A uniformly polarized single-beam SERF atomic magnetometer system

Abstract

This invention relates to a uniformly polarized single-beam SERF atomic magnetometer system. First, a relatively uniform Gaussian distribution is obtained by truncating the central portion of the light spot using an aperture. Then, the pump light is passed through the gas cell again via a reflector placed at the rear end of the gas cell, uniformly distributing the polarizability due to light absorption attenuation. The polarizability signal is acquired by a photodetector and extracted using phase-sensitive detection technology. This SERF atomic magnetometer system has advantages such as simple structure, high accuracy, and ease of miniaturization, and has broad application prospects in weak magnetic field measurement, especially in biomagnetic measurement research.

Description

Technical Field

[0001] This invention relates to the field of atomic magnetometer technology, and in particular to a uniformly polarized single-beam SERF atomic magnetometer system. Background Technology

[0002] Proposed at the beginning of this century, the spin-exchange relaxation-free (SERF) atomic magnetometer has now surpassed superconducting quantum interference devices (SQUIDs), achieving the highest theoretical sensitivity for magnetic field measurements in the low-frequency range. Furthermore, because the SERF atomic magnetometer is based on the interaction of light and atoms and does not require cryogenic operation, it has the potential for miniaturization, meeting the high-resolution requirements of biomagnetic measurements.

[0003] The SERF atomic magnetometer was initially based on a two-beam configuration, using a circularly polarized beam to polarize alkali metal atoms while simultaneously using a linearly polarized beam to detect atomic precession induced by an external magnetic field. However, this configuration is generally bulky and has a complex optical path, limiting its further development. Compared to the two-beam configuration, the single-beam magnetometer configuration has greater potential for miniaturization and higher resolution. However, because the single-beam configuration uses a single beam for pumping and detection, it cannot achieve separate control of the two processes; furthermore, signal detection is limited by acquiring the optical signal, which restricts the light intensity, further leading to problems such as polarization inhomogeneity and difficulty in improving polarization rate.

[0004] Currently, many methods have been used to improve the polarization uniformity of SERF atomic magnetometers, but most of them focus on dual-beam configurations, which have complex optical paths and are difficult to meet miniaturization requirements. In view of this, the inventors have completed the system described in this invention. Summary of the Invention

[0005] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and propose a single-beam SERF atomic magnetometer system with uniform polarization. First, the pump light is collimated into a Gaussian beam with a diameter of about 2.5 times the target diameter by a collimator. Then, the central part of the pump light is intercepted by an aperture to obtain a more uniform Gaussian beam, which achieves the effect of uniform polarization. At the same time, the pump light enters the reflector at a 0° incident angle and re-enters the alkali metal gas cell after reflection. This reduces the light intensity attenuation caused by the light absorption effect of alkali metal atoms and achieves a uniform distribution of polarizability due to light absorption attenuation. Thus, two uniform polarization settings are achieved in the alkali metal gas cell, achieving the effects of uniform polarization and improved polarizability.

[0006] The technical solution of the present invention is as follows:

[0007] A uniformly polarized single-beam SERF atomic magnetometer system is characterized by comprising an aperture disposed on the single-beam incident optical path of an alkali metal gas cell, and a reflector disposed at the single-beam exit end of the alkali metal gas cell aligned with the aperture. The aperture is located between the alkali metal gas cell and a quarter-wave plate. The aperture is used to extract the central portion of the Gaussian beam with a large spot size emitted from the quarter-wave plate to form an incident Gaussian beam with a smaller spot size and more uniform light intensity. The reflector causes the exiting Gaussian beam to return along its original path to form a reflected Gaussian beam used as detection light that passes through the alkali metal gas cell. Both the incident Gaussian beam and the reflected Gaussian beam play a role in uniform polarization within the alkali metal gas cell.

[0008] The emitted Gaussian beam enters the reflector at a 0° incident angle and, after being reflected by the reflector, re-enters the alkali metal gas chamber, reducing the light intensity attenuation caused by the light absorption effect of alkali metal atoms and playing a role in uniformizing the polarizability distribution due to light absorption attenuation.

[0009] The diameter of the larger light spot is 2.5 times the diameter of the smaller light spot.

[0010] The alkali metal gas chamber is surrounded by a non-magnetic electric heating coil, a ceramic oven, a triaxial magnetic field coil, and a magnetic shielding barrel arranged sequentially from the inside out. The triaxial magnetic field coil is connected to a signal generator.

[0011] The quarter-wave plate is connected to the distributed Bragg reflection (DBR) laser in sequence via a polarizing beam splitter, a half-wave plate, and a collimator. The reflecting end of the Gaussian beam of the polarizing beam splitter is connected in series with a transimpedance amplifier, a low-pass filter, a lock-in amplifier, and a host computer via a photodetector. The lock-in amplifier is connected to a signal generator.

[0012] The collimator is connected to the DBR laser via a polarization-maintaining fiber.

[0013] The collimator, half-wave plate, polarizing beam splitter, photodetector, quarter-wave plate, aperture, triaxial magnetic field coil, ceramic oven, alkali metal gas chamber, non-magnetic electric heating coil, and reflector are all located inside the magnetic shielding barrel.

[0014] The non-magnetic electric heating coil is wound with twisted-pair wire and driven by 200kHz AC power to minimize interference with magnetic field measurement. The triaxial magnetic field coil is used to compensate for the residual magnetic field of the triaxial coil and to apply a rotating modulated magnetic field.

[0015] The signal acquired by the photodetector is amplified by the transimpedance amplifier and then enters the low-pass filter. After being filtered by the low-pass filter, it enters the lock-in amplifier to demodulate the first harmonic component of the magnetometer response signal, and then enters the host computer to complete the signal acquisition and processing.

[0016] The technical effects of this invention are as follows: This invention provides a uniformly polarized single-beam SERF atomic magnetometer system. First, the central part of the light spot is intercepted by an aperture to obtain a relatively uniform Gaussian distribution. Then, the pump light is passed through the gas cell again by a reflector placed at the rear end of the gas cell, uniformly distributing the polarizability due to light absorption attenuation. The polarizability signal is acquired by a photodetector and extracted by phase-sensitive detection technology. The SERF atomic magnetometer system has the advantages of simple structure, high accuracy, and easy miniaturization, and has broad application prospects in weak magnetic field measurement, especially in biomagnetism measurement research.

[0017] The advantages of this invention compared with the prior art are: (1) The present invention optimizes polarization uniformity from both the lateral and longitudinal directions, which can effectively improve the performance of the single-beam SERF atomic magnetometer. (2) The present invention is simple to operate and easy to verify, and is of great significance for miniaturization and integration applications. Attached Figure Description

[0018] Figure 1 A schematic diagram of a uniformly polarized single-beam SERF atomic magnetometer system for implementing the present invention.

[0019] The figures are labeled as follows: 1-DBR laser (DBR, distributed Bragg reflector); 2-collimator (the collimator is connected to the DBR laser via a polarization-maintaining fiber); 3-1 / 2 waveplate; 4-polarizing beam splitter; 5-photodetector; 6-1 / 4 waveplate; 7-aperture; 8-three-axis magnetic field coil; 9-ceramic oven; 10-alkali metal gas chamber; 11-non-magnetic electric heating coil; 12-reflector; 13-transimpedance amplifier; 14-low-pass filter; 15-signal generator; 16-lock-in amplifier; 17-magnetic shielding barrel; 18-host computer; xyz-Cartesian coordinate system (x-axis, y-axis, z-axis). Detailed Implementation

[0020] The following is in conjunction with the attached diagram ( Figure 1 The invention will be described in the following sections and examples.

[0021] Figure 1 A schematic diagram of a uniformly polarized single-beam SERF atomic magnetometer system for implementing this invention. (Reference) Figure 1As shown, a uniformly polarized single-beam SERF atomic magnetometer system includes an aperture 7 disposed on the single-beam incident optical path of an alkali metal gas cell 10, and a reflector 12 disposed at the single-beam exit end of the alkali metal gas cell 10 and aligned with the aperture 7. The aperture 7 is located between the alkali metal gas cell 10 and a quarter-wave plate 6. The aperture 7 is used to extract the central portion of the Gaussian beam with a large spot size emitted from the quarter-wave plate 6 to form an incident Gaussian beam with a smaller spot size and more uniform light intensity. The reflector 12 causes the outgoing Gaussian beam to return along its original path to form a reflected Gaussian beam used as detection light that passes through the alkali metal gas cell 10. Both the incident Gaussian beam and the reflected Gaussian beam play a role in uniform polarization in the alkali metal gas cell 10.

[0022] The emitted Gaussian beam enters the reflector 12 at a 0° incident angle and, after reflection by the reflector 12, re-enters the alkali metal gas chamber 10. This reduces the light intensity attenuation caused by the light absorption effect of alkali metal atoms and plays a role in uniformizing the polarization distribution due to light absorption attenuation. The diameter of the larger light spot is 2.5 times that of the smaller light spot. Around the alkali metal gas chamber 10, from the inside out, are arranged a non-magnetic electric heating coil 11, a ceramic oven 9, a triaxial magnetic field coil 8, and a magnetic shielding barrel 17. The triaxial magnetic field coil 8 is connected to the signal generator 15. The quarter-wave plate 6 is connected to the distributed Bragg reflection (DBR) laser 1 via a polarizing beam splitter 4, a half-wave plate 3, and a collimator 2. The reflecting end of the Gaussian beam from the polarizing beam splitter 4 is connected in series with a transimpedance amplifier 13, a low-pass filter 14, a lock-in amplifier 16, and a host computer 18 via a photodetector 5. The lock-in amplifier 16 is connected to the signal generator 15.

[0023] The collimator 2 is connected to the DBR laser 1 via a polarization-maintaining fiber. The collimator 2, half-wave plate 3, polarizing beam splitter 4, photodetector 5, quarter-wave plate 6, aperture 7, triaxial magnetic field coil 8, ceramic oven 9, alkali metal gas chamber 10, non-magnetic electric heating coil 11, and reflector 12 are all located inside the magnetic shielding barrel 17.

[0024] The non-magnetic electric heating coil 11 is wound with twisted-pair wire and driven by 200kHz AC power to minimize interference with the magnetic field measurement. The triaxial magnetic field coil 8 is used to compensate for the residual magnetic field of the three axes and apply a rotating modulated magnetic field. The signal collected by the photodetector 5 is amplified by the transimpedance amplifier 13 and then enters the low-pass filter 14. After being filtered by the low-pass filter 14, it enters the lock-in amplifier 16 to demodulate the first harmonic component of the magnetometer response signal, and then enters the host computer 18 to complete the signal acquisition and processing.

[0025] A uniformly polarized SERF atomic magnetometer system, such as Figure 1 As shown, the collimator 2 collimates the pump light into a Gaussian beam with a diameter approximately 2.5 times the target diameter, and the aperture intercepts the central portion of the pump light to obtain a more uniform Gaussian beam, thereby achieving uniform polarization. After passing through the alkali metal gas chamber, the pump light enters the reflector 12 at a 0° incident angle. After reflection by the reflector 12, it re-enters the alkali metal gas chamber 10, offsetting the light intensity attenuation caused by the light absorption effect of alkali metal atoms, and achieving uniform polarization.

[0026] like Figure 1 As shown, a uniformly polarized SERF atomic magnetometer system includes two uniform polarization settings. One setting involves collimating the pump light emitted by the DBR laser into a Gaussian beam with a diameter approximately 2.5 times the target diameter using a collimator 2, and then using an aperture 7 to cut off the central portion of the pump light to obtain a more uniform Gaussian beam, thereby achieving uniform polarization. The other setting involves passing the pump light through an alkali metal gas chamber 10 and then incident it at a 0° angle into a reflector 12. After being reflected by the reflector 12, the light re-enters the alkali metal gas chamber 10, reducing the light intensity attenuation caused by the light absorption effect of alkali metal atoms and achieving uniform polarization.

[0027] The single-beam magnetometer system uses a single beam of light to simultaneously pump alkali metal atoms and detect magnetic field signals. The pump light emitted by the DBR laser 1 is transmitted to the collimator 2 via a polarization-maintaining fiber. After being collimated by the collimator 2, it passes sequentially through a half-wave plate 3, a polarizing beam splitter 4, a quarter-wave plate 6, and an aperture 7 before entering the alkali metal gas cell 10. After being reflected by the mirror 12 at the rear end of the gas cell, it passes sequentially through the alkali metal gas cell 10, the aperture 7, the quarter-wave plate 6, and the polarizing beam splitter 4 before being collected by the photodetector 5.

[0028] The aperture 7 obtains relatively uniform Gaussian light by truncating the central portion of the Gaussian light spot. Around the alkali metal gas chamber 10, from the inside out, are arranged a non-magnetic electric heating coil 11, a ceramic oven 9, a triaxial magnetic field coil 8, and a magnetic shielding barrel 17. The triaxial magnetic field coil 8 is connected to the signal generator 15. The non-magnetic electric heating coil 11 is wound with twisted-pair wire and driven by 200kHz AC power to minimize interference with the magnetic field measurement.

[0029] The alkali metal atom in the alkali metal chamber 10 is one of potassium atom, rubidium atom, or cesium atom, and should contain a buffer gas and a quenching gas with a total pressure of about 1 atm (atmospheres). Both the buffer gas and the quenching gas are nitrogen.

[0030] The pump light of the single-beam magnetometer system is in the Z direction, and the x-axis is selected as the sensing axis. First, the triaxial magnetic field coil 8 is used to compensate for the residual magnetic field of the three axes, and a rotational modulation magnetic field is applied to the sensing axis. Next, the signal acquired by the photodetector 5 is amplified by the transimpedance amplifier 13 and then enters the low-pass filter 14. After filtering by the low-pass filter 14, it enters the lock-in amplifier 16 to demodulate the first harmonic component of the magnetometer response signal, and then enters the host computer 18 to complete signal acquisition and processing. Finally, the polarizability information of the magnetometer is obtained from the acquired signal, and subsequent parameter optimization operations are performed.

[0031] Contents not described in detail in this specification are prior art known to those skilled in the art. It is hereby indicated that the above description is intended to help those skilled in the art understand this invention, but does not limit the scope of protection of this invention. Any equivalent substitutions, modifications, improvements, and / or simplifications of the above descriptions that do not depart from the essential content of this invention fall within the scope of protection of this invention.

Claims

1. A uniformly polarized single-beam SERF atomic magnetometer system, characterized in that, The system includes an aperture disposed on the single-beam incident optical path of an alkali metal gas cell, and a reflector disposed at the single-beam exit end of the alkali metal gas cell aligned with the aperture. The aperture is located between the alkali metal gas cell and a quarter-wave plate. The aperture is used to extract the central portion of the Gaussian beam with a larger spot size emitted from the quarter-wave plate to form an incident Gaussian beam with a smaller spot size and more uniform light intensity. The reflector causes the outgoing Gaussian beam to return along its original path to form a reflected Gaussian beam used as detection light that passes through the alkali metal gas cell. Both the incident Gaussian beam and the reflected Gaussian beam play a role in uniform polarization within the alkali metal gas cell. The diameter of the larger light spot is 2.5 times the diameter of the smaller light spot; The outgoing Gaussian beam enters the reflector at a 0° incident angle and, after being reflected by the reflector, re-enters the alkali metal gas chamber, reducing the light intensity attenuation caused by the light absorption effect of alkali metal atoms and playing a uniform role in the polarization distribution caused by light absorption attenuation. The alkali metal gas chamber is surrounded by a non-magnetic electric heating coil, a ceramic oven, a triaxial magnetic field coil, and a magnetic shielding barrel arranged sequentially from the inside out. The triaxial magnetic field coil is connected to a signal generator. The quarter-wave plate is connected to the distributed Bragg reflection (DBR) laser in sequence via a polarizing beam splitter, a half-wave plate, and a collimator. The reflecting end of the Gaussian beam of the polarizing beam splitter is connected in series with a transimpedance amplifier, a low-pass filter, a lock-in amplifier, and a host computer via a photodetector. The lock-in amplifier is connected to a signal generator. The collimator is connected to the DBR laser via a polarization-maintaining fiber. The collimator, half-wave plate, polarizing beam splitter, photodetector, quarter-wave plate, aperture, triaxial magnetic field coil, ceramic oven, alkali metal gas chamber, non-magnetic electric heating coil, and reflector are all located inside the magnetic shielding barrel.

2. The uniformly polarized single-beam SERF atomic magnetometer system according to claim 1, characterized in that, The non-magnetic electric heating coil is wound with twisted-pair wire and driven by 200kHz AC power to minimize interference with magnetic field measurement. The triaxial magnetic field coil is used to compensate for the residual magnetic field of the triaxial coil and to apply a rotating modulated magnetic field.

3. The uniformly polarized single-beam SERF atomic magnetometer system according to claim 1, characterized in that, The signal acquired by the photodetector is amplified by the transimpedance amplifier and then enters the low-pass filter. After being filtered by the low-pass filter, it enters the lock-in amplifier to demodulate the first harmonic component of the magnetometer response signal, and then enters the host computer to complete the signal acquisition and processing.

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