CN110849393A - Method and system for aligning pumping laser and background magnetic field for nuclear magnetic resonance gyroscope - Google Patents
Method and system for aligning pumping laser and background magnetic field for nuclear magnetic resonance gyroscopeDownload PDFInfo
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- CN110849393A CN110849393ACN201911133474.2ACN201911133474ACN110849393ACN 110849393 ACN110849393 ACN 110849393ACN 201911133474 ACN201911133474 ACN 201911133474ACN 110849393 ACN110849393 ACN 110849393A
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- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C25/00—Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass
- G01C25/005—Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass initial alignment, calibration or starting-up of inertial devices
- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
- G01C19/58—Turn-sensitive devices without moving masses
- G01C19/60—Electronic or nuclear magnetic resonance gyrometers
- G01C19/62—Electronic or nuclear magnetic resonance gyrometers with optical pumping
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Abstract
Description
Technical Field
The invention belongs to the technical field of inertial measurement sensors, and particularly relates to a method and a system for aligning pumping laser and a background magnetic field for a nuclear magnetic resonance gyroscope.
Background
The nuclear magnetic resonance gyroscope utilizes the precession of atomic nuclei relative to an external magnetic field and realizes high-sensitivity angular velocity measurement by detecting the precession frequency change of atomic spin. In 1952, Leete and Hansen of general electric company first proposed the concept of a nuclear magnetic resonance gyroscope. The Singer-Kearfott company and the Litton company started the research work related to the nuclear magnetic resonance gyroscope in the 60's of the 20 th century, and developed a principle prototype of the nuclear magnetic resonance gyroscope in 1979.
At present, Northrop Grumman company is the fastest technical development of the nuclear magnetic resonance gyroscope, and through the development process of a fourth-generation gyroscope, a nuclear magnetic resonance gyroscope engineering prototype developed by the Northrop Grumman company is used in a typical environment to verify that the stability of the nuclear magnetic resonance gyroscope engineering prototype reaches 0.02 degree/h, becomes a gyroscope reaching the minimum volume in navigation-level precision in the world at present, and marks that breakthrough research progress is made in the technical field of high-precision and small-volume gyroscopes.
The operating principle of the nuclear magnetic resonance gyroscope is as follows: the laser is used for polarizing alkali metal atoms, the collision between the alkali metal atoms and rare gas atoms can realize the polarization of the nuclear spin of the rare gas atoms, and the nuclear magnetic resonance gyroscope senses the external rotation condition by using the frequency shift of the precession frequency of the transverse polarization component of the rare gas atoms in an external magnetic field, so that the measurement of the angular velocity of the carrier is realized.
The method comprises the steps of firstly, building a laboratory nuclear magnetic resonance gyroscope principle verification system, verifying the nuclear magnetic resonance gyroscope principle, and enabling the system components to be as shown in figure 1. The detection process of the nuclear magnetic resonance signal is divided into three steps: the first step is as follows: in B0A stable static magnetic field (background magnetic field) and a circularly polarized pump light are applied to the shaft, the alkali metal atoms in the gas chamber are polarized under the action of the magnetic field and the pump light, and then the alkali metal atoms are freely collided with the working substance to transfer the polarization to the working substanceThe working substance causes a large number of working substance atoms to generate a macroscopic magnetic moment M. The second step is that: and applying a radio frequency field in the transverse direction, wherein the frequency omega of the radio frequency field is the Larmor precession frequency of the atomic nucleus. At this time, the magnetic moment M of the nucleus deviates from B0A shaft wound around B0The shaft precesses. And thirdly, applying a beam of linearly polarized probe light in the direction vertical to the pump light, enabling the polarization plane of the probe light to generate deflection with the same frequency under the action of precession magnetic moment, converting the deflection into power change by utilizing a polarization beam splitter, detecting and receiving at the other end, and measuring the atom precession frequency change. If the carrier is stationary, the measured precession frequency is ω ═ γ B0(ii) a When the carrier is at omegarDuring rotation, the measured precession frequency is omega ═ gamma B0-ωr。
In the process of realizing nuclear spin polarization, the orientation alignment of the background magnetic field and the pumping laser beam is required to improve the utilization efficiency of the pumping laser power. The polarization direction of the electron spin transferred to the nuclear spin is the pump laser direction. When an included angle exists between the background magnetic field and the orientation of the pump laser, an included angle also exists between the polarized nuclear spin and the orientation of the background magnetic field, and at the moment, the nuclear spin can continuously precess around the background magnetic field. This not only reduces the polarizability of the nuclear spins, but also increases the hyperpolarization time of the nuclear spins, reducing the pump laser hyperpolarization efficiency.
Because the winding and installation processes of the magnetic field coil have inevitable errors, the direct alignment of the laser and the magnetic field direction is difficult to realize on the structural design, and the contingency is very large; theoretically, the alignment condition of the pump light and the magnetic field can be judged by adjusting the direction of the pump light beam and detecting the light intensity change of the corresponding transition frequency section of the atomic gas chamber, but the actual atomic polarizability is low, the light intensity change is usually small, the detection process is not visual and the precision is low.
Disclosure of Invention
The invention provides a method and a system for aligning pumping laser and a background magnetic field for a nuclear magnetic resonance gyroscope, aiming at solving the technical problems in the prior art, so that the power of the pumping laser can be efficiently utilized, and the nuclear spin can obtain higher polarizability.
The invention aims to provide a method for aligning pumping laser and a background magnetic field for a nuclear magnetic resonance gyroscope, which comprises the following steps:
s1, linearly polarized light before the pump light is converted into circularly polarized light passes through a Faraday rotator, a sine alternating signal is applied to a background magnetic field coil, the background magnetic field coil generates a sine alternating magnetic field, and the sine alternating magnetic field acts on the pump light beam;
s2, under the action of the sine alternating magnetic field, the linear polarization pump beam which is not converted into circular polarization generates the periodic deflection of the polarization plane, and the deflection angle is in direct proportion to the component of the magnetic field in the transmission direction of the beam;
s3, the change of the output splitting ratio of the polarization beam splitter prism is caused after the rotation of the polarization plane of the linear polarization laser passes through the 1/2 wave plate, the difference value of the light power of the two beams is converted into a voltage signal through the photoelectric detector and then output, and a periodic signal is generated;
s4, adjusting the light guide reflection mirror before the pump light incidence to adjust the relative angle of the pump light and the background magnetic field, when the amplitude of the detected alternating current signal is maximum, the pump light is aligned with the background magnetic field.
Further, the photodetector is a balanced photodetector.
A second object of the present invention is to provide a system of the above method for aligning the pump laser and the background magnetic field for the nmr gyroscope, which at least includes:
a signal generator for applying a sinusoidal alternating signal to the background field coil;
the detection optical path is used for receiving and processing linearly polarized light before the pump light is converted into circularly polarized light; wherein:
the detection optical path includes:
a light guide mirror for guiding the pump beam into the optically active crystal; background magnetic field coils are positioned at two ends of the optically active crystal;
a polarization beam splitter prism for splitting the pump beam into two beams;
the 1/2 wave plate is positioned between the optically active crystal and the polarization beam splitter prism, and the 1/2 wave plate distributes the initial light intensity of the two beams of light to 50%;
and the photoelectric detector is used for receiving the transmission light and reflection light signals after passing through the polarization beam splitter prism, performing differential operation on the transmission light and reflection light signals and outputting detected alternating current signals, wherein the detected alternating current signals have the same frequency and periodicity with the alternating magnetic field.
The invention has the advantages and positive effects that:
by adopting the technical scheme, the invention utilizes the magneto-optical Faraday effect principle and detects the rotation angle change of the polarization plane of the linear polarization beam as the criterion of the alignment condition of the laser beam and the magnetic field; applying alternating current to the background magnetic field coil to generate an alternating magnetic field, and converting the detected signal into an alternating current signal; the change of the rotation angle of the polarization surface of the linearly polarized light beam is reflected through the amplitude change of the detected alternating current signal, and the light beam is aligned with the magnetic field when the amplitude is maximum.
1. The pump laser and background magnetic field alignment method designed by the invention has clear and reliable principle and good realizability and operability;
2. the method for aligning the pump laser and the background magnetic field can monitor the alignment process in real time, has obvious characteristics of detected quantity (sine signal amplitude), has clear criterion and can realize high-precision alignment;
3. the pump laser and background magnetic field alignment method designed by the invention can improve the detection signal intensity by increasing the alternating magnetic field signal intensity, thereby further improving the alignment precision of the light beam and the magnetic field, and is suitable for systems such as a nuclear magnetic resonance gyroscope and the like.
Drawings
FIG. 1 is a block diagram of a nuclear magnetic resonance gyroscope;
fig. 2 is a system diagram in a preferred embodiment of the invention.
Detailed Description
In order to further understand the contents, features and effects of the present invention, the following embodiments are illustrated and described in detail with reference to the accompanying drawings:
fig. 1 is a diagram of a nuclear magnetic resonance gyroscope composition based on spin collision polarization, the nuclear magnetic resonance gyroscope composition being: the device comprises anatomic gas chamber 1, anon-magnetic heating mechanism 2, a magnetic field control coil 4, amagnetic shielding barrel 3, light path parts (a pumping light path, the front end and the rear end of a detection light path), a frequency control board and the like. It can be seen that the pump beam emitted from the pump optical path passes through the atomic gas cell under the action of the magnetic field generated by the magnetic field control coil.
The method for aligning the nuclear magnetic resonance gyroscope pumping laser and the background magnetic field is further detailed by specific implementation in combination with the attached figure 2. The following examples are illustrative only and not intended to be limiting, and are not intended to limit the scope of the alignment method of the present invention.
Referring to FIG. 2, a pump beam passes through an optically active crystal 6 via a light guiding mirror 5; under the action of the magnetic field control coil 4 (namely the background magnetic field coil), the polarization plane of the pump light rotates; the light beam is decomposed into two beams through a PBS (polarization beam splitter 8), the light intensity distribution of the two beams is related to the polarization plane angle of the incident pump light beam, and the power of the two beams of initial light can be distributed to 50% by adjusting an 1/2 wave plate 7 in front of the PBS: 50% (dc offset to cancel the detection signal); one beam of light is incident to the photodetector through the focusing lens a10, and the other beam of light in the vertical direction is deflected by the reflecting mirror 9 and then is incident to the photodetector 12 through the focusing lens B11; the photoelectric detector outputs a periodic signal with the same frequency as the alternating magnetic field after differentiating the two beams of light power signals, the direction of the pump beam is adjusted by adjusting the angle of the light guide reflector at the incident end of the pump beam, and meanwhile, the change of the amplitude of the output signal of the detector is monitored, and when the amplitude of the signal is the maximum, the pump beam is aligned with the background magnetic field.
The purpose realization process of the invention is as follows:
the invention is mainly based on the magneto-optical Faraday effect. When linearly polarized light passes through a medium under the action of a magnetic field, an optical rotation phenomenon is generated, namely, the polarization plane of the linearly polarized light rotates for a certain angle, which is called magneto-optical Faraday effect. For light of a certain wavelength, the angle θ of rotation of the plane of polarization is proportional to the product of the projection H of the external magnetic field in the direction of propagation of the light and the length d of action of the magnetic field, i.e. the angle θ is proportional to the length of the magnetic field
θ＝VHd
V is called the verdet constant, and the value is related to the material composition of the light-transmitting medium itself.
According to the invention, an alternating current is applied to a magnetic field coil to generate an alternating magnetic field by utilizing a magneto-optical Faraday effect principle, so that a linearly polarized pump light beam before circular polarization conversion passes through the magnetic field coil, if the coincidence degree of the light beam and the magnetic field direction is higher, the projection of the magnetic field in the light beam transmission direction is larger, the rotating angle of the corresponding light beam polarization surface is larger, and the alignment condition of the light beam and the magnetic field can be deduced by detecting the rotating angle change of the polarization surface; in order to amplify the detected signal, a Faraday rotator crystal can be arranged in a light-passing area under the action of a magnetic field. The specific alignment process is as follows:
after the pump light path is built, linearly polarized light before being converted into circularly polarized light by pump light passes through the Faraday rotator, and a sine alternating signal is applied to the background magnetic field coil by the signal generator to generate a sine alternating magnetic field which acts on the pump light beam. According to the principle of magneto-optical Faraday effect, under the action of an alternating magnetic field, a light beam generates periodic deflection of a polarization plane, and the deflection angle is in direct proportion to the component of the magnetic field in the transmission direction of the light beam. The rotation of the polarization plane of the linear polarization laser passes through an 1/2 wave plate to cause the change of the output splitting ratio of a PBS (polarization beam splitter prism), and the difference value of the light power of the two beams is converted into a voltage signal to be output after passing through a balanced photoelectric detector, so that a periodic signal is generated. The linear polarization laser beam is closer to being parallel to the magnetic field, the component of the magnetic field acting on the transmission direction of the beam is larger, the optical rotation angle of the polarization surface is larger, the amplitude of the generated periodic signal is larger, and therefore the relative angle between the pump light and the background magnetic field is judged and adjusted by adjusting the light guide reflecting mirror before the pump light is incident, and finally the pump light and the background magnetic field are aligned.
The above description is only for the preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and all simple modifications, equivalent changes and modifications made to the above embodiment according to the technical spirit of the present invention are within the scope of the technical solution of the present invention.
Claims (3)
1. A method for aligning pumping laser and a background magnetic field for a nuclear magnetic resonance gyroscope is characterized by comprising the following steps:
s1, linearly polarized light before the pump light is converted into circularly polarized light passes through a Faraday rotator, a sine alternating signal is applied to a background magnetic field coil, the background magnetic field coil generates a sine alternating magnetic field, and the sine alternating magnetic field acts on the pump light beam;
s2, under the action of the sine alternating magnetic field, the linear polarization pump beam which is not converted into circular polarization generates the periodic deflection of the polarization plane, and the deflection angle is in direct proportion to the component of the magnetic field in the transmission direction of the beam;
s3, the change of the output splitting ratio of the polarization beam splitter prism is caused after the rotation of the polarization plane of the linear polarization laser passes through the 1/2 wave plate, the difference value of the light power of the two beams is converted into a voltage signal through the photoelectric detector and then output, and a periodic signal is generated;
s4, adjusting the light guide reflection mirror before the pump light incidence to adjust the relative angle of the pump light and the background magnetic field, when the amplitude of the detected alternating current signal is maximum, the pump light is aligned with the background magnetic field.
2. The method of claim 1, wherein the photodetector is a balanced photodetector.
3. A system for implementing the method of aligning the pump laser and the background magnetic field for the nmr gyroscope of claim 1, comprising at least:
a signal generator for applying a sinusoidal alternating signal to the background field coil;
the detection optical path is used for receiving and processing linearly polarized light before the pump light is converted into circularly polarized light; wherein:
the detection optical path includes:
a light guide mirror for guiding the pump beam into the optically active crystal; background magnetic field coils are positioned at two ends of the optically active crystal;
a polarization beam splitter prism for splitting the pump beam into two beams;
the 1/2 wave plate is positioned between the optically active crystal and the polarization beam splitter prism, and the 1/2 wave plate distributes the initial light intensity of the two beams of light to 50%;
and the photoelectric detector is used for receiving the transmission light and reflection light signals after passing through the polarization beam splitter prism, performing differential operation on the transmission light and reflection light signals and outputting detected alternating current signals, wherein the detected alternating current signals have the same frequency and periodicity with the alternating magnetic field.
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| CN112833870A (en)* | 2020-12-30 | 2021-05-25 | 中国人民解放军国防科技大学 | An Effective Method to Suppress the Influence of Alkali Metal Atom Polarization Magnetic Field in Nuclear Magnetic Resonance Gyroscope |
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| CN114199276A (en)* | 2021-11-11 | 2022-03-18 | 北京自动化控制设备研究所 | Magnetic resonance phase detection method and system in atomic spin ensemble state |
| CN114441506A (en)* | 2022-04-08 | 2022-05-06 | 港湾之星健康生物(深圳)有限公司 | Quantum magneto-optical sensor |
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Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114061557A (en)* | 2021-11-03 | 2022-02-18 | 北京量子信息科学研究院 | Nuclear magnetic resonance gyroscope and alignment correction method thereof |
| CN114199276A (en)* | 2021-11-11 | 2022-03-18 | 北京自动化控制设备研究所 | Magnetic resonance phase detection method and system in atomic spin ensemble state |
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