization component signal of the alkali metal atom.

[0075] As a preferred embodiment, the step of demodulating the first electrical signal based on preset static magnetic field strength component values, the gyromagnetic ratio of the alkali metal atom nuclei, the modulation magnetic field strength, the modulation magnetic field frequency, the spin exchange rate between the alkali metal atom and the inert gas atom, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the first spin polarization component signal of the alkali metal atom, specifically includes the following steps:

[0076] Based on the preset static magnetic field strength component value, the gyromagnetic ratio of the alkali metal atom nuclei, the modulation magnetic field strength, the modulation magnetic field frequency, the spin exchange rate between the alkali metal atom and the inert gas atom, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, the first electrical signal is demodulated using the following expression to obtain the amplitude of the first spin polarization component signal of the alkali metal atom:

[0077]

[0078] in, B represents the amplitude of the first spin polarization component signal; y Indicates the value of the static magnetic field strength component; γ Rb J1 represents the first-order Bessel function; J2 represents the second-order Bessel function; J0 represents the zeroth-order Bessel function; R represents the gyromagnetic ratio of the alkali metal nuclei; J1 represents the first-order Bessel function; J2 represents the second-order Bessel function; J0 represents the zeroth-order Bessel function; R represents the first-order Bessel function. se T1 represents the spin exchange rate between the alkali metal atoms and the inert gas atoms; M represents the longitudinal relaxation time of the nuclear spin; Xe0 The vector represents the initial magnetization of the spins of the inert gas atoms when the circularly polarized light stops; t represents any moment after the circularly polarized light stops.

[0079] The independent variables of the zeroth-order Bessel function, the first-order Bessel function, and the second-order Bessel function are all: B c ω represents the intensity of the modulated magnetic field; c This indicates the frequency of the modulated magnetic field.

[0080] Specifically, HAPPER et al. from Princeton University developed a perturbation model to systematically describe the spin relaxation caused by a single magnetic field gradient. According to the perturbation model developed by HAPPER et al., under conditions of uniform distribution of inert gas atoms within a spherical atomic chamber and high pressure, the longitudinal relaxation rate of the inert gas atomic nuclei's spin caused by the magnetic field gradient is:

[0081]

[0082] The resulting transverse relaxation rate of the spin of inert gas atomic nuclei is:

[0083]

[0084] Where D represents the diffusion coefficient of the inert gas atom; γ represents the gyromagnetic ratio of the nuclear spin; and Ω0 represents the gradients of the x, y, and z components of the magnetic field, respectively; R represents the nuclear spin precession frequency; and R represents the radius of the atomic gas cell.

[0085] Under high pressure and strong magnetic field conditions, the longitudinal relaxation time of inert gas atoms is mainly affected by the magnetic field gradients in the x and y directions, while the transverse relaxation is mainly affected by the magnetic field gradient in the z direction.

[0086] The equivalent magnetic field generated by the electron spin polarization of alkali metals can be expressed as:

[0087]

[0088] Where κ0≈500 is the Rb-Xe Fermi interaction enhancement factor, μ0 is the free permeability, and g s It is the Landé g-factor of electrons, g s ≈2, μ B For Bohr magneton, n Rb Where Rb is the vapor density, P Rb The z-axis component of electron spin (unit: ) )

[0089] When the pump light is spatially uneven, it leads to P Rb A spatial gradient is generated, and a magnetic field gradient is generated through formula (3), which in turn affects the nuclear spin relaxation time. One manifestation of this problem in the measurement of nuclear spin relaxation time is that the measured nuclear spin relaxation time, especially the transverse relaxation time, is heavily dependent on the pump light intensity.

[0090] The following section uses the Rb-Xe spin system as an example to introduce the principle of measuring nuclear spin relaxation time when the pump light is disconnected. In this system, let the magnetization vectors of the Rb and Xe spins be M... Rb and M Xe They satisfy the following equation:

[0091]

[0092] In the formula, For M Rb The rate of change over time, where B is the applied static magnetic field. Xe The Xe nuclear spin magnetic field sensed by Rb, where L is the magnetic field equivalent to the optical frequency shift, and R... pump R is the pump rate of the pump light, s1 is the spin direction of the pump light, and R is the pump speed. probe To determine the pump rate of the probe light, s2 represents the optical spin direction of the probe light, and R... se R is the spin exchange rate between Rb and Xe. Rb Let Rb be the relaxation rate of the spin.

[0093] When the pump laser is turned off, L and R pump Naturally, the value is zero. Under normal conditions, the probe light is linearly polarized, and its pump rate is negligible. Generally, B... Xe Since it is relatively small, we ignore it. Therefore, equation (4) can be approximated and simplified as:

[0094]

[0095] The principle for measuring nuclear spin longitudinal relaxation time is as follows:

[0096] In a typical atomic gas cell, the transverse magnetic field experienced by the spin system (i.e., the magnetic field components in the x and y directions) is much smaller than the applied static magnetic field strength, i.e., |B x,y |<<|B0|。 The frequency ω of the modulation magnetic field resonating with alkali metal atoms c Satisfy ω c >>1 / τ2, and Rb and Xe are polarized along the direction of the static magnetic field, i.e., the z-direction, so equation (5) can be rewritten as:

[0097]

[0098] In the formula, These are the unit vectors in the x, y, and z directions, respectively, M. e That is, the M mentioned above Rb . It is the longitudinal relaxation time of Rb. When B x =0, while B y When x ≠ 0, the first-order approximate solution of the x-component of rubidium polarization is:

[0099]

[0100] Among them, B y Indicates the value of the static magnetic field strength component; γ RbJ1 represents the gyromagnetic ratio of the alkali metal nuclei's spin; J2 represents the first-order Bessel function; J2 represents the second-order Bessel function; J0 represents the zero-order Bessel function; the independent variables of the zero-order Bessel function, the first-order Bessel function, and the second-order Bessel function are all: B c ω represents the intensity of the modulated magnetic field; c This indicates the frequency of the modulated magnetic field.

[0101] When the pump light is disconnected, M Xe The amplitude of the first spin polarization component signal of the alkali metal atom, obtained by demodulating the first electrical signal with exponential decay, is expressed as follows:

[0102]

[0103] in, R represents the amplitude of the first spin polarization component signal; se T1 represents the spin exchange rate between the alkali metal atoms and the inert gas atoms; M represents the longitudinal relaxation time of the nuclear spin; Xe0 The vector represents the initial magnetization of the spins of the inert gas atoms when the circularly polarized light stops; t represents any moment after the circularly polarized light stops.

[0104] As a preferred embodiment, the step of fitting the amplitude of the first spin polarization component signal using a preset first exponential function to obtain the nuclear spin longitudinal relaxation time specifically includes the following steps:

[0105] Through the preset first exponential function: The amplitude of the first spin polarization component signal is fitted to obtain the nuclear spin longitudinal relaxation time; where a0 and a1 represent the first fitting parameter and the second fitting parameter, respectively.

[0106] It is worth noting that, according to equation (8), it can be found that the amplitude of the first spin polarization component signal of the alkali metal atom obtained by demodulation changes exponentially with the magnetization intensity vector of the spin of the inert gas atom. Therefore, the change process of the amplitude of the first spin polarization component signal with time can be fitted by an exponential function, thereby enabling the measurement of the longitudinal relaxation time of the nuclear spin.

[0107] As a preferred embodiment, the step of converting the second emitted polarized light into a second electrical signal, and demodulating the second electrical signal according to a preset pump rate, the modulation magnetic field strength, the modulation magnetic field frequency, the gyromagnetism ratio of the alkali metal atom nuclei, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the second spin polarization component signal of the alkali metal atom, specifically includes the following steps:

[0108] The second outgoing polarized light is transmitted to a balanced photodetector via a polarizer and a Wollaston prism.

[0109] The second emitted polarized light is converted into a second electrical signal by the balanced photodetector and transmitted to the signal processing module.

[0110] The signal processing module demodulates the second electrical signal based on the preset pump rate, the modulation magnetic field strength, the modulation magnetic field frequency, the gyromagnetic ratio of the alkali metal nuclei spin, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the second spin polarization component signal of the alkali metal atom.

[0111] As a preferred embodiment, the step of demodulating the second electrical signal based on a preset pump rate, the modulation magnetic field strength, the modulation magnetic field frequency, the gyromagnetism ratio of the alkali metal atom nuclei, and the initial magnetization vector of the inert gas atom spins when the circularly polarized light stops, to obtain the amplitude of the second spin polarization component signal of the alkali metal atom, specifically includes the following steps:

[0112] Based on the preset pump rate, the modulation magnetic field strength, the modulation magnetic field frequency, the gyromagnetism ratio of the alkali metal atom nuclei, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, the second electrical signal is demodulated using the following expression to obtain the amplitude of the second spin polarization component signal of the alkali metal atom:

[0113]

[0114] in, R represents the amplitude of the second spin polarization component signal; P J1 represents the pump rate; J0 represents the first-order Bessel function; T2 represents the nuclear spin transverse relaxation time; M represents the pump rate; J1 represents the first-order Bessel function; J0 represents the zero-order Bessel function; T2 represents the nuclear spin transverse relaxation time; M represents the nuclear spin transverse relaxation time; M represents the nuclear spin transverse relaxation time; T2 ... Xe0 The vector represents the initial magnetization of the inert gas atoms' spins when the circularly polarized light stops; t represents any moment after the circularly polarized light stops; i represents the imaginary unit; ω Xe This represents the spin magnetic resonance frequency of inert gas atoms;

[0115] The independent variables of the zeroth-order Bessel function and the first-order Bessel function are both: γ Rb B represents the gyromagnetic ratio of the nuclei of the alkali metal atoms. c ω represents the intensity of the modulated magnetic field; c This indicates the frequency of the modulated magnetic field.

[0116] Specifically, the principle for measuring nuclear spin transverse relaxation time is as follows:

[0117] Based on longitudinal polarization, a π / 2 pulsed magnetic field is used to deflect the inert gas atoms from the direction of the static magnetic field to a plane perpendicular to the direction of the static magnetic field.

[0118]

[0119] In the formula,

[0120] In |B x,y Under conditions close to 0, the approximate solution to the above equation is:

[0121]

[0122] in, R represents the amplitude of the second spin polarization component signal; P J1 represents the pump rate; J0 represents the first-order Bessel function; T2 represents the nuclear spin transverse relaxation time; M represents the pump rate; J1 represents the first-order Bessel function; J0 represents the zero-order Bessel function; T2 represents the nuclear spin transverse relaxation time; M represents the nuclear spin transverse relaxation time; M represents the nuclear spin transverse relaxation time; T2 ... Xe0 The vector represents the initial magnetization of the spins of the inert gas atoms when the circularly polarized light stops; t represents any moment after the circularly polarized light stops.

[0123] The independent variables of the zeroth-order Bessel function and the first-order Bessel function are both: γ Rb B represents the gyromagnetic ratio of the nuclei of the alkali metal atoms. c ω represents the intensity of the modulated magnetic field; c This indicates the frequency of the modulated magnetic field.

[0124] As a preferred embodiment, the step of fitting the amplitude of the second spin polarization component signal using a preset second exponential function to obtain the nuclear spin transverse relaxation time specifically includes the following steps:

[0125] Through a preset second exponential function: The nuclear spin transverse relaxation time is obtained by fitting the amplitude of the second spin polarization component signal; where b0 and b1 represent the third and fourth fitting parameters, respectively.

[0126] Equation (9) contains the nuclear spin transverse relaxation time T2, which can be considered to be only Two variables: time t and exponential function. By fitting the data, the transverse relaxation time of the nuclear spin can be obtained.

[0127] As a preferred embodiment, before inputting a DC current into the static magnetic field coils located on both sides of the atomic gas chamber according to a preset current value, the method further includes the following steps:

[0128] The atomic gas chamber is heated to a preset target temperature by a preset heating module.

[0129] It is worth noting that by heating the atomic gas chamber to the preset target temperature through the preset heating module, it is possible to ensure that the atoms in the atomic gas chamber are at a stable atomic number density.

[0130] As a preferred embodiment, the direction in which the alternating magnetic field is applied is perpendicular to the direction in which the static magnetic field is applied; the direction in which the pulsed magnetic field is applied is perpendicular to the direction in which the static magnetic field is applied.

[0131] In one preferred embodiment, a multi-layered magnetic shielding chamber is provided outside the atomic gas chamber, which can effectively avoid magnetic field interference caused by external factors, thereby further improving the measurement accuracy and stability of nuclear spin relaxation time.

[0132] To better demonstrate the beneficial effects of the embodiments of the present invention, the following description is based on actual measurement results.

[0133] Table 1 below shows a comparison of the results of measuring longitudinal relaxation time using the measurement method (dark state method) of the present invention and the traditional inversion recovery method under typical test conditions. It can be seen that the measurement results of the test method of the present invention and the traditional inversion recovery method are close, because the longitudinal relaxation time is less affected by the magnetic field gradient (pump light gradient).

[0134] Table 1 Comparison of longitudinal relaxation time measurement results

[0135] Pump power / mW Longitudinal relaxation time - inversion recovery method / s Longitudinal relaxation time - dark state method / s 50 78.7 79.2 100 81.7 79.0 150 82.6 82.1

[0136] See Figure 2 The curves marked with "△", "□", and "○" represent the transverse relaxation time trend lines measured using the measurement method of this embodiment of the invention at different temperatures and pump optical powers; the curves marked with "*", "×", and "+" represent the transverse relaxation time trend lines measured using the conventional FID method at different temperatures and pump optical powers. Compared with the conventional FID method, the transverse relaxation time measured using the measurement method of this embodiment of the invention varies very little with pump optical power, effectively eliminating the influence of pump optical power.

[0137] The present invention provides a method for measuring the nuclear spin relaxation time of a spin-exchange optically pumped system. By measuring the nuclear spin relaxation time of the spin-exchange optically pumped system after stopping the emission of circularly polarized light into the atomic gas cell, the measurement error caused by the non-uniform distribution of the pump light can be eliminated, thereby enabling accurate measurement of the nuclear spin relaxation time of the spin-exchange optically pumped system.

[0138] See Figure 3 The second aspect of the present invention provides a nuclear spin relaxation time measurement system for a spin-switched optical pumping system, which applies the nuclear spin relaxation time measurement method for a spin-switched optical pumping system as described in any embodiment of the first aspect, including an atomic gas cell 311, a first coil 306, a circularly polarized light emission module, a second coil 307, a linearly polarized light emission module, and a signal processing component.

[0139] The first coil 306 is located on both sides of the atomic gas chamber 311 and is used to apply a static magnetic field to the atomic gas chamber 311 based on a preset input DC current value. The circularly polarized light emission module is used to emit circularly polarized light in the same direction as the static magnetic field into the atomic gas chamber 311 so as to spin polarize the alkali metal atoms and inert gas atoms in the atomic gas chamber 311.

[0140] The circularly polarized light emission module is also used to stop emitting the circularly polarized light into the atomic gas chamber 311 when the irradiation time of the circularly polarized light reaches a preset time threshold, so that the alkali metal atoms are spin polarized along with the spin polarization of the inert gas atoms.

[0141] When the second coil 307 is used to apply an alternating magnetic field to the atomic gas cell 311 to induce nuclear magnetic resonance in the spin-polarized inert gas atoms, and the first coil 306 is used to apply a modulated magnetic field that resonates with the alkali metal atoms to the atomic gas cell 311, the linearly polarized light emission module is used to emit linearly polarized light in the same direction as the alternating magnetic field into the atomic gas cell 311; wherein, the direction in which the alternating magnetic field is applied is different from the direction in which the static magnetic field is applied;

[0142] The signal processing component is used to acquire the first emitted polarized light passing through the atomic gas cell 311; convert the first emitted polarized light into a first electrical signal, and demodulate the first electrical signal according to a preset static magnetic field strength component value, the gyromagnetic ratio of the alkali metal atom nucleus spin, the modulation magnetic field strength, the modulation magnetic field frequency, the spin exchange rate between the alkali metal atom and the inert gas atom, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the first spin polarization component signal of the alkali metal atom; and fit the amplitude of the first spin polarization component signal using a preset first exponential function to obtain the nuclear spin longitudinal relaxation time.

[0143] When the second coil 307 is used to apply a pulsed magnetic field to the atomic gas cell 311, and the first coil 306 is used to apply a modulated magnetic field that resonates with the alkali metal atoms to the atomic gas cell 311, the linearly polarized light emission module is used to emit linearly polarized light in the same direction as the alternating magnetic field into the atomic gas cell 311; wherein, the direction of applying the pulsed magnetic field is different from the direction of applying the static magnetic field;

[0144] The signal processing component is used to acquire the second emitted polarized light passing through the atomic gas cell 311; convert the second emitted polarized light into a second electrical signal, and demodulate the second electrical signal according to a preset pump rate, the intensity of the modulation magnetic field, the frequency of the modulation magnetic field, the gyromagnetic ratio of the alkali metal atom nucleus spin, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the second spin polarization component signal of the alkali metal atom; and fit the amplitude of the second spin polarization component signal to a preset second exponential function to obtain the nuclear spin transverse relaxation time.

[0145] As a preferred embodiment, the signal processing component includes a first polarizer 312, a Wollaston prism 313, a balanced photodetector 314, and a signal processing module 315.

[0146] Then, the signal processing component is used to acquire the first emitted polarized light passing through the atomic gas cell 311; convert the first emitted polarized light into a first electrical signal, and demodulate the first electrical signal according to a preset static magnetic field strength component value, the gyromagnetic ratio of the alkali metal atom nucleus spin, the modulation magnetic field strength, the modulation magnetic field frequency, the spin exchange rate between the alkali metal atom and the inert gas atom, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the first spin polarization component signal of the alkali metal atom; fit the amplitude of the first spin polarization component signal using a preset first exponential function to obtain the nuclear spin longitudinal relaxation time, specifically including:

[0147] The first polarizer 312 and the Wollaston prism 313 are used to transmit the first outgoing polarized light through the atomic gas cell 311 to the balanced photodetector 314;

[0148] The balanced photodetector 314 is used to convert the first emitted polarized light into a first electrical signal and transmit it to the signal processing module 315.

[0149] The signal processing module 315 is used to demodulate the first electrical signal according to the preset static magnetic field strength component value, the gyromagnetic ratio of the alkali metal atom nucleus spin, the modulation magnetic field strength, the modulation magnetic field frequency, the spin exchange rate between the alkali metal atom and the inert gas atom, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the first spin polarization component signal of the alkali metal atom.

[0150] Then, the signal processing component is used to acquire the second emitted polarized light passing through the atomic gas cell 311; convert the second emitted polarized light into a second electrical signal, and demodulate the second electrical signal according to a preset pump rate, the modulation magnetic field strength, the modulation magnetic field frequency, the gyromagnetic ratio of the alkali metal atom nucleus spin, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the second spin polarization component signal of the alkali metal atom; fit the amplitude of the second spin polarization component signal using a preset second exponential function to obtain the nuclear spin transverse relaxation time, specifically including:

[0151] The first polarizer 312 and the Wollaston prism 313 are used to transmit the second outgoing polarized light through the atomic gas cell 311 to the balanced photodetector 314;

[0152] The balanced photodetector 314 is used to convert the second emitted polarized light into a second electrical signal and transmit it to the signal processing module 315.

[0153] The signal processing module 315 is used to demodulate the second electrical signal according to the preset pump rate, the modulation magnetic field strength, the modulation magnetic field frequency, the gyromagnetic ratio of the alkali metal atom nucleus spin, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the second spin polarization component signal of the alkali metal atom.

[0154] As a preferred embodiment, the signal processing module 315 is used to demodulate the first electrical signal according to a preset static magnetic field strength component value, the gyromagnetic ratio of the alkali metal atom nucleus spin, the modulation magnetic field strength, the modulation magnetic field frequency, the spin exchange rate between the alkali metal atom and the inert gas atom, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the first spin polarization component signal of the alkali metal atom, specifically including:

[0155] Based on the preset static magnetic field strength component value, the gyromagnetic ratio of the alkali metal atom nuclei, the modulation magnetic field strength, the modulation magnetic field frequency, the spin exchange rate between the alkali metal atom and the inert gas atom, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, the first electrical signal is demodulated using the following expression to obtain the amplitude of the first spin polarization component signal of the alkali metal atom:

[0156]

[0157] in, B represents the amplitude of the first spin polarization component signal; y Indicates the value of the static magnetic field strength component; γ Rb J1 represents the first-order Bessel function; J2 represents the second-order Bessel function; J0 represents the zeroth-order Bessel function; R represents the gyromagnetic ratio of the alkali metal nuclei; J1 represents the first-order Bessel function; J2 represents the second-order Bessel function; J0 represents the zeroth-order Bessel function; R represents the first-order Bessel function. se T1 represents the spin exchange rate between the alkali metal atoms and the inert gas atoms; M represents the longitudinal relaxation time of the nuclear spin; Xe0 The vector represents the initial magnetization of the spins of the inert gas atoms when the circularly polarized light stops; t represents any moment after the circularly polarized light stops.

[0158] The independent variables of the zeroth-order Bessel function, the first-order Bessel function, and the second-order Bessel function are all: B c ω represents the intensity of the modulated magnetic field; c This indicates the frequency of the modulated magnetic field.

[0159] As a preferred embodiment, the signal processing module 315 is used to fit the amplitude of the first spin polarization component signal using a preset first exponential function to obtain the nuclear spin longitudinal relaxation time, specifically including the following steps:

[0160] Through the preset first exponential function: The amplitude of the first spin polarization component signal is fitted to obtain the nuclear spin longitudinal relaxation time; where a0 and a1 represent the first fitting parameter and the second fitting parameter, respectively.

[0161] As a preferred embodiment, the signal processing module 315 is used to demodulate the second electrical signal according to a preset pump rate, the modulation magnetic field strength, the modulation magnetic field frequency, the gyromagnetism ratio of the alkali metal atom nucleus spin, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the second spin polarization component signal of the alkali metal atom, specifically including:

[0162] Based on the preset pump rate, the modulation magnetic field strength, the modulation magnetic field frequency, the gyromagnetism ratio of the alkali metal atom nuclei, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, the second electrical signal is demodulated using the following expression to obtain the amplitude of the second spin polarization component signal of the alkali metal atom:

[0163]

[0164] in, R represents the amplitude of the second spin polarization component signal; P J1 represents the pump rate; J0 represents the first-order Bessel function; T2 represents the nuclear spin transverse relaxation time; M represents the pump rate; J1 represents the first-order Bessel function; J0 represents the zero-order Bessel function; T2 represents the nuclear spin transverse relaxation time; M represents the nuclear spin transverse relaxation time; M represents the nuclear spin transverse relaxation time; T2 ... Xe0 The vector represents the initial magnetization of the inert gas atoms' spins when the circularly polarized light stops; t represents any moment after the circularly polarized light stops; i represents the imaginary unit; ω Xe This represents the spin magnetic resonance frequency of inert gas atoms;

[0165] The independent variables of the zeroth-order Bessel function and the first-order Bessel function are both: γ Rb B represents the gyromagnetic ratio of the nuclei of the alkali metal atoms. c ω represents the intensity of the modulated magnetic field; c This indicates the frequency of the modulated magnetic field.

[0166] As a preferred embodiment, the signal processing module 315 is used to fit the amplitude of the second spin polarization component signal using a preset second exponential function to obtain the nuclear spin transverse relaxation time, specifically including the following steps:

[0167] Through a preset second exponential function: The nuclear spin transverse relaxation time is obtained by fitting the amplitude of the second spin polarization component signal; where b0 and b1 represent the third and fourth fitting parameters, respectively.

[0168] As a preferred embodiment, the system further includes a heating module 316, used for:

[0169] Before inputting DC current into the static magnetic field coils located on both sides of the atomic gas chamber 311 according to the preset current value, the temperature of the atomic gas chamber 311 is heated to the preset target temperature.

[0170] As a preferred embodiment, the direction in which the alternating magnetic field is applied is perpendicular to the direction in which the static magnetic field is applied; the direction in which the pulsed magnetic field is applied is perpendicular to the direction in which the static magnetic field is applied.

[0171] As a preferred embodiment, the axis of the first coil 306 is perpendicular to the axis of the second coil 307.

[0172] As a preferred embodiment, the axis of the center of the first coil 306 coincides with the axis of the center of the atomic gas chamber 311, and the atomic gas chamber 311 is located at the center between the two first coils 306.

[0173] As a preferred embodiment, the circularly polarized light emission module includes a pump laser 301 and a beam expander prism 302, a second polarizer 303, a first half-wave plate 304, and a quarter-wave plate 305 sequentially disposed between the pump laser 301 and the first coil 306.

[0174] The pump laser 301 is used to emit pump light in the same direction as the static magnetic field into the atomic gas chamber 311;

[0175] The beam expander prism 302 is used to expand the pump light in the optical path of the pump light.

[0176] The second polarizer 303 is used to adjust the pump light after beam expansion into linearly polarized light;

[0177] The first half-wave plate 304 is used to change the polarization direction of linearly polarized light to the target polarization direction;

[0178] The quarter-wave plate 305 is used to adjust linearly polarized light, after its polarization direction has been changed, into circularly polarized light.

[0179] As a preferred embodiment, the linearly polarized light emission module includes a probe laser 308 and a third polarizer 309 and a second half-wave plate 310 sequentially disposed between the probe laser 308 and the second coil 307.

[0180] The detection laser 308 is used to emit detection light in the same direction as the alternating magnetic field / pulsed magnetic field into the atomic gas chamber 311;

[0181] The third polarizer 309 and the second half-wave plate 310 are used to adjust the probe light into linearly polarized light in the optical path of the probe light.

[0182] As a preferred embodiment, the system further includes a multi-layer magnetic shielding barrel 317;

[0183] The multi-layer magnetic shielding barrel 317 has a accommodating cavity for placing the atomic gas chamber 311, the first coil 306, the second coil 307 and the heating module 316.

[0184] As a preferred embodiment, the system further includes a spare coil 318;

[0185] The axis of the spare coil 318 is perpendicular to the axis of the first coil 306 and the axis of the second coil 307, respectively.

[0186] It is understood that the spare coil 318 can replace the function of the second coil 307.

[0187] The present invention provides a nuclear spin relaxation time measurement system for a spin-exchange optically pumped system. By measuring the nuclear spin relaxation time of the spin-exchange optically pumped system after stopping the emission of circularly polarized light into the atomic gas cell, the measurement error caused by the non-uniform distribution of the pump light can be eliminated, thereby enabling accurate measurement of the nuclear spin relaxation time of the spin-exchange optically pumped system.

[0188] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for measuring the nuclear spin relaxation time of a spin-exchange optically pumped system, characterized in that, Includes the following steps: Based on a preset input DC current value, a static magnetic field is applied to the atomic gas cell, and circularly polarized light in the same direction as the static magnetic field is emitted into the atomic gas cell to spin polarize the alkali metal atoms and inert gas atoms in the atomic gas cell. When the irradiation time of the circularly polarized light reaches a preset time threshold, the emission of the circularly polarized light into the atomic gas cell is stopped, so that the alkali metal atoms are spin polarized along with the spin polarization of the inert gas atoms; When an alternating magnetic field is applied to the atomic gas cell to induce nuclear magnetic resonance in the spin-polarized inert gas atoms, and a modulation magnetic field that resonates with the alkali metal atoms is applied to the atomic gas cell, linearly polarized light in the same direction as the alternating magnetic field is emitted into the atomic gas cell, and the first outgoing polarized light passing through the atomic gas cell is obtained; wherein, the direction of applying the alternating magnetic field is different from the direction of applying the static magnetic field; The first emitted polarized light is converted into a first electrical signal. Based on a preset static magnetic field strength component value, the gyromagnetic ratio of the alkali metal atom nuclei, the modulation magnetic field strength, the modulation magnetic field frequency, the spin exchange rate between the alkali metal atom and the inert gas atom, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, the first electrical signal is demodulated using the following expression to obtain the amplitude of the first spin polarization component signal of the alkali metal atom: in, Indicates the transverse relaxation time of alkali metal atoms; This represents the amplitude of the first spin polarization component signal; This represents the component value of the static magnetic field strength; The gyromagnetic ratio represents the spin of the alkali metal atom nucleus; Represents the first-order Bessel function; Represents the second-order Bessel function; Represents the zeroth-order Bessel function; This indicates the spin exchange rate between the alkali metal atoms and the inert gas atoms; Indicates the longitudinal relaxation time of nuclear spin; The initial magnetization vector represents the spin of the inert gas atoms when the circularly polarized light stops; This represents any moment after the circularly polarized light stops; the independent variables of the zeroth-order Bessel function, the first-order Bessel function, and the second-order Bessel function are all: ; This indicates the intensity of the modulated magnetic field; This indicates the frequency of the modulated magnetic field; The longitudinal relaxation time of the nuclear spin is obtained by fitting the amplitude of the first spin polarization component signal with a preset first exponential function. When a pulsed magnetic field and a modulated magnetic field that resonates with the alkali metal atoms are applied to the atomic gas cell, linearly polarized light in the same direction as the pulsed magnetic field is emitted into the atomic gas cell to obtain a second outgoing polarized light that has passed through the atomic gas cell; wherein, the direction of the applied pulsed magnetic field is different from the direction of the applied static magnetic field; The second emitted polarized light is converted into a second electrical signal, and the second electrical signal is demodulated according to the preset pump rate, the intensity of the modulation magnetic field, the frequency of the modulation magnetic field, the gyromagnetic ratio of the spin of the alkali metal atom nucleus, and the initial magnetization vector of the spin of the inert gas atom when the circularly polarized light stops, to obtain the amplitude of the second spin polarization component signal of the alkali metal atom. The nuclear spin transverse relaxation time is obtained by fitting the amplitude of the second spin polarization component signal to a preset second exponential function.

2. The method for measuring the nuclear spin relaxation time of the spin-exchange optically pumped system as described in claim 1, characterized in that, The step of converting the first emitted polarized light into a first electrical signal, and demodulating the first electrical signal according to a preset static magnetic field strength component value, the gyromagnetic ratio of the alkali metal atom nuclei, the modulation magnetic field strength, the modulation magnetic field frequency, the spin exchange rate between the alkali metal atom and the inert gas atom, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the first spin polarization component signal of the alkali metal atom, specifically includes the following steps: The first emitted polarized light is transmitted to a balanced photodetector via a polarizer and a Wollaston prism. The first emitted polarized light is converted into a first electrical signal by the balanced photodetector and transmitted to the signal processing module. The signal processing module demodulates the first electrical signal based on preset static magnetic field strength component values, the gyromagnetic ratio of the alkali metal atom nuclei, the modulation magnetic field strength, the modulation magnetic field frequency, the spin exchange rate between the alkali metal atom and the inert gas atom, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the first spin polarization component signal of the alkali metal atom.

3. The method for measuring the nuclear spin relaxation time of the spin-exchange optically pumped system as described in claim 1, characterized in that, The step of fitting the amplitude of the first spin polarization component signal using a preset first exponential function to obtain the nuclear spin longitudinal relaxation time specifically includes the following steps: Through the preset first exponential function: The amplitude of the first spin polarization component signal is fitted to obtain the nuclear spin longitudinal relaxation time; wherein... and These represent the first fitting parameter and the second fitting parameter, respectively.

4. The method for measuring the nuclear spin relaxation time of the spin-exchange optically pumped system as described in claim 1, characterized in that, The step of converting the second emitted polarized light into a second electrical signal, and demodulating the second electrical signal according to a preset pump rate, the intensity of the modulation magnetic field, the frequency of the modulation magnetic field, the gyromagnetic ratio of the alkali metal atom nucleus spin, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the second spin polarization component signal of the alkali metal atom, specifically includes the following steps: The second outgoing polarized light is transmitted to a balanced photodetector via a polarizer and a Wollaston prism. The second emitted polarized light is converted into a second electrical signal by the balanced photodetector and transmitted to the signal processing module. The signal processing module demodulates the second electrical signal based on the preset pump rate, the modulation magnetic field strength, the modulation magnetic field frequency, the gyromagnetic ratio of the alkali metal nuclei spin, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the second spin polarization component signal of the alkali metal atom.

5. The method for measuring the nuclear spin relaxation time of the spin-exchange optically pumped system as described in claim 1 or 4, characterized in that, The step of demodulating the second electrical signal based on a preset pump rate, the modulation magnetic field strength, the modulation magnetic field frequency, the gyromagnetism ratio of the alkali metal atom nuclei, and the initial magnetization vector of the inert gas atom spins when the circularly polarized light stops, to obtain the amplitude of the second spin polarization component signal of the alkali metal atom, specifically includes the following steps: Based on the preset pump rate, the modulation magnetic field strength, the modulation magnetic field frequency, the gyromagnetism ratio of the alkali metal atom nuclei, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, the second electrical signal is demodulated using the following expression to obtain the amplitude of the second spin polarization component signal of the alkali metal atom: in, This indicates the amplitude of the second spin polarization component signal; This indicates the pumping rate; Represents the first-order Bessel function; Represents the zeroth-order Bessel function; Indicates the transverse relaxation time of nuclear spin; The initial magnetization vector represents the spin of the inert gas atoms when the circularly polarized light stops; This represents any moment after the circularly polarized light stops; Represents the imaginary unit; This represents the spin magnetic resonance frequency of inert gas atoms; The independent variables of the zeroth-order Bessel function and the first-order Bessel function are both: ; The gyromagnetic ratio represents the spin of the alkali metal atom nucleus; This indicates the intensity of the modulated magnetic field; This indicates the frequency of the modulated magnetic field.

6. The method for measuring the nuclear spin relaxation time of the spin-exchange optically pumped system as described in claim 5, characterized in that, The step of fitting the amplitude of the second spin polarization component signal using a preset second exponential function to obtain the nuclear spin transverse relaxation time specifically includes the following steps: Through a preset second exponential function: The amplitude of the second spin polarization component signal is fitted to obtain the nuclear spin transverse relaxation time; wherein... and These represent the third and fourth fitting parameters, respectively.

7. The method for measuring the nuclear spin relaxation time of the spin-exchange optically pumped system as described in claim 1, characterized in that, Before inputting a DC current into the static magnetic field coils located on both sides of the atomic gas chamber according to a preset current value, the method further includes the following steps: The atomic gas chamber is heated to a preset target temperature by a preset heating module.

8. The method for measuring the nuclear spin relaxation time of the spin-exchange optically pumped system as described in claim 1, characterized in that, The direction in which the alternating magnetic field is applied is perpendicular to the direction in which the static magnetic field is applied; the direction in which the pulsed magnetic field is applied is perpendicular to the direction in which the static magnetic field is applied.

9. A system for measuring the nuclear spin relaxation time of a spin-exchange optically pumped system, comprising the method for measuring the nuclear spin relaxation time of a spin-exchange optically pumped system as described in any one of claims 1 to 8, characterized in that, It includes an atomic gas cell, a first coil, a circularly polarized light emission module, a second coil, a linearly polarized light emission module, and a signal processing component; The first coil is located on both sides of the atomic gas cell and is used to apply a static magnetic field to the atomic gas cell based on a preset input DC current value. The circularly polarized light emission module is used to emit circularly polarized light in the same direction as the static magnetic field into the atomic gas cell so as to spin polarize the alkali metal atoms and inert gas atoms in the atomic gas cell. The circularly polarized light emission module is also used to stop emitting the circularly polarized light into the atomic gas cell when the irradiation time of the circularly polarized light reaches a preset time threshold, so that the alkali metal atoms are spin polarized along with the spin polarization of the inert gas atoms; When the second coil is used to apply an alternating magnetic field to the atomic gas cell to induce nuclear magnetic resonance in the spin-polarized inert gas atoms, and the first coil is used to apply a modulated magnetic field that resonates with the alkali metal atoms to the atomic gas cell, the linearly polarized light emission module is used to emit linearly polarized light in the same direction as the alternating magnetic field into the atomic gas cell; wherein, the direction of applying the alternating magnetic field is different from the direction of applying the static magnetic field; The signal processing component is used to acquire the first emitted polarized light passing through the atomic gas cell; convert the first emitted polarized light into a first electrical signal; and demodulate the first electrical signal according to the preset static magnetic field strength component value, the gyromagnetic ratio of the alkali metal atom nucleus spin, the modulation magnetic field strength, the modulation magnetic field frequency, the spin exchange rate between the alkali metal atom and the inert gas atom, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, using the following expression to obtain the amplitude of the first spin polarization component signal of the alkali metal atom: in, Indicates the transverse relaxation time of alkali metal atoms; This represents the amplitude of the first spin polarization component signal; This represents the component value of the static magnetic field strength; The gyromagnetic ratio represents the spin of the alkali metal atom nucleus; Represents the first-order Bessel function; Represents the second-order Bessel function; Represents the zeroth-order Bessel function; This indicates the spin exchange rate between the alkali metal atoms and the inert gas atoms; Indicates the longitudinal relaxation time of nuclear spin; The initial magnetization vector represents the spin of the inert gas atoms when the circularly polarized light stops; This represents any moment after the circularly polarized light stops; the independent variables of the zeroth-order Bessel function, the first-order Bessel function, and the second-order Bessel function are all: ; This indicates the intensity of the modulated magnetic field; This indicates the frequency of the modulated magnetic field; The longitudinal relaxation time of the nuclear spin is obtained by fitting the amplitude of the first spin polarization component signal with a preset first exponential function. When the second coil is used to apply a pulsed magnetic field to the atomic gas cell, and the first coil is used to apply a modulated magnetic field that resonates with the alkali metal atoms to the atomic gas cell, the linearly polarized light emission module is used to emit linearly polarized light in the same direction as the alternating magnetic field into the atomic gas cell; wherein, the direction of applying the pulsed magnetic field is different from the direction of applying the static magnetic field; The signal processing component is used to acquire the second emitted polarized light passing through the atomic gas cell; convert the second emitted polarized light into a second electrical signal, and demodulate the second electrical signal according to a preset pump rate, the intensity of the modulation magnetic field, the frequency of the modulation magnetic field, the gyromagnetic ratio of the alkali metal atom nucleus spin, and the initial magnetization vector of the inert gas atom spin when the circularly polarized light stops, to obtain the amplitude of the second spin polarization component signal of the alkali metal atom; and fit the amplitude of the second spin polarization component signal using a preset second exponential function to obtain the nuclear spin transverse relaxation time.

Images