High spatial resolution arrayed serf atomic magnetometer based on beam homogenization

Abstract

The application discloses a high spatial resolution array type SERF atomic magnetometer based on beam homogenization, which provides a new idea for the realization of miniaturized multi-channel atomic magnetometer, and lays a foundation for the development of high spatial resolution magnetic field detection, portable multi-channel atomic magnetometer and biological magnetic imaging technology, and is characterized in that: an alkali metal cell is arranged in a magnetic compensation coil; a 3*3 photodiode array is arranged on a laser exit side of the alkali metal cell; a 1 / 4 wave plate is connected with a flat-top beam shaper on a laser incident side of the alkali metal cell; the flat-top beam shaper shapes a light spot with Gaussian distribution of incident light intensity into a flat-top light spot with uniform distribution of light intensity; the flat-top light spot covers the photodiode array on an xy plane after sequentially passing through the 1 / 4 wave plate and the alkali metal cell along a z axis; and nine photodiodes in the photodiode array form nine signal channels for receiving the flat-top light spot from nine positions.

Description

TECHNICAL FIELD

[0001] The application relates to the field of high spatial resolution extremely weak magnetic field measurement of a multi-channel SERF atomic magnetometer, and particularly relates to a high spatial resolution array type SERF atomic magnetometer based on light beam homogenization. BACKGROUND

[0002] The sensitivity of an atomic magnetometer based on the spin-exchange relaxation-free (SERF) effect has reached the order of sub-fT / Hz 1 / 2 , and can realize ultra-high sensitivity extremely weak magnetic field measurement, and has great potential for application in magnetocardiogram (MCG) and magnetoencephalogram (MEG) measurement instruments. MCG and MEG applications usually require multi-channel parallel magnetic imaging, and the efficiency and spatial resolution of magnetic field measurement are effectively improved through multi-channel synchronous detection of a large range of areas. However, the multi-channel scheme of a plurality of single-channel sensors has low spatial resolution, usually only cm order, the performance difference between sensors (or magnetometers) is significant, consistency is difficult to guarantee, and there is a problem of modulation magnetic field crosstalk, which seriously affects the integration of the multi-channel magnetometer system.

[0003] In order to solve the above problems, the application provides a high spatial resolution array type SERF atomic magnetometer based on light beam homogenization. A single gas chamber and a 3x3 photodiode array are used to realize mm-level magnetic field measurement resolution and fT-level sensitivity. The alkali metal atoms are polarized by the flat-top laser beam after beam expansion, which significantly improves the uniformity of the atomic polarization rate in different regions of the gas chamber and enhances the consistency between the performances of the channels. Further, by filling the high-pressure buffer gas and quenching gas in the large gas chamber, the diffusion of the alkali metal atoms is inhibited, and the collision relaxation with the gas chamber wall is reduced. The channel spacing of the designed magnetometer is greater than the diffusion distance of the alkali metal atoms, so that different regions in the gas chamber can be independently used as a magnetometer. The optical path structure of the system is simple and easy to realize, and has the potential of integrated small multi-channel magnetometer. At the same time, the magnetometer only needs a set of magnetic compensation coils, so as to avoid the magnetic field crosstalk between different channels. The innovative method provides a new idea for the realization of small multi-channel atomic magnetometer, and lays a foundation for the development of high-resolution magnetic field detection, portable multi-channel atomic magnetometer and biological magnetic imaging technology. SUMMARY

[0004] The present application aims at the deficiencies in the prior art, and provides a high spatial resolution array type SERF atomic magnetometer based on light beam homogenization, which realizes mm-level magnetic field measurement resolution and fT-level sensitivity by using a single gas chamber and a 3*3 photodiode array. The flat-top laser beam after beam expansion is used to polarize alkali metal atoms, which significantly improves the uniformity of the atom polarization rate in different regions of the gas chamber and enhances the consistency between the performances of each channel. Further, by filling high-pressure buffer gas and quenching gas in the large gas chamber, the diffusion of alkali metal atoms is inhibited, and the collision relaxation with the gas chamber wall is reduced. The channel spacing of the designed device is greater than the diffusion distance of alkali metal atoms, so that different regions in the gas chamber can be independently used as a magnetometer. The light path structure of the system is simple and easy to realize, and has the potential of integrated small multi-channel magnetometer. At the same time, the magnetometer only needs a set of magnetic compensation coils, so as to avoid the magnetic field crosstalk between different channels. The innovative method provides a new idea for the realization of small multi-channel atomic magnetometer, and lays a foundation for the development of high-resolution magnetic field detection, portable multi-channel atomic magnetometer and biological magnetic imaging technology.

[0005] The technical solution of the present application is as follows:

[0006] A high spatial resolution array type SERF atomic magnetometer based on light beam homogenization, characterized by comprising an alkali metal gas chamber located in a magnetic compensation coil, a 3*3 photodiode array is arranged on the laser exit side of the alkali metal gas chamber, a 1 / 4 wave plate is connected to a flat-top beam shaper on the laser incident side of the alkali metal gas chamber, the flat-top beam shaper shapes the Gaussian distribution spot of the incident light intensity into a flat-top spot with uniform light intensity, the flat-top spot covers the photodiode array on the xy plane after passing through the 1 / 4 wave plate and the alkali metal gas chamber along the z axis in turn, and nine photodiodes in the photodiode array form nine signal channels for receiving the flat-top spot from nine positions.

[0007] The spacing between adjacent signal channels is greater than the diffusion distance of alkali metal atoms, so that different regions in the gas chamber can be independently used as a magnetometer.

[0008] The photodiode array is connected to a transimpedance amplifier through a transmission cable, and the transimpedance amplifier is connected to a signal acquisition and processing module through a lock-in amplifier.

[0009] The flat-top beam shaper is connected to the transmission side of a polarization beam splitter prism in turn through a mirror group and an optical expander, the incident side of the polarization beam splitter prism is connected to a laser, and the reflection side of the polarization beam splitter prism is connected to a wavelength meter.

[0010] The magnetic compensation coil is connected to a function source through a transmission cable.

[0011] A magnetic source coil is arranged between the magnetic compensation coil and the alkali metal cell to evaluate the coincidence between the gradient magnetic field theoretical simulation value and the gradient magnetic field actual measurement value.

[0012] The outer size of the single photodiode is 3mm*3mm, and the center distance between adjacent photodiodes is 3.25mm, which is greater than the theoretically calculated alkali metal atom diffusion distance 0.25mm, so that the nine-channel SERF atomic magnetometer device can obtain the measured magnetic field size of 9 positions at the same time.

[0013] The expression includes the following expression:

[0014]

[0015] Wherein I is the light intensity detected by the photodiode, k1 is a proportional coefficient, is the z-axis component of the electronic polarizability of the alkali metal atom, P0 is the electronic polarization vector size of the alkali metal atom under the condition of no external magnetic field at steady state, J0(u) is a 0-order first kind Bessel function, J1(u) is a 1-order first kind Bessel function, Γ is a magnetic resonance line width, B y is the y-axis measured magnetic field, B y0 is the y-axis residual magnetic field, B x0 is the x-axis residual magnetic field, B z0 is the z-axis residual magnetic field; the 9-channel photoelectric signals are calculated 9 times by the above formula in parallel, and finally the measured magnetic field size of 9 positions is obtained at the same time.

[0016] The outer wall of the alkali metal cell is additionally provided with a heating device.

[0017] The technical effects of the application are as follows: the application discloses a high spatial resolution array type SERF atomic magnetometer based on beam homogenization, which realizes mm-level magnetic field measurement resolution and fT-level sensitivity by using a single cell and a photodiode array. The flat-top laser beam after beam expansion is used for polarizing alkali metal atoms, which significantly improves the uniformity of the atom polarization rate in different regions of the cell and enhances the consistency between the performances of the channels. Further, by filling high-pressure buffer gas and quenching gas in the large cell, the diffusion of the alkali metal atoms is inhibited, and the collision relaxation with the cell wall is reduced. The channel spacing of the designed device is greater than the diffusion distance of the alkali metal atoms, so that different regions in the cell can be independently used as a magnetometer. The optical path structure of the system is simple and easy to realize, and has the potential of integrated miniaturized multi-channel magnetometer. At the same time, the magnetometer only needs a set of magnetic compensation coil, so as to avoid the magnetic field crosstalk between different channels. The innovative method provides a new idea for the realization of miniaturized multi-channel atomic magnetometer, lays a foundation for the development of high-resolution magnetic field detection, portable multi-channel atomic magnetometer and biological magnetic imaging technology. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a schematic diagram of a high spatial resolution arrayed SERF atomic magnetometer based on beam homogenization according to an embodiment of the present application.

[0019] Figure 2 is Figure 1 is a plot of the magnetic field sensitivity of the nine channels in the device. Figure 2 is a plot of the magnetic field sensitivity of the nine channels in the device. 1 / 2 1 2 5 Figure 2 is a plot of the magnetic field sensitivity of the nine channels in the device. Figure 2 1 / 2

[0020] Figure 3 is a plot of the magnetic field gradient distribution generated by the magnetic source coil in the device. Figure 1 is a plot of the magnetic field gradient distribution generated by the magnetic source coil in the device. Figure 3 is a plot of the magnetic field gradient distribution generated by the magnetic source coil in the device. Figure 3 is a plot of the magnetic field gradient distribution generated by the magnetic source coil in the device.

[0021] The reference signs are explained as follows: 1 - transimpedance amplifier; 2 - lock-in amplifier; 3 - signal acquisition and processing module; 4 - laser; 5 - optical path; 6 - transmission cable; 7 - polarization beam splitter prism; 8 - wavemeter; 9 - optical beam expander; 10 - mirror; 11 - flattop beam shaper; 12 - 1 / 4 waveplate; 13 - function generator; 14 - magnetic shielded can; 15 - magnetic compensation coil; 16 - heating device; 17 - alkali vapor cell; 18 - photodiode array; 19 - magnetic source coil; xyz - three axes of the rectangular coordinate system (i.e. x-axis, y-axis, and z-axis). DETAILED DESCRIPTION​​​​​​

[0022] The application will be described below in conjunction with the accompanying drawings Figures 1-3 and examples.

[0023] Figure 1 is a schematic diagram of a high spatial resolution arrayed SERF atomic magnetometer based on beam homogenization. Figure 2 is Figure 1 a graph of the magnetic field sensitivity of the nine channels in Figure 3 is a result of measuring Figure 1 the gradient magnetic field distribution generated by the magnetic source coil in Figures 1 to 3 As shown in FIG. 1, a high spatial resolution arrayed SERF atomic magnetometer based on beam homogenization includes an alkali metal cell 17 located in a magnetic compensation coil 15, a 3x3 photodiode array 18 is arranged on the laser exit side of the alkali metal cell 17, and the laser incident side of the alkali metal cell 17 is connected to a flat-top beam shaper 11 through a 1 / 4 wave plate 12. The flat-top beam shaper 11 reshapes the incident light spot with Gaussian distribution of light intensity into a flat-top light spot with uniform distribution of light intensity. The flat-top light spot covers the photodiode array 18 in the xy plane after passing through the 1 / 4 wave plate 12 and the alkali metal cell 17 along the z axis in turn. Nine photodiodes in the photodiode array 18 form nine signal channels that receive the flat-top light spot from nine positions.

[0024] The spacing between adjacent signal channels is greater than the diffusion distance of alkali metal atoms, so that different regions in the cell can be independently used as a magnetometer. The photodiode array is connected to a transimpedance amplifier 1 through a transmission cable 6, and the transimpedance amplifier 1 is connected to a signal acquisition and processing module 3 through a lock-in amplifier 2. The flat-top beam shaper 11 is connected to the transmission side of a polarization beam splitter prism 7 in turn through a mirror group (including two mirrors 10) and an optical expander 9. The incident side of the polarization beam splitter prism 7 is connected to a laser 4, and the reflection side of the polarization beam splitter prism 7 is connected to a wavelength meter 8. The magnetic compensation coil 15 is connected to a function source 13 through a transmission cable 6.

[0025] A magnetic source coil 19 is arranged between the magnetic compensation coil 15 and the alkali metal cell 17 to evaluate the consistency between the theoretical simulation value of the gradient magnetic field and the actual measured value of the gradient magnetic field. The outer size of a single photodiode is 3mmx3mm, and the center-to-center distance between adjacent photodiodes is 3.25mm, which is greater than the theoretically calculated diffusion distance of alkali metal atoms 0.25mm. Therefore, the nine-channel SERF atomic magnetometer device can obtain the magnetic field size at nine positions at the same time, and the resolution of the spatial position of the magnetic field measurement is 3.25mm.

[0026] The following expressions are included:

[0027]

[0028] where I is the light intensity detected by the photodiode, k1 is a proportional coefficient, is the z-axis component of the electronic polarizability of alkali metal atoms, P0 is the magnitude of the electronic polarization vector of alkali metal atoms at steady state without external magnetic field, J0(u) is the 0th order Bessel function of the first kind, J1(u) is the 1st order Bessel function of the first kind, Γ is the magnetic resonance linewidth, B y is the y-axis magnetic field to be measured, B y0 is the y-axis residual magnetic field, B x0 is the x-axis residual magnetic field, B z0 is the z-axis residual magnetic field; the 9-channel photoelectric signals are calculated 9 times in parallel through the above formula, and finally the magnetic field to be measured at 9 positions is obtained at the same time. The alkali metal cell 17 is provided with a heating device 16 on the outer wall.

[0029] The application relates to a high spatial resolution array-type SERF atomic magnetometer based on beam homogenization. A single cell and a 3*3 photodiode array are used to realize mm-level magnetic field measurement resolution and fT-level sensitivity. The flat-top laser beam after beam expansion is used to polarize alkali metal atoms, which significantly improves the uniformity of the atomic polarization rate in different regions of the cell and enhances the consistency between the performances of the channels. Further, high-pressure buffer gas and quenching gas are filled in the large cell to suppress the diffusion of alkali metal atoms and reduce the collision relaxation with the cell wall. The channel spacing of the designed device is greater than the diffusion distance of alkali metal atoms, so that different regions in the cell can be used as magnetometers independently. The optical path structure of the system is simple and easy to realize, and has the potential of integrated small multi-channel magnetometer probe. At the same time, the magnetometer only needs a set of magnetic compensation coils, so as to avoid the magnetic field crosstalk between different channels. The innovative method provides a new idea for the realization of small multi-channel atomic magnetometer, and lays a foundation for the development of spatial high-resolution magnetic field detection, portable multi-channel atomic magnetometer and biological magnetic imaging technology.

[0030] As Figure 1As shown, a high spatial resolution arrayed SERF atomic magnetometer based on beam homogenization includes a transimpedance amplifier (1), a lock-in amplifier (2), a signal acquisition and processing module (3), a laser (4), an optical path (5), a transmission cable (6), a polarization beam splitter prism (7), a wavemeter (8), an optical beam expander (9), a mirror (10), a flat-top beam shaper (11), a 1 / 4 wave plate (12), a function source (13), a magnetic shielding barrel (14), a magnetic compensation coil (15), a heating device (16), an alkali metal cell (17), a photodiode array (18), a magnetic source coil (19). Among them, the laser emitted by the laser (4) is divided into two beams after the polarization beam splitter prism (7). One enters the wavemeter (8) for detecting the wavelength of the laser, and the other is shaped into a flat-top light with uniform light intensity distribution through the optical beam expander (9), the mirror (10) and the flat-top beam shaper (11), and the spot size is sufficient to cover the photodiode array (18). The flat-top light is adjusted to circularly polarized light by the 1 / 4 wave plate (12), and is detected and collected by the photodiode array (18) after passing through the alkali metal cell (17). The signal is processed in the signal acquisition and processing module (3) through the transimpedance amplifier (1) and the lock-in amplifier (2).

[0031] The alkali metal cell (17) contains alkali metal atoms (such as potassium, rubidium or cesium atoms), and in addition to the alkali metal atoms, the alkali metal cell (17) also includes buffer gas (such as nitrogen gas, etc.) and quenching gas (such as helium, neon, etc.).

[0032] The alkali metal cell (17) is placed in the heating device (16) with heating film on the side wall, and the cell is heated to the order of 10 13 ~10 14 cm -3 of the number density of alkali metal atoms to ensure that the atoms work in the SERF state, and the heating device (16) is placed in the center of the magnetic compensation coil (15), and the magnetic compensation coil (15) is located inside the magnetic shielding barrel (14) and their centers coincide.

[0033] The central wavelength of the laser emitted by the laser (4) is the D1 line resonance wavelength of the alkali metal atoms in the alkali metal cell (17).

[0034] The photodiode array (18) is arranged by 3 rows and 3 columns of 9 photodiodes, and the outer size of a single photodiode is 3mm×3mm, and the center distance between adjacent photodiodes is 3.25mm, which is greater than the theoretically calculated diffusion distance of alkali metal atoms 0.25mm, so the magnetic field measurement spatial resolution of the nine-channel SERF atomic magnetometer device is 3.25mm.

[0035] The incident light beam (5) becomes a flat top light after passing through the light expander (9) and the flat top beam shaper (11), which is characterized by the uniform distribution of light intensity at different positions of the light spot. The diameter of the flat top light spot is large enough to cover the photodiode array (18). The inner size of the alkali metal cell (17) is matched with the incident flat top light beam and the size of the photodiode array (18).

[0036] The flat top beam shaper (11) is an optical device that can shape the incident light spot with Gaussian distribution of light intensity into a flat top light spot with uniform distribution of light intensity.

[0037] The magnetic compensation coil (15) and the magnetic source coil (19) are driven and controlled by the function source (13). The magnetic compensation coil (15) is used to compensate the three-dimensional residual magnetism in the magnetic shielding barrel (14), and is also used to generate the measured magnetic field and the modulation magnetic field; the magnetic source coil (19) can generate the measured gradient magnetic field, which is used to verify the effectiveness of the constructed nine-channel magnetometer in high-resolution magnetic field measurement.

[0038] Each sensing channel of the arrayed SERF atomic magnetometer adopts the magnetic field measurement principle of the single-beam transverse modulation type SERF atomic magnetometer. The incident light is along the z-axis, and the z-direction light intensity I collected by the photodiode is proportional to the electron polarizability of the alkali metal atom in this direction where k1 is the proportional coefficient. When a modulation magnetic field is applied in the y-axis direction, is the amplitude of the modulation magnetic field, ω mod is the angular frequency of the modulation magnetic field, and t is the time. The first harmonic component of the 9-channel photoelectric signal collected by the photodiode array about ω mod is demodulated by the lock-in amplifier (2), and the z-direction component of the electron polarizability of the alkali metal atom is obtained. y The relationship about the measured magnetic field B x0 is as follows:

[0039]

[0040] where P0 is the size of the electron polarization vector of the alkali metal atom at steady state without external magnetic field, J0(u) is the 0-order first kind Bessel function, J1(u) is the 1-order first kind Bessel function, Γ is the magnetic resonance line width, B y0 is the residual magnetic field in the x-axis direction, B y is the measured magnetic field in the y-axis direction, and B z0 is the residual magnetic field in the z-axis direction. When the three-dimensional residual magnetic field is compensated to zero and the measured magnetic field B y is small, about B y ​Approximately linear. Therefore, the process of measuring the magnetic field of the nine-channel SERF atomic magnetometer can be described as: z-direction light intensity I→z-direction electron polarizability →the size of the magnetic field to be measured B y , that is, the magnetic field information is ultimately obtained from the light intensity information through a series of transformations. The 9-channel photoelectric signals collected by each sensing channel of the nine-channel SERF atomic magnetometer are calculated 9 times in parallel through the above formula, and finally at the same time, the size of the magnetic field to be measured at 9 positions can be obtained once, and the spatial resolution is 3.25mm.

[0041] Figure 2 The magnetic field measurement sensitivity curve of the high spatial resolution array type SERF atomic magnetometer based on beam homogenization is shown, and the results show that the sensitivity performance of the nine sensing channels (first channel to ninth channel) of the nine-channel SERF atomic magnetometer constructed by the application has good consistency, and the average sensitivity of each channel is about 10.6fT / Hz 1 / 2 .

[0042] Figure 3 The solid square marked with a solid line represents the simulated value of the magnetic field generated by the magnetic source coil (19) at the nine sensing channel positions calculated by the Biot-Savart law, and the dashed circle represents the actual measurement value of the gradient magnetic field generated by the magnetic source coil (19) by the high spatial resolution array type SERF atomic magnetometer based on beam homogenization. The results show that the actual measurement value of the gradient magnetic field of the nine-channel SERF atomic magnetometer constructed by the application is in good agreement with the theoretical simulation value, indicating that the high spatial resolution array type SERF atomic magnetometer based on beam homogenization proposed by the application is effective in measuring the gradient magnetic field.

[0043] The contents not described in detail in the specification of the application belong to the prior art known to those skilled in the art. It is pointed out that the above description is helpful for those skilled in the art to understand the application, but does not limit the protection scope of the application. Any equivalent replacement, modification, improvement and / or deletion of the above description without departing from the essential content of the application falls within the protection scope of the application.

Claims

1. A high spatial resolution arrayed SERF atomic magnetometer based on beam homogenization, characterized in that, The alkali metal cell is located in the magnetic compensation coil, a 3*3 photodiode array is arranged on the laser exit side of the alkali metal cell, the laser incident side of the alkali metal cell is connected with a flat-top beam shaper through a 1 / 4 wave plate, the flat-top beam shaper shapes the light spot with Gaussian distribution of incident light intensity into a flat-top light spot with uniform distribution of light intensity, the flat-top light spot covers the photodiode array on the xy plane after sequentially passing through the 1 / 4 wave plate and the alkali metal cell along the z axis, and nine photodiodes in the photodiode array form nine signal channels for receiving the flat-top light spot from nine positions; The outer size of a single photodiode is 3mm*3mm, and the center distance between adjacent photodiodes is 3.25mm, which is greater than the theoretically calculated diffusion distance of alkali metal atoms 0.25mm, and the SERF atomic magnetometer can obtain the magnetic field size at nine positions in one measurement at the same time, and the resolution of the spatial position of the magnetic field measurement is 3.25mm. The following expression is included: where I is the light intensity sensed by the photodiode, k1 is a proportional coefficient, is the z-axis component of the electronic polarizability of the alkali metal atom, P0 is the magnitude of the electronic polarization vector of the alkali metal atom at steady state in the absence of an external magnetic field, J0(u) is the 0th order Bessel function of the first kind, J1(u) is the 1st order Bessel function of the first kind, Γ is the magnetic resonance linewidth, B y is the y-axis magnetic field to be measured, B y0 is the y-axis residual magnetic field, B x0 is the x-axis residual magnetic field, B z0 is the z-axis residual magnetic field; the 9 optical signals are calculated 9 times in parallel by the above formula, and finally the magnetic field to be measured at 9 positions is obtained at the same time.

2. The high spatial resolution arrayed SERF atomic magnetometer based on beam homogenization of claim 1, wherein, The spacing between adjacent signal channels is greater than the diffusion distance of alkali metal atoms, so that different regions in the cell can be independently used as a magnetometer.

3. The high spatial resolution arrayed SERF atomic magnetometer based on beam homogenization of claim 1, wherein, The photodiode array is connected with a transimpedance amplifier through a transmission cable, the transimpedance amplifier is connected with a signal acquisition and processing module through a lock-in amplifier.

4. The high spatial resolution arrayed SERF atomic magnetometer based on beam homogenization of claim 1, wherein, The flat-top beam shaper is sequentially connected with the transmission side of a polarization beam splitter prism through a mirror group and an optical expander, the incident side of the polarization beam splitter prism is connected with a laser, and the reflection side of the polarization beam splitter prism is connected with a wavelength meter.

5. The high spatial resolution arrayed SERF atomic magnetometer based on beam homogenization of claim 1, wherein, The magnetic compensation coil is connected with a function source through a transmission cable.

6. The high spatial resolution arrayed SERF atomic magnetometer based on beam homogenization of claim 1, wherein, A magnetic source coil is arranged between the magnetic compensation coil and the alkali metal cell to evaluate the coincidence between the theoretical simulation value and the actual measured value of the gradient magnetic field.

7. The high spatial resolution arrayed SERF atomic magnetometer based on beam homogenization of claim 1, wherein, A heating device is attached to the outer wall of the alkali metal cell.

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