Method for stable control of polarizability of atomic spin ensemble based on high-frequency pulsed light pumping

Abstract

Based on the high-frequency pulse light pumping, the atomic spin ensemble polarization rate stable control method is used to polarize the electron spin ensemble with high-frequency and high-power circularly polarized resonance laser pulse. In order to ensure the relative stability of the electron spin ensemble polarization rate, the influence of the pulse laser parameters on the electron spin ensemble polarization rate is calculated. The signal obtained by amplifying and low-pass filtering the feedback light through the photoelectric detector is used as the feedback signal of the equivalent pumping rate. The proportional-integral-derivative control strategy is adopted to adjust the duty cycle or laser power of the pulse light to stabilize the equivalent pumping rate and the longitudinal polarization rate of the electron spin ensemble. This method can suppress the influence of traditional high-power pumping on the system scaling factor and achieve stable control of the electron spin ensemble polarization rate. It can be used in the fields of optically pumped magnetometer, SERF magnetometer and SERF atomic spin gyroscope, and has strong expandability and practical value.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of optical pumping atomic polarization, and particularly relates to a method for stably controlling polarization rate of an atomic spin ensemble based on high-frequency pulsed optical pumping. BACKGROUND

[0002] The atomic cell containing alkali metal elements and inert gas is a core sensitive component of devices such as atomic magnetometers, atomic gyroscopes and atomic clocks. Based on the interaction between the electron spin ensemble (or atomic spin ensemble) or nuclear spin in the atomic cell and the optical field and the magnetic field, the magnetic field, angular velocity or time and frequency can be measured. The circularly polarized laser interacts with the alkali metal electrons, and the angular momentum of the photons is transmitted to the electron spin ensemble, so that the optical pumping atomic polarization of the electron spin ensemble is carried out.

[0003] In practical applications, the optical pumping atomic polarization often has the following requirements: 1. The pumping rate of the circularly polarized laser directly affects the polarization rate of the electron spin ensemble, and in practical applications, the pumping rate of the laser often needs to be stably controlled to stabilize the polarization rate of the electron spin ensemble. 2. The atom has an absorption effect on the pumping laser, which will bring about the non-uniformity of the polarization rate component of the electron spin ensemble in the pumping light direction, and in practical applications, a pumping light with a relatively large power is often used to overcome the non-uniformity of the polarization rate distribution, but a large pumping light power will weaken the useful signal output of the system and reduce the sensitivity and signal-to-noise ratio of the system. SUMMARY

[0004] The problem solved by the present application is that the present application proposes a method for stably controlling the polarization rate of an atomic spin ensemble based on high-frequency pulsed optical pumping, which polarizes the electron spin ensemble in the form of pulsed light, thereby improving the uniformity of the polarization rate of the electron spin ensemble in the pumping light direction; the duty cycle of the pumping light is adjusted by using an acousto-optic modulator (AOM) optical switch or an electro-optic modulator (EOM) optical switch, the pumping rate of the pumping light is adjusted and stabilized, the useful signal output of the system is ensured not to be affected by the large-power pumping light, and the long-term stability of the signal-to-noise ratio of the system is improved.

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

[0006] The method for stably controlling the polarization rate of an atomic spin ensemble based on high-frequency pulsed optical pumping comprises converting the pumping laser from a pumping laser into pulsed pumping laser by setting an optical switch in the pumping light path, polarizing the electron spin ensemble in the atomic cell by the pulsed pumping laser to improve the uniformity of the polarization rate of the electron spin ensemble in the pumping light direction, adjusting the duty cycle and / or the pulsed laser pumping rate of the pulsed pumping laser to adjust the equivalent pumping rate of the pumping laser on the electron spin ensemble, and then stably controlling the polarization rate of the atomic spin ensemble.

[0007]

[0008] wherein T represents the pulse period of the pulsed pump laser, represents the maximum longitudinal polarization rate of the electron spin ensemble, the longitudinal direction being the Z-axis direction, represents the minimum longitudinal polarization rate of the electron spin ensemble, R p0 α represents the equivalent pumping rate, R p0 represents the pumping rate of the pump laser, and α represents the duty cycle of the pulsed laser generated after the pump laser passes through the optical switch, represents the longitudinal relaxation rate of the electron.

[0009]

[0010] wherein R p (t) represents the pulsed light pumping rate as a function of time t, and n represents a positive integer.

[0011] The input side of the optical switch is connected to the pump laser through sequential connection of a first polarizer, a first 1 / 2 wave plate, and a pump beam expander, the output side of the optical switch is sequentially connected to a first polarizing beam splitter prism through a second polarizer and a first mirror, the feedback light of the first polarizing beam splitter prism is connected to an optical switch controller through a photoelectric detection amplifier, the optical switch controller is connected to the optical switch, and the main light of the first polarizing beam splitter prism sequentially passes through a 1 / 4 wave plate and an atomic cell.

[0012] The optical switch adopts an AOM acousto-optic modulator optical switch or an EOM electro-optic modulator optical switch, and the optical switch controller adopts a PID proportional-differential-integral control method to adjust the duty cycle of the pulsed laser.

[0013] The periphery of the atomic cell is sequentially provided with a heating oven, a coil framework supported thereby, a ferrite shielding layer, and a permalloy shielding layer.

[0014] The detection light input side of the atomic cell is sequentially connected to a detection laser through a second polarizer and a detection beam expander, and the detection light output side of the atomic cell is sequentially connected to a data acquisition system through a Wollaston prism and a differential amplifier.

[0015] The method comprises the following steps:

[0016] (1) High-power laser input: In order to strengthen the interaction between light and atomic spins, the frequency of the laser needs to be tuned to the resonance frequency between the ground state and the excited state of the alkali metal electrons. And the pumping rate generated by the power should be several times the relaxation rate of the atomic / electron spin ensemble, and the optical power density is 200 mW / cm 3 above;

[0017] (2) The optical switch generates pulsed light: when the system is pumped by pulsed light, the pumping rate Rp (t) is a function of time t, R p0 is the pumping rate of the pumping laser, α is the duty cycle of the pulse laser generated by the pumping laser after passing through the optical switch, T is the time period of the laser pulse, the frequency of the high-frequency pulse laser pulse should be higher than 10 kHz, N is an integer greater than or equal to 0:

[0018]

[0019] The maximum value and the minimum value of the longitudinal polarization rate of the electron spin ensemble in the quasi-steady state of the system can be expressed as follows, where e represents the natural constant, represents the longitudinal relaxation rate of the electron, and Q is the electron spin ensemble slowing factor:

[0020]

[0021]

[0022] Taking a very short pulse period, i.e. T tends to 0, makes the maximum value of the polarization rate and the minimum value of the polarization rate converge to the same value, where R p0 α is the equivalent pumping rate, and by controlling the equivalent pumping rate, the polarization rate of the electron spin ensemble can be changed:

[0023]

[0024] (3) A polarization device is used to generate linear polarization of the pulse laser, and then a polarization beam splitter prism is used to divide the polarized laser into feedback light and main path light. The feedback light is converted into an electrical signal by a photoelectric detection amplifier, and the main path light passes through a λ / 4 wave plate with an angle of 45° between the fast axis and the linear polarization plane to generate circularly polarized light, which polarizes the electron spin ensemble;

[0025] (4) A proportional-integral-derivative (PID) control strategy is used to generate a control signal: the direct current component of the electrical signal output by the photoelectric detection amplifier is proportional to the equivalent pumping rate, and the direct current component is a closed-loop feedback quantity. By adjusting the pumping light intensity or the duty cycle using the PID control strategy, the error between the feedback quantity and the set value can be zeroed, thereby stably controlling the equivalent pumping rate;

[0026] (5) Adjusting the pulse light power or duty cycle: according to the control signal, the pumping rate R p0 or the duty cycle α of the pumping laser is adjusted by driving the optical switch, so as to adjust the equivalent pumping rate R p0 ​Alpha. Since the system requires the frequency of the pulsed light to be greater than 10 kHz, the modulator that can be used includes an acousto-optic modulator (AOM) optical switch or an electro-optic modulator (EOM) optical switch.

[0027] The high-power pumping laser is pulsed modulated, and when the modulation frequency is high, the polarization rate of the electron spin ensemble tends to be stable; by adjusting the pumping rate and the duty cycle of the pulsed laser, the equivalent pumping rate of the pulsed laser on the electron spin ensemble can be adjusted and stably controlled. Meanwhile, the high pumping rate can reduce the longitudinal polarization gradient of the electron spin ensemble.

[0028] The technical effects of the present application are as follows: the present application is based on the atomic spin ensemble polarization rate stable control method of high-frequency pulsed light pumping, and high-frequency and high-power circularly polarized resonant laser pulses are used to polarize the electron spin ensemble. In order to ensure the relative stability of the electron spin ensemble polarization rate, the influence of the pulsed laser parameters on the electron spin ensemble polarization rate is calculated. The signal obtained by amplifying and low-pass filtering the feedback light through the photoelectric detector is used as the feedback signal of the equivalent pumping rate. A proportional-integral-derivative control strategy is adopted to adjust the duty cycle or the laser power of the pulsed light to stabilize the equivalent pumping rate and the longitudinal polarization rate of the electron spin ensemble. This method can suppress the influence of traditional high-power pumping on the system scaling factor, and can realize the stable control of the electron spin ensemble polarization rate. It can be used in the fields of optical pumping magnetometers, SERF magnetometers, SERF atomic spin gyroscopes, etc., and has strong expandability and practical value.

[0029] The characteristics of the present application are as follows: atoms have the effect of absorbing pumping laser, which will bring about the non-uniformity of the polarization rate component of the electron spin ensemble in the direction of the pumping light. In general optical pumping systems, a pumping light with a relatively large power is needed to overcome the non-uniformity of the polarization rate distribution. However, a large pumping light power will weaken the useful signal output of the system and reduce the sensitivity and signal-to-noise ratio of the system. The present application proposes an atomic spin ensemble polarization rate stable control method based on high-frequency pulsed light pumping. The electron spin ensemble is polarized by using pulsed light, which improves the uniformity of the polarization rate of the electron spin ensemble in the direction of the pumping light. The duty cycle of the pumping light is adjusted by using an acousto-optic modulator (AOM) or an electro-optic modulator (EOM) optical switch, and the pumping rate of the pumping light is adjusted and stabilized to ensure that the useful signal output of the system is not affected by the large-power pumping light and to improve the long-term stability of the signal-to-noise ratio of the system. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a flowchart of the atomic spin ensemble polarization rate stable control method based on high-frequency pulsed light pumping of the present application. Figure 1 Step 1 in includes high-power laser generation (for example, the optical power density is 200 mW / cm 3The above); Step 2, the laser generates pulsed laser (for example, the pulse frequency is above 10 kHz) through the high-frequency optical switch; Step 3, the feedback light is amplified through photoelectric detection and then low-pass filtered to generate a feedback signal (the polarizing beam splitter divides the polarized laser into feedback light and main light, for example Figure 2 The feedback light 12 of the polarizing beam splitter 11, and the main light 21); Step 4, the duty cycle of the pulsed laser is adjusted by the PID control method (PID, proportional, integral, and derivative), so as to stabilize the equivalent pumping rate of the laser on the electron spin; Step 5, the main light passes through the PBS and the 1 / 4 wave plate to generate circularly polarized light to pump the polarized electron spin (PBS, Polarizing Beam Splitter).

[0031] Figure 2 is a system structure schematic diagram of the atomic spin ensemble polarization rate stable control method based on high-frequency pulsed light pumping according to the present application.

[0032] The reference signs are listed as follows: 1, pumping laser; 2, pumping beam expander (including two lenses); 3, first 1 / 2 wave plate (or λ / 2 wave plate); 4, first polarizer; 5, optical switch (using AOM optical switch or EOM optical switch, AOM, acousto-optic modulator, EOM, Electro-Optic Modulator); 6, second polarizer; 7, first mirror; 8, optical switch controller; 9, pumping laser (referring to the entire pumping light or specifically the pumping light path between the pumping laser 1 and the optical switch 5); 10, pulsed pumping laser (specifically referring to the pumping light path after the optical switch 5); 11, first polarizing beam splitter; 12, feedback light; 13, 1 / 4 wave plate (λ / 4 wave plate); 14, data acquisition system; 15, detection laser; 16, detection beam expander (including two lenses); 17, second polarizer; 18, second 1 / 2 wave plate; 19, Wollaston prism; 20, differential amplifier; 21, main light; 22, permalloy shielding layer; 23, ferrite shielding layer; 24, atomic gas chamber; 25, heating oven; 26, coil framework and its support; 27, xyz Cartesian coordinate system. DETAILED DESCRIPTION

[0033] The present application will be described below in conjunction with the accompanying drawings Figures 1-2 ) and examples.

[0034] Figure 1 is a flowchart schematic diagram of the atomic spin ensemble polarization rate stable control method based on high-frequency pulsed light pumping according to the present application. Figure 2 is a system structure schematic diagram of the atomic spin ensemble polarization rate stable control method based on high-frequency pulsed light pumping according to the present application. Reference Figures 1-2As shown, the atomic spin ensemble polarization rate stable control method based on high-frequency pulsed light pumping includes converting the pumping laser from the pumping laser into pulsed pumping laser by setting an optical switch in the pumping light path, the pulsed pumping laser polarizes the electron spin ensemble in the atomic cell to improve the polarization rate uniformity of the electron spin ensemble in the pumping light direction, and adjusts the equivalent pumping rate of the pumping laser on the electron spin ensemble by adjusting the duty cycle and / or pulse laser pumping rate of the pulsed pumping laser, thereby realizing stable control of the atomic spin ensemble polarization rate.

[0035]

[0036] wherein T represents the pulse period of the pulsed pumping laser, represents the maximum longitudinal polarization rate of the electron spin ensemble, the longitudinal direction being the Z-axis direction, represents the minimum longitudinal polarization rate of the electron spin ensemble, R p0 α represents the equivalent pumping rate, R p0 represents the pumping rate of the pumping laser, and α represents the pulse laser duty cycle generated by the pumping laser after passing through the optical switch, represents the longitudinal relaxation rate of the electron.

[0037]

[0038] wherein R p (t) represents the pulse light pumping rate as a function of time t, and n represents a positive integer.

[0039] The input side of the optical switch 5 is connected to the pumping laser 1 by sequentially connecting a first polarizer 4, a first 1 / 2 wave plate 3 and a pumping beam expander 2, the output side of the optical switch 5 is connected to a first polarization beam splitter prism 11 through a second polarizer 6 and a first mirror 7 in sequence, the feedback light 12 of the first polarization beam splitter prism 11 is connected to an optical switch controller 8 through a photoelectric detection amplifier, the optical switch controller 8 is connected to the optical switch 5, and the main light 21 of the first polarization beam splitter prism 11 sequentially passes through a 1 / 4 wave plate 13 and an atomic cell 24. The optical switch 5 uses an AOM acousto-optic modulator optical switch or an EOM electro-optic modulator optical switch, and the optical switch controller 8 adopts a PID proportional-differential-integral control method to adjust the duty cycle of the pulsed laser. The periphery of the atomic cell 24 is sequentially provided with a heating oven 25, a coil framework and a support 26, a ferrite shielding layer 23 and a permalloy shielding layer 22. The detection light input side of the atomic cell 24 is connected to a detection laser 15 through a second polarizer 17 and a detection beam expander 16 in sequence, and the detection light output side of the atomic cell 24 is connected to a data acquisition system 14 through a Wollaston prism 19 and a differential amplifier 20 in sequence.

[0040] The dynamic equations of optically pumped atomic polarization and Larmor precession of atoms in an external magnetic field can be approximately described by the following Bloch equation:

[0041]

[0042] exist Figure 2 In the Cartesian coordinate system, the incident direction of the pumping light is parallel to the z-axis, and the incident direction of the detection light is parallel to the x-axis; "×" represents vector cross product; t is time; the electron spin ensemble polarizability in are the three coordinate axis components of the electronic polarizability; γ e is the gyromagnetic ratio of the electron spin ensemble; Q is the slowing factor of the electron spin ensemble; the pumping rate of the pulsed laser into the cylinder R p (t), photon polarizability S p ; Pumping rate R of detection light m , photon polarizability S m ; External magnetic field B={B x ,B y ,B z} and its three-axis components B x ,B y ,B z , optical frequency shift L={L x ,L y ,L z} and its three-axis components L x ,L y ,L z ; In order to describe the relaxation process of atomic longitudinal and transverse polarizability, the electron longitudinal relaxation rate is introduced Transverse relaxation rate This equation describes the dynamic evolution of the electron spin ensemble under the triple physical states of optical pumping, atomic relaxation, and Larmor precession in a magnetic field.

[0043] When the system is pulsed with light, the pumping rate function is shown in Equation (2), where the pumping rate is a function of time t, R p0 is the pumping rate of the pumping laser, α is the pulse laser duty cycle generated after the pumping laser passes through the optical switch, T is the time period of the laser pulse, and N is an integer greater than or equal to 0.

[0044]

[0045] When studying the longitudinal polarization of atomic spins, the precession effect of the polarizability under the external magnetic field B and the transverse pumping effect R of the detection light are often ignored. m S m Substituting equation (2) into equation (1), the longitudinal polarization of the electron spin ensemble in the quasi-steady state is The maximum value and minimum value where e is the natural constant:

[0046]

[0047]

[0048] Further simplification gives:

[0049]

[0050]

[0051] Taking the extremely short pulse period T to approach 0, we have Taking Taylor expansion of the exponential term in equation (4), we can prove that the maximum value of the polarization rate and the minimum value of the polarization rate all converge to the same value:

[0052]

[0053] Here we define R p0 α is the equivalent pumping rate of the pulsed light pumping system. For the pulsed laser described in equation (2), we can express it in the form of Fourier series:

[0054]

[0055] where n is a positive integer. The feedback light of the pumping beam is monitored by a photodetector amplifier. The collected signal is low-pass filtered. If the cutoff frequency f T of the filter is less than 1 / T, then the final collected signal is proportional to the equivalent pumping rate R p0 α. This value is used as the feedback quantity. A proportional-integral-derivative (PID) controller is used to adjust the pumping rate R p0 or the duty cycle α of the pulsed laser to adjust the equivalent pumping rate, so that the polarization rate of the atomic ensemble can be controlled.

[0056] This method needs to be implemented in five steps to achieve stable control of the polarization rate of the atomic spin ensemble based on high-frequency pulsed light pumping.

[0057] Step 1: High-power laser input

[0058] To enhance the interaction between light and atomic spins, the frequency of the laser needs to be tuned to the resonance frequency between the ground state and the excited state of the alkali metal electrons. The pumping rate generated by this power should be several times the relaxation rate of the atomic (electron) spin ensemble, and the optical power density should be 200 mW / cm 3 or more.

[0059] Step two: the light switch generates pulsed light

[0060] When the system is pumped by pulsed light, the pumping rate R p (t) is a function of time t, R p0 is the pumping rate of the pumping laser, a is the duty cycle of the pulsed light generated by the pumping laser after passing through the light switch, T is the time period of the laser pulse, the frequency of the pulsed light laser pulse should be higher than 10 kHz, and N is an integer greater than or equal to 0.

[0061]

[0062] The longitudinal polarization rate of the electron spin ensemble in the quasi-steady state of the system The maximum value And the minimum value Can be expressed as follows, where e represents the natural constant:

[0063]

[0064]

[0065] Taking a very short pulse period T approaching 0, so that The maximum value of the polarization rate And the minimum value of the polarization rate Both converge to the same value, where R p0 a is the equivalent pumping rate, and by controlling the equivalent pumping rate, the polarization rate of the electron spin ensemble can be changed:

[0066]

[0067] Step three: a polarization device is used to generate linearly polarized pulsed light, and a polarizing beam splitter prism is used to divide the polarized light into feedback light and main path light. The feedback light is converted into an electrical signal by a photodetector amplifier. The main path light passes through a λ / 4 wave plate with a fast axis and a linear polarization plane at an angle of 45° to generate circularly polarized light, which polarizes the electron spin ensemble.

[0068] Step four: a proportional-integral-derivative (PID) control strategy is used to generate a control signal

[0069] The direct current component of the electrical signal output by the photodetector amplifier is proportional to the equivalent pumping rate, and this direct current component is the closed-loop feedback quantity. By adjusting the pumping light intensity or duty cycle using the PID control strategy, the error between the feedback quantity and the set value is zeroed, and the equivalent pumping rate can be stably controlled.

[0070] Step five: adjust the pulsed light power or duty cycle

[0071] According to the control signal, the light switch is driven to adjust the pumping rate R p0or duty cycle α, so as to adjust the equivalent pumping rate R of the laser to the electron spin ensemble p0 α. Since the system has high frequency requirements (more than 10 kHz) for the pulsed light, the modulators that can be used are: acousto-optic modulator (AOM) or electro-optic modulator (EOM) optical switch.

[0072] The high-power pumping laser is pulse-modulated, and when the modulation frequency is high, the polarization rate of the electron spin ensemble tends to be stable; by adjusting the pumping rate and the duty cycle of the pulsed laser, the equivalent pumping rate of the pulsed laser to the electron spin ensemble can be stably controlled. Meanwhile, the high pumping rate can reduce the longitudinal polarization gradient of the electron spin ensemble.

[0073] The contents not described in detail in the specification of the present application belong to the prior art known to those skilled in the art. It is indicated here that the above description is helpful for those skilled in the art to understand the present application, but does not limit the protection scope of the present application. Any implementation of equivalent replacement, modification, improvement and / or deletion of the above description without departing from the essential content of the present application falls within the protection scope of the present application.

Claims

1. A method for stabilizing the polarizability of an atomic spin ensemble based on high-frequency pulsed optical pumping, characterized in that: The method comprises converting a pump laser from a pump laser into a pulsed pump laser by arranging an optical switch in a pumping optical path, wherein the pulsed pump laser polarizes an electron spin ensemble in an atomic gas chamber to improve the polarizability uniformity of the electron spin ensemble in the direction of the pumping light, and adjusting the duty cycle of the pulsed pump laser and / or the pulsed laser pumping rate to adjust the equivalent pumping rate of the pump laser on the electron spin ensemble, thereby achieving stable control of the polarizability of the atomic spin ensemble; Where T represents the pulse period of the pulsed pump laser, Indicates the maximum longitudinal polarizability of the electron spin ensemble, the longitudinal direction is the Z axis direction, represents the minimum longitudinal polarizability of the electron spin ensemble, R p0 α is the equivalent pumping rate, R p0 represents the pumping rate of the pumping laser, α represents the duty cycle of the pulsed laser generated after the pumping laser passes through the optical switch, represents the electron longitudinal relaxation rate.

2. The method for stabilizing the polarizability of an atomic spin ensemble based on high-frequency pulsed light pumping according to claim 1, characterized in that: where R p (t) represents the pulse light pumping rate as a function of time t, and n represents a positive integer.

3. The method for stabilizing the polarizability of an atomic spin ensemble based on high-frequency pulsed light pumping according to claim 1, wherein: The input side of the optical switch is connected to the pump laser by sequentially connecting a first polarizer, a first 1 / 2 wave plate, and a pump beam expander in series. The output side of the optical switch is connected to the first polarization beam splitter prism through a second polarizer and a first reflector in sequence. The feedback light of the first polarization beam splitter prism is connected to the optical switch controller through a photodetection amplifier. The optical switch controller is connected to the optical switch. The main path light of the first polarization beam splitter prism passes through the 1 / 4 wave plate and the atomic gas chamber in sequence.

4. The method for stabilizing the polarizability of an atomic spin ensemble based on high-frequency pulsed light pumping according to claim 3, wherein: The optical switch adopts an AOM acousto-optic modulator optical switch or an EOM electro-optic modulator optical switch, and the optical switch controller adopts a PID proportional differential integral control method to adjust the duty cycle of the pulse laser.

5. The method for stabilizing the polarizability of an atomic spin ensemble based on high-frequency pulsed light pumping according to claim 1, wherein: The periphery of the atomic gas chamber is sequentially provided with a heating oven, a coil frame and its support, a ferrite shielding layer and a permalloy shielding layer.

6. The method for stabilizing the polarizability of an atomic spin ensemble based on high-frequency pulsed light pumping according to claim 1, wherein: The detection light input side of the atomic gas cell is connected to the detection laser through the second polarizer and the detection beam expander in sequence, and the detection light output side of the atomic gas cell is connected to the data acquisition system through the Wollaston prism and the differential amplifier in sequence.

7. The method for stabilizing the polarizability of an atomic spin ensemble based on high-frequency pulsed light pumping according to claim 1, wherein: The following steps are involved: (1) High-power laser input: To enhance the interaction between light and atomic spins, the laser frequency needs to be tuned to the resonant frequency between the ground state and excited state of the alkali metal electrons, and the pumping rate generated by this power should be several times the relaxation rate of the atomic / electron spin ensemble. The optical power density is 200 mW / cm 3 above; (2) The optical switch generates pulsed light: When the system is pumped with pulsed light, the pumping rate R p (t) is a function of time t, R p0 is the pumping rate of the pumping laser, α is the pulse laser duty cycle generated after the pumping laser passes through the optical switch, T is the time period of the laser pulse, and the frequency of the high-frequency pulsed laser pulse should be higher than 10 kHz. N is an integer greater than or equal to 0: Longitudinal polarizability of the electron spin ensemble in the quasi-steady state The maximum value and minimum value It can be expressed as follows, where e represents a natural constant, represents the electron longitudinal relaxation rate, and Q is the electron spin ensemble slowing factor: Take a very short pulse period, that is, T approaches 0, so that Maximum polarizability and the minimum value of polarizability All converge to the same value, where R p0 α is the equivalent pumping rate. By controlling the equivalent pumping rate, the polarizability of the electron spin ensemble can be changed: (3) A polarization device is used to generate linear polarization of the pulsed laser, which is then divided into feedback light and main path light by a polarization beam splitter prism. The feedback light is converted into an electrical signal by a photodetector amplifier, and the main path light is passed through a λ / 4 wave plate with a fast axis and a linear polarization plane angle of 45° to generate circularly polarized light, thereby polarizing the electron spin ensemble. (4) Proportional differential integral (PID) control strategy is used to generate a control signal: the DC component of the electrical signal output by the photodetection amplifier is proportional to the equivalent pumping rate. This DC component is the closed-loop feedback quantity. The PID control strategy is used to adjust the pumping light intensity or duty cycle so that the error between the feedback quantity and the set value is zero, thereby stably controlling the equivalent pumping rate. (5) Adjust the pulse light power or duty cycle: Drive the optical switch according to the control signal to adjust the pumping rate R of the pump laser p0 Or duty cycle α, thereby adjusting the equivalent pumping rate R of the laser on the electron spin ensemble p0 α; Since the system requires the frequency of pulsed light to be greater than 10 kHz, the modulators that can be used are: acousto-optic modulator (AOM) optical switch or electro-optic modulator (EOM) optical switch.

8. The method for stabilizing the polarizability of an atomic spin ensemble based on high-frequency pulsed light pumping according to claim 7, characterized in that: The high-power pump laser is pulse-modulated. When the modulation frequency is high, the polarization rate of the electron spin ensemble tends to be stable. By adjusting the pumping rate and duty cycle of the pulsed laser, the equivalent pumping rate of the electron spin ensemble can be adjusted to stably control the pulsed laser. At the same time, the high pumping rate can reduce the longitudinal polarization gradient of the electron spin ensemble.

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