A two-axis magnetic field measurement gradiometer based on the spin-exchange relaxation effect

Abstract

This invention provides a biaxial magnetic field measurement gradient meter based on the spin-free exchange relaxation effect, comprising: a gas cell unit including a heating element and a magnetic shielding element, wherein the heating element contains an alkali metal gas cell; a pump light unit including a first optical platform and a pump light path disposed on the first optical platform, wherein the pump light generated by the pump light path is used to polarize the alkali metal atoms in the alkali metal gas cell; and a detection light unit including a second optical platform and a detection light path disposed on the second optical platform, wherein the detection light generated by the detection light path passes through the alkali metal gas cell twice to obtain the magnetic field gradients along the X and Y axes. Because the detection light generated by the detection light path can enter the alkali metal gas cell twice, simultaneous measurement of the biaxial magnetic field gradients along the X and Y axes is achieved, thereby reducing the influence on the relaxation of alkali metal atoms and reducing the influence on the signal differential effect in magnetic field measurement, thus reducing the limitations on improving magnetic field sensitivity in magnetic field measurement.

Description

Technical Field

[0001] This invention relates to the field of instrumentation technology, specifically to a biaxial magnetic field measurement gradient meter based on the spin-free exchange relaxation effect. Background Technology

[0002] The precise measurement of physical quantities using atomic spin exchange effects has become an important method in experimental physics in recent years. Furthermore, with improvements in measurement accuracy using existing technologies, some new atomic spin physics effects, manipulation principles, and methods have been discovered and applied. Among these, the manipulation and detection of SERF-state atomic spins can achieve ultra-high sensitivity magnetic field measurements, significantly surpassing previous related measurement methods, thus providing humanity with new tools for understanding the world.

[0003] In existing technology, a magnetometer is an instrument that accurately measures the magnitude of a magnetic field by measuring minute changes in spin polarization. Its basic principle is as follows: First, atomic spin polarization is achieved using pump light. Subsequently, the polarized spins are deflected under the influence of a weak external magnetic field. The deflected spins produce a tiny spin projection in a direction perpendicular to the pump light; this spin polarization projection is proportional to the magnitude of the magnetic field. Therefore, by detecting this spin polarization projection, the magnitude of the magnetic field can be obtained.

[0004] However, with the continuous improvement of the sensitivity of ultra-sensitive magnetic field measurement devices based on SERF state atomic spin and the deepening of theoretical research, factors that limit the further improvement of magnetic field sensitivity in magnetic field measurement have also emerged one by one. For example, the existence of magnetic field gradient not only affects atomic relaxation, but also affects the signal differential effect in magnetic field measurement, thus having limitations. Summary of the Invention

[0005] This invention is made to solve the above-mentioned problems, and aims to provide a biaxial magnetic field measurement gradient instrument based on the spin-free exchange relaxation effect.

[0006] This invention provides a biaxial magnetic field measurement gradient meter based on spin-free exchange relaxation effect, characterized by the following features: a gas chamber unit including a heating element and a magnetic shield surrounding the heating element, wherein an alkali metal gas chamber is disposed inside the heating element; a pump light unit including a first optical platform and a pump light path disposed on the first optical platform, wherein the pump light generated by the pump light path enters the alkali metal gas chamber to polarize the alkali metal atoms in the alkali metal gas chamber; and a detection light unit including a second optical platform and a detection light path disposed on the second optical platform, wherein the detection light path is a reflective detection light path, such that the detection light generated by the detection light path passes through the alkali metal gas chamber for the first time, and then passes through the alkali metal gas chamber again after reflection, thereby passing through the alkali metal gas chamber twice to obtain the magnetic field gradients of the X-axis and Y-axis; wherein the second optical platform is disposed below the first optical platform, and the irradiation direction of the pump light is perpendicular to the irradiation direction of the detection light.

[0007] The biaxial magnetic field measurement gradient instrument based on the spin-free exchange relaxation effect provided by the present invention also has the following features: the pump optical path includes a first laser, a first polarizer, and a metasurface mirror arranged in a straight line in sequence. The first laser generates pump light, which becomes linearly polarized light after passing through the first polarizer, and then becomes circularly polarized light after passing through the metasurface mirror. After entering the metal chamber, it reacts with alkali metal atoms and polarizes the alkali metal atoms.

[0008] The biaxial magnetic field measurement gradient meter based on spin-free exchange relaxation effect provided by this invention also has the following features: the detection optical path includes a second laser, a beam expander, a second polarizer, and a first differential detection device disposed on one side of the gas cell unit, and a quarter-wave plate, a semi-transparent mirror, a reflector, and a second differential detection device disposed on the other side of the gas cell unit. The second laser generates detection light, which passes through the beam expander and the second polarizer to form first linearly polarized light. After passing through the alkali metal gas cell, the first linearly polarized light passes through the quarter-wave plate and the semi-transparent mirror and is split into two second linearly polarized beams of equal intensity. One of the second linearly polarized beams is then received by the second differential detection device to obtain the magnetic field gradient of the X-axis. The other second linearly polarized beam passes through the reflector and the quarter-wave plate, passes through the alkali metal gas cell again, and is finally received by the first differential detection device to obtain the magnetic field gradient of the Y-axis.

[0009] Furthermore, the angle between the first linearly polarized light and the semi-transparent mirror is 45 degrees.

[0010] The biaxial magnetic field measurement gradient instrument based on the spin-free exchange relaxation effect provided by the present invention also has the following feature: a vacuum insulation layer is provided between the heating element and the magnetic shielding element.

[0011] The biaxial magnetic field measurement gradient instrument based on the spin-free exchange relaxation effect provided by this invention also has the following feature: the center of the alkali metal gas cell is located on the irradiation path of the pump light.

[0012] The biaxial magnetic field measurement gradient instrument based on the spin-free exchange relaxation effect provided by this invention also has the following feature: both the first optical platform and the second optical platform are made of non-magnetic materials.

[0013] The biaxial magnetic field measurement gradient instrument based on the spin-free exchange relaxation effect provided by the present invention also has the following feature: the first optical platform and the second optical platform surround the magnetic shielding component and do not contact the outer wall of the magnetic shielding component.

[0014] The biaxial magnetic field measurement gradient instrument based on spin-free exchange relaxation effect provided by this invention also has the following feature: the alkali metal gas chamber contains at least two kinds of alkali metal atoms.

[0015] The biaxial magnetic field measurement gradient instrument based on spin-free exchange relaxation effect provided by the present invention also has the following feature: the centers of the heating element, the magnetic shielding element, the first optical platform and the second optical platform are all located at the same position.

[0016] The role and effect of invention

[0017] The biaxial magnetic field gradient meter based on the spin-free exchange relaxation effect according to the present invention, because the heating element enables the alkali metal atoms in the alkali metal chamber to be in a spin-free exchange relaxation state, allows the pump light generated by the pump optical path to enter the alkali metal chamber and cause the alkali metal atoms to transition from the ground state to an excited state, thereby spin polarizing the alkali metal atoms. Furthermore, because the detection light generated by the detection optical path can enter the alkali metal chamber twice, simultaneous measurement of the X-axis and Y-axis biaxial magnetic field gradients is achieved, thereby reducing the influence on the relaxation of alkali metal atoms and the impact on the signal differential effect in magnetic field measurement, thus reducing the limitations on improving magnetic field sensitivity in magnetic field measurement. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a biaxial magnetic field measurement gradient meter based on the spin-free exchange relaxation effect in an embodiment of the present invention.

[0019] Explanation of reference numerals in the attached figures:

[0020] 100. Biaxial magnetic field measurement gradient meter; 10. Gas cell unit; 11. Heating element; 12. Magnetic shielding element; 13. Vacuum insulation layer; 20. Pump light unit; 21. First laser; 22. First polarizer; 23. Metasurface mirror; 30. Detection light unit; 31. Second laser; 32. Beam expander; 33. Second polarizer; 34. First differential detection element; 35. Quarter wave plate; 36. Semi-transparent mirror; 37. Mirror; 38. Second differential detection element. Detailed Implementation

[0021] To make the technical means, creative features, objectives and effects of this invention easier to understand, the following embodiments are described in detail with reference to the accompanying drawings.

[0022] Example

[0023] Figure 1 This is a schematic diagram of the structure of a biaxial magnetic field measurement gradient meter based on the spin-free exchange relaxation effect in an embodiment of the present invention.

[0024] like Figure 1 As shown, this embodiment provides a biaxial magnetic field measurement gradient meter 100 based on spin-free exchange relaxation effect, including: a gas cell unit 10, a pump optical unit 20, and a detection optical unit 30.

[0025] like Figure 1 As shown, the gas chamber unit 10 includes a heating element 11 and a magnetic shielding element 12 surrounding the heating element 11. An alkali metal gas chamber is located inside the heating element 11. During operation, the heating element 11 heats the internal alkali metal gas chamber, and the magnetic shielding element 12 reduces the influence of the external environment on the alkali metal gas chamber, thereby stably keeping the alkali metal atoms within the gas chamber in a spin-free exchange relaxation state. This facilitates improved sensitivity and stability during magnetic field measurement or magnetic field gradient measurement. In this embodiment, the heating element 11 is preferably an oven, and the magnetic shielding element 12 is preferably a kit made of permalloy or an iron-aluminum alloy.

[0026] In this embodiment, a vacuum insulation layer 13 is provided between the heating element 11 and the magnetic shielding element 12. During operation, the vacuum insulation layer 13 can reduce the heat loss in the alkali metal chamber and assist the magnetic shielding element 12 in reducing the influence of the external environment on the alkali metal chamber, thereby improving the stability of the biaxial magnetic field measuring gradient instrument 100 of the present invention during operation.

[0027] In this embodiment, the alkali metal chamber contains at least two types of alkali metal atoms. For the alkali metal chamber, the polarization uniformity of the alkali metal atoms within it is crucial. Specifically, the rate of light intensity attenuation after light enters the alkali metal chamber can reflect the polarization uniformity of the alkali metal atoms to a certain extent. More specifically, a faster light intensity attenuation indicates less uniform polarization of the alkali metal atoms within the chamber. However, the rate of light intensity attenuation depends on the absorption rate of the alkali metal chamber; a faster attenuation indicates stronger absorption of light by the alkali metal atoms. Therefore, the alkali metal chamber of the biaxial magnetic field measurement gradient meter 100 of this invention contains at least two types of alkali metal atoms, thus ensuring uniform polarization within the chamber and improving the practical effectiveness of the biaxial magnetic field measurement gradient meter 100.

[0028] As shown in Figure 1, the pump optical unit 20 includes a first optical platform and a pump optical path disposed on the first optical platform. The pump light generated by the pump optical path enters the alkali metal gas chamber to polarize the alkali metal atoms in the alkali metal gas chamber. The pump optical path includes a first laser 21, a first polarizer 22, and a metasurface mirror 23 arranged in a straight line in sequence.

[0029] During operation, the first laser 21 generates pump light, which becomes linearly polarized light after passing through the first polarizer 22, and then becomes circularly polarized light after passing through the metasurface mirror 23. At this time, the circularly polarized light can be divided into left-handed circularly polarized light and right-handed circularly polarized light. Thus, after the circularly polarized light enters the alkali metal chamber, it can interact with the alkali metal atoms in the alkali metal chamber, causing the alkali metal atoms to be polarized.

[0030] In this embodiment, because a metasurface mirror 23 is used in the pump optical path, the influence of various interference factors on the measurement results is effectively eliminated while ensuring high measurement accuracy. This further improves the practical effect of the biaxial magnetic field measurement gradient meter 100 of the present invention.

[0031] like Figure 1 As shown, the detection optical unit 30 includes a second optical platform and a detection optical path disposed on the second optical platform. The detection optical path is a reflective detection optical path, so that the detection light generated by the detection optical path passes through the alkali metal gas cell for the first time, and then passes through the alkali metal gas cell again after reflection. Thus, the detection light passes through the alkali metal gas cell twice, thereby obtaining the magnetic field gradients of the X-axis and Y-axis. The detection optical path includes a second laser 31, a beam expander 32, a second polarizer 33, and a first differential detection element 34 disposed on one side of the gas cell unit 10, and a quarter-wave plate 35, a semi-transparent and semi-reflective mirror 36, a reflector 37, and a second differential detection element 38 disposed on the other side of the gas cell unit 10.

[0032] During operation, the second laser generates a detection beam. This detection beam passes through the beam expander 32 and the second polarizer 33 to form a first linearly polarized beam. The first linearly polarized beam then passes through the alkali metal gas cell, followed by a quarter-wave plate 35 and a semi-transparent mirror 36. In this embodiment, the angle between the first linearly polarized beam and the semi-transparent mirror 36 is 45 degrees. Therefore, after passing through the semi-transparent mirror 36, the first linearly polarized beam is split into two beams of equal intensity. One beam of the second linearly polarized beam is then received by the second differential detector 38 to obtain the magnetic field gradient along the X-axis. The other beam of the second linearly polarized beam passes through the mirror 37 and the quarter-wave plate 35, then passes through the alkali metal gas cell again, and is finally received by the first differential detector 34 to obtain the magnetic field gradient along the Y-axis. When there is a spatial gap between the first linearly polarized light and another second linearly polarized light, it can be used as a gradient meter. Specifically, if there is no gradient, the output signal is zero; if there is a gradient (temperature, magnetic field, pump light intensity, etc.), the signals cannot cancel each other out, and thus can be used to measure gradient information.

[0033] In this embodiment, because the detection optical path uses a quarter-wave plate 35, the detection light will have a π phase delay after passing through the quarter-wave plate 35 twice, which can isolate the reflected light during the measurement process and thus improve the accuracy of the measurement results.

[0034] In this embodiment, the irradiation direction of the pump light is perpendicular to the irradiation direction of the detection light, and the center of the alkali metal gas cell is located on the irradiation path of the pump light. During operation, because the center of the alkali metal gas cell is located on the irradiation path of the pump light, the uniformity of the polarization effect of alkali metal atoms within the alkali metal gas cell can be ensured, thereby further improving the accuracy of the measurement results.

[0035] In this embodiment, both the first and second optical platforms are made of non-magnetic materials. The second optical platform is located below the first optical platform. The first and second optical platforms surround the magnetic shield 12 but do not contact the outer wall of the magnetic shield 12. Therefore, the non-magnetic first and second optical platforms can reduce the influence on the magnetic measurement results. Furthermore, the vertical arrangement of the first and second optical platforms can avoid mutual interference between the pump optical path and the detection optical path during operation. Also, the surrounding arrangement of the first and second optical platforms prevents the application of external forces to the magnetic shield 12, thus avoiding any impact on its performance. In summary, this further ensures the stability of the biaxial magnetic field measurement gradient meter 100 during operation.

[0036] The biaxial magnetic field measuring gradient instrument 100 of this invention must be installed in a top-to-bottom, inside-to-outside sequence. In this embodiment, the centers of the heating element 11, the magnetic shielding element 12, the first optical platform, and the second optical platform are all located at the same position. Therefore, each component can be adjusted into position according to the instrument reference, facilitating installation and ensuring that each component meets the requirements of the sub-installation indicators. This also guarantees the accuracy, repeatability, and calibrability of each component after installation. Furthermore, it makes it easier to meet the overall design specifications after installation and commissioning.

[0037] The role and effect of the embodiments

[0038] According to the biaxial magnetic field measurement gradient meter based on the spin-free exchange relaxation effect involved in this embodiment, because the heating element enables the alkali metal atoms in the alkali metal gas chamber to be in a spin-free exchange relaxation state, the pump light generated by the pump optical path can cause the alkali metal atoms to transition from the ground state to an excited state after entering the alkali metal gas chamber, thereby spin polarization of the alkali metal atoms. Furthermore, because the detection light generated by the detection optical path can enter the alkali metal gas chamber twice, simultaneous measurement of the X-axis and Y-axis biaxial magnetic field gradients is achieved, thereby reducing the influence on the relaxation of alkali metal atoms and the impact on the signal differential effect in magnetic field measurement, thus reducing the limitations on improving magnetic field sensitivity in magnetic field measurement.

[0039] Furthermore, because the heating element in the biaxial magnetic field measurement gradient instrument based on the spin-free exchange relaxation effect in this invention can heat the alkali metal gas chamber inside, and the magnetic shielding element can reduce the influence of the external environment on the alkali metal gas chamber, it can stably keep the alkali metal atoms in the alkali metal gas chamber in a spin-free exchange relaxation state, thereby facilitating the improvement of sensitivity and stability during magnetic field measurement or magnetic field gradient measurement.

[0040] Furthermore, because a vacuum insulation layer is provided between the heating element and the magnetic shielding element in the biaxial magnetic field measurement gradient instrument based on the spinless exchange relaxation effect in this invention, the vacuum insulation layer can reduce the heat loss in the alkali metal chamber and assist the magnetic shielding element in reducing the influence of the external environment on the alkali metal chamber, thereby improving the stability of the biaxial magnetic field measurement gradient instrument of this invention during operation.

[0041] Furthermore, because the alkali metal gas chamber in the biaxial magnetic field measurement gradient instrument based on the spin-free exchange relaxation effect of the present invention contains at least two kinds of alkali metal atoms, the polarization in the alkali metal gas chamber can be made uniform, thereby improving the practical effect of the biaxial magnetic field measurement gradient instrument of the present invention.

[0042] Furthermore, because the pump optical path of the biaxial magnetic field measurement gradient meter based on the spin-free exchange relaxation effect in this invention employs a metasurface mirror, it effectively eliminates the influence of various interference factors on the measurement results while ensuring high measurement accuracy. This further improves the practical effect of the biaxial magnetic field measurement gradient meter of this invention.

[0043] Furthermore, because the detection optical path of the biaxial magnetic field measurement gradient meter based on the spin-free exchange relaxation effect in this invention uses a quarter-wave plate, the detection light will have a π-phase delay after passing through the quarter-wave plate twice, which can isolate the reflected light during the measurement process and thus improve the accuracy of the measurement results.

[0044] Furthermore, in the biaxial magnetic field measurement gradient meter based on the spin-free exchange relaxation effect of this invention, both the first and second optical platforms are made of non-magnetic materials. The second optical platform is located below the first optical platform. The first and second optical platforms surround the magnetic shielding component but do not contact its outer wall. Therefore, the non-magnetic first and second optical platforms can reduce the impact on the magnetic measurement results. The vertical arrangement of the first and second optical platforms avoids mutual interference between the pump and detection optical paths during operation. Furthermore, the surrounding arrangement of the first and second optical platforms prevents the application of external forces to the magnetic shielding component, thus avoiding any impact on its performance. In summary, this further ensures the stability of the biaxial magnetic field measurement gradient meter during operation.

[0045] Furthermore, because the heating element, magnetic shield, first optical platform, and second optical platform of the biaxial magnetic field measurement gradient instrument based on the spin-free exchange relaxation effect in this invention are all centered at the same location, each component can be adjusted into position according to the instrument reference, facilitating installation and ensuring that each component meets the requirements of the sub-installation specifications. This also guarantees the accuracy, repeatability, and calibrability of each component after installation. Moreover, it makes it easier to meet the overall design specifications after installation and commissioning.

[0046] The above embodiments are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention.

Claims

1. A two-axis magnetic field measurement gradiometer based on the spin- exchange relaxation effect, characterized in that include: The gas chamber unit includes a heating element and a magnetic shielding element surrounding the heating element, wherein the heating element has an alkali metal gas chamber inside; The pump light unit includes a first optical platform and a pump light path disposed on the first optical platform. The pump light generated by the pump light path enters the alkali metal gas chamber to polarize the alkali metal atoms in the alkali metal gas chamber. as well as The detection light unit includes a second optical platform and a detection light path disposed on the second optical platform. The detection light path is a reflective detection light path, so that the detection light generated by the detection light path passes through the alkali metal gas cell for the first time, and then passes through the alkali metal gas cell again after reflection. Thus, the detection light passes through the alkali metal gas cell twice to obtain the magnetic field gradients of the X-axis and Y-axis. The detection optical path includes a second laser, a beam expander, a second polarizer, and a first differential detection device located on one side of the gas cell unit, and a quarter-wave plate, a semi-transparent mirror, a reflector, and a second differential detection device located on the other side of the gas cell unit. The second laser generates the detection light, which passes through the beam expander and the second polarizer to form first linearly polarized light. After passing through the alkali metal gas cell, the first linearly polarized light then passes through the quarter-wave plate and the semi-transparent mirror, and is split into two beams of second linearly polarized light with equal intensity. Then, one beam of the second linearly polarized light is received by the second differential detector to obtain the magnetic field gradient along the X-axis. The other beam of the second linearly polarized light passes through the mirror and the quarter-wave plate, then passes through the alkali metal gas cell again, and is finally received by the first differential detector to obtain the magnetic field gradient along the Y-axis. The second optical platform is located below the first optical platform, and the irradiation direction of the pump light is perpendicular to the irradiation direction of the detection light.

2. The biaxial magnetic field measurement gradient instrument based on spin-free exchange relaxation effect according to claim 1, characterized in that: wherein, The pump optical path includes a first laser, a first polarizer, and a metasurface mirror arranged in a straight line. The first laser generates the pump light, which becomes linearly polarized after passing through the first polarizer, and then becomes circularly polarized after passing through the metasurface mirror. It then enters the metal chamber and reacts with the alkali metal atoms, polarizing the alkali metal atoms.

3. The biaxial magnetic field measurement gradient instrument based on spin-free exchange relaxation effect according to claim 1, characterized in that: wherein The angle between the first linearly polarized light and the semi-transparent mirror is 45 degrees.

4. The biaxial magnetic field measurement gradient instrument based on spin-free exchange relaxation effect according to claim 1, characterized in that: wherein A vacuum insulation layer is provided between the heating element and the magnetic shielding element.

5. The biaxial magnetic field measurement gradient instrument based on spin-free exchange relaxation effect according to claim 1, characterized in that: in, The center of the alkali metal gas chamber is located on the irradiation path of the pump light.

6. The biaxial magnetic field measurement gradient instrument based on spin-free exchange relaxation effect according to claim 1, characterized in that: in, Both the first optical platform and the second optical platform are made of non-magnetic materials.

7. The biaxial magnetic field measurement gradient instrument based on spin-free exchange relaxation effect according to claim 1, characterized in that: wherein, The first optical platform and the second optical platform surround the magnetic shielding component and do not contact the outer wall of the magnetic shielding component.

8. The biaxial magnetic field measurement gradient instrument based on spin-free exchange relaxation effect according to claim 1, characterized in that: in, The alkali metal chamber contains at least two alkali metal atoms.

9. The biaxial magnetic field measurement gradient instrument based on spin-free exchange relaxation effect according to claim 1, characterized in that: wherein, The centers of the heating element, the magnetic shielding element, the first optical platform, and the second optical platform are all located at the same position.

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