A method for controlling the air chamber temperature of a SERF inertial measurement device based on second harmonic

Abstract

The present invention discloses a gas chamber temperature control method for a SERF inertial measurement device based on second harmonic generation. The method utilizes gas chamber optical depth information obtained by the SERF device's own detection system to perform feedback regulation on the laser heating power of the atomic gas chamber, thereby achieving real-time and stable control of the atomic density or temperature in the gas chamber. This avoids the magnetic field interference introduced by the use of thermal resistors as temperature sensors in existing solutions, thereby achieving truly non-magnetic, all-optical gas chamber heating and its control system, and helping to improve the sensitivity of the SERF inertial measurement device.

Description

Technical Field

[0001] The present invention belongs to the technical field of precision measurement equipment, namely a SERF atomic spin inertial measurement device, and particularly relates to a method for controlling the temperature of an alkali metal gas chamber by utilizing the second harmonic in the detection signal of the device itself. Background Art

[0002] Atomic spin inertial measurements based on the spin-exchange relaxation-free (SERF) effect can theoretically achieve extremely high sensitivity. Related research has developed rapidly in recent years and holds important application prospects in fields such as basic research and inertial navigation. To achieve the SERF state, the atomic density within the alkali metal chamber in the measurement device must be sufficiently high and the magnetic field felt by the atoms sufficiently low.

[0003] To achieve a sufficiently high atomic density, the alkali metal vapor cell must be heated. Once the preset temperature is reached, real-time and precise temperature or atomic density control is required to prevent fluctuations in the scale factor caused by atomic density fluctuations. Currently, the mainstream heating methods are electrical heating and optical heating. Electrical heating involves twisting the heating resistor wires into a pair and modulating the current to a high frequency to minimize magnetic field interference, but a weak residual magnetic field still remains. Optical heating, on the other hand, completely avoids the introduction of magnetic fields. Real-time control of temperature or atomic density typically uses a thermistor attached to the outside of the vapor cell as a temperature sensor, with the signal fed back to the heating power for closed-loop temperature control. This results in a certain control lag for the atomic density within the vapor cell. Furthermore, the need to apply an excitation current to the thermistor generates magnetic field interference, and temperature fluctuations are pronounced at low frequencies. The feedback adjustment of the heating current based on the vapor cell temperature introduces unavoidable low-frequency magnetic field noise. For optical heating systems of alkali metal vapor cells, the temperature feedback based on the thermistor is the final obstacle to achieving true magnetization.

[0004] For SERF devices, high-sensitivity signal detection is generally achieved by detecting the optical rotation angle of linearly polarized light passing through the gas cell. To suppress the more influential low-frequency components of the noise, a modulator is used to rotate the polarization direction of the detection light slightly at a higher frequency. After detection by a phototube, the detection light is demodulated with a phase-locked amplifier. The first harmonic of the modulation frequency contains information about the light intensity and the optical rotation angle, while the second harmonic, or second harmonic, contains information about the light intensity. The light intensity information before and after passing through the gas cell can reflect the optical depth of the gas cell, which can be used to feedback control the atomic density. Modulators include Faraday modulators, electro-optical modulators, and photoelastic modulators. Summary of the Invention

[0005] The present invention addresses the shortcomings of the prior art by providing a second harmonic-based gas chamber temperature control method for a SERF inertial measurement device. This method utilizes the gas chamber optical depth information obtained by the SERF device's own detection system to feedback-regulate the laser heating power of the atomic gas chamber. This method enables real-time, stable control of the atomic density or temperature within the gas chamber, avoiding the magnetic field interference introduced by existing solutions that use thermal resistors as temperature sensors. This method achieves truly non-magnetic, all-optical gas chamber heating and its control system, contributing to improved sensitivity of the SERF inertial measurement device.

[0006] The object of the present invention is achieved through the following technical solutions:

[0007] A method for controlling the gas chamber temperature of a SERF inertial measurement device based on second harmonic generation is disclosed. The SERF inertial measurement device includes a pumping light, a heating laser, a dichroic mirror, a magnetic shielding tube, an alkali metal gas chamber, a thermal resistor, a photothermal structure, a three-axis magnetic compensation coil, a detection light, a polarizer, a reflector, a quarter-wave plate, a photoelastic modulator, an analyzer, a second photodetector, a lock-in amplifier, a data acquisition system, and a computer. The method comprises the following steps:

[0008] (1) A non-polarizing beam splitter and a first photodetector are added to the front end of the detection optical path of the SERF inertial measurement device. The transmission-reflection ratio of the non-polarizing beam splitter is 10:90. The transmitted light is used as the reference light to hit the first photodetector, and the reflected light passes through the polarizer, alkali metal gas chamber, quarter-wave plate, photoelastic modulator, and analyzer to hit the second photodetector. The signal of the first photodetector is amplified by transimpedance and input into the data acquisition system and computer. The amplified voltage signal V a =η a M a I a P a , where η a is the photoelectric conversion efficiency of the first photodetector; M a is the transimpedance amplification factor; I a To detect the light intensity before it passes through the alkali metal gas cell; P a The intensity of the detection light hitting the first photodetector and I a The signal of the second photodetector is processed by the phase-locked amplifier to obtain the first harmonic and second harmonic signals of the modulation frequency and input them into the computer; the second harmonic signal V b =η b M b I b P b δ 2 / 8,η v is the photoelectric conversion efficiency of the second photodetector 17; M bis the preamplification factor of the lock-in amplifier; I v To detect the light intensity after it passes through the alkali metal gas chamber and reaches the reflector; P b To detect the intensity of light after passing through the analyzer and I b The ratio of δ to the modulation amplitude of the photoelastic modulator is:

[0009] (2) Temperature calibration of the optical depth of the alkali metal gas chamber: Turn on the heating laser and heat the alkali metal gas chamber from room temperature to the target temperature of 190°C. During the heating process, the temperature is measured using a thermal resistor. At the same time, the optical depth is measured using the method of step (1) to establish a corresponding relationship between the gas chamber temperature and the optical depth.

[0010] (3) Turn off the power supply of the thermal resistor and make the SERF inertial measurement device officially work, measure the optical depth of the alkali metal gas chamber (5) in real time according to the method of step (1), compare the optical depth with the optical depth corresponding to the target temperature obtained in step 2, use computer PID control to generate a control signal, input the control signal to the external analog control port of the heating laser, and control the laser power by controlling the laser current, thereby achieving stable temperature control of the alkali metal gas chamber.

[0011] The beneficial effects of the present invention are: good compatibility with the general SERF inertial measurement device, and only minor changes to the detection system are required to realize real-time measurement of optical depth based on the second harmonic of the modulated signal, and to be used for stable control of the gas chamber temperature or atomic density; because the power supply of the thermistor is disconnected when the SERF device is officially working, the magnetic noise introduced by the use of the thermistor as a temperature sensor in the general solution is avoided, and on the basis of laser heating, truly non-magnetic all-optical gas chamber heating and its control system are realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Schematic diagram of the system design involved in a method for controlling the air chamber temperature of a SERF inertial measurement device based on second harmonic according to an embodiment of the present invention.

[0013] Explanation of the accompanying drawings: 1-pumping light; 2-heating laser; 3-dichroic mirror; 4-magnetic shielding tube; 5-alkali metal gas chamber; 6-thermal resistor; 7-photothermal structure; 8-three-axis magnetic compensation coil; 9-detection light; 10-non-polarizing beam splitter; 11-first photodetector; 12-polarizer; 13-reflector; 14-quarter wave plate; 15-photoelastic modulator; 16-polarizer; 17-second photodetector; 18-phase-locked amplifier; 19-data acquisition system and computer. DETAILED DESCRIPTION

[0014] The present invention will be described below with reference to the embodiments and the accompanying drawings.

[0015] like Figure 1 As shown, the universal SERF inertial measurement device involved in the embodiment of the present invention includes a pumping light 1, a heating laser 2, a dichroic mirror 3, a magnetic shielding tube 4, an alkali metal gas chamber 5, a thermal resistor 6, a photothermal structure 7, a three-axis magnetic compensation coil 8, a detection light 9, a polarizer 12, a reflector 13, a quarter-wave plate 14, a photoelastic modulator 15, an analyzer 16, a second photodetector 17, a phase-locked amplifier 18, a data acquisition system and a computer 19. For the sake of simplicity, devices such as the pumping laser and the detection laser are not shown in this embodiment. Among them, the heating laser 2 has no requirements on indicators such as laser line width, polarization, and frequency noise, but requires that the laser current can be controlled by external analog control, and the corresponding laser wavelength is far detuned from the atomic energy level in the alkali metal gas chamber. The dichroic mirror 3 is used to combine the two wavelengths of pumping light 1 and heating light. The thermal resistor 6 is a non-magnetic platinum resistor. The photothermal structure 7 is made of bandpass filter glass, which has high transmittance for the wavelength band of the pumping light 1 and high absorption for the heating light. Different thicknesses of filter glass are selected based on the absorptivity of the heating light and attached to both ends of the alkali metal gas chamber 5 to ensure balanced heating. Both the polarizer 12 and analyzer 16 are Glan Taylor prisms.

[0016] like Figure 1 As shown, the specific steps of the embodiment of the present invention are as follows:

[0017] 1. Modify the detection system of the general SERF inertial measurement device: add a non-polarizing beam splitter 10 and a first photodetector 11 at the front end of the detection optical path. The transmission-reflection ratio of the non-polarizing beam splitter 10 is 10:90. The transmitted light is used as the reference light to hit the first photodetector 11, and the reflected light passes through the polarizer 12, alkali metal gas cell 5, quarter-wave plate 14, photoelastic modulator 15, analyzer 16, and then hits the second photodetector 17. The signal from the first photodetector 11 is amplified by transimpedance and input into the data acquisition system and computer 19. The amplified voltage signal V a =η a M a I a P a , where η a is the photoelectric conversion efficiency of the first photodetector 11; M a is the transimpedance amplification factor; I a To detect the light intensity before the light passes through the alkali metal gas chamber 5; a The intensity of the detection light hitting the first photodetector 11 and I aThe ratio will be determined by actual measurement. The signal of the second photodetector 17 is processed by the phase-locked amplifier 18 to obtain the first harmonic and second harmonic signals of the modulation frequency and input them into the computer 19. The second harmonic signal V b =η b M b I b P b δ 2 / 8,η b is the photoelectric conversion efficiency of the second photodetector 17; M b is the preamplification factor of the lock-in amplifier 18; I b To detect the light intensity after the light passes through the alkali metal gas chamber 5 and reaches the reflector 13; P b To detect the intensity of light after passing through the analyzer 16 and I b The ratio will be determined by actual measurement; δ is the modulation amplitude of the photoelastic modulator. Then the optical depth of the alkali metal gas cell 5 is:

[0018] 2. Temperature calibrate the optical depth of the alkali metal gas chamber 5: Turn on the heating laser 2 and heat the alkali metal gas chamber 5 from room temperature to the target temperature of 190°C. During the heating process, measure the temperature using thermistor 6. Simultaneously, measure the optical depth using the method in step 1 to establish a corresponding relationship between the gas chamber temperature and the optical depth. During the gas chamber temperature calibration process and the SERF inertial measurement unit operation, the detection light wavelength must remain consistent. If necessary, splitting can be performed at the front end of the detection light path. One path of light can be input to the wavelength meter and fed back to the detection light laser for frequency stabilization.

[0019] 3. Turn off the power supply to the thermal resistor 6 and enable the SERF inertial measurement device to officially operate. Measure the optical depth of the alkali metal gas chamber 5 in real time according to the method in step 1. Compare the optical depth with the optical depth corresponding to the target temperature obtained in step 2. Use computer PID control to generate a control signal. Input the control signal to the external analog control port of the heating laser 2. Control the laser power by controlling the laser current, thereby achieving stable temperature control of the alkali metal gas chamber 5.

[0020] Finally, it should be noted that the above embodiments and explanations are intended only to illustrate the technical solutions of the present invention and are not intended to limit the present invention. It should be understood by those skilled in the art that modifications or equivalent substitutions to the technical solutions of the present invention may be made without departing from the spirit and scope of the technical solutions disclosed herein, and all such modifications or equivalent substitutions shall be encompassed within the scope of protection of the claims of the present invention.

Claims

1. A method for controlling the gas chamber temperature of a SERF inertial measurement device based on second harmonic generation, wherein the SERF inertial measurement device comprises a pumping light, a heating laser, a dichroic mirror, a magnetic shielding tube, an alkali metal gas chamber, a thermal resistor, a photothermal structure, a three-axis magnetic compensation coil, a detection light, a polarizer, a reflector, a quarter-wave plate, a photoelastic modulator, an analyzer, a second photodetector, a lock-in amplifier, a data acquisition system, and a computer; characterized in that: The method comprises the following steps: (1) A non-polarizing beam splitter and a first photodetector are added to the front end of the detection optical path of the SERF inertial measurement device. The transmission-reflection ratio of the non-polarizing beam splitter is 10:

90. The transmitted light is used as the reference light to hit the first photodetector, and the reflected light passes through the polarizer, alkali metal gas chamber, quarter-wave plate, photoelastic modulator, and analyzer to hit the second photodetector. The signal of the first photodetector is amplified by transimpedance and input into the data acquisition system and computer. The amplified voltage signal V a =η a M a I a P a , where η a is the photoelectric conversion efficiency of the first photodetector; M a is the transimpedance amplification factor; I a To detect the light intensity before it passes through the alkali metal gas cell; P a The intensity of the detection light hitting the first photodetector and I a The signal of the second photodetector is processed by the phase-locked amplifier to obtain the first harmonic and second harmonic signals of the modulation frequency and input them into the computer; the second harmonic signal V b =η b M b I b P b δ 2 / 8,η b is the photoelectric conversion efficiency of the second photodetector 17; M b is the preamplification factor of the lock-in amplifier; I b To detect the light intensity after it passes through the alkali metal gas chamber and reaches the reflector; P b To detect the intensity of light after passing through the analyzer and I b The ratio of δ to the modulation amplitude of the photoelastic modulator is: (2) Temperature calibration of the optical depth of the alkali metal gas chamber: Turn on the heating laser and heat the alkali metal gas chamber from room temperature to the target temperature of 190°C. During the heating process, the temperature is measured using a thermal resistor. At the same time, the optical depth is measured using the method of step (1) to establish a corresponding relationship between the gas chamber temperature and the optical depth. (3) Turn off the power supply of the thermal resistor and make the SERF inertial measurement device officially work, measure the optical depth of the alkali metal gas chamber (5) in real time according to the method of step (1), compare the optical depth with the optical depth corresponding to the target temperature obtained in step 2, use computer PID control to generate a control signal, input the control signal to the external analog control port of the heating laser, and control the laser power by controlling the laser current, thereby achieving stable temperature control of the alkali metal gas chamber.

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