CN116819407A - Atomic magnetometer system and method for testing magnetic field uniformity of biplane coil - Google Patents
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- FHNFHKCVQCLJFQ-UHFFFAOYSA-N xenon atom Chemical compound [Xe] FHNFHKCVQCLJFQ-UHFFFAOYSA-N 0.000 claims description 2
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- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/12—Measuring magnetic properties of articles or specimens of solids or fluids
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
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Abstract
The invention discloses an atomic magnetometer system and a testing method of magnetic field uniformity of a biplane coil, belonging to the technical field of weak magnetic field sensors, wherein the atomic magnetometer system comprises a pump laser, a probe and an optical fiber coupler, and the pump laser, a lambda/2 wave plate, a beam sampler and a polarizer are in a common optical axis state; the probe comprises a cavity, wherein an alkali metal atom air chamber, a first total reflection mirror and a second total reflection mirror are arranged in the cavity, and the first total reflection mirror and the second total reflection mirror are respectively arranged at two sides of the alkali metal atom air chamber; the optical fiber coupler is connected with the first lens through an optical fiber, and light rays output by the first lens sequentially pass through the lambda/4 wave plate and the first total reflection mirror; the biplane compensation coil comprises an upper plane compensation coil and a lower plane compensation coil which are respectively arranged on the upper surface and the lower surface of the cavity. The invention takes the biplane coil as a remanence compensation structure, greatly simplifies the space structure complexity of the coil, and is beneficial to the chip formation of the atomic magnetometer.
Description
Technical Field
The invention belongs to the technical field of weak magnetic field sensors, and particularly relates to an atomic magnetometer system and a method for testing magnetic field uniformity of a biplane coil.
Background
In the field of brain magnetic measurement, the currently commercial instrument is a superconducting quantum interferometer (SQUID), but has the disadvantages of large volume, need of low-temperature cooling, high price and the like, while the spin-exchange relaxation (SERF) atomic magnetometer has ultrahigh sensitivity (1 fT/Hz 1/2 ) The superconducting quantum interferometer has the advantages of being beneficial to chip formation, being capable of working at room temperature and the like, and is hopeful to replace the superconducting quantum interferometer. In the process of the chipping of a SERF atomic magnetometer, there are three main approaches: the single beam is used for replacing double beams, the MEMS alkali metal atomic gas chamber is used for replacing the traditional glass gas chamber, and the volume of the magnetic field compensation coil is reduced. In the aspect of residual magnetic field compensation, three-axis Helmholtz coils and cos gamma coils are commonly used at present, and the two coils have the problem of large volume, so that a single-beam SERF atomic magnetometer is difficult to miniaturize, the volume of a compensation coil in the magnetometer is hopefully greatly reduced by the appearance of a biplane coil, the volume of a magnetic field measurement probe is further reduced, and the spatial resolution of biological magnetic field detection such as cerebral magnetism is greatly improved.
The uniformity of the magnetic field generated by the magnetic field compensation coil has a large influence on the performance, particularly the sensitivity, of the atomic magnetometer, and if the uniformity of the compensation coil is poor, the polarization time of the alkali metal atoms is too short, so that relaxation is caused, resulting in a decrease in the sensitivity of the atomic magnetometer.
Disclosure of Invention
The invention provides an atomic magnetometer system and a testing method for magnetic field uniformity of a biplane coil, which are used for compensating and modulating signals of a residual magnetic field of an SERF magnetometer and improving the sensitivity of the atomic magnetometer.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
an atomic magnetometer system comprises a pump laser, a beam sampler, a lambda/2 wave plate, a polarizer, an optical fiber coupler, a biplane compensation coil and a probe; the pumping laser, the lambda/2 wave plate, the beam sampler and the polarizer are in a common optical axis state; the probe comprises a cavity, wherein an alkali metal atom air chamber, a first total reflection mirror and a second total reflection mirror are arranged in the cavity, and the first total reflection mirror and the second total reflection mirror are respectively arranged at two sides of the alkali metal atom air chamber; the optical fiber coupler is connected with the first lens through an optical fiber, and light rays output by the first lens sequentially pass through the lambda/4 wave plate and the first total reflection mirror; after the light is reflected from the first total reflection mirror, the reflected light sequentially passes through the alkali metal atom air chamber, the second total reflection mirror and the side wall of the cavity, and finally enters the first photoelectric detector; the biplane compensation coil comprises an upper plane compensation coil and a lower plane compensation coil which are respectively arranged on the upper surface and the lower surface of the cavity.
Further, an optical filter and a second photodetector are arranged on the optical path perpendicular to the optical axis.
Further, the upper plane compensation coil and the lower plane compensation coil have the same structure, and the upper plane compensation coil comprises an x-direction coil, a y-direction coil and a z-direction coil.
Further, the y-direction coil is a compensation coil for the pump light direction.
Further, the x-direction coil, the y-direction coil and the z-direction coil are square with side lengths of 15-18 mm.
Further, the alkali metal atom gas chamber is filled with alkali metal atoms, buffer gas and stable isotopes of xenon.
Further, the heating device comprises a heating laser and a second lens, the heating laser is connected with the second lens through an optical fiber, and light rays which are emitted by the heating laser and are collimated by the second lens are used for heating the alkali metal atom gas chamber.
The method for testing the magnetic field uniformity of the biplane coil based on the atomic magnetometer system comprises the following steps of:
step 1: setting the single-beam atomic magnetometer system based on the biplane coil as a working state, and measuring coil constants of an x-direction coil, a y-direction coil and a z-direction coil after compensating a residual magnetic field;
step 2: applying current to the x-direction coil according to the coil constant of the x-direction coil to make the x-direction coil generate magnetic field, changing the magnitude of the x-direction magnetic field and keeping the magnetic field varying within a set range, and measuring 131 Xe nuclear spin transverse relaxation time, recording x-direction magnetic field magnitude and relaxation time, fitting x-direction magnetic field magnitude and relaxation time relation by quadratic function, and according to the relation sum 131 The Xe nuclear spin transverse relaxation time calculates the magnitude of the magnetic field gradient generated by the x-direction coil;
applying a current to the z-direction coil according to the coil constant of the z-direction coil to generate a magnetic field, changing the magnitude of the z-direction magnetic field and keeping the magnetic field varying within a set range, and measuring 131 Xe nuclear spin transverse relaxation time, recording the magnitude of the magnetic field in the z direction and the relaxation time, fitting a relationship between the magnitude of the magnetic field in the z direction and the relaxation time by a quadratic function, and summing according to the relationship 131 The Xe nuclear spin transverse relaxation time calculates the magnitude of the magnetic field gradient generated by the z-direction coil;
the magnitude of the magnetic field gradient produced by the y-direction coil is equal to the magnitude of the magnetic field gradient produced by the x-direction coil.
Further, step 1 includes the steps of:
s1: sticking a planar coil on the upper surface and the lower surface of a cavity, enabling the atomic air chamber to be positioned at the central position of the double-planar coil, and then placing the probe into a magnetic shielding barrel;
s2, adjusting the pumping laser to enable the wavelength of pumping laser emitted by the pumping laser to be the absorption wavelength of alkali metal atoms, and adjusting the power of the heating device to enable the optical depth of the pumping light absorbed by atoms in the alkali metal atom air chamber to be 1-3, namely adjusting the pumping laser to the required working temperature;
s4: controlling direct current and alternating current of the biplane coil to enable a magnetic field generated by the direct current to counteract a residual magnetic field of an external environment, wherein the magnetic field sensed by electron spin of alkali metal atoms is 0;
s5: modulated magnetic field applied to biplane coil with low frequency alternating current in x direction, measured by modulation and demodulation 131 A spin precession signal of the Xe atom;
s6: applying a constant magnetic field to the y-direction and a pulse magnetic field to the z-direction, recording 131 Precession signal of Xe atoms according to 131 The precession frequency of the Xe atoms under the magnetic field is calculated; changing the magnitude of the magnetic field in the y direction, recording a plurality of groups of data, wherein the data comprise precession frequency and the magnitude of the magnetic field in the y direction, calculating the coil constant of the coil in the y direction by straight line fitting the data, and the constant measuring method of the coils in other directions is the same as that of the coils in the other directions.
Further, in step 2:
the relation between the magnetic field of the x-direction coil and the transverse relaxation rate of the nuclear spin is as follows:
the magnetic field magnitude of the z-direction coil and the transverse relaxation rate of the nuclear spin are expressed as follows:
wherein T is 2x Is that 131 Xe at B 0x Spin relaxation time at gamma is 131 The gyromagnetic ratio of Xe, R is the radius of an alkali metal atom air chamber, B 0x For the average magnetic field strength, k, generated by the x-direction coil 0x ＝ε avg And/d is the coefficient to be solved for, ε avg B 0x Is the average value of the bias magnetic field, 2d is the linear length of the gradient region of the magnetic field to be measured, k 0x B 0x The magnitude of the magnetic field gradient for the x-direction coil; t (T) 2z Is that 131 Xe at B 0z Spin relaxation time at k 0z ＝ε avg And/d is the coefficient to be solved for, ε avg B 0z Is the average value of the bias magnetic field, k 0z B 0z The magnitude of the magnetic field gradient for the z-direction coil.
Compared with the prior art, the invention has at least the following beneficial technical effects:
the atomic magnetometer system provided by the invention takes the biplane coil as the remanence compensation structure, the biplane coil can only generate a three-dimensional magnetic field in two planes, and the space structure complexity of the coil can be greatly simplified, so that the volume of the atomic magnetometer probe is greatly reduced, and the chip formation of the atomic magnetometer is facilitated.
The coil uniformity testing method provided by the invention is realized by observing 131 The free decay signal and the transverse relaxation time of Xe calculate the gradient magnetic field of the biplane coil. The method belongs to an in-situ measurement mode and is very suitable for parameter measurement of small-sized coils. The traditional method for measuring the magnetic field gradient of the large coil is to use a fluxgate magnetometer, the volume of the fluxgate magnetometer is larger, the small coil cannot be measured, and the method uses an atomic magnetometer for measurement, and an alkali metal atomic air chamber is arranged between the small biplane coils for measurement, so the method creatively solves the problem that the gradient of the small coil cannot be measured.
Further, a second total reflecting mirror is arranged on one side, opposite to the first total reflecting mirror, of the alkali metal atomic gas chamber, and a first photoelectric detector and a second photoelectric detector of the first photoelectric detector are arranged on the light path of reflected light of the second total reflecting mirror to form a differential detection system, so that background light intensity in an output signal is filtered, and the accuracy of testing is improved.
Drawings
FIG. 1 is a schematic diagram of experimental principles of a single beam Cs atomic magnetometer with a biplane coil as the compensating magnetic field coil;
FIG. 2a is a PCB diagram of an x-direction coil or a y-direction coil;
FIG. 2b is a PCB diagram of a z-direction coil;
FIG. 3 is a diagram of the sum of magnetic fields generated by the x-and y-direction coils 131 Graph of the relationship between Xe relaxation rates.
Detailed Description
In order to make the purpose and technical scheme of the invention clearer and easier to understand. The present invention will now be described in further detail with reference to the drawings and examples, which are given for the purpose of illustration only and are not intended to limit the invention thereto.
In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are merely for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present invention, unless otherwise indicated, the meaning of "a plurality" is two or more. In the description of the present invention, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.
The objects and effects of the present invention will become more apparent from the following detailed description of the preferred embodiments and the accompanying drawings, it being understood that the specific embodiments described herein are merely illustrative of the invention and not limiting thereof.
As shown in fig. 1, the single beam Cs atomic magnetometer system using a biplane coil as a compensation coil of the present invention comprises a pump laser 1, a beam sampler 2, a λ/2 wave plate 3, a polarizer 4, an optical fiber coupler 5, a first total reflection mirror 6, a biplane compensation coil 7, a first photodetector 8, an alkali metal atomic gas chamber 9, a second photodetector 10, a filter 11, a thermal insulation cavity 12, a second total reflection mirror 13, a λ/4 wave plate 14, a first lens 15, a second lens 16, and a heating laser 17.
Wherein the pump laser 1, the lambda/2 wave plate 3, the beam sampler 2 and the polarizer 4 share the optical axis, and the second photodetector 10 and the optical filter 11 are on the optical path perpendicular to the optical axis.
The heat-insulating cavity 12 is a transparent cavity and is made of a high-temperature-resistant PEEK material, has the advantages of high temperature resistance and high hardness, and provides heat insulation for the atomic air chamber; the alkali metal atomic gas chamber 9, the first total reflection mirror 6 and the second total reflection mirror 13 are positioned in the heat insulation cavity 12, and the first total reflection mirror 6 and the second total reflection mirror 13 are respectively arranged at two sides of the alkali metal atomic gas chamber 9; a small amount of buffer gas N of 646Torr of alkali metal atoms Cs is filled in the alkali metal atom gas chamber 9 2 5.7Torr 131 Xe， 131 Xe is used to measure the coil constant and gradient of a biplane coil.
The lambda/4 wave plate 14, the first lens 15, the heating device and the photodetector 8 are located outside the cavity, and when light is reflected from the first total reflection mirror 6, the reflected light sequentially passes through the alkali metal atom gas chamber 9, the second total reflection mirror 13 and the side wall of the cavity, and finally enters the photodetector 8. The heating laser 17 is connected with the second lens 16 through an optical fiber, and the light collimated by the second lens 16 is used for heating the alkali metal atom gas chamber 9.
The biplane coil 7 is composed of three pairs of different coils, as shown in fig. 2, an x-direction coil, a y-direction coil and a z-direction coil, respectively. The shape of the x-direction coil is the same as that of the y-direction coil, and the difference is that the mounting position of the y-direction coil is obtained by rotating the x-direction coil by 90 degrees on the same plane during mounting.
The biplane coil 7 is clung to the upper surface and the lower surface of the heat insulation cavity 12, specifically, an x-direction coil, a y-direction coil and a z-direction coil are clung to the upper surface of the heat insulation cavity 12, another x-direction coil, a y-direction coil and a z-direction coil are clung to the lower surface of the heat insulation cavity 12, the two x-direction coils are oppositely arranged, the two y-direction coils are oppositely arranged, and the two z-direction coils are oppositely arranged. And the center position of the biplane coil 7 coincides with the center position of the alkali metal atom air chamber 9, the biplane coil 7 provides a direct current magnetic field and an alternating current magnetic field for the alkali metal atom air chamber 9, the direct current magnetic field is used for compensating the residual magnetic field in the magnetic shielding barrel, and the alternating current magnetic field is used for modulating the electron spin precession direction of the alkali metal atoms.
A first total reflecting mirror 6, a biplane compensation coil 7, a first photoelectric detector 8, an alkali metal atom air chamber 9, a heat preservation and insulation cavity 12, a second total reflecting mirror 13, a lambda/4 wave plate 14, a first lens 15, a second lens 16,
The biplane coil is positioned at the center 8mm from the two coils, i.e. the distance between the coils facing each other is 16mm, and the height of the probe is designed to be 16mm, as required by the distance between the biplane coil and the upper and lower surfaces, for example, three pairs of coils with a length of 16mm.
The temperature of the alkali metal atom cell 9 is controlled by adjusting the magnitude of the current of the heating laser 17, and when the optical depth of the atom absorbing pumping light is 1 to 3, the temperature is adjusted to the required working temperature. The D1 line absorption peak with the wavelength Cs of the output laser is controlled by adjusting the temperature and the current of the pump laser 1, namely 894nm; the pumping light emitted by the pumping laser 1 sequentially passes through the lambda/2 wave plate 3 and the beam sampler 2 to sample and split the beam. One of the light beams passes through the neutral density filter 11 to attenuate the light intensity and then reaches the second photodetector 10. The other beam of light is changed into linear polarized light through the gram Taylor prism 4, then enters an optical fiber through the optical fiber coupler 5, is changed into parallel light after being expanded through the first lens 15 after being discharged, is changed into circular polarized light through the lambda/4 wave plate 14, is turned back for 2 times through the first total reflection mirror 6, the mixed light pumping atomic air chamber 9 and the second total reflection mirror 13, and the optical signals received by the first photoelectric detector 8 and the second photoelectric detector 10 are converted into photocurrent signals, and background noise is restrained through a differential circuitAcoustic signal and extraction 131 Precession signals of Xe.
The direct current and the alternating current of the three pairs of coils are controlled through the function generator, so that the magnetic field generated by the direct current counteracts the residual magnetic field of the external environment, and the magnetic field sensed by the electron spin of the alkali metal atom is 0; then a modulating magnetic field of low frequency alternating current in x direction is applied to the biplane coil 7, the frequency is in the range of 800-1000Hz, the magnetic field amplitude is 100-300nT, for modulation 131 Precession signals of Xe. Then a constant magnetic field is applied to the y-direction, and the atoms are stably precessed in the y-direction due to the constant magnetic field, and the precession signal is modulated by the modulated magnetic field in the x-direction. Then a pulse magnetic field is applied to the z direction, the precession signal is demodulated by the phase-locked amplifier, and then recorded by the matched software of the phase-locked amplifier 131 The precession signal of the Xe atom, and thus the precession frequency under the magnetic field is calculated from the precession signal. Changing the magnitude of the y magnetic field, recording 10 groups of data, wherein each group of data comprises a y-direction constant magnetic field (expressed by an introduced current) and the calculated precession frequency, calculating the coil constant of a y-direction coil through straight line fitting, and measuring the coil constants of other coils in the same way.
The precession frequency calculation process comprises the following steps: recorded by phase-locked amplifier software 131 In the waveform diagram of the precession signal of Xe atom: the abscissa is time, the ordinate is voltage, a few periods N (peak to peak or trough to trough) are selected, the time difference deltat is recorded, and the precession frequency is N/deltat.
The invention provides a testing method for magnetic field uniformity of a biplane coil, which comprises the following steps:
step one: and setting the single-beam atomic magnetometer system based on the biplane coil as a working state, and measuring coil constants of the coils in the x, y and z directions after compensating the residual magnetic field.
Step two: calculating a current I required for applying 500nT of holding magnetic field to the x-direction coil according to the coil constant, and applying the current I to the x-direction coil to generate 500nT of holding magnetic field as a target magnetic field B 0 Let the actual magnetic field distribution be B (x, y, z), the actual magnetic field is related to the positionDefining the bias magnetic field of the position (x, y, z) as epsilon (x, y, z) = (B (x, y, z) -B 0 )/B 0 Setting the two direction coordinates to 0 may result in a bias magnetic field of the magnetic field in the other direction. According to theory, the three bias magnetic field components generated by one coil are equal in size, so that the bias magnetic field in one direction can be used for representing the magnetic field gradient of the coil. If the bias magnetic field is written as a gradient in the form of equation (5), the gradient is considered to be the same since the current distribution and flow direction of the x-direction coil and the y-direction coil are the same, and the nuclear spin transverse relaxation rate of the y-direction coil can be simplified to equation (6).
Step three: and (3) removing the holding magnetic field in the x direction, applying a 500nT magnetic field to the coil in the z direction, and repeating the second step to obtain the relationship between the deviation magnetic field and the relaxation rate of the coil in the z direction in the x direction, the y direction and the z direction respectively as shown in the formula (4).
Step four: changing the magnitude of the magnetic field in the y direction and keeping the magnetic field varying in the range of 100-500nT, measuring 131 Xe nuclear spin transverse relaxation time, recording the relation between the magnitude of a magnetic field in the y direction and the relaxation time, fitting the relation by a quadratic function formula (7), converting the original gradient calculation into the relation of a relaxation rate of 1/T2 and an average magnetic field B0, and calculating the magnitude of the magnetic field gradient in a certain direction of a direction coil by a theoretical method in the invention, wherein the magnetic field gradient is k of the formula (7) 0x B 0x 。
The principle of the invention is as follows:
non-uniformity of the magnetic field causes relaxation of the polarized nuclear spins, including longitudinal relaxation rate 1/T 1 And transverse relaxation rate 1/T 2 Since transverse relaxation dominates and is related to the magnetic field gradient. Relaxation due to magnetic field inhomogeneities is related to the buffer gas pressure within the atomic gas chamber. The buffer gas pressure affects the diffusion time of the nuclear spins in the atomic gas chamber, and the high buffer gas pressure and the low buffer gas pressure correspond to two different cases, respectively. At the low voltage limit, the diffusion time T of the nuclear spin d Much smaller than the nuclear spin precession period T and vice versa at the high voltage limit. In the system according to the invention, a low pressure limit is assumed.
Atomic spin transverse relaxation rate 1/T at low pressure limit 2 The method comprises the following steps:
wherein R is the inner diameter of the spherical atomic gas chamber, which can be obtained by measurement, and D is the diffusion coefficient of nuclear spin in buffer gas, which can be obtained by reference to data.
Wherein:
Ω I is the angular precession frequency of the nuclear spins under the action of a non-uniform magnetic field. When defining the average magnetic field of the atomic gas chamber as B 0 When the magnetic field is set to +.>And position->In this regard, the inhomogeneous magnetic field is:
therefore, the Larmor precession frequency caused by the nonuniform magnetic field is
The magnetic field gradient generated by the coil can be decomposed intoAnd->Three components, therefore, the gradient component is used to reduce the formula (1).
The transverse relaxation rate of the nuclear spins for the z-direction coil can be reduced to:
the transverse relaxation rate of nuclear spins for the x-and y-direction coils can be reduced to:
for the x-direction coil, i.e. for equation (5), if the magnetic field gradient in all directions is assumed to be the same, it can be further reduced to:
since the y-direction coil and the x-direction coil have the same structure, the magnetic field gradient of the y-direction coil is the same as the magnetic field gradient of the y-direction coil;
for the z-direction coil, i.e. for equation (4), if the magnetic field gradient in all directions is assumed to be the same, it can be further reduced to:
wherein T is 2x Is that 131 Xe at B 0x Spin relaxation time at lower, relaxation time is defined by 131 The free decay signal (precession signal) of X is measured, and gamma is 131 The gyromagnetic ratio of Xe, factor 4, indicates that the magnetic field gradient in all directions is equal, R is the radius of an alkali metal atom air chamber, B 0x For the average magnetic field strength, k, generated by the x-direction coil 0x ＝ε avg And/d is the coefficient to be solved for, ε avg B 0x Is the average value of the deviation magnetic field, the larger the applied magnetic field is, the larger the deviation magnetic field is, the better the coil uniformity is, epsilon avg The smaller 2d is the linear length of the region of the magnetic field gradient to be measured. As can be seen from equation (7), the transverse relaxation rate of nuclear spins is quadratic with the strength of the magnetic field generated by the coil. FIG. 3 is obtained by measuring a plurality of sets of magnetic field intensity and spin relaxation time data fitting, and finally calculating the magnetic field deviation coefficient epsilon of the coil according to the formula (7) avg Wherein ε is avg B 0x /d (i.e. k) 0x B 0x ) The x-direction coil magnetic field gradient magnitude. T (T) 2z Is that 131 Xe at B 0z Spin relaxation time at k 0z ＝ε avg And/d is the coefficient to be solved for, ε avg B 0z Is the average value of the bias magnetic field, k 0z B 0z The magnitude of the magnetic field gradient for the z-direction coil.
It will be appreciated by persons skilled in the art that the foregoing description is a preferred embodiment of the invention, and is not intended to limit the invention, but rather to limit the invention to the specific embodiments described, and that modifications may be made to the technical solutions described in the foregoing embodiments, or equivalents may be substituted for elements thereof, for the purposes of those skilled in the art. Modifications, equivalents, and alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (10)
1. An atomic magnetometer system is characterized by comprising a pump laser (1), a beam sampler (2), a lambda/2 wave plate (3), a polarizer (4), an optical fiber coupler (5), a biplane compensation coil (7) and a probe;
the pumping laser (1), the lambda/2 wave plate (3), the beam sampler (2) and the polarizer (4) are in a common optical axis state;
the probe comprises a cavity, wherein an alkali metal atomic gas chamber (9) and a first total reflection mirror (6) and a second total reflection mirror (13) are arranged in the cavity, and the first total reflection mirror (6) and the second total reflection mirror (13) are respectively arranged at two sides of the alkali metal atomic gas chamber (9);
the optical fiber coupler (5) is connected with the first lens (15) through an optical fiber, and light rays output by the first lens (15) sequentially pass through the lambda/4 wave plate (14) and the first total reflection mirror (6);
after light is reflected from the first total reflection mirror (6), the reflected light sequentially passes through the alkali metal atomic gas chamber (9), the second total reflection mirror (13) and the side wall of the cavity, and finally is injected into the first photoelectric detector (8);
the biplane compensation coil (7) comprises an upper plane compensation coil and a lower plane compensation coil which are respectively arranged on the upper surface and the lower surface of the cavity.
2. An atomic magnetometer system according to claim 1, characterized in that a filter (11) and a second photodetector (10) are arranged in the optical path perpendicular to the optical axis.
3. An atomic magnetometer system according to claim 1, wherein the upper and lower planar compensation coils are identical in structure, the upper planar compensation coil comprising an x-direction coil, a y-direction coil and a z-direction coil.
4. An atomic magnetometer system according to claim 3, characterised in that the x-direction coil, y-direction coil and z-direction coil are square with sides of 15-18 mm.
5. An atomic magnetometer system according to claim 3, characterised in that the y-direction coil is a compensation coil for the pump light direction.
6. An atomic magnetometer system according to claim 1, characterised in that the alkali metal atom gas chamber (9) is filled with alkali metal atoms, buffer gas and stable isotopes of xenon.
7. An atomic magnetometer system according to claim 1, characterized in that the heating means comprise a heating laser (17) and a second lens (16), the heating laser (17) being connected to the second lens (16) by means of an optical fiber, the heating laser (17) emitting laser light collimated by the second lens (16) for heating the alkali metal atomic gas cell (9).
8. A method of testing the magnetic field uniformity of a biplane coil based on the atomic magnetometer system of claim 1, comprising the steps of:
step 1: setting the single-beam atomic magnetometer system based on the biplane coil as a working state, and measuring coil constants of an x-direction coil, a y-direction coil and a z-direction coil after compensating a residual magnetic field;
step 2: applying current to the x-direction coil according to the coil constant of the x-direction coil to make the x-direction coil generate magnetic field, changing the magnitude of the x-direction magnetic field and keeping the magnetic field varying within a set range, and measuring 131 Xe nuclear spin transverse relaxation time, recording x-direction magnetic field magnitude and relaxation time, fitting x-direction magnetic field magnitude and relaxation time relation by quadratic function, and according to the relation sum 131 The Xe nuclear spin transverse relaxation time calculates the magnitude of the magnetic field gradient generated by the x-direction coil;
applying a current to the z-direction coil according to the coil constant of the z-direction coil to generate a magnetic field, changing the magnitude of the z-direction magnetic field and keeping the magnetic field varying within a set range, and measuring 131 Xe nuclear spin transverse relaxation time, recording the magnitude of the magnetic field in the z direction and the relaxation time, fitting a relationship between the magnitude of the magnetic field in the z direction and the relaxation time by a quadratic function, and summing according to the relationship 131 The Xe nuclear spin transverse relaxation time calculates the magnitude of the magnetic field gradient generated by the z-direction coil;
the magnitude of the magnetic field gradient produced by the y-direction coil is equal to the magnitude of the magnetic field gradient produced by the x-direction coil.
9. The method of claim 8, wherein step 1 comprises the steps of:
s1: sticking a planar coil on the upper surface and the lower surface of a cavity, enabling the atomic air chamber to be positioned at the central position of the double-planar coil, and then placing the probe into a magnetic shielding barrel;
s2, adjusting the pumping laser (1) to enable the wavelength of pumping laser emitted by the pumping laser to be the absorption wavelength of alkali metal atoms, and adjusting the power of a heating device to enable the optical depth of the pumping light absorbed by atoms in the alkali metal atom air chamber (9) to be 1-3, namely adjusting the pumping laser to the required working temperature;
s4: controlling direct current and alternating current of the biplane coil (7) to enable a magnetic field generated by the direct current to counteract a residual magnetic field of an external environment, wherein the magnetic field sensed by electron spin of alkali metal atoms is 0;
s5: modulated magnetic field applied to biplane coil with low frequency alternating current in x direction, measured by modulation and demodulation 131 A spin precession signal of the Xe atom;
s6: applying a constant magnetic field to the y-direction and a pulse magnetic field to the z-direction, recording 131 Precession signal of Xe atoms according to 131 The precession frequency of the Xe atoms under the magnetic field is calculated; changing the magnitude of the magnetic field in the y direction, recording a plurality of groups of data, wherein the data comprise precession frequency and the magnitude of the magnetic field in the y direction, calculating the coil constant of the coil in the y direction by straight line fitting the data, and the constant measuring method of the coils in other directions is the same as that of the coils in the other directions.
10. The method for testing magnetic field uniformity of a biplane coil according to claim 8, wherein in step 2:
the relation between the magnetic field of the x-direction coil and the transverse relaxation rate of the nuclear spin is as follows:
the magnetic field magnitude of the z-direction coil and the transverse relaxation rate of the nuclear spin are expressed as follows:
wherein T is 2x Is that 131 Xe at B 0x Spin relaxation time at gamma is 131 The gyromagnetic ratio of Xe, R is the radius of an alkali metal atom air chamber, B 0x For the average magnetic field strength, k, generated by the x-direction coil 0x ＝ε avg And/d is the coefficient to be solved for, ε avg B 0x Is the average value of the bias magnetic field, 2d is the linear length of the gradient region of the magnetic field to be measured, k 0x B 0x The magnitude of the magnetic field gradient for the x-direction coil; t (T) 2z Is that 131 Xe at B 0z Spin relaxation time at k 0z ＝ε avg And/d is the coefficient to be solved for, ε avg B 0z Is the average value of the bias magnetic field, k 0z B 0z The magnitude of the magnetic field gradient for the z-direction coil.
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