Electromagnetic induction imaging device and method based on atomic spin-free exchange relaxation

Abstract

The invention discloses an electromagnetic induction imaging device and method based on atomic spin-exchange relaxation-free. A light beam emitted by the light source unit enters the light path adjusting unit after passing through the gas chamber coil unit, a to-be-imaged sample is placed in the gas chamber coil unit, the to-be-imaged sample generates a magnetic field under the action of the gas chamber coil unit, and the magnetic field acts on an atomic gas chamber in the gas chamber coil unit. The light beam sequentially passes through the atomic gas chamber and the light path adjusting unit and then enters the imaging unit, the imaging unit performs electromagnetic induction imaging on a sample and displays the sample, and the atomic gas chamber is filled with alkali metal atoms in a state without spin exchange relaxation. Based on the spin-exchange relaxation-free state of atoms, according to the electromagnetic induction phenomenon of an imaged sample, two-dimensional imaging of the sample is achieved, and magnetic field information obtained through electromagnetic induction of the sample can be extracted from light intensity information obtained after the sample penetrates through the atomic air chamber and combined imaging is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic induction imaging, and in particular relates to an electromagnetic induction imaging device and method based on atomic spin-free exchange relaxation. Background Art

[0002] Electromagnetic induction imaging technology based on atomic gas chamber is a technology that uses the characteristics of the interaction between atoms and electromagnetic fields to achieve imaging. Common technical solutions include electromagnetic induced transparency (EIT) imaging. EIT is a quantum interference phenomenon. Through the interaction between a specific laser field and atoms, high-sensitivity detection of electromagnetic fields can be achieved. EIT imaging technology can be used for light deceleration and light storage, and its storage life can reach the order of seconds. However, it is a challenge to achieve a narrow linewidth spectrum because the depolarization of the system and the destruction of the phase correlation of different quantum systems are not conducive to obtaining a narrow linewidth spectrum. In addition, the low-frequency electric field waveform measurement technology based on Rydberg atomic antenna can convert the field intensity measurement of the electromagnetic field into frequency measurement through spectral technology to achieve electromagnetic field value traceability imaging. This technology is more used in the field of electromagnetic field parameter measurement, but how to improve the measurement bandwidth and sensitivity is still a challenge. Similar to this is electromagnetic imaging technology (EMT), which is a process tomography technology based on the principle of electromagnetic induction, suitable for detecting and reproducing multiphase flow field space. This technology has the advantages of non-contact, non-invasive, low cost, and real-time imaging. However, the resolution of EMT image reconstruction is low and is also affected by many factors. Regardless of which of the above imaging technologies is used, high-performance micro-atomic gas chambers are the research hotspots of atomic imaging technology. Analyze the multi-body interactions between alkali metal atoms, working gases, and buffer gases, and study the mechanism of action of the filling medium and structure in the atomic gas chamber and the atomic spin polarization relaxation. To achieve a higher-performance atomic gas chamber, the challenges faced include how to increase the polarizability of atoms and increase the relaxation time of atomic spins in the gas chamber. Electromagnetic induction imaging technology based on atomic gas chambers has great potential in achieving high-precision and high-sensitivity electromagnetic field measurement and imaging, but it also faces many challenges such as improving measurement bandwidth, sensitivity, resolution, and reducing system size. The existing technology lacks an electromagnetic induction imaging method with long atomic relaxation time and high sensitivity. Summary of the invention

[0003] In order to solve the problems existing in the background technology, the purpose of the present invention is to provide an electromagnetic induction imaging device and method based on atomic spin-free exchange relaxation.

[0004] The technical solution adopted by the present invention is as follows:

[0005] 1. An electromagnetic induction imaging device based on atomic spin-free exchange relaxation:

[0006] It includes a light source unit, an air chamber coil unit, an optical path adjustment unit and an imaging unit; the light beam emitted by the light source unit enters the optical path adjustment unit after passing through the air chamber coil unit, the sample to be imaged is placed in the air chamber coil unit, the sample to be imaged generates a magnetic field under the action of the air chamber coil unit, the magnetic field acts on the atomic air chamber in the air chamber coil unit, the light beam passes through the atomic air chamber and the optical path adjustment unit in sequence and enters the imaging unit, and the imaging unit performs electromagnetic induction imaging on the sample and displays it.

[0007] The light source unit comprises a laser, a half wave plate, a polarization beam splitter and a quarter wave plate; the light beam emitted by the laser is incident on the polarization beam splitter via the half wave plate, and then reflected and / or transmitted to the quarter wave plate via the splitting surface of the polarization beam splitter, the half wave plate is used to adjust the intensity of the incident light beam, the splitting surface of the polarization beam splitter is used to split the incident light beam into two linear polarized lights with polarization directions perpendicular to each other, one of the linear polarized lights emitted by the polarization beam splitter is used as polarization detection light, the quarter wave plate is used to receive and adjust the polarization direction of the polarization detection light, so that the polarization detection light is changed from linear polarization light to circular polarization light, and the circular polarization light is then input into the air chamber coil unit.

[0008] The gas chamber coil unit comprises an atomic gas chamber, a Helmholtz coil and a non-magnetic conductive coil; the atomic gas chamber is located at the center of the Helmholtz coil, the atomic gas chamber is filled with alkali metal atoms and buffer gas, the outer wall of the atomic gas chamber is wound with a non-magnetic twisted pair wire for heating, so that the alkali metal atoms are in a state of no spin exchange relaxation, the sample to be imaged is placed between the Helmholtz coil and the non-magnetic conductive coil, the non-magnetic conductive coil is used to generate a radio frequency field, the radio frequency field acts on the sample to be imaged to generate an induced current, the induced current generates a magnetic field and acts on the atomic gas chamber, the Helmholtz coil generates a compensation magnetic field for offsetting the excess magnetic field around the atomic gas chamber, so that the magnetic field around the atomic gas chamber is a zero magnetic field.

[0009] The optical path adjustment unit is mainly composed of a first total reflection prism and a second total reflection prism; after the polarized detection light is converted from linearly polarized light into circularly polarized light, it is transmitted through the atomic gas chamber in the gas chamber coil unit, and then is reflected by the first total reflection prism and the second total reflection prism in sequence and output to the imaging unit. The first total reflection prism and the second total reflection prism are arranged between the gas chamber coil unit and the imaging unit, and are used to change the direction of the light beam emitted from the atomic gas chamber to be incident on the imaging unit.

[0010] The imaging unit is mainly composed of a photodetector and an acquisition system. The photodetector is used to receive and record the light intensity information of the polarized detection light after it passes through the atomic gas chamber. The acquisition system obtains the magnetic field information of the electromagnetic induction of the sample according to the absorption change of the light intensity by the alkali metal atoms. Finally, electromagnetic induction imaging is performed on the imaged sample and displayed based on the magnetic field information of the electromagnetic induction of the sample.

[0011] The laser frequency of the laser is tuned to the transition frequency of the alkali metal atoms in the atomic gas cell.

[0012] The alkali metal atoms in the atomic gas chamber are selected from the group consisting of rubidium atoms, sodium atoms, potassium atoms, lithium atoms and cesium atoms.

[0013] The buffer gas in the atomic gas chamber is nitrogen gas.

[0014] 2. An electromagnetic induction imaging method based on atomic spin-free exchange relaxation, comprising the following steps:

[0015] Step S1, setting up an electromagnetic induction imaging device: tuning the laser frequency of the laser in the light source unit to the transition frequency of the alkali metal atoms in the air chamber coil unit, starting the laser, and the light beam emitted by the laser passes through the air chamber coil unit and the optical path adjustment unit in sequence, and is received by the imaging unit;

[0016] Step S2, heating the atomic gas chamber of the gas chamber coil unit so that the alkali metal atoms in the atomic gas chamber are heated to a state without spin exchange relaxation;

[0017] Step S3, applying direct current to the Helmholtz coil of the gas chamber coil unit, so that the Helmholtz coil generates a compensation magnetic field for offsetting the redundant magnetic field around the atomic gas chamber, so that the magnetic field around the atomic gas chamber is a zero magnetic field;

[0018] Step S3, applying an AC voltage to the non-magnetic conductive coil of the gas chamber coil unit, placing a sample to be imaged below the non-magnetic conductive coil, and generating an induced current under the radio frequency field of the non-magnetic conductive coil. The induced current generates a magnetic field and acts on the atomic gas chamber;

[0019] Step S4, the light beam emitted by the laser enters the photodetector of the imaging unit after passing through the atomic gas chamber. The photodetector transmits the light intensity information transmitted through the atomic gas chamber to the acquisition system. The acquisition system of the imaging unit obtains the magnetic field information of the electromagnetic induction of the sample according to the absorption change of the light intensity by the alkali metal atoms. Finally, electromagnetic induction imaging is performed on the sample to be imaged and displayed according to the magnetic field information of the electromagnetic induction of the sample.

[0020] Specifically, the absorption change of light intensity by alkali metal atoms is the absorption change of light intensity before and after filling the atomic gas chamber with alkali metal atoms. The light intensity absorption change is collected by a photoelectric detector and then input into the collection system to obtain the magnetic field information of electromagnetic induction of the sample through the strong absorption change.

[0021] The principle of the present invention is as follows:

[0022] The principle of measuring magnetic field without spin exchange relaxation (SERF) is a magnetic field measurement method based on quantum sensing technology, which uses alkali metal atoms with non-zero nuclear spin (such as lithium, sodium, potassium, rubidium, cesium) as sensors. These atoms can reach a spin exchange relaxation (SERF) state in a buffer gas at high temperature. The key feature of the spin exchange relaxation technology is that it alleviates the relaxation process that usually limits the sensitivity of traditional magnetometers. In conventional atomic magnetometers, atomic spins relax due to collisions with other atoms, which reduces the measurement accuracy. SERF technology can suppress these relaxation effects, thereby achieving higher sensitivity magnetic field measurements. The Helmholtz coil compensates the magnetic field around the atomic gas chamber to near-zero field, and the non-magnetic conductive coil itself has very weak magnetism and will not interfere with the induced magnetic field generated by the sample. When the radio frequency generated by the non-magnetic conductive coil acts on the sample, an induced current is generated, and then an induced magnetic field is generated. This magnetic field will cause the atomic energy level to undergo Zeeman splitting, and the atoms will perform Larmor precession around the magnetic field. The frequency of Larmor precession and the magnetic field satisfy the relationship ω=γB, where ω is the angular frequency of precession, γ is the magnetic gyro ratio of the atom, and B is the magnetic field strength. At the same time, the spin angular momentum of the atom Satisfies the Bloch equation:

[0023]

[0024] In the formula, γ e is the magnetic gyro ratio of the electron, q is the nuclear slowing factor, R OP is the pumping rate of the pumping light, R sel is the relaxation rate of the atom when there is no pump light. s is the polarizability of the pump light (here it is circularly polarized light, so s = 1), is the propagation direction of the pumping light, is the external magnetic field (that is, the induced magnetic field generated by the sample mentioned above), and t represents the time variable; when the atomic spin exchange relaxation rate is much greater than the Larmor precession frequency, the influence of the spin exchange collision on the polarization lifetime is eliminated, achieving the effect of no spin exchange. At this time, the average value of the atomic spin angular momentum detected by the laser is the macroscopic light intensity, which is proportional to the external magnetic field (that is, the induced magnetic field generated by the sample mentioned above). The light intensity directly reflects the magnetic field information at different parts of the sample. By recording the magnetic field information of each part of the sample, the shape of the sample can be obtained.

[0025] The present invention realizes two-dimensional imaging of samples based on the non-spin exchange relaxation state of atoms and the electromagnetic induction phenomenon of the imaged sample. By using a circularly polarized laser beam passing through an atomic gas chamber, the method of recording magnetic field information of atoms in a non-spin exchange relaxation state is demonstrated, so that the magnetic field information of the sample electromagnetically induced can be extracted from the light intensity information after passing through the atomic gas chamber and combined for imaging.

[0026] The beneficial effects of the present invention are:

[0027] 1. The imaging device of the present invention can detect the absorption change of light intensity of atoms in a state without spin exchange relaxation in a simpler and more intuitive way, and then obtain the magnetic field information induced by the electromagnetic field of the sample to accurately image the sample.

[0028] 2. The imaging device of the present invention has a simple structure, a small size, a long atomic relaxation time, and a high sensitivity. It can image samples with low conductivity and can image the magnetic field electromagnetically induced by samples with conductivity.

[0029] 3. The present invention demonstrates a method for recording magnetic field information of atoms in a state without spin exchange relaxation, so that the magnetic field information induced by the electromagnetic induction of the sample can be extracted from the light intensity information after passing through the atomic gas chamber and combined into an image. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a device diagram of the present invention;

[0031] Figure 2 is the power spectrum density diagram of the atomic gas chamber in this device;

[0032] Figure 3 This is the final image of the pure copper sample selected by the present invention;

[0033] In the figure: 1. Laser; 2. Half wave plate; 3. Polarization beam splitter; 4. Quarter wave plate; 5. Atomic gas chamber; 6. Helmholtz coil; 7. Non-magnetic conductive coil; 8. First total reflection prism; 9. Second total reflection prism; 10. Polarized detection light; 11. Photodetector; 12. Collection system. DETAILED DESCRIPTION

[0034] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0035] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0036] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0037] In the description of the present invention, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "include" and / or "comprises" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0038] It should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0039] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "plurality" means two or more, unless otherwise clearly specified.

[0040] In the present invention, unless otherwise clearly specified and limited, the terms "install", "connect", "connect", "fix" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0041] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes the first feature being directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes the first feature being directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0042] like Figure 1As shown, the device includes a light source unit, an air chamber coil unit, an optical path adjustment unit and an imaging unit; the light beam emitted by the light source unit enters the optical path adjustment unit after passing through the air chamber coil unit, the sample to be imaged is placed in the air chamber coil unit, the sample to be imaged generates a magnetic field under the action of the air chamber coil unit, the magnetic field acts on the atomic air chamber 5 in the air chamber coil unit, the light beam passes through the atomic air chamber 5 and the optical path adjustment unit in sequence and enters the imaging unit, and the imaging unit performs electromagnetic induction imaging on the sample and displays it.

[0043] The light source unit includes a laser 1, a half wave plate 2, a polarization beam splitter 3 and a quarter wave plate 4; the light beam emitted by the laser 1 is incident on the polarization beam splitter 3 through the half wave plate 2, and then reflected and / or transmitted to the quarter wave plate 4 through the splitting surface of the polarization beam splitter 3, the half wave plate 2 is used to adjust the intensity of the incident light beam, the splitting surface of the polarization beam splitter 3 is used to split the incident light beam into two linear polarized lights with polarization directions perpendicular to each other, one of the linear polarized lights emitted by the polarization beam splitter 3 is used as the polarization detection light 10, the quarter wave plate 4 is used to receive and adjust the polarization direction of the polarization detection light 10, so that the polarization detection light 10 is changed from linear polarized light to circular polarized light, and the circular polarized light is then input into the air chamber coil unit.

[0044] The gas chamber coil unit includes an atomic gas chamber 5, a Helmholtz coil 6 and a non-magnetic conductive coil 7; the atomic gas chamber 5 is located at the center of the Helmholtz coil 6, and the atomic gas chamber 5 is filled with alkali metal atoms and an appropriate amount of buffer gas, wherein the buffer gas is specifically nitrogen gas. The alkali metal atoms become gaseous after being heated, and the outer wall of the atomic gas chamber 5 is wound with a non-magnetic twisted pair of wires for heating, so that the alkali metal atoms are in a state of no spin exchange relaxation. The non-magnetic twisted pair of wires can uniformly heat the atomic gas chamber 5 to above 120 degrees Celsius. A thermocouple for real-time detection of the temperature of the atomic gas chamber 5 is provided in the atomic gas chamber 5. The sample to be imaged is placed between the Helmholtz coil 6 and the non-magnetic conductive coil 7. The non-magnetic conductive coil 7 is used to generate a radio frequency field, and the radio frequency field acts on the sample to be imaged to generate an induced current. The induced current generates a magnetic field and acts on the atomic gas chamber 5. The Helmholtz coil 6 generates a compensation magnetic field for offsetting the excess magnetic field around the atomic gas chamber 5, so that the magnetic field around the atomic gas chamber 5 is a zero magnetic field.

[0045] The Helmholtz coil 6 uses three groups of orthogonal Helmholtz coils to generate compensation magnetic fields along the X, Y, and Z axes respectively to offset the residual magnetic field around the atomic gas cell to a near-zero field. The non-magnetic conductive coil 7 is wound with a number of turns of coils, and the generated radio frequency field acts on the sample to be imaged to generate an induced current, thereby generating a magnetic field that is sensed by the atomic gas cell 5.

[0046] The optical path adjustment unit is mainly composed of a first total reflection prism 8 and a second total reflection prism 9; after the polarized detection light 10 is converted from linearly polarized light into circularly polarized light, it is transmitted through the atomic gas chamber 5 in the gas chamber coil unit, and then reflected by the first total reflection prism 8 and the second total reflection prism 9 in sequence and output to the imaging unit. The first total reflection prism 8 and the second total reflection prism 9 are arranged between the gas chamber coil unit and the imaging unit, and are used to change the direction of the light beam emitted from the atomic gas chamber 5 to enter the imaging unit.

[0047] The light emitted by the laser 1 is converted into circularly polarized light, passes through the atomic gas chamber 5, passes through the first total reflection prism 8 and the second total reflection prism 9, and then rotates 180° before entering the photoelectric detector 11;

[0048] The imaging unit is mainly composed of a photodetector 11 and a collection system 12. The photodetector 11 is used to receive and record the light intensity information of the polarized detection light 10 after it passes through the atomic gas chamber 5, and convert the light intensity information into a voltage and output it to the collection system 12. The collection system 12 obtains the magnetic field information of the electromagnetic induction of the sample according to the absorption change of the light intensity by the alkali metal atoms, and finally performs electromagnetic induction imaging and displays the imaged sample according to the magnetic field information of the electromagnetic induction of the sample.

[0049] The laser frequency of the laser 1 is tuned to the transition frequency of the alkali metal atoms in the atomic gas cell 5 .

[0050] The alkali metal atoms in the atomic gas cell 5 are selected from the group consisting of rubidium atoms, sodium atoms, potassium atoms, lithium atoms, and cesium atoms.

[0051] The laser 1 emits light to generate polarized detection light 9 and penetrates the atomic gas chamber 5. The Helmholtz coil 6 includes three groups of orthogonal Helmholtz coils. The atomic gas chamber 5 is located at the center of the Helmholtz coil 6. The three groups of orthogonal Helmholtz coils 6 generate magnetic fields along the X, Y, and Z axes respectively. The non-magnetic conductive coil 7 generates a radio frequency field and acts on the sample to be imaged. The photodetector 11 records the intensity of the polarized detection light 10 after it passes through the atomic gas chamber 5. By detecting the change in the absorption of light intensity by atoms, the magnetic field information of the electromagnetic induction of the sample is obtained, and the sample is imaged. Among them, the frequency of the laser 1 is locked to a pair of transition energy levels of the D1 line of the alkali metal atom.

[0052] Embodiments of the present invention are as follows:

[0053] For the special case where the atomic gas chamber is filled with rubidium 87 atoms filled with 1 atmosphere of buffer gas and the imaged sample is pure copper, the following operations are performed during imaging:

[0054] Step 1: Set up the electromagnetic induction imaging device: Tune the laser frequency of the laser 1 in the light source unit to the transition frequency of the alkali metal atoms in the gas chamber coil unit. Specifically, lock the wavelength of the laser 1 to 5 of the D1 line of the rubidium 87 atom.2 S 1 / 2 , F=2→5 2 P 1 / 2 ,F′=1 transition energy level; among them, 5 2 S 1 / 2 , F = 2 represents a certain energy level of the atomic ground state, 5 2 P 1 / 2 , F′=1 represents a certain energy level of the atomic excited state, 5 represents the principal quantum number n=5, the 1 / 2 in the lower right corner represents the total angular momentum of the electron J=1 / 2, the 2 in the upper left corner represents 2J+1, F is the ordinal number of the ground state energy level of the atom, and F′ is the ordinal number of the energy level of the atomic excited state.

[0055] The laser 1 is started, and the light beam emitted by the laser 1 passes through the air chamber coil unit and the light path adjustment unit in sequence, and is then received by the imaging unit;

[0056] Step 2: Turn on the heating: Pass an alternating current with a frequency of more than 500kHz and a power of more than 7W into the heated non-magnetic twisted pair to heat the atomic gas chamber 5 to 150 degrees Celsius, so that the atoms reach a state of no spin exchange relaxation. At this time, the atoms are highly sensitive to the magnetic field, such as Figure 2 As shown in the power density spectrum, the sensitivity reaches 2pT / √Hz.

[0057] Step 3: Turn on residual magnetic field compensation: Apply direct current to three groups of orthogonal Helmholtz coils 6, so that the Helmholtz coils generate compensation magnetic fields along the X, Y, and Z axes respectively, offsetting the magnetic field around the atomic gas chamber 5 to a near-zero field below 1nT.

[0058] Step 4: Turn on the non-magnetic conductive coil 7 and add an AC voltage of a specific frequency, such as 2kHz.

[0059] Step 5: Place a pure copper sheet of the imaged sample under the non-magnetic conductive coil 7 to allow the sample to generate an induced current, thereby generating a magnetic field that is sensed by the atomic gas chamber 5. The light that passes through the atomic gas chamber 5 enters the photodetector 11 and is converted into a voltage signal that is processed and recorded by the acquisition system 12.

[0060] Step 6: Move the sample and repeat step 5 until the magnetic field information of all areas of the sample is recorded.

[0061] Step 7: The acquisition system 12 organizes the magnetic field information of each area of ​​the sample into a color matrix corresponding to the numerical value, and finally outputs the image.

[0062] The present invention demonstrates an electromagnetic induction imaging device and method based on atomic spin-free exchange relaxation, and demonstrates a method for recording magnetic field information of atoms in a spin-free exchange relaxation state, so that the magnetic field information induced by the electromagnetic induction of the sample can be extracted from the light intensity information after passing through the atomic gas chamber and finally combined into an image, such as Figure 3 shown.

[0063] In the description of this specification, the descriptions with reference to the terms "one embodiment", "some embodiments", "an implementation", "specific implementation", "other implementations", "examples", "specific examples" or "some examples" mean that the specific features, structures, materials or characteristics described in combination with the embodiment or example are included in at least one embodiment, implementation or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described above may also be combined in a suitable manner in any one or more embodiments, implementations or examples. The technical solutions described in the present invention also include technical solutions formed by any one or more specific features, structures, materials or characteristics described above in a separate or combined manner.

[0064] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present invention. Ordinary technicians in the field can change, modify, replace, modify, delete some features, add features or re-combine features to form a technical solution in the above embodiments without departing from the principles and purpose of the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the innovative principles of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. An electromagnetic induction imaging device based on atomic spin-free exchange relaxation, characterized in that: The invention comprises a light source unit, an air chamber coil unit, an optical path adjustment unit and an imaging unit; a light beam emitted by the light source unit enters the optical path adjustment unit after passing through the air chamber coil unit; a sample to be imaged is placed in the air chamber coil unit; the sample to be imaged generates a magnetic field under the action of the air chamber coil unit; the magnetic field acts on an atomic air chamber (5) in the air chamber coil unit; the light beam passes through the atomic air chamber (5) and the optical path adjustment unit in sequence and enters the imaging unit; the imaging unit performs electromagnetic induction imaging on the sample and displays the image.

2. The electromagnetic induction imaging device based on atomic spin-free exchange relaxation according to claim 1, characterized in that: The light source unit comprises a laser (1), a half wave plate (2), a polarization beam splitter (3) and a quarter wave plate (4); the light beam emitted by the laser (1) is incident on the polarization beam splitter (3) via the half wave plate (2), and then reflected and / or transmitted to the quarter wave plate (4) via the beam splitting surface of the polarization beam splitter (3); the half wave plate (2) is used to adjust the intensity of the incident light beam; the beam splitting surface of the polarization beam splitter (3) is used to split the incident light beam into two beams of linear polarized light with polarization directions perpendicular to each other; one of the linear polarized lights emitted by the polarization beam splitter (3) is used as polarization detection light (10); the quarter wave plate (4) is used to receive and adjust the polarization direction of the polarization detection light (10), so that the polarization detection light (10) is changed from linear polarization light to circular polarization light, and the circular polarization light is then input into the air chamber coil unit.

3. The electromagnetic induction imaging device based on atomic spin-free exchange relaxation according to claim 2, characterized in that: The gas chamber coil unit comprises an atomic gas chamber (5), a Helmholtz coil (6) and a non-magnetic conductive coil (7); the atomic gas chamber (5) is located at the center of the Helmholtz coil (6); the atomic gas chamber (5) is filled with alkali metal atoms and buffer gas; the outer wall of the atomic gas chamber (5) is wound with a non-magnetic twisted pair of wires for heating, thereby making the alkali metal atoms present a non-spin exchange relaxation state; the sample to be imaged is placed between the Helmholtz coil (6) and the non-magnetic conductive coil (7); the non-magnetic conductive coil (7) is used to generate a radio frequency field; the radio frequency field acts on the sample to be imaged to generate an induced current; the induced current generates a magnetic field and acts on the atomic gas chamber (5); the Helmholtz coil (6) generates a compensation magnetic field for offsetting an excess magnetic field around the atomic gas chamber (5), so that the magnetic field around the atomic gas chamber (5) is a zero magnetic field.

4. The electromagnetic induction imaging device based on atomic spin-free exchange relaxation according to claim 2, characterized in that: The optical path adjustment unit is mainly composed of a first total reflection prism (8) and a second total reflection prism (9); after the polarized detection light (10) is converted from linearly polarized light into circularly polarized light, it is transmitted through the atomic gas chamber (5) in the gas chamber coil unit, and then sequentially reflected by the first total reflection prism (8) and the second total reflection prism (9) before being output to the imaging unit; the first total reflection prism (8) and the second total reflection prism (9) are arranged between the gas chamber coil unit and the imaging unit, and are used to change the direction of the light beam emitted from the atomic gas chamber (5) incident on the imaging unit.

5. The electromagnetic induction imaging device based on atomic spin-free exchange relaxation according to claim 2, characterized in that: The imaging unit is mainly composed of a photodetector (11) and a collection system (12). The photodetector (11) is used to receive and record the light intensity information of the polarized detection light (10) after it passes through the atomic gas chamber (5). The collection system (12) obtains the magnetic field information of electromagnetic induction of the sample according to the absorption change of the light intensity by the alkali metal atoms. Finally, electromagnetic induction imaging is performed on the sample to be imaged and displayed according to the magnetic field information of electromagnetic induction of the sample.

6. The electromagnetic induction imaging device based on atomic spin-free exchange relaxation according to claim 2, characterized in that: The laser frequency of the laser (1) is tuned to the transition frequency of the alkali metal atoms in the atomic gas chamber (5).

7. The electromagnetic induction imaging device based on atomic spin-free exchange relaxation according to claim 3, characterized in that: The alkali metal atoms in the atomic gas chamber (5) are selected from the group consisting of rubidium atoms, sodium atoms, potassium atoms, lithium atoms and cesium atoms.

8. The electromagnetic induction imaging device based on atomic spin-free exchange relaxation according to claim 3, characterized in that: The buffer gas in the atomic gas chamber (5) is nitrogen gas.

9. An electromagnetic induction imaging method based on atomic spin-free exchange relaxation applied to the device of any one of claims 1 to 8, characterized in that: The following steps are involved: Step S1, setting up an electromagnetic induction imaging device: tuning the laser frequency of the laser (1) in the light source unit to the transition frequency of the alkali metal atoms in the air chamber coil unit, starting the laser (1), and the light beam emitted by the laser (1) passes through the air chamber coil unit and the light path adjustment unit in sequence, and is then received by the imaging unit; Step S2, heating the atomic gas chamber (5) of the gas chamber coil unit so that the alkali metal atoms in the atomic gas chamber (5) are heated to a state without spin exchange relaxation; Step S3, applying direct current to the Helmholtz coil (6) of the gas chamber coil unit, so that the Helmholtz coil (6) generates a compensation magnetic field for offsetting the redundant magnetic field around the atomic gas chamber (5), so that the magnetic field around the atomic gas chamber (5) is a zero magnetic field; Step S3, applying an alternating voltage to the non-magnetic conductive coil (7) of the gas chamber coil unit, placing a sample to be imaged below the non-magnetic conductive coil (7), and generating an induced current under the action of the radio frequency field of the non-magnetic conductive coil (7), and the induced current generates a magnetic field and acts on the atomic gas chamber (5); Step S4, the light beam emitted by the laser (1) enters the photodetector (11) of the imaging unit after passing through the atomic gas chamber (5), and the photodetector (11) transmits the light intensity information transmitted through the atomic gas chamber (5) to the acquisition system (12). The acquisition system (12) of the imaging unit obtains the magnetic field information of electromagnetic induction of the sample according to the absorption change of the light intensity by the alkali metal atoms, and finally performs electromagnetic induction imaging on the sample to be imaged and displays it according to the magnetic field information of electromagnetic induction of the sample.

Images