Disclosure of Invention
Aiming at the defects in the prior art, the invention provides the three-dimensional coil coefficient calibration method based on the optical pump nuclear magnetic resonance, which has the advantages of high characteristic precision, no need of using other magnetic field measuring instruments, simple operation and good universality, and can be conveniently applied to the coil coefficient measurement of the three-dimensional coil of the nuclear magnetic resonance gyroscope.
The invention is realized by the following technical scheme:
the atomic glass gas chamber filled with cesium atoms and some buffer gases is arranged in the center of a three-dimensional coil, current is respectively applied to the coil in any one or two directions in the three-dimensional coil to generate a direct-current magnetic field, the atom gas chamber is irradiated by left-handed circularly polarized light, the irradiation direction of the circularly polarized light and the applied direct-current magnetic field are on the same plane, a radio-frequency magnetic field with fixed frequency is applied in the direction perpendicular to the direct-current magnetic field and the plane of the circularly polarized light, the nuclear magnetic resonance state of an optical pump is achieved by adjusting the current, at the moment, the light penetrating through the atom gas chamber is subjected to the maximum modulation of the cesium atoms, the amplitude of emergent light is obtained after the photoelectric conversion and demodulation of the emergent light, and when the current value corresponding to the maximum amplitude is obtained, the coil coefficient calibration is realized.
The optical pump nuclear magnetic resonance state is as follows: frequency omega ═ gamma B of radio frequency magnetic field0Wherein: gamma is the gyromagnetic ratio of cesium atoms, being a fixed constant, B0The field strength of the DC magnetic field and the field strength B of the radio frequency magnetic field1cosωt。
The current value corresponding to the maximum amplitude value obtains the amplitude value of the emergent light after photoelectric conversion and demodulation are carried out on the emergent light, and the maximum modulation point is obtained when the amplitude value is maximum. The corresponding current value I satisfies ω ═ γ I λ, thereby obtaining a coil coefficient λ of the coil in the corresponding direction.
Technical effects
The invention integrally solves the technical problems that the center point of the coil cannot be accurately and effectively calibrated due to the limitation of the volume shape of the coil, the volume shape of the magnetometer and the like when the traditional fluxgate magnetometer is used for calibrating the coil, the calibration is not accurate due to the limitation of the volume shape of a probe of the magnetometer and the complicated installation process is caused by the calibration of a three-dimensional coil.
Compared with the prior art, the invention can accurately calibrate the center of the three-dimensional coil by the optical pump magnetic resonance effect, has high precision and avoids using other magnetic field measuring instruments. The size and shape of the atomic gas chamber used in the invention are easy to change, the minimum size can reach 1mm level at present, and the size of the atomic gas chamber can not be influenced by the shape and size of the calibrated coil. Meanwhile, the coil coefficients of each dimension are calibrated without being assembled and disassembled, so that the method has the advantages of simplicity in operation and good universality, and can be conveniently applied to coil coefficient determination of three-dimensional coils of the nuclear magnetic resonance gyroscope.
Detailed Description
As shown in fig. 1 to fig. 3, the present embodiment relates to a three-dimensional coil coefficient calibration apparatus based on optical pump nuclear magnetic resonance, including: set up pump laser light source 1, linear polarizer 2, lambda/4 wavelength optical lens 3 in proper order in magnetism shielding section of thick bamboo 4 side to and set up photoelectric detector 9 and lock-in amplifier 10 in proper order in magnetism shielding section of thick bamboo 4 side, wherein: three-dimensional Helmholtz coils 5, 6 and 8 are arranged in the center of a magnetic shielding cylinder 4 after being assembled from inside to outside, a cesium atom air chamber 7 is fixed in the center of the three-dimensional Helmholtz coils, laser generated by a pump laser light source 1 is sequentially converted into left-handed circularly polarized light through a linear polarizer 2 and a lambda/4 wavelength optical lens 3, and emergent light of the left-handed circularly polarized light which is transmitted to the cesium atom air chamber 7 in a space free light form is detected by a photoelectric detector 9 and demodulated by a phase-locked amplifier 10 to obtain the amplitude of a photoelectric signal.
The pump laser light source 1 is electrified to generate laser with the wavelength of 894.2 nm.
The linear polarizer 2 is used for converting the light generated at the pump laser light source 1 into linearly polarized light.
The lambda/4 wavelength optical lens 3 is used for converting the linearly polarized light after passing through the linear polarizer 2 into left circularly polarized light.
The magnetic shielding cylinder 4 is used for shielding the interference of an environmental magnetic field, and the coil calibration in the magnetic shielding cylinder is more accurate.
The Helmholtz coils 5, 6 and 8 are mutually perpendicular three-dimensional coils to be calibrated and can be used for generating a direct current or alternating current magnetic field.
The cesium atom gas chamber 7 is a square glass bubble, cesium atom gas and buffer gas are filled in the cesium atom gas chamber, and the size of the cesium atom gas chamber is 4 mm.
The photodetector 9 is used for receiving the light emitted from the cesium atom gas chamber 7 and converting the light into a voltage signal.
The lock-in amplifier 10 is used for demodulating the voltage signal output by the photodetector 9, and the lock-in amplifier 10 can obtain the amplitude of the specific frequency component signal from the complex signal.
The embodiment relates to a calibration method of the device, which comprises the following steps:
x-axis direction coil coefficient lambdaxCalibration:
1.1) polarization of cesium atoms in the x-direction by the pumping direction from a pump laser source 1, generating a magnetic field B parallel to the direction of the pump laser when a current is applied to a Helmholtz coil 5 of the x-axis parallel to the direction of the pump laser0=IxλxWherein: i isxFor reading the value of the current applied to the coil 5 by means of a multimeter, lambdaxThe coil coefficients for the x-axis helmholtz coil. While applying a radio frequency magnetic field B on the y-axis helmholtz coil 6 (or z-axis helmholtz coil 8) perpendicular to the direction of the pump light1cosωt,Wherein the frequency omega of the radio frequency magnetic field is a determined value.
1.2) increasing the current I gradually from zero
xSo that the magnetic field parallel to the direction of the pump laser corresponds to B
0Increasing until optical pump magnetic resonance occurs, wherein the intensity of transmitted light is modulated by cesium atoms at the frequency of the maximum amplitude of RF magnetic field frequency ω (γ B)
0Wherein: gamma is the gyromagnetic ratio of cesium atoms. The sine wave detected by the
photoelectric detector 9 is input into the phase-locked
amplifier 10 and phase-locked by the reference signal with the frequency omega to obtain the amplitude of the signal, and I is adjusted
xThe output of the phase-locked amplifier is maximized, and the current I corresponding to the maximum signal amplitude is searched
xmax. By using a multimeter to read the value of the current I applied to the
coil 5 at that time
xmaxCalculating to obtain corresponding coil coefficient
X coefficient of coil in y-axis directionyCalibration:
2.1) Pump
laser light Source 1 emits a Pump Direction to polarize Cesium atoms in the x-direction while applying Current I to both the x-axis Helmholtz
coil 5 and the y-
axis Helmholtz coil 6
x、I
yThen two orthogonal magnetic field vector sums are generated
Wherein: current I applied to the coil
x、I
yRead out separately by a multimeter. At the time of being perpendicular to the magnetic field B
0Is applied with a radio frequency magnetic field B on the planar z-axis Helmholtz
coil 8
1cos ω t, the frequency ω of the RF magnetic field is set to a certain value.
2.2) constant Current I
xWhile not changing, the current I is gradually increased from zero
yUntil the optical pump magnetic resonance phenomenon is generated, the light intensity of the transmitted light is modulated by the cesium atoms at the frequency with the maximum amplitude of the radio frequency magnetic field frequency omega, wherein omega is gamma B
0Wherein: gamma is the gyromagnetic ratio of cesium atoms. The sine wave detected by the
photoelectric detector 9 is input into the phase-locked
amplifier 10 for useAnd the amplitude of the signal can be obtained by phase-locking the reference signal with the frequency omega. Regulation I
yThe output of the phase-locked amplifier is maximized, and the current I corresponding to the maximum signal amplitude is searched
ymax. By using a multimeter to read the value of the current I applied to the
coil 6 at that time
ymaxCombining the coil coefficient lambda obtained in the step I
xCalculating to obtain corresponding coil coefficient
③ coil coefficient lambda in the z-axis directionzIs calibrated with lambdaySimilarly:
3.1) polarization of Cesium atoms in the X-direction in the pumping direction of the
pump laser source 1, when a current I is applied to the
X-direction coil 5 and the Z-
direction coil 8 respectively
x、I
zThe magnitude of the magnetic field generated at this time is the sum of two orthogonal magnetic field vectors
Current I applied to the coil
x、I
zCan be read out separately by a multimeter. In a direction perpendicular to the magnetic field B
0A radio frequency magnetic field B is applied to the planar y-direction coil
1cos ω t, the frequency ω of the RF magnetic field is set to a certain value.
Setting the current I on the
x-direction coil 5
xIs a fixed value, and gradually increases the current I on the
coil 8 in the z direction from zero
zUntil the optical pump magnetic resonance phenomenon is generated, the light intensity of the transmitted light is modulated by the cesium atoms at the frequency with the maximum amplitude of the radio frequency magnetic field frequency omega, wherein omega is gamma B
0Wherein: gamma is the gyromagnetic ratio of cesium atoms. The sine wave detected by the
photodetector 9 is input to the lock-in
amplifier 10 and is phase-locked by the reference signal with frequency omega to obtain the amplitude of the signal. Regulation I
zThe output of the phase-locked amplifier is maximized, and the current I corresponding to the maximum signal amplitude is searched
zmax. The current applied to
coil 8 at this time is read by using a multimeterFlow value I
zmaxCombining the coil coefficient lambda obtained in the step I
xCalculating to obtain corresponding coil coefficient
By mounting the device of fig. 1 on an optical bench, the atomic gas cell and its fixture are shown in fig. 2, and the coil and magnetic shield are shown in fig. 3. Through specific practical experiments, the coil coefficients of the three-dimensional coil obtained by the method are respectively as follows: lambda [ alpha ]x=285.17nT/mA,λy=350.26nT/mA,λz381.79 nT/mA. The phase-locked amplifier outputs the maximum output by adjusting the current on the corresponding coil, and a phase-locked output curve can be obtained by scanning the current value as shown in fig. 4 and 5, so as to find the current value corresponding to the output maximum point.
Compared with the prior art, the size of the cesium atom gas chamber of the sensitive substance used in the method is only 4mm square, and the calibration of the magnetic field generated by the center of the coil is more accurate.
The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.