A method for laser frequency stabilization control of an NMOR atomic magnetometer based on optical rotation signal

Abstract

The present application relates to the technical field of atomic magnetometer, and particularly relates to a laser frequency stability control method of NMOR atomic magnetometer based on optical rotation signal, which comprises the following steps: irradiating an atomic cell with linearly polarized laser to pump atoms and detecting optical rotation signal; once demodulating the optical rotation signal to obtain magnetic resonance signal; applying a fixed frequency modulation signal to the laser frequency; twice demodulating the magnetic resonance signal to obtain a demodulation signal corresponding to the laser frequency offset; and feeding back and adjusting the laser frequency according to the demodulation signal. The present application is used to reduce the influence of laser frequency drift on the magnetic resonance signal of NMOR atomic magnetometer, improve the stability of long-term work of NMOR atomic magnetometer, and reduce the system volume and system complexity.

Description

Technical Field

[0001] This invention relates to the field of atomic magnetometer technology, and specifically to a method for stabilizing and controlling the laser frequency of an NMOR atomic magnetometer based on optical rotation signals. Background Technology

[0002] The measurement and application of magnetic fields have always played a vital role in the advancement of human science and technology. With the rapid development of modern science and technology, the accuracy and sensitivity of magnetic field measurements have continuously improved. In recent years, with breakthroughs in quantum physics and laser technology, atomic magnetometers based on the nonlinear magneto-optical rotation (NMOR) effect have become a research hotspot. Compared with other atomic magnetometer technologies, NMOR atomic magnetometers have advantages such as high sensitivity, high accuracy, and simple structure, which makes them demonstrate broad application potential in various fields such as health monitoring, mineral exploration, magnetic anomaly detection, geomagnetic monitoring, and cutting-edge scientific research.

[0003] The NMOR atomic magnetometer achieves precise magnetic field measurement based on the interaction between lasers and atomic hyperfine levels. Therefore, the NMOR atomic magnetometer places higher demands on laser frequency stability. However, in practical long-term magnetic field monitoring scenarios, laser frequency drift can cause measurement errors or decreased sensitivity in the NMOR atomic magnetometer. Therefore, stable control of the laser frequency is crucial for the performance of the NMOR atomic magnetometer. Currently, mainstream stabilization methods mainly utilize saturated absorption of alkali metal atoms or rely on external optical devices. For the NMOR atomic magnetometer, the method utilizing the linear saturated absorption of alkali metal atoms depends on a reference gas cell, making it difficult to stabilize the frequency at the magnetometer's optimal operating conditions. On the other hand, stabilization methods relying on external devices significantly increase size and cost, hindering the miniaturization and integration of the NMOR atomic magnetometer.

[0004] Therefore, it is necessary to propose a frequency stabilization control method based on the output signal of an NMOR atomic magnetometer, which uses the magnetometer's own output signal to stabilize the laser frequency and solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a laser frequency stabilization control method for NMOR atomic magnetometers based on optical rotation signals in order to solve the above-mentioned technical problems, thereby reducing the impact of laser frequency drift on the magnetic resonance signal of NMOR atomic magnetometers, improving the long-term stability of NMOR atomic magnetometers, and reducing system size and complexity.

[0006] The objective of this invention can be achieved through the following technical solutions: A method for stabilizing and controlling the laser frequency of an NMOR atomic magnetometer based on optical rotation signals, the method comprising: S1. Atoms are pumped by irradiating the atomic gas cell with a linearly polarized laser, and the optical rotation signal is detected. S2. Demodulate the optical rotation signal once to obtain the magnetic resonance signal; S3. Apply a modulation signal of fixed frequency to the laser frequency; S4. Perform secondary demodulation on the magnetic resonance signal to obtain the demodulated signal corresponding to the laser frequency shift; S5. Adjust the laser frequency based on the demodulated signal.

[0007] Furthermore, step S2 includes: modulating the laser frequency using a first modulation signal output from a first lock-in amplifier, and demodulating the optical rotation signal using the first lock-in amplifier to obtain a magnetic resonance signal. The frequency of the first modulation signal is twice the atomic Larmor precession frequency, and the external magnetic field information is determined based on the atomic Larmor precession frequency and the gyromagnetic ratio.

[0008] Furthermore, step S2 also includes: performing a linear scan of the laser frequency near the D1 line transition frequency of the Rb atom to obtain the amplitude curve of the magnetic resonance signal changing with the laser frequency, and setting the laser frequency to the frequency corresponding to the largest amplitude value in the amplitude curve.

[0009] Furthermore, linear scanning of the laser frequency includes: using a second lock-in amplifier to output a ramp signal, and adjusting the laser frequency according to the ramp signal.

[0010] Furthermore, step S3 includes: using a second lock-in amplifier to output a second modulation signal to modulate the laser frequency, wherein the second modulation signal is a sinusoidal modulation signal.

[0011] Furthermore, step S4 includes: receiving the amplitude of the magnetic resonance signal using a second lock-in amplifier, and demodulating the amplitude of the magnetic resonance signal using the second lock-in amplifier to obtain a demodulated signal.

[0012] Furthermore, step S5 includes: adjusting the bias of the second modulation signal according to the demodulated signal, and adjusting the laser frequency according to the bias.

[0013] Further, step S1 includes: passing the emitted light through the atomic gas cell sequentially through a half-wave plate and a balanced differential detection module, and having the balanced differential detection module output a voltage signal corresponding to the optical rotation signal.

[0014] Furthermore, the balanced differential detection module includes a polarization beam splitter, a first photodetector, a second photodetector, and a differential amplifier. The polarization beam splitter splits the outgoing light after passing through the half-wave plate into a first optical signal and a second optical signal. The first photodetector receives the first optical signal, the second photodetector receives the second optical signal, and the differential amplifier performs differential processing on the output signals of the first and second photodetectors.

[0015] Furthermore, the frequency-tunable laser includes an RF modulation port and a signal control port. The RF modulation port receives a first modulation signal, and the signal control port receives a feedback control signal corresponding to the bias of the second modulation signal.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention performs primary and secondary demodulation on the optical rotation signal, and adjusts the laser frequency based on the demodulated signal obtained from the secondary demodulation, thereby reducing the impact of laser frequency drift on the magnetic resonance signal of the NMOR atomic magnetometer and improving the stability of the NMOR atomic magnetometer during long-term operation.

[0017] 2. This invention uses the magnetic resonance signal output by the NMOR atomic magnetometer to stably control the laser frequency, eliminating the need for an additional reference gas cell and external frequency stabilization optical devices, thereby reducing the complexity of the system structure.

[0018] 3. This invention uses a single-beam linearly polarized laser to complete atomic pumping, optical rotation signal detection, and laser frequency stabilization control, thereby reducing system size and hardware cost. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the implementation of a laser frequency stabilization control method for an NMOR atomic magnetometer based on optical rotation signals according to the present invention. Figure 2 This is a diagram of the apparatus involved in implementing the present invention, a laser frequency stabilization control method for an NMOR atomic magnetometer based on optical rotation signals; Figure 3 This is a signal diagram involved in implementing the present invention, a laser frequency stabilization control method for an NMOR atomic magnetometer based on optical rotation signals; Among them, 1. tunable laser; 2. optical fiber; 3. collimator; 4. linear polarizer; 5. atomic gas cell; 6. half-wave plate; 7. polarization beam splitter; 8. first photodetector; 9. second photodetector; 10. differential amplifier; 11. first lock-in amplifier; 12. second lock-in amplifier; 13. curve of magnetic resonance signal amplitude as a function of laser frequency detuning; 14. curve of magnetic resonance signal demodulated as a function of laser frequency detuning. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0021] like Figures 1 to 3 The method shown is a laser frequency stabilization control method for NMOR atomic magnetometers based on optical rotation signals. The method includes: In this embodiment, the frequency-tunable laser outputs linearly polarized laser light. This linearly polarized laser light sequentially passes through an optical fiber, a collimator, and a linear polarizer before entering the atomic gas cell, pumping Rb atoms within the cell. Step S1 includes: passing the emitted light through the atomic gas cell sequentially through a half-wave plate and a balanced differential detection module, and the balanced differential detection module outputs a voltage signal corresponding to the optical rotation signal. For example... Figure 2 As shown, the apparatus for implementing the method of this embodiment includes a frequency-tunable laser 1, an optical fiber 2, a collimator 3, a linear polarizer 4, an atomic gas cell 5, a half-wave plate 6, a polarization beam splitter 7, a first photodetector 8, a second photodetector 9, a differential amplifier 10, a first lock-in amplifier 11, and a second lock-in amplifier 12 connected in sequence. The transmission surface of the polarization beam splitter 7 is connected to the first photodetector 8, and the reflection surface of the polarization beam splitter 7 is connected to the second photodetector 9. The first photodetector 8 and the second photodetector 9 are respectively connected to the input ports of the differential amplifier 10. The output port of the differential amplifier 10 is connected to the input port In of the first lock-in amplifier 11. The first lock-in amplifier 11 contains an input port In, an output port Out1, an output port Out2, and an oscillator Ocs. The input port In is used to receive optical rotation signals, the output port Out1 outputs magnetic field information, and the output port Out2 is connected to the input port of the second lock-in amplifier 12. The oscillator Ocs inside the first lock-in amplifier 11 is connected to the radio frequency (RF) port of the frequency-tunable laser 1. Polarization beam splitter 7 splits the outgoing light from half-wave plate 6 into a first optical signal and a second optical signal. First photodetector 8 receives the first optical signal, and second photodetector 9 receives the second optical signal. Differential amplifier 10 performs differential processing on the output signals of first photodetector 8 and second photodetector 9 to obtain a voltage signal corresponding to the optical rotation signal. Tunable laser 1 includes an RF modulation port and a signal control port. The RF modulation port receives a first modulation signal, and the signal control port receives a feedback control signal corresponding to the bias of the second modulation signal.

[0022] Step S1 generates an optical rotation effect by utilizing the interaction between atoms and linearly polarized laser, and obtains the optical rotation signal corresponding to the atomic magnetic resonance state through balanced differential detection, thereby providing input signals for subsequent magnetic resonance detection and laser frequency stabilization control.

[0023] S2. Demodulate the optical rotation signal once to obtain the magnetic resonance signal; step S2 includes: modulating the laser frequency using a first modulation signal output from a first lock-in amplifier, the first modulation signal being expressed as: in, This is the output signal of the first lock-in amplifier. for The amplitude of the signal, for The signal frequency is determined, and the optical rotation signal is demodulated using a first lock-in amplifier to obtain the magnetic resonance signal; the laser frequency is tuned to the Rb atom D1 line transition frequency, and the output frequency of the internal oscillator of the first lock-in amplifier is... The modulation signal modulates the laser frequency and scans. The magnetic resonance curve was obtained by demodulating the optical rotation signal output from the NMOR atomic magnetometer, and the modulation frequency of the laser was set. The external magnetic field information is determined based on the atomic Larmor precession frequency and gyromagnetic ratio, which is twice the Larmor precession frequency. in, The Larmor precession frequency of the atom. It is the gyromagnetic ratio. B The external magnetic field to be measured; Simultaneously, the magnetic resonance signal amplitude is input to the second lock-in amplifier; a linear scan of the laser frequency is performed near the D1 line transition frequency of the Rb atom to obtain the amplitude curve of the magnetic resonance signal as a function of the laser frequency, and the laser frequency is set to the frequency corresponding to the maximum amplitude value in the amplitude curve. The linear scan includes using a ramp signal output from the second lock-in amplifier to adjust the laser frequency based on the ramp signal; in this embodiment, when the laser frequency is detuned to -0.4 GHz, the magnetic resonance signal reaches its maximum value, therefore the corresponding laser frequency is set as the operating frequency. Figure 3 As shown in the figure, laser frequency detuning refers to the laser center frequency relative to... 87 Rb atom D1 line ground state to excited state Detuning of the transition frequency. The figure, from top to bottom, shows the curves of the amplitude of the magnetic resonance signal after the optical rotation signal is demodulated once, versus the laser frequency detuning, and the curves of the demodulated magnetic resonance signal versus the laser frequency detuning. Step S2 uses the first lock-in amplifier to demodulate the optical rotation signal once to obtain the NMOR atomic magnetic resonance signal, and determines the laser operating frequency corresponding to the maximum magnetic resonance signal by scanning, providing a reference operating point for subsequent laser frequency stabilization control.

[0024] S3. Apply a fixed-frequency modulation signal to the laser frequency; Step S3 includes: modulating the laser frequency using a second modulation signal output from a second lock-in amplifier, wherein the second modulation signal is a sinusoidal modulation signal, and the second modulation signal output from the second lock-in amplifier is: in, This is the output signal of the second lock-in amplifier. This is the bias signal. for The amplitude of the signal, for The frequency of the signal; applying a small-amplitude periodic modulation at a fixed frequency near the laser's operating frequency causes a slight change in the laser frequency near the operating frequency, thereby generating a frequency deviation signal for subsequent secondary demodulation.

[0025] S4. Perform secondary demodulation on the magnetic resonance signal to obtain a demodulated signal corresponding to the laser frequency offset. Step S4 includes: receiving the amplitude of the magnetic resonance signal using a second lock-in amplifier, and demodulating the amplitude of the magnetic resonance signal using the second lock-in amplifier to obtain a demodulated signal. The second lock-in amplifier uses the second modulation signal as a reference signal to perform secondary lock-in demodulation on the amplitude of the magnetic resonance signal to obtain a demodulated signal corresponding to the direction and degree of laser frequency offset. When the laser frequency is at the operating frequency, the demodulated signal is close to zero; when the laser frequency deviates from the operating frequency, the demodulated signal deviates from zero. In this embodiment, when the laser frequency detuning is -0.4 GHz, the secondary demodulated signal of the optical rotation signal is 0. As the laser frequency detuning increases or decreases, the secondary demodulated signal gradually deviates from 0, indicating that the laser frequency deviates from the optimal operating point of the NMOR atomic magnetometer. At this time, the bias of the modulation signal is changed through the output port Out of the second lock-in amplifier 12. By using a feedback control loop to stabilize the laser frequency and consistently keeping the secondary demodulated signal of the optical rotation signal close to zero, stable control of the laser frequency can be achieved. The error signal corresponding to the laser frequency offset is extracted using secondary demodulation, providing a control basis for laser frequency feedback control.

[0026] S5. Feedback adjustment of the laser frequency based on the demodulated signal; Step S5 includes: adjusting the bias of the second modulation signal based on the demodulated signal, and adjusting the laser frequency based on the bias. The second lock-in amplifier adjusts the bias signal according to the change of the demodulated signal, and changes the output frequency of the tunable laser through a feedback control loop, so that the demodulated signal approaches zero again. When the demodulated signal approaches zero, it indicates that the current laser frequency has returned to the vicinity of the operating frequency corresponding to the maximum of the magnetic resonance signal. Step S5 realizes closed-loop feedback adjustment of the laser frequency based on the error signal obtained from the second demodulation, so as to keep the laser frequency stable near the operating frequency corresponding to the maximum of the magnetic resonance signal.

[0027] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0028] It should be noted that the terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in sequences other than those illustrated or described herein.

[0029] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the nature and scope of the present invention. Various modifications made to the above embodiments by those skilled in the art after reading this specification are all within the scope of protection of the present invention.

Claims

1. A method for stabilizing and controlling the laser frequency of an NMOR atomic magnetometer based on optical rotation signals, characterized in that, The method includes: S1. Atoms are pumped by irradiating the atomic gas cell with a linearly polarized laser, and the optical rotation signal is detected. S2. Demodulate the optical rotation signal once to obtain the magnetic resonance signal; S3. Apply a modulation signal of fixed frequency to the laser frequency; S4. The magnetic resonance signal is demodulated a second time to obtain a demodulated signal corresponding to the laser frequency shift; S5. Adjust the laser frequency based on the demodulated signal.

2. The method for stabilizing and controlling the laser frequency of an NMOR atomic magnetometer based on optical rotation signals according to claim 1, characterized in that, Step S2 includes: modulating the laser frequency using a first modulation signal output from a first lock-in amplifier, and demodulating the optical rotation signal using the first lock-in amplifier to obtain the magnetic resonance signal; the frequency of the first modulation signal is twice the atomic Larmor precession frequency, and the external magnetic field information is determined based on the atomic Larmor precession frequency and the gyromagnetic ratio.

3. The method for stabilizing and controlling the laser frequency of an NMOR atomic magnetometer based on optical rotation signals according to claim 1, characterized in that, Step S2 further includes: performing a linear scan of the laser frequency near the D1 line transition frequency of the Rb atom to obtain the amplitude curve of the magnetic resonance signal as a function of the laser frequency, and setting the laser frequency to the frequency corresponding to the largest amplitude value in the amplitude curve.

4. The method for stabilizing and controlling the laser frequency of an NMOR atomic magnetometer based on optical rotation signals according to claim 3, characterized in that, Linear scanning of the laser frequency includes: using a second lock-in amplifier to output a ramp signal, and adjusting the laser frequency according to the ramp signal.

5. The method for stabilizing and controlling the laser frequency of an NMOR atomic magnetometer based on optical rotation signals according to claim 1, characterized in that, Step S3 includes: using a second lock-in amplifier to output a second modulation signal to modulate the laser frequency, wherein the second modulation signal is a sinusoidal modulation signal.

6. The method for stabilizing and controlling the laser frequency of an NMOR atomic magnetometer based on optical rotation signals according to claim 5, characterized in that, Step S4 includes: receiving the amplitude of the magnetic resonance signal using the second lock-in amplifier, and demodulating the amplitude of the magnetic resonance signal using the second lock-in amplifier to obtain the demodulated signal.

7. The method for stabilizing and controlling the laser frequency of an NMOR atomic magnetometer based on optical rotation signals according to claim 6, characterized in that, Step S5 includes: adjusting the bias of the second modulation signal according to the demodulated signal, and adjusting the laser frequency according to the bias.

8. The method for stabilizing and controlling the laser frequency of an NMOR atomic magnetometer based on optical rotation signals according to claim 1, characterized in that, Step S1 includes: passing the emitted light through the atomic gas cell sequentially through a half-wave plate and a balanced differential detection module, and having the balanced differential detection module output a voltage signal corresponding to the optical rotation signal.

9. The method for stabilizing and controlling the laser frequency of an NMOR atomic magnetometer based on optical rotation signals according to claim 8, characterized in that, The balanced differential detection module includes a polarization beam splitter, a first photodetector, a second photodetector, and a differential amplifier. The polarization beam splitter splits the outgoing light from the half-wave plate into a first optical signal and a second optical signal. The first photodetector receives the first optical signal, the second photodetector receives the second optical signal, and the differential amplifier performs differential processing on the output signals of the first photodetector and the second photodetector.

10. The method for stabilizing and controlling the laser frequency of an NMOR atomic magnetometer based on optical rotation signals according to claim 2 or 5, characterized in that, The frequency-tunable laser includes an RF modulation port and a signal control port. The RF modulation port receives the first modulation signal, and the signal control port receives a feedback control signal corresponding to the bias of the second modulation signal.

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