A method for rapid self-stabilization of nuclear spin polarization based on optical and magnetic control

Abstract

The present invention relates to a method for rapid self-stabilization of nuclear spin polarization rate based on optical and magnetic regulation. The method utilizes the interaction between light, magnetism and atoms in the system, adopts a closed-loop control method, and comprehensively manipulates the optical field and magnetic field to quickly and automatically achieve the dynamic balance of the polarization of the atomic ensemble. The ratio of the pumping rate to the relaxation rate can be increased so that the device can quickly reach the steady state of polarization rate during the startup process; the pumping rate and the relaxation rate can be comprehensively regulated so that the device can be stabilized as soon as possible after the pumping light working conditions are changed; and the efficiency of the device reaching the working state can be increased by more than one time by reasonably selecting the control parameters. The present invention can speed up the startup speed of the device, shorten the stabilization time, save experimental manpower, and is beneficial to the atomic spin inertial measurement device to improve the experimental efficiency of scientific research and its future engineering application.

Description

Technical Field

[0001] The invention belongs to the field of atomic spin inertial measurement, and relates to a rapid automatic stabilization technology for the working state of an atomic spin inertial measurement device based on the interaction between light, magnetism and atoms, in particular to a rapid self-stabilization method for nuclear spin polarization rate based on optical and magnetic regulation. Background Art

[0002] The atomic spin inertial measurement device is based on the spin-exchange relaxation-free (SERF) state proposed in the 1970s and developed in the early 21st century. It is a measurement device that uses the nuclear spin sensitive inertial information of inert gas atoms. In recent years, in order to improve its measurement sensitivity, inert gases with large nuclear spin gyromagnetic ratios (such as 21 Ne atoms) as the working medium, thus achieving high-precision inertial information measurement. However, the selection of the above atomic source also brings about problems such as slow device startup speed and long stabilization time after changing working conditions, which affects its engineering application. Therefore, in order to improve the device startup speed, shorten the stabilization time, and realize closed-loop control, it is necessary to study the fast and automatic stabilization method of the working state of the device.

[0003] Generally, inertial measurement systems based on atomic SERF states are based on the interaction between light, magnetism and atoms. In a natural state, an atomic ensemble composed of alkali metal atoms and inert gases has a chaotic distribution inside and does not show its spin direction to the outside. Under appropriate magnetic field, temperature, and atomic number density conditions, a pumping laser with an appropriate frequency that can resonate alkali metal atoms is used to irradiate the atomic ensemble. Photons collide with alkali metal atoms to transfer angular momentum from the former to the latter. Continuous collisions make the electronic spin direction of alkali metal atoms consistent on a macroscopic level. Alkali metal atoms will also undergo spin exchange collisions with inert gas atoms, so that the nuclear spins of inert gas atoms also have angular momentum in the same direction. After a period of optical pumping, the steady state of optically polarized atoms can be achieved, so that the atomic ensemble has consistent angular momentum on a macroscopic level and exhibits a macroscopic magnetic moment. The size of the external magnetic field is then determined by cross-modulation of an external three-dimensional magnetic field. The main purpose is to determine the magnitude of the main magnetic field in the polarization direction of the atomic ensemble, so that the atoms can feel a magnetic field of equal magnitude and opposite to themselves, ensuring that the atomic ensemble is in a SERF state or a near-SERF state. At this time, the atomic ensemble is said to be located at the magnetic field compensation point, which can make the nuclear spins of the inert gas atoms in a self-compensation state, that is, the working state of the device and the steady state of nuclear spin polarization are achieved, and inertial measurement can be performed.

[0004] During the above startup process of the device, it takes a long time for the optically pumped atoms to reach a steady state, and the time to determine the magnetic field compensation point can be ignored. The optical pumping of alkali metal atoms can be considered to be completed instantly, and the pumping process is mainly the collision of alkali metal atoms with polarized inert gas atoms. Therefore, the stabilization time of the former's electronic spin is negligible compared to the latter's nuclear spin. On the other hand, in order to conduct scientific research and explore the limits of measurement sensitivity, it is often necessary to change the working state of the device. When it comes to changes in the intensity of the pumping light, the time it takes to reach a new steady state is often much longer than changing conditions such as temperature and magnetic field. Therefore, in order to reach the working state of the device as quickly as possible, it is necessary to study a fast self-stabilization method for the nuclear spins of inert gas atoms polarized by pumping light.

[0005] Under normal circumstances, after the device is started normally or the conditions are changed and stabilized, a low-frequency square wave modulated magnetic field is applied to the inertial sensitive axis, and the corresponding signal difference ΔS is zero. This is the magnetic field compensation point, the nuclear spin self-compensation point, the working state of the device, and the nuclear spin polarization steady state; conversely, the larger the signal difference, the farther the current state is from the working state. Therefore, a closed-loop control method can be used to first use the magnetic field to determine the current polarization state of the atomic ensemble, and then manipulate the light field and magnetic field to achieve rapid self-stabilization of the nuclear spin polarization rate. Summary of the invention

[0006] The problem solved by the present invention is: to overcome the shortcoming that the existing atomic spin inertial measurement device reaches a normal working state, that is, reaches a nuclear spin polarization steady state, which requires a long stabilization time, and provides a nuclear spin polarization rate rapid self-stabilization method based on optical and magnetic regulation, which utilizes the interaction between light, magnetism and atoms in the system, adopts a closed-loop control method, and comprehensively manipulates the optical field and magnetic field to quickly and automatically achieve the dynamic balance of the atomic ensemble polarization. The device can quickly reach the polarization rate steady state during the startup process by increasing the ratio of the pumping rate to the relaxation rate; the device can be stabilized as soon as possible after changing the pumping light working conditions by comprehensively regulating the size of the pumping rate and the relaxation rate; and the efficiency of the device reaching the working state can be increased by more than one time by reasonably selecting the control parameters. The present invention can speed up the startup speed of the device, shorten the stabilization time, save experimental manpower, and is beneficial to the atomic spin inertial measurement device to improve the experimental efficiency of scientific research, and is beneficial to its future engineering application.

[0007] The technical solution of the present invention is as follows:

[0008] A method for rapid self-stabilization of nuclear spin polarization rate based on optical and magnetic regulation, characterized in that it comprises utilizing the interaction between light, magnetism and atoms in a system device, and determining whether a magnetic field compensation point B in a steady state of the system is known. z0 Different closed-loop control processes are adopted to comprehensively manipulate the light field and magnetic field to quickly achieve rapid self-stabilization of the nuclear spin polarization rate after startup or to quickly achieve dynamic balance of the atomic ensemble polarization after changing the optical pumping rate.

[0009] The following steps are involved:

[0010] Step 1, start the program;

[0011] Step 2: Set the optical pumping rate R at steady state op0 , the logical relationship between input ΔS and the system polarization state, ΔS is the signal steady-state difference;

[0012] Step 3: Is the magnetic field compensation point B of the system in steady state known? z0 If yes, then jump to step A4; if no, then jump to step B4;

[0013] Step A4, input B z0 , steady-state accuracy preset value Δ1;

[0014] Step A5: Start the device under a large longitudinal magnetic field, or operate at a steady-state magnetic field compensation point B. z0 Next, the action lasts for t1;

[0015] Step A6, set the pumping rate R op0 , no large magnetic field in the horizontal direction, longitudinal magnetic field B z0 , vertical direction, i.e., Z-axis direction, determine whether |ΔS|<Δ1 holds, if yes, jump to step 8, if no, jump to step A7;

[0016] Step A7, determining whether to perform pumping or relaxation action according to the sign and algebraic value of ΔS, and jumping to step A5;

[0017] Step B4, inputting the preset steady-state accuracy values ​​Δ2 and Δ3;

[0018] Step B5, start the device under a large longitudinal magnetic field, or operate under the current conditions unchanged, and after the continuous operation time t2, set the pumping rate R op0 , there is no large magnetic field in the horizontal direction, let |ΔS|<Δ2, and use the dichotomy method to determine the current compensation magnetic field B z1 ;

[0019] Step B6, after waiting for a period of time t3, determine the compensation magnetic field B at this time z2 , judge |B z1 -B z2 |<Δ3 is true, if yes, jump to step 8, if no, jump to step B7;

[0020] Step B7, determining whether to perform pumping or relaxation action according to the change of the compensation magnetic field, and jumping to step B5;

[0021] Step 8, reaching the target polarization state of the atomic ensemble;

[0022] Step 9, end the program.

[0023] By increasing the ratio of pumping rate to relaxation rate, the device can quickly reach a steady state of polarization rate during startup; or by comprehensively adjusting the pumping rate and relaxation rate, the device can be stabilized as soon as possible after the pumping light working conditions are changed; or by reasonably selecting control parameters, the efficiency of the device reaching the working state can be more than doubled.

[0024] By utilizing the characteristics of the light field, a higher pumping rate is used to quickly pump to the working point when the nuclear spin polarization rate has not reached the target value; and / or, by utilizing the characteristics of the magnetic field, a large transverse magnetic field is applied when the nuclear spin polarization rate exceeds the target value to quickly relax to the working point.

[0025] The duration of the continuous action t1 and / or t2 is determined by the specific working conditions and is set to a fixed value or a decaying series number to ensure that the time step can be shortened when approaching the working state and the steady-state accuracy can be improved.

[0026] The system device includes an air chamber that carries an atomic ensemble, an oven that wraps the air chamber and provides an operating temperature, a three-axis magnetic field coil generator that provides a spatial magnetic field means for manipulating atoms, and a multi-layer magnetic shielding tube that is used to shield the external environmental magnetic field to provide a stable internal magnetic field environment. The longitudinal pumping light input side of the air chamber is connected to a pumping laser through a 1 / 4 wave plate and a pumping beam expander lens group in sequence, the transverse detection light input side of the air chamber is connected to a detection laser through a reflector, a detection beam expander lens group and a polarizer in sequence, the detection light output side of the air chamber is connected to a polarization beam splitter prism, the transmitted light of the polarization beam splitter prism is connected to the positive input end of a differential detection circuit through a first photodetector, the reflected light of the polarization beam splitter prism is connected to the negative input end of the differential detection circuit through a second photodetector, and the output end of the differential detection circuit is connected to a host computer.

[0027] The steady-state value of the electron spin polarization of alkali metal atoms is affected by the combined effect of optical pumping and alkali metal atom relaxation, and its expression is:

[0028]

[0029] in represents the steady-state value of the electron spin polarization of the alkali metal atom, R op is the optical pumping rate, R rel is the electron relaxation rate, R tot is the total electron relaxation rate.

[0030] The steady-state value of the nuclear spin polarization rate of the noble gas atom is affected by the combined effects of the alkali metal atom collision and the relaxation of the noble gas atom, and its expression is:

[0031]

[0032] in represents the steady-state value of the nuclear spin polarization of the noble gas atoms, is the pumping rate of the electron spin of the alkali metal atom to the nuclear spin of the noble gas atom, is the longitudinal relaxation time of the nuclear spin, which is usually dominated by the electric quadrupole relaxation and is related to the gas pressure of the atomic ensemble.

[0033] Using a three-axis magnetic field coil generator, a small peak-to-peak value ΔB is applied on the Y axis. y The low-frequency square wave magnetic field is used to obtain the steady-state difference ΔS of the measurement signal corresponding to the high-level and low-level magnetic fields on the X-axis. The ratio of the two is:

[0034]

[0035] Where, ΔB y represents the amplitude of the low-frequency square wave magnetic field applied in the Y-axis direction, ΔS represents the difference of the X-axis steady-state response signal corresponding to the Y-axis square wave magnetic field, the first factor K on the right side of the equation represents the constant related to optical and electrical factors, and the Z-axis polarizability of the alkali metal atom Rb Total electron relaxation rate Electron gyromagnetic ratio γ e , the density ratio of alkali metal atoms K to Rb is D r , the Z-direction optical frequency shift of K atoms Z-direction optical frequency shift of Rb atoms The longitudinal magnetic field B generated by the magnetic field coil at this moment z , the magnetic field compensation point B′ at the current moment z , the nuclear spin magnetic field B at this time n .

[0036] The method for rapid self-stabilization of nuclear spin polarization rate comprises the following steps:

[0037] (1) After starting the device or changing the pumping light working conditions, input relevant parameters into the closed-loop control system according to the two situations in which the magnetic field compensation point in the steady state of the system is known or unknown;

[0038] (2) The control system operates the two working conditions according to two cyclic control processes respectively. By applying transverse low-frequency magnetic field modulation to observe the signal steady-state difference ΔS and comparing the magnetic field compensation points at different times, the distance between the polarization state of the atomic ensemble at the current moment and the target steady state is determined;

[0039] (3) Pumping or relaxation is performed to continue approaching the target polarization state of the atomic ensemble. After a period of time, the action is stopped and the relevant parameters are tested again to determine whether the current round of rapid self-stabilization control of the polarization state has reached the set control accuracy. If the relevant judgment conditions are not met, this step is continuously cycled;

[0040] (4) Until the criterion in the cyclic step (3) meets the requirement of being less than a certain preset accuracy Δ, the closed-loop control is terminated. At this time, the system reaches a stable polarization state and can operate normally.

[0041] The technical effects of the present invention are as follows: compared with the prior art, the advantages of the present invention are that, after the conventional starting device or changing the pumping working conditions, the pumping rate is always a certain value, and it often takes a long time to reach the working point, and it depends on the experience of the experimenter to judge whether the system has reached a steady state through the magnetic field response of the atomic ensemble; while the method involved in the present invention utilizes the interaction between light, magnetism and atoms in the system, adopts a closed-loop control method, and comprehensively manipulates the light field and the magnetic field to quickly and automatically achieve the dynamic balance of the polarization of the atomic ensemble; by increasing the ratio of the pumping rate to the relaxation rate, the device can quickly reach the steady state of the polarization rate during the starting process; by comprehensively regulating the size of the pumping rate and the relaxation rate, the device can be stabilized as soon as possible after changing the pumping light working conditions; by reasonably selecting the control parameters, the efficiency of the device reaching the working state can be increased by more than one time; the present invention can speed up the starting speed of the device, shorten the stabilization time, save experimental manpower, and is beneficial to the atomic spin inertial measurement device to improve the experimental efficiency of scientific research, and is beneficial to its future engineering application. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic flow chart of a method for rapidly stabilizing nuclear spin polarization rate based on photomagnetic control according to the present invention. Figure 1 The process includes step 1, starting the program; step 2, setting the optical pumping rate R in the steady state of the device. op0 , input the logical relationship between ΔS and the system polarization state (ΔS is the signal steady-state difference); Step 3, whether the magnetic field compensation point B of the system in steady state is known z0 If yes, then jump to step A4; if no, then jump to step B4; Step A4, input B z0 , steady-state accuracy preset value Δ1; step A5, start the device under a large longitudinal magnetic field, or work at the steady-state magnetic field compensation point B z0 The action lasts for t1; Step A6, set the pumping rate R op0 , no large magnetic field in the horizontal direction, longitudinal magnetic field B z0 (longitudinal direction, i.e., Z-axis direction), determine whether |ΔS|<Δ1 is true, if yes, jump to step 8, if not, jump to step A7; step A7, determine whether to perform pumping or relaxation action according to the sign and algebraic value of ΔS, jump to step A5; step B4, input steady-state accuracy preset values ​​Δ2 and Δ3; step B5, start the device under a large longitudinal magnetic field, or work under the current conditions unchanged. After the action lasts for t2, set the pumping rate R op0 , there is no large magnetic field in the horizontal direction, let |ΔS|<Δ2, and use the dichotomy method to determine the current compensation magnetic field B z1Step B6, after waiting for a period of time t3, determine the compensation magnetic field B at this time z2 , judge |B z1 -B z2 |<Δ3 is true, if yes, jump to step 8, if not, jump to step B7; step B7, determine whether to perform pumping or relaxation action according to the change of the compensation magnetic field, jump to step B5; step 8, reach the target polarization state of the atomic ensemble; step 9, end the program.

[0043] Figure 2 It is a schematic diagram of the structure of an experimental system device for implementing a method for rapid self-stabilization of nuclear spin polarization rate based on optical and magnetic regulation of the present invention.

[0044] The reference numerals are listed as follows: 1-detection laser, 2-polarizer, 3-detection beam expander, 4-reflector, 5-multilayer magnetic shielding tube, 6-three-axis magnetic field coil generator, 7-oven, 8-air chamber, 9-polarization beam splitter prism, 10-first photodetector, 11-second photodetector, 12-differential detection circuit, 13-host computer, 14-1 / 4 wave plate, 15-pumping beam expander, 16-pumping laser. DETAILED DESCRIPTION

[0045] Below is the attached figure ( Figure 1-Figure 2 ) and Examples illustrate the present invention.

[0046] Figure 1 It is a schematic flow chart of a method for rapidly stabilizing nuclear spin polarization rate based on photomagnetic control according to the present invention. Figure 2 This is a schematic diagram of the experimental system structure for implementing a method for rapid self-stabilization of nuclear spin polarization rate based on optical and magnetic control of the present invention. Figure 1 to Figure 2 As shown, a method for rapid self-stabilization of nuclear spin polarization rate based on optical and magnetic regulation includes utilizing the interaction between light, magnetism and atoms in the system device, and determining whether the magnetic field compensation point B in the steady state of the system is known. z0 Different closed-loop control processes are adopted to comprehensively manipulate the light field and magnetic field to quickly achieve rapid self-stabilization of the nuclear spin polarization rate after startup or to quickly achieve dynamic balance of the atomic ensemble polarization after changing the optical pumping rate.

[0047] The following steps are included: Step 1, start the program; Step 2, set the optical pumping rate R of the device in the steady state op0 , input ΔS and the logical relationship between the system polarization state, ΔS is the signal steady-state difference; Step 3, is the magnetic field compensation point B of the system in steady state known? z0 If yes, then jump to step A4; if no, then jump to step B4; Step A4, input B z0 , steady-state accuracy preset value Δ1; step A5, start the device under a large longitudinal magnetic field, or work at the steady-state magnetic field compensation point Bz0 The action lasts for t1; Step A6, set the pumping rate R op0 , no large magnetic field in the horizontal direction, longitudinal magnetic field B z0 , longitudinal direction, i.e., Z-axis direction, determine whether |ΔS|<Δ1 is established, if yes, jump to step 8, if not, jump to step A7; step A7, determine whether to perform pumping or relaxation action according to the sign and algebraic value of ΔS, jump to step A5; step B4, input steady-state accuracy preset values ​​Δ2 and Δ3; step B5, start the device in a longitudinal large magnetic field, or work under the current conditions unchanged, and after the continuous action time t2, set the pumping rate R op0 , there is no large magnetic field in the horizontal direction, let |ΔS|<Δ2, and use the dichotomy method to determine the current compensation magnetic field B z1 Step B6, after waiting for a period of time t3, determine the compensation magnetic field B at this time z2 , judge |B z1 -B z2 |<Δ3 is true, if yes, jump to step 8, if not, jump to step B7; step B7, determine whether to perform pumping or relaxation action according to the change of the compensation magnetic field, jump to step B5; step 8, reach the target polarization state of the atomic ensemble; step 9, end the program.

[0048] By increasing the ratio of pumping rate to relaxation rate, the device can quickly reach the steady state of polarization rate during startup; or by comprehensively adjusting the size of pumping rate and relaxation rate, the device can be stabilized as soon as possible after changing the working conditions of pumping light; or by reasonably selecting control parameters, the efficiency of the device reaching the working state can be increased by more than double. By utilizing the characteristics of the light field, a higher pumping rate is used to quickly pump to the working point when the nuclear spin polarization rate has not reached the target value; by utilizing the characteristics of the magnetic field, a large transverse magnetic field is applied when the nuclear spin polarization rate exceeds the target value to quickly relax to the working point. The duration of the continuous action t1 and / or t2 is determined by the specific working conditions and is set to a fixed value or a series of attenuation to ensure that the time step can be shortened when approaching the working state and improve the steady-state accuracy.

[0049] The system device includes an air chamber 8 that carries the atomic ensemble, an oven 7 that wraps the air chamber 8 and provides the working temperature, a three-axis magnetic field coil generator 6 that provides a spatial magnetic field means for manipulating atoms, and a multi-layer magnetic shielding tube 5 that is used to shield the external environmental magnetic field to provide a stable internal magnetic field environment. The longitudinal pumping light input side of the air chamber 8 is connected to the pumping laser 16 through a 1 / 4 wave plate 14 and a pumping beam expander lens group 15 in sequence, and the transverse detection light input side of the air chamber 8 is connected to the detection laser 1 through a reflector 4, a detection beam expander lens group 3 and a polarizer 2 in sequence. The detection light output side of the air chamber 8 is connected to a polarization beam splitter prism 9, and the transmitted light of the polarization beam splitter prism 9 is connected to the positive input end (+) of the differential detection circuit 12 through a first photodetector 10, and the reflected light of the polarization beam splitter prism 9 is connected to the negative input end (-) of the differential detection circuit 12 through a second photodetector 11, and the output end of the differential detection circuit 12 is connected to a host computer 13.

[0050] The steady-state value of the electron spin polarization of alkali metal atoms is affected by the combined effect of optical pumping and alkali metal atom relaxation, and its expression is:

[0051]

[0052] in represents the steady-state value of the electron spin polarization of the alkali metal atom, R op is the optical pumping rate, R rel is the electron relaxation rate, R tot is the total electron relaxation rate. The steady-state value of the nuclear spin polarization rate of the noble gas atom is affected by the combined effects of the alkali metal atom collision and the relaxation of the noble gas atom, and its expression is:

[0053]

[0054] in represents the steady-state value of the nuclear spin polarization of the noble gas atoms, is the pumping rate of the electron spin of the alkali metal atom to the nuclear spin of the noble gas atom, T1 n is the longitudinal relaxation time of the nuclear spin, which is usually dominated by the electric quadrupole relaxation and is related to the gas pressure of the atomic ensemble. Using a three-axis magnetic field coil generator, a small peak-to-peak value ΔB is applied on the Y axis. y The low-frequency square wave magnetic field is used to obtain the steady-state difference ΔS of the measurement signal corresponding to the high-level and low-level magnetic fields on the X-axis. The ratio of the two is:

[0055]

[0056] Where, ΔB yrepresents the amplitude of the low-frequency square wave magnetic field applied in the Y-axis direction, ΔS represents the difference of the X-axis steady-state response signal corresponding to the Y-axis square wave magnetic field, the first factor K on the right side of the equation represents the constant related to optical and electrical factors, and the Z-axis polarizability of the alkali metal atom Rb Total electron relaxation rate Electron gyromagnetic ratio γ e , the density ratio of alkali metal atoms K to Rb is D r , the Z-direction optical frequency shift of K atoms Z-direction optical frequency shift of Rb atoms The longitudinal magnetic field B generated by the magnetic field coil at this moment z , the magnetic field compensation point B' at the current moment z , the nuclear spin magnetic field B at this time n .

[0057] A method for rapid self-stabilization of nuclear spin polarization rate based on optical and magnetic control, the implementation method and steps are as follows:

[0058] (1) After starting the device or changing the pumping light working conditions, input relevant parameters into the closed-loop control system according to the two situations in which the magnetic field compensation point in the steady state of the system is known or unknown;

[0059] (2) The control system operates the two working conditions according to two cyclic control processes respectively. By applying transverse low-frequency magnetic field modulation to observe the signal steady-state difference ΔS and comparing the magnetic field compensation points at different times, the distance between the polarization state of the atomic ensemble at the current moment and the target steady state is determined;

[0060] (3) Pumping or relaxation is performed to continue approaching the target polarization state of the atomic ensemble. After a period of time, the action is stopped and the relevant parameters are tested again to determine whether the current round of rapid self-stabilization control of the polarization state has reached the set control accuracy. If the relevant judgment conditions are not met, this step is continuously cycled;

[0061] (4) Until the criterion in the cyclic step (3) meets the requirement of being less than a certain preset accuracy Δ, the closed-loop control is terminated. At this time, the system reaches a stable polarization state and can operate normally.

[0062] The principle of the present invention is that the steady-state value of the electron spin polarization rate of the alkali metal atom is affected by the combined effect of optical pumping and alkali metal atom relaxation, and its expression is:

[0063]

[0064] Among them, the left side of the equation The superscript e and subscript 0 represent the steady-state value of the electron spin polarization of the alkali metal atom; R on the right side of the equation op is the optical pumping rate, R rel is the electron relaxation rate, Rtot is the total relaxation rate of electrons. The steady-state value of the nuclear spin polarization rate of the inert gas atoms is affected by the combined effects of the alkali metal atom collision and the relaxation of the inert gas atoms, and its expression is:

[0065]

[0066] Among them, the left side of the equation The superscript n and subscript 0 represent the steady-state value of the nuclear spin polarization rate of the noble gas atom; the right side of the equation is the pumping rate of the electron spin of the alkali metal atom to the nuclear spin of the noble gas atom, is the longitudinal relaxation time of the nuclear spin, which is usually dominated by the electric quadrupole relaxation and is related to the gas pressure of the atomic ensemble. From the above formula, it can be seen that the steady-state value of the nuclear spin polarization is related to the electron spin polarization, and when the optical pumping rate is fixed, the final steady-state value of the nuclear spin is fixed, that is, the ultimate state of the atomic ensemble is determined.

[0067] During the startup of the device, the nuclear spin polarization rate increases from zero to a steady-state value. The total pumping time is determined by the longitudinal relaxation time The relationship between nuclear spin polarization rate and pumping time is y = 1-e -t Curve, where y is the nuclear spin polarization rate, t is the pumping time, and e is a natural constant. As the second-order derivative of the curve is less than zero, it can be seen that when the pumping time is in the first half of the curve, the polarization rate rises faster; when it is in the second half of the curve, the speed at which the polarization rate tends to the steady state slows down, and it takes more time to reach the working point. Under the condition that the relaxation rate of the same atomic ensemble remains unchanged, the optical pumping rate R op1 , R op2 (and R op1 >R op2 The nuclear spin polarization intensity increases from zero to steady state under the two pumping rates. The relationship between the steady-state values ​​of nuclear spin polarization under the two pumping rates is: That is, the higher the optical pumping rate, the greater the nuclear spin polarization intensity achieved in the steady state. In the first half of the optical pumping, the optical pumping rate R op1 The corresponding nuclear spin polarization rate growth rate is greater than R op2 , that is, the former takes less time to achieve the same polarization rate during the pumping process. Therefore, the above-mentioned light field characteristics can be used to quickly pump to the working point by using a higher pumping rate when the nuclear spin polarization rate has not reached the target value.

[0068] When the actual nuclear spin polarization rate exceeds the target polarization rate, the light field can also be manipulated to reduce the polarization rate, that is, the nuclear spin is relaxed by reducing the pumping rate. However, when using the light field method, the polarization rate decays in the longitudinal direction, and the speed is slow. The magnetic field can also be manipulated to relax it, and a large magnetic field is applied in the transverse direction perpendicular to the nuclear spin polarization and magnetic moment, so that the nuclear spin feels the main magnetic field that deviates from its quantized main axis, destroying its polarization state. At this time, P n The transverse component of Attenuation, while Much smaller than Therefore, the polarization rate decays much faster in the transverse direction than in the longitudinal direction, causing the nuclear spin to depolarize quickly. Therefore, the above magnetic field characteristics can be used to apply a large transverse magnetic field when the nuclear spin polarization rate exceeds the target value to quickly relax to the working point.

[0069] like Figure 1 , Figure 2 As shown, the specific implementation steps of the present invention are as follows:

[0070] (1) After starting the device or changing the pumping light operating point, the optical pumping rate R required to maintain the target polarization state of the system is first input into the closed-loop control system. op0 , as a control reference value. When changing the pumping working conditions of the device, R op0 That is the changed optical pumping rate.

[0071] (2) The atomic spin inertial measurement device uses an air chamber to carry the atomic ensemble, an oven wraps the air chamber and provides the working temperature, a three-axis magnetic field coil generator provides a spatial magnetic field means for manipulating atoms, and a multi-layer magnetic shielding tube is used to shield the external environmental magnetic field to provide a stable internal magnetic field environment. The device uses a beam of circularly polarized pumping light that has been expanded along the Z-axis direction to polarize the atomic spins. The polarization direction of the atomic ensemble is also called the longitudinal direction; a beam of linearly polarized detection light that has been expanded along the X-axis direction is transmitted through the atomic air chamber, and the angular velocity signal on the Y-axis is output through a balanced differential detection processing method. The X-axis and Y-axis are both perpendicular to the longitudinal direction, so it is called the transverse direction. Using a magnetic field generating device composed of a three-axis coil, a small peak-to-peak value ΔB is applied on the Y-axis. y The low-frequency square wave magnetic field can be used to obtain the steady-state difference ΔS of the measurement signal corresponding to the high-level and low-level magnetic fields output on the X-axis. According to theoretical derivation, the ratio of the two is:

[0072]

[0073] Among them, ΔB on the left side of the equation y represents the amplitude of the low-frequency square wave magnetic field applied in the Y-axis direction, ΔS represents the difference of the X-axis steady-state response signal corresponding to the Y-axis square wave magnetic field; the first factor K on the right side of the equation represents a constant related to factors such as light and electricity, and the second and third factors include the Z-direction polarizability of the alkali metal atom Rb Total electron relaxation rate Electron gyromagnetic ratio γ e , the density ratio of alkali metal atoms K and Rb D r , Z-direction optical frequency shift of K atoms Z-direction optical frequency shift of Rb atoms The longitudinal magnetic field B generated by the magnetic field coil at this moment z , the magnetic field compensation point B′ at the current moment z , the nuclear spin magnetic field B at this time n It can be found that when the coil magnetic field B is set z Equal to the actual magnetic field compensation point B' at this moment z When B z -B′ z =0, then And by ΔB y ≠0, we get ΔS=0, which means that the output measurement signal is insensitive to the transverse interference magnetic field, which meets the definition of the nuclear spin self-compensation point. Then, at each moment, we can get the magnetic field compensation point B′ at that time by commanding ΔS=0. z On the other hand, how to judge B when the signal difference ΔS deviates from the zero point z and B′ z How to judge whether the current polarization state has not been reached or exceeded is generally determined by the specific device structure. Therefore, it is necessary to input the positive and negative signs of ΔS into the closed-loop system and the logical relationship between whether the target polarization state of the atomic ensemble has been reached: if ΔS>0 means that the target polarization state has been exceeded, then ΔS<0 means that the target polarization state has not been reached. The larger the algebraic value of ΔS, the more the system deviates from the operating point, and the longer the pumping or relaxation operation time is required.

[0074] (3) Generally speaking, for an atomic ensemble, when other conditions remain unchanged, the magnitude of the optical pumping rate determines the magnitude of the nuclear polarization rate of the system in the steady state, that is, the optical pumping rate corresponds to the steady-state magnetic field compensation point. Therefore, the preliminary experimental data of the device can be summarized to set the pumping working conditions R of the device. op0 After that, the corresponding steady-state magnetic field compensation point B is synchronously input into the closed-loop control system. z0 As a reference for the system to reach a steady state. When there is a lack of relevant experimental data, the method of comparing the magnetic field compensation points at different times can be used to determine whether the system has reached a working state.

[0075] (4) In fact, closed-loop control has precision limitations. Therefore, when executing the control system, it is necessary to input a steady-state precision preset value Δ1 (applied to Figure 1 Steady-state compensation point B z0 ), or input Δ2 and Δ3 (applied to Figure 1 Steady-state compensation point B z0Right control loop when unknown). At this time, the control system uses the absolute value of the steady-state signal |ΔS|<Δ1 or the absolute difference between the magnetic field compensation points at two moments |B z1 -B z2 |<Δ3 is used as a criterion to measure whether the atomic ensemble has reached the target polarization state.

[0076] (5) Known steady-state magnetic field compensation point B z0 When the device is in the startup process, ensure that the atomic ensemble is in a longitudinal large magnetic field environment, which is to bind the atomic spins in the longitudinal main magnetic field direction and speed up the pumping efficiency. If the device has just changed the pumping working conditions, ensure that it has been working at the steady-state magnetic field compensation point B. z0 The action duration t1 is determined by the specific working conditions and can be set to a fixed value or a decaying series number to ensure that the time step can be shortened when approaching the working state and improve the steady-state accuracy. Next, the system performs the "judgment" process: the pumping rate is placed at R op0 , cancel the large transverse magnetic field (if any), and place the longitudinal magnetic field at B z0 , at this time, a low-frequency square wave magnetic field is added to the Y axis to obtain the current steady-state signal difference ΔS. If |ΔS|<Δ1 holds, it proves that the target steady state has been reached, and the loop can be exited to end the program. If the condition is not met, the control system will proceed with the "action" process: according to the sign and algebraic value of ΔS, it is determined whether to perform pumping or relaxation action. The pumping action will increase the pumping rate R op0 Increase to a certain appropriate value, the relaxation action will add a large magnetic field of appropriate value in the horizontal direction. Then the control system returns to the "resetting" process: ensure that the system is always in a large longitudinal magnetic field when it starts, and the system always works at the steady-state magnetic field compensation point B when the pumping working conditions are changed. z0 The action continues for a duration of t1.

[0077] (6) Steady-state magnetic field compensation point B z0 When it is unknown, input the preset steady-state accuracy values ​​Δ1 and Δ2 to the control system. The closed-loop control system follows the cyclic control process of "determination-judgment-action-redetermination". Specifically, the control system first performs the initial "determination" process: ensure that the atomic ensemble is pumped in a longitudinal large magnetic field environment when the device is in the startup process, or ensure that other working conditions remain unchanged after the device changes the pumping rate. After the continuous action time t2, the pumping rate is placed at R op0 , cancel the large lateral magnetic field (if any), apply Y-direction square wave magnetic field modulation, change the Z-direction magnetic field compensation point to make |ΔS|<Δ2, and use the bisection method to approximate the magnetic field compensation point B at the current moment z1Next, the system performs the "judgment" process: the device is placed at the magnetic field compensation point B z1 After a period of time, test again to get a new magnetic field compensation point B z2 If |B z1 -B z2 |<Δ3 holds true, it means that the steady state has been reached and the program can be terminated. If the inequality does not hold true, the control system will proceed with the "action" process: according to the magnetic field compensation point from B z1 Change to B z2 The control system then returns to the "redetermine" process and continues the cycle according to the above steps.

[0078] 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 method for rapid self-stabilization of nuclear spin polarization rate based on optical and magnetic regulation, characterized in that: It includes using the interaction between light, magnetism and atoms in the system device, and according to whether the magnetic field compensation point B in the steady state of the system is known z0 Different closed-loop control processes are used to comprehensively manipulate the optical and magnetic fields to quickly achieve rapid self-stabilization of the nuclear spin polarization rate after startup or to quickly achieve dynamic balance of the atomic ensemble polarization after changing the optical pumping rate; The following steps are involved: Step 1, start the program; Step 2: Set the optical pumping rate R at steady state op0 , the logical relationship between input ΔS and the system polarization state, ΔS is the signal steady-state difference; Step 3: Is the magnetic field compensation point B of the system in steady state known? z0 If yes, then jump to step A4; if no, then jump to step B4; Step A4, input B z0 , steady-state accuracy preset value Δ1; Step A5: Start the device under a large longitudinal magnetic field, or operate at a steady-state magnetic field compensation point B. z0 Next, the action lasts for t1; Step A6, set the pumping rate R op0 , no large magnetic field in the horizontal direction, longitudinal magnetic field B z0 , vertical direction, i.e., Z-axis direction, determine whether |ΔS|<Δ1 holds, if yes, jump to step 8, if no, jump to step A7; Step A7, determining whether to perform pumping or relaxation action according to the sign and algebraic value of ΔS, and jumping to step A5; Step B4, inputting the preset steady-state accuracy values ​​Δ2 and Δ3; Step B5, start the device under a large longitudinal magnetic field, or operate under the current conditions unchanged, and after the continuous operation time t2, set the pumping rate R op0 , there is no large magnetic field in the horizontal direction, let |ΔS|<Δ2, and use the dichotomy method to determine the current compensation magnetic field B z1 ; Step B6, after waiting for a period of time t3, determine the compensation magnetic field B at this time z2 , judge |B z1 -B z2 |<Δ3 is true, if yes, jump to step 8, if no, jump to step B7; Step B7, determining whether to perform pumping or relaxation action according to the change of the compensation magnetic field, and jumping to step B5; Step 8, reaching the target polarization state of the atomic ensemble; Step 9, end the program.

2. The method for rapid self-stabilization of nuclear spin polarization rate based on optical and magnetic control according to claim 1, characterized in that: By increasing the ratio of pumping rate to relaxation rate, the device can quickly reach the steady state of polarizability during startup; Either by comprehensively regulating the pumping rate and relaxation rate, the device can be stabilized as soon as possible after the pumping light working conditions are changed; or by reasonably selecting control parameters, the efficiency of the device in the working state can be increased by more than double.

3. The method for rapid self-stabilization of nuclear spin polarization rate based on optical and magnetic control according to claim 1, characterized in that: By utilizing the characteristics of the light field, a higher pumping rate is used to quickly pump to the working point when the nuclear spin polarization rate has not reached the target value; and / or, by utilizing the characteristics of the magnetic field, a large transverse magnetic field is applied when the nuclear spin polarization rate exceeds the target value to quickly relax to the working point.

4. The method for rapid self-stabilization of nuclear spin polarization rate based on optical and magnetic control according to claim 1, characterized in that: The duration of the continuous action t1 and / or t2 is determined by the specific working conditions and is set to a fixed value or a decaying series number to ensure that the time step can be shortened when approaching the working state and the steady-state accuracy can be improved.

5. The method for rapid self-stabilization of nuclear spin polarization rate based on optical and magnetic control according to claim 1, characterized in that: The system device includes an air chamber that carries an atomic ensemble, an oven that wraps the air chamber and provides an operating temperature, a three-axis magnetic field coil generator that provides a spatial magnetic field means for manipulating atoms, and a multi-layer magnetic shielding tube that is used to shield the external environmental magnetic field to provide a stable internal magnetic field environment. The longitudinal pumping light input side of the air chamber is connected to a pumping laser through a 1 / 4 wave plate and a pumping beam expander lens group in sequence, the transverse detection light input side of the air chamber is connected to a detection laser through a reflector, a detection beam expander lens group and a polarizer in sequence, the detection light output side of the air chamber is connected to a polarization beam splitter prism, the transmitted light of the polarization beam splitter prism is connected to the positive input end of a differential detection circuit through a first photodetector, the reflected light of the polarization beam splitter prism is connected to the negative input end of the differential detection circuit through a second photodetector, and the output end of the differential detection circuit is connected to a host computer.

6. The method for rapid self-stabilization of nuclear spin polarization rate based on optical and magnetic control according to claim 1, characterized in that: The steady-state value of the electron spin polarization of alkali metal atoms is affected by the combined effect of optical pumping and alkali metal atom relaxation, and its expression is: in represents the steady-state value of the electron spin polarization of the alkali metal atom, R op is the optical pumping rate, R rel is the electron relaxation rate, R tot is the total electron relaxation rate.

7. The method for rapid self-stabilization of nuclear spin polarization rate based on optical and magnetic control according to claim 1, characterized in that: The steady-state value of the nuclear spin polarization rate of the noble gas atom is affected by the combined effects of the alkali metal atom collision and the relaxation of the noble gas atom, and its expression is: in represents the steady-state value of the nuclear spin polarization of the noble gas atoms, is the pumping rate of the electron spin of the alkali metal atom to the nuclear spin of the noble gas atom, is the longitudinal relaxation time of the nuclear spin, which is dominated by the electric quadrupole relaxation and is related to the gas pressure of the atomic ensemble.

8. The method for rapid self-stabilization of nuclear spin polarization rate based on optical and magnetic control according to claim 1, characterized in that: Using a three-axis magnetic field coil generator, a small peak-to-peak value ΔB is applied on the Y axis. y The low-frequency square wave magnetic field is used to obtain the steady-state difference ΔS of the measurement signal corresponding to the high-level and low-level magnetic fields on the X-axis. The ratio of the two is: Where, ΔB y represents the amplitude of the low-frequency square wave magnetic field applied in the Y-axis direction, ΔS represents the difference of the X-axis steady-state response signal corresponding to the Y-axis square wave magnetic field, the first factor K on the right side of the equation represents a constant related to optical and electrical factors, and the Z-direction polarizability of the alkali metal atom Rb Total electron relaxation rate Electron gyromagnetic ratio γ e , the density ratio of alkali metal atoms K to Rb is D r , the Z-direction optical frequency shift of K atoms Z-direction optical frequency shift of Rb atoms The longitudinal magnetic field B generated by the magnetic field coil at this moment z , the magnetic field compensation point B′ at the current moment z , the nuclear spin magnetic field B at this time n .

9. A method for rapid self-stabilization of nuclear spin polarization rate based on optical and magnetic regulation, characterized in that: It includes using the interaction between light, magnetism and atoms in the system device, and according to whether the magnetic field compensation point B in the steady state of the system is known z0 Different closed-loop control processes are used to comprehensively manipulate the optical and magnetic fields to quickly achieve rapid self-stabilization of the nuclear spin polarization rate after startup or to quickly achieve dynamic balance of the atomic ensemble polarization after changing the optical pumping rate; The method for rapid self-stabilization of nuclear spin polarization rate comprises the following steps: (1) After starting the device or changing the pumping light working conditions, input relevant parameters into the closed-loop control system according to the two situations in which the magnetic field compensation point in the steady state of the system is known or unknown; (2) The control system operates the two working conditions according to two cyclic control processes respectively. By applying transverse low-frequency magnetic field modulation to observe the signal steady-state difference ΔS and comparing the magnetic field compensation points at different times, the distance between the polarization state of the atomic ensemble at the current moment and the target steady state is determined; (3) Pumping or relaxation is performed to continue approaching the target polarization state of the atomic ensemble. After a period of time, the action is stopped and the relevant parameters are tested again to determine whether the current round of rapid self-stabilization control of the polarization state has reached the set control accuracy. If the relevant judgment conditions are not met, this step is continuously cycled; (4) Until the criterion in the cyclic step (3) meets the requirement of being less than a certain preset accuracy Δ, the closed-loop control is terminated. At this time, the system reaches a stable polarization state and can operate normally.

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