Coil constant measurement method based on atomic spin magnetometer to detect optical pumping effect

Abstract

The present invention relates to a coil constant measurement method based on the optical pumping effect detected by an atomic spin magnetometer. Conventional atomic spin magnetometer coil constants are externally calibrated using a fluxgate magnetometer before use. However, due to the coupling between the coil and the shield in the atomic spin magnetometer, the coil constant varies with the strength of the coupling, leading to inaccurate magnetic fields generated by the coil and affecting the sensitivity accuracy of the atomic spin magnetometer. The method designed by the present invention utilizes the optical pumping effect, which is difficult to completely suppress in the atomic spin magnetometer, to obtain a compensation magnetic field without the optical pumping effect. This magnetic field is then connected to a signal generator at this point to achieve in-situ calibration of the coil constant.

Description

Technical Field

[0001] The invention relates to a coil constant measurement method based on an atomic spin magnetometer for detecting an optical pumping effect, and belongs to the technical field of atomic spin magnetometers. Background Art

[0002] In the field of magnetic field measurement, magnetic field measurement devices based on atomic spins have achieved ultra-high sensitivity magnetic field measurement at the sub-fT level, which is expected to further help the development of basic scientific research. In addition, miniaturized magnetometers developed based on magnetic field measurement devices have achieved imaging applications of weak magnetic field signals such as cardiac magnetism and brain magnetism, and are expected to be widely used in the medical field.

[0003] Currently, magnetic field measurement systems based on atomic spins primarily consist of magnetic shielding and compensation systems, optical systems, sensitive element systems, and electronic control systems. Depending on the optical system, magnetometers can be categorized into single-beam and dual-beam atomic spin magnetometers. Dual-beam atomic spin magnetometers offer higher sensitivity and broader potential for application. The magnetic compensation system is a crucial subsystem of an atomic spin magnetometer. It consists of a three-axis shim coil that generates the magnetic field and a signal generator that drives the coil. It compensates for the residual magnetic field and provides precise modulation of the magnetic field. To accurately determine the central magnetic field, the proportional coefficient between the coil current and the generated magnetic field is called the coil constant. This constant is typically obtained by calibrating the coil using a fluxgate magnetometer. However, as the magnetometer's operating temperature increases, the central magnetic field value varies with temperature, leading to inaccuracies in the applied magnetic field and affecting the accuracy of magnetic field measurement sensitivity. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the problems that the central magnetic field changes with increasing temperature and the traditional method cannot achieve real-time measurement of the magnetic field. The atomic spin magnetometer is used to detect the pumping effect of the laser and realize in-situ calibration of the coil constant.

[0005] The technical solutions of the present invention are as follows:

[0006] A method for measuring a coil constant based on detecting an optical pumping effect using an atomic spin magnetometer is characterized by comprising the following steps:

[0007] Step 1: starting the atomic spin magnetometer device and measuring the residual magnetic field Br at the atomic spin magnetometer operating temperature;

[0008] Step 2: Adjust the output current of the three-axis signal generator to complete the three-axis magnetic field compensation, and record the output current value of the signal generator at this time;

[0009] Step 3, changing the detection laser power, drawing a curve of the detection optical power and the signal generator current value, and recording the vertical intercept I0 of the curve;

[0010] Step 4: Change the detection laser wavelength, measure the vertical intercept of the curve under different detection light wavelengths, and take the average vertical intercept

[0011] Step 5, residual magnetic field Br and average vertical intercept The quotient is the coil constant k to be measured. That is, the coil constant is measured in situ, and k is the proportional coefficient between the current flowing through the coil and the generated magnetic field.

[0012] The step 1 includes: using a fluxgate magnetometer to measure the residual magnetic field Br at the location of the alkali metal gas chamber.

[0013] The step 2 includes determining the actual compensation magnetic field according to the following formula:

[0014]

[0015] Among them, Byc is the actual compensation magnetic field, Br is the residual magnetic field, γ e is the electron gyromagnetic ratio, Bc is the compensation point in the pumping direction, which is a fixed value when the pumping direction condition remains unchanged, and R tot is the total relaxation rate, which is a fixed value when the pumping direction remains unchanged, L x It is the lateral optical frequency shift, which is related to the wavelength and power of the laser in the detection direction. By changing the detection laser power, the L x Other parameters are not affected.

[0016] The atomic spin magnetometer device in step 1 comprises a pumping laser (1), a first convex lens (2), a second convex lens (3), a first 1 / 2 wave plate (4), a liquid crystal retarder (5), a second 1 / 2 wave plate (6), a first polarization beam splitter (7), a first reflector (8), a first 1 / 4 wave plate (9), a detection laser (10), a third 1 / 2 wave plate (11), a second reflector (12), a second polarization beam splitter (13), a noise attenuator (14), a third convex lens (15), a fourth convex lens (16), a first Glan-Taylor prism (17), a second 1 / 4 wave plate (18), a photoelastic modulator (19), a second Glan-Taylor prism (20), a photodetector (21), a ferrite magnetic shielding barrel (22), a three-axis magnetic compensation coil (23), and a magnetic field detector (24). ), fluxgate magnetometer (24), non-magnetic electric heating oven (25), alkali metal gas chamber (26), permalloy magnetic shielding barrel (27), wave meter (28), first signal generator (29), second signal generator (30), third signal generator (31), inside the permalloy magnetic shielding barrel (27), from outside to inside are: ferrite magnetic shielding barrel (22), three-axis magnetic compensation coil (23), non-magnetic electric heating oven (25), alkali metal gas chamber (26). The ferrite magnetic shielding barrel (22) is used to provide the alkali metal gas chamber (26) with a weak magnetic field environment required for the atomic spin to be in a spin-free state, the three-axis magnetic compensation coil (23) is used to compensate for the residual magnetic field felt by the atoms in the shielding barrel, and the non-magnetic electric heating oven (25) is used to heat the alkali metal gas chamber (26).

[0017] The alkali metal atoms in the alkali metal gas chamber (26) are one of potassium, rubidium and cesium, or a mixture of two of them.

[0018] The atoms in the alkali metal gas chamber (26) need to work in a state without spin exchange relaxation.

[0019] The wavelength of the laser light emitted by the pumping laser (1) is at the center of the D1 line of the alkali metal atom, and the wavelength of the laser light emitted by the detection laser (10) is detuned near the D2 line of the alkali metal atom.

[0020] The residual magnetic field in the direction of the coil to be calibrated needs to be measured at the operating temperature of the atomic magnetometer.

[0021] Adjust the laser power stabilization system Noise Eater to change the optical power of the detection laser before it enters the gas chamber, keep the pump laser power, spot size, and incident angle consistent, adjust the signal generator voltage to compensate for the internal magnetic field, and record the signal generator reading.

[0022] By changing the detection laser wavelength and utilizing the compensation position signal generator's real number to detect the vertical intercept of the optical power curve and the residual magnetic field, the in-situ measurement of the coil constant is achieved.

[0023] The technical effects of the present invention are as follows: Conventional atomic spin magnetometer coil constants are externally calibrated using a fluxgate magnetometer before use. However, due to the coupling between the coil and the shield in the atomic spin magnetometer, the coil constant in this case varies with the strength of the coupling, causing problems such as inaccurate magnetic fields generated by the coil, thus affecting the sensitivity accuracy of the atomic spin magnetometer. The present invention, however, utilizes the optical pumping effect detected in the atomic spin magnetometer, which is difficult to completely suppress, to obtain a compensation magnetic field without the detection optical pumping effect. This magnetic field is then connected to a signal generator at this time to achieve in-situ calibration of the coil constant.

[0024] The advantages of this invention over existing technologies lie in that the coil constant varies with internal conditions such as temperature, leading to inaccuracies in the actual magnetic field generated by the magnetic compensation coil. Conventional coil constant calibration methods are unable to calibrate the internal magnetic field in real time. The method designed in this invention utilizes the pumping effect of the detection light to record the magnetic compensation points corresponding to different detection laser powers, fit these magnetic compensation points to the detection laser power curve, and use the magnetic compensation point corresponding to zero detection laser power as the magnetic compensation point corresponding to the residual magnetic field. Using these magnetic compensation points and the pre-calibrated residual magnetism, the coil constant can be calibrated in situ. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The present invention is a schematic structural diagram of an atomic spin magnetometer device involved in the coil constant measurement method for detecting optical pumping effect based on an atomic spin magnetometer.

[0026] Figure 2 The present invention is a schematic flow chart of a coil constant measurement method for detecting optical pumping effect based on an atomic spin magnetometer. Figure 2 The coil constant measurement method in the invention belongs to in-situ measurement, and the name of the invention is also a coil constant in-situ measurement method based on atomic spin magnetometer detection of optical pumping effect. Figure 2 The method includes the following steps: 1. measuring the residual magnetic field Br at the operating temperature of the atomic spin magnetometer; 2. adjusting the output current of the three-axis signal generator (the three axes are the three axes in the xyz rectangular coordinate system) to complete the three-axis magnetic field compensation, and recording the output current value of the signal generator at this time; 3. changing the detection laser power, drawing a curve of the detection light power and the signal generator current value, and recording the vertical intercept I0 of the curve; 4. changing the detection laser wavelength, measuring the vertical intercept of the curve under different detection light wavelengths, and taking the average vertical intercept Step 5, residual magnetic field Br and average vertical intercept The quotient is the coil constant k to be measured. That is to say, the in-situ measurement of the coil constant is realized.

[0027] The reference numerals are as follows: 1-pumping laser; 2-first convex lens; 3-second convex lens; 4-first 1 / 2 wave plate; 5-liquid crystal retarder; 6-second 1 / 2 wave plate; 7-first polarization beam splitter prism; 8-first reflector; 9-first 1 / 4 wave plate; 10-detection laser; 11-third 1 / 2 wave plate; 12-second reflector; 13-second polarization beam splitter prism; 14-noise attenuator; 15-third convex lens; 16-fourth convex lens; 17-first Glan-Taylor prism Mirror; 18-second 1 / 4 wave plate; 19-photoelastic modulator; 20-second Glan Taylor prism; 21-photodetector; 22-ferrite magnetic shielding barrel; 23-three-axis magnetic compensation coil; 24-fluxgate magnetometer; 25-non-magnetic electric heating oven; 26-alkali metal gas chamber; 27-Permalloy magnetic shielding barrel; 28-wavemeter; 29-first signal generator; 30-second signal generator; 31-third signal generator; 32-first fiber optic coupling head; 33-second fiber optic coupling head. DETAILED DESCRIPTION

[0028] Below is the attached figure ( Figure 1-Figure 2 ) and Examples illustrate the present invention.

[0029] Figure 1 The present invention is a schematic structural diagram of an atomic spin magnetometer device involved in the coil constant measurement method for detecting optical pumping effect based on an atomic spin magnetometer. Figure 2 This is a flow chart of the coil constant measurement method for detecting optical pumping effect based on atomic spin magnetometer according to the present invention. Figures 1 to 2 As shown, the coil constant measurement method based on the atomic spin magnetometer to detect the optical pumping effect includes the following steps: Step 1, starting the atomic spin magnetometer device and measuring the residual magnetic field Br at the atomic spin magnetometer operating temperature; Step 2, adjusting the output current of the three-axis signal generator to complete the three-axis magnetic field compensation, and recording the output current value of the signal generator at this time; Step 3, changing the detection laser power, drawing a curve of the detection light power and the signal generator current value, and recording the vertical intercept I0 of the curve; Step 4, changing the detection laser wavelength, measuring the vertical intercept of the curve under different detection light wavelengths, and taking the average vertical intercept Step 5, residual magnetic field Br and average vertical intercept The quotient is the coil constant k to be measured. That is, the coil constant is measured in situ, and k is the proportional coefficient between the current flowing through the coil and the generated magnetic field.

[0030] The step 1 includes: using a fluxgate magnetometer to measure the residual magnetic field Br at the alkali metal gas chamber. The step 2 includes determining the actual compensation magnetic field according to the following formula:

[0031]

[0032] Among them, Byc is the actual compensation magnetic field, Br is the residual magnetic field, γ e is the electron gyromagnetic ratio, B c is the compensation point in the pumping direction, which is a fixed value when the pumping direction condition remains unchanged. tot is the total relaxation rate, which is a fixed value when the pumping direction remains unchanged, L x It is the lateral optical frequency shift, which is related to the wavelength and power of the laser in the detection direction. By changing the detection laser power, the L x Other parameters are not affected.

[0033] Figure 1 The structure of the device used in the present invention is shown in the figure. As can be seen from the figure, the device of the present invention includes a pumping laser (1), a first convex lens (2), a second convex lens (3), a first 1 / 2 wave plate (4), a liquid crystal retarder (5), a second 1 / 2 wave plate (6), a first polarization beam splitter prism (7), a first reflector (8), a first 1 / 4 wave plate (9), a detection laser (10), a third 1 / 2 wave plate (11), a second reflector (12), a second polarization beam splitter prism (13), a noise attenuator (14), a third convex lens (15), a fourth convex lens (16), a first Glan-Taylor prism (17), a second 1 / 4 wave plate (18), a photoelastic modulator (19), a second Glan-Taylor prism (20), a photodetector (21), a ferrite magnetic shielding barrel (22), and a three-axis magnetic compensation line. The invention relates to a method for manufacturing a magnetic field of the alkali metal gas chamber (26), a magnetic fluxgate magnetometer (24), a non-magnetic electric heating oven (25), an alkali metal gas chamber (26), a permalloy magnetic shielding barrel (27), a wave meter (28), a first signal generator (29), a second signal generator (30), a third signal generator (31), and a magnetic field of the alkali metal gas chamber (26). The magnetic field of the alkali metal gas chamber (26) is provided with a weak magnetic field environment required for the atomic spin to be in a spin-free state. The magnetic field of the alkali metal gas chamber (26) is provided with a three-axis magnetic compensation coil (23). The magnetic field of the alkali metal gas chamber (26) is provided with a three-axis magnetic compensation coil (23). The magnetic field of the alkali metal gas chamber (26) is provided with a three-axis magnetic shielding barrel (22). The magnetic field of the alkali metal gas chamber (26) is provided with a three-axis magnetic compensation coil (23). The magnetic field of the alkali metal gas chamber (26) is provided with a three-axis magnetic shielding barrel ...

[0034] In this device, inside the ferrite layer 22 of the magnetic shielding barrel, from the inside out, are a three-axis magnetic compensation coil 23, a non-magnetic electric heating oven 25, and an alkali metal gas chamber 26. The alkali metal gas chamber 26 is filled with alkali metal atoms (one or a mixture of potassium, rubidium, and cesium) to sense magnetic field changes, as well as a buffer gas, neon, and a quenching gas, helium. The ferrite layer 22 of the magnetic shielding barrel is used to reduce the internal magnetic field noise of the atomic spin magnetometer. The three-axis magnetic compensation coil 23 is driven by three signal generators to compensate for the residual magnetic field inside the shielding barrel. Specifically, the X-axis signal generator 29, the Y-axis signal generator 30, and the Z-axis signal generator 31 provide current to the three-axis magnetic compensation coil. The non-magnetic electric heating oven 25 is used to heat the alkali metal atoms and maintain them in the SERF state.

[0035] The pumping laser 1 emits a laser, and the fiber coupling head 32 is used to monitor the wavelength of the pumping laser. The beam is expanded by the combination of the first convex lens 2 and the second convex lens 3. The pumping laser power is stabilized by the combination of the first 1 / 2 wave plate 4 and the liquid crystal delay device 5. A beam of linearly polarized light with a polarization plane in the horizontal direction is generated by the combination of the second 1 / 2 wave plate 6 and the first polarization beam splitter prism 7. The output laser power can be adjusted by rotating the angle of the fast axis of the second 1 / 2 wave plate 6. The propagation direction of the optical path is changed by the first reflector 8 to ensure that the pumping laser is incident vertically along the Z axis into the alkali metal gas chamber 26. The pumping laser is adjusted to a circularly polarized state through the 1 / 4 wave plate 9 to polarize the alkali metal atoms inside the alkali metal gas chamber 26.

[0036] The detection laser 10 emits a laser, which is passed through the combination of the third 1 / 2 wave plate 11 and the second polarization beam splitter prism 13 to generate a beam of linearly polarized light with a polarization plane in the horizontal direction. The output laser power can be adjusted by rotating the angle of the fast axis of the third 1 / 2 wave plate 11. The output light from the reflection surface of the second polarization beam splitter prism 13 enters the second fiber coupling head 33 and is detected by the wavelength meter 28 to monitor the laser wavelength. The laser power is stabilized by the noise attenuator 14. The beam is expanded by the combination of the third convex lens 15 and the fourth convex lens 16. The linearly polarized light with a higher linear polarization degree is generated by the first Glan-Taylor prism 17 and then enters the alkali metal gas chamber 26. The residual circular polarization component in the detection laser is eliminated by the second 1 / 4 wave plate 18. After being modulated to a high frequency by the photoelastic modulator 19, it is polarized by the second Glan-Taylor prism 20 and then the signal is collected by the photodetector 21.

[0037] Before the pumping and detection system operates normally, the temperature of the non-magnetic electric heating oven 25 is set to the operating temperature of the atomic magnetometer, and the fluxgate magnetometer 24 is used to measure the residual magnetic field value B at the position of the alkali metal gas chamber 26. r .

[0038] After the residual magnetic field measurement is completed, the alkali metal gas chamber 26 is reinstalled, and the pumping and detection systems are ensured to function properly. The temperature of the non-magnetic electric heating oven 25 is set to the operating temperature of the atomic magnetometer. The knob of the noise attenuator 14 is adjusted to change the detection laser power incident on the alkali metal gas chamber 26. At this power, the current output values ​​of the X-axis signal generator 29, Y-axis signal generator 30, and Z-axis signal generator 31 are adjusted to compensate for the residual magnetic field within the ferrite layer 22 of the magnetic shielding barrel, and the signal generator current output values ​​are recorded. A curve is plotted showing the incident laser power and the signal generator current output value. The vertical intercept, I0, corresponds to the current value corresponding to the residual magnetic field compensation alone, without the detection optical pumping effect.

[0039]

[0040] Among them, B yc To actually compensate the magnetic field, B r is the residual magnetic field, γ e is the electron gyromagnetic ratio, B c is the compensation point in the pumping direction, which is a fixed value when the pumping direction condition remains unchanged. tot is the total relaxation rate, which is a fixed value when the pumping direction remains unchanged, L x It is the lateral optical frequency shift, which is related to the wavelength and power of the laser in the detection direction. By changing the detection laser power, the L x The other parameters are not affected

[0041] Adjust the temperature of the detection laser and repeat the above experiment at different detection laser wavelengths. The curves of incident laser power and signal generator current output value at different detection light wavelengths intersect at the same point on the vertical axis. The average of the vertical intercepts measured at different detection light wavelengths is recorded as Under this condition, the coil constant k is:

[0042]

[0043] This method can realize in-situ measurement of coil constants and avoid the influence of coil constant fluctuations caused by coupling.

[0044] The alkali metal atoms in the alkali metal gas chamber are one or a mixture of potassium, rubidium and cesium.

[0045] The atoms in the alkali metal gas chamber need to work in a state without spin exchange relaxation.

[0046] Among them, the residual magnetic field in the direction of the coil to be calibrated needs to be measured in advance at the working temperature of the atomic magnetometer.

[0047] The coil constant to be calibrated refers to the proportional coefficient between the current flowing through the coil and the generated magnetic field.

[0048] The noise eater is adjusted to change the optical power of the detection laser before it enters the gas chamber, keeping the pump laser power, spot size, and incident angle consistent. The signal generator voltage is adjusted to compensate for the internal magnetic field, and the signal generator reading is recorded.

[0049] The detection laser wavelength is changed, the above steps are repeated, and the in-situ measurement of the coil constant is achieved by using the real number of the compensation position signal generator and the vertical intercept of the detection light power curve and the residual magnetic field.

[0050] Any content not described in detail in this specification is prior art known to those skilled in the art. It should be noted that the above description is intended to help those skilled in the art understand the present invention, but does not limit the scope of protection of the present invention. Any equivalent substitution, modification, improvement, and / or simplification of the above description that does not depart from the essence of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A coil constant measurement method based on an atomic spin magnetometer to detect optical pumping effect, characterized in that: The following steps are involved: Step 1: Start the atomic spin magnetometer device and measure the residual magnetic field B at the atomic spin magnetometer operating temperature. r ; Step 2: Adjust the output current of the three-axis signal generator to complete the three-axis magnetic field compensation, and record the output current value of the signal generator at this time; Step 3, changing the detection laser power, drawing a curve of the detection laser power and the output current value of the signal generator, and recording the vertical intercept I0 of the curve; Step 4: Change the detection laser wavelength, measure the vertical intercept of the curve under different detection laser wavelengths, and take the average vertical intercept ; Step 5, residual magnetic field B r and the mean vertical intercept The quotient is the coil constant k to be measured. , that is, to realize the in-situ measurement of the coil constant.

2. The coil constant measurement method based on atomic spin magnetometer detection of optical pumping effect according to claim 1, characterized in that: The step 1 includes: using a fluxgate magnetometer to measure the residual magnetic field B at the alkali metal gas chamber position. r .

3. The coil constant measurement method based on atomic spin magnetometer detection of optical pumping effect according to claim 1, characterized in that: The step 2 includes determining the actual compensation magnetic field according to the following formula: , Among them, B yc To actually compensate the magnetic field, B r is the residual magnetic field, is the electron gyromagnetic ratio, B c is the compensation point in the pumping direction, which is a fixed value when the pumping direction condition remains unchanged. tot is the total relaxation rate, which is a fixed value when the pumping direction remains unchanged, L x It is the lateral optical frequency shift, which is related to the wavelength and power of the laser in the detection direction. By changing the detection laser power, the L x Other parameters are not affected.

4. The coil constant measurement method based on atomic spin magnetometer detection of optical pumping effect according to claim 1, characterized in that: The atomic spin magnetometer device in step 1 includes a pumping laser (1), a first convex lens (2), a second convex lens (3), a first 1 / 2 wave plate (4), a liquid crystal retarder (5), a second 1 / 2 wave plate (6), a first polarization beam splitter (7), a first reflector (8), a first 1 / 4 wave plate (9), a detection laser (10), a third 1 / 2 wave plate (11), a first polarization beam splitter (12), a first reflector (13), a first polarization beam splitter (14), a first polarization beam splitter (15), a first polarization beam splitter (16), a first polarization beam splitter (17), a first polarization beam splitter (18), a first polarization beam splitter (19), a first polarization beam splitter (20), a first polarization beam splitter (21), a first polarization beam splitter (22), a first polarization beam splitter (23), a first polarization beam splitter (24), a Wave plate (11), second reflector (12), second polarization beam splitter prism (13), noise attenuator (14), third convex lens (15), fourth convex lens (16), first Glan Taylor prism (17), second quarter wave plate (18), photoelastic modulator (19), second Glan Taylor prism (20), photodetector (21), ferrite magnetic shielding barrel (22), three-axis magnetic compensation coil (23), fluxgate magnetometer (24), non-magnetic electric heating oven (25), alkali metal gas chamber (26), Permalloy magnetic shielding barrel (27), wave meter (28), X-axis signal generator (29), Y-axis signal generator (30), Z-axis signal generator (31), inside the Permalloy magnetic shielding barrel (27), from outside to inside are: A ferrite magnetic shielding barrel (22), a three-axis magnetic compensation coil (23), a non-magnetic electric heating oven (25), and an alkali metal gas chamber (26); the ferrite magnetic shielding barrel (22) is used to provide the alkali metal gas chamber (26) with a weak magnetic field environment required for the atomic spin to be in a spin-free exchange state; the three-axis magnetic compensation coil (23) is used to compensate for the residual magnetic field felt by the atoms in the shielding barrel; and the non-magnetic electric heating oven (25) is used to heat the alkali metal gas chamber (26).

5. The coil constant measurement method based on atomic spin magnetometer detection of optical pumping effect according to claim 4, characterized in that: The alkali metal atoms in the alkali metal gas chamber (26) are one of potassium, rubidium, and cesium, or a mixture of two of them.

6. The coil constant measurement method based on atomic spin magnetometer detection of optical pumping effect according to claim 4, characterized in that: The atoms in the alkali metal gas chamber (26) need to work in a state without spin exchange relaxation.

7. The coil constant measurement method based on atomic spin magnetometer detection of optical pumping effect according to claim 4, characterized in that: The wavelength of the laser light emitted by the pumping laser (1) is at the center of the D1 line of the alkali metal atom, and the wavelength of the laser light emitted by the detection laser (10) is detuned near the D2 line of the alkali metal atom.

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