CN117367619A - Device and method suitable for measuring internal temperature of sealed alkali metal gas chamber of atomic magnetometer - Google Patents
Device and method suitable for measuring internal temperature of sealed alkali metal gas chamber of atomic magnetometer Download PDFInfo
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- 150000001340 alkali metals Chemical class 0.000 title claims abstract description 113
- 229910052783 alkali metal Inorganic materials 0.000 title claims abstract description 77
- 238000000034 method Methods 0.000 title claims abstract description 34
- 238000012937 correction Methods 0.000 claims abstract description 12
- 238000005086 pumping Methods 0.000 claims description 36
- 238000005259 measurement Methods 0.000 claims description 27
- 230000010287 polarization Effects 0.000 claims description 15
- 238000001514 detection method Methods 0.000 claims description 14
- 238000010438 heat treatment Methods 0.000 claims description 14
- 239000003513 alkali Substances 0.000 claims description 13
- 238000004364 calculation method Methods 0.000 claims description 13
- 230000003287 optical effect Effects 0.000 claims description 13
- 239000011159 matrix material Substances 0.000 claims description 12
- 229920006395 saturated elastomer Polymers 0.000 claims description 7
- 230000008859 change Effects 0.000 claims description 4
- 238000009792 diffusion process Methods 0.000 claims description 4
- 230000005283 ground state Effects 0.000 claims description 4
- 230000008569 process Effects 0.000 claims description 4
- 230000001133 acceleration Effects 0.000 claims description 3
- 238000000354 decomposition reaction Methods 0.000 claims description 3
- 230000005251 gamma ray Effects 0.000 claims description 3
- 238000007689 inspection Methods 0.000 claims description 3
- 230000007935 neutral effect Effects 0.000 claims description 3
- 238000007789 sealing Methods 0.000 claims description 2
- 230000035945 sensitivity Effects 0.000 abstract description 9
- 239000007789 gas Substances 0.000 description 29
- 238000009529 body temperature measurement Methods 0.000 description 8
- 238000010586 diagram Methods 0.000 description 8
- 239000000523 sample Substances 0.000 description 4
- 238000012827 research and development Methods 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical group [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000000691 measurement method Methods 0.000 description 2
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 238000004088 simulation Methods 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 1
- 235000003140 Panax quinquefolius Nutrition 0.000 description 1
- 240000005373 Panax quinquefolius Species 0.000 description 1
- 230000005678 Seebeck effect Effects 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 210000004556 brain Anatomy 0.000 description 1
- 229910052792 caesium Inorganic materials 0.000 description 1
- TVFDJXOCXUVLDH-UHFFFAOYSA-N caesium atom Chemical compound [Cs] TVFDJXOCXUVLDH-UHFFFAOYSA-N 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000005281 excited state Effects 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 239000001307 helium Substances 0.000 description 1
- 229910052734 helium Inorganic materials 0.000 description 1
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 1
- 238000012625 in-situ measurement Methods 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 238000002595 magnetic resonance imaging Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 238000013139 quantization Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 229910052701 rubidium Inorganic materials 0.000 description 1
- IGLNJRXAVVLDKE-UHFFFAOYSA-N rubidium atom Chemical compound [Rb] IGLNJRXAVVLDKE-UHFFFAOYSA-N 0.000 description 1
- 238000013076 uncertainty analysis Methods 0.000 description 1
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/28—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using measurements of density
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/02—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using evaporation or sublimation, e.g. by observing boiling
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
- G01R33/032—Measuring direction or magnitude of magnetic fields or magnetic flux using magneto-optic devices, e.g. Faraday or Cotton-Mouton effect
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
- Y02A90/30—Assessment of water resources
Abstract
The invention discloses a method for measuring the internal temperature of a sealed alkali metal air chamber of an atomic magnetometer, which comprises the steps of firstly, constructing an atomic magnetometer measuring model; applying an external magnetic field to enable the line width of the atomic magnetometer to reach a steady state, and obtaining the steady state line width of the atomic magnetometer; based on the steady-state line width of the atomic magnetometer, the alkali metal atom vapor density is calculated, the internal temperature of the air chamber is calculated according to the relation between the alkali metal atom vapor density and the internal temperature of the air chamber, and the calculated internal temperature of the air chamber is subjected to temperature correction to obtain the actual internal temperature of the air chamber. The invention solves the limit that the sensor can not directly detect the temperature inside the sealed air chamber, provides a new thought for measuring and correcting the temperature inside the air chamber, and improves the sensitivity of the atomic magnetometer.
Description
Technical Field
The invention belongs to the technical field of optical detection and temperature detection, and particularly relates to a device and a method for measuring the internal temperature of an alkali metal gas chamber sealed by an atomic magnetometer.
Background
An atomic magnetometer is a magnetic sensor with excellent performance and can detect the slightest change in magnetic field. The special attribute endows the atomic magnetometer with ultra-high sensitivity, so that the atomic magnetometer becomes a powerful detection tool and is used for measuring magnetic fields of various applications in science and technology, including fields of basic physics, geophysical exploration, magnetic resonance imaging, navigation, brain research and the like.
Atomic magnetometers are typically composed of several key components, including: pumping and detection light source systems, passive magnetic shielding and active magnetic compensation systems, and alkali metal gas cells. The heating of the atomic magnetometer air chamber plays a vital role in optimizing sensitivity and precision, and is specifically embodied in the following two aspects: (1) The number of gas phase alkali metal atoms is increased, so that the gas phase alkali metal atoms are distributed more densely and uniformly in the gas chamber, and meanwhile, the interaction with an external magnetic field is enhanced, thereby obviously improving the sensitivity; (2) In certain atomic magnetometer mechanisms (such as spin-exchange non-relaxation SERF magnetometers), high temperature plays a key role in suppressing relaxation, collisions of alkali metal atoms at high temperature help reduce spin-exchange relaxation, increase relaxation time, allow atoms to remain polarized for longer periods of time, and help improve measurement accuracy.
The existing atomic magnetometer air chamber temperature measurement method mainly comprises the following steps: thermocouples are commonly used temperature sensors in many applications, the principle of operation of which is based on the seebeck effect, i.e. the voltage generated by two different metals is proportional to the temperature difference at the junction thereof. The temperature measurement can be realized by placing a thermocouple on the outer wall of the air chamber. Resistance Thermometers (RTDs) are temperature sensors that rely on the principle of temperature variation of the resistance of certain materials, platinum being a common RTD material due to its stable and repeatable resistance-temperature characteristics. Typically, the PT1000 is brought into direct contact with the outer wall of the magnetometer air chamber for temperature measurement. Thermistors are temperature sensitive resistors whose resistance changes with temperature. Similar to RTD, a thermistor is also attached to the outer wall of the air chamber for temperature measurement. However, the above-mentioned classical methods are all contact measurement methods, because the air chamber is sealed, it is difficult to place the sensor in the air chamber to perform internal actual temperature measurement, and secondly, the sensitivity of the magnetometer will be affected due to the metal material of the sensor. Sheng et al propose a method for measuring the temperature distribution in the interior of a gas cell based on the optical density principle, which reveals the temperature distribution in the interior of the gas cell by utilizing the relationship between the optical density and the atomic vapor density. The device comprises a light source system, a heating system, an alkali metal air chamber and a signal detection system; the light source system is used for generating laser for measuring temperature distribution in the alkali metal gas chamber and comprises a laser, a wave plate, PBS, a coupler, NPBS, a diaphragm and a reflector. The invention evaluates the temperature distribution condition and the thermal steady-state time in the alkali metal gas chamber by a SERF atomic magnetometer.
However, although this method is a contactless measurement, the measurement accuracy is not high.
Disclosure of Invention
The technical problems to be solved by the invention are as follows: aiming at the problems of low measurement precision and insufficient sensitivity in the existing method for measuring the internal temperature of the sealed air chamber of the atomic magnetometer, the invention provides the device and the method for measuring the internal temperature of the sealed alkali metal air chamber of the atomic magnetometer, which can improve the measurement sensitivity and the measurement precision of the magnetic field of the atomic magnetometer.
The invention adopts the following technical scheme for solving the technical problems:
according to one aspect of the present application, there is provided a method of measuring the internal temperature of a sealed alkali metal cell adapted for use in an atomic magnetometer, the method comprising the steps of:
s1, constructing an atomic magnetometer measurement model;
s2, applying an external magnetic field to enable the line width of the atomic magnetometer to reach a steady state, and obtaining the steady state line width of the atomic magnetometer;
s3, calculating and obtaining the vapor density n of the alkali metal atoms based on the steady-state line width of the atomic magnetometer alkali ；
In sigma se Is the spin-exchange cross-sectional area between alkali metal atoms;is the relative thermal velocity of alkali metal atoms; Γ is the atomic magnetometer steady-state linewidth;
s4, constructing a relational expression between the vapor density of the alkali metal atoms and the temperature in the air chamber by adopting saturated vapor pressure, and calculating to obtain the temperature T in the air chamber:
wherein A and B are density parameters;
s5, correcting the temperature inside the air chamber with the steady-state linewidth of the atomic magnetometer to obtain the actual temperature inside the air chamber.
According to one aspect of the application, in step S1, the atomic magnetometer measurement model is quantitatively described by a density matrix equation, and the calculation formula is as follows:
wherein ρ is a density matrix; alpha hf Is a hyperfine constant;is a reduced planck constant; i is nuclear angular momentum; b is a magnetic field; mu (mu) B Is Bohr magneton; g s G-factor for electrons; />Is a pure number part of a density matrix<S>＝Tr(ρS)；T se Is spin-exchange collision time; t (T) sd Is spin-break time; r is R op Is the pumping rate; s is an optical pumping vector with the amplitude equal to the circular polarization degree and the direction along the pumping beam direction; d is a diffusion constant; d is a derivative symbol, t isTime, S is the electron spin and i is the imaginary part.
According to one aspect of the present application, in step S2, an external magnetic field is applied to bring the atomic magnetometer linewidth to a steady state, and the process of obtaining the atomic magnetometer steady state linewidth includes the following sub-steps:
applying a direct current application magnetic field along the z direction and applying a sinusoidal scanning magnetic field along the y direction;
recording the frequency of a scanning magnetic field and an output signal of the atomic magnetometer, and obtaining the steady-state linewidth gamma of the atomic magnetometer by fitting according to the following formula, wherein the full width at half maximum of a fitting function is the steady-state linewidth of the atomic magnetometer;
wherein f (v) is an atomic magnetometer output signal, v 0 For the center frequency of the output signal of the atomic magnetometer, α is the fitting parameter (α=γ e PB 1 ，γ e For electron gyromagnetic ratio, P is spin polarization of alkali metal, B 1 The magnitude of the y-direction scanning magnetic field), v is the frequency of change of the y-direction magnetic field.
According to one aspect of the application, the alkali metal atom vapor density n is calculated based on the atomic magnetometer steady-state linewidth obtained in step S2 alkali Comprises the following sub-steps:
s31, when the pumping rate is far higher than the spin-destruction rate, the magnitude is equal to the circular polarization degree, and the optical pumping vector s=1, the nuclear angular momentum i=3/2 along the pumping beam direction, the atomic magnetometer linewidth is expanded in the form of the power of the spin-destruction rate, the power form is expanded and the transverse relaxation time T 2 The relationship of (2) is as follows:
wherein Γ' is the atomic magnetometer linewidth; r is R se Is the alkali metal atom spin-exchange rate; r is R sd Is the spin-destruction rate of alkali metal atoms; v hf Hyperfine splitting for the ground state; omega 0 Is larmor precession frequency; r is R op Is the pumping rate; g is a parameter that depends on the degree of single zeeman resonance decomposition; i is the imaginary part;
s32, the contribution of spin exchange collisions to the atomic magnetometer linewidth Γ is expressed as:
wherein omega is q Is the spin precession frequency; i is nuclear angular momentum; r is R se Is the alkali metal atom spin-exchange rate; omega 0 Is larmor precession frequency; q is a nuclear acceleration factor; gamma ray e Is the electron gyromagnetic ratio; b is a magnetic field; g s G-factor for electrons; mu (mu) B Is Bohr magneton;is a reduced planck constant;
s33, the spin polarization of alkali metal is weakened under the condition of low pumping power, P<<1, the transverse relaxation time between the alkali metal atoms is dominant, and the alkali metal spin-exchange rate R is calculated by measuring the atomic magnetometer steady-state linewidth se The following are provided:
wherein Γ is the atomic magnetometer steady-state linewidth;
s34, spin exchange Rate R se Proportional to the density of the alkali metal atom vapor, the calculation formula is as follows:
wherein n is alkali Is the density of alkali metal atom vapor; sigma (sigma) se Is the spin-exchange cross-sectional area between alkali metal atoms;is the relative thermal velocity of alkali metal atoms;
density of alkali metal atom vapor n alkali The expression is as follows:
in sigma se Is the spin-exchange cross-sectional area between the alkali metal atoms,is the relative thermal velocity of the alkali metal atoms.
According to one aspect of the application, in step S5, the following formula is used to correct the internal temperature of the gas cell of the atomic magnetometer steady state linewidth:
ΔT＝0.004413T set +1.12129；
wherein DeltaT is a theoretical deviation correction value; t (T) set Is a set temperature;
corrected actual temperature T inside the air chamber actuality The method comprises the following steps:
T actuality ＝ΔT+T measurement ；
wherein T is measurement The temperature value of the air chamber is the temperature value in the air chamber which is not corrected; Δt is the theoretical deviation correction value.
According to another aspect of the application, a measuring device for sealing an interior temperature of an alkali metal gas cell for an atomic magnetometer according to any one of the above claims, the measuring device comprising an inspection laser, a pump laser, a magnetic shielding device, a first beam expander, a second beam expander, a photodetector, a first beam splitter, a second beam splitter, a 1/2 wave plate, a 1/4 wave plate, a digital lock-in amplifier, a photo balance detector, a mirror, a convex lens, and a polarizer;
the detection laser emits initial laser to the magnetic shielding device through the first beam expander and the polarizer; the pumping laser emits initial laser to a 1/2 wave plate, and then is divided into two beams through a first beam splitter, one beam enters the photoelectric detector, and the other beam enters the magnetic shielding device after passing through a second beam expander to the 1/4 wave plate;
the magnetic shielding device comprises five layers of magnetic shielding barrels, three-dimensional coils, a heating device and an alkali metal air chamber; a three-dimensional coil, a heating device and an alkali metal air chamber are sequentially arranged in the five-layer magnetic shielding barrel; the laser processed by the magnetic shielding device is transmitted to a second beam splitter through a convex lens, the second beam splitter divides the laser into two beams, one beam enters the digital lock-in amplifier through the photoelectric balance detector, and the other beam enters the photoelectric balance detector through the reflecting mirror and is transmitted to the digital lock-in amplifier.
According to one aspect of the present application, the magnetic shielding device further includes a neutral filter for canceling interference.
According to one aspect of the application, the heating device is an oven, inside which an alkali metal plenum is placed.
Compared with the prior art, the invention adopts the technical scheme and has the following technical effects:
the device and the method for measuring the internal temperature of the sealed alkali metal gas chamber of the atomic magnetometer, which are provided by the invention, realize the acquisition of the density of the alkali metal atom vapor by measuring the line width of the steady-state magnetometer in the direct-current magnetic field, thereby calculating the actual internal temperature of the gas chamber by using the saturated vapor pressure and carrying out temperature correction. The invention effectively solves the limit that the sensor cannot directly detect the internal temperature of the sealed air chamber, provides a new thought for measuring and correcting the internal temperature of the air chamber, and simultaneously lays a foundation for improving the sensitivity of the atomic magnetometer.
Drawings
FIG. 1 is a schematic flow chart of a method for measuring the internal temperature of a sealed alkali metal gas chamber of an atomic magnetometer.
FIG. 2 is a schematic diagram of the structure of the device for measuring the internal temperature of the sealed alkali metal gas chamber of the atomic magnetometer.
Fig. 3 is a theoretical simulation diagram of the magnitude of the applied magnetic field of the direct current required for reaching the steady-state linewidth, which is suitable for the internal temperature measuring device of the sealed alkali metal gas chamber of the atomic magnetometer.
Figure 4 shows a theoretical comparison of steady state linewidth density versus saturated vapor pressure.
Fig. 5 is a schematic diagram showing a theoretical correction of the temperature measuring device in the sealed alkali metal gas chamber of the atomic magnetometer.
FIG. 6 is a schematic diagram of the results of a temperature test of a temperature measurement device in an atomic magnetometer sealed alkali metal plenum of the present invention.
Detailed Description
The invention is described in further detail below with reference to the drawings and the detailed description.
Fig. 1 is a schematic flow chart of a method for measuring the internal temperature of an alkali metal gas chamber sealed by an atomic magnetometer, and the embodiment of the invention discloses a method for measuring the internal temperature of the alkali metal gas chamber sealed by the atomic magnetometer, which comprises the following steps:
s1, constructing an atomic magnetometer measurement model.
S2, applying an external magnetic field to enable the line width of the atomic magnetometer to reach a steady state, and obtaining the steady state line width of the atomic magnetometer.
S3, calculating the density n of the alkali metal atom vapor based on the steady-state linewidth of the atomic magnetometer obtained in the step S2 alkali The calculation formula is as follows:
in sigma se Is the spin-exchange cross-sectional area between alkali metal atoms;is the relative thermal velocity of alkali metal atoms; Γ is the atomic magnetometer steady state linewidth.
S4, constructing a relational expression between the vapor density of the alkali metal atoms and the temperature in the air chamber by adopting saturated vapor pressure, and calculating to obtain the temperature T in the air chamber:
wherein A and B are both density parameters.
S5, correcting the temperature inside the air chamber with the steady-state linewidth of the atomic magnetometer to obtain the actual temperature inside the air chamber.
Further, in step S1, the atomic magnetometer measurement model is quantitatively described by a density matrix equation, and the calculation formula is as follows:
wherein ρ is a density matrix; alpha hf Is a hyperfine constant;is a reduced planck constant; i is nuclear angular momentum; b is a magnetic field; mu (mu) B Is Bohr magneton; g s G-factor for electrons; />Is a pure number part of a density matrix<S>＝Tr(ρS)；T se Is spin-exchange collision time; t (T) sd Is spin-break time; r is R op Is the pumping rate; s is an optical pumping vector with the amplitude equal to the circular polarization degree and the direction along the pumping beam direction; d is a diffusion constant; d is the derivative symbol, t is time, S is electron spin, and i is the imaginary part.
FIG. 2 is a schematic diagram of the structure of the device for measuring the internal temperature of the sealed alkali metal gas chamber of the atomic magnetometer. The working principle of the method for measuring the internal temperature of the sealed alkali metal gas chamber of the atomic magnetometer is described in detail below by a specific example.
Step 1, firstly, constructing an atomic magnetometer measurement model, quantitatively describing the atomic magnetometer measurement model through a density matrix equation, and adopting the following calculation formula:
wherein ρ is a density matrix; alpha hf Is a hyperfine constant;is a reduced planck constant; i is nuclear angular momentum; b is a magnetic field; mu (mu) B Is Bohr magneton; g s G-factor for electrons; />Is a pure number part of a density matrix<S>＝Tr(ρS)；T se Is spin-exchange collision time; t (T) sd Is spin-break time; r is R op Is the pumping rate; s is an optical pumping vector with the amplitude equal to the circular polarization degree and the direction along the pumping beam direction; d is a diffusion constant; d is the derivative symbol, t is time, S is electron spin, and i is the imaginary part.
When the pumping rate is far higher than the spin-destruction rate, the amplitude is equal to the circular polarization degree, and the optical pumping vector s=1, the nuclear angular momentum i=3/2 along the pumping beam direction, the atomic magnetometer linewidth is developed in the form of the power of the spin-destruction rate, the power form is developed and the transverse relaxation time T 2 The relationship of (2) is as follows:
wherein Γ' is the atomic magnetometer linewidth; r is R se For the spin-exchange speed of alkali metal atomsA rate; r is R sd Is the spin-destruction rate of alkali metal atoms; v hf Hyperfine splitting for the ground state; omega 0 Is larmor precession frequency; r is R op Is the pumping rate; g is a parameter that depends on the degree of single zeeman resonance decomposition; i is the imaginary part;
the contribution of spin-exchange collisions to the atomic magnetometer linewidth Γ' can be expressed as:
wherein omega is q Is the spin precession frequency; i is nuclear angular momentum; r is R se Is the alkali metal atom spin-exchange rate; omega 0 Is larmor precession frequency; q is a nuclear acceleration factor; gamma ray e Is the electron gyromagnetic ratio; b is a magnetic field; g s G-factor for electrons; mu (mu) B Is Bohr magneton;is a reduced planck constant.
And obtaining the amplitude of the applied direct current magnetic field required by reaching the line width of the steady-state magnetometer according to the calculation.
Under low pumping power conditions, the spin polarization of the alkali metal is reduced, i.e. P<<1, the transverse relaxation time between alkali metal atoms dominates, and the spin-exchange rate R is calculated by measuring the atomic magnetometer steady-state linewidth se The following are provided:
where Γ is the atomic magnetometer steady-state linewidth.
It should be noted that, because of the different parameter configurations, the power for realizing P < <1 is different, for example, for the configuration related to this embodiment, the pumping power of several tens of microwatts is low, but if the configuration is changed to another configuration, for example, it becomes a small air chamber, the pumping power of several tens of microwatts is enough to cause P to approach 1, that is, not low pumping rate.
In this embodiment, P < <1 is a quantization index for low pumping conditions.
Spin exchange Rate R se Proportional to the density of the alkali metal atom vapor, the calculation formula is as follows:
wherein n is alkali Is the density of alkali metal atom vapor; sigma (sigma) se Is the spin-exchange cross-sectional area between alkali metal atoms;is the relative thermal velocity of the alkali metal atoms.
In conclusion, the vapor density of alkali metal atoms n alkali Can be expressed as:
and 2, starting the non-magnetic heating system, setting the heating temperature of the air chamber to 140 ℃ when the temperature is measured for the first time, and waiting for the temperature to be stable.
And 3, adjusting pumping light power to 32 mu W and adjusting detection light power to 50 mu W.
And 4, compensating the residual magnetic field in the magnetic shielding barrel to be near zero value by utilizing the three-dimensional coil.
Fig. 3 is a theoretical simulation diagram of the magnitude of the applied magnetic field of the direct current required for reaching the steady-state linewidth, which is suitable for the internal temperature measuring device of the sealed alkali metal gas chamber of the atomic magnetometer. As shown in fig. 3, in step 5, a dc applied magnetic field having an amplitude of 5000nT is applied in the z direction, while a sinusoidal scan magnetic field having an amplitude of 3nT is applied in the y direction.
And 6, recording the scanning magnetic field frequency and an output signal of the atomic magnetometer, and obtaining a steady-state linewidth Γ of the magnetometer according to the following fitting, wherein the calculation formula is as follows:
wherein f (v) is an atomic magnetometer output signal, v 0 For the center frequency of the output signal of the atomic magnetometer, α is the fitting parameter (α=γ e PB 1 ，γ e For electron gyromagnetic ratio, P is spin polarization of alkali metal, B 1 The magnitude of the y-direction scanning magnetic field), v is the frequency of change of the y-direction magnetic field.
Step 7, introducing the steady-state line bandwidth of the atomic magnetometer measured in the step 6 into the following formula to obtain the alkali metal atomic vapor density n alkali The calculation formula is as follows:
in sigma se Is the spin-exchange cross-sectional area between alkali metal atoms; sigma for potassium atom se ＝1.8×10 -14 cm -2 ；Is the relative thermal velocity of the alkali metal atoms.
Step 8, obtaining the internal temperature T of the air chamber according to the density of the alkali metal atom vapor and the saturated vapor pressure formula of the alkali metal atom, which are obtained in the step 7, wherein the calculation formula is as follows:
wherein A and B are density parameters; for potassium atoms, a=4.402, b=4453.
Fig. 5 is a schematic diagram showing a theoretical correction of the temperature measuring device in the sealed alkali metal gas chamber of the atomic magnetometer. As shown in fig. 5, in step 9, the theoretical deviation of the gas chamber internal temperature measurement method based on the steady-state line width of the atomic magnetometer is corrected, and the calculation formula is as follows:
ΔT＝0.004413×T set +1.12129。
wherein DeltaT is a theoretical deviation correction value; t (T) set Is a set temperature;
step 10, the corrected actual temperature T in the air chamber actuality The following are provided:
ΔT＝0.004413T set +1.12129；
wherein T is measurement The temperature value of the air chamber is the temperature value in the air chamber which is not corrected; Δt is the theoretical deviation correction value.
And 11, repeating the steps 5-10, performing multiple measurements of the actual temperature inside the air chamber at the same set temperature, and averaging and measuring uncertainty.
FIG. 6 is a schematic diagram of the results of a temperature test of a temperature measurement device in an atomic magnetometer sealed alkali metal plenum of the present invention. As shown in FIG. 6, step 12, changing the set temperature, taking each 5 ℃ interval as a test point, repeating step 4-step 11, and measuring to obtain the actual temperature after the internal correction of the alkali metal gas chamber with the set temperature within the range of 140-190 ℃.
On the basis of the measurement method, as shown in fig. 1, the embodiment of the invention provides a device suitable for measuring the internal temperature of an alkali metal gas chamber sealed by an atomic magnetometer, which comprises a laser, a magnetic shielding device, a first beam expander, a second beam expander, a photoelectric detector, a first beam splitter, a second beam splitter, a 1/2 wave plate, a 1/4 wave plate, a digital lock-in amplifier, a photoelectric balance detector, a reflecting mirror, a convex lens and a polarizer.
The lasers include inspection lasers and pump lasers; the detection laser emits initial laser to the magnetic shielding device through the first beam expander and the polarizer; the pumping laser emits initial laser to the 1/2 wave plate, and then is divided into two beams through the first beam splitter, one beam enters the photoelectric detector, and the other beam enters the magnetic shielding device after passing through the second beam expander to the 1/4 wave plate.
The magnetic shielding device comprises five layers of magnetic shielding barrels, three-dimensional coils, a heating device and an alkali metal air chamber; a three-dimensional coil, a heating device and an alkali metal air chamber are sequentially arranged in the five-layer magnetic shielding barrel; wherein the heating device is an oven, and the alkali metal air chamber is arranged in the oven.
In addition, a neutral filter is provided in the magnetic shield apparatus for eliminating interference.
The laser processed by the magnetic shielding device is transmitted to a second beam splitter through a convex lens, the second beam splitter divides the laser into two beams, one beam enters the digital lock-in amplifier through the photoelectric balance detector, and the other beam enters the photoelectric balance detector through the reflecting mirror and is transmitted to the digital lock-in amplifier.
Briefly, the main concepts of the present application are: and obtaining the steady-state line width of the atomic magnetometer, obtaining the vapor density n based on the density relation between the steady-state line width and the alkali atom vapor, obtaining the temperature T based on the relation between the vapor density and the temperature, and finally correcting the temperature.
In a subsequent step, it can be calculated by means of a formula. In the first step, the process of obtaining the atomic magnetometer steady state linewidth is described as follows:
alkali metal atoms (e.g., rubidium, cesium, etc.) and buffer gases (e.g., nitrogen, helium, etc.) are selected and filled into a sealed glass gas chamber.
The heating system heats and controls the temperature of the air chamber to enable the alkali metal atoms to generate enough vapor density.
A beam of circularly polarized pump light and a beam of linearly polarized probe light are generated by the light source system and respectively enter the air chamber along two axes perpendicular to the direction of the external magnetic field. The pump light causes alkali metal atoms to transit from the ground state to the excited state and generates spin polarization. Under the action of the external magnetic field, alkali metal atoms do Larmor precession around the external magnetic field, and the precession frequency is in direct proportion to the external magnetic field.
When the probe light passes through the alkali metal vapor, faraday rotation effect occurs, that is, the polarization direction of the probe light rotates with the spin direction of the alkali metal atom. By measuring the rotation angle of the probe light, the larmor precession frequency of the alkali metal atoms can be obtained, and the magnitude of the external magnetic field can be obtained. The signal detection system is used for receiving and processing signals of the reference light and the detection light, and comprises a photoelectric detector, an amplifier, a filter, a sampler and a computer.
The photodetector converts the reference light and the detection light into voltage signals and transmits them to the amplifier. The amplifier amplifies the voltage signal and outputs the amplified voltage signal to the filter. The filter carries out filtering processing on the voltage signal, removes noise interference and outputs the voltage signal to the sampler. The sampler samples and digitizes the voltage signal and transmits it to a computer. The computer calculates the rotation angle of the detection light according to the voltage signals of the reference light and the detection light, and calculates the Larmor precession frequency of the alkali metal atom and the magnitude of the external magnetic field according to a preset functional relation.
Repeating the above steps under different external magnetic fields to obtain a series of data points of larmor precession frequency and external magnetic field size. Magnetic resonance curves were plotted with these data points and fitted with either a gaussian or lorentz function. The full width at half maximum of the fitting function is the steady state linewidth of the atomic magnetometer.
The next two steps are calculated by formulas. Compared with the prior art, the implementation process of the method does not need multiple times of estimation, and the accuracy and the sensitivity of the result are higher.
Different from the measurement in the prior art by adopting the principle of optical depth, the method adopts the thought of the magnetometer steady-state linewidth to perform in-situ measurement, and can realize the measurement without changing configuration, light path and laser wavelength. Whereas if the measurement is made on an atomic magnetometer based on an optical depth method, the magnetometer configuration, optical path and associated laser wavelength need to be altered. In the embodiment, no additional measuring equipment is needed, and the output signal of the atomic magnetometer is obtained, so that additional errors are avoided, and meanwhile, the result correction and the uncertainty analysis are carried out, so that the measuring precision is higher. The measurement accuracy of the prior art depends on the accuracy and stability of external measurement devices such as a power meter, and furthermore, the laser wavelength, the accuracy and stability of the laser wavelength, and thus the accuracy is not high. And thirdly, the fitting precision of the steady-state line width is greatly improved through a new fitting model. The method solves the defect that the existing fitting model has low fitting precision on steady line width, and further reduces the measurement precision of the internal temperature of the air chamber. Finally, as shown in fig. 4 and 5, at low temperatures, the theoretical value is matched to the saturated vapor pressure by measuring the density using the steady-state line width, but as the temperature increases, the temperature deviation between the two increases, as shown in fig. 4. Since the theoretical deviation is not corrected in the prior art, the temperature is obtained by the uncorrected atomic density, and the deviation is large and the accuracy is low. And this patent has corrected this deviation, promotes measurement accuracy when reducing temperature deviation by a wide margin.
The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereto, and any modification made on the basis of the technical scheme according to the technical idea of the present invention falls within the protection scope of the present invention.
Claims (8)
1. A method for measuring the internal temperature of a sealed alkali metal gas cell suitable for use in an atomic magnetometer, said method comprising the steps of:
s1, constructing an atomic magnetometer measurement model;
s2, applying an external magnetic field to enable the line width of the atomic magnetometer to reach a steady state, and obtaining the steady state line width of the atomic magnetometer;
s3, calculating and obtaining the vapor density n of the alkali metal atoms based on the steady-state line width of the atomic magnetometer alkali ；
In sigma se Is the spin-exchange cross-sectional area between alkali metal atoms;is the relative thermal velocity of alkali metal atoms; Γ is the atomic magnetometer steady-state linewidth;
s4, constructing a relational expression between the vapor density of the alkali metal atoms and the temperature in the air chamber by adopting saturated vapor pressure, and calculating to obtain the temperature T in the air chamber:
wherein A and B are density parameters;
s5, correcting the temperature inside the air chamber with the steady-state linewidth of the atomic magnetometer to obtain the actual temperature inside the air chamber.
2. The method for measuring the internal temperature of the sealed alkali metal gas chamber for the atomic magnetometer according to claim 1, wherein in the step S1, the atomic magnetometer measurement model is quantitatively described by a density matrix equation, and the calculation formula is as follows:
wherein ρ is a density matrix; alpha hf Is a hyperfine constant;is a reduced planck constant; i is nuclear angular momentum; b is a magnetic field; mu (mu) B Is Bohr magneton; g s G-factor for electrons; />Is a pure number part of a density matrix<S>＝Tr(ρS)；T se Is spin-exchange collision time; t (T) sd Is spin-break time; r is R op Is the pumping rate; s is an optical pumping vector with the amplitude equal to the circular polarization degree and the direction along the pumping beam direction; d is a diffusion constant; d is the derivative symbol, t is time, S is electron spin, and i is the imaginary part.
3. The method for measuring the internal temperature of a sealed alkali metal gas cell for an atomic magnetometer according to claim 1, wherein in step S2, an external magnetic field is applied to bring the line width of the atomic magnetometer to a steady state, and the process of obtaining the steady state line width of the atomic magnetometer comprises the following sub-steps:
applying a direct current application magnetic field along the z direction and applying a sinusoidal scanning magnetic field along the y direction;
recording the frequency of a scanning magnetic field and an output signal of the atomic magnetometer, and obtaining the steady-state linewidth gamma of the atomic magnetometer by fitting according to the following formula, wherein the full width at half maximum of a fitting function is the steady-state linewidth of the atomic magnetometer;
wherein f (v) is an atomic magnetometer output signal, v 0 For the center frequency of the output signal of the atomic magnetometer, α is the fitting parameter, α=γ e PB 1 ，γ e For electron gyromagnetic ratio, P is spin polarization of alkali metal, B 1 The amplitude of the y-direction scanning magnetic field is v, and the change frequency of the y-direction magnetic field is v.
4. The method for measuring the internal temperature of a sealed alkali metal gas cell of an atomic magnetometer according to claim 3, wherein the density n of the vapor of the alkali metal atom is calculated based on the steady-state line width of the atomic magnetometer obtained in the step S2 alkali Comprises the following sub-steps:
s31, when the pumping rate is far higher than the spin-destruction rate, the magnitude is equal to the circular polarization degree, and the optical pumping vector s=1, the nuclear angular momentum i=3/2 along the pumping beam direction, the atomic magnetometer linewidth is expanded in the form of the power of the spin-destruction rate, the power form is expanded and the transverse relaxation time T 2 The relationship of (2) is as follows:
wherein Γ' is the atomic magnetometer linewidth; r is R se Is the alkali metal atom spin-exchange rate; r is R sd Is the spin-destruction rate of alkali metal atoms; v hf Hyperfine splitting for the ground state; omega 0 Is larmor precession frequency; r is R op Is the pumping rate; g is a parameter that depends on the degree of single zeeman resonance decomposition; i is the imaginary part;
s32, the contribution of spin exchange collisions to the atomic magnetometer linewidth Γ is expressed as:
wherein omega is q Is the spin precession frequency; i is nuclear angular momentum; r is R se Is the alkali metal atom spin-exchange rate; omega 0 Is larmor precession frequency; q is a nuclear acceleration factor; gamma ray e Is the electron gyromagnetic ratio; b is a magnetic field; g s G-factor for electrons; mu (mu) B Is Bohr magneton;is a reduced planck constant;
s33, the spin polarization of alkali metal is weakened under the condition of low pumping power, P<<1, the transverse relaxation time between the alkali metal atoms is dominant, and the alkali metal spin-exchange rate R is calculated by measuring the atomic magnetometer steady-state linewidth se The following are provided:
wherein Γ is the atomic magnetometer steady-state linewidth;
s34, spin exchange Rate R se Proportional to the density of the alkali metal atom vapor, the calculation formula is as follows:
wherein n is alkali Is the density of alkali metal atom vapor; sigma (sigma) se Is the spin-exchange cross-sectional area between alkali metal atoms;is the relative thermal velocity of alkali metal atoms;
density of alkali metal atom vapor n alkali The expression is as follows:
in sigma se Is the spin-exchange cross-sectional area between the alkali metal atoms,is the relative thermal velocity of the alkali metal atoms.
5. The method for measuring the internal temperature of the sealed alkali metal gas cell for the atomic magnetometer according to claim 1, wherein in step S5, the internal temperature of the gas cell for the steady-state line width of the atomic magnetometer is corrected by using the following formula:
ΔT＝0.004413T set +1.12129；
wherein DeltaT is a theoretical deviation correction value; t (T) set Is a set temperature;
corrected actual temperature T inside the air chamber actuality The method comprises the following steps:
T actuality ＝ΔT+T measurement ；
wherein T is measurement The temperature value of the air chamber is the temperature value in the air chamber which is not corrected; Δt is the theoretical deviation correction value.
6. A measuring device suitable for sealing an interior temperature of an alkali metal cell with an atomic magnetometer according to any one of claims 1 to 5, characterized in that the measuring device comprises an inspection laser, a pump laser, a magnetic shielding device, a first beam expander, a second beam expander, a photodetector, a first beam splitter, a second beam splitter, a 1/2 wave plate, a 1/4 wave plate, a digital lock-in amplifier, a photo balance detector, a mirror, a convex lens and a polarizer;
the detection laser emits initial laser to the magnetic shielding device through the first beam expander and the polarizer; the pumping laser emits initial laser to a 1/2 wave plate, and then is divided into two beams through a first beam splitter, one beam enters the photoelectric detector, and the other beam enters the magnetic shielding device after passing through a second beam expander to the 1/4 wave plate;
the magnetic shielding device comprises five layers of magnetic shielding barrels, three-dimensional coils, a heating device and an alkali metal air chamber; a three-dimensional coil, a heating device and an alkali metal air chamber are sequentially arranged in the five-layer magnetic shielding barrel; the laser processed by the magnetic shielding device is transmitted to a second beam splitter through a convex lens, the second beam splitter divides the laser into two beams, one beam enters the digital lock-in amplifier through the photoelectric balance detector, and the other beam enters the photoelectric balance detector through the reflecting mirror and is transmitted to the digital lock-in amplifier.
7. The apparatus for measuring the internal temperature of an atomic magnetometer sealed off alkali metal plenum according to claim 6, wherein said magnetic shielding means further comprises a neutral filter for eliminating interference.
8. The apparatus for measuring the internal temperature of an atomic magnetometer sealed alkali metal plenum according to claim 6, wherein said heating means is an oven within which the alkali metal plenum is placed.
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