CN104051942A - Longitudinal Zeeman laser frequency locking method and device based on thermoelectric cooling and acousto-optic frequency shifting - Google Patents

Abstract

The invention discloses a longitudinal Zeeman laser frequency locking method and device based on thermoelectric refrigeration and acousto-optic frequency shift, and belongs to the technical field of laser application. The acousto-optic frequency shift technology is adopted to lock output laser frequencies of a plurality of longitudinal Zeeman lasers based on thermoelectric refrigeration on the output laser frequency of the same reference longitudinal Zeeman frequency stabilized laser, and therefore the output lasers of all the lasers have the unified frequency value, the defect that frequency consistency of traditional frequency stabilized lasers is low is overcome, and a novel laser source is provided for ultra-precision laser interference measurement.

Description

Longitudinal Zeeman laser frequency locking method and device based on thermoelectric cooling and acousto-optic frequency shifting

technical field

The invention belongs to the technical field of laser applications, in particular to a longitudinal Zeeman laser frequency locking method and device based on thermoelectric refrigeration and acousto-optic frequency shifting.

Background technique

In recent years, ultra-precision measurement and processing technologies represented by lithography machines and CNC machine tools have developed towards large-scale, high-precision, multi-space degrees of freedom simultaneous measurement, and the total laser power consumption of the laser interferometry system has increased sharply. The output laser power exceeds the output laser power of a single frequency-stabilized laser, so it is necessary to use multiple frequency-stabilized lasers for combined measurement at the same time. However, there are differences in the relative frequency stability, laser wavelength value, and wavelength drift direction of different frequency-stabilized lasers, which will bring about the measurement accuracy of different spatial degrees of freedom of the laser interferometry system, and the inconsistent wavelength reference and spatial coordinates. It affects the comprehensive measurement accuracy of the entire multi-dimensional laser interferometry system. In order to ensure the comprehensive measurement accuracy of the laser interferometry system, the frequency consistency of multiple frequency-stabilized lasers used in combination is required to reach 10 ^-8 , so the frequency consistency between frequency-stabilized lasers has become an urgent issue in the development of ultra-precision measurement and processing One of the key issues to be resolved.

The frequency-stabilized laser sources currently used in laser interferometry systems mainly include dual-longitudinal-mode frequency-stabilized lasers, transverse Zeeman frequency-stabilized lasers, and longitudinal Zeeman lasers. The center frequency of the laser gain curve is used as the frequency stabilization reference for such lasers. The reference frequency of frequency stabilization control, while the center frequency of the laser gain curve changes with the working gas pressure and discharge conditions, and the physical parameters of multiple frequency stabilization lasers cannot be highly consistent, so there are differences in the reference frequency of frequency stabilization control , resulting in low frequency consistency of laser output from multiple frequency-stabilized lasers, which can only reach 10 ^-6 -10 ^-7 .

In order to solve the problem of poor frequency consistency between frequency-stabilized lasers, Harbin Institute of Technology proposed a dual longitudinal mode laser bias frequency locking method (Chinese Patent Application Nos. The output laser frequency of the frequency-stabilized laser or the dual longitudinal mode laser is used as a reference, and the remaining multiple dual longitudinal mode lasers are locked by a certain value relative to the reference frequency, so that the output lasers of multiple dual longitudinal mode lasers have the same wavelength ( frequency), but this method needs to adjust the internal working parameters of the laser during the laser frequency locking process. On the one hand, because the adjustment method is an indirect adjustment, the response speed of the system is relatively slow. On the other hand, due to the characteristic parameters of each laser There are certain differences, and changes in the internal operating parameters of the laser may have a negative impact on the frequency stability of the laser, and in severe cases, it may even cause the laser to lose lock.

Contents of the invention

Aiming at the deficiencies in the prior art, the present invention proposes a longitudinal Zeeman laser frequency locking method based on thermoelectric refrigeration and acousto-optic frequency shifting, the purpose of which is to combine the frequency-shifting characteristics of the acousto-optic frequency shifter and the longitudinal Zeeman The advantages of frequency-stabilized lasers provide a laser light source with excellent wavelength consistency for ultra-precision processing and measurement technology. The invention also provides a longitudinal Zeeman laser frequency locking device based on thermoelectric cooling and acousto-optic frequency shifting.

The object of the present invention is achieved through the following technical solutions:

A longitudinal Zeeman laser frequency locking method based on thermoelectric refrigeration and acousto-optic frequency shifting, the method comprises the following steps:

(1) Turn on the power of the reference longitudinal Zeeman frequency-stabilized laser. After preheating and frequency stabilization, the laser outputs two laser components with orthogonal polarization, and use a polarization beam splitter to separate one of the laser components as the reference longitudinal Zeeman-stabilized laser. frequency laser output light, its light wave frequency is denoted as ν _r , and the output light is split into n≥1 paths by the fiber beam splitter, denoted as beam X _i (i=1,2,…,n), which are respectively used as longitudinal plugs Mann laser L _i (i=1,2,…,n) frequency-locked reference beam;

(2) Turn on the power of the longitudinal Zeeman laser L _i (i=1,2,…,n), all longitudinal Zeeman lasers enter the preheating process at the same time, measure the temperature value of the current environment, and set the preheating target accordingly temperature T _set , and T _set is higher than the ambient temperature, using a thermoelectric cooler to heat the laser tube placed in the longitudinal magnetic field, so that the temperature of the laser tube tends to the preset temperature value T _set and reaches a thermal equilibrium state, where Based on the preheating algorithm, the positive and negative currents of the thermoelectric cooler are fine-tuned, so that the laser tube works in the single longitudinal mode light output state, and the single longitudinal mode light is split into left-handed and right-handed circular polarization under the action of the longitudinal magnetic field. The laser component is output from the main output end and the auxiliary output end of the laser tube;

(3) The longitudinal Zeeman laser L _i (i=1,2,…,n) enters the frequency stabilization control process after the preheating process, and the left-handed and right-handed circularly polarized light at the secondary output end of the laser tube passes through the 1/4 wave plate Transformed into mutually orthogonal linearly polarized light and separated by a Wollaston prism, its optical power P _i ¹ (i=1,2,…,n) and P _i ² (i=1,2,…, n) Measured by the two-quadrant photodetector, the frequency stabilization control module calculates the power difference ΔP _i =P _i ¹ –P _i ² (i=1,2,…,n) of the two laser components, and according to The positive and negative sum of ΔP _i (i=1,2,…,n) adjusts the positive and negative sum of the working current of the thermoelectric cooler, so that ΔP _i (i=1,2,…,n) tends to zero, and then makes The frequency of the laser tends to a stable value;

(4) The left-handed and right-handed circularly polarized light at the main output end of the laser tube is converted into two mutually orthogonal linearly polarized lasers by a 1/4 wave plate, and one of the linearly polarized laser components is separated by a polarization beam splitter, which is recorded as a beam T _i (i=1,2,…,n), its frequency is denoted as ν _i (i=1,2,…,n), the beam T _i (i=1,2,…,n) enters the drive frequency The acousto-optic frequency shifter S _i (i=1,2,…,n) for f _i (i=1,2,…,n) performs frequency shifting, and the corresponding output laser frequency is denoted as ν _i + f _i (i=1,2,…,n), the laser is divided into two parts with an intensity ratio of 9:1 by the beam splitter, and the part with relatively high intensity is recorded as the beam Z _i (i=1, 2,…,n), respectively as the output laser light of the longitudinal Zeeman laser L _i (i=1,2,…,n), and the light with relatively small intensity is recorded as the beam Y _i (i=1,2,… ,n);

(5) Optically mix the light beam X _i (i=1,2,…,n) with the light beam Y _i (i=1,2,…,n) respectively to form an optical beat frequency signal, and use the photodetector to convert the optical The beat frequency signal is converted into an electrical signal, and its frequency value Δν _i =ν _i + f _i –ν _r (i=1,2,…,n) is measured by the frequency measurement module, and the frequency adjustment module is based on the measured optical beat frequency The frequency value of the signal Δν _i (i=1,2,…,n), calculates the beam X _i (i=1,2,…,n) and Y _i (i=1,2,…,n) Frequency difference ν _r –ν _i = f _i –Δν _i (i=1,2,…,n), and the driving frequency f of the acousto-optic frequency shifter S _i (i=1,2,…,n) _i (i=1,2,…,n) is adjusted to ν _r –ν _i (i=1,2,…,n), so that the longitudinal Zeeman laser L _i (i=1,2,…,n) The frequency of the output beam Z _i (i=1,2,…,n) is equal to the frequency of the reference beam X _i (i=1,2,…,n), that is, ν _i + f _i = ν _r (i=1, 2,...,n);

(6) Repeat steps (4) to (5) cyclically, by adjusting the operating frequency f _i (i=1,2,…,n) of the acousto-optic frequency shifter S _i (i=1,2,…,n) , so that the frequency of the output laser Z _i (i=1,2,...,n) of the longitudinal Zeeman laser L _i (i=1,2,...,n) is always locked at the same frequency value ν _r .

A longitudinal Zeeman laser frequency-locking device based on thermoelectric refrigeration and acousto-optic frequency shifting, including a laser power supply A, a frequency stabilization status indicator, a reference longitudinal Zeeman frequency stabilization laser, a polarization beam splitter A, and a fiber beam splitter, its features The device also includes n≥1 longitudinal Zeeman lasers (L ₁ , L ₂ ,…, L _n ) with the same structure in parallel relationship, each of which is a longitudinal Zeeman laser (L ₁ , L ₂ ,…, L The assembly structure of _n ) is: the laser power supply B is connected to the laser tube, the laser tube is placed in the heat-conducting metal cavity, the gap between the laser tube and the heat-conducting metal cavity is filled with a heat-conducting silica gel layer, and the laser tube temperature sensor is placed in the heat-conducting silica gel layer, And close to the outer wall of the laser tube, its output terminal is connected to the frequency stabilization control module, the thermoelectric cooler is attached to the outer wall of the heat-conducting metal cavity, its input terminal is connected to the frequency stabilization control module, the laser tube, heat-conducting silicone layer, heat-conducting metal cavity and thermoelectric cooling The thermal control structure composed of the laser tube and the laser tube is placed in the cylindrical longitudinal magnetic field module, and the axis of the laser tube is parallel to the direction of the magnetic field. The ambient temperature sensor is connected to the frequency stabilization control module. The 1/4 wave plate A, Wollaston prism and The two-quadrant photodetector is placed behind the secondary output end of the laser tube in sequence, the output end of the two-quadrant photodetector is connected to the frequency stabilization control module, and the 1/4 wave plate B, polarization beam splitter B and acousto-optic frequency shifter are placed in sequence In front of the main output end of the laser tube, the beam splitter is placed between the acousto-optic frequency shifter and one input end of the fiber combiner, and the other input end of the fiber combiner is connected to one of the output ends of the fiber splitter. The polarizer is placed between the output end of the fiber combiner and the high-speed photodetector, and the high-speed photodetector, frequency measurement module, frequency adjustment module, and acousto-optic frequency shifter are connected in sequence, and the frequency lock status indicator is connected to the frequency adjustment module .

The present invention has following characteristics and good effect:

(1) The present invention uses an acousto-optic frequency shifter to perform parallel frequency locking on multiple longitudinal Zeeman lasers, and all longitudinal Zeeman frequency-stabilized lasers output laser light with a uniform frequency value. Due to the extremely high frequency adjustment resolution of the acousto-optic frequency shifter The frequency consistency of multiple lasers can be as high as 10 ^-9 , which is one to two orders of magnitude higher than the existing method, which is one of the innovative points different from the existing technology.

(2) The present invention uses an acousto-optic frequency shifter to lock multiple longitudinal Zeeman lasers in parallel. Due to the high frequency adjustment response speed of the acousto-optic frequency shifter, the laser wavelength drift and jump caused by external interference factors can be effectively suppressed. change, thereby improving the stability and environmental applicability of the light source, which is the second innovation point different from the existing technology.

(3) The present invention uses an acousto-optic frequency shifter to lock multiple longitudinal Zeeman lasers in parallel. Since the frequency adjustment method of the final output laser of the laser is an external adjustment method for the internal laser tube of the laser, it will not It has adverse effects on the frequency stabilization control mechanism of the laser tube, which is conducive to improving the stability of the system and the accuracy of frequency stabilization. This is the third innovation point different from the existing technology.

(4) The present invention uses a thermoelectric cooler for temperature control and adjustment. Because changing the direction of its working current allows the thermoelectric cooler to generate heat or absorb heat, thereby reducing the dependence on the heat dissipation performance of the environment, it is beneficial to realize the laser tube The rapid control and adjustment of temperature improves the response speed of the control system, which is the fourth innovation point different from the existing technology.

Description of drawings

Fig. 1 is the schematic diagram of the principle of the device of the present invention

Fig. 2 is the schematic diagram of the vertical Zeeman laser frequency stabilization structure in the device of the present invention

Fig. 3 is the cross-sectional view of longitudinal Zeeman laser thermal control mechanical structure in the device of the present invention

Fig. 4 is the closed-loop control functional block diagram of longitudinal Zeeman laser preheating process in the device of the present invention

Fig. 5 is the closed-loop control functional block diagram of longitudinal Zeeman laser frequency stabilization process in the device of the present invention

Fig. 6 is the closed-loop control functional block diagram of longitudinal Zeeman laser frequency locking process in the device of the present invention

In the figure, 1-laser power supply A, 2-frequency stabilization status indicator, 3-reference longitudinal Zeeman frequency stabilization laser, 4-polarization beam splitter A, 5-fiber beam splitter, 6-laser tube, 7-cylinder Shaped longitudinal magnetic field module, 8-1/4 wave plate A, 9-Wollaston prism, 10-two-quadrant photodetector, 11-frequency stabilization control module, 12-laser tube temperature sensor, 13-thermoelectric cooler, 14-Heat-conducting silica gel layer, 15-Heat-conducting metal cavity, 16-Ambient temperature sensor, 17-Laser power supply B, 18-1/4 wave plate B, 19-Polarizing beam splitter B, 20-Acousto-optic frequency shifter, 21- Spectroscope, 22-fiber beam combiner, 23-polarizer, 24-high-speed photodetector, 25-frequency measurement module, 26-frequency adjustment module, 27-frequency lock status indicator.

Detailed ways

The implementation examples of the present invention will be described in detail below in conjunction with the accompanying drawings.

As shown in Fig. 1, Fig. 2 and Fig. 3, the longitudinal Zeeman laser frequency locking device based on thermoelectric refrigeration and acousto-optic frequency shifting in the device of the present invention includes a laser power supply A1, a frequency stabilization status indicator light 2, a reference longitudinal Zeeman stabilization frequency laser 3, polarization beam splitter A4, fiber beam splitter 5, the device also includes n≥1 longitudinal Zeeman lasers L ₁ , L ₂ ,..., L _n with the same structure and in parallel relationship, each of which is longitudinal The assembly structure of the Zeeman lasers L ₁ , L ₂ ,..., L _n is: the laser power supply B17 is connected to the laser tube 6, the laser tube 6 is placed in the heat-conducting metal cavity 15, and the gap between the laser tube 6 and the heat-conducting metal cavity 15 Fill the heat-conducting silica gel layer 14, the laser tube temperature sensor 12 is placed in the heat-conducting silica gel layer 14, and cling to the outer wall of the laser tube 6, its output terminal is connected to the frequency stabilization control module 11, and the thermoelectric cooler 13 is attached to the outer wall of the heat-conducting metal cavity 15 , its input terminal is connected to the frequency stabilization control module 11, and the thermal control structure composed of the laser tube 6, the heat-conducting silica gel layer 14, the heat-conducting metal cavity 15 and the thermoelectric cooler 13 is placed in the cylindrical longitudinal magnetic field module 7, and the laser tube 6 The axis of the axis is parallel to the direction of the magnetic field, the ambient temperature sensor 16 is connected to the frequency stabilization control module 11, the 1/4 wave plate A8, the Wollaston prism 9 and the two-quadrant photodetector 10 are sequentially placed behind the output end of the laser tube 6, The output end of the two-quadrant photodetector 10 is connected to the frequency stabilization control module 11, the 1/4 wave plate B18, the polarization beam splitter B19 and the acousto-optic frequency shifter 20 are placed in sequence before the main output end of the laser tube 6, and the beam splitter 21 is placed Between the acousto-optic frequency shifter 20 and an input end of the fiber beam combiner 22, the other input end of the fiber beam combiner 22 is connected with one of the output ends of the fiber beam splitter 5, and the polarizer 23 is placed on the optical fiber Between the output terminal of the beam combiner 22 and the high-speed photodetector 24, the high-speed photodetector 24, the frequency measurement module 25, the frequency adjustment module 26, and the acousto-optic frequency shifter 20 are connected in sequence, and the frequency lock status indicator light 27 is connected with the frequency adjustment Module 26 is connected.

Since the device includes multiple longitudinal Zeeman frequency-stabilized lasers L ₁ , L ₂ ,…, L _n with the same structure, the working process of these longitudinal Zeeman frequency-stabilized lasers is exactly the same, and only one of the longitudinal Zeeman frequency-stabilized lasers is described below _L1 describes the working process, and these descriptions are also applicable to other similar longitudinal Zeeman frequency-stabilized lasers in the device.

When starting to work, turn on the laser power supply A1, and refer to the longitudinal Zeeman frequency stabilization laser 3 to enter the preheating and frequency stabilization process. When the above process is completed, enable the frequency stabilization status indicator 2, indicating that the reference longitudinal Zeeman frequency stabilization laser 3 enters In a stable working state, the internal laser tube outputs two laser components whose polarization directions are orthogonal to each other, and one of the laser components is taken out by the polarization beam splitter A4 as the output light, and coupled into the fiber beam splitter 5, which is separated into n-channel frequency reference Beams, denoted as beams X ₁ , X ₂ ,…, X _n , whose frequency is denoted by ν _r , are used as reference frequencies for frequency locking of longitudinal Zeeman lasers L ₁ , L ₂ ,…, L _n .

When the frequency stabilization status indicator light 2 is enabled, the laser tube power supply B17 is turned on, and the longitudinal Zeeman frequency stabilization laser _L1 enters the preheating process. The frequency stabilization control module 11 sets the target temperature _Tset for preheating according to the ambient temperature value measured by the ambient temperature sensor 16, and _Tset is higher than the ambient temperature, and _Tset is used as the preheating closed-loop control system as shown in Figure 4 The reference input quantity of the laser tube temperature sensor 12 is used to measure the actual temperature T _real of the laser tube 6 as a feedback signal, and the frequency stabilization control module 11 calculates the difference between the two, and adjusts the temperature of the thermoelectric cooler 13 according to the frequency stabilization control algorithm. The size and positive and negative of the working current, heating or cooling the laser tube 6, so that its temperature tends to the preset target temperature T _set to reach a thermal equilibrium state, on this basis, fine-tune the positive and negative working current of the thermoelectric cooler 13 according to the preheating algorithm Inverse and large, so that the laser tube 6 works in a single longitudinal mode light output state, the single longitudinal mode light is split into two laser components of left-handed and right-handed circular polarization under the action of the longitudinal magnetic field, and the laser tube 6 is output from the main output end of the laser tube 6 and Sub-output output.

After the preheating process is completed, the frequency stabilization control module 11 switches the longitudinal Zeeman frequency stabilization laser _L1 to enter the frequency stabilization control process. The left-handed and right-handed laser components output by the secondary output end of the laser tube 6 are transformed into mutually orthogonal linearly polarized light components by the 1/4 wave plate A8, and separated by the Wollaston prism 9, and its optical power P ₁ ¹ and P ₁ ² are measured by the two-quadrant photodetector 10, and the power difference ΔP=P ₁ ¹ -P ₁ ² of the two longitudinal modes is used as the feedback input quantity of the frequency stabilization closed-loop control system shown in Figure 5, refer to The input quantity is set to zero, and the frequency stabilization control module 11 calculates the difference between the reference input quantity and the feedback input quantity, and adjusts the size and direction of the working current winding the thermoelectric cooler 13 according to the frequency stabilization control algorithm, and then adjusts the laser tube 6. The temperature and the length of the resonant cavity make the power of the two laser components P ₁ ¹ = P ₁ ² , and the frequency of the two laser components tends to a stable value at this time.

After the frequency stabilization process is over, the laser _L1 enters the frequency locking process, and the left-handed and right-handed circularly polarized laser components output by the main output end of the laser tube 6 are transformed into mutually orthogonal linearly polarized light by the 1/4 wave plate B18, and One of the laser components is separated by the polarization beam splitter B19, and used as the input light of the acousto-optic frequency shifter 20, its frequency is denoted as ν ₁ , and the operating frequency of the acousto-optic frequency shifter 20 is denoted as f ₁ , due to the acousto-optic interaction, The frequency of the laser light output by the acousto-optic frequency shifter 20 is ν ₁₊ f ₁ , and the light beam is separated into two parts of light with an intensity of 9:1 by the beam splitter 21, and the part of light with a relatively high intensity is recorded as beam Z ₁ , as The output laser light of the longitudinal Zeeman laser L ₁ , the part of the light with relatively small intensity is recorded as the beam Y ₁ , and the beam and the beam X ₁ are coupled into the optical fiber by the fiber beam combiner 22 and synthesized into a coaxial beam, the coaxial beam After passing through the polarizer 23, an optical beat frequency signal is formed, and after the photoelectric conversion is carried out by the high-speed photodetector 24, its frequency value Δν ₁ =ν ₁ + f ₁ -ν _r is measured by the frequency measurement module 25, and is obtained as shown in FIG. 6 For the feedback input of the frequency-locked closed-loop control system shown, the reference input is set to zero, and the frequency adjustment module 26 calculates the frequency difference between the beam X ₁ and the beam Y ₁ as ν _r according to the difference between the two Δν ₁ −ν ₁ = f ₁ −Δν ₁ , and the driving frequency f ₁ of the acousto-optic frequency shifter 20 is adjusted to ν _r −ν ₁ , so that the laser L ₁ outputs the frequency of the beam Z ₁ (beam Z ₁ and beam Y ₁ same frequency) is equal to the frequency ν _r of the reference beam X ₁ . After the above frequency locking process is completed, the frequency adjustment module 26 enables the frequency locking status indicator light 27 .

When the external environment changes or other factors cause the frequency of the output laser of the reference longitudinal Zeeman frequency stabilized laser 3 or longitudinal Zeeman laser _L1 to change, the above-mentioned frequency stabilization and locking process is automatically cycled, and the operating frequency of the acousto-optic frequency shifter 20 is adjusted. f ₁ , so that the laser output frequency ν ₁ of the longitudinal Zeeman laser L ₁ is always locked at the reference frequency ν _r . Similarly, the frequencies ν ₂ , ν ₃ , ..., ν _n of the laser output from the longitudinal Zeeman lasers L ₂ , L ₃ ,..., L _n are always locked at the reference frequency ν _r .

Claims (2)

1. A longitudinal Zeeman laser frequency-locking method based on thermoelectric refrigeration and acousto-optic frequency shifting, characterized in that the method may further comprise the steps: (1) Turn on the power of the reference longitudinal Zeeman frequency-stabilized laser. After preheating and frequency stabilization, the laser outputs two laser components with orthogonal polarization, and use a polarization beam splitter to separate one of the laser components as the reference longitudinal Zeeman-stabilized laser. frequency laser output light, its light wave frequency is denoted as ν _r , and the output light is split into n≥1 paths by the fiber beam splitter, denoted as beam X _i (i=1,2,…,n), which are respectively used as longitudinal plugs Mann laser L _i (i=1,2,…,n) frequency-locked reference beam; (2) Turn on the power of the longitudinal Zeeman laser L _i (i=1,2,…,n), all longitudinal Zeeman lasers enter the preheating process at the same time, measure the temperature value of the current environment, and set the preheating target accordingly temperature T _set , and T _set is higher than the ambient temperature, using a thermoelectric cooler to heat the laser tube placed in the longitudinal magnetic field, so that the temperature of the laser tube tends to the preset temperature value T _set and reaches a thermal equilibrium state, where Based on the preheating algorithm, the positive and negative currents of the thermoelectric cooler are fine-tuned, so that the laser tube works in the single longitudinal mode light output state, and the single longitudinal mode light is split into left-handed and right-handed circular polarization under the action of the longitudinal magnetic field. The laser component is output from the main output end and the auxiliary output end of the laser tube; (3) The longitudinal Zeeman laser L _i (i=1,2,…,n) enters the frequency stabilization control process after the preheating process, and the left-handed and right-handed circularly polarized light at the secondary output end of the laser tube passes through the 1/4 wave plate Transformed into mutually orthogonal linearly polarized light and separated by a Wollaston prism, its optical power P _i ¹ (i=1,2,…,n) and P _i ² (i=1,2,…, n) Measured by the two-quadrant photodetector, the frequency stabilization control module calculates the power difference ΔP _i =P _i ¹ –P _i ² (i=1,2,…,n) of the two laser components, and according to The positive and negative sum of ΔP _i (i=1,2,…,n) adjusts the positive and negative sum of the working current of the thermoelectric cooler, so that ΔP _i (i=1,2,…,n) tends to zero, and then makes The frequency of the laser tends to a stable value; (4) The left-handed and right-handed circularly polarized light at the main output end of the laser tube is converted into two mutually orthogonal linearly polarized lasers by a 1/4 wave plate, and one of the linearly polarized laser components is separated by a polarization beam splitter, which is recorded as a beam T _i (i=1,2,…,n), its frequency is denoted as ν _i (i=1,2,…,n), the beam T _i (i=1,2,…,n) enters the drive frequency The acousto-optic frequency shifter S _i (i=1,2,…,n) for f _i (i=1,2,…,n) performs frequency shifting, and the corresponding output laser frequency is denoted as ν _i + f _i (i=1,2,…,n), the laser is divided into two parts with an intensity ratio of 9:1 by the beam splitter, and the part with relatively high intensity is recorded as the beam Z _i (i=1, 2,…,n), respectively as the output laser light of the longitudinal Zeeman laser L _i (i=1,2,…,n), and the light with relatively small intensity is recorded as the beam Y _i (i=1,2,… ,n); (5) Optically mix the light beam X _i (i=1,2,…,n) with the light beam Y _i (i=1,2,…,n) respectively to form an optical beat frequency signal, and use the photodetector to convert the optical The beat frequency signal is converted into an electrical signal, and its frequency value Δν _i =ν _i + f _i –ν _r (i=1,2,…,n) is measured by the frequency measurement module, and the frequency adjustment module is based on the measured optical beat frequency The frequency value of the signal Δν _i (i=1,2,…,n), calculates the beam X _i (i=1,2,…,n) and Y _i (i=1,2,…,n) Frequency difference ν _r –ν _i = f _i –Δν _i (i=1,2,…,n), and the driving frequency f of the acousto-optic frequency shifter S _i (i=1,2,…,n) _i (i=1,2,…,n) is adjusted to ν _r –ν _i (i=1,2,…,n), so that the longitudinal Zeeman laser L _i (i=1,2,…,n) The frequency of the output beam Z _i (i=1,2,…,n) is equal to the frequency of the reference beam X _i (i=1,2,…,n), that is, ν _i + f _i = ν _r (i=1, 2,...,n); (6) Repeat steps (4) to (5) cyclically, by adjusting the operating frequency f _i (i=1,2,…,n) of the acousto-optic frequency shifter S _i (i=1,2,…,n) , so that the frequency of the output laser Z _i (i=1,2,...,n) of the longitudinal Zeeman laser L _i (i=1,2,...,n) is always locked at the same frequency value ν _r . 2. A longitudinal Zeeman laser frequency-locking device based on thermoelectric cooling and acousto-optic frequency shifting, including a laser power supply A (1), a frequency stabilization status indicator light (2), a reference longitudinal Zeeman frequency stabilization laser (3), a polarization Spectroscope A (4), fiber optic beam splitter (5), characterized in that the device also includes n≥1 longitudinal Zeeman lasers (L ₁ , L ₂ ,..., L _n ) with the same structure and in parallel relationship, The assembly structure of each of the longitudinal Zeeman lasers (L ₁ , L ₂ ,..., L _n ) is: the laser power supply B (17) is connected to the laser tube (6), and the laser tube (6) is placed in the heat-conducting metal cavity (15 ), the gap between the laser tube (6) and the heat-conducting metal cavity (15) is filled with a heat-conducting silica gel layer (14), and the laser tube temperature sensor (12) is placed in the heat-conducting silica gel layer (14) and closely attached to the laser tube ( 6) The outer wall, the output terminal of which is connected to the frequency stabilization control module (11), the thermoelectric cooler (13) is attached to the outer wall of the heat-conducting metal cavity (15), the input terminal of which is connected to the frequency stabilization control module (11), the laser tube (6 ), the heat-conducting silica gel layer (14), the heat-conducting metal cavity (15) and the thermoelectric cooler (13) are placed in the cylindrical longitudinal magnetic field module (7), and the axis of the laser tube (6) is in line with The direction of the magnetic field is parallel, the ambient temperature sensor (16) is connected to the frequency stabilization control module (11), the 1/4 wave plate A (8), the Wollaston prism (9) and the two-quadrant photodetector (10) are sequentially placed on the After the auxiliary output of the laser tube (6), the output of the two-quadrant photodetector (10) is connected to the frequency stabilization control module (11), and the 1/4 wave plate B (18), polarizing beam splitter B (19) and acoustic The optical frequency shifter (20) is sequentially placed in front of the main output end of the laser tube (6), and the beam splitter (21) is placed between the acousto-optic frequency shifter (20) and an input end of the fiber combiner (22), The other input end of the optical fiber combiner (22) is connected to one of the output ends of the optical fiber splitter (5), and the polarizer (23) is placed at the output end of the optical fiber combiner (22) to connect with the high-speed photodetector (24), the high-speed photodetector (24), frequency measurement module (25), frequency adjustment module (26), acousto-optic frequency shifter (20) are connected in sequence, and the frequency lock status indicator light (27) is connected with the frequency adjustment Module (26) is connected.