SERF magnetic field measurement high-uniformity atomic polarization method and module based on vector optical pumping

Abstract

According to the SERF magnetic field measurement high-uniformity atomic polarization method and module based on vector light pumping, vector light with adjustable spatial polarization state distribution is adopted as pumping light to polarize atoms, and the response and three-dimensional space electron polarization uniformity of an SERF magnetic field measurement device are effectively improved. On the basis of pumping light polarization state spatial distribution when the electron polarizability of the central plane of the air chamber is 0.5 everywhere, the spatial light modulator modulates the phase of incident light, and spatial polarization state distribution with more uniform polarizability of the air chamber is obtained. Compared with a device without using a high-uniformity atomic polarization module, the device provided by the invention can regulate and control the value of the electron polarizability to enable the electron polarizability to be distributed near the optimal polarizability, can improve the uniformity of the electron polarizability in a three-dimensional space, enables the SERF magnetic field measurement device to have larger frequency response and more uniform polarizability distribution, and improves the measurement accuracy of the SERF magnetic field measurement device. Noise caused by non-uniform polarizability distribution can be reduced, and the gradient differential sensitivity limit of the SERF magnetic field measurement device is improved.

Description

Technical Field

[0001] This invention relates to the field of SERF atomic magnetic field measurement technology, specifically to a method and module for measuring highly uniform atomic polarization in SERF magnetic fields based on vector light pumping. Background Technology

[0002] Ultra-sensitive magnetic field measurements based on the spin-free exchange relaxation (SERF) effect of atoms benefit from the development of quantum technology and currently hold the world record for the highest magnetic field measurement sensitivity. In SERF magnetic field measurement devices, the polarizability gradient is a key factor limiting sensitivity improvement. The polarizability gradient prevents the polarizability of the central plane of the gas cell from being distributed near the optimal polarizability and causes uneven distribution of electron transverse polarizability, thus reducing the sensitivity of magnetic field measurements. To reduce the polarizability gradient, the pump light needs to be modulated. Currently, the only modifiable parameters for the pump light are intensity, phase, and frequency. Increasing the polarization parameter can further control the three-dimensional spatial distribution of atomic polarizability, thereby reducing the spatial polarizability gradient and improving the output response of the device. Therefore, a high-uniformity atomic polarization module for SERF magnetic field measurement based on the vector light pump method was designed.

[0003] To address the issue of the polarizability distribution in the central plane of the gas cell not being near the optimal polarizability, researchers have proposed schemes such as beam shaping, pump light tuning, and broadband pumping. Beam shaping optimizes the polarizability distribution in the central plane of the gas cell by controlling the distribution of pump light intensity. However, beam shaping suffers from excessive complexity in solving certain intensity distributions, making inversion impossible. Furthermore, the pump light intensity itself has some fluctuations, and adding complex beam shaping devices introduces more noise and more severe intensity fluctuations. Schemes such as pump light tuning and broadband pumping are limited by the spatial degrees of freedom of adjustable parameters, resulting in limited improvement in the uniformity of electron transverse polarization. This invention designs a SERF magnetic field measurement module for highly uniform atomic polarization based on a vector light pumping method. On the one hand, it can control the decay rate of longitudinal electron polarizability by changing the polarization state of the pump light, thereby bringing the polarizability closer to the optimal value and improving the uniformity of longitudinal polarization. On the other hand, the vector light field can control the polarization state of each region in the transverse plane of the alkali metal gas cell, thus significantly improving the uniformity of electron transverse polarization. Summary of the Invention

[0004] The purpose of this invention is to design a method and module for measuring highly uniform atomic polarization using a SERF magnetic field based on vector light pumping. By using a spatial light modulator to convert a scalar light field into a vector light field as pump light to polarize atoms, and by controlling the spatial polarization state distribution of the pump light to change the longitudinal light intensity attenuation rate, the polarizability of each point on the central plane of the gas cell can be made close to the optimal value, thereby improving the output response of the SERF magnetic field measurement device and improving the uniformity of the transverse polarizability of electrons.

[0005] The technical solution of the present invention is as follows: A method for measuring highly uniform atomic polarization using SERF magnetic field based on vector light pumping, characterized by the following steps: Step 1: For the alkali metal atom gas cell in the SERF magnetic field measurement device, obtain the spatial distribution of the pump light polarization state when the electronic polarizability of the central plane of the gas cell is 0.5 everywhere, and form a pump light phase spatial distribution map based on the spatial distribution of the pump light polarization state. Step 2: Load the pump light phase space distribution map onto the spatial light modulator set on the pump light path, and drive it to modulate the incident scalar pump light into the outgoing vector pump light according to the phase space distribution map, so as to control the single polarization state of the scalar light into the spatial polarization state distribution of the vector light. Step 3: Measure the three-dimensional spatial electronic steady-state polarization distribution and the magnitude of the device output response signal using the detection optical path of the SERF magnetic field measuring device; Step 4: Determine whether the electronic polarizability of the central plane of the gas cell is distributed in the range of 0.5±0.05 everywhere. If yes, proceed to step 5. If no, change the pump light phase spatial distribution diagram and return to step 2. Step 5: Determine that the vector pump light generated by loading the pump light phase spatial distribution map onto the spatial light modulator is the most suitable pump light for this device.

[0006] In step 2, the polarization ellipticity of the vector pump light is ≥0.7.

[0007] Step 4 includes: when the electronic polarizability is greater than the upper limit of the range, the proportion of circularly polarized light in the pump light at that location is increased; when the electronic polarizability is less than the lower limit of the range, the proportion of circularly polarized light in the pump light at that location is decreased, thereby changing the phase spatial distribution map of the pump light.

[0008] In step 1, the SERF magnetic field measurement device includes a pump laser, a horizontal linear polarizer, a half-wave plate, a 45° linear polarizer, a spatial light modulator, a non-polarized beam splitter, and an alkali metal atom gas cell connected in sequence. The spatial light modulator is connected to a host computer. The alkali metal atom gas cell is located within a non-magnetic electric heating system. The non-magnetic electric heating system is located within a triaxial magnetic compensation coil. The triaxial magnetic compensation coil is located within a magnetic shielding barrel. The triaxial magnetic compensation coil is connected to the host computer via a function generator.

[0009] In step 1, the SERF magnetic field measurement device includes a detection laser, a polarizer, a photoelastic modulator, a quarter-wave plate, an alkali metal atom gas cell, an analyzer, a photodetector, a lock-in amplifier, and a host computer connected in sequence. The lock-in amplifier is connected to a modulation controller.

[0010] The lock-in amplifier obtains the DC component, first harmonic component, and second harmonic component of the detection electrical signal based on the detection electrical signal input from the photodetector and the reference signal input from the modulation controller, and feeds it back to the host computer for real-time display.

[0011] Step 1 includes the following expression: , , , in It is the steady-state polarizability at the coordinate point (x, y, z). It is the pumping rate at the coordinate point (x, y, z). It is the relaxation rate at the coordinate point (x, y, z).

[0012] Step 2 includes the following expression: , ≥0.7, in It is the atomic number density of alkali metals. It is the atomic absorption cross section. It is the average photon spin vector. It is related to the polarization state of the pump light.

[0013] The SERF magnetic field measurement module based on vector light pumping is characterized by including a spatial light modulator for carrying a pump light phase spatial distribution map. The spatial light modulator converts the scalar light field into a vector light field through the pump light phase spatial distribution map to polarize the atoms in the alkali metal atom gas chamber. Furthermore, by adjusting the spatial polarization state distribution of the pump light, the longitudinal light intensity attenuation rate is changed, so that the polarizability of each point on the central plane of the gas chamber approaches the optimal value.

[0014] The control terminal of the spatial light modulator is connected to the host computer. The input terminal of the spatial light modulator is connected to the pump laser in sequence through a 45° linear polarizer, a half-wave plate, and a horizontal linear polarizer. The output terminal of the spatial light modulator is connected to the alkali metal atom gas cell through a non-polarized beam splitter. The alkali metal atom gas cell is located within a non-magnetic electric heating system, which is located within a three-axis magnetic compensation coil. The three-axis magnetic compensation coil is located within a magnetic shielding barrel. The three-axis magnetic compensation coil is connected to the host computer through a function generator. The incident side of the detection light from the alkali metal atom gas cell is connected to the detection laser in sequence through a quarter-wave plate, a photoelastic modulator, and a polarizer. The exit side of the detection light from the alkali metal atom gas cell is connected to the host computer in sequence through an analyzer, a photodetector, and a lock-in amplifier. The lock-in amplifier is connected to the modulation controller.

[0015] The technical effects of this invention are as follows: This invention is based on a vector-light pump-based SERF magnetic field measurement method and module for highly uniform atomic polarization. It uses vector light with tunable spatial polarization state distribution as pump light to polarize atoms, effectively improving the response and three-dimensional spatial electronic polarization uniformity of the SERF magnetic field measurement device. Based on the spatial distribution of the pump light polarization state when the electronic polarizability is 0.5 everywhere in the central plane of the gas cell, a spatial light modulator modulates the phase of the incident light, obtaining a more uniform spatial polarization state distribution of the gas cell polarizability. Compared to SERF magnetic field measurement devices without a highly uniform atomic polarization module, this invention modulates the spatial polarization distribution of the pump light using a spatial light modulator. This not only controls the value of the electronic polarizability, distributing it near the optimal polarizability, but also improves the three-dimensional spatial electronic polarizability uniformity. This results in a larger frequency response and a more uniform polarizability distribution in the SERF magnetic field measurement device, which helps reduce noise introduced by non-uniform polarizability distribution and improves the gradient difference sensitivity limit of the SERF magnetic field measurement device.

[0016] The advantages of this invention compared with the prior art are: (1) The polarization state of a certain point in the transverse plane of the pump light can be controlled to regulate the light absorption rate, thereby making the polarizability distributed near the optimal polarizability in the central plane of the gas cell, thus improving the output response of the device; (2) By changing the spatial polarization state distribution of the pump light, a new adjustable dimension is provided; (3) Pixel-level control can be performed on the transverse plane, which greatly improves the uniformity of alkali metal electron transverse polarization; (4) Compared with light intensity modulation and other schemes, the change in polarization state of the pump light after refraction and reflection by the pump light through the optical device is smaller than the change in light intensity. The device structure is simple and the modulation effect is stable. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the high-uniformity atomic polarization module structure for SERF magnetic field measurement based on vector light pumping, which implements the present invention.

[0018] Figure 2 This is a schematic flowchart of the method for measuring highly uniform atomic polarization based on vector light pumping for SERF magnetic field measurement according to the present invention.

[0019] Figure 3 The graph shows the relationship between the steady-state polarizability P0 and the normalized output response of the SERF magnetic field measurement device. Figure 3 The horizontal axis represents the steady-state polarizability P0 (scale values ​​are 0, 0.1, ..., 1), and the vertical axis represents the normalized output response (scale values ​​are 0, 0.1, ..., 1). Figure 3 It can be seen from the pumping rate equal to relaxation rate Under the condition that the steady-state polarizability P0 = 0.5, the output response is the highest, which is called the optimal polarizability.

[0020] Figure 4 Pumping rate before entering the air chamber =3000 and Pumping rate in alkali metal gas chamber at 200°C Distribution curve along the pump light direction. Figure 4 The horizontal axis represents the distance z (mm, scale values ​​are 0, 5, ... 30) of the beam propagation within the air chamber, and the vertical axis represents the steady-state polarizability P0 (scale values ​​are 0, 0.1, ... 1). Figure 4The curves include eight line types (from bottom to top in the middle: s=0.5, s=0.6, s=0.7, s=0.8, s=0.9, s=1), representing different values ​​of the average photon spin vector s, i.e., different polarization states of the pump light. These curves show that by changing the polarization state of the pump light to change the value of the average photon spin vector s, the decay rate of the pump rate in the gas cell can be controlled, thereby ensuring that the polarizability distribution in the central plane of the gas cell is near the optimal polarizability (0.5), and at the same time, the uniformity of transverse electronic polarization can be improved.

[0021] The reference numerals in the attached diagram are explained as follows: 1-Pump laser; 2-Horizontal linear polarizer; 3-1 / 2 waveplate; 4-45° linear polarizer; 5-Spatial light modulator; 6-Non-polarized beam splitter; 7-Magnetic shielding barrel; 8-Triaxial magnetic compensation coil; 9-Non-magnetic electric heating system; 10-Alkali metal atom gas chamber; 11-Detection laser; 12-Polarizer; 13-Photoelastic modulator; 14-1 / 4 waveplate; 15-Analyzer; 16-Photodetector; 17-Modulation controller; 18-Lock-in amplifier; 19-Function generator; 20-Host computer; XYZ-Cartesian coordinate system (i.e., X-axis, Y-axis, and Z-axis). Detailed Implementation

[0022] The following is in conjunction with the attached diagram ( Figures 1-4 The present invention will be described in conjunction with the examples.

[0023] Figure 1 This is a schematic diagram of the high-uniformity atomic polarization module structure for SERF magnetic field measurement based on vector light pumping, which implements the present invention. Figure 2 This is a schematic flowchart of the method for measuring highly uniform atomic polarization based on vector light pumping for SERF magnetic field measurement according to the present invention. Figure 3 The graph shows the relationship between the steady-state polarizability P0 and the normalized output response of the SERF magnetic field measurement device. Figure 4 Pumping rate before entering the air chamber =3000 and Pumping rate in alkali metal gas chamber at 200°C Distribution curve along the pump light direction. (Reference) Figures 1 to 4As shown, a method for measuring highly uniform atomic polarization using a SERF magnetic field based on vector light pumping includes the following steps: Step 1, for the alkali metal atom gas cell in the SERF magnetic field measuring device, obtain the spatial distribution of the pump light polarization state when the electronic polarizability at the center plane of the gas cell is everywhere 0.5, and form a pump light phase spatial distribution map based on the pump light polarization state spatial distribution; Step 2, load the pump light phase spatial distribution map onto a spatial light modulator set on the pump light path, and drive it to modulate the incident scalar pump light into an outgoing vector pump light according to the phase spatial distribution map, so as to achieve high uniform atomic polarization. Step 3: Modulate the single polarization state of the light into the spatial polarization state distribution of the vector light; Step 4: Measure the three-dimensional spatial electronic steady-state polarizability distribution and the magnitude of the device output response signal using the detection optical path of the SERF magnetic field measuring device; Step 5: Determine whether the electronic polarizability of the central plane of the gas cell is distributed everywhere within the range of 0.5±0.05. If yes, proceed to Step 6; if no, change the pump light phase spatial distribution map and return to Step 2; Step 6: Determine that loading the pump light phase spatial distribution map onto the spatial light modulator so that the vector pump light generated is the most suitable pump light for this device.

[0024] In step 2, the polarization ellipticity of the vector pump light is ≥0.7. Step 4 includes: when the electronic polarizability is greater than the upper limit of the range, increasing the proportion of circularly polarized light in the pump light at that location; when the electronic polarizability is less than the lower limit of the range, decreasing the proportion of circularly polarized light in the pump light at that location, thereby changing the phase spatial distribution map of the pump light.

[0025] The SERF magnetic field measurement device in step 1 includes a pump laser 1, a horizontal linear polarizer 2, a half-wave plate 3, a 45° linear polarizer 4, a spatial light modulator 5, a non-polarized beam splitter 6, and an alkali metal atom gas cell 10 connected in sequence. The spatial light modulator 5 is connected to a host computer 20. The alkali metal atom gas cell 10 is located within a non-magnetic electric heating system 9, which is located within a triaxial magnetic compensation coil 8. The triaxial magnetic compensation coil 8 is located within a magnetic shielding barrel 7, and is connected to the host computer 20 via a function generator 19. The SERF magnetic field measurement device in step 1 also includes a detection laser 11, a polarizer 12, a photoelastic modulator 13, a quarter-wave plate 14, an alkali metal atom gas cell 10, an analyzer 15, a photodetector 16, a lock-in amplifier 18, and a host computer 20 connected in sequence. The lock-in amplifier 18 is connected to a modulation controller 17. The lock-in amplifier 18 obtains the DC component, first harmonic component, and second harmonic component of the detection electrical signal based on the detection electrical signal input from the photodetector and the reference signal input from the modulation controller, and feeds it back to the host computer for real-time display.

[0026] Step 1 includes the following expression: , , , in It is the steady-state polarizability at the coordinate point (x, y, z). It is the pumping rate at the coordinate point (x, y, z). It is the relaxation rate at the coordinate point (x, y, z).

[0027] Step 2 includes the following expression: , ≥0.7, in It is the atomic number density of alkali metals. It is the atomic absorption cross section. It is the average photon spin vector. It is related to the polarization state of the pump light.

[0028] The SERF magnetic field measurement module based on vector light pumping includes a spatial light modulator 5 for carrying a pump light phase spatial distribution map. The spatial light modulator 5 converts the scalar light field into a vector light field through the pump light phase spatial distribution map to polarize the atoms in the alkali metal atom gas chamber. Furthermore, by adjusting the spatial polarization state distribution of the pump light, the longitudinal light intensity attenuation rate is changed, so that the polarizability of each point on the central plane of the gas chamber is close to the optimal value.

[0029] The control terminal of the spatial light modulator 5 is connected to the host computer 20. The input terminal of the spatial light modulator 5 is connected to the pump laser 1 in sequence through a 45° linear polarizer 4, a 1 / 2 wave plate 3, and a horizontal linear polarizer 2. The output terminal of the spatial light modulator 5 is connected to the alkali metal atom gas cell 10 in sequence through a non-polarized beam splitter 6. The alkali metal atom gas cell 10 is located inside a non-magnetic electric heating system 9, which is located inside a triaxial magnetic compensation coil 8. The triaxial magnetic compensation coil 8 is located inside a magnetic shielding barrel 7. The triaxial magnetic compensation coil 8 is connected to the host computer 20 through a function generator 19. The incident side of the detection light of the alkali metal atom gas cell 10 is connected to the detection laser 11 in sequence through a 1 / 4 wave plate 14, a photoelastic modulator 13, and a polarizer 12. The exit side of the detection light of the alkali metal atom gas cell 10 is connected to the host computer 20 in sequence through an analyzer 15, a photodetector 16, and a lock-in amplifier 18. The lock-in amplifier 18 is connected to the modulation controller 17.

[0030] A method for measuring highly uniform atomic polarization in SERF magnetic fields based on vector light pumping employs vector light with tunable spatial polarization distribution as pump light to polarize atoms, effectively improving the response and three-dimensional spatial electron polarization uniformity of the SERF magnetic field measurement device. The pump light polarization state is determined by applying a phase map to a spatial light modulator via a host computer, modulating the phase of the incident light. This results in a spatial polarization distribution calculated from the gas cell parameters and light intensity distribution, leading to a more uniform gas cell polarizability. Compared to SERF magnetic field measurement devices without this method, this invention modulates the spatial polarization distribution of the pump light using a spatial light modulator. This not only controls the electron polarizability value, ensuring it is distributed near the optimal polarizability, but also improves the three-dimensional spatial electron polarizability uniformity. Consequently, the SERF magnetic field measurement device exhibits a larger frequency response and a more uniform polarizability distribution, which helps reduce noise introduced by non-uniform polarizability distribution and improves the gradient differential sensitivity limit of the SERF magnetic field measurement device.

[0031] The SERF magnetic field measurement module based on the vector light pumping method includes a pump laser for generating pump light, a spatial light modulator for modulating the polarization state of the pump light, a phase map applied to the spatial light modulator by a host computer, an alkali metal gas cell, and a detection and magnetic field control system. The scalar pump light generated by the laser is used as the vector light output after passing through the spatial light modulator to polarize the alkali metal gas cell. The polarization state distribution of the vector light is adjusted by controlling the phase map applied to the spatial light modulator by the host computer to modulate the single polarization state of the scalar light into a specific spatial polarization state distribution.

[0032] The pump light is a vector light field, and the polarization state of the vector light is determined by the pump light intensity distribution and parameters such as the atomic absorption cross section, atomic number density, laser power, gas chamber radius, and gas chamber temperature of the alkali metal atoms in the alkali metal gas chamber.

[0033] The laser output from the pump laser passes sequentially through a horizontal linear polarizer, a half-wave plate, a 45° linear polarizer, a spatial light modulator, and a non-polarized beam splitter before being used as pump light to polarize alkali metal atoms in an alkali metal gas chamber. Around the alkali metal gas chamber, from the inside out, are a non-magnetic electric heating system, a triaxial magnetic compensation coil, and a magnetic shielding barrel. The detection light output from the detection laser passes sequentially through a polarizer, a photoelastic modulator, a quarter-wave plate, an alkali metal gas chamber, and an analyzer before being incident on a photodetector. The photodetector converts the optical signal into an electrical signal, which is then transmitted to a lock-in amplifier via a coaxial cable. The lock-in amplifier is connected to a modulation controller and a host computer. The modulation controller is connected to the photoelastic modulator, and the host computer is connected to the triaxial magnetic compensation coil via a function generator.

[0034] The photoelastic modulator is driven by a modulation controller. The electrical signal and the reference signal of the modulation controller are demodulated by a lock-in amplifier to obtain the DC component, first harmonic component and second harmonic component of the inspection electrical signal, and then fed back to the host computer.

[0035] A method for measuring highly uniform atomic polarization using SERF magnetic field measurement based on vector light pumping includes the following steps: Step 1: Calculate the spatial distribution of the polarization state of the pump light when the polarizability of the central plane of the gas cell is 0.5, based on the pump light intensity distribution (measured using a CCD camera) and the parameters of the alkali metal atom gas cell. Then, calculate the phase spatial distribution map from the polarization state distribution. Step 2: Build and adjust the optical path, set the temperature of the alkali metal atom source gas chamber to 160-200℃, adjust the triaxial magnetic compensation coil, and use three-dimensional in-situ magnetic compensation technology to compensate for the residual magnetism of the system (cross-compensate the magnetic fields in the X and Z directions, and finally compensate the magnetic field in the Y direction) so that the device works in SERF state. Step 3: Load the phase diagram calculated in Step 1 onto the spatial light through the host computer to generate the target vector light. Use the function generator to add a calibration magnetic field to the sensitive axis Y, adjust the pump light power to make the first harmonic component of the lock-in amplifier output the maximum, that is, the magnetic field response signal is the strongest, and record the magnitude of the Y-axis remanence and the strength of the first harmonic signal at this time. Step 4: Measure the distribution of the steady-state electronic polarization in three-dimensional space and the output magnitude of the device; Step 5: Determine whether the electronic polarizability of the central plane of the gas cell is distributed in the range of 0.5±0.05 everywhere. If yes, proceed to step 7. If not, change the phase diagram applied to the spatial light modulator and proceed to step 6. Step 6: Based on the electronic steady-state polarizability measurement results in Step 4, change the polarization state distribution of the pump light. If the polarizability of the target region is less than 0.5, increase the proportion of circularly polarized light in the corresponding region of the pump light; otherwise, decrease the proportion of circularly polarized light. Then calculate a new phase diagram and repeat Steps 3-6 until the electronic polarizability of the central plane of the gas cell is distributed around 0.5. Step 7: At this point, the highly uniform atomic polarization module is in normal working condition. The vector light generated by the spatial light modulator driven by the loading phase map is the most suitable pump light for this device.

[0036] Preferably, in step 3, the polarization ellipticity of the target vector pump light is generally greater than or equal to 0.7.

[0037] refer to Figures 1 to 4A high-uniformity atomic polarization module for SERF magnetic field measurement based on the vector light pumping method includes a laser for generating pump light (i.e., pump laser 1), a spatial light modulator 5 for modulating the pump light into vector light, an alkali metal atom gas cell 10, and a detection optical system and an active / passive magnetic field control system. The light generated by the pump laser 1, after passing through the spatial light modulator 5, outputs vector light as the pump light to polarize the atomic ensemble within the alkali metal atom gas cell 10. The polarization state of the vector light is adjusted to the optimal spatial polarization state by controlling a phase diagram applied to the spatial light modulator 5 by a host computer. At this time, the high-uniformity atomic polarization module is in normal working condition.

[0038] The spatial light modulator 5 receives the phase diagram output by the host computer 20; the pump light output by the pump laser 1 passes sequentially through the horizontal linear polarizer 2, the half-wave plate 3, the 45° linear polarizer 4, the spatial light modulator 5, and the non-polarized beam splitter 6, and then acts as vector pump light to polarize alkali metal atoms in the alkali metal atom gas chamber 10. Around the alkali metal atom gas chamber 10, from the inside out, are arranged a non-magnetic electric heating system 9, a triaxial magnetic compensation coil 8, and a magnetic shielding barrel 7; the detection light output by the detection laser 11 passes sequentially through the polarizer 12, the photoelastic modulator 13, the half-wave plate 14, the alkali metal atom gas chamber 10, and the analyzer 15, and then enters the photodetector 16. The photodetector converts the optical signal into an electrical signal and transmits it to the lock-in amplifier 18 via a coaxial cable. The lock-in amplifier 18 is connected to the modulation controller 17 and the host computer 20. The modulation controller 17 is connected to the photoelastic modulator 13, and the host computer 20 is connected to the triaxial magnetic compensation coil 8 via a function generator 19. The photoelastic modulator 13 is driven by the modulation controller 17. The electrical signal and the reference signal of the modulation controller 17 are demodulated by the lock-in amplifier 18 to obtain the DC component, first harmonic component and second harmonic component of the detection electrical signal, and are fed back to the host computer 20 for real-time display.

[0039] The principle of this invention for measuring the high-uniformity atomic polarization system using the SERF magnetic field based on the vector light pumping method is as follows: For the SERF magnetic field measuring device, the output response optical rotation angle can be expressed as: (1) in It is the rotation angle. This indicates the length of the interaction between light and atoms. The number density of alkali metal atoms. For the classical radius of the electron, At the speed of light, The polarizability component is along the direction of the detection light (x direction). The intensity of the transition oscillation of line D1. It is the imaginary number in a complex number. The Lorentz curve is the shape of line D1. The intensity of the D2 line transition oscillation. It is a Lorentz line type for line D2.

[0040] The rotation angle can be seen from equation (1). and Proportional. The specific expression for the polarizability component in the x-direction under the weak magnetic condition of the SERF state is: (2) in It is the average photon spin vector. The gyromagnetic ratio of alkali metal atoms. Let be the magnitude of the magnetic field along the y-axis. For steady-state polarizability, For pumping rate, The relaxation rate, It is the x-axis coordinate. It is the y-axis coordinate. It is the z-axis coordinate.

[0041] steady-state polarization It can be represented as: (3) Combining equations (2) and (3), we can find the value of any point at the center of the air chamber. steady-state polarizability At this time, the polarizability component in the x-direction reaches its maximum value, thus increasing the optical rotation angle. To obtain the maximum value is... Figure 3 The normalized output response of the device shown varies with the steady-state polarization rate, therefore, it is necessary to adjust the pumping rate. satisfy .

[0042] When light passes through an atomic gas cell, light absorption can be expressed as: (4) in Indicates the intensity of the pump light. It is the atomic absorption cross section. It is the average photon spin vector, which is related to the polarization state of the pump light.

[0043] Due to pumping rate It can be represented as: (5) in is Planck's constant. Laser frequency, This indicates the area of ​​the light spot.

[0044] The pumping rate can be calculated by combining equations (4) and (5). and average photon vector Relationship: (6) As can be seen from equation (6), changing the polarization state of the pump light is equivalent to adjusting the average photon spin vector at different plane coordinates. This allows for the regulation of the three-dimensional pumping rate. By adjusting the pumping rate This can improve the output response of the device. For example... Figure 4 As shown, for a point on the central plane of the air chamber The average photon spin vector is changed by altering the polarization state of the pump light. The value of can be used to adjust the steady-state polarization. This ensures that the distribution is near the optimal polarizability (0.5), while simultaneously improving the uniformity of electronic polarizability. On the other hand, from equation (2), the average photon spin vector... polarizability components in the x-direction Relatedly, to ensure a sufficiently large output response, the average photon spin vector... The value should be greater than or equal to 0.7; otherwise, the intensity of the incident light should be reduced.

[0045] Contents not described in detail in this specification are prior art known to those skilled in the art. It is hereby indicated that the above description is intended to help those skilled in the art understand this invention, but does not limit the scope of protection of this invention. Any equivalent substitutions, modifications, improvements, and / or simplifications of the above descriptions that do not depart from the essential content of this invention fall within the scope of protection of this invention.

Claims

1. A method for measuring highly uniform atomic polarization using SERF magnetic field based on vector light pumping, characterized in that, Includes the following steps: Step 1: For the alkali metal atom gas cell in the SERF magnetic field measurement device, obtain the spatial distribution of the pump light polarization state when the electronic polarizability of the central plane of the gas cell is 0.5 everywhere, and form a pump light phase spatial distribution map based on the spatial distribution of the pump light polarization state. Step 2: Load the pump light phase space distribution map onto the spatial light modulator set on the pump light path, and drive it to modulate the incident scalar pump light into the outgoing vector pump light according to the phase space distribution map, so as to control the single polarization state of the scalar light into the spatial polarization state distribution of the vector light. Step 3: Measure the three-dimensional spatial electronic steady-state polarization distribution and the magnitude of the device output response signal using the detection optical path of the SERF magnetic field measuring device; Step 4: Determine whether the electronic polarizability of the central plane of the gas cell is distributed in the range of 0.5±0.05 everywhere. If yes, proceed to step 5. If no, change the pump light phase spatial distribution diagram and return to step 2. Step 5: Determine that the vector pump light generated by loading the pump light phase spatial distribution map onto the spatial light modulator is the most suitable pump light for this device.

2. The method for measuring highly uniform atomic polarization using SERF magnetic field based on vector light pumping according to claim 1, characterized in that, In step 2, the polarization ellipticity of the vector pump light is ≥0.

7.

3. The method for measuring highly uniform atomic polarization using SERF magnetic field based on vector light pumping according to claim 1, characterized in that, Step 4 includes: when the electronic polarizability is greater than the upper limit of the range, the proportion of circularly polarized light in the pump light at that location is increased; when the electronic polarizability is less than the lower limit of the range, the proportion of circularly polarized light in the pump light at that location is decreased, thereby changing the phase spatial distribution map of the pump light.

4. The method for measuring highly uniform atomic polarization using SERF magnetic field based on vector light pumping according to claim 1, characterized in that, In step 1, the SERF magnetic field measurement device includes a pump laser, a horizontal linear polarizer, a half-wave plate, a 45° linear polarizer, a spatial light modulator, a non-polarized beam splitter, and an alkali metal atom gas cell connected in sequence. The spatial light modulator is connected to a host computer. The alkali metal atom gas cell is located within a non-magnetic electric heating system. The non-magnetic electric heating system is located within a triaxial magnetic compensation coil. The triaxial magnetic compensation coil is located within a magnetic shielding barrel. The triaxial magnetic compensation coil is connected to the host computer via a function generator.

5. The method for measuring highly uniform atomic polarization using SERF magnetic field based on vector light pumping according to claim 1, characterized in that, In step 1, the SERF magnetic field measurement device includes a detection laser, a polarizer, a photoelastic modulator, a quarter-wave plate, an alkali metal atom gas cell, an analyzer, a photodetector, a lock-in amplifier, and a host computer connected in sequence. The lock-in amplifier is connected to a modulation controller.

6. The method for measuring highly uniform atomic polarization using SERF magnetic field based on vector light pumping according to claim 5, characterized in that, The lock-in amplifier obtains the DC component, first harmonic component, and second harmonic component of the detection electrical signal based on the detection electrical signal input from the photodetector and the reference signal input from the modulation controller, and feeds it back to the host computer for real-time display.

7. The method for measuring highly uniform atomic polarization using SERF magnetic field based on vector light pumping according to claim 1, characterized in that, Step 1 includes the following expression: ， ， ， in It is the steady-state polarizability at the coordinate point (x, y, z). It is the pumping rate at the coordinate point (x, y, z). It is the relaxation rate at the coordinate point (x, y, z).

8. The method for measuring highly uniform atomic polarization using SERF magnetic field based on vector light pumping according to claim 1, characterized in that, Step 2 includes the following expression: ， ≥0.7， in It is the atomic number density of alkali metals. It is the atomic absorption cross section. It is the average photon spin vector. It is related to the polarization state of the pump light.

9. A high-uniformity atomic polarization module for SERF magnetic field measurement based on vector light pumping, characterized in that, It includes a spatial light modulator for carrying a pump light phase spatial distribution map. The spatial light modulator converts a scalar light field into a vector light field through the pump light phase spatial distribution map to polarize the atoms in the alkali metal atom gas chamber. Furthermore, it modulates the spatial polarization state distribution of the pump light to change the longitudinal light intensity attenuation rate, so that the polarizability of each point on the central plane of the gas chamber is close to the optimal value.

10. The high-uniformity atomic polarization module for SERF magnetic field measurement based on vector light pumping according to claim 9, characterized in that, The control terminal of the spatial light modulator is connected to the host computer. The input terminal of the spatial light modulator is connected to the pump laser in sequence through a 45° linear polarizer, a half-wave plate, and a horizontal linear polarizer. The output terminal of the spatial light modulator is connected to the alkali metal atom gas cell through a non-polarized beam splitter. The alkali metal atom gas cell is located within a non-magnetic electric heating system, which is located within a three-axis magnetic compensation coil. The three-axis magnetic compensation coil is located within a magnetic shielding barrel. The three-axis magnetic compensation coil is connected to the host computer through a function generator. The incident side of the detection light from the alkali metal atom gas cell is connected to the detection laser in sequence through a quarter-wave plate, a photoelastic modulator, and a polarizer. The exit side of the detection light from the alkali metal atom gas cell is connected to the host computer in sequence through an analyzer, a photodetector, and a lock-in amplifier. The lock-in amplifier is connected to the modulation controller.

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