Ellipsometry atomic magnetometer device and method for eliminating optical frequency shift

Abstract

A device and method for an ellipsometric atomic magnetometer that eliminates optical frequency shift utilizes a laser and integrated devices to generate elliptically polarized modulated light with symmetrical frequency detuning as the laser source of a single-beam atomic magnetometer, enabling measurement of weak magnetic fields under a modulated magnetic field. The device combines two pulsed light beams, each with a detuning amount symmetrical about the center frequency of an alkali metal atom and a phase difference of π, into a single beam. This light beam is converted into modulated elliptically polarized light via a polarization device for pumping and detecting the alkali metal atoms. This eliminates the virtual magnetic field generated by the optical frequency shift within the coherence period of the alkali metal atoms through multiple rapid reversals. Furthermore, the interaction between the alkali metal atoms and the light converts the modulation of the ellipsometric light frequency into modulation of the optical rotation angle. Finally, polarization differential detection and difference frequency demodulation techniques are used to extract an output signal containing information about the weak magnetic field to be measured from the optical rotation angle signal. This method eliminates optical frequency shift errors while suppressing low-frequency noise caused by pump light frequency fluctuations. The device also features high integration and miniaturization.

Description

Technical Field

[0001] The present invention relates to the technical field of quantum precision magnetic field measurement, and in particular to an ellipsometric atomic magnetometer device and method for eliminating optical frequency shift. Background Art

[0002] Atomic magnetometers utilize the relationship between the energy difference between atomic Zeeman levels and the magnitude of the magnetic field to achieve extremely weak magnetic measurements. SERF (Spin-Exchange-Relaxation-Free) atomic magnetometers suppress atomic spin relaxation by making the atomic spin exchange rate much larger than the atomic Larmor precession frequency. Their sensitivity can reach the femtoliter level, playing an important role in biomagnetic detection, weak magnetic metrology testing, and basic physics research.

[0003] Ellipsometry atomic magnetometer is a single-beam atomic magnetometer that uses a detuned elliptically polarized light beam to illuminate the gas cell. The circularly polarized component of the elliptically polarized light is used for pumping, and the linearly polarized component is used for detection. Compared with circularly polarized single-beam atomic magnetometers, it has higher sensitivity because it can use polarization differential detection technology. Compared with dual-beam structures, it has the characteristics of compactness and miniaturization, making it more suitable for miniaturized applications. Therefore, the ellipsometer is a single-beam magnetometer solution that takes into account both sensitivity and size advantages. However, the ellipsometer SERF magnetometer uses detuned elliptically polarized light to interact with atoms, which produces a virtual magnetic field with uneven spatial distribution, restricting its further performance improvement. Summary of the Invention

[0004] The present invention provides an ellipsoidal polarization atomic magnetometer device and method for eliminating optical frequency shift. The positively detuned and negatively detuned laser beams generated by two narrow-linewidth semiconductor lasers are modulated by semiconductor optical amplifiers respectively and converted into two beams of pulsed modulated light with detuning amounts symmetrical about the center frequency of the alkali metal atom and a phase difference of π. The positively detuned and negatively detuned laser beams are combined into one laser beam through a 2×1 optical fiber combiner and then connected to the magnetometer head system. As a result, the optical polarization device in the head converts it into an elliptically polarized light beam whose frequency is periodically modulated over time. This can eliminate the optical frequency shift error of the ellipsoidal polarization SERF magnetometer and also suppress the low-frequency noise caused by the pump light frequency fluctuation. In addition, the semiconductor optical amplifier and 2×1 optical fiber combiner used are compact and highly integrated, and the magnetometer head system with a single-beam configuration has a simple structure, which makes the entire invention device highly integrated and miniaturized.

[0005] The technical solutions of the present invention are as follows:

[0006] An ellipsoidal atomic magnetometer device for eliminating optical frequency shift comprises an optical drive system, a magnetometer head system and a circuit system connected in sequence, characterized in that the optical drive system comprises a 2*1 fiber combiner, the output end of the 2*1 fiber combiner is connected to the magnetometer head system via a fifth polarization-maintaining fiber, the first input end of the 2*1 fiber combiner is connected to the output end of a first semiconductor optical amplifier in a first laser driver via a second polarization-maintaining fiber, the input end of the first semiconductor optical amplifier is connected to a positively detuned narrow-linewidth semiconductor laser via a first polarization-maintaining fiber, the second input end of the 2*1 fiber combiner is connected to the output end of a second semiconductor optical amplifier in a second laser driver via a fourth polarization-maintaining fiber, the input end of the second semiconductor optical amplifier is connected to a negatively detuned narrow-linewidth semiconductor laser via a third polarization-maintaining fiber, and the first laser driver and the second laser driver are respectively connected to an FPGA signal generation module.

[0007] The FPGA signal generation module generates a driving signal to control the working state of the first semiconductor optical amplifier through the first laser to achieve modulation of the positive detuned light, and controls the working state of the second semiconductor optical amplifier through the second laser to achieve modulation of the negative detuned light. The modulated positive detuned light and the modulated negative detuned light pass through the 2*1 fiber combiner to form positively detuned and negatively detuned alternating combined light.

[0008] The 2*1 fiber combiner combines two pulse-modulated optical beams with a detuning amount symmetrical about the center frequency of the alkali metal atoms and a phase difference of π into one beam. The beam is converted into modulated elliptically polarized light by a polarization device for pumping and detecting the alkali metal atoms. This eliminates the multiple rapid reversals of the virtual magnetic field generated by the optical frequency shift within the coherence period of the alkali metal atoms. Furthermore, the interaction between the alkali metal atoms and the light converts the modulation of the elliptically polarized light frequency into modulation of the optical rotation angle. Finally, polarization differential detection and difference frequency demodulation techniques are used to extract an output signal containing information about the weak magnetic field to be measured from the optical rotation angle signal.

[0009] The magnetometer head system includes an alkali metal atom gas cell, the laser input side of the alkali metal atom gas cell is connected to the fifth polarization-maintaining optical fiber via a quarter-wave plate, a linear polarizer, and an optical fiber collimator in sequence, the laser output side of the alkali metal atom gas cell is connected to a lateral-displacement polarization beam splitter prism via a half-wave plate, the first output side of the lateral-displacement polarization beam splitter prism is connected to the first input end of the differential amplifier in the circuit system via a first photodetector, the second output side of the lateral-displacement polarization beam splitter prism is connected to the second input end of the differential amplifier via a second photodetector, the output end of the differential amplifier is connected to a phase-locked amplifier, and the phase-locked amplifier provides a magnetometer output signal, the alkali metal atom gas cell is located in a non-magnetic electric heating device, the non-magnetic electric heating device is located in a three-axis magnetic field coil, and the three-axis magnetic field coil is connected to a function signal generator in the circuit system.

[0010] include:

[0011]

[0012] Among them, P z-ω is the first harmonic signal of the alkali metal atom polarizability projected along the z direction when the x-direction modulating magnetic field is applied, S0 is the spin value of the alkali metal atom in the initial state, Ψ0(k) and Ψ1(k) are the zero-order first-kind Bessel function and the first-order first-kind Bessel function, Γ is the sum of the pumping rate and the relaxation rate, γ elec is the electron gyromagnetic ratio, B0 is the magnitude of the weak magnetic field to be measured in the x direction, f1 is the frequency of the modulated magnetic field applied in the x direction, and t is the time.

[0013] include:

[0014]

[0015] where Δχ is the detuning of the positive and negative detuned elliptically polarized light frequency from the alkali metal D1 line resonance frequency, Δχ(t) is the time-varying Δχ value, χ is the detuning of the positive detuned elliptically polarized light frequency, f2 is the frequency at which the elliptically polarized light frequency switches between positive and negative detuning, and N is a positive integer.

[0016] include:

[0017]

[0018] where θ ω Because P z-ω The optical rotation angle signal caused by the optical rotation is shown in Figure 2, where c is the speed of light, r is the classical electron radius, f is the resonance intensity of the alkali metal D1 line, n is the atomic number density, d is the length of the gas chamber in the direction of the pumping light, and P is the wavelength of the gas chamber in the direction of the pumping light. z-ωis the first harmonic signal of the polarizability of the alkali metal atoms projected along the z direction when the x-direction modulating magnetic field is applied, χ is the detuning amount of the positively detuned elliptically polarized light frequency, D is the pressure broadening value of the gas cell, and f2 is the frequency at which the modulated elliptically polarized light frequency switches between positive and negative detuning.

[0019] include:

[0020]

[0021] Where V ω is the output signal of the atomic magnetometer after demodulating the atomic precession signal and the optical rotation angle modulation signal, S0 is the initial polarizability, e is the natural constant, OD is the optical depth, c is the speed of light, r is the classical electron radius, f is the resonance intensity of the alkali metal D1 line, n is the atomic number density, d is the length of the gas cell in the direction of the pumping light, χ is the detuning amount of the positively detuned elliptically polarized light frequency, D is the pressure broadening value of the gas cell, Ψ0(k) and Ψ1(k) are the zero-order first-kind Bessel function and the first-order first-kind Bessel function, Γ is the sum of the pumping rate and the relaxation rate, γ elec is the electron gyromagnetic ratio, B0 is the magnitude of the weak magnetic field to be measured in the x direction, f1 is the frequency of the modulation magnetic field applied in the x direction, and f2 is the frequency at which the modulated elliptically polarized light frequency switches between positive detuning and negative detuning.

[0022] A method for realizing an ellipsometric atomic magnetometer that eliminates optical frequency shift, characterized by comprising the use of the above-mentioned ellipsometric atomic magnetometer device that eliminates optical frequency shift, and the following steps:

[0023] Step 1, adjusting the lasers emitted by the positively detuned narrow linewidth semiconductor laser and the negatively detuned narrow linewidth semiconductor laser to be positively and negatively tuned to the alkali metal atom D1 line resonance frequency, respectively, and the absolute values ​​of the tuning are the same, both being χ, and adjusting the output powers of the positively detuned narrow linewidth semiconductor laser and the negatively detuned narrow linewidth semiconductor laser to be the same, and the polarization directions of both are parallel to the slow axis of the connected polarization-maintaining optical fiber;

[0024] Step 2: Adjust the two signal output pins controlled by the FPGA signal generation module to generate two square wave signals respectively, with a phase difference of π, a signal frequency of f2, a duty cycle of 50%, and an amplitude greater than the turn-on voltage of the semiconductor optical amplifier.

[0025] Step 3: Rotate the quarter wave plate in the magnetometer head system so that the angle between its optical axis and the optical axis of the linear polarizer is α, so that the emitted laser light becomes elliptically polarized light with an ellipticity of α. The elliptically polarized light is used as a light source to illuminate the gas chamber. At room temperature, adjust the slow axis angle between the half wave plate and the quarter wave plate to

[0026] Step 4: Heat the alkali metal atom gas cell using a non-magnetic electric heating device to put the alkali metal atoms into the SERF state. A function signal generator generates a control signal to control the three-axis magnetic field coil to compensate the ambient magnetic field at the gas cell location to zero and apply a modulated magnetic field in the x-direction with a modulation frequency of f1.

[0027] Step 5: Demodulate at the frequency f2-f1 in a phase-locked amplifier to obtain a demodulated atomic precession signal and an optical rotation angle modulation signal as an atomic magnetometer signal output.

[0028] The technical effects of the present invention are as follows: The present invention proposes an ellipsometric atomic magnetometer device and method for eliminating optical frequency shift. Based on the existing magnetic field modulation of atomic precession, a modulated elliptically polarized light source with a frequency that rapidly switches between positive and negative equal detuning and a stable ellipticity, principal axis direction, and optical power is used instead of the traditional steady-state light source as the pump light for the single-beam atomic magnetometer. This eliminates the virtual magnetic field caused by optical frequency shift in the ellipsometric magnetometer, while suppressing optical frequency shift noise and optical rotation angle noise caused by frequency fluctuation. In addition, the optical path system adopted by the present invention uses miniaturized optical devices, and the semiconductor optical amplifier using micro-nano processing technology can reach mm-level dimensions. Combined with the optical fiber design, it has the technical advantages of compact structure, high integration, and strong flexibility.

[0029] The advantages of the present invention compared with the prior art are:

[0030] (1) Compared with the traditional ellipsometric atomic magnetometer, the present invention constructs a beam of elliptically polarized light with symmetrical frequency modulation characteristics, which can quickly reverse the optical frequency-shifted magnetic field multiple times within the coherence time, thereby eliminating the errors caused by the optical frequency-shifted virtual magnetic field and its gradient.

[0031] (2) Compared with the traditional ellipsometric atomic magnetometer, the present invention realizes the modulation of the optical rotation angle by frequency modulation of elliptically polarized light, and demodulates the difference frequency signal through phase-locked amplification technology to suppress the noise generated by the low-frequency fluctuation of the pumping laser frequency.

[0032] (3) Compared with the traditional ellipsometric atomic magnetometer, the present invention uses a compact and integrated semiconductor optical amplifier and a 2×1 fiber combiner. The entire device is highly integrated, and the magnetometer head system adopts a single-beam configuration, which makes the present invention have the advantages of miniaturization and high flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The present invention is a schematic structural diagram of an ellipsometric atomic magnetometer device for eliminating optical frequency shift.

[0034] The accompanying drawings are described as follows: 1-optical drive system; 2-magnetometer head system; 3-circuit system; 101-positive detuned narrow linewidth semiconductor laser; 102-first polarization-maintaining fiber; 103-first semiconductor optical amplifier; 104-first laser driver; 105-second polarization-maintaining fiber; 106-FPGA signal generation module (FPGA, Field Programmable Gate Array, field programmable logic gate array); 107-negatively detuned narrow-linewidth semiconductor laser; 108-third polarization-maintaining fiber; 109-second semiconductor optical amplifier; 110-second laser driver; 111-fourth polarization-maintaining fiber; 112-2×1 fiber combiner (2*1, i.e., 2 in 1, combining 2 input light paths into 1 output light path); 113-fifth polarization-maintaining fiber; 201-fiber collimator; 202-linear polarizer; 203-quarter-wave plate; 204-alkali metal atom gas chamber; 205-non-magnetic electric heating device; 206-three-axis magnetic field coil; 207-half-wave plate; 208-laterally displaced polarization beam splitter; 209-first photodetector; 210-second photodetector; 301-function signal generator; 302-differential amplifier; 303-locked amplifier; 304-magnetometer output signal. DETAILED DESCRIPTION

[0035] Below is the attached figure ( Figure 1 ) and Examples illustrate the present invention.

[0036] Figure 1 This is a schematic diagram of the structure of an ellipsometric atomic magnetometer device for eliminating optical frequency shift according to the present invention. Figure 1 As shown, an ellipsoidal polarization atomic magnetometer device for eliminating optical frequency shift includes an optical drive system 1, a magnetometer head system 2, and a circuit system 3 connected in sequence. The optical drive system 1 includes a 2*1 fiber combiner 112, the output end of the 2*1 fiber combiner 112 is connected to the magnetometer head system 2 through a fifth polarization-maintaining fiber 113, the first input end of the 2*1 fiber combiner 112 is connected to the output end of the first semiconductor optical amplifier 103 in the first laser driver 104 through a second polarization-maintaining fiber 105, and the first semiconductor optical amplifier The input end of the device 103 is connected to the positively detuned narrow linewidth semiconductor laser 101 through the first polarization-maintaining optical fiber 102, the second input end of the 2*1 optical fiber combiner 112 is connected to the output end of the second semiconductor optical amplifier 109 in the second laser driver 110 through the fourth polarization-maintaining optical fiber 111, the input end of the second semiconductor optical amplifier 109 is connected to the negatively detuned narrow linewidth semiconductor laser 107 through the third polarization-maintaining optical fiber 108, and the first laser driver 104 and the second laser driver 110 are respectively connected to the FPGA signal generation module 106.

[0037] The FPGA signal generating module 106 generates a driving signal to control the working state of the first semiconductor optical amplifier 103 through the first laser driver 104 to achieve modulation of the positive detuned light, and controls the working state of the second semiconductor optical amplifier 109 through the second laser driver 110 to achieve modulation of the negative detuned light. The modulated positive detuned light and the modulated negative detuned light pass through the 2*1 fiber combiner 112 to form positive detuned and negative detuned alternating combined light.

[0038] The 2*1 fiber combiner 112 combines two pulse-modulated optical beams with a detuning amount symmetrical about the center frequency of the alkali metal atoms and a phase difference of π into one beam. The beam is converted into modulated elliptically polarized light by a polarization device for pumping and detecting the alkali metal atoms. This eliminates the multiple rapid reversals of the virtual magnetic field generated by the optical frequency shift within the coherence period of the alkali metal atoms. The interaction between the alkali metal atoms and the light converts the modulation of the elliptically polarized light frequency into modulation of the optical rotation angle. Finally, polarization differential detection and difference frequency demodulation techniques are used to extract an output signal containing the weak magnetic field information to be measured from the optical rotation angle signal.

[0039] The magnetometer head system 2 includes an alkali metal atom gas cell 204. The laser input side of the alkali metal atom gas cell 204 is connected to the fifth polarization-maintaining optical fiber 113 through a quarter-wave plate 203, a linear polarizer 202, and an optical fiber collimator 201 in sequence. The laser output side of the alkali metal atom gas cell 204 is connected to a lateral displacement polarization beam splitter prism 208 through a half-wave plate 207. The first output side of the lateral displacement polarization beam splitter prism 208 is connected to the first input of the differential amplifier 302 in the circuit system 3 through a first photodetector 209. The second output side of the lateral displacement polarization splitter prism 208 is connected to the second input end of the differential amplifier 302 through the second photodetector 210. The output end of the differential amplifier 302 is connected to the phase-locked amplifier 303. The phase-locked amplifier 303 provides a magnetometer output signal 304. The alkali metal atom gas chamber 204 is located in the non-magnetic electric heating device 205. The non-magnetic electric heating device 205 is located in the three-axis magnetic field coil 206. The three-axis magnetic field coil 206 is connected to the function signal generator 301 in the circuit system 3.

[0040] A method for realizing an ellipsometric atomic magnetometer for eliminating optical frequency shift comprises adopting the above-mentioned ellipsometric atomic magnetometer device for eliminating optical frequency shift, and the following steps: step 1, adjusting the lasers emitted by a positively detuned narrow linewidth semiconductor laser and a negatively detuned narrow linewidth semiconductor laser to be positively and negatively tuned to the D1 line resonance frequency of the alkali metal atom, respectively, and adjusting the absolute values ​​of the tuning to be the same, both being χ, adjusting the output powers of the positively detuned narrow linewidth semiconductor laser and the negatively detuned narrow linewidth semiconductor laser to be the same, and adjusting the polarization directions of both to be parallel to the slow axis of the connected polarization-maintaining optical fiber; step 2, adjusting The two signal output pins controlled by the FPGA signal generation module respectively generate two square wave signals, and the phase difference between the two signals is π, the signal frequency is f2, the duty cycle is 50%, the signal amplitude is the same and both are greater than the turn-on voltage of the semiconductor optical amplifier; Step 3, rotate the quarter wave plate in the magnetometer head system so that the angle between its optical axis and the optical axis direction of the linear polarizer is α, so that the emitted laser is converted into elliptically polarized light with an ellipticity of α. The elliptically polarized light is used as a light source to illuminate the gas chamber, and the slow axis angle between the half wave plate and the quarter wave plate is adjusted to In step 4, the alkali metal atom gas cell is heated using a non-magnetic electric heating device to cause the alkali metal atoms to enter the SERF state. A control signal is generated by a function signal generator to control the three-axis magnetic field coil to compensate the ambient magnetic field at the location of the gas cell to zero and apply a modulated magnetic field in the x-direction with a modulation frequency of f1. In step 5, demodulation is performed at the frequency f2-f1 in a phase-locked amplifier to obtain a demodulated atomic precession signal and an optical rotation angle modulation signal as the atomic magnetometer signal output.

[0041] Includes the following formulas:

[0042]

[0043] Among them, P z-ω is the first harmonic signal of the alkali metal atom polarizability projected along the z direction when the x-direction modulating magnetic field is applied, S0 is the spin value of the alkali metal atom in the initial state, Ψ0(k) and Ψ1(k) are the zero-order first-kind Bessel function and the first-order first-kind Bessel function, Γ is the sum of the pumping rate and the relaxation rate, γ elec is the electron gyromagnetic ratio, B0 is the magnitude of the weak magnetic field to be measured in the x direction, f1 is the frequency of the modulated magnetic field applied in the x direction, and t is the time.

[0044] where Δχ is the detuning of the positive and negative detuned elliptically polarized light frequency from the alkali metal D1 line resonance frequency, Δχ(t) is the time-varying Δχ value, χ is the detuning of the positive detuned elliptically polarized light frequency, f2 is the frequency at which the elliptically polarized light frequency switches between positive and negative detuning, and N is a positive integer.

[0045] where θ ω Because P z-ωThe optical rotation angle signal caused by is, c is the speed of light, r is the classical electron radius, f is the resonance intensity of the alkali metal D1 line, n is the atomic number density, d is the length of the gas cell in the direction of the pumping light, and D is the pressure broadening value of the gas cell.

[0046] Where V ω is the output signal of the atomic magnetometer after demodulating the atomic precession signal and the optical rotation angle modulation signal, e is a natural constant, and OD is the optical depth.

[0047] A device and method for an ellipsometric atomic magnetometer that eliminates optical frequency shift utilizes a laser and integrated devices to generate elliptically polarized modulated light with symmetrical frequency detuning as the laser source of a single-beam atomic magnetometer, enabling the measurement of weak magnetic fields under a modulated magnetic field. The device combines two pulsed light beams, each with a detuning amount symmetrical about the center frequency of an alkali metal atom and a phase difference of π, into a single beam. This light beam is converted into modulated elliptically polarized light by a polarization device for pumping and detecting the alkali metal atoms. This eliminates the virtual magnetic field generated by the optical frequency shift within the coherence period of the alkali metal atoms through multiple rapid reversals. Furthermore, the interaction between the alkali metal atoms and the light converts the modulation of the ellipsometric light frequency into modulation of the optical rotation angle. Finally, polarization differential detection and difference frequency demodulation techniques are used to extract an output signal containing information about the weak magnetic field to be measured from the optical rotation angle signal. Compared to conventional single-beam atomic magnetometers, the device can eliminate the optical frequency shift error of ellipsometric SERF magnetometers while suppressing the low-frequency noise caused by pump light frequency fluctuations. It also offers the advantages of high integration and miniaturization.

[0048] refer to Figure 1 As shown, an ellipsoidal atomic magnetometer device for eliminating optical frequency shift includes an optical drive system 1, a magnetometer head system 2 and a circuit system 3. The output ends of the positive detuned narrow linewidth semiconductor laser 101 and the negative detuned narrow linewidth semiconductor laser 102 of the optical drive system 1 are respectively connected to the input ends of the first semiconductor optical amplifier 103 and the second semiconductor optical amplifier 109. The output ends of the first semiconductor optical amplifier 103 and the second semiconductor optical amplifier 109 are connected to the input end of the 2×1 fiber combiner 112. The laser output by the beam splitter 112 is emitted through the polarization-maintaining fiber 113 and the collimator 201, and then passes through the linear polarizer 202, the quarter-wave plate 203, the alkali metal atom gas chamber 204, the half-wave plate 207 and the lateral displacement polarization beam splitter 208 in sequence, and is received by the first photodetector 209 and the second photodetector 210. The output signals of the first photodetector 209 and the second photodetector 210 are input to the differential amplifier 302. The amplified signals are demodulated by the phase-locked amplifier 303 to obtain the atomic magnetometer output signal 304.

[0049] Polarization-maintaining fibers are fused at both ends of the first semiconductor optical amplifier 103 and the second semiconductor optical amplifier 109, and the polarization-maintaining fibers at the output ends of the first semiconductor optical amplifier 103 and the second semiconductor optical amplifier 109 are connected to the two input ends of the 2×1 fiber combiner by fusion splicing. The fifth polarization-maintaining fiber 113 at the output end of the 2×1 fiber combiner is integrated with a collimator 201.

[0050] The FPGA signal generation module 106 controls two signal output pins, which are respectively connected to the control input ends of the first laser driver 104 and the second laser driver 110. The first semiconductor optical amplifier 103 is installed on the first laser driver 104, and the second semiconductor optical amplifier 109 is installed on the second laser driver 110.

[0051] The slow axes of the first polarization-maintaining optical fiber 102 , the second polarization-maintaining optical fiber 105 , the third polarization-maintaining optical fiber 108 , the fourth polarization-maintaining optical fiber 111 and the fifth polarization-maintaining optical fiber 113 are all processed to be parallel.

[0052] The alkali metal atom gas chamber 204 is installed in a non-magnetic electric heating device 205, which is surrounded by a three-axis magnetic field coil 206. The three-axis magnetic field coil 206 is controlled by a signal generated by a function signal generator 301 to generate corresponding compensation magnetic field and modulation magnetic field.

[0053] The magnetometer head system 2 encapsulates a linear polarizer 202 , a quarter-wave plate 203 , an alkali metal atom gas cell 204 , a half-wave plate 207 , a lateral displacement polarization beam splitter prism 208 , a first photodetector 209 , and a second photodetector 210 .

[0054] The modulated laser light passing through the gas chamber 204 is elliptically polarized light with symmetrical frequency periodic modulation characteristics, and its frequency is quickly switched between equal positive detuning and negative detuning with the alkali metal D1 line resonance frequency as the center.

[0055]

[0056] Among them, P z-ω is the first harmonic signal of the alkali metal atom polarizability projected along the z direction when the x-direction modulating magnetic field is applied, S0 is the spin value of the alkali metal atom in the initial state, Ψ0(k) and Ψ1(k) are the zero-order first-kind Bessel function and the first-order first-kind Bessel function, Γ is the sum of the pumping rate and the relaxation rate, γ elec is the electron gyromagnetic ratio, B0 is the magnitude of the weak magnetic field to be measured in the x direction, f1 is the frequency of the modulated magnetic field applied in the x direction, and t is the time.

[0057]

[0058] where Δχ is the detuning of the positive and negative detuned elliptically polarized light frequency from the alkali metal D1 line resonance frequency, Δχ(t) is the time-varying Δχ value, χ is the detuning of the positive detuned elliptically polarized light frequency, f2 is the frequency at which the elliptically polarized light frequency switches between positive and negative detuning, and N is a positive integer.

[0059]

[0060] where θ ω Because P z-ω The optical rotation angle signal caused by the optical rotation is shown in Figure 2, where c is the speed of light, r is the classical electron radius, f is the resonance intensity of the alkali metal D1 line, n is the atomic number density, d is the length of the gas chamber in the direction of the pumping light, and P is the wavelength of the gas chamber in the direction of the pumping light. z-ω is the first harmonic signal of the polarizability of the alkali metal atoms projected along the z direction when the x-direction modulating magnetic field is applied, χ is the detuning amount of the positively detuned elliptically polarized light frequency, D is the pressure broadening value of the gas cell, and f2 is the frequency at which the modulated elliptically polarized light frequency switches between positive and negative detuning.

[0061]

[0062] Where V ω is the output signal of the atomic magnetometer after demodulating the atomic precession signal and the optical rotation angle modulation signal, S0 is the initial polarizability, e is the natural constant, OD is the optical depth, c is the speed of light, r is the classical electron radius, f is the resonance intensity of the alkali metal D1 line, n is the atomic number density, d is the length of the gas cell in the direction of the pumping light, χ is the detuning amount of the positively detuned elliptically polarized light frequency, D is the pressure broadening value of the gas cell, Ψ0(k) and Ψ1(k) are the zero-order first-kind Bessel function and the first-order first-kind Bessel function, Γ is the sum of the pumping rate and the relaxation rate, γ elec is the electron gyromagnetic ratio, B0 is the magnitude of the weak magnetic field to be measured in the x direction, f1 is the frequency of the modulation magnetic field applied in the x direction, and f2 is the frequency at which the modulated elliptically polarized light frequency switches between positive detuning and negative detuning.

[0063] The specific implementation steps of the present invention are as follows:

[0064] (1) First, adjust the positive detuned narrow linewidth semiconductor laser 101 and the negative detuned narrow linewidth semiconductor laser 107 to the positive and negative frequencies respectively. 87 The resonance frequency of the Rb alkali metal atom D1 line is χ0 = 377106.92 GHz, and the absolute tuning value is the same, both χ = 90 GHz. The output power of the positive detuned narrow linewidth semiconductor laser 101 and the negative detuned narrow linewidth semiconductor laser 107 are adjusted to 4 mW, and the polarization directions are parallel to the slow axis of the connected polarization-maintaining optical fiber.

[0065] (2) Then, the two signal output pins controlled by the FPGA signal generation module 106 are adjusted to generate two square wave signals respectively, and the phase difference between the two signals is π, the signal frequency is f2 = 1kHz, the duty cycle is 50%, the signal amplitude is the same and both are greater than the turn-on voltage of the semiconductor optical amplifier, respectively controlling the modulation of the input optical signal by the first semiconductor optical amplifier 103 and the second semiconductor optical amplifier 109. The fiber collimator 201 generates a Gaussian beam with a diameter of 3.5 mm as the pump light input to the magnetometer head system 2. At this time, the output optical frequency of the collimator 201 is:

[0066]

[0067] where Δχ is the detuning of the positive and negative detuned elliptically polarized light frequency from the alkali metal D1 line resonance frequency, Δχ(t) is the time-varying Δχ value, χ is the detuning of the positive detuned elliptically polarized light frequency, f2 is the frequency at which the elliptically polarized light frequency switches between positive and negative detuning, and N is a positive integer.

[0068] (3) Rotate the quarter wave plate 203 in the magnetometer head system 2 so that the angle between its optical axis and the optical axis of the linear polarizer 202 is The emitted laser becomes elliptical The elliptically polarized light is used as a light source to illuminate the cubic air chamber 204 with a side length of 3 mm. At room temperature, the slow axis angle between the half wave plate 207 and the quarter wave plate 203 is adjusted to

[0069] (4) The alkali metal atom gas chamber 204 is heated by the non-magnetic electric heating device 205 to make the atomic number density reach 10 14 pieces / cm 3 The alkali metal atoms enter the SERF state. The function signal generator 301 generates a control signal to control the three-axis magnetic field coil 206 to compensate the ambient magnetic field at the location of the gas chamber 204 to zero and apply a modulated magnetic field in the x-direction. The modulation frequency is f1 = 900 Hz and the amplitude is Bmod = 60 nT. At this time, the first harmonic signal of the polarizability of the alkali metal atoms projected along the z-direction is expressed as:

[0070]

[0071] Among them, P Z-ω is the first harmonic signal of the alkali metal atom polarizability projected along the z direction when the x-direction modulating magnetic field is applied, S0 is the spin value of the alkali metal atom in the initial state, Ψ0(k) and Ψ1(k) are the zero-order first-kind Bessel function and the first-order first-kind Bessel function, Γ is the sum of the pumping rate and the relaxation rate, γ elec is the electron gyromagnetic ratio, B0 is the magnitude of the weak magnetic field to be measured in the x direction, and f1 is the frequency of the modulated magnetic field applied in the x direction.

[0072] By P z-ω The optical rotation angle signal θ caused ω Expressed as:

[0073]

[0074] where θ ω Because P z-ω The optical rotation angle signal caused by the optical rotation is shown in Figure 2, where c is the speed of light, r is the classical electron radius, f is the resonance intensity of the alkali metal D1 line, n is the atomic number density, d is the length of the gas chamber in the direction of the pumping light, and P is the wavelength of the gas chamber in the direction of the pumping light. z-ω is the first harmonic signal of the polarizability of the alkali metal atoms projected along the z direction when the x-direction modulating magnetic field is applied, χ is the detuning amount of the positively detuned elliptically polarized light frequency, D is the pressure broadening value of the gas cell, and f2 is the frequency at which the modulated elliptically polarized light frequency switches between positive and negative detuning.

[0075] (5) Demodulate at the frequency f2-f1 in the lock-in amplifier 303 to obtain the atomic magnetometer difference frequency output signal V after demodulating the atomic precession signal and the optical rotation angle modulation signal. ω 304 is:

[0076]

[0077] Where V ω is the output signal of the atomic magnetometer after demodulating the atomic precession signal and the optical rotation angle modulation signal, S0 is the initial polarizability, e is the natural constant, OD is the optical depth, c is the speed of light, c is the classical electron radius, f is the resonance intensity of the alkali metal D1 line, n is the atomic number density, d is the length of the gas cell in the direction of the pumping light, χ is the detuning amount of the positively detuned elliptically polarized light frequency, D is the gas cell pressure broadening value, Ψ0(k) and Ψ1(k) are the zero-order first-kind Bessel function and the first-order first-kind Bessel function, respectively, and Γ is the relationship between the pumping rate and R rel The sum of relaxation rates, γ elec is the electron gyromagnetic ratio, B0 is the magnitude of the weak magnetic field to be measured in the x direction, f1 is the frequency of the modulation magnetic field applied in the x direction, and f2 is the frequency at which the modulated elliptically polarized light frequency switches between positive detuning and negative detuning.

[0078] In summary, the present invention provides an ellipsometric atomic magnetometer device and method for eliminating optical frequency shift. The positively detuned and negatively detuned lasers generated by two narrow-linewidth semiconductor lasers are modulated separately through a semiconductor optical amplifier, converting them into two pulsed light beams with detuning amounts symmetrical about the center frequency of the alkali metal atom and a phase difference of π. The positively detuned and negatively detuned lasers are combined into a single beam via a 2×1 fiber combiner and then connected to the magnetometer head system. Within the head system, the beam is then converted through an optical polarization device into an elliptically polarized light beam whose frequency is periodically modulated over time. This eliminates the optical frequency shift error of the ellipsometric SERF magnetometer while also suppressing low-frequency noise caused by pump light frequency fluctuations.

[0079] Any content not described in detail in this specification is prior art known to those skilled in the art. It should be noted that the above description is intended to help those skilled in the art understand the present invention, but does not limit the scope of protection of the present invention. Any equivalent substitution, modification, improvement, and / or simplification of the above description that does not depart from the essence of the present invention shall fall within the scope of protection of the present invention.

Claims

1. An ellipsometric atomic magnetometer device for eliminating optical frequency shift, comprising an optical drive system, a magnetometer head system, and a circuit system connected in sequence, characterized in that: The optical drive system includes a 2*1 fiber combiner, the output end of the 2*1 fiber combiner is connected to the magnetometer head system through a fifth polarization-maintaining fiber, the first input end of the 2*1 fiber combiner is connected to the output end of the first semiconductor optical amplifier in the first laser driver through a second polarization-maintaining fiber, the input end of the first semiconductor optical amplifier is connected to a positively detuned narrow-linewidth semiconductor laser through a first polarization-maintaining fiber, the second input end of the 2*1 fiber combiner is connected to the output end of the second semiconductor optical amplifier in the second laser driver through a fourth polarization-maintaining fiber, the input end of the second semiconductor optical amplifier is connected to a negatively detuned narrow-linewidth semiconductor laser through a third polarization-maintaining fiber, and the first laser driver and the second laser driver are respectively connected to an FPGA signal generation module; The 2*1 fiber combiner combines two pulse-modulated optical beams with a detuning amount symmetrical about the center frequency of the alkali metal atoms and a phase difference of π into one beam. The beam is converted into modulated elliptically polarized light by a polarization device for pumping and detecting the alkali metal atoms. This eliminates the multiple rapid reversals of the virtual magnetic field generated by the optical frequency shift within the coherence period of the alkali metal atoms. Furthermore, the interaction between the alkali metal atoms and the light converts the modulation of the elliptically polarized light frequency into modulation of the optical rotation angle. Finally, polarization differential detection and difference frequency demodulation techniques are used to extract an output signal containing information about the weak magnetic field to be measured from the optical rotation angle signal.

2. The ellipsometric atomic magnetometer device for eliminating optical frequency shift according to claim 1, characterized in that: The FPGA signal generation module generates a driving signal to drive and control the working state of the first semiconductor optical amplifier through the first laser to achieve modulation of the positive detuned light, and drives and controls the working state of the second semiconductor optical amplifier through the second laser to achieve modulation of the negative detuned light. The modulated positive detuned light and the modulated negative detuned light pass through the 2*1 fiber combiner to form positively detuned and negatively detuned alternating combined light.

3. The ellipsometric atomic magnetometer device for eliminating optical frequency shift according to claim 1, characterized in that: The magnetometer head system includes an alkali metal atom gas cell, the laser input side of the alkali metal atom gas cell is connected to the fifth polarization-maintaining optical fiber via a quarter-wave plate, a linear polarizer, and an optical fiber collimator in sequence, the laser output side of the alkali metal atom gas cell is connected to a lateral-displacement polarization beam splitter prism via a half-wave plate, the first output side of the lateral-displacement polarization beam splitter prism is connected to the first input end of the differential amplifier in the circuit system via a first photodetector, the second output side of the lateral-displacement polarization beam splitter prism is connected to the second input end of the differential amplifier via a second photodetector, the output end of the differential amplifier is connected to a phase-locked amplifier, and the phase-locked amplifier provides a magnetometer output signal, the alkali metal atom gas cell is located in a non-magnetic electric heating device, the non-magnetic electric heating device is located in a three-axis magnetic field coil, and the three-axis magnetic field coil is connected to a function signal generator in the circuit system.

4. The ellipsometric atomic magnetometer device for eliminating optical frequency shift according to claim 1, wherein: include: Among them, P z-ω is the first harmonic signal of the alkali metal atom polarizability projected along the z direction when the x-direction modulating magnetic field is applied, S0 is the spin value of the alkali metal atom in the initial state, ψ0(k) and ψ1(k) are the zero-order first-kind Bessel function and the first-order first-kind Bessel function, Γ is the sum of the pumping rate and the relaxation rate, γ elec is the electron gyromagnetic ratio, B0 is the magnitude of the weak magnetic field to be measured in the x direction, f1 is the frequency of the modulated magnetic field applied in the x direction, and t is the time.

5. The ellipsometric atomic magnetometer device for eliminating optical frequency shift according to claim 1, characterized in that: include: where Δχ is the detuning of the positive and negative detuned elliptically polarized light frequency from the alkali metal D1 line resonance frequency, Δχ(t) is the time-varying Δχ value, χ is the detuning of the positive detuned elliptically polarized light frequency, f2 is the frequency at which the elliptically polarized light frequency switches between positive and negative detuning, and N is a positive integer.

6. The ellipsometric atomic magnetometer device for eliminating optical frequency shift according to claim 1, characterized in that: include: where θ ω Because P z-ω The optical rotation angle signal caused by the optical rotation is shown in Figure 2, where c is the speed of light, r is the classical electron radius, f is the resonance intensity of the alkali metal D1 line, n is the atomic number density, d is the length of the gas chamber in the direction of the pumping light, and P is the wavelength of the gas chamber in the direction of the pumping light. z-ω is the first harmonic signal of the polarizability of the alkali metal atoms projected along the z direction when the x-direction modulating magnetic field is applied, χ is the detuning amount of the positively detuned elliptically polarized light frequency, D is the pressure broadening value of the gas cell, and f2 is the frequency at which the modulated elliptically polarized light frequency switches between positive and negative detuning.

7. The ellipsometric atomic magnetometer device for eliminating optical frequency shift according to claim 1, characterized in that: include: Where V ω is the output signal of the atomic magnetometer after demodulating the atomic precession signal and the optical rotation angle modulation signal, S0 is the initial polarizability, e is the natural constant, OD is the optical depth, c is the speed of light, r is the classical electron radius, f is the resonance intensity of the alkali metal D1 line, n is the atomic number density, d is the length of the gas cell in the direction of the pumping light, χ is the detuning amount of the positively detuned elliptically polarized light frequency, D is the pressure broadening value of the gas cell, Ψ0(k) and Ψ1(k) are the zero-order first-kind Bessel function and the first-order first-kind Bessel function, Γ is the sum of the pumping rate and the relaxation rate, γ elec is the electron gyromagnetic ratio, B0 is the magnitude of the weak magnetic field to be measured in the x direction, f1 is the frequency of the modulation magnetic field applied in the x direction, and f2 is the frequency at which the modulated elliptically polarized light frequency switches between positive detuning and negative detuning.

8. A method for realizing an ellipsometric atomic magnetometer that eliminates optical frequency shift, characterized in that: The invention comprises an ellipsometric atomic magnetometer device for eliminating optical frequency shift according to any one of claims 1 to 7, and the following steps: Step 1, adjusting the lasers emitted by the positively detuned narrow linewidth semiconductor laser and the negatively detuned narrow linewidth semiconductor laser to be positively and negatively tuned to the alkali metal atom D1 line resonance frequency, respectively, and the absolute values ​​of the tuning are the same, both being χ, and adjusting the output powers of the positively detuned narrow linewidth semiconductor laser and the negatively detuned narrow linewidth semiconductor laser to be the same, and the polarization directions of both are parallel to the slow axis of the connected polarization-maintaining optical fiber; Step 2: Adjust the two signal output pins controlled by the FPGA signal generation module to generate two square wave signals respectively, with a phase difference of π, a signal frequency of f2, a duty cycle of 50%, and an amplitude greater than the turn-on voltage of the semiconductor optical amplifier. Step 3: Rotate the quarter wave plate in the magnetometer head system so that the angle between its optical axis and the optical axis of the linear polarizer is α, so that the emitted laser light becomes elliptically polarized light with an ellipticity of α. The elliptically polarized light is used as a light source to illuminate the gas chamber. At room temperature, adjust the slow axis angle between the half wave plate and the quarter wave plate to Step 4: Heat the alkali metal atom gas cell using a non-magnetic electric heating device to put the alkali metal atoms into the SERF state. A function signal generator generates a control signal to control the three-axis magnetic field coil to compensate the ambient magnetic field at the gas cell location to zero and apply a modulated magnetic field in the x-direction with a modulation frequency of f1. Step 5: Demodulate at the frequency f2-f1 in a phase-locked amplifier to obtain a demodulated atomic precession signal and an optical rotation angle modulation signal as an atomic magnetometer signal output.

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