A real-time closed-loop control device and method for laser polarization in an optically pumped atomic gas chamber

Abstract

The present invention discloses a real-time closed-loop control device and method for laser polarization in an optically pumped atomic gas chamber, and belongs to the technical field of high-precision atomic spin magnetic field and inertial measurement. The present invention is based on atomic spin optical pumping technology and first-order differential control technology, and uses a liquid crystal phase retarder to realize polarization state modulation of the pumping light. The optical power change of the pumping laser passing through the polarized atomic gas chamber is detected by a photodetector, and a first-order differential signal is extracted as an error signal by a phase-locked amplifier. The polarization state of the pumping light is stably controlled at a circular polarization point, and laser polarization modulation detection and closed-loop control are realized. The present invention effectively improves the optical pumping efficiency and the long-term stability of the electronic polarization rate, and can be widely used in quantum precision measuring instruments including optically pumped atomic gas chambers, such as atomic gyroscopes, atomic magnetometers, atomic gravimeters, etc., and is particularly suitable for small quantum sensors that pursue high integration.

Description

Technical Field

[0001] The invention belongs to the technical field of high-precision atomic spin magnetic field and inertial measurement, and in particular relates to a real-time closed-loop control device and method for laser polarization in an optically pumped atomic gas chamber. Background Art

[0002] Precision measuring instruments based on quantum technology have been widely developed in recent years due to their extremely high sensitivity, especially atomic magnetometers, atomic gyroscopes, atomic clocks, etc. based on optically pumped alkali metal atom technology, and are widely used in inertial navigation, magnetic field measurement, zero-magnetic medicine and zero-magnetic biology research. Most of the above-mentioned quantum precision measuring instruments use laser pumping of alkali metal atoms to achieve atomic polarization. The stability of the polarizability is closely related to the sensitivity and long-term stability of inertial measurement and magnetic field measurement. Therefore, it is of great significance to improve the long-term stability of electronic polarizability.

[0003] The electronic polarizability is affected by laser light power, frequency, light field distribution, polarization state and gas chamber temperature. According to the principle of optical pumping, only the circularly polarized component in the pumping laser plays a pumping role, and the laser polarization state will gradually depolarize the original circularly polarized light due to the influence of the device itself in the optical path, the atomic gas chamber, ambient temperature and vibration, thereby causing the electronic polarization rate to drift. In addition, traditional polarization measurement methods require multiple optical devices, occupy a large volume and are not easy to operate. For miniature instruments, a simple and easy-to-operate real-time detection and closed-loop control method for the polarization state of the pumping laser is needed. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a real-time closed-loop control device and method for laser polarization in an optically pumped atomic gas chamber. The device has a simple structure, does not add additional optical devices, only needs to use a photodetector, and is simple and convenient to operate; the first-order differential signal of the transmitted light intensity of the pumping light passing through the polarized atomic gas chamber is used as the feedback control signal for online control of the polarization state, and decoupling from other signals is achieved through modulation, with high measurement accuracy and good control stability, suppressing the long-term drift of the polarization state, which is conducive to improving the long-term stability of the electronic polarizability.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] On the one hand, the present invention provides a real-time closed-loop control device for laser polarization in an optically pumped atomic gas chamber, comprising a pumping laser, a magneto-optical isolator, a beam expansion component, a polarizer, a liquid crystal phase retarder, a heating oven, a polarized atomic gas chamber, a three-dimensional coil, a multi-layer magnetic shielding tube, a photodetector, a phase-locked amplifier, a closed-loop control module, an adder, and a signal generator; wherein the light beam emitted by the pumping laser passes through the magneto-optical isolator, the beam expansion component, the polarizer, the liquid crystal phase retarder, the polarized atomic gas chamber, and the photodetector in sequence before reaching the phase-locked amplifier, the output end of the phase-locked amplifier is connected to the closed-loop control module, the closed-loop control module is used to calculate a control voltage signal, the signal generator generates a reference signal respectively and inputs it into the phase-locked amplifier to provide a frequency reference, and generates a modulation signal and inputs it into the adder; the adder receives the control voltage signal calculated by the closed-loop control module and the modulation signal generated by the signal generator, adds them, and then inputs them into the liquid crystal phase retarder, controls the phase delay amount of the liquid crystal phase retarder to realize closed-loop control of the polarization state;

[0007] The polarized atomic gas chamber is located in the heating oven, and the three-dimensional coil is attached to the outside of the heating oven; the heating oven, the polarized atomic gas chamber, and the three-dimensional coil are placed in a multi-layer magnetic shielding tube.

[0008] Furthermore, the heating oven is a boron nitride material cylinder with a spherical cavity in the center for placing a spherical polarized atomic gas chamber. The surface of the heating oven is symmetrically affixed with a twisted flexible heating film, and the three-dimensional coil is affixed to the outside of the heating film. The multi-layer magnetic shielding tube has holes in the z-axis direction for the light beam emitted by the pumping laser to pass through. The magneto-optical isolator is used to allow the laser to pass in one direction and isolate the back-reflected laser; the light transmission axis of the polarizer is along the x-axis direction; the fast axis of the liquid crystal phase retarder is at an angle of 45 degrees to the x-axis, and is used to change the phase delay amount according to different control voltages, so that the laser polarization state changes from linear polarization to circular polarization; the polarized atomic gas chamber is a spherical glass filled with potassium, rubidium and neon atoms.

[0009] On the other hand, the present invention also provides a method for real-time closed-loop control of laser polarization in an optically pumped atomic gas chamber, comprising the following steps:

[0010] Step 1: Use the heating oven to heat the polarized atomic gas chamber, and use the thermistor to feedback the temperature to achieve closed-loop stable temperature control; use a precision signal generator to control the three-dimensional coil to perform active magnetic field compensation;

[0011] Step 2: The signal generator generates a modulation signal and transmits it to the adder, generates a reference signal and transmits it to the phase-locked amplifier to provide a frequency reference; the modulation signal is , is the modulation amplitude, is the modulation frequency, is the frequency of the liquid crystal AC control voltage, and t is the time;

[0012] Step 3: The photodetector converts the acquired transmitted light intensity signal into a voltage signal and transmits it to the lock-in amplifier, which extracts the first-order differential signal as an error signal. Transmitted to the closed-loop control module; the transmitted light intensity and the effective value of the LCD AC control voltage There is an even function relationship ; The effective value of the liquid crystal AC control voltage is the center voltage When the error signal is zero, the laser polarization state is circular polarization; when the effective value of the liquid crystal AC control voltage is Less than center voltage When the error signal is positive, the effective value of the liquid crystal AC control voltage is Greater than center voltage When , the error signal is negative;

[0013] Step 4: The closed-loop control module calculates the effective value of the liquid crystal AC control voltage according to the error signal And transmitted to the adder, when the error signal When it is positive, the effective value of the liquid crystal AC control voltage increases , error signal When it is negative, the effective value of the LCD AC control voltage is reduced The adder adds the modulation signal and the effective value of the liquid crystal AC control voltage After addition, the signals are applied to the liquid crystal retarder.

[0014] The beneficial effects of the present invention are:

[0015] Based on the principle of light absorption, only one photodetector is used to detect the first-order differential signal of the transmitted light intensity of the pumping light passing through the polarized atomic gas chamber, and the modulation and control are simultaneously realized through the liquid crystal phase retarder, so as to realize the modulation detection and closed-loop control of the polarization state of the pumping light. No additional optical devices are added, the operation is simple, the structure is compact, and the measurement accuracy is high, which can effectively improve the optical pumping efficiency and the long-term stability of the electron polarization rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a structural block diagram of a real-time closed-loop control device for laser polarization in an optically pumped atomic gas chamber of the present invention;

[0017] Figure 2 The present invention is a flow chart of a method for real-time closed-loop control of laser polarization in an optically pumped atomic gas chamber.

[0018] Reference numerals:

[0019] 1. Pumping laser; 2. Magneto-optical isolator; 3. Beam expansion assembly; 4. Polarizer; 5. Liquid crystal phase retarder; 6. Heating oven; 7. Polarized atomic gas chamber; 8. Three-dimensional coil; 9. Multi-layer magnetic shielding tube; 10. Photodetector; 11. Phase-locked amplifier; 12. Closed-loop control module; 13. Adder; 14. Signal generator. DETAILED DESCRIPTION

[0020] The present invention is further described below with reference to the accompanying drawings and specific embodiments.

[0021] like Figure 1 As shown, the structural block diagram of the real-time closed-loop control device for laser polarization in the optically pumped atomic gas chamber of the present invention. The device comprises a pumping laser 1, a magneto-optical isolator 2, a beam expander 3, a polarizer 4, a liquid crystal phase retarder 5, a heating oven 6, a polarized atomic gas chamber 7, a three-dimensional coil 8, a multi-layer magnetic shielding tube 9, a photodetector 10, a lock-in amplifier 11, a closed-loop control module 12, an adder 13, and a signal generator 14, and the positional relationship thereof is as follows:

[0022] The light beam emitted by the pumping laser passes through the magneto-optical isolator 2, the beam expansion component 3, the polarizer 4, the liquid crystal phase retarder 5, the polarized atomic gas chamber 7 and the photodetector 10 in sequence and then reaches the phase-locked amplifier 11. The output end of the phase-locked amplifier 11 is connected to the closed-loop control module 12. The closed-loop control module 12 is used to calculate the control voltage signal. The signal generator 14 generates a reference signal and inputs it into the phase-locked amplifier 11 to provide a frequency reference and generates a modulation signal and inputs it into the adder 13. The adder 13 receives the control voltage signal calculated by the closed-loop control module 12 and the modulation signal generated by the signal generator 14, and then adds them and inputs them into the liquid crystal phase retarder 5 to control the phase delay amount of the liquid crystal phase retarder 5, thereby realizing the closed-loop control of the polarization state.

[0023] The polarized atomic gas chamber 7 is located in the heating oven 6, and the three-dimensional coil 8 is attached to the outside of the heating oven 6; the heating oven 6, the polarized atomic gas chamber 7, the three-dimensional coil 8 is placed in the multi-layer magnetic shielding tube 9;

[0024] The heating oven 6 is a cylinder made of boron nitride material, with a spherical cavity in the center for placing a spherical polarized atomic gas chamber 7. The surface of the heating oven 6 is symmetrically affixed with a twisted flexible heating film, and the three-dimensional coil 8 is affixed to the outside of the heating film. The multi-layer magnetic shielding tube 9 has a hole in the z-axis direction for the light beam emitted by the pumping laser 1 to pass through. The magneto-optical isolator 2 is used to allow the laser to pass in one direction and isolate the back-reflected laser; the light transmission axis of the polarizer is along the x-axis direction; the fast axis of the liquid crystal phase retarder 5 is at an angle of 45 degrees to the x-axis, and is used to change the phase delay amount according to different control voltages, so that the laser polarization state changes from linear polarization to circular polarization; the polarized atomic gas chamber 7 is a spherical glass filled with potassium, rubidium and neon atoms.

[0025] The best embodiment of the present invention is Figure 1 As shown in the figure, its core components are selected and configured to achieve the best performance. Among them, the pump laser 1 uses a DFB semiconductor laser with a wavelength of 795nm to ensure the stability and accuracy of the laser source. The magneto-optical isolator 2 has a high isolation of 35dB, which effectively reduces the reflection interference in the optical path. The beam expansion component 3 is designed as a lens group with 5 times beam expansion to enhance the divergence of the light beam. The polarizer 4 uses a Glan Taylor polarization prism made of calcite, which has an excellent extinction ratio of more than 10 -5 , ensuring the purity of light polarization. The liquid crystal phase retarder 5 uses a liquid crystal phase retarder with a minimum delay of 30nm, which provides precise control for the phase modulation of light. The polarized atomic gas chamber 7 is the core part of the device, consisting of a mixture of K and Rb alkali metal atoms and 3 atmospheres of inert gas 21Ne, where the density ratio of K and Rb is set to 1:82. This ratio optimizes the polarization effect. The three-dimensional coil 8 adopts the Helmholtz coil design to ensure the uniformity and stability of the magnetic field distribution. Finally, the photodetector 10 is composed of a photodiode and a preamplifier circuit, which provides a high-sensitivity and low-noise solution for the detection and conversion of optical signals. The entire system has been carefully designed and optimized to ensure its excellent performance in experiments and applications.

[0026] like Figure 2 As shown, the present invention also provides a real-time closed-loop control method for laser polarization in an optically pumped atomic gas chamber, comprising the following steps:

[0027] Step 1: Use the heating oven 6 to heat the polarized atomic gas chamber 7, and use the thermistor to feedback the temperature to achieve temperature closed-loop stable control; use a precision signal generator to control the three-dimensional coil 8 to perform active magnetic field compensation;

[0028] Step 2, the signal generator 14 generates a modulation signal and transmits it to the adder 13, generates a reference signal and transmits it to the phase-locked amplifier 11 to provide a frequency reference; the modulation signal is , is the modulation amplitude, which is set to 0.3V in this embodiment; is the modulation frequency, which is set to 300 Hz in this embodiment; is the frequency of the liquid crystal AC control voltage, which is set to 2 kHz in this embodiment; t is the time;

[0029] Step 3: The photodetector 10 converts the acquired transmitted light intensity signal into a voltage signal and transmits it to the lock-in amplifier 11. The lock-in amplifier 11 extracts the first-order differential signal as an error signal. Transmitted to the closed-loop control module 12; the transmitted light intensity and the effective value of the LCD AC control voltage There is an even function relationship In this embodiment The initial value is set to 2.5V; the effective value of the LCD AC control voltage Equal to the center voltage When the error signal is zero, the laser polarization state is circular polarization; when the effective value of the liquid crystal AC control voltage is Less than center voltage When the error signal is positive, the effective value of the liquid crystal AC control voltage is Greater than center voltage When , the error signal is negative;

[0030] Step 4: The closed-loop control module 12 calculates the effective value of the liquid crystal AC control voltage according to the error signal And transmitted to adder 13, when the error signal When it is positive, the effective value of the liquid crystal AC control voltage increases , error signal When it is negative, reduce the effective value of the LCD AC control voltage , LCD AC control voltage effective value The calculation adopts the incremental PID algorithm; the adder 13 adds the modulation signal and the effective value of the liquid crystal AC control voltage After addition, it is applied to the liquid crystal phase retarder 5; the liquid crystal AC control voltage signal is The added signal output by the adder, that is, the control signal of the liquid crystal phase retarder 5 is .

[0031] The working principle of the present invention is as follows: the pump light generated by the pump laser 1 controls the laser polarization state through the liquid crystal phase retarder 5. Based on the principle of light absorption, the polarized alkali metal vapor chamber absorbs lasers of different polarization states differently, with the weakest absorption of circularly polarized light and the strongest absorption of linearly polarized light. Therefore, the magnitude of the transmitted light intensity can reflect the polarization state of the pump light before it enters the gas chamber, and a photoelectric detector can be used to detect the light intensity change signal. In addition, if the polarization state of the pumping light is changed by the liquid crystal phase retarder 5, as the liquid crystal control voltage increases, the polarization state of the pumping light will change from linear polarization to circular polarization and then to linear polarization within a certain range, and the transmitted light intensity will increase first and then decrease. The transmitted light intensity is the largest at the circular polarization point, and this is the extreme point of the transmitted light intensity, and the first-order differential is zero. Therefore, the modulation and demodulation method can be used through the liquid crystal phase retarder 5 and the phase-locked amplifier 11, and the first-order differential signal of the light intensity extracted by the phase-locked amplifier 11 can be used. As an error signal, a modulation signal and a reference signal can be generated by a signal generator. The first-order differential at the circular polarization is zero, and the voltage here is called the center voltage. When the liquid crystal control voltage is less than the center voltage, the error signal is positive, and when the liquid crystal control voltage is greater than the center voltage, the signal is negative. At the center voltage, the error signal is zero. Moreover, within a certain range, the farther the control voltage is from the center voltage, the greater the absolute value of the error signal. The positive and negative values ​​of the error signal can be used to determine the position of the current control voltage relative to the center voltage, that is, the position where the polarization state deviates from the circular polarization. The liquid crystal control voltage is calculated using the PID algorithm through the closed-loop control module, and the modulation signal and the liquid crystal control signal are added using an adder, and the voltage signal is applied to the liquid crystal phase retarder 5, that is, the polarization closed loop is realized using the first-order differential of the transmitted light signal.

[0032] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A real-time closed-loop control device for laser polarization in an optically pumped atomic gas chamber, characterized in that: It includes a pumping laser (1), a magneto-optical isolator (2), a beam expander (3), a polarizer (4), a liquid crystal phase retarder (5), a heating oven (6), a polarized atomic gas chamber (7), a three-dimensional coil (8), a multi-layer magnetic shielding tube (9), a photodetector (10), a phase-locked amplifier (11), a closed-loop control module (12), an adder (13), and a signal generator (14); wherein: The light beam emitted by the pumping laser (1) passes through the magneto-optical isolator (2), the beam expander (3), the polarizer (4), the liquid crystal phase retarder (5), the polarized atomic gas chamber (7) and the photodetector (10) in sequence and then reaches the phase-locked amplifier (11). The output end of the phase-locked amplifier (11) is connected to the closed-loop control module (12). The closed-loop control module (12) is used to calculate the control voltage signal. The signal generator (14) generates a reference signal and inputs it to the phase-locked amplifier (11) to provide a frequency reference and generates a modulation signal and inputs it to the adder (13). The adder (13) receives the control voltage signal calculated by the closed-loop control module (12) and the modulation signal generated by the signal generator (14), adds them together and then inputs them to the liquid crystal phase retarder (5), thereby controlling the phase delay of the liquid crystal phase retarder (5) and realizing polarization state closed-loop control. The polarized atomic gas chamber (7) is located in the heating oven (6), and the three-dimensional coil (8) is attached to the outside of the heating oven (6); the heating oven (6), the polarized atomic gas chamber (7), and the three-dimensional coil (8) are placed in a multi-layer magnetic shielding cylinder (9).

2. The real-time closed-loop control device for laser polarization in an optically pumped atomic gas chamber according to claim 1, characterized in that: The heating oven (6) is a boron nitride material cylinder with a spherical cavity in the center for accommodating a spherical polarized atomic gas chamber (7). The surface of the heating oven (6) is symmetrically affixed with a double-twisted flexible heating film, and the outside of the heating film is affixed with the three-dimensional coil (8). The multi-layer magnetic shielding tube (9) has a hole in the z-axis direction for the light beam emitted by the pumping laser (1) to pass through.

3. The real-time closed-loop control device for laser polarization in an optically pumped atomic gas chamber according to claim 1, characterized in that: The heating oven (6) adopts non-magnetic alternating current heating to provide the required high-temperature working conditions for the polarized atomic gas chamber (7); the multi-layer magnetic shielding cylinder (9) is used to passively shield the external magnetic field, and the three-dimensional coil (8) is used to actively compensate for the residual magnetic field.

4. The real-time closed-loop control device for laser polarization in an optically pumped atomic gas chamber according to claim 1, characterized in that: The magneto-optical isolator (2) is used to allow laser light to pass in one direction and to isolate the back-reflected laser light; the light transmission axis of the polarizer (4) is along the x-axis direction; the fast axis of the liquid crystal phase retarder (5) forms an angle of 45 degrees with the x-axis and is used to change the phase delay amount according to different control voltages so that the polarization state of the laser light changes from linear polarization to circular polarization; the polarization atomic gas chamber (7) is spherical glass and is filled with potassium, rubidium and neon atoms.

5. A method for real-time closed-loop control of laser polarization in an optically pumped atomic gas chamber, applied to a real-time closed-loop control device for laser polarization in an optically pumped atomic gas chamber as claimed in any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: using the heating oven (6) to heat the polarized atomic gas chamber (7), and using a thermistor to feedback the temperature to achieve closed-loop stable temperature control; using a precision signal generator to control the three-dimensional coil (8) to perform active magnetic field compensation; Step 2, the signal generator (14) generates a modulation signal and transmits it to the adder (13), generates a reference signal and transmits it to the phase-locked amplifier (11) to provide a frequency reference; the modulation signal is , is the modulation amplitude, is the modulation frequency, is the frequency of the liquid crystal AC control voltage, and t is the time; Step 3: The photodetector (10) converts the acquired transmitted light intensity signal into a voltage signal and transmits it to the lock-in amplifier (11). The lock-in amplifier (11) extracts the first-order differential signal as an error signal. Transmitted to the closed-loop control module; the transmitted light intensity And the effective value of the LCD AC control voltage There is an even function relationship ; Effective value of LCD AC control voltage Equal to the center voltage When the error signal is zero, the laser polarization state is circular polarization; when the effective value of the liquid crystal AC control voltage is Less than center voltage When the error signal is positive, the effective value of the liquid crystal AC control voltage is Greater than center voltage When , the error signal is negative; Step 4: The closed-loop control module (12) calculates the effective value of the liquid crystal AC control voltage according to the error signal. And transmitted to the adder (13), when the error signal When it is positive, the effective value of the liquid crystal AC control voltage increases , error signal When it is negative, reduce the effective value of the LCD AC control voltage The adder (13) adds the modulation signal and the effective value of the liquid crystal AC control voltage After addition, the signals are applied to the liquid crystal phase retarder (5).

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