A Faraday closed-loop detection device and detection method for SERF atomic measurement technology

Abstract

The present invention relates to a Faraday closed-loop detection device and a detection method for SERF atomic measurement technology, which are characterized in that: after the detection laser output light is linearly polarized by a polarizer, it enters a Faraday modulator driven by a Faraday closed-loop detection control circuit, so that the linear polarization plane of the detection light undergoes periodic rotation modulation; after the detection laser enters an atomic gas chamber, it carries spin information, and the polarization plane rotates by θ, and then is injected into a photodetector through a polarization plane angle compensator and an analyzer, and the optical signal is converted into an electrical signal and transmitted to a signal demodulation module; the PID control module of the Faraday closed-loop detection control circuit calculates and outputs a control signal, adjusts the birefringence principal axis direction of a 1 / 2 wave plate of a polarization plane angle compensator, and rotates the linear polarization plane by an angle α, so as to realize closed-loop detection. The present invention suppresses the detection scale factor error and improves the detection accuracy.

Description

Technical Field

[0001] The invention belongs to the technical field of quantum precision measurement, and in particular relates to a Faraday closed-loop detection device and a measurement method for SERF atomic measurement technology. Background Art

[0002] SERF atomic spin precision measurement technology can greatly prolong the spin relaxation time and improve the measurement accuracy based on the spin-free exchange relaxation mechanism. It has broad application prospects in inertial measurement, weak magnetic measurement, basic physics exploration and other fields. The direct output result of the SERF atomic measurement device is a low-frequency or DC signal, which has a great influence on 1 / f noise. Faraday modulation detection is a mainstream method that converts low-frequency signals into high-frequency signals by modulating the detection light to reduce measurement noise. It has the advantage of high sensitivity. The specific principle is that the current drives the magnetic field coil to generate a changing magnetic field, and the linearly polarized light passes through the internal optical rotation crystal. Based on the Faraday magneto-optical effect, the polarization plane of the light changes periodically. The modulated linearly polarized light passes through the atomic gas chamber, and the spin signal causes the linearly polarized light to deflect. The deflection angle is superimposed on the modulation rotation and detected by the photodetector. The required spin signal can be obtained by demodulation.

[0003] However, in Faraday modulation detection, a large amount of heat is released when the current drives the modulation coil, causing the internal temperature of the modulator to change, which affects the performance of the optical rotation crystal, causes fluctuations in the modulation amplitude, and makes the detection scale factor unstable, resulting in errors in the detection results. In addition, in the general Faraday closed-loop detection method, since the closed-loop actuator is also based on the Faraday magneto-optical effect and cannot isolate the temperature influence, the scale factor is not stable enough. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and to provide a Faraday closed-loop detection device and a detection method for SERF atomic measurement technology, which can suppress the detection scale factor error, improve the detection accuracy, and can be applied to SERF atomic measurement technology to improve its performance indicators.

[0005] One of the above-mentioned purposes of the present invention is achieved through the following technical solution:

[0006] A Faraday closed-loop detection device for SERF atomic measurement technology, characterized in that it includes a detection laser, a polarizer, a Faraday modulator, an atomic gas chamber, a polarization plane angle compensator, an analyzer, a photodetector, a Faraday closed-loop detection control circuit, and a signal acquisition and processing system; the polarization plane angle compensator includes a high-precision electric control adjustment frame, a 1 / 2 wave plate and a fixed connection structure; the Faraday closed-loop detection control circuit includes a modulation drive module, a signal demodulation module, and a PID control module, wherein:

[0007] After the output light of the detection laser is linearly polarized by the polarizer, it enters the Faraday modulator driven by the control circuit, so that the linear polarization plane of the detection light undergoes periodic rotation modulation; after the detection laser enters the atomic gas chamber, it carries spin information, and the polarization plane rotates by θ, and then is injected into the photodetector through the polarization plane angle compensator and the analyzer, and the optical signal is converted into an electrical signal and transmitted to the signal demodulation module; wherein, the PID control module calculates and outputs a control signal to the high-precision electrically controlled adjustment frame of the polarization plane angle compensator, and the direction of the birefringence principal axis of the 1 / 2 wave plate is adjusted by the high-precision electrically controlled adjustment frame, so that the polarization plane of the linear polarized light rotates by an angle α, α=-θ, to realize closed-loop detection; the signal acquisition and processing system is used to process and store the output signal of the PID control module.

[0008] The second of the above-mentioned objects of the present invention is achieved by the following technical solutions:

[0009] A Faraday closed-loop detection method for SERF atomic measurement technology, characterized in that, based on the above-mentioned Faraday closed-loop detection device for SERF atomic measurement technology, the method comprises the following steps:

[0010] Step (1), adjusting the 1 / 2 wave plate in the polarization plane angle compensator so that the direction of its initial birefringence axis is parallel to the direction of the polarization axis of the polarizer; adjusting the direction of the polarization axis of the analyzer so that it is perpendicular to the direction of the polarization axis of the polarizer.

[0011] Step (2), adjusting the SERF atomic measurement device to a normal working state. The SERF atomic measurement device includes an atomic gas chamber, a non-magnetic heating system, a magnetic shielding barrel, a three-dimensional magnetic field compensation coil, a pump optical path, and a detection optical path; adjusting the SERF atomic measurement device to a normal working state means: heating the atomic gas chamber filled with working material to a working temperature by a non-magnetic alternating current, and isolating the external environmental magnetic field by the magnetic shielding barrel and the magnetic field compensation coil, so that the system works in a stable weak magnetic environment; the pump optical path uses circularly polarized light to polarize atomic spins; the detection laser in the detection optical path is linearly polarized light, and the optical path direction is perpendicular to the pump light direction. When the detection light passes through the atomic gas chamber, the polarization plane of the detection light rotates by an angle θ due to the influence of the atomic spin, and the rotation angle carries spin information.

[0012] Step (3), using the modulation drive module in the control circuit to output an alternating current to drive the Faraday modulator, the current amplitude is constant at 15V, the frequency is 5kHz, and the circuit capacitor forms an LC oscillation circuit to drive the Faraday modulator with maximum efficiency to achieve modulation of the polarization plane of the detection laser. The Faraday modulator modulates the polarization plane of the light by a small amount, which must be less than 0.1rad.

[0013] Step (4), using a polarizer plus a photodetector combination to monitor the polarization change of the detection light, and using a demodulation module in the control circuit to use the AC signal driving the Faraday modulator as a reference signal to extract the amplitude of the signal with the same frequency and phase.

[0014] Step (5), the demodulated signal amplitude is input as an error signal into the PID control module in the control circuit, and the PID control system controls the direction of the birefringence principal axis of the 1 / 2 wave plate in the polarization plane angle compensator according to the error signal, and compensates for the rotation angle carrying spin information, even if the polarization direction of the detection light rotates α, and α=-θ, the error signal of the SERF atomic measurement device is compensated to zero in real time. The polarization plane angle compensator can achieve a polarization plane rotation accuracy of 1 arc second, and the PID control signal is linearly related to the polarization angle compensation signal, which meets the experimental requirements.

[0015] Step (6), since the input measurement to be measured of the SERF atomic measurement device is linearly related to the polarization angle compensation signal, the PID control signal is collected, the atomic spin-carrying information is calculated, and then the external input measurement to be measured is obtained.

[0016] The advantages of the present invention compared with the prior art are:

[0017] (1) The present invention uses a polarization plane angle compensator to rotate the polarization plane of the detection light to achieve closed-loop detection. Compared with Faraday open-loop detection, the detection result is not affected by the Faraday modulation amplitude and the detection light power, which solves the problem of unstable Faraday modulation scale factor and effectively improves the detection accuracy of SERF atomic measurement technology.

[0018] (2) Compared with the traditional closed-loop detection in which the core component of the Faraday actuator, the optical rotation crystal, is easily affected by temperature, the polarization plane angle compensator in the present invention uses a mechanical structure to achieve polarization plane compensation, and its compensation result is not easily affected by temperature and is more accurate.

[0019] (3) The rotation angle generated by the polarization plane rotation angle compensator of the present invention can be directly read out. According to the closed-loop principle, the rotation angle of the linear polarization plane can be obtained, which is simple and clear and easy to analyze.

[0020] (4) The device of the present invention is simple and has sensitive detection, and can be used in SERF atomic inertia and magnetic sensor technology to improve the spin signal detection performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a diagram of the SERF atomic measurement experimental device using the Faraday closed-loop detection method of the present invention.

[0022] Figure 2 It is a schematic diagram of the Faraday closed-loop detection device of the present invention. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0024] like Figure 1 This is a diagram of the SERF atomic measurement technology device using the Faraday closed-loop detection method of the present invention.

[0025] The SERF atomic measurement technology device includes an atomic gas chamber, a non-magnetic heating device, a magnetic shielding barrel, a three-dimensional magnetic field coil, a pump optical path, and a detection optical path; the pump optical path includes a pump laser and a 1 / 4 wave plate, and the detection optical path is specifically described in the closed-loop detection device below.

[0026] When the SERF atomic measurement device is in normal working state, the atomic gas chamber is heated to the working temperature by non-magnetic alternating current heating. The working material inside the gas chamber is in a gas state. The magnetic shielding and magnetic compensation components are used to shield the earth's magnetism and compensate for the residual magnetic field, so that the system works in a stable weak magnetic environment. The laser beam generated by the pump laser is converted into circularly polarized light through a 1 / 4 wave plate and incident on the atomic gas chamber to pump the atomic spin polarization. The detection laser in the detection light path is linearly polarized light, and the direction of the light path is perpendicular to the direction of the pump light. When the detection light passes through the atomic gas chamber, the polarization plane rotates by an angle θ due to the influence of the atomic spin. The angle carries the spin information.

[0027] like Figure 2 The diagram of the Faraday closed-loop detection device provided by the present invention. The experimental device includes a detection laser 1, a polarizer 2, a Faraday modulator 3, an atomic gas chamber 4, a polarization plane angle compensator 5, an analyzer 6, a photodetector 7, a closed-loop detection control circuit 8, and a signal acquisition and processing system 12. The polarization plane angle compensator includes a high-precision electric control adjustment frame, a 1 / 2 wave plate and a fixed connection structure; the control circuit includes a drive module 9, a demodulation module 10, and a PID control module 11, wherein:

[0028] The detection laser generates a laser beam which is input into the Faraday modulator through the polarizer. The driving module in the control circuit outputs a suitable alternating current to drive the Faraday modulator to make the polarization plane of the linear polarized light rotate periodically. The modulated linear polarized light is incident on the alkali metal gas chamber and carries the spin signal deflection angle. The adjustable 1 / 2 wave plate structure generates a reverse deflection angle through the PID circuit control. The detection light is emitted into the photodetector through the analyzer and fed back to the PID control module. The control amount of the adjustable wave plate by the PID module is a closed-loop output signal, which is processed by the signal acquisition system.

[0029] The following describes the specific process of the Faraday closed-loop detection method in combination with the working principle of the Faraday closed-loop detection device as follows: It includes the following steps:

[0030] Step (1), adjusting the controllable 1 / 2 wave plate so that its initial birefringence principal axis direction is parallel to the birefringence principal axis direction of the polarizer, and adjusting the birefringence principal axis direction of the analyzer so that it is perpendicular to the principal axis direction of the polarizer.

[0031] Step (2), adjusting the SERF atomic measurement device to a normal working state.

[0032] Among them, the SERF atomic measurement device includes an atomic gas chamber, a non-magnetic heating system, a magnetic shielding barrel, a three-dimensional magnetic field compensation coil, a pump optical path, and a detection optical path; adjusting the SERF atomic measurement device to a normal working state means: the atomic gas chamber filled with working material is heated to the working temperature by a non-magnetic alternating current, and the magnetic shielding barrel and the magnetic field compensation coil isolate the external environmental magnetic field, so that the system works in a stable weak magnetic environment; the pump optical path uses circularly polarized light to polarize atomic spins; the detection laser in the detection optical path is linearly polarized light, and the direction of the optical path is perpendicular to the direction of the pump light. When the detection light passes through the atomic gas chamber, the polarization plane of the detection light rotates by an angle θ due to the influence of the atomic spin, and the angle carries the spin information.

[0033] Assuming that the initial intensity of the detection laser after polarization is I0, the frequency modulated by Faraday is ω, the amplitude is A, and the phase is 0, the intensity of the light projected in the direction of the polarization axis of the analyzer can be expressed as:

[0034] I1=I0*sin 2 (A*cosωt)

[0035] Step (3), use the driving module in the control circuit to output alternating current to drive the Faraday modulator to achieve modulation of the polarization plane of the detection laser. The Faraday modulator driving current amplitude is constant at 15V, the frequency is 5kHz, and it forms an LC oscillation circuit with the circuit capacitor to drive the Faraday modulator with maximum efficiency. Assume that the frequency of the detection laser modulated by Faraday is ω and the amplitude is A. The light intensity projected in the direction of the polarization axis of the analyzer becomes:

[0036] I2=I0*sin 2 (θ+A*cosωt)

[0037] The linear polarization plane of the detection laser is rotated by an angle α through the polarization plane angle compensator. Then the light intensity I detected by the photodetector after the analyzer can be expressed as:

[0038] I=I0*sin 2 (θ+α+A*cosωt)

[0039] Step (4), input the result detected by the photodetector into the demodulation module in the control circuit, use the AC signal that drives the Faraday modulator as the reference signal, and extract the signal amplitude with the same frequency and phase.

[0040] Since θ, α, and A are small, the control circuit demodulation module extracts the component I corresponding to the frequency ω in I ω for:

[0041] I ω ≈2I0A*(θ+α)

[0042] Step (5): the amplitude of the demodulated same-frequency signal I ω As the error signal, it is input into the PID control module in the control circuit. According to the above formula, I ω The result is linearly related to (α+θ). The PID control system controls the polarization plane angle compensator according to the error signal to rotate the polarization direction of the detection light by α. When α=-θ, the above I ω The PID control signal is linearly related to the polarization angle compensation signal, which is the closed-loop output result.

[0043] Step (6): Since the input measurement value of the SERF atomic measurement device is linearly related to the polarization angle compensation signal, the input measurement value of the SERF atomic measurement device is calculated according to the PID control signal.

[0044] The above process shows that the angle θ to be measured in the closed-loop detection is only related to the angle α of the polarization plane angle compensator, and has nothing to do with the light intensity I0 and the Faraday modulation amplitude A. This isolates the influence of these parameter fluctuations on the detection system in principle, making the scale factor of the closed-loop Faraday modulation detection easy to stabilize.

[0045] In summary, the Faraday closed-loop detection device and detection method using a polarization plane angle compensator designed in the present invention generates an angle of rotation opposite to the polarization plane rotation of the detection light caused by the spin signal through an adjustable wave plate, so that the detection result is not affected by the Faraday modulation amplitude, solves the problem of instability of the Faraday modulation scale factor due to temperature fluctuations, and effectively improves the detection accuracy of the SERF atomic measurement technology.

[0046] The following contents which are not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in this field.

[0047] Including detection laser, polarizer, Faraday modulator, atomic gas chamber, polarization plane angle compensator, analyzer, photodetector, etc.

[0048] The present invention provides more options for atomic spin weak magnetic signal detection technology, accelerates the development of quantum components such as atomic inertial measurement and atomic magnetometers, and has broad application potential in inertial navigation, geological exploration, biomedicine and other fields.

[0049] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A Faraday closed-loop detection device for SERF atomic measurement technology, characterized in that: It includes a detection laser, a polarizer, a Faraday modulator, an atomic gas chamber, a polarization plane angle compensator, an analyzer, a photodetector, a Faraday closed-loop detection control circuit, and a signal acquisition and processing system; the polarization plane angle compensator includes a high-precision electric control adjustment frame, a 1 / 2 wave plate and a fixed connection structure; the Faraday closed-loop detection control circuit includes a modulation drive module, a signal demodulation module, and a PID control module, wherein: After the output light of the detection laser is linearly polarized by the polarizer, it enters the Faraday modulator driven by the control circuit, so that the linear polarization plane of the detection light undergoes periodic rotation modulation; after the detection laser enters the atomic gas chamber, it carries spin information, and the polarization plane rotates by θ, and then is injected into the photodetector through the polarization plane angle compensator and the analyzer, and the optical signal is converted into an electrical signal and transmitted to the signal demodulation module; wherein, the PID control module calculates and outputs a control signal to the high-precision electrically controlled adjustment frame of the polarization plane angle compensator, and the direction of the birefringence principal axis of the 1 / 2 wave plate is adjusted by the high-precision electrically controlled adjustment frame, so that the polarization plane of the linear polarized light rotates by an angle α, α=-θ, to realize closed-loop detection; the signal acquisition and processing system is used to process and store the output signal of the PID control module.

2. A Faraday closed-loop detection method for SERF atomic measurement technology, characterized in that: The Faraday closed-loop detection device for SERF atomic measurement technology according to claim 1 comprises the following steps: Step (1), adjusting the polarization plane angle compensator so that the direction of the initial birefringence axis of the 1 / 2 wave plate is parallel to the direction of the polarization axis of the polarizer; adjusting the polarization axis direction of the analyzer so that it is perpendicular to the direction of the polarization axis of the polarizer; Step (2), adjusting the SERF atomic measurement device to a normal working state; Step (3), using the modulation drive module in the Faraday closed-loop detection control circuit to output an alternating current to drive the Faraday modulator to achieve modulation of the polarization plane of the detection laser; Step (4), using the signal demodulation module in the Faraday closed-loop detection control circuit, taking the AC signal driving the Faraday modulator as the reference signal, demodulating the photodetector result, and extracting the signal amplitude with the same frequency and phase as the reference signal; Step (5), inputting the demodulated signal amplitude as an error signal into a PID control module in a control circuit, and the PID control system controls the polarization plane angle compensator according to the error signal to compensate the error signal of the SERF atomic measurement device to zero in real time; Step (6), collecting the PID control signal, calculating the information carried by the atomic spin, and then obtaining the external input to be measured.

3. A Faraday closed-loop detection method for SERF atomic measurement technology according to claim 2, characterized in that: In the step (2), the SERF atomic measurement device includes an atomic gas chamber and a heating device, a magnetic shielding barrel, a three-dimensional magnetic field coil, a pump optical path and a detection optical path; Adjusting the SERF atomic measurement device to a normal working state means: heating the atomic gas chamber filled with working material by non-magnetic alternating current heating to reach the working temperature, and isolating the external environmental magnetic field with the magnetic shielding barrel and the three-dimensional magnetic field coil so that the system works in a stable weak magnetic environment; the pump laser in the pump optical path polarizes the atomic spin using circularly polarized light; the detection optical path is perpendicular to the direction of the pump light, and the detection light passes through the atomic gas chamber and is affected by the atomic spin, causing the polarization plane to rotate by an angle θ, which carries spin information.

4. A Faraday closed-loop detection method for SERF atomic measurement technology according to claim 2, characterized in that: In the step (3), the current amplitude driving the Faraday modulator is constant at 15V, the frequency matches the circuit capacitance to form an LC oscillation circuit, and the driving frequency is 5kHz.

5. The Faraday closed-loop detection method for SERF atomic measurement technology according to claim 2, characterized in that: In the step (3), the Faraday modulator modulates the light polarization plane at an angle less than 0.1 rad.

6. A Faraday closed-loop detection method for SERF atomic measurement technology according to claim 2, characterized in that: In the step (5), the error signal is compensated in real time by controlling the electric wave plate frame in the polarization plane angle compensator to change the direction of the birefringence principal axis of the 1 / 2 wave plate, so that the polarization direction of the detection light is rotated by α, and the rotation angle α is equal to the angle θ of the linear polarization direction change caused by the spin information, but opposite in direction, thereby completing the angle compensation and realizing closed-loop detection.

7. A Faraday closed-loop detection method for SERF atomic measurement technology according to claim 2, characterized in that: In the step (5), the polarization plane rotation compensator has an accuracy of 1 arc second for polarization plane rotation.

8. The Faraday closed-loop detection method for SERF atomic measurement technology according to claim 2, characterized in that: In the step (5), the PID control variable is linearly related to the polarization angle compensation signal.

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