CN108267407A - Device and method for measuring transverse spin relaxation time of alkali metal atoms - Google Patents

Abstract

The invention provides a device for measuring the transverse spin relaxation time of alkali metal atoms, which includes a pumping optical path device, a detection optical path device, an atomic gas chamber, a three-dimensional Helmholtz coil, a polarization plane detection device and a signal processing system; the atomic gas The chamber is filled with alkali metal atoms and buffer gas; the pumping optical path device includes a first laser, a first beam expander collimator and a circular polarization conversion device arranged in series; the detection optical path device includes a second laser, a second beam expander collimator straight device as well as the first linear polarizer. The invention also discloses a method for measuring the transverse spin relaxation time of the alkali metal atom. Applying the technical solution of the present invention, the effect is: the overall structure is simplified; the rotating magnetic field in different directions is used to realize the accurate measurement of the transverse spin relaxation time of alkali metal atoms with different hyperfine energy levels in the ground state; it can be applied to the study of optical pumping This is related to spin relaxation and evaluation of the performance of atomic magnetometers and atomic spin gyroscopes, among others.

Description

Device and method for measuring transverse spin relaxation time of alkali metal atoms

technical field

The invention relates to the field of measurement technology, in particular to a device and method for measuring the transverse spin relaxation time of alkali metal atoms.

Background technique

The outermost shell of an alkali metal atom has only one electron, which makes the alkali metal atom exhibit many unique properties and attracts extensive research interest. At present, alkali metal atoms are widely used in atomic clocks, Faraday filters, atomic interferometers, atomic spin gyroscopes, and atomic magnetometers. For some application fields of alkali metal atoms, such as atomic spin gyroscopes and atomic magnetometers, the transverse spin relaxation time of alkali metal atoms is an extremely important parameter. The transverse spin relaxation time of alkali metal atoms directly determines the limit sensitivity and response linewidth of the atomic magnetometer, and the accuracy of the atomic spin gyroscope is also directly related to the transverse spin relaxation time of alkali metal atoms. Therefore, the precise measurement of the transverse spin relaxation time of alkali metal atoms is helpful to effectively evaluate the performance of atomic magnetometers and atomic spin gyroscopes. In addition, for the application field of alkali metal atoms, it is generally necessary to change the population of atoms by optical pumping. Because the transverse spin relaxation time of alkali metal atoms is related to optical pumping, the accurate measurement of the transverse spin relaxation time of alkali metal atoms is helpful to the study of optical pumping.

With the in-depth research on alkali metal atoms, people have found a variety of effective ways to increase the transverse spin relaxation time of alkali metal atoms, such as filling the alkali metal atom gas cell with buffer gas, and improving the inner wall of the alkali metal atom gas chamber. Anti-relaxation coating. These pathways allow one to achieve longer relaxation times for the lateral spin of alkali metal atoms. When the transverse spin relaxation time of alkali metal atoms is extended, the magnetic response line width of alkali metal atoms becomes narrow, and the hyperfine structure of alkali metal atoms becomes resolvable and needs to be considered. In this case, in order to study optical pumping and spin relaxation and to evaluate the performance of atomic magnetometers and atomic spin gyroscopes, it is necessary to measure the transverse spin relaxation of alkali metal atoms in different hyperfine energy levels in the ground state separately. time.

At present, the traditional free induction decay method is commonly used to measure the transverse spin relaxation time of alkali metal atoms. This method is simple in experimental operation and accurate in experimental results, so it has been used as a standard method for measuring transverse spin relaxation time for a long time. It requires the application of a linearly biased oscillating magnetic field with a frequency equal to the magnetic resonance frequency, which is used to excite and create the transverse spin component of the alkali metal atoms. When the hyperfine structure is considered, under the excitation of the oscillating magnetic field, the transverse spin components of the alkali metal atoms in different hyperfine energy levels of the ground state will be created. Therefore, if the traditional free induction decay method is used to measure the transverse spin relaxation time of an alkali metal atom in a certain hyperfine energy level of the ground state, the measurement will be affected by the alkali metal atom in another hyperfine energy level of the ground state. In order to accurately measure the transverse spin relaxation time of alkali metal atoms in different hyperfine energy levels of the ground state, it is necessary to separately excite the alkali metal atoms in different hyperfine energy levels of the ground state. To achieve this, new incentives need to be considered.

Contents of the invention

The invention utilizes rotating magnetic fields in different directions to separately excite alkali metal atoms in different hyperfine energy levels of the ground state, and realize accurate measurement of the transverse spin relaxation time of alkali metal atoms of different hyperfine energy levels in the ground state. The specific technical scheme is as follows :

A device for measuring the transverse spin relaxation time of an alkali metal atom, including a pumping optical path device, a detection optical path device, an atomic gas chamber, a three-dimensional Helmholtz coil, a polarization plane detection device, and a signal processing system;

The atomic gas chamber is filled with alkali metal atoms and buffer gas;

The pumping optical path device includes a first laser, a first beam expander collimator and a circularly polarized light conversion device arranged in series in sequence, the first laser is used to output pumping light, and the first beam expander collimator It is used to perform beam expansion and collimation processing on the pumping light output by the first laser, and the circularly polarized light conversion device is used to transform the pumping light after beam expansion and collimation processing by the first beam expansion and collimation device For circularly polarized light, circularly polarized light is used to polarize the alkali metal atoms in the atomic gas cell;

The detection optical path device includes a second laser, a second beam expander and collimator, and a first linear polarizer, the second laser is used to output detection light, and the second beam expander and collimator is used to combine the first The probe light output by the second laser is subjected to beam expansion and collimation processing, and the first linear polarizer is used to increase the degree of linear polarization of the probe light after beam expansion and collimation processing by the second beam expander and collimation device, and the high linear polarization After the probing light with a high degree interacts with the alkali metal atoms in the atomic gas cell, its polarization plane will be modulated by the spin polarization of the alkali metal atoms in the propagation direction of the probing light;

The three-dimensional Helmholtz coil is used to generate a static magnetic field and a rotating magnetic field at the atomic gas chamber;

The polarization plane detection device is used to detect the change of the polarization plane of the probe light;

The signal processing system is connected to the three-dimensional Helmholtz coil and the polarization plane detection device at the same time, and is used to collect the change information of the polarization plane of the probe light detected by the polarization plane detection device and adjust the input to the three-dimensional The current in the Helmholtz coil controls the static and rotating magnetic fields it generates.

Preferably in the above technical solutions, the first laser is a DFB semiconductor laser, which can be adjusted to the resonance frequency of the alkali metal atom D1 line transition, and outputs pumping light; the second laser is a DFB semiconductor laser, which can be adjusted to the alkaline The metal atom D2 line jumps the resonant frequency, and outputs the detection light.

In the above technical solution, preferably, the first beam expander and collimator and the first beam expander and collimator both include two sets of convex lenses arranged in series along the propagation direction of the optical path.

In the above technical solutions, preferably, the circularly polarized light converting device includes a second linear polarizing plate and a λ/4 glass plate arranged in series along the propagation direction of the optical path.

Preferably in the above technical solution, the three-dimensional Helmholtz coil is wound by copper wire.

Preferably in the above technical solutions, the polarization plane detection device includes a λ/2 glass slide, a Wollaste prism and a balance detector arranged in series along the propagation direction of the optical path, and the λ/2 glass slide is used to adjust the The direction of the polarization plane of the detection light of the atomic gas cell, the Wollaste prism is used to divide the linearly polarized light into two beams of light polarized along different axes, and the balance detector is used to differentiate the light intensity of the two beams of light Amplify to output a signal reflecting the change in the polarization plane of the probe light.

In the above technical solutions, preferably, the signal processing system includes a data acquisition card and a computer, and the data acquisition card is connected to the three-dimensional Helmholtz coil, the balance detector and the computer at the same time.

Preferably in the above technical solutions, the pumping light propagates along the z-axis direction; the probe light propagates along the x-axis direction, and is used to detect the alkali metal atoms in the ground state F=I+1/2 hyperfine energy level at x The spin polarization P _+x in the axial direction or the spin polarization P _-x of the alkali metal atom in the ground state F=I-1/2 hyperfine energy level in the x-axis direction, wherein: F represents an alkali metal atom The quantum number of the total angular momentum, I represents the quantum number of the nuclear spin of the alkali metal atom; the Wollaste prism divides the linearly polarized light into two beams of light polarized along the y-axis and the z-axis; the signal processing system drives The three-dimensional Helmholtz coil generates a rotating magnetic field and a static magnetic field in the z-axis direction, and the rotating magnetic field is a magnetic field that rotates counterclockwise or clockwise relative to the static magnetic field.

Concrete principle of the present invention is as follows:

Select a three-dimensional Cartesian coordinate system, and the three axes of the coordinate system are x-axis, y-axis and z-axis respectively. Apply pump light and static magnetic field along the z-axis Where: B ₀ represents the strength of the static magnetic field, and B ₀ >0, represents a unit vector in the z-axis direction.

Under the action of pumping light, a large number of alkali metal atoms will be polarized, and the polarization vector can be used to characterize the polarized alkali metal atom ensemble macroscopically. For alkali metal atoms in the ground state F=I+1/2 and F=I-1/2 hyperfine levels, their macroscopic polarization vectors are denoted as P ₊ and P ₋ respectively.

When a rotating magnetic field is applied When , the evolution of the macroscopic polarization vectors P ₊ and P _- with time t satisfies the following Bloch equation:

Where: B ₁ and ω represent the strength and frequency of the rotating magnetic field, respectively; and represent the unit vectors on the x-axis and the y-axis direction respectively; γ ₊ and γ _- represent the gyromagnetic ratios of the alkali metal atoms in the ground state F=I+1/2 and F=I-1/2 hyperfine energy levels respectively, γ ₊ <0, γ _- >0; P _+x , P _+y and P _+z are the components of P ₊ along the x-axis, y-axis and z-axis respectively; P _-x , P _-y and P _-z are respectively is the component of P _- along the x-axis, y-axis and z-axis; P ₊₀ and P _-0 are respectively P _+z and P _-z when the excitation magnetic field is not applied and thermal equilibrium; T ₂₊ and T _2- represent Transverse spin relaxation times of alkali metal atoms in the ground state F=I+1/2 and F=I-1/2 hyperfine levels; T ₁₊ and T _1- represent the ground state F=I+1/ 2 and F=I-1/2 the longitudinal spin relaxation time of the alkali metal atom in the hyperfine energy level.

when When , the rotating magnetic field is clockwise relative to the static magnetic field. From equation (1), it can be obtained that P _+x ≈ 0, P _{+ y} ≈ 0, and P _-x and P _-y can be larger values;

Similarly, when When , the rotating magnetic field is counterclockwise relative to the static magnetic field. According to equation (1), P _-x ≈ 0, P _-y = 0, and P _+x and P _+y can be larger values. Therefore, we can separately excite the alkali metal atoms in the ground state F=I-1/2 hyperfine energy level with a clockwise rotating magnetic field, and separately excite the alkali metal atoms in the ground state F=I+1/2 hyperfine energy level with a counterclockwise rotating magnetic field. alkali metal atoms.

When the clockwise rotating magnetic field is applied for a few seconds and then removed, it can be obtained from equation (1) that P _-x will decay exponentially with T _2- as the characteristic time. Therefore, the detection of the freely decaying P _-x signal can be fitted to obtain T _2- ; Similarly, when the counterclockwise rotating magnetic field is applied for a few seconds and then removed, the P _+x signal that is freely attenuated can be fitted to obtain T ₂₊ .

The present invention also discloses a method for measuring using the above-mentioned transverse spin relaxation time measuring device of alkali metal atoms, which specifically includes the following steps:

Step 1. The signal processing system drives the three-dimensional Helmholtz coil to generate a static magnetic field in the z-axis direction Turn on the first laser, adjust it to the resonance frequency of the alkali metal atom D1 line transition, output the pumping light, and the pumping light propagates along the pumping optical path in the z-axis direction, and successively passes through the first beam expanding collimation device and the Circularly polarized light is processed by the circularly polarized light conversion device, and the circularly polarized light begins to polarize the alkali metal atoms in the atomic gas cell; at the same time, turn on the second laser, adjust it to the resonance frequency of the D2 line transition of the alkali metal atoms, and output the probe light. The probe light propagates along the detection optical path in the x-axis direction, and is processed by the second beam expander collimator and the first linear polarizer successively to obtain the probe light with a high degree of linear polarization. The probe light interacts with the alkali metal atoms in the atomic gas cell, Probe P _+x or P _-x ;

Step 2, applying a rotating magnetic field, specifically including applying a clockwise rotating magnetic field and applying a counterclockwise rotating magnetic field, specifically:

The process of applying a clockwise rotating magnetic field: the signal processing system drives the three-dimensional Helmholtz coil to generate a relative static magnetic field magnetic field rotating clockwise Among them: B _c represents the clockwise rotating magnetic field; B ₀ represents the strength of the static magnetic field, and B ₀ >0; B ₁ represents the strength of the rotating field; and Respectively represent the unit vectors in the x-axis, y-axis and z-axis directions; γ _- represents the gyromagnetic ratio of the alkali metal atom in the ground state F=I-1/2 hyperfine energy level, and γ->0; 5-10 Seconds later, the clockwise rotating magnetic field B _c is removed, and the signal processing system detects the freely attenuated P _-x signal output by the balanced amplifier;

The process of applying a counterclockwise rotating magnetic field: the signal processing system drives the three-dimensional Helmholtz coil to generate a relative static magnetic field Magnetic field rotating counterclockwise Among them: B _cc represents the counterclockwise rotating magnetic field; γ ₊ represents the gyromagnetic ratio of the alkali metal atom in the ground state F=I+1/2 hyperfine energy level, and γ ₊ <0; after 5-10 seconds, remove the counterclockwise The rotating magnetic field B _cc , the signal processing system detects the freely decaying P _+x signal output by the balanced amplifier;

Step 3, fitting the detected free-decaying P _+x signal with an exponential function to obtain the transverse spin relaxation time T ₂₊ of the alkali metal atom in the ground state F=I+1/2 hyperfine energy level; The function fits the detected free-decaying P _-x signal to obtain the transverse spin relaxation time T _2- of the alkali metal atom in the ground state F=I-1/2 hyperfine energy level.

Preferably in the above technical scheme, the exponential function in the step 3 is specifically: Indicates the function of the unknown quantity y on the unknown quantity x, where: a and T ₂ are the parameters to be fitted, and the fitting result of T ₂ is taken as T ₂₊ or T _2- .

Applying the measurement method of the present invention, the effect is: the measurement steps are simplified; the alkali metal atoms in the different hyperfine energy levels of the ground state are separately excited by using the rotating magnetic fields in different directions, so as to realize the lateral self-mobility of the alkali metal atoms in the different hyperfine energy levels of the ground state. Accurate measurement of spin relaxation time; the invention can be applied to the study of optical pumping and spin relaxation, as well as evaluating the performance of atomic magnetometers and atomic spin gyroscopes, etc., and has strong practicability.

In addition to the objects, features and advantages described above, the present invention has other objects, features and advantages. The present invention will be described in further detail below with reference to the accompanying drawings.

Description of drawings

The accompanying drawings constituting a part of this application are used to provide further understanding of the present invention, and the schematic embodiments and descriptions of the present invention are used to explain the present invention, and do not constitute an improper limitation of the present invention. In the attached picture:

Fig. 1 is the structural representation of the transverse spin relaxation time measuring device of alkali metal atom in embodiment 1;

Fig. 2 is the P _-x signal of free decay detected by experiment and its fitting result;

Fig. 3 is the P _+x signal of free decay detected by the experiment and its fitting result;

Fig. 4 is a schematic diagram of the signal detected by the balance detector when a linearly deflected oscillating magnetic field is applied in the x-axis direction and the frequency of the oscillating magnetic field is equal to γ _- B ₀ ;

Among them: 1. Pumping optical path device, 1.1, the first laser, 1.2, the first beam expander collimator, 1.3, circular polarization conversion device, 1.31, the second linear polarizer, 1.32, λ/4 glass plate, 2, Detection optical path device, 2.1, second laser, 2.2, second beam expander collimator, 2.3, first linear polarizer, 3, atomic gas chamber, 4, three-dimensional Helmholtz coil, 5, polarization plane detection device, 5.1, λ/2 glass slide, 5.2, Wollaste prism, 5.3, balanced detector, 6, signal processing system, T, convex lens.

Detailed ways

The embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention can be implemented in various ways defined and covered by the claims.

Example 1:

A device for measuring the transverse spin relaxation time of an alkali metal atom, see Figure 1 for details, including a pumping optical path device 1, a detection optical path device 2, an atomic gas chamber 3, a three-dimensional Helmholtz coil 4, and a polarization plane detection device 5 and the signal processing system 6, details are as follows:

The atomic gas chamber 3 is filled with alkali metal atoms and buffer gas, and the buffer gas is preferably nitrogen.

The pumping optical path device 1 forms a pumping optical path, which includes a first laser 1.1, a first beam expander collimator 1.2, and a circularly polarized light conversion device 1.3 arranged in series in sequence. The first laser 1.1 is a DFB semiconductor laser, which can be Adjust to the resonant frequency of the alkali metal atom D1 line transition, and output the pumping light; the first beam expanding and collimating device 1.2 is used for beam expanding and collimating the pumping light output by the first laser 1.1; the circle The polarized light conversion device 1.3 is used to convert the pumping light processed by the first beam expanding and collimating device 1.2 into circularly polarized light, and the circularly polarized light is used to polarize the alkali metal atoms in the atomic gas cell 3 , the circularly polarized light conversion device 1.3 includes a second linear polarizing plate 1.31 and a λ/4 glass plate 1.32 arranged in series along the propagation direction of the optical path.

The detection optical path device 2 forms a detection optical path, which includes a second laser 2.1, a second beam expander collimator 2.2 and a first linear polarizer 2.3, and the second laser 2.1 is a DFB semiconductor laser, which can be adjusted to alkali metal The atomic D2 line transitions the resonant frequency to output the probe light; the second beam expander and collimator device 2.2 is used to expand and collimate the probe light output by the second laser 2.1, and the first linear polarizer 2.3 uses In order to increase the degree of linear polarization of the probe light after beam expansion and collimation treatment by the second beam expander and collimator device 2.2, after the probe light with a high degree of linear polarization interacts with the alkali metal atoms in the atomic gas chamber 3, its polarization plane will be modulated by the spin polarization of the alkali metal atoms in the direction of probe light propagation.

The three-dimensional Helmholtz coil 4 is used to generate a static magnetic field and a rotating magnetic field at the atomic gas chamber 3 , and the three-dimensional Helmholtz coil 4 is wound by copper wire.

The polarization plane detection device 5 is used to detect the change of the probe light polarization plane, and it includes a λ/2 glass slide 5.1, a Wollaste prism 5.2 and a balance detector 5.3 arranged in series along the propagation direction of the optical path, the λ/2 The glass slide 5.1 is used to adjust the direction of the polarization plane of the probe light passing through the atomic gas cell 3, and the Wolast prism 5.2 is used to divide the linearly polarized light into two beams of light polarized along the y-axis and the z-axis, The balance detector 5.3 is used to differentially amplify the light intensity of the two beams to output a signal reflecting the change of the polarization plane of the detected light.

The signal processing system 6 includes a data acquisition card and a computer, and the data acquisition card is connected with the three-dimensional Helmholtz coil 4, the balance detector 5.3 and the computer at the same time, and the signal processing system 6 is used for collecting all The change information of the polarization plane of the probe light detected by the polarization plane detection device 5 and the current input to the three-dimensional Helmholtz coil 4 are adjusted to control the static magnetic field in the z-axis direction generated by it and rotate clockwise or relative to the static magnetic field. A rotating magnetic field that rotates counterclockwise.

Both the first beam expander and collimator 1.2 and the second beam expander and collimator 2.2 include two sets of convex lenses T arranged in series along the propagation direction of the optical path.

Apply the technical scheme of this embodiment, specifically:

The pumping light output by the first laser 1.1 (DFB semiconductor laser) (the pumping light propagates along the z-axis direction) passes through the first beam expander and collimator device 1.2 (passes through two sets of convex lenses T in turn) and then is circularly polarized The light conversion device 1.3 (through the second linear polarizer 1.31 and the λ/4 glass plate 1.32 in turn) converts it into circularly polarized light; subsequently, the circularly polarized light irradiates the atomic gas chamber 3, realizing the alkali metal atoms in the atomic gas chamber 3 polarization.

The probe light output by the second laser 2.1 (DFB semiconductor laser) (the probe light propagates along the x-axis direction) is expanded and collimated by the second beam expander and collimator device 2.2 (through two sets of convex lenses T in sequence), and then passed through the first linear polarization The atomic gas cell 3 is irradiated after the sheet 2.3, and after the probe light interacts with the alkali metal atoms in the atomic gas cell 3, the polarization plane of the probe light will be modulated by P _+x or P _-x .

The probe light passing through the atomic gas chamber 3 passes through the polarization plane detection device 5 (through the λ/2 glass slide 5.1, the Wollaste prism 5.2 and the balance detector 5.3 in turn), and the output signal of the balance detector 5.3 reflects the probe light polarization plane change; the output signal of the balance detector 5.3 is collected by the signal processing system 6, and at the same time, the signal processing system 6 drives and controls the three-dimensional Helmholtz coil 4 to provide a static magnetic field and a rotating magnetic field.

The method for measuring the transverse spin relaxation time of an alkali metal atom using the device of this embodiment may further comprise the steps:

Step 1: The signal processing system 6 drives the three-dimensional Helmholtz coil 4 to generate a static magnetic field in the z-axis direction Turn on the first laser 1.1, adjust it to the resonance frequency of the alkali metal atom D1 line transition, output the pumping light, the pumping light propagates along the pumping optical path in the z-axis direction, and successively passes through the first beam expander collimation device 1.2 and the circularly polarized light conversion device 1.3 process to obtain circularly polarized light, and the circularly polarized light starts to polarize the alkali metal atoms in the atomic gas cell 3; at the same time, turn on the second laser 2.1 and adjust it to the D2 line transition resonance frequency of the alkali metal atoms , output the detection light, the detection light propagates along the detection light path in the x-axis direction, and is successively processed by the second beam expander collimation device 2.2 and the first linear polarizer 2.3 to obtain the detection light with a high degree of linear polarization, the detection light and the atomic gas chamber 3. Alkali metal atom interaction, detecting P _+x or P _-x ;

Step 2, applying a rotating magnetic field, specifically:

Apply a clockwise rotating magnetic field: the signal processing system 6 drives the three-dimensional Helmholtz coil 4 to generate a relative static magnetic field magnetic field rotating clockwise After 5-10 seconds, the clockwise rotating magnetic field B _c is removed, and the signal processing system 6 detects the freely decaying P _-x signal output by the balanced amplifier 5.3;

Apply a counterclockwise rotating magnetic field: the signal processing system 6 drives the three-dimensional Helmholtz coil 4 to generate a relative static magnetic field Magnetic field rotating counterclockwise After 5-10 seconds, the counterclockwise rotating magnetic field B _cc is removed, and the signal processing system 6 detects the freely decaying P _+x signal output by the balance amplifier 5.3;

Step 3, fitting the detected free-decaying P _+x signal with an exponential function to obtain the transverse spin relaxation time T ₂₊ of the alkali metal atom in the ground state F=I+1/2 hyperfine energy level; The function fits the detected free-decaying P _-x signal to obtain the transverse spin relaxation time T _2- of the alkali metal atom in the ground state F=I-1/2 hyperfine energy level.

Preferably in the above technical scheme, the exponential function in the step 3 is specifically: Indicates the function of the unknown quantity y on the unknown quantity x, where: a and T ₂ are the parameters to be fitted, and the fitting result of T ₂ is taken as T ₂₊ or T _2- .

Figure 2 is the experimentally detected P _-x signal of free decay and its fitting results. It can be seen from the figure that we can obtain the transverse spin relaxation time T _2- of the alkali metal atom in the ground state F=I-1/2 hyperfine energy level through the exponential fitting function.

Figure 3 is the experimentally detected P _+x signal of free decay and its fitting results. It can be seen from the figure that we can obtain the transverse spin relaxation time T ₂₊ of the alkali metal atom in the ground state F=I+1/2 hyperfine energy level through the exponential fitting function.

Figure 4 is the signal detected by the balance detector when a linearly deflected oscillating magnetic field is applied in the x-axis direction and the frequency of the oscillating magnetic field is equal to γ _- B ₀ . It can be seen from the figure that it is difficult for us to fit the transverse spin relaxation time T _2- or T ₂ of the alkali metal atom in the ground state F=I-1/2 or F=I+1/2 hyperfine energy level ₊ .

Comparing the experimental results in Fig. 2, Fig. 3 and Fig. 4, it can be obtained that by using rotating magnetic fields in different directions, the alkali metal atoms in different hyperfine energy levels in the ground state can be separately excited, and the alkali metal atoms in different hyperfine energy levels in the ground state can be excited. Precise measurement of transverse spin relaxation times.

Applying the technical solution of this embodiment, the effect is: the overall structure is simplified; using rotating magnetic fields in different directions to separately excite the alkali metal atoms at different hyperfine energy levels in the ground state, and realize the lateral movement of the alkali metal atoms at different hyperfine energy levels in the ground state. Accurate measurement of spin relaxation time; can be applied to the study of optical pumping and spin relaxation, and to evaluate the performance of atomic magnetometers and atomic spin gyroscopes.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. A transverse spin relaxation time measurement device for an alkali metal atom, characterized in that it comprises a pumping optical path device (1), a detection optical path device (2), an atomic gas chamber (3), and a three-dimensional Helmholtz coil (4), polarization plane detection device (5) and signal processing system (6); The atomic gas chamber (3) is filled with alkali metal atoms and buffer gas; The pumping optical path device (1) includes a first laser (1.1), a first beam expander collimator (1.2) and a circularly polarized light conversion device (1.3) arranged in series in sequence, and the first laser (1.1) uses In order to output the pumping light, the first beam expanding and collimating device (1.2) is used for beam expanding and collimating the pumping light output by the first laser (1.1), and the circularly polarized light converting device (1.3 ) is used to convert the pumping light after the beam expansion and collimation treatment of the first beam expansion and collimation device (1.2) into circularly polarized light, and the circularly polarized light is used to polarize the alkali metal atoms in the atomic gas cell (3) ; The detection optical path device (2) includes a second laser (2.1), a second beam expander collimator (2.2) and a first linear polarizer (2.3), and the second laser (2.1) is used to output detection light, The second beam expander and collimator (2.2) is used to expand and collimate the probe light output by the second laser (2.1), and the first linear polarizer (2.3) is used to improve the The degree of linear polarization of the probe light processed by the second beam expander and collimator (2.2), after the probe light with a high degree of linear polarization interacts with the alkali metal atoms in the atomic gas chamber (3), its polarization plane will be affected by Modulation of spin polarization of alkali metal atoms in the direction of probe light propagation; The three-dimensional Helmholtz coil (4) is used to generate a static magnetic field and a rotating magnetic field at the atomic gas chamber (3); The polarization plane detection device (5) is used to detect the change of the polarization plane of the probe light; The signal processing system (6) is simultaneously connected with the three-dimensional Helmholtz coil (4) and the polarization plane detection device (5), for collecting the probe light detected by the polarization plane detection device (5) The polarization plane change information and the current input to the three-dimensional Helmholtz coil (4) are adjusted to control the static magnetic field and the rotating magnetic field generated by it. 2. the transverse spin relaxation time measuring device of alkali metal atoms according to claim 1, is characterized in that: the first laser (1.1) is a DFB semiconductor laser, which can be adjusted to the D1 line transition resonance of alkali metal atoms Frequency, output pumping light; the second laser (2.1) is a DFB semiconductor laser, which can be adjusted to the resonance frequency of the D2 line transition of alkali metal atoms, and output detection light. 3. the transverse spin relaxation time measurement device of alkali metal atom according to claim 1, is characterized in that: described first beam expander collimation device (1.2) and described second beam expander collimation device (2.2 ) both include two sets of convex lenses (T) arranged in series along the propagation direction of the optical path. 4. the transverse spin relaxation time measurement device of alkali metal atom according to claim 1, is characterized in that: described circularly polarized light conversion device (1.3) comprises the second linear polarizer (1.31 that is arranged in series along light path propagating direction ) and λ/4 slides (1.32). 5. The device for measuring the transverse spin relaxation time of alkali metal atoms according to any one of claims 1-4, characterized in that: the three-dimensional Helmholtz coil (4) is wound by copper wire. 6. the transverse spin relaxation time measuring device of alkali metal atom according to claim 5, is characterized in that: described polarization plane detecting device (5) comprises the λ/2 slide (5.1 ), a Wollaste prism (5.2) and a balance detector (5.3), the λ/2 glass slide (5.1) is used to adjust the direction of the polarization plane of the probe light passing through the atomic gas chamber (3), so The Volast prism (5.2) is used to divide the linearly polarized light into two beams of light polarized along different axes, and the balance detector (5.3) is used to differentially amplify the light intensity of the two beams of light to output a reflection A signal that detects changes in the polarization plane of light. 7. the transverse spin relaxation time measuring device of alkali metal atom according to claim 6, is characterized in that: described signal processing system (6) comprises data acquisition card and computer, and described data acquisition card is simultaneously with described The three-dimensional Helmholtz coil (4), the balance detector (5.3) and the computer are connected. 8. The transverse spin relaxation time measuring device of alkali metal atoms according to claim 7, characterized in that: the pumping light propagates along the z-axis direction; the probe light propagates along the x-axis direction for detecting The spin polarization of an alkali metal atom in the ground state F=I+1/2 hyperfine energy level in the x-axis direction P _+x or an alkali metal atom in the ground state F=I-1/2 hyperfine energy level at x Spin polarization P _-x on the axial direction, wherein: F represents the quantum number of the total angular momentum of the alkali metal atom, and I represents the quantum number of the nuclear spin of the alkali metal atom; the Wollaste prism (5.2) The linearly polarized light is divided into two beams of light polarized along the y-axis and the z-axis; the signal processing system (6) drives the three-dimensional Helmholtz coil (4) to generate a rotating magnetic field and a static magnetic field in the direction of the z-axis, and the rotating magnetic field is A magnetic field that rotates counterclockwise or clockwise relative to the static magnetic field. 9. A method for measuring the transverse spin relaxation time of an alkali metal atom, characterized in that: comprising the following steps: Step 1. The signal processing system (6) drives the three-dimensional Helmholtz coil (4) to generate a static magnetic field in the z-axis direction Turn on the first laser (1.1), adjust it to the transition resonance frequency of the D1 line of alkali metal atoms, output pumping light, and the pumping light propagates along the pumping optical path in the z-axis direction, and successively passes through the first beam expanding quasi- The straight device (1.2) and the circularly polarized light conversion device (1.3) are processed to obtain circularly polarized light, and the circularly polarized light begins to polarize the alkali metal atoms in the atomic gas cell (3); meanwhile, the second laser (2.1) is turned on, and its Adjust to the resonance frequency of the D2 line transition of alkali metal atoms, output the detection light, the detection light propagates along the detection light path in the x-axis direction, and is processed by the second beam expander collimator (2.2) and the first linear polarizer (2.3) successively to obtain Probing light with a high degree of linear polarization, the probing light interacts with the alkali metal atoms in the atomic gas chamber (3), and detects P _+x or P _-x ; Step 2, applying a rotating magnetic field, specifically including applying a clockwise rotating magnetic field and applying a counterclockwise rotating magnetic field, specifically: The process of applying a clockwise rotating magnetic field: the signal processing system (6) drives the three-dimensional Helmholtz coil (4) to generate a relative static magnetic field magnetic field rotating clockwise Among them: B _c represents the clockwise rotating magnetic field; B ₀ represents the strength of the static magnetic field, and B ₀ >0; B ₁ represents the strength of the rotating field; and Respectively represent the unit vectors in the x-axis, y-axis and z-axis directions; γ _- represents the gyromagnetic ratio of the alkali metal atom in the ground state F=I-1/2 hyperfine energy level, and γ->0; 5-10 Seconds later, the clockwise rotating magnetic field _Bc is removed, and the signal processing system (6) detects the freely decaying P _-x signal output by the balanced amplifier (5.3); The process of applying a counterclockwise rotating magnetic field: the signal processing system (6) drives the three-dimensional Helmholtz coil (4) to generate a relative static magnetic field Magnetic field rotating counterclockwise Among them: B _cc represents the counterclockwise rotating magnetic field; γ ₊ represents the gyromagnetic ratio of the alkali metal atom in the ground state F=I+1/2 hyperfine energy level, and γ ₊ <0; after 5-10 seconds, remove the counterclockwise The rotating magnetic field B _cc , the signal processing system (6) detects the freely decaying P _+x signal output by the balance amplifier (5.3); Step 3, fitting the detected free-decaying P _+x signal with an exponential function to obtain the transverse spin relaxation time T ₂₊ of the alkali metal atom in the ground state F=I+1/2 hyperfine energy level; The function fits the detected free-decaying P _-x signal to obtain the transverse spin relaxation time T _2- of the alkali metal atom in the ground state F=I-1/2 hyperfine energy level. 10. the measuring method of the transverse spin relaxation time of alkali metal atom according to claim 9, is characterized in that: the exponential function in described step 3 is specifically: Indicates the function of the unknown quantity y on the unknown quantity x, where: a and T ₂ are the parameters to be fitted, and the fitting result of T ₂ is taken as T ₂₊ or T _2- .