SERF magnetic field weak measurement detection method based on laser space mode

Abstract

The invention relates to an SERF magnetic field weak measurement detection method based on a laser space mode, which is used for directly measuring the space displacement of a detection laser beam and avoiding the detection signal drift caused by the power fluctuation of the detection laser. A Sagnac interference loop is established by using transmission light and reflected light formed by a first polarization splitting prism on a detection laser emergent side light path of the alkali metal gas chamber; 2, the transmission light and the reflection light which are interfered with each other return to the first polarization splitting prism to be combined, are emitted out of the Sagnac interference loop and sequentially pass through a second lambda / 2 wave plate and a second polarization splitting prism, and then the post-selection process is completed; step 3, utilizing a quadrant detector to identify and detect the displacement change of the detection light beam caused by the laser linear polarization rotation angle after the post selection process is completed; and 4, determining a linear polarization rotation angle by detecting the displacement change of the light beam, and determining an x-direction component of an electron spin polarization vector through the linear polarization rotation angle so as to realize SERF magnetic field weak measurement.

Description

Technical Field

[0001] The invention relates to the technical field of spin exchange relaxation-free atomic spin magnetic field measurement, and in particular to a SERF magnetic field weak measurement detection method based on laser spatial mode. Background Art

[0002] The spin-exchange relaxation-free (SERF) magnetic field measurement device has an ultra-high theoretical magnetic field measurement sensitivity. Its subsystems include pumping optical system, detection optical system, magnetic shielding and magnetic compensation system, and electronic control and acquisition systems. The detection optical system is based on the optical rotation effect of linearly polarized light. It detects the optical rotation angle of the detection laser that rotates after passing through the SERF state alkali metal gas chamber. The optical rotation angle is related to the magnetic field to be measured. This method is used to measure weak magnetic fields. Therefore, the detection laser light power fluctuation and the detection system noise have an important influence on the sensitivity of SERF atomic spin magnetic field measurement.

[0003] In SERF atomic spin magnetic field measurement, the magnetic field causes optical rotation of linearly polarized light passing through the alkali metal gas chamber. The size of the optical rotation angle is proportional to the output detection laser light power. Therefore, the detection laser error and noise caused by the optical power fluctuation will be directly introduced into the measured signal, thereby affecting the accuracy and sensitivity of the magnetic field measurement. Therefore, a new detection method that can avoid the detection laser fluctuation is needed to solve the influence of the detection laser light power fluctuation on the measured signal. Summary of the invention

[0004] In order to solve the influence of the fluctuation of the detection laser light power in the SERF atomic spin magnetic field measurement, the present invention proposes a SERF magnetic field weak measurement detection method based on the laser spatial mode. Based on the weak measurement theory, the spatial mode of the detection laser is used as the measurement pointer, and a SERF magnetic field weak measurement detection model based on the detection laser spatial mode is established. The lateral displacement of the detection laser caused by the magnetic field is directly measured, thereby realizing the measurement of the magnetic field sensitivity. The method suppresses the influence of the fluctuation of the detection laser light power in the SERF magnetic field measurement on the signal to be measured.

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

[0006] A SERF magnetic field weak measurement detection method based on laser spatial mode, characterized in that it comprises the following steps:

[0007] Step 1, using the transmitted light and reflected light formed by the first polarization beam splitter prism on the optical path of the detection laser output side of the alkali metal gas cell to establish a Sagnac interference loop;

[0008] Step 2, the transmitted light and the reflected light that interfere with each other in the Sagnac interference loop return to the first polarization beam splitter prism to be combined and then exit the Sagnac interference loop and sequentially pass through the second λ / 2 wave plate and the second polarization beam splitter prism to complete the post-selection process;

[0009] Step 3, using a quadrant detector to identify the change in the displacement of the detection beam caused by the detection laser linear polarization rotation angle after the selection process is completed;

[0010] Step 4, determine the linear polarization rotation angle by detecting the change in light beam displacement, determine the x-direction component of the electron spin polarization vector by the linear polarization rotation angle, and then realize the SERF weak magnetic field measurement.

[0011] The weak coupling effect is realized by a weak coupling module mainly based on a Sagnac interference loop, wherein the weak coupling module includes a second reflector connected to the transmission side of the first polarization beam splitter prism, and a first reflector respectively connected to the reflection side of the first polarization beam splitter prism and the second reflector, wherein the transmitted light formed by the first polarization beam splitter prism propagates in a clockwise direction in the Sagnac interference loop, and the reflected light formed by the first polarization beam splitter prism propagates in a counterclockwise direction in the Sagnac interference loop.

[0012] The first reflector is arranged on a dual-axis displacement platform. The dual-axis displacement platform adjusts the displacement g of the first reflector so that after the detection light beam is weakly coupled in space, the coupling intensity of the detection light beam in space is g.

[0013] The second λ / 2 wave plate and the second polarization beam splitter prism constitute a post-selection module, the right side of the post-selection module is connected to the quadrant detector, and the left side of the post-selection module is connected to the first polarization beam splitter prism via a third reflector.

[0014] The detection laser incident side of the alkali metal gas chamber is connected to a narrow line width laser through a λ / 4 wave plate, a photoelastic modulator, a first λ / 2 wave plate and a Glan-Taylor prism in sequence.

[0015] The alkali metal gas chamber is located in the three-axis magnetic compensation coil, and the three-axis magnetic compensation coil is located in the passive magnetic shielding layer.

[0016] The wavelength of the laser emitted by the narrow linewidth laser is far detuned from the resonance peak of the D2 line of the alkali metal atom.

[0017] The step 4 includes the following formula:

[0018]

[0019] Among them U output is the detection signal of the quadrant detector, K 1It represents the scale factor between the displacement and the final output voltage signal. It is the product of the detector's photoelectric conversion coefficient and the current amplification factor. θ is the linear polarization rotation angle, σ is the waist of the Gaussian beam, and g is the displacement of the detection beam in space.

[0020] The technical effects of the present invention are as follows: The present invention is a SERF magnetic field weak measurement detection method based on laser spatial mode, which avoids the detection signal drift caused by the detection laser power fluctuation by measuring the magnetic field of the spatial displacement of the detection laser beam.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) According to the general process of the weak measurement detection method, the present invention establishes a weak measurement magnetic field detection model based on detecting laser spatial modes, and realizes quantum precision measurement of the magnetic field.

[0023] (2) The present invention directly measures the spatial displacement of the detection laser beam, thereby avoiding the detection signal drift caused by the fluctuation of the detection laser power. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the structure of a device involved in implementing a SERF magnetic field weak measurement detection method based on detecting laser spatial modes of the present invention.

[0025] The reference numerals are as follows: 1- narrow linewidth laser; 2- Glan Taylor prism; 3- first λ / 2 wave plate; 4- photoelastic modulator (PEM, Photo-elastic Modulator); 5-λ / 4 wave plate; 6- first polarization beam splitter prism; 7- first reflector; 8- second reflector; 9- third reflector; 10- two-axis translation stage; 11- second λ / 2 wave plate; 12- second polarization beam splitter prism; 13- quadrant detector; 14- alkali metal gas chamber; 15- three-axis magnetic compensation coil; 16- passive magnetic shielding layer; 17- weak coupling module; 18- post-selection module. DETAILED DESCRIPTION

[0026] Below is the attached figure ( Figure 1 ) and Examples illustrate the present invention.

[0027] Figure 1 This is a schematic diagram of the structure of a device involved in implementing a SERF magnetic field weak measurement detection method based on laser spatial mode of the present invention. Figure 1As shown, a SERF magnetic field weak measurement detection method based on laser spatial mode includes the following steps: step 1, using the transmitted light and reflected light formed by the first polarization beam splitter prism on the optical path of the detection laser output side of the alkali metal gas chamber to establish a Sagnac interference loop; step 2, the transmitted light and reflected light that interfere with each other on the Sagnac interference loop return to the first polarization beam splitter prism to be combined and emit the Sagnac interference loop, and then pass through the second λ / 2 wave plate and the second polarization beam splitter prism in sequence to complete the post-selection process; step 3, using a quadrant detector to identify the detection laser linear polarization rotation angle caused by the detection laser after the selection process is completed; step 4, determining the linear polarization rotation angle by detecting the beam displacement change, and determining the x-direction component of the electron spin polarization vector by the linear polarization rotation angle, thereby realizing SERF magnetic field weak measurement.

[0028] The Sagnac interference loop is realized by a weak coupling module 17, and the weak coupling module 17 includes a second reflector 8 connected to the transmission side of the first polarization beam splitter prism 6, and a first reflector 7 connected to the reflection side of the first polarization beam splitter prism 6 and the second reflector 8, respectively. The transmitted light formed by the first polarization beam splitter prism 6 propagates in the clockwise direction in the Sagnac interference loop, and the reflected light formed by the first polarization beam splitter prism 6 propagates in the counterclockwise direction in the Sagnac interference loop. The first reflector 7 is arranged on a dual-axis translation stage 10, and the dual-axis translation stage 10 adjusts the displacement g of the first reflector so that the detection light beam generates weak coupling with a coupling intensity g in space.

[0029] The second λ / 2 wave plate 11 and the second polarization beam splitter prism 12 constitute a post-selection module 18, the right side of the post-selection module 18 is connected to the quadrant detector 13, and the left side of the post-selection module 18 is connected to the first polarization beam splitter prism 6 through the third reflector 9. The detection laser incident side of the alkali metal gas chamber 14 is connected to the narrow linewidth laser 1 through the λ / 4 wave plate 5, the photoelastic modulator 4, the first λ / 2 wave plate 3 and the Glan-Taylor prism 2 in sequence. The alkali metal gas chamber 14 is located in the three-axis magnetic compensation coil 15, and the three-axis magnetic compensation coil 15 is located in the passive magnetic shielding layer 16. The laser wavelength emitted by the narrow linewidth laser 1 is far detuned from the resonance peak of the alkali metal atom D2 line.

[0030] The step 4 includes the following formula:

[0031]

[0032] Among them, K 1 It represents the scale factor between the displacement and the final output voltage signal, which is the product of the detector photoelectric conversion coefficient and the current magnification factor. outputis the detection signal of the quadrant detector, and θ is the linear polarization rotation angle.

[0033] The present invention discloses a SERF magnetic field weak measurement detection method based on laser spatial mode, including a narrow line width laser 1, a Glan Taylor prism 2, a first λ / 2 wave plate 3, a photoelastic modulator 4, a λ / 4 wave plate 5, a first polarization beam splitter prism 6, a first reflector 7, a second reflector 8, a third reflector 9, a dual-axis translation stage 10, a second λ / 2 wave plate 11, a second polarization beam splitter prism 12, a quadrant detector 13, an alkali metal gas chamber 14, a three-axis magnetic compensation coil 15 and a passive magnetic shielding layer 16, as well as a weak coupling module 17 and a post-selection module 18. The present invention uses weak measurement detection theory to detect the optical rotation angle of linear polarized light in the SERF atomic spin precession magnetic field measurement system, and realizes ultra-high sensitive measurement of the magnetic field. In addition, the present invention uses the beam spatial mode as a measurement pointer, and directly measures the lateral displacement of the Gaussian beam in the measurement space caused by the optical rotation angle of linear polarized light, so as to avoid the influence of the detection laser power drift on the magnetic field measurement signal and improve the SERF magnetic field measurement sensitivity index.

[0034] The laser emitted by the semiconductor narrow linewidth laser is converted into linear polarized light with horizontal polarization direction by the Glan Taylor prism. After passing through the first λ / 2 wave plate, the horizontal linear polarized light is converted into linear polarized light with an angle of 45° with the horizontal direction. After passing through the combination of the photoelastic modulator and the λ / 4 wave plate, it is modulated and enters the alkali metal gas chamber to produce optical rotation. The detection laser emitted from the alkali metal gas chamber carries the information of the optical rotation angle, and the size of the optical rotation angle is proportional to the magnetic field to be measured. The detection laser emitted from the alkali metal gas chamber passes through the first polarization beam splitter prism, and the transmitted light enters the Sagnac interference loop and propagates in the clockwise direction, and the reflected light enters the Sagnac interference loop and propagates in the counterclockwise direction. The two laser beams pass through the first polarization beam splitter prism for the second time to be combined and emit the Sagnac interference loop. After passing through the second λ / 2 wave plate and the combination of the second polarization beam splitter prism, the post-selection process is completed.

[0035] The laser is a narrow line width laser, and the emitted laser wavelength is far detuned from the resonance peak of the D2 line of the alkali metal atom.

[0036] The alkali metal gas chamber contains one or two alkali metals of potassium, rubidium and cesium as an atomic system sensitive to magnetic fields, and the alkali metal atoms in the gas chamber are in a SERF state.

[0037] The quadrant detector can detect the spatial mode of the light beam and has the ability to measure the displacement of the light beam with high resolution.

[0038] The weak measurement detection process includes the preparation of the pre-selected state, the weak coupling process and the post-selection process, wherein the polarization rotation angle of the detection light caused by the SERF system acts on the pre-selected state preparation process, and the weak coupling process and the post-selection process are realized by optical devices in the weak coupling module and the post-selection module.

[0039] The measuring pointer of the weak measurement process is the spatial mode of the detection laser, and the direct measurement quantity is the displacement of the detection light beam at the dark port.

[0040] The weak coupling module is implemented through a Sagnac interference loop. The transmitted light and reflected light of the detection laser passing through the first polarization beam splitter prism interfere in the loop, and form a dark port and a bright port at the transmission and reflection exits of the second polarization beam splitter prism respectively.

[0041] In the weak coupling module, the displacement of the first reflector 7 is adjusted to introduce a weak coupling displacement g of the detection light beam in the spatial mode.

[0042] The laser emitted by the semiconductor narrow linewidth laser is polarized after passing through the Glan Taylor prism. The Glan Taylor prism angle is adjusted to produce linear polarized light with a horizontal polarization direction. The polarization plane direction is adjusted through the first λ / 2 wave plate so that the initial laser polarization plane direction is at an angle of 45° to the horizontal direction. Using horizontal linear polarized light |H> and vertical linear polarized light |V> as the basis, the quantum state of the initial laser |ψ i0 >For:

[0043]

[0044] After that, it is modulated by the combination of the photoelastic modulator and the λ / 4 wave plate. The modulation amplitude and frequency can be controlled by the controller of the photoelastic modulator. When the linearly polarized light passes through the alkali metal gas cell in the SERF state, optical rotation occurs, and the generated optical rotation angle is θ, which contains the information of the magnetic field to be measured. In the SERF atomic spin magnetic field measurement, the relationship between the optical rotation angle θ and the magnetic field to be measured can be expressed as:

[0045]

[0046] Among them, n alkali is the density of the alkali metal, c is the speed of light, r e is the classical radius of the electron, l represents the optical path, which is equal to the length of the gas chamber in the formula, and v D1 is the alkali metal gas cell D1 line resonance frequency, f D1 is the resonance intensity on line D1, ν D2 is the alkali metal gas cell D2 line resonance frequency, f D2 is the resonance intensity on the D2 line. is the component of the electron spin polarization vector in the x direction, which is proportional to the magnetic field to be measured. Therefore, the relationship between the optical rotation angle and the magnetic field is established. The measurement of the magnetic field can be converted into the measurement of the optical rotation angle of linear polarized light after passing through the SERF state alkali metal atom. D(vv D1 ) and D(vv D2 ) represent the absorption of alkali metal gas under D1 line and D2 line respectively, where:

[0047]

[0048] Γ L To detect the pressure broadening of the laser.

[0049] After passing through the alkali metal gas chamber in the SERF state, the polarization plane of the detection laser rotates. The quantum state of the detection laser that undergoes optical rotation is called the pre-selection state, which is expressed as:

[0050] |ψ i >=cos(π / 4-θ)|H>+sin(π / 4-θ)|V>

[0051] After the pre-selected laser passes through the first polarization beam splitter prism in the coupling module, it generates transmitted light and reflected light. The transmitted light is in the clockwise direction, and the reflected light is in the counterclockwise direction. Finally, after passing through the first polarization beam splitter prism, they converge and interfere, and the displacement of the first reflector is adjusted to g, so that the detection light after the pre-selection generates weak coupling with a coupling intensity of g in space in the coupling module. After passing through the post-selection module, the detection laser spatial mode of the dark port can be observed, and the post-selection state is:

[0052]

[0053] When θ is very small and slightly larger than the coupling parameter g, the detection beam of the dark port has a double-peak configuration. When the magnetic field causes the linear polarization rotation angle θ to change, the detection beam has a double-peak change in space. At this time, the displacement of the detection beam can be expressed as:

[0054]

[0055] Where σ is the waist of the Gaussian beam. The quadrant detector can be used to identify the displacement change caused by the linear polarization rotation angle θ, thereby realizing magnetic field measurement. Based on this method, the first frequency of the quadrant detector is collected and the power spectrum density analysis is performed to detect the change in magnetic field sensitivity. This method does not rely on the change in the detection laser light power, so it can avoid the influence of the detection laser fluctuation on the detection signal.

[0056] Preferably, the laser is a narrow linewidth laser, and the emitted laser wavelength is far detuned from the resonance peak of the D2 line of the alkali metal atom.

[0057] Preferably, the alkali metal gas chamber contains one or two alkali metals of potassium, rubidium and cesium as an atomic system sensitive to the magnetic field, and the alkali metal atoms in the gas chamber are in a SERF state.

[0058] Preferably, the quadrant detector can detect the spatial mode of the light beam and has the ability to measure the light beam displacement with high resolution.

[0059] Preferably, the weak measurement detection process includes the preparation of a pre-selected state, a weak coupling process and a post-selection of a joint state, wherein the polarization rotation angle of the detection light induced by the SERF system acts on the pre-selected state preparation process.

[0060] Preferably, the measurement pointer of the weak measurement process is the spatial mode of the detection laser, and the direct measurement quantity is the displacement of the detection light beam at the dark port.

[0061] Preferably, the Sagnac interference loop has a high interference ratio, and the transmitted light and reflected light passing through the first polarization beam splitter prism interfere in the loop, and form a dark port and a bright port at the transmission and reflection exits of the second polarization beam splitter prism, respectively.

[0062] The implementation steps of the present invention are as follows:

[0063] First, the alkali metal atoms in the alkali metal gas chamber are ensured to be in the SERF state, which can be sensitive to changes in the external magnetic field. A narrow linewidth laser whose laser frequency is far detuned from the resonance peak of the D2 line of the alkali metal atoms is used as the detection light source. After completing the three-axis magnetic compensation process, the detection laser of the alkali metal gas chamber is connected to the weak measurement module for coupling, and the coupling strength is g. Finally, the post-selected successful detection laser spatial mode is observed, and the displacement of the detection laser is detected using a quadrant detector. The quadrant detector signal is collected and the demodulated first-order harmonic signal is recorded for power spectrum density analysis.

[0064] 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. A SERF magnetic field weak measurement detection method based on laser spatial mode, characterized in that: The following steps are involved: Step 1, using the transmitted light and reflected light formed by the first polarization beam splitter prism on the optical path of the detection laser output side of the alkali metal gas cell to establish a Sagnac interference loop; Step 2, the transmitted light and the reflected light that interfere with each other in the Sagnac interference loop return to the first polarization beam splitter prism to be combined and emitted from the Sagnac interference loop, and then sequentially pass through the second λ / 2 wave plate and the second polarization beam splitter prism to complete the post-selection process; Step 3, using a quadrant detector to identify the change in the displacement of the detection beam caused by the detection laser linear polarization rotation angle after the selection process is completed; Step 4, determine the linear polarization rotation angle by detecting the change in light beam displacement, determine the x-direction component of the electron spin polarization vector by the linear polarization rotation angle, and then realize the SERF weak magnetic field measurement.

2. The SERF magnetic field weakness measurement detection method based on laser spatial mode according to claim 1 is characterized in that: The Sagnac interference loop is realized by a weak coupling module, which includes a second reflector connected to the transmission side of the first polarization beam splitter prism, and a first reflector respectively connected to the reflection side of the first polarization beam splitter prism and the second reflector. The transmitted light formed by the first polarization beam splitter prism propagates in a clockwise direction in the Sagnac interference loop, and the reflected light formed by the first polarization beam splitter prism propagates in a counterclockwise direction in the Sagnac interference loop.

3. The SERF magnetic field weakness measurement detection method based on laser spatial mode according to claim 1 is characterized in that: The first reflector is arranged on a dual-axis displacement stage, and the dual-axis displacement stage adjusts the position of the first reflector so as to cause the detection light beam to generate a small displacement g in space, that is, a weak coupling effect with a coupling intensity of g.

4. The SERF magnetic field weakness measurement detection method based on laser spatial mode according to claim 1 is characterized in that: The second λ / 2 wave plate and the second polarization beam splitter prism constitute a post-selection module, the right side of the post-selection module is connected to the quadrant detector, and the left side of the post-selection module is connected to the first polarization beam splitter prism via a third reflector.

5. The SERF magnetic field weak measurement detection method based on laser spatial mode according to claim 1 is characterized in that: The detection laser incident side of the alkali metal gas chamber is connected to a narrow line width laser through a λ / 4 wave plate, a photoelastic modulator, a first λ / 2 wave plate and a Glan-Taylor prism in sequence.

6. The SERF magnetic field weakness measurement detection method based on laser spatial mode according to claim 1 is characterized in that: The alkali metal gas chamber is located in the three-axis magnetic compensation coil, and the three-axis magnetic compensation coil is located in the passive magnetic shielding layer.

7. The SERF magnetic field weak measurement detection method based on laser spatial mode according to claim 1 is characterized in that: The wavelength of the laser emitted by the narrow linewidth laser is far detuned from the resonance peak of the D2 line of the alkali metal atom.

8. The SERF magnetic field weakness measurement detection method based on laser spatial mode according to claim 1 is characterized in that: The step 4 includes the following formula: Among them U output is the detection signal of the quadrant detector, K1 represents the scale factor between the displacement and the final output voltage signal, which is the product of the detector photoelectric conversion coefficient and the current amplification factor, θ is the linear polarization rotation angle, σ is the waist of the Gaussian beam, and g is the displacement of the detection beam in space.

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