Elliptically polarized light atom magnetometer device and method for eliminating optical frequency shift

Abstract

The invention discloses an elliptically polarized light atom magnetometer device and method for eliminating optical frequency shift, and the device employs a laser and an integrated device to generate elliptically polarized modulated light with symmetrical and detuned frequency as a laser source of a single-beam atom magnetometer, and achieves the measurement of a to-be-measured weak magnetic field under a modulated magnetic field. According to the invention, two beams of pulse modulation light whose detuning amounts are symmetrical about the center frequency of alkali metal atoms and the phase difference is pi are combined into one beam, and the beam is converted into modulated elliptically polarized light through a polarization device to pump and detect the alkali metal atoms, so that a virtual magnetic field generated by optical frequency shift in the coherence period of the alkali metal atoms can be eliminated through multiple times of rapid inversion; modulation of elliptically polarized light frequency is converted into modulation of an optical rotation angle through interaction of alkali metal atoms and light, and finally, an output signal containing information of a weak magnetic field to be measured is extracted from an optical rotation angle signal by using polarization difference detection and difference frequency demodulation technologies, so that an optical frequency shift error can be eliminated; and meanwhile, low-frequency noise caused by pumping light frequency fluctuation is suppressed, and the device has the characteristic of high integration and the advantage of 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 use the relationship between the energy difference between atomic Zeeman energy levels and the magnitude of the magnetic field to achieve extremely weak magnetic measurements. Among them, the SERF (Spin-Exchange-Relaxation-Free) atomic magnetometer suppresses atomic spin relaxation by making the atomic spin exchange rate much larger than the atomic Larmor precession frequency. Its sensitivity can reach the fT level, and it plays an important role in the fields of biomagnetic detection, weak magnetic metrology testing, and basic physics research.

[0003] The ellipsometer atomic magnetometer is a single-beam atomic magnetometer that uses a beam of detuned elliptically polarized light to illuminate the gas chamber. The circularly polarized component in the elliptically polarized light is used for pumping, and the linearly polarized component is used for detection. Compared with the circularly polarized single-beam atomic magnetometer, it has higher sensitivity because it can use polarization differential detection technology. Compared with the dual-beam structure, it has the characteristics of compact structure and miniaturization, and is more suitable for miniaturized applications. Therefore, the ellipsometer is a single-beam magnetometer solution that takes into account both sensitivity and volume advantages. However, the ellipsometer SERF magnetometer uses detuned elliptically polarized light to interact with atoms, which will produce 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 pulse modulated lights with detuning amounts symmetrical about the center frequency of alkali metal atoms and a phase difference of π. The positively detuned and negatively detuned lasers are combined into one laser beam through a 2×1 optical fiber combiner and then connected to the magnetometer head system. Thereby, it is converted into an elliptically polarized light beam whose frequency is periodically modulated with time through an optical polarization device in the head, which can eliminate the optical frequency shift error of the ellipsoidal polarization SERF magnetometer, and also suppress the low-frequency noise caused by the frequency fluctuation of the pumping light. In addition, the semiconductor optical amplifier and 2×1 optical fiber combiner used have a compact structure and a high degree of integration, and the magnetometer head system with a single beam configuration has a simple structure, so that the entire invention device has the characteristics of high integration and miniaturization advantages.

[0005] The technical solution of the present invention is as follows:

[0006] An ellipsoidal atomic magnetometer device for eliminating optical frequency shift comprises an optical drive system, a magnetometer header 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 header system through a fifth polarization-maintaining optical 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 through a second polarization-maintaining optical 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 optical 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 through a fourth polarization-maintaining optical 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 optical fiber, and the first laser driver and the second laser driver are respectively connected to FPGA signal generation modules.

[0007] The FPGA signal generating 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 optical fiber combiner to form positively detuned and negatively detuned alternating combined light.

[0008] The 2*1 optical fiber combiner combines two beams of pulse modulated light with symmetric detuning amounts about the central frequency of alkali metal atoms and a phase difference of π into one beam, which is converted into modulated elliptically polarized light by a polarization device to pump and detect alkali metal atoms, so that multiple rapid reversals of the virtual magnetic field generated by the optical frequency shift within the coherent period of the alkali metal atoms are eliminated, and the modulation of the elliptically polarized light frequency is converted into the modulation of the optical rotation angle through the interaction between the alkali metal atoms and the light, and finally the output signal containing the weak magnetic field information to be measured is extracted from the optical rotation angle signal by using polarization differential detection and difference frequency demodulation technology.

[0009] The magnetometer head system includes an alkali metal atom gas chamber, the laser input side of the alkali metal atom gas chamber is connected to the fifth polarization-maintaining optical fiber through a quarter wave plate, a linear polarizer and an optical fiber collimator in sequence, the laser output side of the alkali metal atom gas chamber is connected to a lateral displacement polarization beam splitter prism through 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 through 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 through 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 chamber 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] Where P z-ω is the first harmonic signal of the projection of the polarizability of the alkali metal atom 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 amount of the positive and negative detuned modulated elliptically polarized light frequency with the alkali metal D1 line resonance frequency, Δχ(t) is the Δχ value that changes with time, χ is the detuning amount of the positive detuned elliptically polarized light frequency, f2 is the frequency at which the modulated elliptically polarized light frequency switches between positive detuning 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 pump 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 chamber in the direction of the pump light, P 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 gas cell pressure broadening value, and f2 is the frequency at which the modulated elliptically polarized light frequency switches between positive detuning 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 positive 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, 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 for eliminating optical frequency shift, characterized in that it comprises using the above-mentioned ellipsometric atomic magnetometer device for eliminating optical frequency shift, and the following steps:

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

[0024] Step 2, adjusting the two signal output pins controlled by the FPGA signal generation module to generate two square wave signals respectively, and the two signals have a phase difference of π, a signal frequency of f2, a duty cycle of 50%, and a same signal amplitude that is greater than the 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 ellipsometric degree 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, using a non-magnetic electric heating device to heat the alkali metal atom gas chamber to make the alkali metal atoms enter the SERF state, and using a function signal generator to generate a control signal to control the three-axis magnetic field coil to compensate the ambient magnetic field at the location of the gas chamber 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 the phase-locked amplifier to obtain the demodulated atomic precession signal and the optical rotation angle modulation signal as the atomic magnetometer signal output.

[0028] The technical effects of the present invention are as follows: The present invention proposes an ellipsoid light atomic magnetometer device and method for eliminating optical frequency shift. On the basis of the original magnetic field modulation of atomic precession, a modulated elliptically polarized light source with a frequency that quickly switches between positive and negative equal detuning and a stable ellipticity, main axis direction and optical power is used instead of a traditional steady-state light source as the pumping light of a single-beam atomic magnetometer, thereby eliminating the virtual magnetic field caused by optical frequency shift in the ellipsoid light magnetometer, and suppressing the optical rotation angle noise caused by optical frequency shift noise and frequency fluctuation. In addition, the optical path system used in the present invention uses miniaturized optical devices, and the semiconductor optical amplifier using micro-nano processing technology can reach mm-level size, which is combined with optical fiber design and 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 error 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 reference numerals are 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 drive; 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 lights into 1 output light); 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-lateral displacement polarization splitter prism; 209-first photodetector; 210-second photodetector; 301-function signal generator; 302-differential amplifier; 303-phase-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 comprises an optical drive system 1, a magnetometer head system 2 and a circuit system 3 connected in sequence, wherein the optical drive system 1 comprises a 2*1 optical fiber combiner 112, the output end of the 2*1 optical fiber combiner 112 is connected to the magnetometer head system 2 via a fifth polarization-maintaining optical fiber 113, the first input end of the 2*1 optical fiber combiner 112 is connected to the output end of the first semiconductor optical amplifier 103 in the first laser driver 104 via a second polarization-maintaining optical fiber 105, and the first semiconductor optical amplifier 103 is connected to the output end of the first laser driver 104 via a second polarization-maintaining optical fiber 105. 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 generating 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 positively detuned and negatively detuned alternating combined light.

[0038] The 2*1 fiber combiner 112 combines two beams of pulse modulated light with a detuning amount symmetrical about the center frequency of the alkali metal atoms and a phase difference of π into one beam, which is converted into modulated elliptically polarized light by a polarization device to pump and detect the alkali metal atoms, so that the virtual magnetic field generated by the optical frequency shift within the coherent period of the alkali metal atoms can be eliminated by multiple rapid reversals, and the modulation of the elliptically polarized light frequency is converted into the modulation of the optical rotation angle through the interaction between the alkali metal atoms and the light. Finally, the output signal containing the weak magnetic field information to be measured is extracted from the optical rotation angle signal by using polarization differential detection and difference frequency demodulation technology.

[0039] The magnetometer head system 2 includes an alkali metal atom gas chamber 204, the laser input side of the alkali metal atom gas chamber 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 chamber 204 is connected to a lateral displacement polarization beam splitter prism 208 through a half wave plate 207, and 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, and 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 alkali metal atoms respectively, and the absolute values ​​of the tuning are the same, both are 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 the polarization directions are both 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, and 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 Step 4, use a non-magnetic electric heating device to heat the alkali metal atom gas chamber to make the alkali metal atoms enter the SERF state, and use a function signal generator to generate a control signal to control the three-axis magnetic field coil to compensate the ambient magnetic field at the location of the gas chamber 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 the atomic magnetometer signal output.

[0041] Includes the following formulas:

[0042]

[0043] Where P z-ω is the first harmonic signal of the projection of the polarizability of the alkali metal atom 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 amount of the positive and negative detuned modulated elliptically polarized light frequency with the alkali metal D1 line resonance frequency, Δχ(t) is the Δχ value that changes with time, χ is the detuning amount of the positive detuned elliptically polarized light frequency, f2 is the frequency at which the modulated elliptically polarized light frequency switches between positive detuning and negative detuning, and N is a positive integer.

[0045] where θ ω Because P z-ωThe optical rotation angle signal caused by the oscillation is shown in Figure 2, 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] An ellipsoidal atomic magnetometer device and method for eliminating optical frequency shift, using a laser and an integrated device to generate frequency-symmetrically detuned elliptically polarized modulated light as the laser source of a single-beam atomic magnetometer, to achieve measurement of a weak magnetic field to be measured under a modulated magnetic field. The present invention combines two beams of pulsed modulated light whose detuning amount is symmetrical about the central frequency of alkali metal atoms and whose phase difference is π into one beam, and converts it into modulated elliptically polarized light through a polarization device to pump and detect alkali metal atoms, so that the virtual magnetic field generated by the optical frequency shift within the coherent period of the alkali metal atoms can be eliminated by multiple rapid reversals, and the modulation of the ellipsoidal light frequency is converted into modulation of the optical rotation angle through the interaction between the alkali metal atoms and the light, and finally the output signal containing the information of the weak magnetic field to be measured is extracted from the optical rotation angle signal using polarization differential detection and difference frequency demodulation technology. Compared with the conventional single-beam atomic magnetometer, the present invention can eliminate the optical frequency shift error of the ellipsoidal SERF magnetometer, while suppressing the low-frequency noise caused by the pumping light frequency fluctuation, and has the characteristics of high integration and miniaturization advantages.

[0048] refer to Figure 1 As shown, an ellipsoidal atomic magnetometer device for eliminating optical frequency shift comprises 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 a 2×1 optical fiber combiner 112. The 2×1 optical fiber combiner The laser output by the beam optic 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 splitter prism 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, and 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, and a collimator 201 is integrated at the fifth polarization-maintaining fiber 113 port at the output end of the 2×1 fiber combiner.

[0050] The FPGA signal generating 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 during processing.

[0052] The alkali metal atom gas chamber 204 is installed in a non-magnetic electric heating device 205, and the non-magnetic electric heating device 205 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 chamber 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 an 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] Where P z-ω is the first harmonic signal of the projection of the polarizability of the alkali metal atom 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 amount of the positive and negative detuned modulated elliptically polarized light frequency with the alkali metal D1 line resonance frequency, Δχ(t) is the Δχ value that changes with time, χ is the detuning amount of the positive detuned elliptically polarized light frequency, f2 is the frequency at which the modulated elliptically polarized light frequency switches between positive detuning 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 pump 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 chamber in the direction of the pump light, P 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 gas cell pressure broadening value, and f2 is the frequency at which the modulated elliptically polarized light frequency switches between positive detuning 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 positive 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, 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 value of the tuning is the same, both are 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 conduction voltage of the semiconductor optical amplifier, and the first semiconductor optical amplifier 103 and the second semiconductor optical amplifier 109 are respectively controlled to modulate the input optical signal. The optical fiber collimator 201 generates a Gaussian beam with a diameter of 3.5 mm as the pumping light input into the magnetometer head system 2. At this time, the collimator 201 outputs the optical frequency:

[0066]

[0067] Where Δχ is the detuning amount of the positive and negative detuned modulated elliptically polarized light frequency with the alkali metal D1 line resonance frequency, Δχ(t) is the Δχ value that changes with time, χ is the detuning amount of the positive detuned elliptically polarized light frequency, f2 is the frequency at which the modulated elliptically polarized light frequency switches between positive detuning 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 light 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) Using the non-magnetic electric heating device 205 to heat the alkali metal atom gas chamber 204 to make the atomic number density reach 10 14 Pieces / cm 3 The magnitude of the alkali metal atoms is made to 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 alkali metal atom polarizability projected along the z direction is expressed as:

[0070]

[0071] Where P Z-ω is the first harmonic signal of the projection of the polarizability of the alkali metal atom 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 ω Expressed as:

[0073]

[0074] where θ ω Because P z-ω The optical rotation angle signal caused by the pump 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 chamber in the direction of the pump light, P 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 gas cell pressure broadening value, and f2 is the frequency at which the modulated elliptically polarized light frequency switches between positive detuning and negative detuning.

[0075] (5) Demodulate at the frequency f2-f1 in the phase-locked 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 positive 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 ellipsoidal polarization 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 by semiconductor optical amplifiers respectively, and converted into two pulse modulated lights with detuning amounts symmetrical about the center frequency of alkali metal atoms and a phase difference of π. The positively detuned and negatively detuned lasers are combined into one laser beam through a 2×1 fiber combiner and then connected to the magnetometer head system. Thus, it is converted into an elliptically polarized light beam whose frequency is periodically modulated with time through an optical polarization device in the head, which can eliminate the optical frequency shift error of the ellipsoidal polarization SERF magnetometer, and also suppress the low-frequency noise caused by the frequency fluctuation of the pumping light.

[0079] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. It is pointed out here that the above description helps those skilled in the art to understand the invention, but does not limit the protection scope of the invention. Any equivalent replacement, modification and / or simplification of the above description without departing from the essence of the invention falls within the protection scope of the 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 optical 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 optical 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 optical 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 optical 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 optical fiber, and the first laser driver and the second laser driver are respectively connected to FPGA signal generation modules.

2. The ellipsometric atomic magnetometer device for eliminating optical frequency shift according to claim 1, characterized in that: The FPGA signal generating 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 optical 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 2*1 optical fiber combiner combines two beams of pulse modulated light with symmetric detuning amounts about the central frequency of alkali metal atoms and a phase difference of π into one beam, which is converted into modulated elliptically polarized light by a polarization device to pump and detect alkali metal atoms, so that multiple rapid reversals of the virtual magnetic field generated by the optical frequency shift within the coherent period of the alkali metal atoms are eliminated, and the modulation of the elliptically polarized light frequency is converted into the modulation of the optical rotation angle through the interaction between the alkali metal atoms and the light, and finally the output signal containing the weak magnetic field information to be measured is extracted from the optical rotation angle signal by using polarization differential detection and difference frequency demodulation technology.

4. 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 chamber, the laser input side of the alkali metal atom gas chamber is connected to the fifth polarization-maintaining optical fiber through a quarter wave plate, a linear polarizer and an optical fiber collimator in sequence, the laser output side of the alkali metal atom gas chamber is connected to a lateral displacement polarization beam splitter prism through 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 through 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 through 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 chamber 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.

5. The ellipsometric atomic magnetometer device for eliminating optical frequency shift according to claim 1, characterized in that: include: Where P z-ω is the first harmonic signal of the projection of the polarizability of the alkali metal atom 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.

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

7. 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 pump 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 chamber in the direction of the pump light, P 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 gas cell pressure broadening value, and f2 is the frequency at which the modulated elliptically polarized light frequency switches between positive detuning and negative detuning.

8. 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 positive 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, 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.

9. A method for realizing an ellipsometric atomic magnetometer for eliminating 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 8, and the following steps: Step 1, adjusting the lasers emitted by the positive detuned narrow linewidth semiconductor laser and the negative detuned narrow linewidth semiconductor laser to be positively and negatively tuned to the resonance frequency of the alkali metal atom D1 line respectively, and the absolute values ​​of the tuning are the same, both are χ, adjusting the output powers of the positive detuned narrow linewidth semiconductor laser and the negative detuned narrow linewidth semiconductor laser to be the same, and the polarization directions are both 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 to generate two square wave signals respectively, and the two signals have a phase difference of π, a signal frequency of f2, a duty cycle of 50%, and a same signal amplitude that is greater than the 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 ellipsometric degree 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, using a non-magnetic electric heating device to heat the alkali metal atom gas chamber to make the alkali metal atoms enter the SERF state, and using a function signal generator to generate a control signal to control the three-axis magnetic field coil to compensate the ambient magnetic field at the location of the gas chamber 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 the phase-locked amplifier to obtain the demodulated atomic precession signal and the optical rotation angle modulation signal as the atomic magnetometer signal output.

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