Wide spectrum hybrid pumping method based on SERF magnetic field measurement device

Abstract

Based on the wide spectrum hybrid pumping method of SERF magnetic field measurement device, a laser with a spectral line width of the same magnitude as the pressure broadening of the gas chamber is used as the pumping light to polarize the mixed alkali metal atomic ensemble. The wide spectrum light source is realized by external phase modulation of the narrow line width seed light through an electro-optical phase modulator. The voltage modulation signal is driven by a pseudo-random bit sequence, and the spectral line width of the output laser is adjusted by the bit rate of the pseudo-random bit sequence. Compared with the SERF magnetic field measurement device that uses a narrow line width laser to pump a single alkali metal atom, the use of an adjustable wide spectrum laser to pump a mixed alkali metal atom source not only has the advantage of suppressing optical frequency shift noise, but also further improves the uniformity of electronic polarization, improves the stability of the SERF magnetic field measurement device, and enhances the differential performance of the device, which is beneficial to improve the gradient differential sensitivity of the SERF magnetic field measurement device.

Description

Technical Field

[0001] The invention relates to the technical field of SERF atomic magnetic field measurement, and in particular to a wide spectrum hybrid pumping method based on a SERF magnetic field measurement device. Background Art

[0002] Ultra-high-sensitivity magnetic field measurement based on the spin exchange relaxation free regime (SERF) effect of atomic spins has benefited from the development of quantum technology and currently has the highest magnetic field measurement sensitivity in the world. The temperature of the gas chamber of the SERF magnetic field measurement device is generally 160-200°C. At this time, the density of alkali metal atoms in the gas chamber is relatively large. The large optical depth will cause the atoms to absorb light, resulting in the attenuation of the pumping light, making the spatial distribution of the electronic polarization of the alkali metal atoms uneven. In addition, due to the fluctuation of the pumping light frequency, it will cause large optical frequency shift noise, reducing the sensitivity of the magnetic field measurement. Therefore, a high-performance optical pumping method based on the SERF magnetic field measurement device is needed.

[0003] In order to solve the problem of uneven electron polarization, the researchers proposed a mixed pumping scheme, namely potassium K-rubidium Rb mixed pumping. When a larger potassium-rubidium density ratio of more than 1:100 is selected, the spatial uniformity of electron polarization is greatly improved. However, due to the optical frequency shift of mixed pumping, a larger density ratio will cause the optical frequency shift to increase sharply. When a smaller density ratio is selected, such as less than 1:10, the optical frequency shift of mixed pumping can be canceled to an order of magnitude less than 10 -12 T (Tesla), but the uniformity of electron polarization cannot be met at this time. The present invention adopts a smaller density ratio to achieve a frequency shift cancellation of the mixed pump light of an order of magnitude less than 10 -12 T (Tesla), and using a wide-spectrum laser to pump the mixed atomic ensemble at the same time, on the one hand, can reduce the attenuation rate of the laser in the gas chamber, improve the uniformity of electronic polarization, and make up for the disadvantage of a smaller density ratio; on the other hand, since the center frequency of the wide-spectrum laser is located on the resonance peak of the alkali metal atom, and the frequency is symmetrical about the center of the resonance peak of the alkali metal atom, it can reduce the optical frequency shift noise caused by the laser frequency fluctuation, thereby enhancing the stability of the magnetic field measurement device and improving the gradient differential sensitivity of the SERF magnetic field measurement device. Summary of the invention

[0004] The present invention aims to provide a wide spectrum hybrid pumping method based on a SERF magnetic field measurement device, which uses a low density ratio mixed alkali metal atomic source gas chamber to achieve an optical frequency shift cancellation of less than 10 -12T (Tesla), and then use an electro-optic phase modulator to broaden the line width of the narrow linewidth seed spectrum to a wide-spectrum laser of the order of the gas chamber pressure broadening as the pumping light to polarize the alkali metal atoms, and set the center frequency of the wide-spectrum laser to the resonance peak of the alkali metal atoms with lower density in the mixed alkali metal atom source gas chamber, which can effectively reduce the atomic electronic polarization rate gradient and suppress the optical frequency shift noise.

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

[0006] A wide spectrum hybrid pumping method based on a SERF magnetic field measurement device is characterized by comprising the following steps:

[0007] Step 1, setting the density ratio of potassium atoms to rubidium atoms in the mixed alkali metal atom source gas chamber in the SERF magnetic field measurement device to K:Rb=1:4-6;

[0008] Step 2, construct and adjust the pumping optical path and the detection optical path in the SERF magnetic field measurement device, the pumping light on the pumping optical path is a wide-spectrum pumping laser generated by an external cavity phase modulation narrow linewidth seed light generated by a voltage with adjustable amplitude and bit rate generated by a pseudo-random bit sequence waveform generator and applied to an electro-optical phase modulator, the temperature of the mixed alkali metal atomic source gas chamber is 160-200° C., the three-axis magnetic compensation coil is adjusted, and the three-dimensional in-situ magnetic compensation technology is used to compensate for the system residual magnetism, so that the device works in the SERF state;

[0009] Step 3, turn on the pseudo-random bit sequence waveform generator, set the modulation frequency, use the function generator to add a calibration magnetic field to the sensitive axis Y, adjust the pumping light power, so that the lock-in amplifier outputs the largest frequency component, that is, the magnetic field response signal is the strongest, and record the Y-axis residual magnetism and the frequency signal strength at this time;

[0010] Step 4, measuring the optical frequency shift noise caused by the pump light frequency fluctuation and the uniformity of the electron steady-state polarizability;

[0011] Step 5, judging whether the optical frequency shift noise and the electronic polarization uniformity meet the requirements, if not, returning to step 3, if yes, proceeding to step 6;

[0012] Step 6, enter the subsequent magnetic field measurement.

[0013] In step 2, the three-dimensional in-situ magnetic compensation technology is used to compensate for the residual magnetism of the system, including cross-compensation of the magnetic field in the X-axis direction and the magnetic field in the Z-axis direction, and finally compensation of the magnetic field in the Y-axis direction.

[0014] In step 2, the spectral line width of the wide-spectrum pumping laser is adjusted by controlling the driving voltage applied to the electro-optical phase modulator to broaden the spectral line width of the narrow-linewidth laser to the order of mixed atomic ensemble pressure broadening, and the driving voltage is regulated by a pseudo-random bit sequence with adjustable amplitude and bit rate with a bit sequence of "0" and "1" values ​​randomly selected with a probability of 50%.

[0015] Step 4 includes changing the pumping light frequency to detune by 10 MHz to 1000 MHz and measuring the corresponding optical frequency shift noise.

[0016] Step 5 includes determining whether the optical frequency shift noise is less than 10 -15 T / MHz, whether the uniformity of electronic polarization is greater than 80%.

[0017] The narrow linewidth seed light comes from a narrow linewidth seed light laser, the narrow linewidth seed light laser is connected to a tapered amplifier through an electro-optical phase modulator, the electro-optical phase modulator is connected to a pseudo-random bit sequence waveform generator through a radio frequency amplifier, and the tapered amplifier is connected to a mixed alkali metal atom source gas chamber through a concave lens, a first convex lens, a reflector, a first 1 / 2 wave plate, a first polarization beam splitter prism and a first 1 / 4 wave plate in sequence, so that a wide spectrum pumping laser passing through the mixed alkali metal atom source gas chamber along a Z axis polarizes low-density potassium atoms, and the potassium atoms collide with high-density rubidium atoms to polarize the rubidium atoms.

[0018] The detection light on the detection light path comes from a detection laser, and the detection laser is connected to a phase-locked amplifier in sequence through a second 1 / 2 wave plate, a second polarization beam splitter, a polarizer, a photoelastic modulator, a second 1 / 4 wave plate, a mixed alkali metal atom source gas chamber, an analyzer, a second convex lens and a photodetector. The phase-locked amplifier is respectively connected to a modulation controller and a host computer, the host computer is connected to a function generator, the modulation controller is connected to the photoelastic modulator, and the function generator is connected to a three-axis magnetic compensation coil.

[0019] The mixed alkali metal atom source gas chamber is located in a non-magnetic electric heating system, the non-magnetic electric heating system is located in a three-axis magnetic compensation coil, and the three-axis magnetic compensation coil is located in a magnetic shielding barrel.

[0020] The technical effects of the present invention are as follows: The present invention is based on a wide spectrum hybrid pumping method of a SERF magnetic field measuring device, and uses a laser with a spectral line width of the same order of magnitude as the chamber pressure broadening as the pumping light to polarize the mixed alkali metal atomic ensemble. The wide spectrum light source is realized by external phase modulation of a narrow line width seed light by an electro-optical phase modulator. The voltage modulation signal is driven by a pseudo-random bit sequence, and the spectral line width of the output laser is adjusted by the bit rate of the pseudo-random bit sequence. Compared with the SERF magnetic field measuring device that uses a narrow line width laser to pump a single alkali metal atom, the use of an adjustable wide spectrum laser to pump a mixed alkali metal atomic source is a wide spectrum hybrid pumping method, which not only has the advantage of suppressing optical frequency shift noise, but also further improves the uniformity of electronic polarization, improves the stability of the SERF magnetic field measuring device, and enhances the differential performance of the device, which is beneficial to improving the gradient differential sensitivity of the SERF magnetic field measuring device.

[0021] The advantages of the present invention over the prior art are: (1) by adjusting the density ratio of the mixed alkali metal atom source gas chamber, the optical frequency shift can be canceled to an order of magnitude less than 10 -12 T (Tesla); (2) Using a mixed alkali metal atomic source gas chamber to pump low-density alkali metal atoms can reduce the attenuation of laser light intensity along the pumping direction caused by the absorption of alkali metal atoms and improve the uniformity of electron polarization; (3) Using a wide-spectrum laser can further significantly reduce the attenuation of pumping light and greatly improve the uniformity of electron polarization; (4) The spectrum of the narrow-linewidth laser after being broadened by the electro-optic phase modulator is symmetrically distributed. By setting the center frequency at the resonance absorption peak of low-density alkali metal atoms, the optical frequency shift noise caused by frequency fluctuations can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of a SERF magnetic field measuring device involved in implementing the wide spectrum hybrid pumping method based on a SERF magnetic field measuring device of the present invention.

[0023] Figure 2 It is a schematic flow chart of implementing the wide spectrum hybrid pumping method based on the SERF magnetic field measurement device of the present invention.

[0024] Figure 3 It is a schematic diagram of the distribution curve of the steady-state electronic polarizability P0 of alkali metal atoms in the alkali metal gas cell along the direction of the pumping light.

[0025] Figure 4 This is a schematic diagram of the size of the optical frequency shift noise caused by the pumping light frequency fluctuation.

[0026] The accompanying drawings are marked as follows: 1-pseudo-random bit sequence waveform generator; 2-RF amplifier; 3-narrow linewidth seed light laser; 4-electro-optic phase modulator; 5-tapered amplifier; 6-concave lens; 7-first convex lens; 8-reflector; 9-first 1 / 2 wave plate; 10-first polarization beam splitter prism; 11-first 1 / 4 wave plate; 12-magnetic shielding barrel; 13-three-axis magnetic compensation coil; 14-non-magnetic electric heating system; 15-mixed alkali metal atom source gas chamber; 16-detection laser; 17-second 1 / 2 wave plate; 18-second polarization beam splitter prism; 19-polarizer; 20-photoelastic modulator; 21-second 1 / 4 wave plate; 22-polarizer; 23-second convex lens; 24-photodetector; 25-modulation controller; 26-phase-locked amplifier; 27-function generator; 28-host computer; XYZ-Cartesian coordinate system (X axis, Y axis, Z axis). DETAILED DESCRIPTION

[0027] Below is the attached figure ( Figure 1-Figure 4 ) and examples illustrate the present invention.

[0028] Figure 1 The structure diagram of the SERF magnetic field measuring device involved in the wide spectrum hybrid pumping method based on the SERF magnetic field measuring device of the present invention is shown in FIG. SERF is a spin exchange relaxation free regime. Figure 2 It is a schematic flow chart of implementing the wide spectrum hybrid pumping method based on the SERF magnetic field measurement device of the present invention. Figure 2 The method includes step 1, density ratio of potassium atoms and rubidium atoms; step 2, building a SERF magnetic field measurement device and making the device work normally; step 3, setting the modulation frequency and optimizing the parameters to achieve the best device performance; step 4, measuring the optical frequency shift noise and electronic polarization uniformity; step 5, judging whether the optical frequency shift noise and electronic polarization uniformity meet the requirements, if not, returning to step 3, if yes, entering step 6; step 6, the optimization is completed and subsequent measurements can be performed. Figure 3 It is a schematic diagram of the distribution curve of the steady-state electronic polarizability P0 of alkali metal atoms in the alkali metal gas cell along the direction of the pumping light. Figure 3 The solid line in the middle indicates narrow line width potassium atomic pumping, the dotted line indicates narrow line width potassium-rubidium (density ratio K: Rb = 1:4-1:6) mixed pumping, and the dashed line indicates wide line width potassium-rubidium (density ratio K: Rb = 1:4-1:6) mixed pumping. These three lines show that the use of mixed pumping can reduce the electronic polarization gradient. On the basis of mixed pumping, the use of wide line width laser pumping can further significantly reduce the electronic polarization gradient, and the effect is particularly obvious within ±2.5mm (detection spot size) in the center of the gas chamber. Figure 3 The vertical axis is the steady-state electronic polarizability P0, and the horizontal axis is the distance from the gas cell surface / mm. Figure 3 The vertical axis scale values ​​are 0, 0.1, 0.2,..., 1. Figure 3 The horizontal axis scale values ​​are 0, 5, 10,..., 25. Figure 4 This is a schematic diagram of the size of the optical frequency shift noise caused by the pumping light frequency fluctuation. Figure 4 The solid line in the middle represents narrow-linewidth potassium atom pumping, the dotted line represents narrow-linewidth potassium-rubidium (density ratio K: Rb = 1:4-1:6) mixed pumping, and the dashed line represents wide-linewidth potassium-rubidium (density ratio K: Rb = 1:4-1:6) mixed pumping. These three lines show that when mixed pumping is used, the optical frequency shift noise caused by the pumping light frequency fluctuation is two orders of magnitude larger than when a single alkali metal gas cell is used. When wide-linewidth laser pumping is used on the basis of mixed pumping, the optical frequency shift noise can be greatly reduced, and it is more than one order of magnitude lower than narrow-linewidth potassium atom pumping, and it is particularly obvious when the frequency fluctuation is large. Figure 4 The horizontal axis is frequency fluctuation / MHz, and the vertical axis is the optical frequency shift fluctuation size / nT. Figure 4 The horizontal axis scale values ​​are 0, 100, 200,..., 1000. Figure 4 The vertical scale values ​​are 0, 0.05, 0.1, ···, 0.4. Figures 1 to 4 As shown, a wide spectrum hybrid pumping method based on a SERF magnetic field measuring device comprises the following steps: step 1, setting a potassium atom to rubidium atom density ratio of K:Rb=1:4-6 for a mixed alkali metal atom source gas chamber in the SERF magnetic field measuring device; step 2, constructing and adjusting a pumping optical path and a detection optical path in the SERF magnetic field measuring device, wherein the pumping light on the pumping optical path is a wide spectrum pumping laser generated by applying a voltage with adjustable amplitude and bit rate generated by a pseudo-random bit sequence waveform generator to an electro-optical phase modulator for external cavity phase modulation and narrow linewidth seed light, the temperature of the mixed alkali metal atom source gas chamber is 160-200°C, the three-axis magnetic compensation coil is adjusted, and a three-axis magnetic compensation coil is used. The in-situ magnetic compensation technology is used to compensate the residual magnetism of the system, so that the device works in the SERF state; Step 3, turn on the pseudo-random bit sequence waveform generator, set the modulation frequency, use the function generator to add a calibration magnetic field to the sensitive axis Y, adjust the pumping light power, so that the phase-locked amplifier outputs the largest frequency component, that is, the magnetic field response signal is the strongest, and record the Y-axis residual magnetism and the frequency signal strength at this time; Step 4, measure the optical frequency shift noise caused by the pumping light frequency fluctuation and the uniformity of the electronic steady-state polarization rate; Step 5, determine whether the optical frequency shift noise and the electronic polarization uniformity meet the requirements, if not, return to step 3, if yes, enter step 6; Step 6, enter the subsequent magnetic field measurement.

[0029] In step 2, three-dimensional in-situ magnetic compensation technology is used to compensate for the residual magnetism of the system, including cross-compensation of the magnetic field in the X-axis direction and the magnetic field in the Z-axis direction, and finally compensation of the magnetic field in the Y-axis direction. In step 2, the spectral line width of the wide-spectrum pumping laser is adjusted by controlling the driving voltage applied to the electro-optical phase modulator to broaden the narrow-linewidth laser spectral line width to the mixed atomic ensemble pressure broadening level, and the driving voltage is regulated by a pseudo-random bit sequence with adjustable amplitude and bit rate and a bit sequence of "0" and "1" values ​​randomly selected with a probability of 50%. Step 4 includes measuring the corresponding optical frequency shift noise by changing the pumping light frequency detuning by 10MHz to 1000MHz. Step 5 includes determining whether the optical frequency shift noise is less than 10 -15 T / MHz, whether the uniformity of electronic polarization is greater than 80%.

[0030] The narrow linewidth seed light comes from a narrow linewidth seed light laser 3, the narrow linewidth seed light laser 3 is connected to a tapered amplifier 5 through an electro-optical phase modulator 4, the electro-optical phase modulator 4 is connected to a pseudo-random bit sequence waveform generator 1 through a radio frequency amplifier 2, and the tapered amplifier 5 is connected to a mixed alkali metal atom source gas chamber 15 through a concave lens 6, a first convex lens 7, a reflector 8, a first 1 / 2 wave plate 9, a first polarization beam splitter prism 10 and a first 1 / 4 wave plate 11 in sequence, so that the wide spectrum pumping laser passing through the mixed alkali metal atom source gas chamber 15 along the Z axis polarizes low-density potassium atoms, and the potassium atoms collide with high-density rubidium atoms to polarize the rubidium atoms.

[0031] The detection light on the detection optical path comes from the detection laser 16, and the detection laser 16 is connected to the phase-locked amplifier 26 through the second 1 / 2 wave plate 17, the second polarization beam splitter prism 18, the polarizer 19, the photoelastic modulator 20, the second 1 / 4 wave plate 21, the mixed alkali metal atom source gas chamber 15, the analyzer 22, the second convex lens 23 and the photodetector 24 in sequence. The phase-locked amplifier 26 is respectively connected to the modulation controller 25 and the host computer 28, the host computer 28 is connected to the function generator 27, the modulation controller 25 is connected to the photoelastic modulator 20, and the function generator 27 is connected to the three-axis magnetic compensation coil 13. The mixed alkali metal atom source gas chamber 15 is located in the non-magnetic electric heating system 14, the non-magnetic electric heating system 14 is located in the three-axis magnetic compensation coil 13, and the three-axis magnetic compensation coil 13 is located in the magnetic shielding barrel 12.

[0032] The present invention proposes to improve the uniformity of electronic polarization of SERF magnetic field measurement device and suppress optical frequency shift based on the method of wide-spectrum laser pumping mixed atomic ensemble, select a suitable alkali metal atom source density ratio gas chamber according to the mixed pumping optical frequency shift cancellation theory, and use a laser with a spectral line width of the same magnitude as the gas chamber pressure broadening as the pumping light to polarize the mixed atomic ensemble. The spectral line width of the light source is controlled by applying voltage to the electro-optical phase modulator, so that the narrow line width seed light passing through the modulator is externally phase modulated to achieve laser spectral line broadening. The modulation signal uses a pseudo-random bit sequence, and the spectral line width of the output laser is controlled by adjusting the bit rate of the sequence, and lasers with different spectral line widths are suitable for mixed alkali metal atom source gas chambers with different density ratios. After setting the density ratio, the spectral line width of the laser is adjusted to obtain the best effect. Compared with the SERF magnetic field measurement device that uses a narrow linewidth laser to pump a single alkali metal atom, the use of a wide linewidth laser to pump a mixed alkali metal atom ensemble not only suppresses the optical frequency shift noise, but also further improves the uniformity of electronic polarization, thereby making the SERF magnetic field measurement device have better stability, which is beneficial to improving the gradient differential sensitivity of the SERF magnetic field measurement device.

[0033] refer to Figures 1 to 4 , a wide spectrum hybrid pumping device and method based on SERF magnetic field measurement, comprising a laser 3 for generating narrow line width seed light, an electro-optical phase modulator 4 for modulating the narrow line width seed light into a wide spectrum, a pseudo-random bit sequence waveform generator 1 with adjustable amplitude and bit rate applied to the electro-optical phase modulator 4, a mixed alkali metal atom source gas chamber 15, and a detection optical system and an active and passive magnetic field control system. The light generated by the narrow line width seed light laser 3 passes through the electro-optical phase modulator 4 and then outputs a wide spectrum adjustable laser as a pumping laser to polarize the atomic ensemble in the mixed alkali metal atom source gas chamber 15. The spectral line width of the wide spectrum laser is adjusted by controlling the driving voltage applied to the electro-optical phase modulator 4 to broaden the spectral line width of the narrow line width laser to the pressure broadening level of the mixed atomic ensemble. The driving voltage is regulated by the pseudo-random bit sequence waveform generator 1 with adjustable amplitude and bit rate according to the bit sequence of "0" and "1" values ​​randomly selected with a probability of 50%. The mixed alkali metal atom source gas chamber 15 contains two alkali metal atoms, potassium and rubidium. The wide-spectrum pumping laser polarizes low-density potassium atoms. The potassium atoms collide with high-density rubidium atoms to polarize the rubidium atoms. The detection system detects the optical rotation angle of the dichroism of the rubidium atoms to obtain the size of the magnetic field to be measured. The central frequency of the wide-spectrum laser is the same as the resonance peak frequency of the D1 line of the potassium atoms.

[0034] The pseudo-random bit sequence waveform generator 1 is input to the electrical port of the electro-optic phase modulator 4 after passing through the radio frequency amplifier 2 to exert a driving effect; the laser output by the narrow linewidth seed light laser 3 passes through the optical port of the electro-optic phase modulator 4, the tapered amplifier 5, the concave lens 6, the first convex lens 7, the reflector 8, the first 1 / 2 wave plate 9, the first polarization beam splitter prism 10, and the first 1 / 4 wave plate 11 in sequence, and then is incident on the mixed alkali metal atomic source gas chamber 15 as a wide-spectrum pumping light to polarize potassium atoms, and the potassium atoms collide with rubidium atoms to polarize the rubidium atoms. The detection laser 16 of the detection optical system outputs the detection light, which passes through the second 1 / 2 wave plate 17, the second polarization beam splitter prism 18, the polarizer 19, the photoelastic modulator 20, the second 1 / 4 wave plate 21, the mixed alkali metal atom source gas chamber 15, the analyzer 22, and the second convex lens 23 in sequence, and then enters the photodetector 24 to convert the optical signal into an electrical signal, which is then transmitted to the phase-locked amplifier 26 through a coaxial cable. The phase-locked amplifier 26 is respectively connected to the modulation controller 25 and the host computer 28, and the modulation controller 25 is connected to the photoelastic modulator 20. The magnetic field measurement device is sequentially provided with a non-magnetic electric heating system 14, a three-axis magnetic compensation coil 13, and a magnetic shielding barrel 12 from the center of the gas chamber 15 to the outside. The photoelastic modulator 20 is driven by the modulation controller 25. The electrical signal and the reference signal of the modulation controller 25 are demodulated by the phase-locked amplifier 26 to obtain the DC component, the first harmonic component, and the second harmonic component of the detection electrical signal, and are fed back to the host computer 28 for real-time display.

[0035] The mixed alkali metal atom source gas chamber 15 contains potassium atoms and rubidium atoms, and the density of potassium atoms is lower than that of rubidium atoms. It is filled with helium to slow down atomic diffusion and nitrogen as a quenching gas, wherein the nitrogen pressure is about 2.5 atm and the helium pressure is about 50 Torr.

[0036] A wide spectrum hybrid pumping method based on a SERF magnetic field measuring device, using the wide spectrum hybrid pumping device based on a SERF magnetic field measuring device, comprises the following steps:

[0037] Step (1), according to the mixed pump light frequency shift calculation formula, the mixed pump light frequency shift magnitude is obtained to be less than 10 -12 T (Tesla) of the mixed alkali metal atomic source potassium atoms and rubidium atoms density ratio and fill the gas chamber;

[0038] Step (2), construct and adjust the optical path, set the temperature of the mixed alkali metal atom source gas chamber to 160-200°C, adjust the three-axis magnetic compensation coil, and use the three-dimensional in-situ magnetic compensation technology to compensate for the system residual magnetism (cross-compensate the magnetic fields in the X and Z directions, and finally compensate the magnetic field in the Y direction), so that the device works in the SERF state;

[0039] Step (3), turn on the pseudo-random bit sequence waveform generator, set the modulation frequency, use the function generator to add a calibration magnetic field to the sensitive axis Y, adjust the pumping light power, so that the phase-locked amplifier outputs the largest frequency component, that is, the magnetic field response signal is the strongest, and record the Y-axis residual magnetism and the frequency signal strength at this time;

[0040] Step (4), measuring the optical frequency shift noise caused by the optical frequency shift and the pump light frequency fluctuation and the uniformity of the electron steady-state polarizability;

[0041] Step (5), determine whether the optical frequency shift noise is less than 10 -15 T / MHz, whether the uniformity of the electronic polarization rate is greater than 80%, if so, go to step (7), if not, change the bit rate of the pseudo-random bit sequence, go to step (6);

[0042] Step (6), repeating steps (3) to (5) until the optical frequency shift, optical frequency shift noise and electronic polarization uniformity meet the requirements;

[0043] Step (7), at this time, the pseudo-random bit sequence drives the electro-optic phase modulator to modulate the narrow linewidth seed light to generate a wide spectrum laser, which is the most suitable pumping light for this device and can be used for subsequent measurements.

[0044] Preferably, in step (4), when measuring the optical frequency shift noise caused by the pump light frequency fluctuation in a short period of time, the pump light frequency is detuned by 10 MHz to 1000 MHz, and the corresponding optical frequency shift noise is measured.

[0045] The principle of the wide spectrum hybrid pumping method based on the SERF magnetic field measurement device of the present invention is as follows:

[0046] The mixed alkali metal atom source gas chamber contains two alkali metal atoms, potassium and rubidium, and the density of potassium atoms is lower than that of rubidium atoms. The pumped light interacts with potassium atoms to achieve the polarization of potassium atoms, and the potassium atoms and rubidium atoms undergo spin exchange collisions, thereby achieving the polarization of rubidium atoms.

[0047] For the wide-spectrum pump laser, its propagation direction is the z direction, and the first intersection point between the pump light and the mixed alkali metal atom source gas chamber is the z-axis zero point. Then the initial light intensity of each frequency component in the wide-spectrum laser is The distribution is shown below:

[0048] (1)

[0049] in, is the total incident light intensity on the cell surface (z=0), is the phase modulation amplitude of the pseudo-random bit sequence, is the i-th frequency contained in the broad spectrum laser, is the laser center frequency, T is the pseudo-random bit sequence bit rate, is the Symgine function.

[0050] When the broad-spectrum circularly polarized light passes through the mixed alkali metal atom source gas chamber, the i-th frequency of the broad-spectrum laser Pumping rate The change in z along the propagation direction follows the following formula:

[0051]

[0052] in, is the differential of the pumping rate, is the differential of the propagation distance, is the density of potassium atoms in the mixed alkali metal atom source gas chamber, is the ith frequency in the broadband laser The absorption cross-sectional area, is the steady-state polarizability of potassium atoms, and ,

[0053] is the spin destruction relaxation rate of the rubidium atom, is the relaxation of the rubidium atom caused by the spin exchange between potassium and rubidium atoms, To integrate the frequency of the light at each pump light propagation point, is the relaxation of potassium atom caused by spin exchange between rubidium atom and potassium atom, is the spin destruction relaxation rate of potassium atoms.

[0054] When no external magnetic field is applied, the steady-state polarizability of the rubidium atomic spin under the influence of pump light and relaxation effect It can be expressed as:

[0055]

[0056] Depend on Figure 3 It can be seen that the use of hybrid pumping can reduce the polarization gradient. On the basis of hybrid pumping, broadening the pumping laser can further significantly reduce the polarization gradient. The effect is particularly obvious within ±2.5mm (detection spot size) of the center of the gas chamber.

[0057] The optical frequency shift of broadband hybrid pumping is caused by the interaction between the pump light and rubidium atoms, as well as the interaction between the pump light and potassium atoms. The optical frequency shift under the combined action of the two is expressed as:

[0058]

[0059] in, is the density ratio of potassium atoms to rubidium atoms, is the i-th frequency of the broadband laser The luminous flux is, c is the speed of light, is the electron radius, is the oscillator strength of the D1 line of potassium atom, is the gyromagnetic ratio of electrons, A is the area of ​​the pumping light spot, is the D1 line frequency of potassium atoms, is the D2 line frequency of potassium atoms, The pressure of the mixed alkali metal atomic source gas chamber is widened. is the oscillator strength of the D1 line of the rubidium atom, is the D1 line frequency of potassium atoms, is the D2 line frequency of potassium atoms, and s is the polarization vector of the pumping light photon.

[0060] By adjusting the density ratio of the mixed alkali metal atom source gas chamber The total optical frequency shift cancellation is less than 10 -12 Tesla. It can be seen from the formula that the total optical frequency shift is sensitive to the fluctuation of the pumping light frequency. Figure 4 It can be seen that the optical frequency shift of the mixed alkali metal atomic source gas cell pumped by narrow-spectrum laser is greatly affected by the laser frequency fluctuation, which is more than one order of magnitude higher than that of the single potassium atomic gas cell. However, the optical frequency shift of the mixed alkali metal atomic source gas cell using wide-spectrum pumping is very little affected by the laser frequency fluctuation, which is about two orders of magnitude lower than that of narrow-spectrum mixed pumping.

[0061] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. It is pointed out here that the above description helps those skilled in the art to understand the invention, but does not limit the protection scope of the invention. Any equivalent replacement, modification and / or simplification of the above description without departing from the essence of the invention falls within the protection scope of the invention.

Claims

1. A wide spectrum hybrid pumping method based on a SERF magnetic field measurement device, characterized in that: The following steps are involved: Step 1, setting the density ratio of potassium atoms to rubidium atoms in the mixed alkali metal atom source gas chamber in the SERF magnetic field measurement device to K:Rb=1:4-6; Step 2, construct and adjust the pumping optical path and the detection optical path in the SERF magnetic field measurement device, the pumping light on the pumping optical path is a wide-spectrum pumping laser generated by an external cavity phase modulation narrow linewidth seed light generated by a voltage with adjustable amplitude and bit rate generated by a pseudo-random bit sequence waveform generator and applied to an electro-optical phase modulator, the temperature of the mixed alkali metal atomic source gas chamber is 160-200° C., the three-axis magnetic compensation coil is adjusted, and the three-dimensional in-situ magnetic compensation technology is used to compensate for the system residual magnetism, so that the device works in the SERF state; Step 3, turn on the pseudo-random bit sequence waveform generator, set the modulation frequency, use the function generator to add a calibration magnetic field to the sensitive axis Y, adjust the pumping light power, so that the lock-in amplifier outputs the largest frequency component, that is, the magnetic field response signal is the strongest, and record the Y-axis residual magnetism and the frequency signal strength at this time; Step 4, measuring the optical frequency shift noise caused by the pump light frequency fluctuation and the uniformity of the electron steady-state polarizability; Step 5, judging whether the optical frequency shift noise and the electronic polarization uniformity meet the requirements, if not, returning to step 3, if yes, proceeding to step 6; Step 6, enter the subsequent magnetic field measurement; The narrow linewidth seed light comes from a narrow linewidth seed light laser, the narrow linewidth seed light laser is connected to a tapered amplifier through an electro-optical phase modulator, the electro-optical phase modulator is connected to a pseudo-random bit sequence waveform generator through a radio frequency amplifier, and the tapered amplifier is connected to a mixed alkali metal atom source gas chamber through a concave lens, a first convex lens, a reflector, a first 1 / 2 wave plate, a first polarization beam splitter prism and a first 1 / 4 wave plate in sequence, so that a wide spectrum pumping laser passing through the mixed alkali metal atom source gas chamber along a Z axis polarizes low-density potassium atoms, and the potassium atoms collide with high-density rubidium atoms to polarize the rubidium atoms.

2. The wide spectrum hybrid pumping method based on the SERF magnetic field measurement device according to claim 1, characterized in that: In step 2, the three-dimensional in-situ magnetic compensation technology is used to compensate for the residual magnetism of the system, including cross-compensation of the magnetic field in the X-axis direction and the magnetic field in the Z-axis direction, and finally compensation of the magnetic field in the Y-axis direction.

3. The wide spectrum hybrid pumping method based on the SERF magnetic field measurement device according to claim 1, characterized in that: In step 2, the spectral line width of the wide-spectrum pumping laser is adjusted by controlling the driving voltage applied to the electro-optical phase modulator to broaden the spectral line width of the narrow-linewidth laser to the mixed atomic ensemble pressure broadening level, and the driving voltage is regulated by a pseudo-random bit sequence with adjustable amplitude and bit rate with a bit sequence of "0" and "1" values ​​randomly selected with a probability of 50%.

4. The wide spectrum hybrid pumping method based on the SERF magnetic field measurement device according to claim 1, characterized in that: Step 4 includes changing the pumping light frequency to detune by 10 MHz to 1000 MHz and measuring the corresponding optical frequency shift noise.

5. The wide spectrum hybrid pumping method based on the SERF magnetic field measurement device according to claim 1, characterized in that: Step 5 includes determining whether the optical frequency shift noise is less than 10 -15 T / MHz, whether the uniformity of electronic polarization is greater than 80%.

6. The wide spectrum hybrid pumping method based on the SERF magnetic field measurement device according to claim 1, characterized in that: The detection light on the detection light path comes from a detection laser, and the detection laser is connected to a phase-locked amplifier in sequence through a second 1 / 2 wave plate, a second polarization beam splitter, a polarizer, a photoelastic modulator, a second 1 / 4 wave plate, a mixed alkali metal atom source gas chamber, an analyzer, a second convex lens and a photodetector. The phase-locked amplifier is respectively connected to a modulation controller and a host computer, the host computer is connected to a function generator, the modulation controller is connected to the photoelastic modulator, and the function generator is connected to a three-axis magnetic compensation coil.

7. The wide spectrum hybrid pumping method based on the SERF magnetic field measurement device according to claim 1, characterized in that: The mixed alkali metal atom source gas chamber is located in a non-magnetic electric heating system, the non-magnetic electric heating system is located in a three-axis magnetic compensation coil, and the three-axis magnetic compensation coil is located in a magnetic shielding barrel.

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