Ellipsometry atomic magnetometer device and method based on rotating fiber polarization

Abstract

An ellipsoidal light atomic magnetometer device and method based on rotating fiber polarization utilizes a rotating fiber polarizer to emit elliptically polarized light of a set ellipticity, and directs this light beam into the atomic magnetometer head to cause it to interact with alkali metal atoms to achieve magnetic field measurement. The device and method designed in the present invention calculates the torsion length and torsion angle of the rotating fiber polarizer based on the set ellipticity, thereby causing the rotating fiber polarizer to emit elliptically polarized light of the set ellipticity. This elliptically polarized light is directed into the atomic magnetometer head, thereby polarizing the alkali metal atoms and generating an optical rotation angle for signal detection. A high-frequency modulated magnetic field is applied in a direction perpendicular to the light beam, and polarization differential detection technology and phase-locked amplification technology are used to obtain the magnetic field information to be measured. Compared with conventional atomic magnetometer configurations, the present invention uses a rotating fiber polarizer and an ellipsoidal light configuration to construct an atomic magnetometer, resulting in a more compact structure and enhanced temperature stability of the atomic magnetometer head.

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 based on rotating optical fiber polarization. Background Art

[0002] Atomic magnetometers, a type of quantum precision measurement instrument, utilize the interaction between light and atoms to measure magnetic fields. They have been widely used in biomagnetic measurements, geomagnetic exploration, and fundamental physics research. Among various types of atomic magnetometers, SERF (Spin-Exchange-Relaxation-Free) atomic magnetometers operate in a spin-exchange-free state and possess the highest measurement sensitivity. Ellipsometry SERF atomic magnetometers utilize a single elliptically polarized pump laser beam to simultaneously pump and detect atomic spins. They offer a compact design and high measurement sensitivity, and hold great potential for application in biomagnetic applications such as magnetocardiography and magnetoencephalography. The light source of a conventional ellipsometric SERF atomic magnetometer is typically generated by an external laser and transmitted to the atomic magnetometer head through a polarization-maintaining fiber, or by a built-in VCSEL (Vertical-Cavity Surface-Emitting Laser) within the head. The linearly polarized laser emitted by the light source must pass through optical devices such as a polarizer and a quarter-wave plate within the head to generate elliptically polarized light with a specific ellipticity for use as the pump laser. These optical devices not only increase the size of the head but are also susceptible to high-temperature heating in the atomic gas chamber, resulting in performance degradation. Summary of the Invention

[0003] The present invention provides an ellipsometric atomic magnetometer device and method based on rotating fiber polarization. A rotating fiber polarizer is constructed by melting and twisting a polarization-maintaining optical fiber, then connecting it to a conventional polarization-maintaining optical fiber. The polarization state and ellipticity of the output polarized light are modified by adjusting the twist length and twist angle. The twist length and twist angle are adjusted to specific values, and a light source is coupled to the rotating fiber polarizer, causing it to emit elliptically polarized light with a specific ellipticity. This elliptically polarized light is then introduced into the atomic magnetometer head as a pump laser, eliminating the need for optical devices to convert the polarization state. This reduces the size of the atomic magnetometer head and eliminates the performance degradation of the optical devices caused by high-temperature heating of the atomic gas chamber.

[0004] The technical solutions of the present invention are as follows:

[0005] An ellipsoidal atomic magnetometer device based on rotating fiber polarization is characterized in that it includes a three-axis magnetic field coil and a polarization differential module located in the atomic magnetometer head housing, the laser input end of the polarization differential module is connected to the laser output end of the atomic gas chamber in the three-axis magnetic field coil, the output end of the polarization differential module is connected to a phase-locked amplifier, and the phase-locked amplifier forms the atomic magnetometer output signal, the laser incident end of the atomic gas chamber is connected to a narrow linewidth semiconductor laser through a non-magnetic fiber collimator and a rotating fiber polarizer in sequence, and the three-axis magnetic field coil is connected to a function generator.

[0006] The rotating optical fiber polarizer includes two sections of optical fiber, a front half section and a rear half section in a twisted state, which are connected by fusion and then fixed with a clamp. The front half section and the rear half section are polarization-maintaining optical fibers made of the same material and structure. The length of the front half section is arbitrary and is not twisted. The initial fast and slow axis directions of the rear half section coincide with those of the front half section and are twisted. The twist length is related to the beat length of the polarization-maintaining optical fiber, and the twist angle is related to the ellipticity α of the elliptically polarized light.

[0007] The twisted length of the second half of the optical fiber is (1 / 2)l, where l is the beat length of the polarization-maintaining optical fiber, and the twisted angle is (π / 2)·tanα, where α is the ellipticity of the elliptically polarized light.

[0008] The polarization differential module includes a lateral displacement polarization beam splitter prism, the input end of the lateral displacement polarization beam splitter prism is connected to the laser output end of the atomic gas cell through a half-wave plate, and the output end of the lateral displacement polarization beam splitter prism is connected to the lock-in amplifier through a photodetector and a differential amplifier circuit in sequence.

[0009] The narrow linewidth semiconductor laser, function generator and phase-locked amplifier constitute a photoelectric measurement and control system.

[0010] A non-magnetic electric heating device is provided between the atomic gas chamber and the three-axis magnetic field coil. The non-magnetic electric heating device heats the atomic gas chamber so that the number density of alkali metal vapor atoms in the atomic gas chamber reaches 10 13 ~10 14 pieces / cm 3 .

[0011]

[0012] Where θ is the optical rotation angle formed by elliptically polarized light after passing through the atomic gas cell, n is the atomic number density, c is the speed of light, r is the classical electron radius, P z is the longitudinal polarizability of the alkali metal atom, f is the alkali metal D1 line resonance intensity, l is the atomic gas cell length, v0 is the alkali metal D1 line resonance frequency, v is the laser frequency, and Г is the atomic gas cell pressure broadening.

[0013] V=Ke -OD θcos(2α)

[0014] Where V is the differential amplified signal output by the differential amplifier circuit, K is the conversion coefficient of the photodetector, OD is the optical depth, θ is the optical rotation angle, α is the ellipticity of the elliptically polarized light, and e is a natural constant.

[0015]

[0016] Where V B is the output signal of the atomic magnetometer, G is the measurement amplification factor, e is a natural constant, OD is the optical depth, c is the speed of light, r is the classical electron radius, c is the speed of light, r is the classical electron radius, f is the alkali metal D1 line resonance intensity, n is the atomic number density, l is the atomic gas cell length, v is the laser frequency, v0 is the alkali metal D1 line resonance frequency, Г is the atomic gas cell pressure broadening, R op is the pumping rate, R rel is the transverse relaxation rate, α is the ellipticity of elliptically polarized light, and B0 is the magnetic field to be measured.

[0017] A method for realizing an ellipsometric atomic magnetometer based on rotating fiber polarization is characterized by comprising adopting the above-mentioned ellipsometric atomic magnetometer device based on rotating fiber polarization and the following steps:

[0018] Step 1, adjusting the frequency of the light source generated by the narrow linewidth semiconductor laser to be detuned from the alkali metal D1 line resonance frequency, and the polarization state is linearly polarized light;

[0019] Step 2: Make a rotating fiber polarizer, where the length of the first half is arbitrary, the twisted length of the second half is (1 / 2)l, where l is the beat length of the polarization-maintaining fiber, and the twist angle is π / 2·tanα;

[0020] Step 3, coupling the laser generated in step 1 to the rotating fiber polarizer obtained in step 2, and then passing it through a non-magnetic fiber collimator to generate collimated elliptically polarized light with an ellipticity of α, using the elliptically polarized light as a pump laser to irradiate the atomic gas chamber, thereby achieving pumping of alkali metal atoms while generating an optical rotation angle for signal detection;

[0021] Step 4: Use the function generator to control the three-axis magnetic field coil to compensate the magnetic field felt around the atomic gas chamber to zero, and at the same time apply a high-frequency modulated magnetic field in the direction of the magnetic field to be measured, and adjust the amplitude and frequency of the modulated magnetic field to the set value B. m 、w m ;

[0022] Step 5: Use polarization differential detection technology to detect the elliptically polarized light passing through the atomic gas chamber, and connect the differential amplified signal obtained after differential amplification to a phase-locked amplifier using a frequency of w. mThe demodulated signal is demodulated on the differential amplified signal using the phase-locked amplification technology to obtain the output signal of the atomic magnetometer.

[0023] The technical effects of the present invention are as follows: The present invention proposes an ellipsoidal light atomic magnetometer device and method based on rotating fiber polarization, which uses a rotating fiber polarizer to emit elliptically polarized light of set ellipticity, and introduces the light beam into the atomic magnetometer so that it interacts with alkali metal atoms to achieve magnetic field measurement. The device and method designed by the present invention calculates the torsion length and torsion angle of the rotating fiber polarizer according to the set ellipticity, so that the rotating fiber polarizer emits elliptically polarized light of the ellipticity, introduces the elliptically polarized light into the atomic magnetometer to polarize the alkali metal atoms, applies a high-frequency modulated magnetic field in a direction perpendicular to the light beam, and uses polarization differential detection technology and phase-locked amplification technology to obtain the magnetic field information to be measured. Compared with the conventional atomic magnetometer configuration, the present invention uses a rotating fiber polarizer and an ellipsoidal light configuration to build an atomic magnetometer, which has a more compact and small structure while enhancing the temperature stability of the atomic magnetometer head.

[0024] The advantages of the present invention compared with the prior art are:

[0025] (1) The light source of a conventional atomic magnetometer is usually introduced by a polarization-maintaining fiber or generated by a built-in VCSEL. The light source needs to pass through an optical device to convert it into circularly polarized light or elliptically polarized light. The present invention uses a rotating fiber polarizer to emit elliptically polarized light of a specific ellipticity and introduces it into the atomic magnetometer head, thereby avoiding the use of optical devices for polarization state conversion and utilizing the space outside the head, thereby simplifying the internal structure of the atomic magnetometer and reducing the volume of the atomic magnetometer head.

[0026] (2) When a conventional atomic magnetometer is operating, the non-magnetic electric heating device is in a high-temperature state. The optical device used by the atomic magnetometer to complete the polarization state conversion of the light source is relatively sensitive to temperature but is relatively close to the non-magnetic electric heating device. During use, the high temperature of the non-magnetic electric heating device may cause the performance of the optical device to degrade. The present invention uses a rotating fiber polarizer to convert the polarization state of the light source. The rotating fiber polarizer is far away from the non-magnetic electric heating device, which reduces the sensitivity of the pump laser to temperature.

[0027] (3) The present invention uses an ellipsoidal polarization structure to build an atomic magnetometer, which has the advantages of compact structure and high sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The present invention is a schematic structural diagram of an ellipsometric atomic magnetometer device based on rotating optical fiber polarization.

[0029] Figure 2 yes Figure 1 Schematic diagram of the structure of the rotating fiber polarizer. Figure 2where l is the beat length of the polarization-maintaining fiber and α is the ellipticity of the elliptically polarized light.

[0030] The accompanying drawings are marked as follows: 1-narrow linewidth semiconductor laser; 2-function generator; 3-rotating fiber polarizer; 4-non-magnetic fiber collimator; 5-atomic gas chamber; 6-half wave plate; 7-lateral displacement polarization spectrometer; 8-photodetector; 9-differential amplifier circuit; 10-non-magnetic electric heating device; 11-differential amplification signal; 12-three-axis magnetic field coil; 13-atomic magnetometer head housing; 14-phase-locked amplifier; 15-atomic magnetometer output signal; 16-polarization differential module; 17-photoelectric measurement and control system. DETAILED DESCRIPTION

[0031] Below is the attached figure ( Figure 1-Figure 2 ) and Examples illustrate the present invention.

[0032] Figure 1 The present invention is a schematic structural diagram of an ellipsometric atomic magnetometer device based on rotating optical fiber polarization. Figure 2 yes Figure 1 Schematic diagram of the structure of the rotating fiber polarizer. Figures 1 to 2 As shown, an ellipsoidal polarization atomic magnetometer device based on rotating fiber polarization includes a three-axis magnetic field coil 12 and a polarization differential module 16 located in an atomic magnetometer head housing 13. The laser input end of the polarization differential module 16 is connected to the laser output end of the atomic gas chamber 5 in the three-axis magnetic field coil 12, and the output end of the polarization differential module 16 is connected to a phase-locked amplifier 14. The phase-locked amplifier 14 forms an atomic magnetometer output signal 15. The laser incident end of the atomic gas chamber 5 is connected to a narrow linewidth semiconductor laser 1 through a non-magnetic fiber collimator 4 and a rotating fiber polarizer 3 in sequence. The three-axis magnetic field coil 12 is connected to a function generator 2.

[0033] The rotating optical fiber polarizer 3 includes two sections of optical fiber, a front half section of optical fiber and a rear half section of optical fiber in a twisted state, which are fixed with a clamp after being fused together. The front half section of optical fiber and the rear half section of optical fiber are made of the same material and structure as polarization-maintaining optical fiber. The front half section of optical fiber and the rear half section of optical fiber are made of the same material and structure as polarization-maintaining optical fiber. The length of the first half section of optical fiber is arbitrary and is not twisted. The initial fast and slow axis directions of the rear half section coincide with those of the first half section and are twisted. The twist length is related to the beat length of the polarization-maintaining optical fiber, and the twist angle is related to the ellipticity α of the elliptically polarized light. The twist length of the rear half section of optical fiber is (1 / 2)l, where l is the beat length of the polarization-maintaining optical fiber, and the twist angle is (π / 2)·tanα, where α is the ellipticity of the elliptically polarized light.

[0034] The polarization differential module 16 includes a lateral displacement polarization beam splitter prism 7. The input end of the lateral displacement polarization beam splitter prism 7 is connected to the laser output end of the atomic gas cell 5 through a half-wave plate 6. The output end of the lateral displacement polarization beam splitter prism 7 is connected to the phase-locked amplifier 14 through a photodetector 8 and a differential amplifier circuit 9. The narrow linewidth semiconductor laser 1, the function generator 2 and the phase-locked amplifier 14 constitute a photoelectric measurement and control system 17. A non-magnetic electric heating device 10 is provided between the atomic gas cell 5 and the three-axis magnetic field coil 12. The non-magnetic electric heating device 10 heats the atomic gas cell 5 so that the number density of alkali metal vapor atoms in the atomic gas cell 5 reaches 10 13 ~10 14 pieces / cm 3 .

[0035]

[0036] Where θ is the optical rotation angle of elliptically polarized light in the atomic gas cell, n is the atomic number density, c is the speed of light, r is the classical electron radius, P z is the longitudinal polarizability of the alkali metal atom, f is the alkali metal D1 line resonance intensity, l is the atomic gas cell length, v0 is the alkali metal D1 line resonance frequency, v is the laser frequency, and Г is the atomic gas cell pressure broadening.

[0037] V=Ke -OD θcos(2α)

[0038] Where V is the differential amplified signal output by the differential amplifier circuit, K is the conversion coefficient of the photodetector, OD is the optical depth, θ is the optical rotation angle, α is the ellipticity of the elliptically polarized light, and e is a natural constant.

[0039]

[0040] Where V B is the output signal of the atomic magnetometer, G is the measurement amplification factor, e is a natural constant, OD is the optical depth, c is the speed of light, r is the classical electron radius, c is the speed of light, r is the classical electron radius, f is the alkali metal D1 line resonance intensity, n is the atomic number density, l is the atomic gas cell length, v is the laser frequency, v0 is the alkali metal D1 line resonance frequency, Г is the atomic gas cell pressure broadening, R op is the pumping rate, R rel is the transverse relaxation rate, α is the ellipticity of elliptically polarized light, and B0 is the magnetic field to be measured.

[0041] A method for realizing an ellipsometric atomic magnetometer based on rotating fiber polarization comprises the following steps: step 1, adjusting the frequency of a light source generated by a narrow-linewidth semiconductor laser to be detuned from the linear resonance frequency of the alkali metal D1 line, so that the polarization state is linearly polarized light; step 2, manufacturing a rotating fiber polarizer, wherein the length of the first half is arbitrary and the twist length of the second half is (1 / 2)l, where l is the beat length of the polarization-maintaining fiber and the twist angle is π / 2·tanα; step 3, coupling the laser generated in step 1 to the rotating fiber polarizer obtained in step 2, and then generating collimated elliptically polarized light with an ellipticity of α through a non-magnetic fiber collimator, using the elliptically polarized light as a pumping laser to irradiate an atomic gas chamber, thereby achieving pumping of the alkali metal atoms and generating an optical rotation angle for signal detection; and step 4, using a function generator to control a three-axis magnetic field coil to compensate the magnetic field felt around the atomic gas chamber to zero, and simultaneously applying a high-frequency modulated magnetic field in the direction of the magnetic field to be measured, and adjusting the amplitude and frequency of the modulated magnetic field to a set value B. m 、w m Step 5, using polarization differential detection technology to detect the elliptically polarized light passing through the atomic gas chamber, the differential amplified signal obtained after differential amplification is connected to the phase-locked amplifier, using a frequency of w m The demodulated signal is demodulated using the phase-locked amplification technology to demodulate the differential amplified signal to obtain the output signal of the atomic magnetometer

[0042] The present invention provides an ellipsometric atomic magnetometer device and method based on rotating fiber polarization. The device constructs a rotating fiber polarizer that fuses a conventional polarization-maintaining fiber with a twisted polarization-maintaining fiber. The rotating fiber polarizer directly emits elliptically polarized light with a specific ellipticity, reducing the volume of the meter head and the temperature sensitivity of the pump laser. The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are merely illustrative and are not intended to limit the scope of the invention. After reading this disclosure, modifications of various equivalent forms of the invention by those skilled in the art fall within the scope of the appended claims.

[0043] See Figure 1 The present invention provides an ellipsometric atomic magnetometer device and method based on rotating optical fiber polarization. Figure 1 As shown, an ellipsometric atomic magnetometer device and method based on rotating fiber polarization includes: a narrow linewidth semiconductor laser 1, a function generator 2, a rotating fiber polarizer 3, a non-magnetic fiber collimator 4, an atomic gas chamber 5, a half-wave plate 6, a lateral displacement polarization beam splitter prism 7, a photodetector 8, a differential amplifier circuit 9, a non-magnetic electric heating device 10, a differential amplification signal 11, a three-axis magnetic field coil 12, an atomic magnetometer head housing 13, a lock-in amplifier 14, an atomic magnetometer output signal 15, a polarization differential module 16, and a photoelectric measurement and control system 17;

[0044] See Figure 2 The present invention provides a rotating optical fiber polarizer structure. Figure 2 As shown, a rotating fiber polarizer structure includes: a rotating fiber polarizer 3 is composed of two sections of polarization-maintaining optical fibers of the same material and structure that are fused and connected, wherein the length of the first half of the optical fiber is arbitrary and is not twisted, and the length of the second half of the optical fiber is (1 / 2)l, and one end of the clamp is clamped at the fusion point, and the other end is clamped at the tail end of the second half of the optical fiber, and the two ends of the clamp are twisted relative to each other by an angle of tanα·π / 2.

[0045] like Figure 1 and Figure 2 As shown, the specific implementation steps of the present invention are as follows:

[0046] (1) First, complete the preparation of the rotating fiber polarizer. Take two sections of polarization-maintaining optical fiber with the same material and structure. The length of the first section is arbitrary, and the length of the second section is 1 / 2. After melting the two ends of the optical fiber, connect them and clamp them at the fusion point. Twist the second half of the optical fiber clockwise by an angle of tanα·π / 2 and fix it with the clamp. Encapsulate the rotating fiber polarizer 3 and the non-magnetic fiber collimator 4 in a port with a diameter of 5 mm. The port outputs elliptically polarized light with an ellipticity of α.

[0047] (2) The second end of the rotating fiber polarizer 3, the non-magnetic fiber collimator 4, the atomic gas chamber 5, the non-magnetic electric heating device 10, the three-axis magnetic field coil 12, and the polarization differential module 16 are placed in the atomic magnetometer head housing 13 to form the atomic magnetometer head. The half-wave plate 6 is used to adjust the splitting ratio of the two vertical components of the lateral displacement polarization splitter prism 7 to 50% and 50% before pumping occurs. The horizontal direction of the lateral displacement polarization splitter prism 7 is adjusted to align with the fast axis direction of the rotating fiber polarizer 3. The atomic magnetometer head is placed in a weak magnetic environment. The non-magnetic electric heating device 10 is used to heat the atomic gas chamber 5 so that the atomic number density of the alkali metal vapor reaches 10 13 ~10 14 pieces / cm 3 ;

[0048] (3) The frequency of the linearly polarized light emitted by the narrow-linewidth semiconductor laser 1 is adjusted to be detuned to the linear resonance frequency of the alkali metal D1 at 50 GHz, and the vibration direction of the linearly polarized light is adjusted to coincide with the fast axis direction of the rotating fiber polarizer 3. The light source is coupled to the rotating fiber polarizer 3 in step (1). The elliptically polarized light emitted by the non-magnetic fiber collimator 4 is then introduced into the atomic gas chamber 5 as a pump laser to polarize the alkali metal atoms. At this time, the linearly polarized component in the elliptically polarized light will undergo a rotation in polarization direction. The angle of rotation is called the optical rotation angle θ, which is expressed as:

[0049]

[0050] Where n is the atomic number density, c is the speed of light, r is the classical electron radius, P z is the longitudinal polarizability of the alkali metal atom, f is the alkali metal D1 line resonance intensity, l is the atomic gas cell length, v0 is the alkali metal D1 line resonance frequency, v is the frequency of the laser, and Г is the atomic gas cell pressure broadening;

[0051] (4) Use the function generator 2 to control the three-axis magnetic field coil 12 to compensate the surrounding magnetic field felt by the atomic gas chamber 5 to zero, and apply a high-frequency modulated magnetic field in the direction of the magnetic field to be measured, and adjust the amplitude and frequency of the modulated magnetic field to the set value B m =150nT,w m =1kHz;

[0052] (5) After step (4), the P mentioned in step (3) z Oscillation will occur, generating an infinite order resonance signal. At this time, the magnetic field signal to be measured has been modulated by the high-frequency magnetic field, isolating the low-frequency noise. In step (3), the laser light passing through the atomic gas chamber 5 passes through the half-wave plate 6 and the lateral displacement polarization beam splitter prism 7, and is incident on the photodetector 8. After passing through the differential amplifier circuit 9, a differential amplification signal 11 is obtained, which is expressed as:

[0053] V=Ke -OD θcos(2α)

[0054] Where K is the conversion coefficient of the photodetector, and OD is the optical depth;

[0055] (6) After step (5), the common mode noise in the photodetector 8 is suppressed, and only the useful differential mode information is retained. The differential amplified signal 11 is connected to the phase-locked amplifier 14, and the frequency is w m The demodulated signal of the differential amplified signal 11 is demodulated to obtain the atomic magnetometer output signal 15, which is expressed as:

[0056]

[0057] Where R op is the pumping rate, R rel is the transverse relaxation rate, G is the measurement amplification factor, and B0 is the magnetic field to be measured.

[0058] In summary, the present invention provides an ellipsometric atomic magnetometer device and method based on rotating fiber polarization. This device constructs a rotating fiber polarizer by melting and twisting a polarization-maintaining fiber, then connecting it to a conventional polarization-maintaining fiber. This device converts the polarization state of a light source into elliptically polarized light with a specific polarization degree. This elliptically polarized light is then used as a pump laser to illuminate alkali metal atoms. Polarization differential detection and phase-locked amplification techniques are then employed to measure the magnetic field. This device avoids the use of optical devices for polarization state conversion, reducing the size of the atomic magnetometer head. Furthermore, the rotating fiber polarizer is located relatively far from the non-magnetic electric heating device, thus avoiding pump laser fluctuations caused by the temperature sensitivity of the optical device.

[0059] An ellipsometric atomic magnetometer device and method based on rotating optical fiber polarization are characterized by comprising: a narrow linewidth semiconductor laser (1), a function generator (2), a rotating optical fiber polarizer (3), a non-magnetic optical fiber collimator (4), an atomic gas chamber (5), a half-wave plate (6), a lateral displacement polarization beam splitter (7), a photodetector (8), a differential amplifier circuit (9), a non-magnetic electric heating device (10), a differential amplifier signal (11), a three-axis magnetic field coil (12), an atomic magnetometer head housing (13), a phase-locked amplifier (14), an atomic magnetometer output signal (15), a polarization differential module (16), and a photoelectric measurement and control system (17). The linearly polarized light generated by the narrow linewidth semiconductor laser (1) is coupled to a rotating fiber polarizer (3), so that the laser passes through the rotating fiber polarizer (3) and a non-magnetic fiber collimator (4) to generate collimated elliptically polarized light as a pumping laser, and then the pumping laser is used to irradiate an atomic gas chamber (5) to polarize alkali metal atoms; a function generator (2) is used to control a three-axis magnetic field coil (12) to compensate the magnetic field felt around the atomic gas chamber (5) to zero, and a high-frequency modulated magnetic field is applied in the direction of the magnetic field to be measured; then, the differential amplification signal (11) is obtained by passing through a polarization differential module (16) and then a differential amplifier circuit (9); finally, the differential amplification signal (11) is connected to a phase-locked amplifier (14) and demodulated using a phase-locked amplification technology to obtain an atomic magnetometer output signal (15).

[0060] The invention also includes a narrow-linewidth semiconductor laser (1), a rotating fiber polarizer (3), and a non-magnetic fiber collimator (4); the narrow-linewidth semiconductor laser (1) emits linearly polarized light to provide a light source; the rotating fiber polarizer (3) is used to generate elliptically polarized light with a specific ellipticity, which is used as a pumping laser to pump alkali metal atoms and generate an optical rotation angle; the non-magnetic fiber collimator (4) is connected after the rotating fiber polarizer (3) to adjust the pumping laser to become collimated light; the end of the rotating fiber polarizer (3) and the non-magnetic fiber collimator (4) are encapsulated in a cylindrical port.

[0061] The invention also includes a half-wave plate (6), a lateral displacement polarization beam splitter prism (7), a photoelectric detector (8), a differential amplifier circuit (9), and a polarization differential module (16); the half-wave plate (6) is used to realize that the splitting ratio of the two perpendicular components of the lateral displacement polarization beam splitter prism (7) is 50% and 50% before pumping occurs; the photoelectric detector (8) is used to collect the light intensity information of the two linear polarized lights with perpendicular vibration directions emitted by the lateral displacement polarization beam splitter prism (7); the differential amplifier circuit (9) is used to perform a differential operation on the signals collected by the photoelectric detector (8) to obtain a differential signal and amplify the signal; the polarization differential module (16) is composed of the half-wave plate (6), the lateral displacement polarization beam splitter prism (7), the photoelectric detector (8), and the differential amplifier circuit (9), and is used to realize polarization differential detection technology.

[0062] The invention also includes an atomic gas chamber (5) and a non-magnetic electric heating device (10); the atomic gas chamber (5) is placed and surrounded by the non-magnetic electric heating device (10) to heat the alkali metal atoms to obtain 10 13 ~10 14 pieces / cm 3 The atomic number density of

[0063] The rotating optical fiber polarizer (3), the non-magnetic optical fiber collimator (4), the atomic gas chamber (5), the non-magnetic electric heating device (10), the three-axis magnetic field coil (12), and the polarization differential module (16) are placed in an atomic magnetometer head housing (13), and together with the atomic magnetometer head housing (13) form an atomic magnetometer head.

[0064] The photoelectric measurement and control system (17) is composed of a narrow linewidth semiconductor laser (1), a function generator (2), and a phase-locked amplifier (14). The physical space in which the system is located is the space outside the atomic magnetometer head, and is used to realize the processing and control of optical and electrical signals.

[0065] The rotating fiber polarizer (3) is composed of two polarization-maintaining optical fibers of the same material and structure that are fused and connected, wherein the length of the first half of the optical fiber is arbitrary and does not undergo any twisting, and the initial fast and slow axis directions of the second half coincide with those of the first half and undergo twisting, and the twisting length and twisting angle are calculated based on the ellipticity α of the expected elliptically polarized light; laser light passes through the rotating fiber polarizer (3) and the non-magnetic fiber collimator (4) to generate elliptically polarized light with an ellipticity of α; the vibration direction of the polarized light emitted by the narrow linewidth semiconductor laser (1) is aligned with the fast axis direction of the rotating fiber polarizer (3), and the optical axis direction of the lateral displacement polarization splitter prism (7) is aligned with the fast axis direction of the rotating fiber polarizer (3).

[0066] The atomic gas chamber (5) is in a weak magnetic environment and is filled with alkali metal atoms with an atomic number density of 10 13 ~10 14 pieces / cm3 .

[0067] The laser frequency emitted by the narrow linewidth semiconductor laser (1) is adjusted to be detuned from the alkali metal D1 line resonance frequency.

[0068] 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 based on rotating fiber polarization, characterized in that: The invention comprises a three-axis magnetic field coil and a polarization differential module located in the housing of the atomic magnetometer head. The laser input end of the polarization differential module is connected to the laser output end of the atomic gas chamber in the three-axis magnetic field coil. The output end of the polarization differential module is connected to a phase-locked amplifier. The phase-locked amplifier forms the output signal of the atomic magnetometer. The laser incident end of the atomic gas chamber is connected to a narrow-linewidth semiconductor laser via a non-magnetic fiber collimator and a rotating fiber polarizer in sequence. The three-axis magnetic field coil is connected to a function generator. The rotating optical fiber polarizer includes two sections of optical fiber, a front half section of optical fiber and a rear half section of optical fiber in a twisted state, which are connected by fusion and then fixed with a clamp. The front half section of optical fiber and the rear half section of optical fiber are polarization-maintaining optical fibers of the same material and structure. The length of the front half section of optical fiber is arbitrary and is not twisted. The initial fast and slow axis directions of the rear half section coincide with those of the front half section and are twisted. The twist length is related to the beat length of the polarization-maintaining optical fiber, and the twist angle is related to the ellipticity α of the elliptically polarized light. The twisted length of the second half of the optical fiber is (1 / 2)l, where l is the beat length of the polarization-maintaining optical fiber, and the twisted angle is (π / 2)·tanα, where α is the ellipticity of the elliptically polarized light.

2. The ellipsometric atomic magnetometer device based on rotating fiber polarization according to claim 1, characterized in that: The polarization differential module includes a lateral displacement polarization beam splitter prism, the input end of the lateral displacement polarization beam splitter prism is connected to the laser output end of the atomic gas cell through a half-wave plate, and the output end of the lateral displacement polarization beam splitter prism is connected to the lock-in amplifier through a photodetector and a differential amplifier circuit in sequence.

3. The ellipsometric atomic magnetometer device based on rotating fiber polarization according to claim 1, characterized in that: The narrow linewidth semiconductor laser, function generator and phase-locked amplifier constitute a photoelectric measurement and control system.

4. The ellipsometric atomic magnetometer device based on rotating fiber polarization according to claim 1, characterized in that: A non-magnetic electric heating device is provided between the atomic gas chamber and the three-axis magnetic field coil. The non-magnetic electric heating device heats the atomic gas chamber so that the number density of alkali metal vapor atoms in the atomic gas chamber reaches 10 13 ~10 14 pieces / cm 3 .

5. The ellipsometric atomic magnetometer device based on rotating fiber polarization according to claim 1, characterized in that: include: Where θ is the optical rotation angle of elliptically polarized light in the atomic gas cell, n is the atomic number density, c is the speed of light, r is the classical electron radius, P z is the longitudinal polarizability of the alkali metal atom, f is the alkali metal D1 line resonance intensity, l is the atomic gas cell length, v0 is the alkali metal D1 line resonance frequency, v is the laser frequency, and Г is the atomic gas cell pressure broadening.

6. The ellipsometric atomic magnetometer device based on rotating fiber polarization according to claim 1, characterized in that: include: V =Ke -OD θcos(2α) Where V is the differential amplified signal output by the differential amplifier circuit, K is the conversion coefficient of the photodetector, OD is the optical depth, θ is the optical rotation angle, α is the ellipticity of the elliptically polarized light, and e is a natural constant.

7. The ellipsometric atomic magnetometer device based on rotating fiber polarization according to claim 1, characterized in that: include: Where V B is the output signal of the atomic magnetometer, G is the measurement amplification factor, e is a natural constant, OD is the optical depth, c is the speed of light, r is the classical electron radius, f is the alkali metal D1 line resonance intensity, n is the atomic number density, l is the atomic gas cell length, v is the laser frequency, v0 is the alkali metal D1 line resonance frequency, Г is the atomic gas cell pressure broadening, and R op is the pumping rate, R rel is the transverse relaxation rate, α is the ellipticity of elliptically polarized light, and B0 is the magnetic field to be measured.

8. A method for realizing an ellipsometric atomic magnetometer based on rotating optical fiber polarization, characterized in that: The invention comprises the following steps: Step 1, adjusting the frequency of the light source generated by the narrow linewidth semiconductor laser to be detuned from the alkali metal D1 line resonance frequency, and the polarization state is linearly polarized light; Step 2: Make a rotating fiber polarizer, where the length of the first half is arbitrary, the twisted length of the second half is (1 / 2)l, where l is the beat length of the polarization-maintaining fiber, and the twist angle is π / 2·tanα; Step 3, coupling the laser generated in step 1 to the rotating fiber polarizer obtained in step 2, and then passing it through a non-magnetic fiber collimator to generate collimated elliptically polarized light with an ellipticity of α, using the elliptically polarized light as a pump laser to irradiate the atomic gas chamber, thereby achieving pumping of alkali metal atoms while generating an optical rotation angle for signal detection; Step 4: Use the function generator to control the three-axis magnetic field coil to compensate the magnetic field felt around the atomic gas chamber to zero, and at the same time apply a high-frequency modulated magnetic field in the direction of the magnetic field to be measured, and adjust the amplitude and frequency of the modulated magnetic field to the set value B. m 、w m ; Step 5: Use polarization differential detection technology to detect the elliptically polarized light passing through the atomic gas chamber, and connect the differential amplified signal obtained after differential amplification to a phase-locked amplifier using a frequency of w. m The demodulated signal is demodulated on the differential amplified signal using the phase-locked amplification technology to obtain the output signal of the atomic magnetometer.

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