CN112556677A - Nuclear magnetic resonance atomic gyroscope based on multiple reflection cavities and implementation method - Google Patents
Nuclear magnetic resonance atomic gyroscope based on multiple reflection cavities and implementation method Download PDFInfo
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Abstract
The invention relates to a nuclear magnetic resonance atomic gyroscope based on a multi-reflection cavity and an implementation method thereof. Polarization is imparted to the nuclear spins of the noble gas atoms by spin exchange collisions of the polarized alkali metal atoms. The inert gas atoms are continuously driven by the excitation magnetic field, and the frequency of the inert gas atoms keeps resonance through the phase-locked loop, so that the closed-loop work of the gyroscope is realized. The Herriott multi-reflection cavity is introduced into the atomic pool, so that the sensitivity of the system is improved, and meanwhile, the interference caused by the introduction of an additional modulation magnetic field can be avoided, and the stability of the system is improved. The built-in rubidium atom magnetometer is used for obtaining a nuclear spin signal of a xenon atom, so that rotation information measured by nuclear spin is obtained, and the function of a gyroscope is realized.
Description
Technical Field
The invention relates to the field of atomic devices, in particular to a nuclear magnetic resonance gyroscope and an implementation method thereof, wherein the nuclear magnetic resonance gyroscope is based on a nuclear magnetic resonance technology and utilizes a plurality of reflecting cavities to improve the sensitivity and the system stability.
Background
Gyroscopes have been widely used as a core component for inertial measurement, and have been in great demand in both military and civilian fields. Among them, the atomic gyroscope has been developed rapidly in recent years, and has been advanced rapidly in performance, practicality, and the like. The method has good application prospect in the fields of basic physical research, aviation, spaceflight, navigation, traffic navigation and the like closely related to inertial measurement. Currently, the field of atomic gyroscopes is mainly divided into gyroscopes using atomic spins and atomic interference. The gyroscopes using atomic spin correlation can be classified into a compensation type gyroscope, a nuclear magnetic resonance gyroscope, and the like. The compensation type gyroscope experimental device is complex, data processing is complex, and numerous difficulties can be met in the future miniaturization and practical process. Nuclear magnetic resonance gyroscopes may solve these problems, however, they also encounter other challenges.
The nuclear magnetic resonance gyroscope works by utilizing a nuclear spin-alkali metal system, and Rb-129Xe/131Xe system. The rubidium atoms have two functions, one is to polarize the xenon atoms through collision, and the other is to detect the precession signal of xenon nuclear spin as a built-in rubidium atom magnetometer. Nuclear spin magnetometers, which are the basis of nuclear spin coercisers, utilize the response of polarized nuclear spins to a magnetic field to detect changes in the magnetic field. Among the inert gas atoms, the collision cross section of xenon with the alkali metal atom is largest. Thus, on the one hand, it can be polarized very quickly by alkali metal (polarization time of about 1 minute), and on the other hand, the polarized magnetic field of xenon can also be detected most sensitively by alkali metal atom magnetometers. The detected signals are processed to obtain rotation information.
After being charged with inert gas atoms, the relaxation of the alkali metal atoms is mainly limited by collisions with the inert gas atoms. The sensitivity of the noble gas nuclear spin co-magnetometer is limited by the sensitivity of the alkali metal atom magnetometer, which is inversely proportional to its resonance linewidth. Some solutions proposed at present for increasing the detection sensitivity of alkali metal atoms in nuclear spin gas need to combine with magnetic field modulation with high frequency to realize the decoupling of spin and environment, which brings great interference to the system and affects the stability of the system. The passive approach of using multiple reflective cavities can significantly reduce this interference while increasing sensitivity.
Since 1979, Litton and Singer-Kearfott, Inc. in the United states, respectively, developed a new technology based on87Rb-83Kr/129Xe and199Hg/201experiment of nuclear magnetic resonance gyroscope of Hg system. In the same year, stanThe university of Fujian also started to perform relevant experiments and applied for patents. The angle random walk and drift stability of the NMR gyroscope realized by Singer-Kearfott corporation in 1980 were 0.053 °/h, respectively1/20.02 degree/h. The index of Litton company reaches 0.002 degree/h in 19831/2And 0.01 °/h. Experiment at Stuttgart university in Germany in 1993 at Rb-129The random angular walk on Xe was 1.7 °/h1/2. The random walk and drift stabilities of the Northrop Grumman company in the United states reached in four stages from 2005 to 2014 at an angle of 0.005 DEG/h respectively1/20.02 degree/h. Related researches are also carried out by a plurality of units in China, a model machine of the nuclear magnetic resonance gyroscope is successfully developed by Beijing automated control equipment research institute in 2013, and a miniaturized model machine is developed in 2016, and the drift stability of the model machine is better than 1 degree/h. Other domestic units are more researched on the auxiliary module of the nuclear magnetic resonance gyroscope at the present stage, and the test results of the whole nuclear magnetic resonance gyroscope are not reported more yet.
Disclosure of Invention
The invention solves the problems: the nuclear magnetic resonance atomic gyroscope based on the multiple reflection cavities and the implementation method have the advantages of being simple in structure, high in sensitivity and stability. Conventional experiments require additional large field modulation of the main magnetic field to improve sensitivity, affecting the stability of the system. The passive method of the invention using multiple reflecting cavities can greatly reduce the interference while improving the sensitivity. Typical parameters of the method can reach: the angle random walk and the drift stability are respectively 0.09 degree/h1/2，0.2°/h。
The invention provides a nuclear magnetic resonance atomic gyroscope implementation scheme based on nuclear magnetic resonance and a multi-reflection cavity. Alkali metal atoms, inert gas atoms and the like are filled in the atomic pool, nuclear spin is polarized by utilizing electron spin, and the alkali metal atoms can be used as a built-in magnetometer to detect precession signals of the nuclear spin. An excitation magnetic field with the same frequency as the inert gas atom lamor precession frequency is applied in the direction of the vertical pumping light for driving the nuclear spins of the inert gas atoms. A Herriott multi-reflection cavity is introduced into an atomic pool to improve the sensitivity and stability, linear polarization detection light is emitted after being reflected for 21 times in the multi-reflection cavity, and a differential photoelectric detector is used for receiving the detection light. The phase signal can be fed back to the frequency of the excitation magnetic field via a phase-locked loop circuit, thereby achieving closed-loop operation. And a built-in alkali metal atom magnetometer is used for acquiring a nuclear spin signal of an inert gas atom to obtain rotation information, so that the function of a gyroscope is realized.
The invention relates to a nuclear magnetic resonance atomic gyroscope based on a multi-reflection cavity, which comprises: the system comprises an atomic pool containing a Herriott multi-reflection cavity, a heating unit, a magnetic field unit, a photoelectric detector, a phase-locked amplifier and a frequency measurement acquisition system;
an atomic pool containing Herriott multi-reflection cavities, a heating unit and a magnetic field unit are placed in a magnetic shielding barrel made of permalloy, and the magnetic shielding barrel shields the interference of a geomagnetic field and an external stray magnetic field;
the heating unit is used for heating atoms in an atom pool containing the Herriott multi-reflection cavity to enable the atoms to be in a stable high atom number density; the heating unit heats the atomic cell containing the Herriott multi-reflecting cavity because the atomic number density of alkali metal atoms at normal temperature is relatively low, and the detection sensitivity of the magnetometer and the degree of hyperpolarized xenon gas are weak. Typical systems need to operate at temperatures around 110 c to achieve a sufficient signal-to-noise ratio. The heating unit consists of two nonmagnetic heating sheets, the heating is realized by high-frequency alternating current, the two heating sheets are respectively attached to the upper surface and the lower surface of the atomic pool, and the atomic pool and the heating sheets are assembled together by utilizing a 3D printed box;
the magnetic field unit comprises X, Y magnetic field coils in three directions of Z and is used for providing a bias magnetic field and an excitation magnetic field required by the operation of the gyroscope respectively, wherein the bias magnetic field is used for defining the direction of a polarization axis of the system, pumping light continuously polarizes rubidium atoms, the polarization is transferred to xenon atoms through collision, and the bias magnetic field is applied by the Z-direction magnetic field unit; the bias magnetic field and the pumping light are consistent in direction, the polarization of atoms is along the direction of the pumping light, and meanwhile, the lamor precession frequency of xenon is also determined by the bias magnetic field; driven by an alternating current excitation magnetic field with single frequency applied to a Y-direction magnetic field unit, partial xenon polarization can precess in the direction vertical to a bias magnetic field at the frequency of the excitation magnetic field, the excitation magnetic field in the Y direction is provided by an oscillator when a gyroscope works in a closed loop mode, the magnetic field in the X direction is vacant, but when the direction of detection light changes, the excitation magnetic field needs to be applied to the X direction, and the excitation magnetic field can be reserved for standby; an atom pool containing a Herriott multi-reflection cavity and a heating unit are both arranged in the magnetic field unit, and the atom pool is close to the central position of the magnetic field coil as much as possible;
the detection circuit of the photoelectric detector consists of two photoelectric detectors which respectively measure the light power of two linear polarization components of the detection light, and then a differential circuit is utilized to obtain a light polarization rotation signal which is an input signal of the phase-locked amplifier;
the phase-locked amplifier comprises a phase-locked loop and an oscillator; the phase-locked amplifier makes phase sensitive detection to the signal and makes separation detection to the part near some frequency in the signal; on one hand, the reference signal of the phase-locked amplifier is used as an output signal to drive the xenon isotope to precess; on the other hand, the reference signal is also used for demodulating the output signal of the photoelectric detector, and the phase and amplitude signals of the respective precession of the xenon isotopes can be obtained after demodulation; the phase signal is locked at a set phase value in a closed loop mode by using a phase-locked loop, and the closed loop adjusts the frequency of the excitation magnetic field by outputting the phase-locked loop to an oscillator;
and the frequency measurement acquisition system is used for measuring the output frequency of the oscillator to obtain the rotation information of the gyroscope.
The front cavity mirror and the rear cavity mirror of the Herriott multi-reflection cavity are fixed on a silicon chip by an anodic bonding method, and both the cavity mirrors are cylindrical mirrors; the glass cover is bonded on the silicon wafer by the cavity mirror, then the silicon wafer is sealed by an anodic bonding method, atoms are filled through a tail pipe on the glass cover, all the atoms are filled into the atom pool, finally the atom pool is taken down from a vacuum system by flame burning, and the atom pool with the multiple reflection cavities is manufactured.
The heating unit adopts two nonmagnetic heating sheets to heat the atomic pool by alternating current; and the rubidium atoms are polarized by pumping light and then transfer the polarization to xenon gas through collision.
The Herriott multi-reflection cavity is placed in a 3D printing box in the using process, and the 3D printing can accurately realize the fixation of the position of the atomic pool. Thus, the experiment can be started without the need of adjusting the optical path in a complicated way. In addition, the combination of 3D printing and Herriott multi-reflection cavity makes the structure of experimental system more compact, and provides possibility for integration and miniaturization. In general, the sensitivity of alkali metal magnetometers limits the sensitivity of nuclear spin magnetometers and thus the performance of gyroscopes, by being flushed into atomic pools of alkali metal atoms and inert gas atoms. In the experiment, rubidium atoms and xenon are both in a Herriott multi-reflection cavity bonded with an anode, so that the acting distance between detection light and rubidium atoms is increased through the Herriott multi-reflection cavity, the signal to noise ratio is improved, and other complex extra modulation is not required to be introduced to influence the stability of the system.
The implementation method of the invention comprises the following steps: an atomic pool containing Herriott multi-reflection cavities, a heating unit, X, Y magnetic field units in the Z direction and the magnetic field units in the Z direction are all placed in five layers of magnetic shielding barrels, the magnetic shielding barrels play a role in shielding external stray magnetic fields, other constituent units are placed on a platform to collect experimental data, and then the experimental data are processed; the designed non-magnetic heating sheet heats atoms by alternating current, the temperature needs to reach about 110 ℃, and the atoms are positioned under a stable high atom number density to obtain a high enough signal-to-noise ratio; the pumping light is to continuously polarize rubidium atoms in the working process of the atomic gyroscope, the polarization is transferred to xenon atoms through collision, and a stable bias magnetic field is generated on a Z-direction magnetic field coil through a high-stability current source; under the working condition that the bias magnetic field is 160mG, polarized xenon atoms are driven by an alternating current excitation magnetic field applied by a Y-direction magnetic field unit, the polarization of partial xenon gas precesses in the direction vertical to the bias magnetic field at the frequency of the excitation magnetic field, and when the frequency of the excitation magnetic field is equal to the lamor precession frequency of xenon isotopes, the detected nuclear magnetic resonance signal is maximum; the operating distance between the detection light and atoms is increased after the detection light passes through the multi-reflection cavity, a rubidium magnetometer detects xenon precession signals which are reflected on the polarization change of the detection light through the interaction between alkali metal atoms and the detection light, the detection light signals are converted into electric signals by using a photoelectric detector system, then the electric signals are further demodulated by a phase-locked amplifier by taking previous excitation signals as reference signals respectively, the demodulated amplitude and phase information of the xenon precession signals are obtained, and the phase and the frequency of an excitation magnetic field are in a dispersion relation; the excitation magnetic field frequency and xenon lamor precession frequency resonance point correspond to the middle point of a dispersion curve, and are the most sensitive points relative to the magnetic field change, and the signal response is also the maximum, the point is used as a setting point for the closed loop locking of a phase-locked loop, the frequency of the excitation field is controlled by the output feedback of the phase-locked loop, so that the system is in a closed loop working state, the external rotation is equivalent to the change of a bias magnetic field, the change of the bias magnetic field can cause the change of the closed loop feedback signal of the phase-locked loop, the frequency of the excitation magnetic field output by an oscillator is changed, the detection of the rotation is realized by acquiring the feedback quantity of the frequency at a frequency measuring end, and the function of the nuclear magnetic resonance atomic gyroscope based on the multi-reflection cavity.
The invention has the advantages and positive effects that:
(1) the atomic pool containing a plurality of reflecting cavities is used, so that the sensitivity of the alkali metal magnetometer can be effectively improved while the miniaturization of the system is kept. Typically, the sensitivity of an alkali metal magnetometer limits the sensitivity of the nuclear spin magnetometer and thus the performance of the gyroscope by being flushed into a pool of atoms of alkali metal and inert gas atoms.
(2) The atomic pool containing the Herriott multi-reflection cavity is used, so that the nuclear magnetic resonance atomic gyroscope does not need to be additionally provided with an extra parameter modulation magnetic field, and interference caused by extra modulation is avoided.
(3) Under the assistance of multi-reflection cavity and 3D printing, the system disclosed by the invention can avoid complicated light path adjustment, simplify the system and provide convenience for realizing a miniaturized nuclear magnetic resonance gyroscope in the future.
(4) In the present invention, two kinds of inert gas atoms: (129Xe and131xe) are bound in the same atomic pool, they can simultaneously and simultaneously sense the change of magnetic field, so that the signals of these two atoms can be used to eliminate the influence of magnetic field fluctuation, and can utilize nuclear spin to make precision measurement.
(5) The nuclear magnetic resonance gyroscope utilizes the phase-locked loop technology to realize the closed-loop continuous work of the system and improve the working bandwidth of the system.
Drawings
FIG. 1 is a block diagram of a nuclear magnetic resonance atomic gyroscope based on multiple reflective cavities according to the present invention;
FIG. 2 is an atomic pool containing a Herriott multiple-reflection cavity, in which: the device comprises a front cavity mirror 1, a rear cavity mirror 2, a glass cover 3 and a silicon wafer 4;
FIG. 3 is a schematic diagram of pumping light and probe light and excitation magnetic field application;
fig. 4 is a diagram of a real object after the 3D printing platform is combined with the atomic pool, in which: a detection optical fiber output head 5 and a printing platform 6.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
As shown in FIG. 1, the test of the present invention was conducted in a 5-layer magnetic shielding barrel made of permalloy, which can shield the interference of the earth magnetic field and the external stray magnetic field. An atom pool containing a Herriott multi-reflection cavity is a core part of an atom gyroscope, and when the atom gyroscope works, rotation information is measured by using atoms inside the atom pool. The atomic air chamber is matched with a 3D printing platform for use, so that the step of adjusting the light path is omitted. In practice, atoms at about 110 ℃ are required because higher temperatures can give greater signal, thereby improving the signal-to-noise ratio. To achieve this operating temperature, the cell was heated by alternating current using two non-magnetic heating plates of autonomous design. The atomic gas chamber part is wrapped by a heat-insulating material to play a role in heat insulation and heat preservation during heating, the requirement on heating power is reduced, and rubidium atoms are polarized by pumping light and then collideThe polarization is imparted to the xenon gas. The detection light is linearly polarized light which is line blue detuned relative to rubidium atoms D1, and after passing through the multi-reflection cavity, the action distance between the detection light and alkali metal atoms is increased. In principle, the experimental signal comes from the Faraday rotation effect of the detection light, the polarization of the detection light is measured by the photoelectric detector, the optical signal is converted into an electric signal, and the signal acquired by the photoelectric detector is input into the phase-locked amplifier. The phase-locked amplifier demodulates the detection signal by using the phase sensitive detection technology, wherein the modulation frequency is129Xe and131part of the resonance frequency of Xe. On the other hand, the oscillator provides an excitation field for driving xenon atoms to precess, the phase-locked loop is composed of a phase detector, a low-pass filter and a voltage-controlled oscillator, the phase-locked loop can lock the input phase on a set value by changing the frequency of the drive field, and therefore the oscillator can always keep the frequency of the output excitation magnetic field at the xenon resonance frequency. The magnetic field unit is a magnetic field coil containing X, Y and Z directions in 3 directions, the Y direction and the Z direction are respectively used for providing a bias magnetic field and an excitation magnetic field required in the test, and the coil in the X direction is vacant for standby. The frequency measurement acquisition system measures the output frequency of the oscillator to obtain rotation information of the gyroscope.
The front cavity mirror and the rear cavity mirror of the Herriott multi-reflection cavity are fixed on a silicon chip through an anodic bonding method, the two cavity mirrors are cylindrical mirrors, the distance between the two cavity mirrors is 19.2mm, and the main shaft rotates 52.2 degrees relatively. The glass cover is bonded on the silicon wafer by the cavity mirror, then the silicon wafer is sealed by an anodic bonding method, atoms are filled through a tail pipe on the glass cover, all the atoms are filled into the atom pool, finally the atom pool is taken down from a vacuum system by flame burning, and the atom pool with the multiple reflection cavities is manufactured.
The heating unit adopts two nonmagnetic heating sheets to heat the atomic pool by alternating current; and the rubidium atoms are polarized by pumping light and then transfer the polarization to xenon gas through collision.
The atomic pool containing a plurality of reflecting cavities is used, so that the sensitivity of the alkali metal magnetometer can be effectively improved while the miniaturization of the system is kept. In general, the sensitivity of alkali metal magnetometers limits the sensitivity of nuclear spin magnetometers and thus the performance of gyroscopes, by being flushed into atomic pools of alkali metal atoms and inert gas atoms. The atomic pool containing the Herriott multi-reflection cavity is used, so that the system does not need additional modulation to improve the signal-to-noise ratio of measurement, and the interference on the stability of the system caused by the additional modulation is avoided.
The purpose of the invention is realized by the following technical scheme:
1. an atom pool containing a Herriott multi-reflecting cavity was made and filled with atoms. Under the assistance of a mould, an anode bonding method is used for fixing the cavity mirror of the multi-reflection cavity on a silicon wafer at the bottom of the atomic pool according to a pre-designed position, and then the glass cover and the bottom silicon wafer are bonded into a whole by the same method. The length, width and height of the bonded atomic pool are respectively 30 × 18 × 17mm, the Herriott multi-reflection cavity is arranged in the atomic pool, the diameter of the used cylindrical mirror is 12.7mm, the thickness is 2.5mm, the curvature radius is 100mm, the distance between the two cylindrical mirrors is 19.2mm, and the relative rotation angle of the main shaft is 52.2 degrees. A small hole with the diameter of 2.5mm is formed in the center of the front cavity mirror, the detection light enters the multi-reflection cavity from the small hole at an angle of 5 degrees horizontally, and is emitted from the same small hole after being reflected for 21 times. The natural abundance rubidium atoms (among them) are filled into the atomic pool85Rb and87the contents of Rb were 72.2% and 27.8%, respectively), 3Torr129Xe，35Torr 131Xe, 5Torr hydrogen and 150Torr nitrogen as a buffer gas.
2. And pumping light and detection light optical path systems. And adjusting a laser controller to enable pumping light frequency and rubidium atoms D1 which are widened by buffer gas nitrogen to perform linear resonance, converting the rubidium atoms into circularly polarized light through a quarter-wave plate, and then passing through an atom pool to polarize the atoms. And measuring the transmitted pumping light power by using a photoelectric detector, and controlling the transmission power of the pumping light to be unchanged by using a PID (proportion integration differentiation) feedback method so as to ensure that the atomic polarization effect is unchanged. The detection light is linearly polarized light which is in line blue detuning relative to rubidium atoms D1, and the detuning amount is optimized to minimize phase noise. The detection light is emitted into the multi-reflection cavity in the atom gas chamber in the direction perpendicular to the pumping light, and is emitted after 21 times of reflection, and a differential photoelectric detector is used for receiving signals of the detection light.
3. A main magnetic field and a transverse excitation magnetic field. And a magnetic field with proper magnitude is added on the Z-direction magnetic field coil of the magnetic field unit through a current source, and the magnitude of the main magnetic field is 160 mG. Radio frequency excitation magnetic fields with different amplitudes are used in the Y direction to drive precession of the xenon isotope in the direction perpendicular to the magnetic field. In that129Xe and131the magnitude of the scanning frequency in the vicinity of the lamor frequency of Xe. The phase of the xenon signal obtained by detection is in dispersive linear relation with the frequency detuning of the excitation magnetic field. Thus, the phase signal can be fed back to the frequency of the excitation magnetic field through the phase-locked loop, so that the frequency of the excitation magnetic field is always kept in a resonance state. The frequencies of the excitation magnetic fields in the Y direction are respectively equal to129Xe and131the lamor frequency of Xe remains resonant.
4. The photoelectric detector collects data, the phase-locked amplifier processes the data, and the oscillator outputs excitation magnetic field frequency. The photoelectric detector obtains a detection light signal and inputs the detection light signal into a phase-locked amplifier, a reference signal of the phase-locked amplifier is provided by a built-in oscillator, and the reference signal also provides an excitation field signal for driving the xenon isotope to precess. The phase information output by the phase-locked amplifier can be input to the phase-locked loop to realize closed loop, and when the frequency of the excitation magnetic field deviates from a resonance point due to external fluctuation, the phase output of the phase-locked loop is fed back to the oscillator through the control circuit to change the frequency of the excitation magnetic field and realize closed loop operation. Meanwhile, the feedback signal can provide rotation information under the condition of rotation, so that the rotation angle is obtained, and the function of the gyroscope is realized.
5. And (5) working process of the atomic gyroscope. The atom pool containing Herriott multi-reflection cavities, the heating unit and the X, Y and Z-direction magnetic field units are all placed in five-layer magnetic shielding barrels, and the magnetic shielding barrels can play a role in shielding external stray magnetic fields, for example, the influence of the earth magnetic field can be greatly suppressed, and a pure magnetic field environment is provided for internal atoms. Other components are placed on the platform to collect experimental data and then process the data. The designed non-magnetic heating sheet heats atoms by alternating current, the temperature needs to reach about 110 ℃, the atoms are positioned under a stable high atom number density, and a high enough signal-to-noise ratio is ensured. The pumping light is to continuously polarize rubidium atoms in the working process of the atomic gyroscope, the polarization is transferred to xenon atoms through collision, and a current with a rated magnitude is output on the Z-direction magnetic field coil through a current source, so that a bias magnetic field is generated. Under the condition of 160mG, the polarized xenon atoms are driven by an excitation magnetic field applied by a Y-direction magnetic field unit, the polarization of partial xenon gas precesses in the direction vertical to the magnetic field at the frequency of the excitation magnetic field, and the signal of nuclear magnetic resonance is maximum when the frequency of the excitation magnetic field is respectively equal to the larmor precession frequency of xenon isotopes. The detection light increases the action distance with atoms after passing through the multi-reflection cavity, the detection light has the effects that xenon precession signals measured by a rubidium magnetometer are converted into electric signals to be read by a photoelectric detector, the obtained signals are output to a phase-locked amplifier to be respectively demodulated by taking the frequency of an excitation magnetic field as reference frequency, and the demodulated amplitude and phase information of the xenon precession signals are obtained. The phase of xenon precession signal demodulated by the phase-locked amplifier is in dispersion relation with the frequency of the excitation magnetic field. The resonance point of the excitation magnetic field frequency and the xenon lamor precession frequency corresponds to the middle point of the dispersion curve, and is the most sensitive point relative to the magnetic field change, and the signal response is the maximum. The point is used as a set point of the closed loop locking of the phase-locked loop, so that the system can be in a closed loop working state. To reduce the source of noise, the signal output of the oscillator is used as an excitation magnetic field, applied to the Y-directional magnetic field coil to drive the xenon atoms. The external rotation can be equivalent to the change of the bias magnetic field, the rotation can cause the change of the closed loop feedback signal of the phase-locked loop, and the frequency of the excitation magnetic field output by the oscillator is changed accordingly. The rotation detection can be realized by collecting the feedback quantity of the frequency at the frequency measuring end, so that the rotation information can be measured by the nuclear magnetic resonance atomic gyroscope based on the multi-reflection cavity, and the function of the nuclear magnetic resonance atomic gyroscope based on the multi-reflection cavity is realized.
As shown in fig. 2, a front cavity mirror 1 and a rear cavity mirror 2 which form a Herriott multi-reflection cavity are fixed on a silicon wafer 4 by an anodic bonding method, the two cavity mirrors are cylindrical mirrors, the distance between the two cavity mirrors is 19.2mm, and the main shaft rotates 52.2 degrees relatively. The glass cover 3 is sealed with the silicon chip 4 by using an anodic bonding method after the cavity mirror is bonded on the silicon chip 4. The filling of atoms is realized through a tail pipe on a glass cover, after all the atoms are filled into the atom pool, the atom pool is finally taken down from a vacuum system through flame burning, and the atom pool with a plurality of reflecting cavities is manufactured.
Fig. 3 shows the pumping light and probe light path composition of the nmr gyroscope. The pump light is first coupled into the tapered amplifier and the power of the pump light can be increased. The locking of the pumping light power can be realized by utilizing the change of the transmission light size of the pumping light after passing through the atomic pool. The method is characterized in that a PID feedback system is formed by utilizing transmitted light signals, and feedback signals of the PID feedback system are fed to a cone amplifier to ensure the stability of atomic polarization. The pump light is changed to circularly polarized light by a quarter-glass before entering the atom pool for polarizing the atoms. The detection light is emitted by a laser, then is coupled into an optical fiber through an acousto-optic modulator (AOM), then is injected into a Herriott multi-reflection cavity in an atomic pool through the optical fiber, is emitted after 21 times of reflection, and is divided into two beams by a polarization beam splitter. The sum of the outputs of the two photodetectors is used as a feedback signal to be input to a PID controller for controlling an acousto-optic modulator (AOM) to lock the light intensity of the detection light.
Fig. 4 shows the combination of an atomic pool with a 3D printing platform 6, into which the pumping light is driven through a window. The detection light optical fiber output head 5 is specially designed, is manufactured by a 3D printing method, and integrates an output collimating lens, so that the detector can be directly used without manual adjustment after being output by the optical fiber. Meanwhile, with the help of a 3D printing technology, the incidence relation between the detection light and the multi-reflection cavity can be accurately defined, so that complicated light path adjustment is avoided.
Claims (5)
1. A nuclear magnetic resonance atomic gyroscope based on a multi-reflection cavity, comprising: the system comprises an atomic pool containing a Herriott multi-reflection cavity, a heating unit, a magnetic field unit, a photoelectric detector, a phase-locked amplifier and a frequency measurement acquisition system;
an atomic pool containing Herriott multi-reflection cavities, a heating unit and a magnetic field unit are placed in a magnetic shielding barrel made of permalloy, and the magnetic shielding barrel shields the interference of a geomagnetic field and an external stray magnetic field;
the heating unit is used for heating atoms in the atom pool containing the Herriott multi-reflection cavity to enable the atoms to be under a stable atom number density; the heating unit consists of two nonmagnetic heating sheets, the heating is realized by high-frequency alternating current, the two heating sheets are respectively attached to the upper surface and the lower surface of the atomic pool, and the atomic pool and the heating sheets are assembled together by utilizing a 3D printed box;
the magnetic field unit comprises X, Y magnetic field coils in three directions of Z and is used for providing a bias magnetic field and an excitation magnetic field required by the operation of the gyroscope respectively, wherein the bias magnetic field is used for determining the direction of a polarization axis, pumping light continuously polarizes rubidium atoms, the polarization is transferred to xenon atoms through collision, and the bias magnetic field is applied by the Z-direction magnetic field unit; the bias magnetic field and the pumping light are consistent in direction, the polarization of atoms is along the direction of the pumping light, and meanwhile, the lamor precession frequency of xenon is determined by the bias magnetic field; driven by an alternating current excitation magnetic field with single frequency applied to a Y-direction magnetic field unit, partial xenon polarization can precess in the direction vertical to the bias magnetic field at the frequency of the excitation magnetic field, the excitation magnetic field in the Y direction is provided by an oscillator when the gyroscope works in a closed loop mode, the X-direction magnetic field is vacant, but when the direction of the detection light changes, the excitation magnetic field needs to be applied to the X direction; an atom pool containing a Herriott multi-reflection cavity and a heating unit are both arranged in the magnetic field unit, and the atom pool is close to the central position of the magnetic field coil;
the detection circuit of the photoelectric detector consists of two photoelectric detectors which respectively measure the light power of two linear polarization components of the detection light, and then a differential circuit is utilized to obtain a light polarization rotation signal which is an input signal of the phase-locked amplifier;
the phase-locked amplifier comprises a phase-locked loop and an oscillator; the phase-locked amplifier makes phase sensitive detection to the signal and makes separation detection to the part near some frequency in the signal; on one hand, the reference signal of the phase-locked amplifier is used as an output signal to drive the xenon isotope to precess; on the other hand, the reference signal is used for demodulating the output signal of the photoelectric detector, and phase and amplitude signals of respective precession of xenon isotopes are obtained after demodulation; the phase signal is locked at a set phase value by a phase-locked loop, and the closed loop is output to an oscillator through the phase-locked loop to adjust the frequency of an excitation magnetic field to obtain the frequency of the excitation magnetic field which resonates with the respective lamor frequency of the xenon isotope;
and the frequency measurement acquisition system is used for measuring the output frequency of the oscillator to obtain the rotation information of the gyroscope.
2. The multi-reflecting cavity-based nuclear magnetic resonance atomic gyroscope of claim 1, wherein: the front cavity mirror and the rear cavity mirror of the Herriott multi-reflection cavity are fixed on a silicon chip by an anodic bonding method, and both the cavity mirrors are cylindrical mirrors; the glass cover is bonded on the silicon wafer by the cavity mirror, then the silicon wafer is sealed by an anodic bonding method, the atoms are filled through a tail pipe on the glass cover, all the atoms are filled into an atom pool, finally the atom pool is taken down from a vacuum system by flame burning, the atom pool containing a plurality of reflection cavities is manufactured, and atoms of two inert gases are bonded on the silicon wafer129Xe and131xe is bound in the same atomic pool, and the sensing magnetic field of the same place is changed.
3. The multi-reflecting cavity-based nuclear magnetic resonance atomic gyroscope of claim 1, wherein: the adding unit adopts two nonmagnetic heating sheets to heat the atomic pool through alternating current; and the rubidium atoms are polarized by pumping light and then transfer the polarization to xenon gas through collision.
4. The multi-reflecting cavity-based nuclear magnetic resonance atomic gyroscope of claim 1, wherein: the Herriott multi-reflection cavity is placed in a 3D printing box in the using process, and the 3D printing can accurately realize the fixation of the position of the atomic pool.
5. The method for implementing a nuclear magnetic resonance atomic gyroscope based on multiple reflective cavities according to claim 1, is characterized in that: an atomic pool containing Herriott multi-reflection cavities, a heating unit, X, Y magnetic field units in the Z direction and the magnetic field units in the Z direction are all placed in five layers of magnetic shielding barrels, the magnetic shielding barrels play a role in shielding external stray magnetic fields, other constituent units are placed on a platform to collect experimental data, and then the experimental data are processed; the designed non-magnetic heating sheet heats atoms by alternating current, the temperature needs to reach about 110 ℃, and the atoms are positioned under a stable high atom number density to obtain a high enough signal-to-noise ratio; the pumping light is to continuously polarize rubidium atoms in the working process of the atomic gyroscope, the polarization is transferred to xenon atoms through collision, and a stable bias magnetic field is generated on a Z-direction magnetic field coil through a high-stability current source; under the working condition that the bias magnetic field is 160mG, polarized xenon atoms are driven by an alternating current excitation magnetic field applied by a Y-direction magnetic field unit, the polarization of partial xenon gas precesses in the direction vertical to the bias magnetic field at the frequency of the excitation magnetic field, and when the frequency of the excitation magnetic field is equal to the lamor precession frequency of xenon isotopes, the detected nuclear magnetic resonance signal is maximum; the operating distance between the detection light and atoms is increased after the detection light passes through the multi-reflection cavity, a rubidium magnetometer detects xenon precession signals which are reflected on the polarization change of the detection light through the interaction between alkali metal atoms and the detection light, the detection light signals are converted into electric signals by using a photoelectric detector system, then the electric signals are further demodulated by a phase-locked amplifier by taking previous excitation signals as reference signals respectively, the demodulated amplitude and phase information of the xenon precession signals are obtained, and the phase and the frequency of an excitation magnetic field are in a dispersion relation; the excitation magnetic field frequency and xenon lamor precession frequency resonance point correspond to the middle point of a dispersion curve, and are the most sensitive points relative to the magnetic field change, and the signal response is also the maximum, the point is used as a setting point of phase-locked loop closed-loop locking, the frequency of the excitation field is controlled by the output feedback of the phase-locked loop, so that the nuclear magnetic resonance atomic gyroscope is in a closed-loop working state, the external rotation is equivalent to the change of a bias magnetic field, the change of the bias magnetic field can cause the change of a phase-locked loop feedback signal, the frequency of the excitation magnetic field output by an oscillator is changed, the detection of the rotation is realized by acquiring the feedback quantity of the frequency at a frequency measuring end, and the function of the nuclear magnetic resonance atomic gyroscope based on the multi-reflection cavity is completed.
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| CN114035129A (en) * | 2021-11-05 | 2022-02-11 | 中国科学技术大学 | Atomic gas cell with high transmittance, manufacturing method thereof and atomic magnetometer |
| CN114061558A (en) * | 2021-11-03 | 2022-02-18 | 北京量子信息科学研究院 | Nuclear magnetic resonance gyroscope |
| CN114235711A (en) * | 2022-02-24 | 2022-03-25 | 朗思传感科技(深圳)有限公司 | Miniaturized portable high-sensitivity gas measurement system |
| CN114487945A (en) * | 2021-12-29 | 2022-05-13 | 中国科学技术大学 | Scalar atom magnetometer without detection blind area and capable of eliminating optical frequency shift and method |
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| CN114061558A (en) * | 2021-11-03 | 2022-02-18 | 北京量子信息科学研究院 | Nuclear magnetic resonance gyroscope |
| CN114061558B (en) * | 2021-11-03 | 2022-11-22 | 北京量子信息科学研究院 | Nuclear magnetic resonance gyroscope |
| CN114035129A (en) * | 2021-11-05 | 2022-02-11 | 中国科学技术大学 | Atomic gas cell with high transmittance, manufacturing method thereof and atomic magnetometer |
| CN114035129B (en) * | 2021-11-05 | 2022-12-30 | 中国科学技术大学 | Atomic gas cell with high transmittance, manufacturing method thereof and atomic magnetometer |
| CN114487945A (en) * | 2021-12-29 | 2022-05-13 | 中国科学技术大学 | Scalar atom magnetometer without detection blind area and capable of eliminating optical frequency shift and method |
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