An ellipsometric magneto-optical signal detection system and method based on cascaded super surfaces

Abstract

The application discloses an ellipsoidal light magnetic signal detection system and method based on a cascade super surface, wherein the system utilizes a cascade super surface polarization conversion device to emit elliptical polarized light with specific ellipticity, and guides the elliptical polarized light into an atomic chamber to interact with alkali metal atoms to realize magnetic field measurement. According to the required ellipticity, the application designs the Jones matrix of the cascade super surface, designs the material, structure and period of the super surface, converts the light emitted by a laser into elliptical polarized light with a predetermined ellipticity, and after the elliptical polarized light enters the atomic chamber, the optical rotation effect is generated while the alkali metal atoms are polarized, and the differential detection technology and the lock-in amplification technology are utilized to obtain the magnetic field information to be measured. Compared with a conventional magnetic signal detection system, the magnetic signal detection system built by using the cascade super surface polarization conversion device has the advantages of small volume and easy integration due to the compact structure and the miniaturized design concept.

Description

Technical Field

[0001] This invention belongs to the field of quantum precision magnetic field measurement technology, and relates to an ellipsoidal optical magnetic signal detection system and method based on cascaded metasurfaces. Background Technology

[0002] Magnetism is one of the earliest physical phenomena recognized by humankind, and the compass invented in ancient China is a classic example of utilizing the Earth's magnetic field. With the advancement of science and technology, the detection technology of weak magnetic fields has received increasing attention and has played a vital role in many fields such as geological exploration, military protection, earthquake early warning, industrial production, and archaeological exploration.

[0003] The core sensor for magnetic field measurement technology is the magnetometer. Commonly used high-performance magnetometers for measuring the Earth's magnetic field can be classified according to their measurement principles into fluxgate magnetometers, superconducting quantum interference magnetometers, proton magnetometers, inductive magnetometers, fiber optic magnetometers, and optically pumped atomic magnetometers. Among them, the optically pumped atomic magnetometer based on the optical magnetic resonance effect has shown significant advantages such as fast response speed, wide measurement range, and no need for cryogenic cooling.

[0004] However, in practical applications, especially for wearable devices requiring portable magnetic resonance imaging (MRI) of the heart and brain, the bulky structure of existing optically pumped atomic magnetometers greatly limits their application scope. The laser sources commonly used in optically pumped atomic magnetometers still require large-volume optical components such as collimating lenses, polarizers, and quarter-wave plates to produce elliptically polarized light with a specific ellipticity during polarization conversion. These traditional large-volume optical components are not only large and bulky, but also lack sufficient polarization conversion accuracy, hindering system miniaturization and integration.

[0005] Metasurfaces, as artificial electromagnetic materials composed of micro- and nano-structures, can arbitrarily control the polarization, phase, and amplitude dimensions of light fields, exhibiting superior optical performance at the subwavelength scale. Compared to traditional waveplates, they offer advantages such as greater flexibility, smaller size, lighter weight, simpler fabrication, thinner profiles, easier integration, and lower loss. Therefore, by utilizing the revolutionary technology of metasurfaces, polarization devices based on waveplate cascades can be significantly miniaturized.

[0006] Therefore, based on the above-mentioned technical problems, the development of a new type of optically pumped magnetometer with small size and high sensitivity is crucial for its promotion in outdoor applications. Summary of the Invention

[0007] (I) Purpose of the Invention

[0008] The purpose of this invention is to provide an ellipsoidal magnetic signal detection system and method based on cascaded metasurfaces. A cascaded metasurface polarization conversion device is constructed, which changes the polarization state and ellipticity of the emitted light by adjusting the angle between the transmission axis of the metal grating structure and the fast axis of the quarter-wave plate superatoms. The beam is collimated by adjusting the arrangement of the quarter-wave plate superatoms. This collimated ellipsoidally polarized light is then used as a pump laser and guided into the atomic gas cell. This avoids the use of traditional large-volume optical devices for polarization state conversion, thereby reducing the size of the system's optical components, improving polarization conversion accuracy, and ultimately enhancing the sensitivity of the magnetic signal detection system.

[0009] (II) Technical Solution

[0010] To address the aforementioned technical problems, this invention provides an ellipsoidal magnetic signal detection system based on a cascaded metasurface, comprising: a laser unit 1, a cascaded metasurface polarization conversion device 2, a magnetic probe unit 3, and a signal processing unit 4. The cascaded metasurface polarization conversion device 2 is arranged at the light-emitting end of the laser unit 1, the magnetic probe unit 3 is arranged at the emission end of the cascaded metasurface polarization conversion device 2, and the signal processing unit 4 is located at the output end of the magnetic probe unit 3 and receives the optical signal output by the magnetic probe unit 3. The laser unit 1 emits a linearly polarized laser beam with a fixed wavelength and set power, which is emitted to the cascaded metasurface polarization conversion device 2. The ellipsoidally polarized light converted by the cascaded metasurface polarization conversion device 2 enters the heated atomic gas chamber 10 of the magnetic probe unit 3, polarizing the atomic gas inside the atomic gas chamber 10. Simultaneously, the ellipsoidally polarized light passing through the atomic gas chamber 10 serves as the probe light and enters the signal processing unit 4. After differential detection and phase-locked amplification, the magnetic field information to be measured is obtained.

[0011] The laser unit 1 includes a laser 5 and a controller 6. The controller 6 controls the laser 5 to emit a linearly polarized laser beam with a fixed wavelength and a set power. The fixed-wavelength laser beam emitted by the laser 5 enters the cascaded metasurface polarization converter 2.

[0012] The cascaded metasurface polarization conversion device 2 includes a silicon substrate 9, a metal grating structure 7 formed on the front surface of the silicon substrate 9, and a quarter-wave plate superatom 8 formed on the rear surface of the silicon substrate 9. The metal grating structure 7 is used to convert the laser source into linearly polarized light with a defined direction, and the quarter-wave plate superatom 8 is used to convert the linearly polarized light into elliptically polarized light. By adjusting the angle between the transmission axis of the metal grating structure 7 and the fast axis of the quarter-wave plate superatom 8, elliptically polarized light with a set ellipticity is obtained and emitted to the magnetic probe unit 3.

[0013] The metal grating structure 7 and the quarter-wave plate superatom 8 are cascaded by etching on both sides of the silicon substrate 9, and the materials, structures and periods of the metal grating structure 7 and the quarter-wave plate superatom 8 are different.

[0014] The magnetic probe unit 3 includes: an atomic gas chamber 10, an oven 11 located around the atomic gas chamber 10, and a temperature control system 12 for controlling the temperature of the oven 11. Under the control of the temperature control system 12, the temperature of the oven 11 is adjusted to heat the atomic gas chamber 10. An elliptically polarized light beam enters the heated atomic gas chamber 10 to polarize the internal atomic gas and enters the signal processing unit 4 as a probe light.

[0015] The atomic gas chamber 10 is filled with alkali metal atoms and an inert buffer gas. After heating, the number density of alkali metal vapor atoms in the atomic gas chamber 10 reaches 10. 13 ~10 14 pcs / cm 3 .

[0016] The signal processing unit 4 includes: a polarization beam splitter 14, a balanced photodetector 15 located behind the polarization beam splitter 14, a lock-in amplifier 16 connected to the balanced photodetector 15, and a data processing system 17 connected to the lock-in amplifier 16 and used to calculate the magnetic field value to be measured. After the probe light is incident on the polarization beam splitter 14, it is split into two linearly polarized beams. After being introduced into the balanced photodetector 15, it is converted into a photocurrent signal after differential amplification. The lock-in amplifier 16 uses a demodulation signal to demodulate the photocurrent signal to obtain a lock-in amplified signal. Finally, the magnetic field value to be measured is calculated by the data processing system 17.

[0017] 8. The ellipsoidal magnetic signal detection system based on cascaded metasurfaces as described in claim 7, characterized in that the magnetic probe unit 3 further includes radio frequency coils 13 arranged at both ends of the oven 11, the radio frequency coils 13 are connected to lock-in amplifiers 16, the lock-in amplifiers 16 sweep the radio frequency magnetic field of the radio frequency coils 13, and when the radio frequency magnetic field signal is consistent with the magnetic field signal to be measured, the signal measured by the balanced photodetector 15 reaches its maximum, and the magnetic field value to be measured is obtained after the signal is processed by the data processing system 17.

[0018] The present invention also provides a method for detecting ellipsometric magnetic signals, comprising the following steps:

[0019] S1. Use controller 6 to adjust the frequency of the laser source generated by laser 5 to the alkali metal D1 linear resonant frequency, so that the polarization state is linearly polarized light, and at the same time adjust the intensity of the laser source to the set power.

[0020] S2. Adjust the cascaded metasurface polarization converter 2 so that the transmission axis of the metal grating structure 7 and the fast axis of the quarter-wave plate superatom 8 form a set angle.

[0021] S3. The laser source generated in step S1 is incident into the cascaded metasurface polarization converter 2 modulated in step S2, and converted into collimated elliptically polarized light with a set ellipticity. This elliptically polarized light is used as both pump light and probe light to irradiate the atomic gas cell 10, thereby achieving polarization of alkali metal atoms and generating optical rotation angle for magnetic field detection.

[0022] S4. The atomic gas chamber 10 is directly heated by the heating film on the oven 11 to make the atoms in the atomic gas chamber 10 reach a vapor state to improve the polarizability of the atoms in the atomic gas chamber 10. The temperature of the atomic gas chamber 10 is monitored in real time by the thermistor and the temperature of the atomic gas chamber 10 is stabilized by the PID control of the temperature control system 12.

[0023] S5. Place the magnetic signal detection system under the geomagnetic field or a simulated geomagnetic field, detect the elliptically polarized light passing through the atomic gas cell 10 using differential detection technology, connect the differential amplified signal to the lock-in amplifier, demodulate the differential amplified signal using lock-in amplification technology using the demodulation signal to obtain the lock-in amplified signal, and finally calculate the magnetic field value to be measured through the data processing system 17.

[0024] In step S2, the Jones matrix of the metal grating structure when the angle between the light transmission axis and the horizontal direction is α is G1, which is represented as:

[0025]

[0026] The Jones matrix of the quarter-wave plate superatomic structure, with an angle β between the fast axis and the horizontal direction, is G2, and is represented as:

[0027]

[0028] The difference between α and β is the angle between the transmission axis of the metal grating structure 7 and the fast axis of the quarter-wave plate superatom 8.

[0029] In step S3, the linearly polarized component of the elliptically polarized light undergoes a magneto-optical effect after passing through the polarized atomic gas cell, producing an optical rotation angle θ, expressed as:

[0030]

[0031] Where v′ is the optical frequency, v0′ is the resonance frequency of the alkali metal D1 transition, and r e Where f is the classical electron radius, c is the speed of light in a vacuum, and f is the speed of light in a vacuum. osc It is the strength of the oscillator. is the alkali metal atomic density, d is the length of the interaction between light and polarized atoms, V is the Voigt function, and P z Spin polarization, a function of the transverse external magnetic field, is defined as P. z =2<Sz >, where <S z > is the average atomic spin value along the z-direction; the optical rotation angle θ is monitored and detected by a balanced photodetector consisting of a linear polarization beam splitter and two photodetectors, and the differential amplified signal is output to the lock-in amplifier 16.

[0032] (III) Beneficial Effects

[0033] The above-mentioned technical solution provides an ellipsometric magnetic signal detection system and method based on cascaded metasurfaces, which has the following beneficial effects:

[0034] (1) The detection system of the present invention uses a cascaded metasurface polarization converter to change the polarization state of the incident laser, outputs elliptically polarized light with a set ellipticity, and guides the light beam into the atomic gas cell so that it interacts with alkali metal atoms to achieve magnetic field measurement.

[0035] (2) The detection system of the present invention calculates the Jones matrix of the cascaded metasurface polarization converter based on the set ellipticity, and selects the structure, material, period and arrangement of the metasurface accordingly, so that the cascaded metasurface polarization converter emits elliptically polarized light with the set ellipticity, guides the elliptically polarized light into the atomic gas cell to polarize alkali metal atoms, and applies a modulated magnetic field in the direction perpendicular to the beam, and obtains the information of the magnetic field to be measured by using differential detection technology and lock-in amplification technology.

[0036] (3) Compared with conventional atomic magnetometers, the present invention uses cascaded metasurface polarization conversion devices to replace traditional large-volume collimating lenses, polarizers and quarter-wave plates, making the magnetic signal detection system more compact, smaller in size, more portable, and more suitable for outdoor working environments. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the ellipsometric magnetic signal detection system based on cascaded metasurfaces disclosed in an embodiment of the present invention.

[0038] Figure 2 yes Figure 1 A schematic diagram illustrating the working principle of a cascaded metasurface polarization converter.

[0039] Figures 3 to 5 They are respectively Figure 2 Left, top, and right views of a cascaded metasurface polarization converter.

[0040] The annotations in the attached figures are explained as follows:

[0041] 1. Laser unit; 2. Cascaded metasurface polarization conversion device; 3. Magnetic probe unit; 4. Signal processing unit; 5. Laser; 6. Controller; 7. Metal grating; 8. Quarter-wave plate superatom; 9. Silicon substrate; 10. Atomic gas cell; 11. Oven; 12. Temperature control system; 13. Radio frequency coil; 14. Polarization beam splitter; 15. Balanced photodetector; 16. Lock-in amplifier; 17. Data processing system. Detailed Implementation

[0042] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0043] This embodiment of the ellipsometric magnetic signal detection system and method based on cascaded metasurfaces utilizes a cascaded metasurface polarization conversion device to emit ellipsometric light with a specific ellipticity, which is then guided into an atomic gas chamber to interact with alkali metal atoms to achieve magnetic field measurement. The core of this embodiment lies in: designing the Jones matrix of the cascaded metasurface according to the required ellipticity; precisely designing the metasurface's material, structure, and periodicity; converting the light emitted by the laser into ellipsometric light with a predetermined ellipticity; and, after entering the atomic gas chamber, generating optical rotation while polarizing alkali metal atoms. Differential detection and lock-in amplification techniques are then used to obtain the magnetic field information to be measured.

[0044] Reference Figures 1 to 5 As shown, the ellipsoidal magnetic signal detection system based on cascaded metasurfaces in this embodiment includes a laser unit 1, a cascaded metasurface polarization conversion device 2, a magnetic probe unit 3, and a signal processing unit 4. The cascaded metasurface polarization conversion device 2 is arranged at the light-emitting end of the laser unit 1, the magnetic probe unit 3 is arranged at the emission end of the cascaded metasurface polarization conversion device 2, and the signal processing unit 4 is located at the output end of the magnetic probe unit 3 and receives the optical signal output by the magnetic probe unit 3. The laser unit 1 emits a linearly polarized laser beam with a fixed wavelength and a set power, and emits it to the cascaded metasurface polarization conversion device 2. The ellipsoidally polarized light converted by the cascaded metasurface polarization conversion device 2 enters the heated atomic gas chamber 10 of the magnetic probe unit 3 to polarize the atomic gas inside the atomic gas chamber 10. At the same time, the ellipsoidally polarized light passing through the atomic gas chamber 10 is used as the probe light and enters the signal processing unit 4. After differential detection and phase-locked amplification, the magnetic field information to be measured is obtained.

[0045] The laser unit 1 includes a laser 5 and a controller 6. The controller 6 controls the laser 5 to emit a linearly polarized laser beam with a fixed wavelength and a set power. The fixed-wavelength laser beam emitted by the laser 5 enters the cascaded metasurface polarization converter 2.

[0046] The cascaded metasurface polarization conversion device 2 includes a silicon substrate 9 and two metasurface structures formed on its two side surfaces. The two metasurface structures are a metal grating structure 7 for generating linearly polarized light and a quarter-wave plate superatom 8 for beam collimation. The metal grating structure 7 and the quarter-wave plate superatom 8 are cascaded by etching them onto both sides of the silicon substrate 9. The front half of the silicon substrate 9 is the metal grating structure 7, which is used to convert the laser source into linearly polarized light with a defined direction. The rear half of the silicon substrate 9 is the quarter-wave plate superatom 8, which can convert linearly polarized light into elliptically polarized light. The metal grating structure 7 and the quarter-wave plate superatom 8 are made of different materials, have different structures, and different periods. By adjusting the angle between the transmission axis of the metal grating structure 7 and the fast axis of the quarter-wave plate superatom 8, elliptically polarized light with a set ellipticity is obtained and emitted to the magnetic probe unit 3.

[0047] The magnetic probe unit 3 includes: an atomic gas chamber 10, an oven 11 located around the atomic gas chamber 10, a temperature control system 12 for controlling the temperature of the oven 11, and radio frequency coils 13 arranged at both ends of the oven 11; an elliptically polarized beam enters the heated atomic gas chamber 10 to polarize the internal atomic gas and enters the signal processing unit 4 as a probe light.

[0048] The atomic gas chamber 10 is filled with alkali metal atoms and inert buffer gas. Under the control of the temperature control system 12, the temperature of the oven 11 is adjusted to heat the atomic gas chamber 10, so that the number density of alkali metal vapor atoms in the atomic gas chamber 10 reaches 10. 13 ~10 14 pcs / cm 3 .

[0049] The signal processing unit 4 includes: a polarization beam splitter 14, a balanced photodetector 15 located behind the polarization beam splitter 14, a lock-in amplifier 16 connecting the balanced photodetector 15 and the radio frequency coil 13, and a data processing system 17 connected to the lock-in amplifier 16 and used to calculate the magnetic field value to be measured. After the probe light is incident on the polarization beam splitter 14, it is split into two linearly polarized beams. After being introduced into the balanced photodetector 15, it is converted into a photocurrent signal after differential amplification. The lock-in amplifier 16 uses a demodulation signal to demodulate the photocurrent signal to obtain a lock-in amplified signal. Finally, the magnetic field value to be measured is calculated by the data processing system 17. The lock-in amplifier 16 sweeps the radio frequency magnetic field of the radio frequency coil 13. When the radio frequency magnetic field signal is consistent with the magnetic field signal to be measured, the signal measured by the balanced photodetector 15 reaches its maximum. This signal is then processed by the data processing system 17 to obtain the magnetic field value to be measured.

[0050] The working principle of the ellipsoidal magnetic signal detection system based on cascaded metasurfaces in this embodiment is as follows: The controller 6 adjusts the laser 5 to emit a linearly polarized laser beam with a set wavelength and power. The laser beam is incident on the incident surface of the cascaded metasurface polarization conversion device 2 and converted into collimated ellipsoidal light with a set ellipticity. The ellipsoidal light is used as pump light to enter the heated atomic gas chamber 10, which polarizes the alkali metal gas inside the atomic gas chamber 10. At the same time, it is used as probe light to be incident on the polarization beam splitter 14 and split into two linearly polarized beams. After being introduced into the balanced photodetector 15, it is converted into a photocurrent signal. The photocurrent signal is demodulated by the lock-in amplifier 16 using the demodulation signal to obtain the lock-in amplified signal. Finally, the magnetic field value to be measured is calculated by the data processing system 17.

[0051] Based on the aforementioned ellipsometric magnetic signal detection system, the ellipsometric magnetic signal detection method in this embodiment includes the following steps:

[0052] S1. Use controller 6 to adjust the frequency of the light source generated by laser 5 to the alkali metal D1 line resonance frequency, enhance the interaction between light and atomic spin, and make the polarization state linearly polarized light. At the same time, adjust the intensity of the laser source to the set power.

[0053] S2. Adjust the cascaded metasurface polarization converter 2 so that the transmission axis of the metal grating structure 7 and the fast axis of the quarter-wave plate superatom 8 form a set angle.

[0054] S3. The laser source generated in step S1 is incident into the cascaded metasurface polarization converter 2 modulated in step S2, and converted into collimated elliptically polarized light with a set ellipticity. This elliptically polarized light is used as both pump light and probe light to irradiate the atomic gas cell 10, thereby achieving polarization of alkali metal atoms and generating optical rotation angle for magnetic field detection.

[0055] S4. The atomic gas chamber 10 is directly heated by the heating film on the oven 11 to make the atoms in the atomic gas chamber 10 reach a vapor state to improve the polarizability of the atoms in the atomic gas chamber 10. The temperature of the atomic gas chamber 10 is monitored in real time by the thermistor and the temperature of the atomic gas chamber 10 is stabilized by the PID control of the temperature control system 12.

[0056] S5. Place the magnetic signal detection system under the geomagnetic field or a simulated geomagnetic field, detect the elliptically polarized light passing through the atomic gas cell 10 using differential detection technology, connect the differential amplified signal to the lock-in amplifier, demodulate the differential amplified signal using lock-in amplification technology using the demodulation signal to obtain the lock-in amplified signal, and finally calculate the magnetic field value to be measured through the data processing system 17.

[0057] In step S2, the Jones matrix of the metal grating structure when the angle between the light transmission axis and the horizontal direction is α is G1, which is represented as:

[0058]

[0059] The Jones matrix of the quarter-wave plate superatomic structure, with an angle β between the fast axis and the horizontal direction, is G2, and is represented as:

[0060]

[0061] The difference between α and β is the angle between the transmission axis of the metal grating and the quarter-superatomic fast axis.

[0062] In step S3, the linearly polarized component of the elliptically polarized light undergoes a magneto-optical effect after passing through the polarized atomic gas cell, producing an optical rotation angle θ, expressed as:

[0063]

[0064] Where v′ is the optical frequency, ν0′ is the resonance frequency of the alkali metal D1 transition, and r e Where f is the classical electron radius, c is the speed of light in a vacuum, and f is the speed of light in a vacuum. osc It is the strength of the oscillator. is the density of alkali metal atoms, d is the length of the interaction between light and polarized atoms, and V is the Voigt function. z Representing spin polarization, it is a function of the transverse external magnetic field and is defined as P. z =2<S z >, where <S z > is the average atomic spin value along the z-direction.

[0065] The optical rotation angle θ is precisely monitored and detected by a balanced photodetector consisting of a linear polarization beam splitter and two photodetectors, and outputs a differential amplified signal to a lock-in amplifier. The lock-in amplifier demodulates the differential amplified signal using lock-in amplification technology through demodulation signal to obtain the atomic magnetometer output signal, which is then entered into the data processing system to calculate the magnetic field value to be measured.

[0066] As can be seen from the above technical solution, the magnetic signal detection system built by the present invention using cascaded metasurface polarization conversion devices replaces the traditional cascaded metasurface polarization conversion devices consisting of large-volume collimating lenses, polarizers, and quarter-wave plates. The cascaded metasurface polarization conversion devices perform high-precision optical field manipulation on the incident linearly polarized laser and output elliptically polarized light with a set collimation ellipticity, reducing the volume of the magnetometer while increasing the polarization conversion accuracy.

[0067] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for detecting ellipsoidally polarized magnetic signals based on cascaded metasurfaces, characterized in that, The detection method employs an ellipsoidized magnetic signal detection system, which includes a laser unit (1), a cascaded metasurface polarization converter (2), a magnetic probe unit (3), and a signal processing unit (4). The cascaded metasurface polarization converter (2) is located at the output end of the laser unit (1), the magnetic probe unit (3) is located at the output end of the cascaded metasurface polarization converter (2), and the signal processing unit (4) is located at the output end of the magnetic probe unit (3) and receives the optical signal output by the magnetic probe unit (3). The laser unit (1) emits a linearly polarized laser beam with a fixed wavelength and set power, and outputs it to the cascaded metasurface polarization converter. (2) The elliptically polarized light converted by the cascaded metasurface polarization converter (2) enters the heated atomic gas chamber (10) of the magnetic probe unit (3), polarizing the atomic gas inside the atomic gas chamber (10). At the same time, the elliptically polarized light passing through the atomic gas chamber (10) enters the signal processing unit (4) as the probe light. After differential detection and phase-locked amplification, the magnetic field information to be measured is obtained. The laser unit (1) includes a laser (5) and a controller (6). The controller (6) controls the laser (5) to emit a linearly polarized laser beam with a fixed wavelength and a set power. The fixed wavelength laser beam emitted by the laser (5) enters the cascaded metasurface polarization converter (2). The detection method includes the following steps: S1. Use controller (6) to adjust the frequency of the laser source generated by laser (5) to the alkali metal D1 line resonance frequency, the polarization state is linearly polarized light, and at the same time adjust the intensity of the laser source to the set power. S2. Adjust the cascaded metasurface polarization converter (2) so that the transmission axis of the metal grating structure (7) and the fast axis of the quarter-wave plate superatom (8) form a set angle. The cascaded metasurface polarization converter (2) includes a silicon substrate (9), a metal grating structure (7) formed on the front surface of the silicon substrate (9), and a quarter-wave plate superatom (8) formed on the rear surface of the silicon substrate (9). The metal grating structure (7) is used to convert the laser source into linearly polarized light with a defined direction, and the quarter-wave plate superatom (8) is used to convert the linearly polarized light into elliptically polarized light. By adjusting the angle between the transmission axis of the metal grating structure (7) and the fast axis of the quarter-wave plate superatom (8), elliptically polarized light with a set ellipticity is obtained and emitted to the magnetic probe unit (3). S3. The laser source generated in step S1 is incident into the cascaded metasurface polarization converter (2) modulated in step S2, and converted into collimated elliptically polarized light with a set ellipticity. The elliptically polarized light is used as both pump light and probe light to irradiate the atomic gas cell (10), thereby realizing the polarization of alkali metal atoms and generating optical rotation angle for magnetic field detection. S4. The atomic gas chamber (10) is heated by DC through the heating film on the oven (11) so that the atoms in the atomic gas chamber (10) reach the vaporization state to improve the polarization rate of the atoms in the atomic gas chamber (10). The temperature of the atomic gas chamber (10) is monitored in real time by the thermistor and the temperature of the atomic gas chamber (10) is stabilized by the PID control of the temperature control system (12). S5. Place the magnetic signal detection system under the geomagnetic field or simulated geomagnetic field, detect the elliptically polarized light passing through the atomic gas cell (10) by differential detection technology, connect the differential amplified signal obtained by differential amplification to the lock-in amplifier, use the demodulation signal to demodulate the differential amplified signal using lock-in amplification technology to obtain the lock-in amplified signal, and finally calculate the magnetic field value to be measured through the data processing system (17). In step S2, the Jones matrix of the metal grating structure when the angle between the light transmission axis and the horizontal direction is α is G1, which is represented as: The Jones matrix of the quarter-wave plate superatomic structure, with an angle β between the fast axis and the horizontal direction, is G2, and is represented as: The difference between α and β is the angle between the transmission axis of the metal grating structure (7) and the fast axis of the quarter-wave plate superatom (8); In step S3, the linearly polarized component of the elliptically polarized light undergoes a magneto-optical effect after passing through the polarized atomic gas cell, producing an optical rotation angle θ, expressed as: in, It is the frequency of light. It is the resonance frequency of the D1 transition in alkali metals, r e Where f is the classical electron radius, c is the speed of light in a vacuum, and f is the speed of light in a vacuum. osc It is the strength of the oscillator. is the alkali metal atomic density, d is the length of the interaction between light and polarized atoms, V is the Voigt function, and P z Spin polarization, a function of the transverse external magnetic field, is defined as P. z =2〈S z > , where <S z > is the average atomic spin value along the z direction; the optical rotation angle φ is monitored and detected by a balanced photodetector consisting of a linear polarization beam splitter and two photodetectors, and the differential amplified signal is output to the lock-in amplifier (16).

2. The method for detecting ellipsometric magnetic signals based on cascaded metasurfaces as described in claim 1, characterized in that, The metal grating structure (7) and the quarter-wave plate superatom (8) are cascaded by etching on both sides of the silicon substrate (9), and the materials, structures and periods of the metal grating structure (7) and the quarter-wave plate superatom (8) are different.

3. The method for detecting ellipsometric magnetic signals based on cascaded metasurfaces as described in claim 1, characterized in that, The magnetic probe unit (3) includes: an atomic gas chamber (10), an oven (11) located around the atomic gas chamber (10), and a temperature control system (12) for controlling the temperature of the oven (11); the temperature of the oven (11) is adjusted under the control of the temperature control system (12) to heat the atomic gas chamber (10), and the elliptically polarized beam enters the heated atomic gas chamber (10) to polarize the internal atomic gas and enter the signal processing unit (4) as a probe light.

4. The method for detecting ellipsometric magnetic signals based on cascaded metasurfaces as described in claim 3, characterized in that, The atomic gas chamber (10) is filled with alkali metal atoms and inert buffer gas. After heating, the number density of alkali metal vapor atoms in the atomic gas chamber (10) reaches 10. 13 ~10 14 pcs / cm 3 .

5. The method for detecting ellipsometric magnetic signals based on cascaded metasurfaces as described in claim 4, characterized in that, The signal processing unit (4) includes: a polarization beam splitter (14), a balanced photodetector (15) located behind the polarization beam splitter (14), a lock-in amplifier (16) connected to the balanced photodetector (15), and a data processing system (17) connected to the lock-in amplifier (16) and used to calculate the magnetic field value to be measured. After the probe light is incident on the polarization beam splitter (14), it is split into two linearly polarized beams. After being introduced into the balanced photodetector (15), it is converted into a photocurrent signal after differential amplification. The lock-in amplifier (16) uses the demodulation signal to demodulate the photocurrent signal to obtain the lock-in amplified signal. Finally, the magnetic field value to be measured is calculated by the data processing system (17).

6. The method for detecting ellipsometric magnetic signals based on cascaded metasurfaces as described in claim 5, characterized in that, The magnetic probe unit (3) also includes radio frequency coils (13) arranged at both ends of the oven (11). The radio frequency coils (13) are connected to a lock-in amplifier (16). The lock-in amplifier (16) sweeps the radio frequency magnetic field of the radio frequency coil (13). When the radio frequency magnetic field signal is consistent with the magnetic field signal to be measured, the balanced photodetector (15) measures the signal to the maximum. This signal is then processed by the data processing system (17) to obtain the magnetic field value to be measured.

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