Vector magnetic field measurement method based on correlated structured light

Abstract

The invention discloses a vector magnetic field measurement method based on correlated structured light. Firstly, special correlated structured light is designed, the correlated structured light is divided into two beams after entering a beam splitter, one beam is called reference light and is emitted to a CCD, and information is recorded by the CCD; and the other beam of light is signal light, the signal light enters the atomic pool, the light is irradiated to the PD detector after penetrating through the atomic pool, and information is recorded by the PD. Because the light interacts with the magnetic field and the atoms in the atom pool, the information recorded by the PD detector changes along with the change of the size and the direction of the magnetic field. Information recorded by the CCD and information recorded by the PD are subjected to correlation operation, so that a light absorption diagram of atoms can be obtained, and information of a magnetic field can be obtained through the light absorption diagram. The vector magnetic field measurement method based on the correlated structured light can be applied to the fields of space flight and aviation, geophysics, military affairs and the like. According to the scheme provided by the invention, the special correlated structured light can be generated by controlling the hologram, the light passes through the ghost imaging system, and then correlated imaging is carried out, so that the information of the magnetic field can be obtained. In addition, the device is simple, and a new path is provided for developing a small and compact magnetometer.

Description

Technical Field

[0001] The present invention provides a vector magnetic field measurement method based on correlated structured light, which can perform non-local measurement of the direction of the magnetic field. The present invention relates to the field of magnetic field measurement technology. Background Art

[0002] The development of magnetic field measurement technology based on the interaction between light and atoms has undergone a significant transition from scalar to vector measurements. In the early days, magnetic field measurements mainly relied on scalar atomic magnetometers, which could only measure the magnitude of the magnetic field. With technological advancements, vector magnetometers were developed that can simultaneously measure the magnitude and direction of the magnetic field, which is crucial for aerospace, geophysics, and military fields. Scalar atomic magnetometers determine the magnitude of the magnetic field by measuring the Zeeman splitting intensity of atomic energy levels in a magnetic field. They usually use optical pumping technology to polarize atoms and indirectly reflect the magnitude of the magnetic field by detecting changes in the absorption signal. However, they are insensitive to the direction of the magnetic field. Vector atomic magnetometers track the changes in the phase and direction of the precession of atomic spins in an external magnetic field, and combine multi-axis sensing or modulation technology to resolve the three-dimensional components of the magnetic field, thereby obtaining information on the strength and direction of the magnetic field. However, the high-dimensional nature of magnetic field vector information requires the simultaneous detection of multiple physical parameters. Traditional point or surface sensors are limited by hardware integration complexity and spatial resolution. Furthermore, environmental noise (such as thermal fluctuations and electromagnetic crosstalk) and the inhomogeneity of the detection medium (such as the atomic gas chamber) introduce signal distortion, leading to a sharp decrease in reconstruction accuracy in weak magnetic fields or complex field distributions. These challenges urgently require a new method that balances high-dimensional information extraction, noise suppression, and spatial resolution.

[0003] In order to solve the problem of high-dimensional information extraction in vector magnetic field measurement, the present invention uses correlated structured light with multi-dimensional light field control capabilities for vector magnetic detection. Correlated structured light is a high-dimensional light beam with partial coherence, which has multiple degrees of freedom such as amplitude, phase, coherence, polarization, orbital angular momentum, etc. Correlated structured light can suppress noise coupling in the atomic pumping process by regulating spatial coherence. The special non-uniform polarization distribution of the light beam (such as radial / angular polarization) is efficiently matched with the Zeeman energy level transition of alkali metal atoms (such as rubidium and cesium) to achieve spatial selective enhancement of magnetic field sensitivity. At the same time, correlated structured light can also convert the "point-by-point scanning" detection of the atomic absorption image into "parallel correlation" detection through multi-degree-of-freedom correlation, thereby more quickly obtaining vector magnetic field information in the absorption image.

[0004] In order to solve the hardware integration problem in vector magnetic field measurement, the present invention adopts ghost imaging method for non-local magnetic field detection. Ghost imaging is based on the statistical characteristics of the intensity fluctuations of the correlated light field, separates the light field information of the reference arm and the detection arm, and reconstructs the target image using the second-order correlation function. Its core advantage lies in "non-locality". The imaging result does not rely on the spatial resolution capability of the detection path, but extracts hidden information from statistical noise through light field correlation. This feature circumvents the bottleneck of insufficient detector resolution and noise sensitivity of traditional vector magnetometers. Even under high noise or weak signal conditions, this method can recover the spatial distribution of the magnetic field vector from low signal-to-noise ratio data through the correlation algorithm, providing a solution for high-precision, high-dimensional magnetic detection in complex environments.

[0005] In existing vector magnetic measurement research, schemes [1] and [2] ([1] F. Castellucci, T. W. Clark, A. Selyem, J. Wang, and S. Franke-Arnold, Phys. Rev. Lett. 127, 233202 (2021). [2] G. Cai, K. Tian, ​​Z. Wang, Laser Photonics Rev. 18, 2400465 (2024)) are based on atom interferometer technology and two-photon Λ transition schemes, and the spatial interference fringes of the atomic absorption pattern are used to measure magnetic field information. However, such methods rely on the strict collinear design of the measurement optical path and the detection optical path. The optical path system needs to integrate high-precision polarization control, spatial mode separation and multi-level imaging modules, which significantly increases the size and complexity of the device and is difficult to meet the miniaturization requirements of portable devices. To address these challenges, this paper innovatively incorporates correlated structured light and ghost imaging techniques to compress the complex spatial light field information of the atomic absorption pattern into a bucket detector, separating the detection and imaging optical paths and significantly simplifying the optical architecture. This method not only enables high-precision magnetic field measurement with a single measurement but also overcomes the volume limitations of traditional coaxial optical paths, enabling the evolution of magnetic measurement systems towards miniaturization and integration, providing a new path for the development of real-time, compact quantum magnetometers. Summary of the Invention

[0006] This paper aims to overcome the shortcomings of existing methods by providing a method for measuring vector magnetic fields using correlated structured light. This method utilizes the interaction between correlated structured light and atoms, extracts atomic absorption patterns through ghost imaging, and deciphers the direction and magnitude of the magnetic field. This method achieves high-precision magnetic field measurement with a single imaging pass, overcomes the volume limitations of traditional coaxial optical paths, offers a simple layout, and is less susceptible to interference from the external environment.

[0007] The technical solution to achieve the purpose of the present invention is to provide a vector magnetic field measurement method based on correlated structured light, which includes the following three steps: (1) Produce circularly coherent partially coherent light, whose cross spectral density function is: Where r = (r, θ) = (x, y) represents the spatial coordinates, w is the beam width, δ0 is the beam circular coherence width, sinc() represents the Sinker function, and c is a positive real number satisfying 2 / c < δ0. The method for generating the above beam is as follows: A. Using drift perturbation, a perturbation is introduced into the single-mode beam. The expression H(r,v) is as follows: H(r,v)=τ(r)exp[2πivr 2 ] (2) Where v is the coordinate in the spatial frequency domain, τ(r)=exp(-r 2 / w 2 ) is the complex amplitude function of the single-mode beam; B. The perturbed single-mode beam is distributed in the spatial frequency domain with a specific probability. The probability function p(v) is a real function, as follows p(v)=δ0 2 rect(δ0 2 v) (3) Where rect() is a rectangle function; C. Construct a large number of perturbed single-mode beams and make them incoherently superimposed to form partially coherent light. The instantaneous light field is as follows: In the above expression, E(x,y) is a sub-light field of the associated structured light; v n It is the one-dimensional discrete form of the spatial frequency domain coordinate v, that is Where n=-N,-N+1,… N-1,N; spatial frequency point v n exist Uniformly distributed within the range; φ n and φ m is a random phase; (a m ,b m ) is the center of the spatial frequency domain disturbance, which is randomly distributed in a circular area with a radius of c; N and N m is a positive integer greater than 500; a digital hologram CGH is generated by a computer, and the digital hologram generates the instantaneous light field E(x,y) above; D. Load the digital hologram CGH of the instantaneous light field E(x, y) onto the spatial light modulator SLM. The spatial light modulator then generates a sub-light field of correlated structured light. To construct correlated structured light, repeatedly run the CGH program that generates E(x, y) on the computer to generate multiple CGH images, forming a CGH sequence. Send the CGH sequence to the SLM. The SLM plays the CGH sequence at a constant rate, and the camera continuously captures the dynamic light generated by the SLM. By averaging the M frames of images captured by the camera, incoherent superposition of the M sub-light fields can be achieved. Through the incoherent superposition, correlated structured light can be obtained. The correlated structured light has a cross-spectral density function W(r1, r2). Convert the polarization state of the correlated structured light into radial polarization. (2) Using ghost imaging to obtain atomic absorption images, the method is: A. Using a laser and an SLM to generate the radially polarized correlated structured light described in step (1); a beam splitter divides the correlated structured light into a reference light (reflected to a CCD camera) and a detection light (transmitted to an atom pool and then received by a bucket detector); the information of the reference light is recorded by the CCD; the detection light enters the atom pool and interacts with the atoms, and the atom pool is placed in a magnetic field to be measured, and the magnetic field to be measured changes the atomic absorption coefficient through the Zeeman effect; the detection light is emitted from the atom pool and collected by the bucket detector; B. Perform a second-order correlation between the data recorded by the CCD and the data recorded by the bucket detector to obtain the atomic absorption map; (3) Using atomic absorption images to obtain vector magnetic field information, the method is: ① Place the rubidium atom cluster in a controllable magnetic environment; use gradient coils and Helmholtz coils to construct a calibration magnetic field with adjustable full-space orientation: in, are the three unit vectors of the rectangular coordinate system, the light transmission direction is the z axis, the cross section of the optical axis is the xy plane, B0 is the amplitude of the magnetic field, and the direction of the magnetic field is given by (θ B ,φ B ) represents; where θ B is the angle between the magnetic field and the direction of light propagation (z axis), φ B is the angle between the projection of the magnetic field on the cross section of the optical axis and the x-axis; ②Calibrate the magnetic field direction: A. Fix the magnetic field amplitude B0 and scan the magnetic field direction; B and φ B Continuously change in the range of 0-180°; first fix θ B , φ B Change in the range of 0-180°, and then the data recorded by CCD and bucket detector can obtain different φB The atomic absorption diagram below; B. Change θ B , repeat the above operation to obtain different θ B and φ B The atomic absorption diagram below; ③ Calibrate the magnetic field size: After completing step ②, change the magnetic field strength B0 and repeat the above process at each strength point to obtain the atomic absorption image under different B0. Finally, a magnetic field strength B0, direction (θ B ,φ B )’s atomic absorption image mapping database; ④ Magnetic field calculation: Remove the calibration magnetic field, apply the magnetic field to be measured, collect the atomic absorption image under the magnetic field to be measured and compare it with the data in the database, so as to determine the size B0 and direction (θ B ,φ B ).

[0008] Due to the application of the above technical solution, the present invention has the following advantages compared with the existing technology:

[0009] 1. This paper proposes a vector magnetic field measurement method based on correlated structured light. Compared to other vector magnetic field measurement methods, it has the advantage of real-time performance. Once the initial calibration is completed, the measurement process no longer requires an auxiliary magnetic field, resulting in faster measurements and higher accuracy.

[0010] 2. The present invention is not easily disturbed by external factors during the measurement of the magnetic field.

[0011] 3. Compared with other measurement methods, the device mentioned in this article has a simpler optical path, is easier to operate, and is easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 1 is a schematic structural diagram of a vector magnetic field measurement method based on correlated structured light provided by an embodiment of the present invention; In the figure, 1: laser; 2: spatial light modulator; 3: computer; 4: beam splitter; 5: CCD; 6: atom pool; 7: coil; 8: magnetic field shield; 9: PD; 10: computer; 11: VR; 12: half-wave plate.

[0013] Figure 2 is a schematic diagram of the magnetic field and the direction of light transmission; in the figure, φ B is the angle between the magnetic field and the x-axis after projection on the optical axis cross section (xy plane), θ B It is the angle between the magnetic field and the direction of light propagation (z-axis). DETAILED DESCRIPTION

[0014] The present invention will be further described in detail below with reference to the examples. The following examples are provided to explain the present invention and are also preferred application forms of the present invention, but the present invention is not limited to the following examples.

[0015] like Figure 1 As shown, it is a schematic diagram of a device for a vector magnetic field measurement method based on correlated structured light provided in this embodiment, which includes a laser 1; a spatial light modulator 2; a first computer 3; a beam splitter 4; a CCD camera 5; an atomic pool 6; a coil 7; a magnetic field shield 8; a PD detector 9; a second computer 10; 11: VR vortex wave plate 12: half-wave plate.

[0016] The working steps of this embodiment are as follows: The first computer 3 is used to generate a superimposed light field, and the first computer 3 is connected to the spatial light modulator 2; the digital hologram for generating correlated structured light is loaded into the spatial light modulator 2; the laser 1 is turned on to generate polarization-stable linearly polarized light; the generated linearly polarized light is emitted into the spatial light modulator 2; since the spatial light modulator 2 is connected to the first computer 3, the light emitted from the spatial light modulator 2 is the correlated structured light we set; the correlated structured light emitted from the spatial light modulator 2 is emitted into the half-wave plate 12 and then into the VR vortex wave plate 11, and the polarization state of the light beam is changed from linear polarization to radial polarization, and then the correlated structured light with radial polarization enters the beam splitter 4; after the correlated structured light passes through the beam splitter, its reflected light is emitted into the CCD camera 5; the light transmitted in the beam splitter The correlated structured light is incident on objects 6 and 7 consisting of an atomic pool and a coil, where 8 is a magnetic field shield for shielding interference from the external magnetic field; by controlling the current of the coil, we can change the direction of the magnetic field; the light emitted from the object is incident on the PD detector 9; the light incident on the CCD camera is called reference light, and the light incident on the object is called detection light; the image in the CCD camera 5 and the image in the PD detector 9 are connected to the second computer 10, and the two are correlated to form an image, so that the optical density image behind the atomic pool of the object can be obtained; since the interaction between the correlated structured light with radial polarization and the atoms will be affected by the direction and size of the magnetic field, the second computer 10 will present different images, and the direction and size of the magnetic field can be judged according to the changes in the image.

Claims

1. The technical solution to achieve the purpose of the present invention is to provide a vector magnetic field measurement method based on correlated structured light, which includes the following three steps: (1) Produce circularly coherent partially coherent light, whose cross spectral density function is: Where r = (r, θ) = (x, y) represents the spatial coordinates, w is the beam width, δ0 is the circular coherence width of the beam, sinc() represents the Sinker function, and c is a positive real number that satisfies 2 / c < δ0. The method for generating the above beam is as follows: A. Using drift perturbation, a perturbation is introduced into the single-mode beam. The expression H(r,v) is as follows: H(r,v)=τ(r)exp[2πivr 2 ] (2) Where v is the coordinate in the spatial frequency domain, τ(r)=exp(-r 2 / w 2 ) is the complex amplitude function of the single-mode beam; B. The perturbed single-mode beam is distributed in the spatial frequency domain with a specific probability. The probability function p(v) is a real function, as follows p(v)=δ0 2 rect(δ0 2 v) (3) Where rect() is a rectangle function; C. Construct a large number of perturbed single-mode beams and make them incoherently superimposed to form partially coherent light. The instantaneous light field is as follows: In the above expression, E(x,y) is a sub-light field of the associated structured light; v n It is the one-dimensional discrete form of the spatial frequency domain coordinate v, that is Where n=-N,-N+1,… N-1,N; spatial frequency point v n exist Uniformly distributed within the range; φ n and φ m is a random phase; (a m ,b m ) is the center of the spatial frequency domain disturbance, which is randomly distributed in a circular area with a radius of c; N and N m is a positive integer greater than 500; a digital hologram CGH is generated by a computer, and the digital hologram generates the instantaneous light field E(x,y) above; D. Load the digital hologram CGH of the instantaneous light field E(x, y) onto the spatial light modulator SLM. The spatial light modulator then generates a sub-light field of correlated structured light. To construct correlated structured light, repeatedly run the CGH program that generates E(x, y) on the computer to generate multiple CGH images, forming a CGH sequence. Send the CGH sequence to the SLM. The SLM plays the CGH sequence at a constant rate, and the camera continuously captures the dynamic light generated by the SLM. By averaging the M frames of images captured by the camera, incoherent superposition of the M sub-light fields can be achieved. Through the incoherent superposition, correlated structured light can be obtained. The correlated structured light has a cross-spectral density function W(r1, r2). Convert the polarization state of the correlated structured light into radial polarization. (2) Using ghost imaging to obtain atomic absorption images, the method is: A. Using a laser and an SLM to generate the radially polarized correlated structured light described in step (1); a beam splitter divides the correlated structured light into a reference light (reflected to a CCD camera) and a detection light (transmitted to an atom pool and then received by a bucket detector); the information of the reference light is recorded by the CCD; the detection light enters the atom pool and interacts with the atoms, and the atom pool is placed in a magnetic field to be measured, and the magnetic field to be measured changes the atomic absorption coefficient through the Zeeman effect; the detection light is emitted from the atom pool and collected by the bucket detector; B. Perform a second-order correlation between the data recorded by the CCD and the data recorded by the bucket detector to obtain the atomic absorption map; (3) Using atomic absorption images to obtain vector magnetic field information, the method is: ① Place the rubidium atom cluster in a controllable magnetic environment; use gradient coils and Helmholtz coils to construct a calibration magnetic field with adjustable full-space orientation: in, are the three unit vectors of the rectangular coordinate system, the light transmission direction is the z axis, the cross section of the optical axis is the xy plane, B0 is the amplitude of the magnetic field, and the direction of the magnetic field is given by (θ B ,φ B ) represents; where θ B is the angle between the magnetic field and the direction of light propagation (z axis), φ B is the angle between the projection of the magnetic field on the cross section of the optical axis and the x-axis; ②Calibrate the magnetic field direction: A. Fix the magnetic field amplitude B0 and scan the magnetic field direction; B and φ B Continuously change in the range of 0-180°; first fix θ B , φ B Change in the range of 0-180°, and then the data recorded by CCD and bucket detector can obtain different φ B The atomic absorption diagram below; B. Change θ B , repeat the above operation to obtain different θ B and φ B The atomic absorption diagram below; ③ Calibrate the magnetic field size: After completing step ②, change the magnetic field strength B0 and repeat the above process at each strength point to obtain the atomic absorption image under different B0. Finally, a magnetic field strength B0, direction (θ B ,φ B )’s atomic absorption image mapping database; ④ Magnetic field calculation: Remove the calibration magnetic field, apply the magnetic field to be measured, collect the atomic absorption image under the magnetic field to be measured and compare it with the data in the database, so as to determine the size B0 and direction (θ B ,φ B ).

Images