Hybrid optical pumping hyperpolarization nuclear spinning system and method for current measurement

Abstract

The invention discloses a mixed light pumping hyperpolarization nuclear spinning system and method for current measurement, the system comprises a pumping laser light path, a heating laser light path and an alkali metal gas chamber, a signal pickup coil is installed near the gas chamber, the gas chamber is filled with two kinds of alkali metal atoms and nuclear spinning gas atoms 3He, and the densities of the two kinds of alkali metal atoms are different; the heating laser light path is used for emitting laser to heat the gas chamber, and the pumping laser light path is used for emitting pumping laser to the gas chamber so as to utilize spin exchange collision between two alkali metals to hyperpolarize 3He nuclear spin; the signal pickup coil is used for exciting 3He nuclear spin to deviate from the direction of a high-intensity magnetic field to be measured and picking up a nuclear spin precession signal projection magnetic field in the direction perpendicular to the pumping laser; the gas chamber is filled with the two kinds of alkali metal atoms, the overall density of the alkali metal atoms in the gas chamber is improved, nuclear spin can be hyperpolarized by high-density alkali metal electron spin, and finally the polarizability of the nuclear spin is improved.

Description

Technical Field

[0001] The invention relates to the technical field of strong current measurement and strong magnetic measurement, and in particular to a hybrid optical pumping hyperpolarized nuclear spin system and method for current measurement. Background Art

[0002] With the development of quantum science and technology, technology based on hyperpolarized nuclear spins has been proposed. The precession properties of hyperpolarized nuclear spins in external magnetic fields can be used to measure external magnetic fields. In particular, nuclear spins can be used to measure strong magnetic fields above 0.1T. It has the advantage of a large measurement range and can measure high currents generated by ultra-high / ultra-high voltage transmission lines, high currents generated by turbines, and high currents in new energy distribution networks with high precision. Using the quantum properties of nuclear spins, the magnetic field generated by currents can be measured with high precision, low temperature drift, and high stability, and is expected to be widely used in power grid current measurement.

[0003] In many quantum technology-based magnetic field measurements, hyperpolarized nuclear spins are based on inert gas nuclear spins such as 3 He, etc., the collision interaction between gases is weak, the relaxation time of nuclear spins is long, the signal-to-noise ratio of the measurement signal is high, and the gyromagnetic ratio of nuclear spins is about 1000 times smaller than that of electrons. Therefore, under the same magnetic field, the precession frequency of nuclear spins is about 1000 times lower, and generally works at a radio frequency of about 10MHz. In comparison, for example, NV color center quantum current sensors use electron spins as magnetic field sensitive units, often working in the microwave band, requiring complex and high-power microwave conditioning circuits. In addition, the relaxation time of electron spins is several orders of magnitude lower than that of nuclear spins, which further limits the signal-to-noise ratio and accuracy of measuring magnetic fields.

[0004] The hyperpolarized nuclear spin quantum current sensor first hyperpolarizes the nuclear spin through an optical method, and uses a specially developed pulse drive circuit to make the nuclear spin deviate from the direction of the magnetic field to be measured. The nuclear spin will precess around the magnetic field to be measured, and the pickup coil can sense the alternating electromagnetic field generated by the nuclear spin precession, thereby detecting the weak spin precession signal. The size of the external magnetic field can be extracted by measuring the frequency of the precession signal, and the precession frequency is linearly related to the size of the magnetic field. It is related to external parameters such as optical power and temperature, and has strong anti-interference capabilities.

[0005] First, hyperpolarized nuclear spins require optical hyperpolarization, that is, the nuclear spins need to point in the direction of the pump light. The high nuclear spin polarization directly determines the size of the measurement signal, thereby improving the measurement sensitivity and accuracy of the sensor. In traditional nuclear spin hyperpolarization, a single alkali metal atom is generally used. 3 For nuclear spins that are difficult to polarize, such as He, the polarization rate is low.

[0006] In the related art, a patent application document with publication number CN116449267A proposes a coil constant measurement method based on detecting the optical pumping effect by an atomic spin magnetometer. The magnetic field is measured by using an atomic spin magnetometer device, and the atomic spin magnetometer device includes an alkali metal gas chamber. The alkali metal atoms in the alkali metal gas chamber are one or a mixture of potassium, rubidium, and cesium. However, this scheme uses the detection of the optical pumping effect to achieve the measurement of the coil constant. Summary of the invention

[0007] The technical problem to be solved by the present invention is how to improve 3 The polarizability of He nuclear spin solves the problem of low measurement signal caused by low nuclear spin polarization.

[0008] The present invention solves the above technical problems by the following technical means:

[0009] The present invention proposes a hybrid optical pumping hyperpolarized nuclear spin system for current measurement, the system comprising a pumping laser optical path, a heating laser optical path and an alkali metal gas chamber, a signal pickup coil is installed near the alkali metal gas chamber, and the alkali metal gas chamber is filled with two alkali metal atoms and nuclear spin gas atoms. 3 He, and the density of the two alkali metal atoms is different;

[0010] The heating laser optical path is used to emit laser to heat the alkali metal gas chamber, and the pump laser optical path is used to emit pump laser to the alkali metal gas chamber to utilize the spin exchange collision hyperpolarization between the two alkali metals. 3 He nuclear spin;

[0011] The signal pickup coil is used to excite 3 The He nuclear spin deviates from the direction of the strong magnetic field to be measured, and the projection magnetic field of the nuclear spin precession signal perpendicular to the pump laser is picked up.

[0012] Furthermore, the two alkali metal atoms filled in the alkali metal gas chamber are Rb atoms and Cs atoms, respectively, and the density ratio of the Rb atoms to the Cs atoms is between 0.02 and 0.2.

[0013] Furthermore, the pump laser optical path includes a pump laser, a polarizer, a coupling lens, a shaping lens, a 1 / 4 glass plate and a total reflection mirror;

[0014] The pump laser is introduced into the quantum current sensor probe through an optical fiber, a polarizer is arranged on the optical path of the pump laser emitted by the pump laser to purify the light emitted by the laser into linearly polarized light, a coupling lens is arranged on the optical path of the linearly polarized light to couple the spatial light beam of the pump laser into the optical fiber, the shaping lens is arranged on the optical path of the optical fiber output light to perform spot beam expansion, the 1 / 4 glass slide is arranged on the laser light after beam expansion to convert the laser light after beam expansion into circularly polarized light, and the total reflection mirror is arranged on the optical path of the circularly polarized light to deflect the circularly polarized light by 90 degrees before entering the alkali metal gas chamber.

[0015] Furthermore, the total reflection mirror is arranged on one side of the alkali metal gas chamber, and a reflection mirror is arranged on the other side of the alkali metal gas chamber, and the pump laser after passing through the alkali metal gas chamber returns to the alkali metal gas chamber through the reflection mirror.

[0016] Furthermore, the heating laser optical path includes a heating laser and a beam expander lens, the beam expander lens is arranged on the optical path of the laser output by the heating laser, and the output light of the beam expander lens is irradiated to the alkali metal gas chamber.

[0017] Furthermore, the alkali metal gas chamber, the total reflection mirror and the reflection mirror are all arranged in a thermal insulation layer, and a side of the thermal insulation layer close to the 1 / 4 glass slide is a light-transmitting window.

[0018] Furthermore, the heating temperature of the alkali metal gas chamber is between 130 degrees Celsius and 180 degrees Celsius.

[0019] In addition, the present invention also proposes a hybrid optical pumping hyperpolarized nuclear spin method for current measurement, characterized in that it is used to realize hybrid optical pumping hyperpolarized nuclear spin using the system as described above, and the method includes:

[0020] The pump laser light path is used to emit a pump laser to irradiate the alkali metal gas chamber to cause spin exchange collision hyperpolarization between the two alkali metals. 3 He nuclear spin, the wavelength of the pump laser is the absorption wavelength of the alkali metal atom with higher density among the two alkali metal atoms;

[0021] irradiating the alkali metal gas chamber with the heating laser emitted by the heating laser optical path, so that the heating temperature of the alkali metal gas chamber reaches a set working temperature;

[0022] placing the hybrid light-pumped hyperpolarized nuclear spin system into a strong magnetic field to be measured, wherein the propagation direction of the pump laser in the alkali metal gas chamber is the same as the direction of the strong magnetic field to be measured;

[0023] generating a pulsed magnetic field and loading the pulsed magnetic field into the signal pickup coil to perform spatial angle shift on the nuclear spins;

[0024] The signal pickup coil is used to pick up the projection magnetic field of the nuclear spin precession signal perpendicular to the pump laser direction to calculate the strong magnetic field to be measured.

[0025] Furthermore, the pump laser light path is used to emit a pump laser to irradiate the alkali metal gas chamber to cause spin exchange collision hyperpolarization between the two alkali metals. 3 He nuclear spins, including:

[0026] The pump laser light path is used to emit a pump laser to irradiate the alkali metal gas chamber so that the spins of two alkali metal atoms in the gas chamber are exchanged and collided to polarize the low-density alkali metal atoms;

[0027] Through the low density of alkali metal atoms and 3 He collision hyperpolarization 3 And nuclear spin.

[0028] Furthermore, the step of irradiating the alkali metal gas chamber with the heating laser emitted by the heating laser optical path so that the heating temperature of the alkali metal gas chamber reaches a set working temperature includes:

[0029] The heating laser emitted by the heating laser optical path is used to irradiate the alkali metal gas chamber, and when the optical depth of the atoms in the alkali metal gas chamber absorbing the pump light is 1-3, it is determined that the heating temperature of the alkali metal gas chamber reaches the set working temperature.

[0030] Further, the generating of the pulsed magnetic field and loading the pulsed magnetic field into the signal pickup coil to perform spatial angle shift on the nuclear spins comprises:

[0031] Apply a radio frequency field with a frequency of ω0 to the strong magnetic field to be measured Set the time t so that the magnetic moment Rotated around the z-axis to an angle α, where the RF field Perpendicular to the strong magnetic field to be measured, the relationship between the nuclear spin pointing angle α and the pulse magnetic field duration t is:

[0032] t=α / γB1

[0033] Where γ is the rotating magnetic ratio, B1 is the RF pulse magnetic field The amplitude of .

[0034] The advantages of the present invention are:

[0035] against 3 He is difficult to polarize nuclear spins and has a low polarization rate. The present invention uses hybrid optical pumping to fill two alkali metal atoms in the alkali metal gas chamber. The hybrid optical pumping is achieved by combining the two alkali metal atoms. 3The hyperpolarization of He nuclear spin and hybrid optical pumping can directly increase the overall density of alkali metal atoms inside the alkali metal gas chamber, so that the nuclear spin can be hyperpolarized by the high-density alkali metal electron spins, ultimately increasing the polarization rate of the nuclear spin and laying the foundation for a high signal-to-noise ratio nuclear spin precession signal.

[0036] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic structural diagram of a hybrid optically pumped hyperpolarized nuclear spin system for current measurement proposed in one embodiment of the present invention;

[0038] Figure 2 Schematic diagram of the atomic species filled into the alkali metal gas chamber in one embodiment of the present invention;

[0039] Figure 3 It is a flow chart of a hybrid optical pumping hyperpolarized nuclear spin method for current measurement proposed in one embodiment of the present invention.

[0040] In the figure:

[0041] 1- pump laser; 2- polarizer; 3- coupling lens; 4- shaping lens; 5- 1 / 4 glass slide; 6- total reflection mirror; 7- alkali metal gas chamber; 8- reflection mirror; 9- signal pickup coil; 10- strong magnetic field to be measured; 11- thermal insulation layer; 12- light-transmitting window; 13- beam expansion lens; 14- heating laser. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] like Figure 1 to Figure 2 As shown, the first embodiment of the present invention proposes a hybrid optical pumping hyperpolarized nuclear spin system for current measurement, the system includes a pumping laser optical path, a heating laser optical path and an alkali metal gas chamber 7, a signal pickup coil 9 is installed near the alkali metal gas chamber 7, and the alkali metal gas chamber 7 is filled with two kinds of alkali metal atoms and nuclear spin gas atoms. 3He, and the densities of the two alkali metal atoms are different; the heating laser optical path is used to emit laser to heat the alkali metal gas chamber 7, and the pump laser optical path is used to emit pump laser to the alkali metal gas chamber 7 to utilize the spin exchange collision hyperpolarization between the two alkali metals 3 He nuclear spin; the signal pickup coil 9 is used to excite 3 The He nuclear spin deviates from the direction of the strong magnetic field 10 to be measured, and the projection magnetic field of the nuclear spin precession signal perpendicular to the pump laser is picked up, that is, the strong magnetic field 10 to be measured.

[0044] Specifically, if it is a single alkali metal, as the temperature of the alkali metal gas chamber 7 increases, the saturated vapor pressure of the alkali metal atoms inside the gas chamber will increase, and the pump laser incident on the gas chamber will be strongly absorbed, resulting in the alkali metal atoms being mostly absorbed before they leave the gas chamber, resulting in the inability to effectively pump the alkali metal. The hybrid optically pumped hyperpolarized nuclear spin system proposed in this embodiment uses two alkali metal atoms to work simultaneously to hyperpolarize the nuclear spins, and controls the optical properties of the entire alkali metal gas chamber 7 by controlling the density ratio of the two alkali metal atoms. If two alkali metal atoms are filled into the gas chamber, the density of one alkali metal atom can be controlled to be low, while the density of the other alkali metal atom can be controlled to be very high, which is equivalent to the alkali metal in the entire gas chamber being an optically rarefied gas, and light can easily pass through the alkali metal gas chamber 7. In this process, since the density of the second alkali metal atom is quite high, the polarization process is completed through spin exchange collisions between the two alkali metals. Since the spin exchange collision rate is very large, the transfer of angular momentum can be carried out effectively in this process, thereby increasing the polarization rate of the nuclear spin, so that 3 When the He nuclear spin precesses, a larger spatial magnetic field is generated, which will induce a larger electromotive force signal in the signal pickup coil 9, thereby improving the signal-to-noise ratio of the measurement signal.

[0045] Furthermore, in this embodiment, the nuclear spin gas atoms are preferably 3 He atoms, because the gas chamber with a pressure exceeding 3 atmospheres is difficult to manufacture, the system signal-to-noise ratio is 3 The density of He atoms is positively correlated, so it is necessary to increase the gas chamber 3 He atomic pressure to further increase 3 He atomic density is used to improve the signal-to-noise ratio of the system. Due to the limitation of the high-pressure gas chamber manufacturing process, this scheme adopts 3 atmospheres of pressure. 3 He atomic gas.

[0046] As a further preferred technical solution, the two alkali metal atoms filled in the alkali metal gas chamber 7 are Rb atoms and Cs atoms, respectively, and the density ratio of the Rb atoms to the Cs atoms is between 0.02 and 0.2.

[0047] It should be noted that if the density ratio of the two alkali metal atoms is too large, the polarization rate of the pump nuclear spin will be too low, thereby affecting the detection signal. If the density ratio is too small, the pump laser power requirement is high, which will cause excessive power consumption of the probe. This embodiment sets the density ratio of Rb atoms to Cs atoms between 0.02 and 0.2, which can well balance the polarization rate of nuclear spins and probe loss.

[0048] In addition, when potassium and rubidium are mixed, the potassium-rubidium ratio is about 0.02-0.2. This embodiment uses rubidium and cesium for polarization. The biggest difference is that the working temperature of rubidium and cesium is about 120 degrees, which is lower than the working temperature of potassium and rubidium at 220 degrees.

[0049] As a further preferred technical solution, Figure 1 As shown, the pump laser optical path includes a pump laser 1, a polarizer 2, a coupling lens 3, a shaping lens 4, a 1 / 4 glass slide 5 and a total reflection mirror 6;

[0050] The pump laser 1 is introduced into the quantum current sensor probe through an optical fiber. The polarizer 2 is arranged on the optical path of the pump laser emitted by the pump laser 1 to purify the light emitted by the laser into linearly polarized light. The coupling lens 3 is arranged on the optical path of the linearly polarized light to couple the spatial light beam of the pump laser 1 into the optical fiber. The shaping lens 4 is arranged on the optical path of the optical fiber output light to expand the light spot. The 1 / 4 glass slide 5 is arranged on the laser light after expansion to convert the laser light after expansion into circularly polarized light. The total reflection mirror 6 is arranged on the optical path of the circularly polarized light to deflect the circularly polarized light by 90 degrees before entering the alkali metal gas chamber 7.

[0051] As a further preferred technical solution, the total reflection mirror 6 is arranged on one side of the alkali metal gas chamber 7, and a reflection mirror 8 is arranged on the other side of the alkali metal gas chamber 7. The pump laser after passing through the alkali metal gas chamber 7 returns to the alkali metal gas chamber 7 through the reflection mirror 8.

[0052] It should be noted that the left and right side walls of the alkali metal gas chamber 7 are made of glass to form an optical window of the alkali metal gas chamber 7 , and the total reflection mirror 6 and the reflection mirror 8 are arranged on the left and right sides of the alkali metal gas chamber 7 respectively so that the laser can penetrate.

[0053] Preferably, the alkali metal gas chamber 7 is located at the center of the entire quantum current sensor, and the propagation direction of the pump laser is the same as the direction of the strong magnetic field 10 to be measured. After passing through the alkali metal gas chamber 7, the pump laser is reflected back to the alkali metal gas chamber 7 by the reflector 8 again to reuse the pump laser. The pump laser is used for hyperpolarization. 3After the He nuclear spin passes through the gas chamber, there is still high-power laser light left. If it is not used, it will be wasted. For this reason, a reflector 8 can be arranged on the other side of the alkali metal gas chamber 7 relative to the total reflector 6, and the pump laser light is reflected into the alkali metal gas chamber 7 again. The reflected laser light can also be realized. 3 The hyperpolarization of He nuclear spin can reduce the power of pump laser by half, so that the pump laser can be fully utilized.

[0054] As a further preferred technical solution, the heating laser optical path includes a heating laser 14 and a beam expander lens 13, wherein the beam expander lens 13 is arranged on the optical path of the infrared laser output by the heating laser 14, and the output light of the beam expander lens 13 is irradiated to the alkali metal gas chamber 7. The alkali metal gas chamber 7 is heated by utilizing the heating laser optical path so that the atomic spins inside the gas chamber reach the desired heating temperature.

[0055] As a further preferred technical solution, the alkali metal gas chamber 7 , the total reflection mirror 6 and the reflection mirror 8 are all arranged in a thermal insulation layer 11 , and a side of the thermal insulation layer 11 close to the 1 / 4 glass slide 5 is a light-transmitting window 12 .

[0056] Specifically, in this embodiment, the alkali metal gas chamber 7 is encapsulated in a thermal insulation layer 11, and the thermal insulation layer 11 is used to maintain the insulation of the heated alkali metal gas chamber 7 so that the atomic spin inside the alkali metal gas chamber 7 reaches the required heating temperature, and the light-transmitting window 12 is used as a part of the thermal insulation layer 11 for the passage of the light path while avoiding heat loss to increase the power consumption of the probe.

[0057] As a further preferred technical solution, the heating temperature of the alkali metal gas chamber 7 is between 130 degrees Celsius and 180 degrees Celsius.

[0058] It should be noted that since the two side walls of the alkali metal gas chamber 7 are made of glass, too low a temperature will affect the pumping effect and the probe sensitivity will be low, while too high a temperature will cause the alkali metal to corrode the glass and cause the alkali metal to be consumed. In this embodiment, the heating temperature of the alkali metal gas chamber 7 is controlled between 130 degrees Celsius and 180 degrees Celsius, which can ensure a relatively high sensitivity of the probe while avoiding the corrosion of the glass by the alkali metal.

[0059] Therefore, the working process of the hybrid optical pumping hyperpolarized nuclear spin system for current measurement proposed in this embodiment is:

[0060] The pump laser 1 is introduced into the sensor probe through the optical fiber, the polarizer 2 purifies the light emitted by the laser into linear polarized light, the coupling lens 3 couples the spatial light beam of the laser into the optical fiber, the optical fiber output light is expanded by the shaping lens 4, the expanded laser light becomes circularly polarized light after passing through the 1 / 4 glass slide 5, the circularly polarized light is deflected 90 degrees after passing through the total reflection mirror 6 and enters the alkali metal gas chamber 7, the expanded spot size completely covers the size of the optical window (the optical window is made of glass material) of the alkali metal gas chamber 7, and the full coverage of the atoms is achieved. The laser light after passing through the alkali metal gas chamber 7 is reflected back to the alkali metal gas chamber 7 by the reflection mirror 8 again, which can further enhance the effect of optical pumping.

[0061] The heating laser is introduced through the optical fiber and enters the beam expander lens 13 to form parallel light to irradiate the alkali metal gas chamber 7 to heat the gas chamber, and the heat insulation layer 11 is used to maintain the heat preservation of the heated alkali metal gas chamber 7.

[0062] The signal pickup coil 9 is installed around the upper and lower surfaces of the alkali metal gas chamber 7. The signal pickup coil 9 is used as a pulse excitation coil for the spin deflection angle, so that the nuclear spin deviates from the direction of the magnetic field to be measured. At the same time, the coil picks up the nuclear spin precession signal projection magnetic field in the direction perpendicular to the Puguang laser. Since the strong magnetic field 10 to be measured is generated by electric current, the magnitude of the current can be inferred by the magnitude of the magnetic field. This is the principle of measuring current by the quantum current sensor.

[0063] In addition, if Figure 3 As shown, the second embodiment of the present invention further proposes a hybrid light pumping hyperpolarized nuclear spin method for current measurement, which is used to realize hybrid light pumping hyperpolarized nuclear spin using the system described in the first embodiment above, and the method includes the following steps:

[0064] S10, using the pump laser optical path to emit a pump laser to irradiate the alkali metal gas chamber to achieve hyperpolarization through spin exchange collision between the two alkali metals 3 He nuclear spin, the wavelength of the pump laser is the absorption wavelength of the alkali metal atom with higher density among the two alkali metal atoms;

[0065] Specifically, in this embodiment, the pump laser is adjusted so that the wavelength of the pump laser emitted by it is the absorption wavelength of the alkali metal atom Rb, the alkali metal atom Rb is directly polarized by the pump light, and then the spin exchange collision of Rb-Cs is hyperpolarized. 3 He.

[0066] S20, irradiating the alkali metal gas chamber with the heating laser emitted by the heating laser optical path, so that the heating temperature of the alkali metal gas chamber reaches a set working temperature;

[0067] It should be noted that, in this embodiment, the infrared laser emitted by the heating laser light path is used to irradiate the alkali metal gas chamber, so that the heating temperature of the alkali metal gas chamber is between 130 degrees Celsius and 180 degrees Celsius.

[0068] S30, placing the hybrid light-pumped hyperpolarized nuclear spin system into a strong magnetic field to be measured, wherein the propagation direction of the pump laser in the alkali metal gas chamber is the same as the direction of the strong magnetic field to be measured;

[0069] S40, generating a pulsed magnetic field and loading the pulsed magnetic field into the signal pickup coil to perform a spatial angle shift on the nuclear spin;

[0070] It should be noted that the hybrid optically pumped hyperpolarized nuclear spin system is placed in a strong magnetic field to be measured, and the propagation direction of the pump laser in the alkali metal gas chamber is the same as the direction of the strong magnetic field to be measured. After the nuclear spin is stably pumped for tens of minutes, the current measurement state can be achieved. Then a pulsed magnetic field is generated through a pulse amplifier circuit, wherein the pulsed magnetic field contains a sinusoidal signal near the nuclear spin precession frequency, that is, the pulsed magnetic field modulates the sinusoidal signal, and the pulsed magnetic field is added to the signal pickup coil to achieve the operation of spatial angle shift of the nuclear spin.

[0071] S50, picking up the nuclear spin precession signal projection magnetic field perpendicular to the pump laser direction through the signal pickup coil to calculate the strong magnetic field to be measured.

[0072] It should be noted that the nuclear spin will precess in the external magnetic field, and the polarized nuclear spin will generate a magnetic field in the same direction as the nuclear spin polarization. This magnetic field is an alternating magnetic field, and its projection in the direction of the pump light is close to a constant, and no induced magnetic field can be generated. However, an alternating magnetic field can be generated in the direction perpendicular to the pump light. The cross-edge signal can be extracted through the signal pickup coil, and an induced electromotive force is induced in the coil. The weak signal is amplified through a weak voltage amplifier circuit, and finally the external magnetic field, that is, the size of the strong magnetic field to be measured, is sensed by measuring the frequency of the induced signal.

[0073] As a further preferred technical solution, the step S10: using the pump laser optical path to emit a pump laser to irradiate the alkali metal gas chamber to hyperpolarize the spin exchange collision between the two alkali metals. 3 He nuclear spin, including the following steps:

[0074] The pump laser light path is used to emit a pump laser to irradiate the alkali metal gas chamber so that the spins of two alkali metal atoms in the gas chamber are exchanged and collided to polarize the low-density alkali metal atoms;

[0075] Through the low density of alkali metal atoms and 3 He collision hyperpolarization 3 And nuclear spin.

[0076] In this embodiment, the pump light directly polarizes Rb, and then polarizes Cs through the spin exchange collision between Rb and Cs. 3 He collision to hyperpolarize 3 He can directly increase the overall density of alkali metal atoms, so that the nuclear spin can be hyperpolarized by the high-density alkali metal electron spins, ultimately increasing the polarization rate of the nuclear spin.

[0077] As a further preferred technical solution, the step S20: using the heating laser emitted by the heating laser optical path to irradiate the alkali metal gas chamber so that the heating temperature of the alkali metal gas chamber reaches a set working temperature, comprises:

[0078] The heating laser emitted by the heating laser optical path is used to irradiate the alkali metal gas chamber, and when the optical depth of the atoms in the alkali metal gas chamber absorbing the pump light is 1-3, it is determined that the heating temperature of the alkali metal gas chamber reaches the set working temperature.

[0079] It should be noted that the optical depth OD reflects the ratio of the transmitted laser to the incident laser, that is, OD is equal to Ln (outgoing laser power / incident laser power).

[0080] As a further preferred technical solution, the step S40: generating a pulsed magnetic field and loading the pulsed magnetic field into the signal pickup coil to perform a spatial angle shift on the nuclear spin, specifically includes:

[0081] Apply a radio frequency field with a frequency of ω0 to the strong magnetic field to be measured Set the time t so that the magnetic moment Rotated around the z-axis to an angle α, where the RF field Perpendicular to the strong magnetic field to be measured, the relationship between the nuclear spin pointing angle α and the pulse magnetic field duration t is:

[0082] t=α / γB1

[0083] Where γ is the rotating magnetic ratio, B1 is the RF pulse magnetic field The amplitude of .

[0084] For example, when the rotation angle is π / 2, the required pulse signal duration t 1 / 2 for:

[0085]

[0086] After rotating the precession into the transverse plane using such a π / 2 pulse, the induced current can be picked up from the precession using a pick-up coil. The signal from the coil is called the free induction decay (FID) signal, providing a measure of the B0 magnetic field.

[0087] This embodiment can achieve precise control of the nuclear spin pointing angle by precisely controlling the radio frequency pulse working time.

[0088] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0089] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0090] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A hybrid optically pumped hyperpolarized nuclear spin system for current measurement, characterized in that: The system comprises a pump laser optical path, a heating laser optical path and an alkali metal gas chamber, wherein a signal pickup coil is installed near the alkali metal gas chamber, and the alkali metal gas chamber is filled with two kinds of alkali metal atoms and nuclear spin gas atoms. 3 He, and the density of the two alkali metal atoms is different; The heating laser optical path is used to emit laser to heat the alkali metal gas chamber, and the pump laser optical path is used to emit pump laser to the alkali metal gas chamber to utilize the spin exchange collision hyperpolarization between the two alkali metals. 3 He nuclear spin; The signal pickup coil is used to excite 3 The He nuclear spin deviates from the direction of the strong magnetic field to be measured, and the projection magnetic field of the nuclear spin precession signal perpendicular to the pump laser is picked up.

2. The hybrid optically pumped hyperpolarized nuclear spin system for current measurement according to claim 1, characterized in that: The two alkali metal atoms filled in the alkali metal gas chamber are Rb atoms and Cs atoms, respectively, and the density ratio of the Rb atoms to the Cs atoms is between 0.02 and 0.

2.

3. The hybrid optically pumped hyperpolarized nuclear spin system for current measurement according to claim 1, characterized in that: The pump laser optical path includes a pump laser, a polarizer, a coupling lens, a shaping lens, a 1 / 4 glass slide and a total reflection mirror; The pump laser is introduced into the quantum current sensor probe through an optical fiber, a polarizer is arranged on the optical path of the pump laser emitted by the pump laser to purify the light emitted by the laser into linearly polarized light, a coupling lens is arranged on the optical path of the linearly polarized light to couple the spatial light beam of the pump laser into the optical fiber, the shaping lens is arranged on the optical path of the optical fiber output light to perform spot beam expansion, the 1 / 4 glass slide is arranged on the laser light after beam expansion to convert the laser light after beam expansion into circularly polarized light, and the total reflection mirror is arranged on the optical path of the circularly polarized light to deflect the circularly polarized light by 90 degrees before entering the alkali metal gas chamber.

4. The hybrid optically pumped hyperpolarized nuclear spin system for current measurement according to claim 3, characterized in that: The total reflection mirror is arranged on one side of the alkali metal gas chamber, and a reflection mirror is arranged on the other side of the alkali metal gas chamber. The pump laser passing through the alkali metal gas chamber returns to the alkali metal gas chamber through the reflection mirror.

5. The hybrid optically pumped hyperpolarized nuclear spin system for current measurement according to claim 1, characterized in that: The heating laser optical path includes a heating laser and a beam expander lens, wherein the beam expander lens is arranged on the optical path of the heating laser output laser, and the output light of the beam expander lens is irradiated to the alkali metal gas chamber.

6. The hybrid optically pumped hyperpolarized nuclear spin system for current measurement according to claim 4, characterized in that: The alkali metal gas chamber, the total reflection mirror and the reflection mirror are all arranged in a heat preservation and insulation layer, and a side of the heat preservation and insulation layer close to the 1 / 4 glass slide is a light-transmitting window.

7. The hybrid optically pumped hyperpolarized nuclear spin system for current measurement according to claim 1, characterized in that: The heating temperature of the alkali metal gas chamber is between 130 degrees Celsius and 180 degrees Celsius.

8. A hybrid optically pumped hyperpolarized nuclear spin method for current measurement, characterized in that: The method for realizing hybrid optical pumping of hyperpolarized nuclear spins using the system according to any one of claims 1 to 7 comprises: The pump laser light path is used to emit a pump laser to irradiate the alkali metal gas chamber to cause spin exchange collision hyperpolarization between the two alkali metals. 3 He nuclear spin, the wavelength of the pump laser is the absorption wavelength of the alkali metal atom with higher density among the two alkali metal atoms; irradiating the alkali metal gas chamber with the heating laser emitted by the heating laser optical path, so that the heating temperature of the alkali metal gas chamber reaches a set working temperature; placing the hybrid light-pumped hyperpolarized nuclear spin system into a strong magnetic field to be measured, wherein the propagation direction of the pump laser in the alkali metal gas chamber is the same as the direction of the strong magnetic field to be measured; generating a pulsed magnetic field and loading the pulsed magnetic field into the signal pickup coil to perform spatial angle shift on the nuclear spins; The signal pickup coil is used to pick up the projection magnetic field of the nuclear spin precession signal perpendicular to the pump laser direction to calculate the strong magnetic field to be measured.

9. The hybrid optical pumping hyperpolarized nuclear spin method for current measurement according to claim 8, characterized in that: The pump laser light path is used to emit a pump laser to irradiate the alkali metal gas chamber to cause spin exchange collision hyperpolarization between the two alkali metals. 3 He nuclear spins, including: The pump laser light path is used to emit a pump laser to irradiate the alkali metal gas chamber so that the spins of two alkali metal atoms in the gas chamber are exchanged and collided to polarize the low-density alkali metal atoms; Through the low density of alkali metal atoms and 3 He collision hyperpolarization 3 And nuclear spin.

10. The hybrid optical pumping hyperpolarized nuclear spin method for current measurement according to claim 8, characterized in that: The step of irradiating the alkali metal gas chamber with the heating laser emitted by the heating laser optical path so that the heating temperature of the alkali metal gas chamber reaches a set working temperature comprises: The heating laser emitted by the heating laser optical path is used to irradiate the alkali metal gas chamber, and when the optical depth of the atoms in the alkali metal gas chamber absorbing the pump light is 1-3, it is determined that the heating temperature of the alkali metal gas chamber reaches the set working temperature.

11. The hybrid optical pumping hyperpolarized nuclear spin method for current measurement according to claim 8, characterized in that: The step of generating a pulsed magnetic field and loading the pulsed magnetic field into the signal pickup coil to perform spatial angle shift on the nuclear spins comprises: Apply a radio frequency field with a frequency of ω0 to the strong magnetic field to be measured Set the time t so that the magnetic moment Rotated around the z-axis to an angle α, where the RF field Perpendicular to the strong magnetic field to be measured, the relationship between the nuclear spin pointing angle α and the pulse magnetic field duration t is: t=α / γB1 Where γ is the rotating magnetic ratio, B1 is the RF pulse magnetic field The amplitude of .

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