Alkali metal gas chamber optimal quenching gas pressure intensity measuring method based on atomic fluorescence effect

Abstract

A method for measuring the optimal quenching gas pressure of an alkali metal gas chamber based on an atomic fluorescence effect belongs to the technical field of quantum precision measurement, atoms in the alkali metal gas chamber are heated and shielded in an ultrahigh-sensitivity magnetic field measurement device based on atomic spinning, and the alkali metal atoms are pumped by using circularly polarized light to reach an SERF state. Quenching gas is used for absorbing photons spontaneously radiated by alkali metal atoms and inhibiting frequency broadening caused by re-absorption of the photons, meanwhile, device output responses corresponding to air chambers with different air pressures are detected, a maximum output signal is found, the optimal content of the quenching gas is determined, and reduction of fluorescence intensity indicates that the quenching gas effectively absorbs the photons. According to the method, by determining the optimal quenching gas pressure intensity, spin damage collision relaxation is reduced, the relaxation time of the system is prolonged, and the sensitivity and the overall performance of the magnetic field measurement device are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of quantum precision measurement, and in particular to a method for measuring the optimal quenching gas pressure in an alkali metal gas cell based on the atomic fluorescence effect. By using the quenching gas to absorb the photons spontaneously emitted by alkali metal atoms, and detecting the fluorescence intensity and the device output response corresponding to the gas cells with different quenching gas pressures, the spin-destruction collision relaxation is reduced, the relaxation time of the system is increased, so as to determine the optimal quenching gas pressure in the alkali metal atom gas cell of the atomic magnetic field measurement device, improve the sensitivity and overall performance of the device, and is applicable to atomic spin magnetic field and inertial measurement systems. Background Art

[0002] With the proposal and development of new theories and new technologies in the field of quantum precision measurement, various precision measurement instruments and equipment based on quantum effects are constantly breaking through the measurement limits of traditional instruments. Among them, the atomic spin magnetic field measurement device based on the SERF effect (SERF, Spin-Exchange Relaxation-Free) has a measurement level of ultra-high precision and sensitivity, and can play a significant role in frontier basic physical research, which is of great significance to the scientific and technological development of our country.

[0003] In the SERF atomic spin magnetic field measurement device, the atomic polarizability of the alkali metal atom gas cell as a sensitive element determines the sensitivity of the device. Increasing the spin coherence time of alkali metal atoms is one of the important means to improve the sensitivity of the device. The factors affecting spin relaxation include spin-exchange collision relaxation, spin-destruction collision relaxation, wall collision relaxation, and magnetic field gradient relaxation. The excited alkali metal atoms return to the ground state by spontaneously emitting photons. When the photons are reabsorbed by the alkali metal atoms, it will lead to the loss of spin polarization, thereby reducing the polarization degree of the atoms and affecting the sensitivity of the device. Adding a quenching gas in the gas cell can absorb the photons radiated by the alkali metal atoms, thereby improving the sensitivity of the system. However, the interaction between the quenching gas and the alkali metal atoms will cause spin-destruction collision relaxation and affect the relaxation rate of the system. Too much quenching gas will instead reduce the sensitivity of the device. Therefore, determining the gas pressure of the quenching gas is a very important task. However, there is currently no method to quantitatively determine the optimal content of the quenching gas in the working state of the device. The present invention determines the optimal content of the quenching gas by detecting the fluorescence intensity and the device output response corresponding to the gas cells with different gas pressures. This method can also be applied to a series of atomic sensors containing alkali metals and quenching gases, such as atomic inertial measurement devices based on the SERF effect, and has broad application prospects. Summary of the Invention

[0004] In view of the deficiencies of the prior art, the present invention proposes a method for measuring the optimal quenching gas pressure in an alkali metal gas cell based on the atomic fluorescence effect. By using the quenching gas to absorb the photons spontaneously emitted by alkali metal atoms, and detecting the fluorescence intensity and the output response of the device corresponding to the gas cells with different quenching gas pressures, the spin-destruction collision relaxation is reduced, and the relaxation time of the system is increased, thereby determining the optimal quenching gas pressure in the alkali metal atom gas cell of the atomic magnetic field measurement device, improving the sensitivity and overall performance of the device, and being applicable to atomic spin magnetic field and inertial measurement systems.

[0005] The technical solution of the present invention is as follows: A method for measuring the optimal quenching gas pressure in an alkali metal gas cell based on the atomic fluorescence effect, characterized by comprising the following steps: Step 1, prepare a series of alkali metal atom gas cells with different quenching gas pressures; Step 2, select one of the alkali metal atom gas cells in Step 1, place it in the atomic magnetic field measurement and fluorescence detection device, and start the atomic magnetic field measurement and fluorescence detection device to make the atoms in the alkali metal atom gas cell reach the SERF state; Step 3, pump the alkali metal atoms with a laser to polarize them; Step 4, use a spectrometer to detect the fluorescence wavelength and intensity emitted by the alkali metal atom gas cell; Step 5, determine the magnitude of the magnetic field to be measured by detecting the change in the optical rotation angle of the light; Step 6, judge whether the magnetic field measurement output response signal is the maximum value. If not, return to Step 1 to select the next alkali metal atom gas cell with a different quenching gas pressure; if so, enter Step 7; Step 7, determine the optimal quenching gas pressure in the alkali metal gas cell.

[0006] The optimal quenching gas pressure in the alkali metal gas cell determined in Step 7 can avoid increasing the spin-destruction collision relaxation due to excessive quenching gas, and at the same time avoid reducing the polarization rate of alkali metal atoms due to insufficient quenching gas.

[0007] The alkali metal atoms in the alkali metal atom gas cell in Step 1 are pure potassium, pure rubidium or a mixture of potassium and rubidium. The alkali metal atom gas cell is filled with buffer gas helium and quenching gas nitrogen. The pressures of the buffer gas and the quenching gas are determined during the gas cell filling process. The quenching gas pressures of the first to fifth alkali metal atom gas cells are 40 Torr, 45 Torr, 50 Torr, 55 Torr and 60 Torr respectively, and the alkali metal atom densities in each alkali metal atom gas cell are kept consistent.

[0008] Step 4 includes: if an increase in fluorescence intensity is detected, it indicates that the quenching gas is insufficient; if a decrease in fluorescence intensity is detected, it indicates that the quenching gas has effectively absorbed photons. The quenching gas absorbs the photons released by the spontaneous radiative transition of alkali metal atoms to prevent the photons from being reabsorbed by the alkali metal atoms, thereby reducing the pumping efficiency, and further preventing the reduction of the output response signal intensity of the magnetic field measurement. If no fluorescence intensity is detected, it indicates that an excessive amount of quenching gas will increase the spin-destruction collision relaxation and reduce the sensitivity of the magnetic field measurement device.

[0009] It includes the following expressions: , where is the spin-destruction collision relaxation between alkali metal atoms and the quenching gas nitrogen, is the density of the quenching gas nitrogen, is the effective collision cross-sectional area of the quenching gas nitrogen, is the relative thermal motion rate of the quenching gas nitrogen.

[0010] The atomic magnetic field measurement and fluorescence detection device includes a pumping laser, a first reflector, a first half-wave plate, a first polarization beam splitter prism, a first lens beam expander system, a first aperture, a second half-wave plate, a second polarization beam splitter prism, a second reflector, a first quarter-wave plate, an alkali metal atomic gas cell, an integrating sphere, a multimode optical fiber, and a fluorescence spectrometer, which are connected in sequence. The alkali metal atomic gas cell is located in an oven, the oven is located in a three-axis magnetic compensation coil, the three-axis magnetic compensation coil is located in a thermal insulation layer, and the thermal insulation layer is located in a shielding barrel.

[0011] The atomic magnetic field measurement and fluorescence detection device includes a detection laser, a third reflector, a third half-wave plate, a third polarization beam splitter prism, a second lens beam expander system, a second aperture, a fourth half-wave plate, a fourth polarization beam splitter prism, a first Glan-Taylor prism, a photoelastic modulator, a second quarter-wave plate, an alkali metal atomic gas cell, a second Glan-Taylor prism, a convex lens, and a photodetector, which are connected in sequence. The third polarization beam splitter prism is connected to a wavelength meter, and the third polarization beam splitter prism and the wavelength meter are used to determine the wavelength of the detection light for detecting different alkali metal atoms.

[0012] Step 1 includes the following expressions:

[0013] where is the density of the quenching gas nitrogen, P is the pressure of the quenching gas, k B is the Boltzmann constant, and T is the temperature of the gas cell.

[0014] The technical effects of the present invention are as follows: The method for measuring the optimal quenching gas pressure of an alkali metal gas cell based on the atomic fluorescence effect heats and shields the alkali metal atoms in the gas cell in an atomic spin ultra-high sensitivity magnetic field measurement device, and uses circularly polarized light to pump the alkali metal atoms to reach the spin-exchange relaxation-free (SERF) state. The quenching gas is used to absorb the photons spontaneously emitted by the alkali metal atoms, suppress the frequency broadening caused by the re-absorption of photons, and at the same time, by detecting the output response of the device corresponding to gas cells with different gas pressures, the maximum output signal is found to determine the optimal content of the quenching gas. The decrease in fluorescence intensity indicates that the quenching gas has effectively absorbed photons. The collision between the quenching gas and the alkali metal atoms will cause spin-destroying relaxation, reduce the relaxation time of the system, and thus reduce the signal intensity and affect the sensitivity of the device. The present invention determines the optimal quenching gas pressure, reduces the spin-destroying collision relaxation, increases the relaxation time of the system, and effectively improves the sensitivity and overall performance of the magnetic field measurement device.

[0015] The advantages of the present invention compared with the prior art are as follows: The optimal quenching gas pressure of the alkali metal atom gas cell can be confirmed by the fluorescence detection method, which can reduce the spin-destroying collision relaxation caused by excessive quenching gas in the gas cell, increase the relaxation time of the system, and at the same time avoid the insufficient quenching gas from affecting the polarizability of the alkali metal atoms, effectively improving the sensitivity and overall performance of the magnetic field measurement device. Brief Description of the Drawings

[0016] Figure 1 It is a schematic structural diagram of an atomic magnetic field measurement and fluorescence detection device involved in implementing the method for measuring the optimal quenching gas pressure of an alkali metal gas cell based on the atomic fluorescence effect of the present invention.

[0017] Figure 2 It is a schematic flow diagram of implementing the method for measuring the optimal quenching gas pressure of an alkali metal gas cell based on the atomic fluorescence effect of the present invention. Figure 2It includes Step 1: Select alkali metal atomic cells with different quenching gas pressures (for example, 40 Torr, 45 Torr, 50 Torr, 55 Torr, 60 Torr respectively); Step 2: Place the alkali metal cell in an oven inside a shielding barrel and heat it to reach the SERF state (SERF, Spin-Exchange Relaxation-Free); Step 3: Pump the alkali metal atoms with a laser to polarize them; Step 4: Use a spectrometer to detect the fluorescence wavelength and intensity emitted by the alkali metal atomic cell; Step 5: Determine the magnitude of the magnetic field to be measured by detecting the change in the optical rotation angle of the detection light; Step 6: Judge whether the magnetic field measurement output response signal is the maximum value. If not, return to Step 1 to select the next alkali metal atomic cell with a different quenching gas pressure. If so, enter Step 7 to determine the optimal quenching gas pressure of the alkali metal cell.

[0018] Figure 3 It is a schematic diagram of the fluorescence spectrum emitted by a potassium-rubidium mixed alkali metal cell at 180 °C. Figure 3 In it, the abscissa is the wavelength (nm, and the scale values are 400, 410, ···, 430), and the ordinate is the relative intensity (dimensionless, and the scale values are 0, 5000, ···, 30000). Figure 3 The two peaks in it are at wavelengths of 414.98 nm and 423.22 nm respectively.

[0019] Appendix Figure 1 The marking explanations are as follows: 1 - Pumping laser; 2 - First reflector; 3 - First half-wave plate; 4 - First polarization beam splitter prism; 5 - First lens beam expander system; 6 - First aperture; 7 - Second half-wave plate; 8 - Second polarization beam splitter prism; 9 - Second reflector; 10 - First quarter-wave plate; 11 - Shielding barrel; 12 - Oven; 13 - Alkali metal cell; 14 - Triaxial magnetic compensation coil; 15 - Thermal insulation layer; 16 - Detection laser; 17 - Third reflector; 18 - Third half-wave plate; 19 - Third polarization beam splitter prism; 20 - Wavemeter; 21 - Second lens beam expander system; 22 - Second aperture; 23 - Fourth half-wave plate; 24 - Fourth polarization beam splitter prism; 25 - First Glan-Taylor prism; 26 - Photoelastic modulator; 27 - Second quarter-wave plate; 28 - Second Glan-Taylor prism; 29 - Convex lens; 30 - Photoelectric detector; 31 - Integrating sphere; 32 - Multimode optical fiber; 33 - Fluorescence spectrometer. Detailed implementation manners

[0020] The following describes the present invention in conjunction with the accompanying drawings ( Figures 1-3 ) and embodiments.

[0021] Figure 1It is a schematic structural diagram of an atomic magnetic field measurement and fluorescence detection device involved in implementing the method for measuring the optimal quenching gas pressure of an alkali metal gas cell based on the atomic fluorescence effect of the present invention. Figure 2 It is a schematic flow diagram of the method for measuring the optimal quenching gas pressure of an alkali metal gas cell based on the atomic fluorescence effect of the present invention. Figure 3 It is a schematic diagram of the fluorescence spectrum emitted by a potassium-rubidium mixed alkali metal gas cell at 180 °C. Figure 3 In [reference], a laser with a wavelength of 770 nm is used to excite the fluorescence spectrum emitted by a potassium-rubidium mixed gas cell (density ratio K:Rb = 1:59.17, broadening of 40.98 Hz, helium gas pressure of 400 Torr, nitrogen gas pressure of 50 Torr) at 180 °C, and two relatively obvious peaks can be obtained, with wavelengths of 414.98 nm and 423.22 nm respectively. Figures 1 to 3 As shown in [reference], the method for measuring the optimal quenching gas pressure of an alkali metal gas cell based on the atomic fluorescence effect includes the following steps: Step 1, prepare a series of alkali metal atomic gas cells with different quenching gas pressures; Step 2, select one of the alkali metal atomic gas cells in Step 1, place it in the atomic magnetic field measurement and fluorescence detection device, and start the atomic magnetic field measurement and fluorescence detection device to make the atoms in the alkali metal atomic gas cell reach the SERF state; Step 3, use a laser to pump the alkali metal atoms to polarize them; Step 4, use a spectrometer to detect the fluorescence wavelength and intensity emitted by the alkali metal atomic gas cell; Step 5, determine the magnitude of the magnetic field to be measured by detecting the change in the optical rotation angle of the detection light; Step 6, determine whether the magnetic field measurement output response signal is the maximum value. If not, return to Step 1 to select the next alkali metal atomic gas cell with a different quenching gas pressure; if so, enter Step 7; Step 7, determine the optimal quenching gas pressure of the alkali metal gas cell.

[0022] The optimal quenching gas pressure of the alkali metal gas cell determined in Step 7 can avoid increasing the spin-destruction collision relaxation due to excessive quenching gas, and at the same time avoid reducing the polarization rate of alkali metal atoms due to insufficient quenching gas. The alkali metal atoms in the alkali metal atomic gas cell in Step 1 are pure potassium, pure rubidium, or potassium-rubidium mixed atoms. The alkali metal atomic gas cell is filled with buffer gas helium and quenching gas nitrogen, and the pressures of the buffer gas and the quenching gas have been determined when filling the gas cell. The quenching gas pressures of the first to fifth alkali metal atomic gas cells are 40 Torr, 45 Torr, 50 Torr, 55 Torr, and 60 Torr respectively, and the alkali metal atom densities in each alkali metal atomic gas cell are kept consistent.

[0023] Step 4 includes: if an increase in fluorescence intensity is detected, it indicates that the quenching gas is insufficient; if a decrease in fluorescence intensity is detected, it indicates that the quenching gas has effectively absorbed photons. The quenching gas absorbs the photons released by the spontaneous radiative transition of alkali metal atoms to prevent the photons from being reabsorbed by alkali metal atoms and reducing the pumping efficiency, thereby avoiding a decrease in the intensity of the magnetic field measurement output response signal. If no fluorescence intensity is detected, it indicates that an excessive amount of quenching gas will increase the spin-destruction collision relaxation and reduce the sensitivity of the magnetic field measurement device.

[0024] It includes the following expressions: , where is the spin-destruction collision relaxation between alkali metal atoms and the quenching gas nitrogen, is the density of the quenching gas nitrogen, is the effective collision cross-sectional area of the quenching gas nitrogen, is the relative thermal motion rate of the quenching gas nitrogen.

[0025] The atomic magnetic field measurement and fluorescence detection device includes a pumping laser 1, a first reflecting mirror 2, a first half-wave plate 3, a first polarization beam splitter prism 4, a first lens beam expander system 5, a first aperture 6, a second half-wave plate 7, a second polarization beam splitter prism 8, a second reflecting mirror 9, a first quarter-wave plate 10, an alkali metal gas cell 13, an integrating sphere 31, a multimode optical fiber 32, and a fluorescence spectrometer 33, which are connected in sequence. The alkali metal gas cell 13 is located in an oven 12, the oven 12 is located in a three-axis magnetic compensation coil 14, the three-axis magnetic compensation coil 14 is located in a thermal insulation layer 15, and the thermal insulation layer 15 is located in a shielding barrel 11. The atomic magnetic field measurement and fluorescence detection device also includes a detection laser 16, a third reflecting mirror 17, a third half-wave plate 18, a third polarization beam splitter prism 19, a second lens beam expander system 21, a second aperture 22, a fourth half-wave plate 23, a fourth polarization beam splitter prism 24, a first Glan-Taylor prism 25, a photoelastic modulator 26, a second quarter-wave plate 27, the alkali metal gas cell 13, a second Glan-Taylor prism 28, a convex lens 29, and a photodetector 30, which are connected in sequence. The third polarization beam splitter prism 19 is connected to a wavelength meter 20, and the third polarization beam splitter prism 19 and the wavelength meter 20 are used to determine the wavelength of the detection light for detecting different alkali metal atoms.

[0026] Step 1 includes the following expressions:

[0027] where is the density of the quenching gas nitrogen, P is the pressure of the quenching gas, k B is the Boltzmann constant, and T is the temperature of the gas cell.

[0028] The present invention discloses a method for measuring the optimal quenching gas pressure in an alkali metal gas cell based on the atomic fluorescence effect. By heating and shielding the alkali metal atoms in the alkali metal gas cell in an atomic spin ultra-high sensitivity magnetic field measurement device, circularly polarized light is used to pump the alkali metal atoms to reach the Spin-Exchange Relaxation-Free (SERF) state. The quenching gas absorbs the photons spontaneously emitted by the alkali metal atoms, inhibits the frequency broadening caused by the re-absorption of photons, and at the same time, by detecting the output response of the device corresponding to gas cells with different gas pressures, the maximum output signal is found to determine the optimal content of the quenching gas. The decrease in fluorescence intensity indicates that the quenching gas has effectively absorbed photons. The collision between the quenching gas and the alkali metal atoms will cause spin-destruction relaxation, reducing the relaxation time of the system and thus decreasing the signal intensity and affecting the sensitivity of the device. The present invention determines the optimal quenching gas pressure, reduces the spin-destruction collision relaxation, increases the relaxation time of the system, and effectively improves the sensitivity and overall performance of the magnetic field measurement device.

[0029] In view of the deficiencies of the prior art, the present invention proposes a method for measuring the optimal quenching gas pressure in an alkali metal gas cell based on the atomic fluorescence effect. After the pumping light excites the alkali metal atoms, the atoms will release photons and return to the ground state through spontaneous emission. The quenching gas in the gas cell will absorb the photons released by the atoms. By placing an integrating sphere outside the oven of the alkali metal gas cell and connecting it to a spectrometer through a multimode optical fiber, the fluorescence intensity of the photons released by the alkali metal atoms is obtained. By detecting the fluorescence intensity and the output response of the device corresponding to gas cells with different gas pressures, the maximum output signal is found to determine the optimal content of the quenching gas. The decrease in fluorescence intensity indicates that the quenching gas has effectively absorbed photons. The present invention can effectively increase the polarization rate of alkali metal atoms and avoid increasing the spin-destruction collision relaxation, and can effectively improve the sensitivity and overall performance of the magnetic field measurement device.

[0030] Reference Figure 1 As shown, a method for measuring the optimal quenching gas pressure in an alkali metal gas cell based on the atomic fluorescence effect. After the pumping laser excites the alkali metal atoms, the atoms will release photons and return to the ground state through spontaneous emission. The quenching gas in the gas cell will absorb the photons released by the atoms. By placing an integrating sphere outside the oven of the alkali metal gas cell and connecting it to a spectrometer through a multimode optical fiber, the fluorescence intensity of the photons released by the alkali metal atoms is obtained. When the quenching gas is excessive, no fluorescence will appear, which will increase the destruction relaxation of the system. By detecting the output response of the device corresponding to gas cells with different gas pressures, the maximum output signal is found to determine the optimal content of the quenching gas, avoiding increasing the spin-destruction collision relaxation of the device and avoiding the decrease in the polarization rate of alkali metal atoms due to insufficient quenching gas.

[0031] The pumping system of the atomic magnetic field measurement device is such that the light from the pumping laser 1 sequentially passes through the first half-wave plate 3, the first polarization beam splitter prism 4, the first lens beam expander system 5, and the first aperture 6 to obtain pumping light with appropriate power and spot size. Then, it sequentially passes through the second half-wave plate 7, the second polarization beam splitter prism 8, and the first quarter-wave plate 10 to be converted into circularly polarized light, which is incident along the z-axis to excite alkali metal atoms.

[0032] The alkali metal gas cell 13 can be a gas cell of pure potassium, pure rubidium, or a potassium-rubidium mixture, and is filled with buffer gas (such as helium) and quenching gas (such as nitrogen). The gas cell is placed in the oven 12 for heating. The oven 12 is located in the three-axis magnetic compensation coil 14, and the three-axis compensation coil 14 is located in the shielding barrel 11 to ensure that the atoms can meet the conditions of the SERF state.

[0033] The function of the quenching gas is that since the excited alkali metal atoms will transition to the ground state by emitting photons, if the photons are reabsorbed by the atoms, it will reduce the pumping efficiency, affect the signal intensity, and cause frequency broadening. Therefore, the quenching gas is added to absorb the photons released by the radiative transition.

[0034] The device of the fluorescence detection system is that the integrating sphere 31 is placed at the outlet of the thermal insulation layer 15 of the oven 12 to collect the fluorescence emitted by the gas cell. The integrating sphere 31 is connected to the spectrometer 33 through the multimode optical fiber 32 to obtain the fluorescence intensity signal. When the quenching gas is insufficient, the fluorescence released by the alkali metal atoms will be detected.

[0035] The detection system of the atomic magnetic field measurement device is amplified by the detection laser 16 passing through the third half-wave plate 18, the third polarization beam splitter prism 19, the second lens beam expander system 21, and the second aperture 22. Then, the linearly polarized light obtained by passing through the fourth half-wave plate 23, the fourth polarization beam splitter prism 24, the first Glan-Taylor prism (polarizer) 25, the photoelastic modulator 26, and the second quarter-wave plate 27 is incident along the x-axis to interact with the alkali metal atoms. The change in the optical rotation angle is detected using the second Glan-Taylor prism (analyzer) 28, the convex lens 29, and the photodetector 30. The wavelength of the detection light is determined using the third polarization beam splitter prism 19 and the wavelength meter 20.

[0036] Reference Figure 2As shown in the figure, we selected gas chambers with quenching gas pressures of 40 Torr, 45 Torr, 50 Torr, 55 Torr, and 60 Torr respectively and the same alkali metal atom density. The gas chambers were placed in an oven inside a shielding barrel and heated to ensure that the alkali metal atoms met the conditions for the SERF state. The alkali metal atoms were pumped with a laser to polarize them. The fluorescence wavelength and intensity emitted by the alkali metal gas chamber were detected using a spectrometer. At the same time, the output response signal of the magnetic field measurement device was recorded by detecting the change in the optical rotation angle of the light. When the response signal of the device reached the maximum value, the quenching gas pressure inside the corresponding alkali metal gas chamber was the optimal gas pressure.

[0037] A method for measuring the optimal quenching gas pressure of an alkali metal gas chamber based on the atomic fluorescence effect. The alkali metal atom gas chamber is placed in an oven of an atomic magnetic field measurement device and heated, and then placed inside a shielding device. A circularly polarized light beam is used to pump the gas chamber to make the alkali metal atoms reach the SERF state. To increase the polarization rate of the alkali metal, a quenching gas is filled in the gas chamber to absorb the photons spontaneously emitted by the alkali metal atoms. By detecting the output response of the device corresponding to gas chambers with different gas pressures, the maximum output signal is found to determine the optimal content of the quenching gas. The decrease in fluorescence intensity indicates that the quenching gas has effectively absorbed the photons. However, the collision between the quenching gas and the alkali metal atoms will cause spin-destruction relaxation, reducing the relaxation time of the system and thus decreasing the signal intensity and affecting the sensitivity of the device. Finally, the linearly polarized light interacts with the atoms after passing through the gas chamber, and the magnetic field is measured by detecting the change in the optical rotation angle. By determining the optimal quenching gas pressure, the present invention reduces the spin-destruction collision relaxation, increases the relaxation time of the system, and effectively improves the sensitivity and overall performance of the magnetic field measurement device.

[0038] The device of the fluorescence detection system is to place an integrating sphere at the outlet of the outer insulation layer of the oven to collect the fluorescence emitted by the gas chamber, and connect it to a spectrometer through a multimode optical fiber to obtain the fluorescence signal, which can reflect the wavelength and intensity of the fluorescence. The wavelength is related to the type of alkali metal atoms. When the quenching gas is insufficient, the fluorescence released by the alkali metal atoms will be detected. When the quenching gas is excessive, no fluorescence will appear, which will increase the destruction relaxation of the system. The relationship between spin-destruction relaxation and the quenching gas is expressed as , where is the spin-destruction relaxation between alkali metal atoms, is the spin-destruction relaxation between alkali metal atoms and buffer gas (helium), is the spin-destruction relaxation between alkali metal atoms and quenching gas (nitrogen), which is related to the density of the quenching gas and can be expressed as , where is the density of the quenching gas, is the effective collision cross-sectional area. is the relative thermal motion rate. According to the ideal gas equation, the relationship between the density and pressure of the quenching gas can be obtained , where P is the pressure of the quenching gas k B = 1.38×10 -23 J / K is the Boltzmann constant, and T is the temperature of the gas chamber. By measuring gas chambers with different alkali metal atoms at different quenching gas pressures, the gas chamber with the maximum output response of the device is obtained, and the corresponding pressure is the optimal quenching gas pressure of the device

[0039] The content not described in detail in the specification of the present invention belongs to the prior art well-known to those skilled in the art. It is hereby specified that the above description helps those skilled in the art to understand the present invention, but does not limit the protection scope of the present invention. Any implementation that makes equivalent replacements, modifications and improvements, and / or simplifies the above description without departing from the substantial content of the present invention falls within the protection scope of the present invention

Claims

1. A method for measuring the optimal quenching gas pressure of an alkali metal gas chamber based on the atomic fluorescence effect, characterized in that: The following steps are involved: Step 1, preparing a series of alkali metal atom gas chambers with different quenching gas pressures; Step 2, selecting an alkali metal atom gas cell in step 1, placing it in an atomic magnetic field measurement and fluorescence detection device, starting the atomic magnetic field measurement and fluorescence detection device, and making the atoms in the alkali metal atom gas cell reach a SERF state; Step 3, using laser to pump alkali metal atoms to polarize them; Step 4, using a spectrometer to detect the wavelength and intensity of fluorescence emitted by the alkali metal atom gas chamber; Step 5, determining the magnitude of the magnetic field to be measured by detecting the change in the optical rotation angle of the light; Step 6, determining whether the magnetic field measurement output response signal is a maximum value, if not, returning to step 1 to select the next alkali metal atom gas chamber with a different quenching gas pressure; if yes, proceeding to step 7; Step 7, determining the optimal quenching gas pressure of the alkali metal gas chamber.

2. The method for measuring the optimal quenching gas pressure of an alkali metal gas chamber based on the atomic fluorescence effect according to claim 1, characterized in that: The optimal quenching gas pressure of the alkali metal gas chamber determined in step 7 can avoid increasing spin-destruction collision relaxation due to excessive quenching gas, and at the same time avoid reducing the polarizability of the alkali metal atoms due to insufficient quenching gas.

3. The method for measuring the optimal quenching gas pressure of an alkali metal gas chamber based on the atomic fluorescence effect according to claim 1, characterized in that: In step 1, the alkali metal atoms in the alkali metal atom gas chamber are pure potassium, pure rubidium or potassium-rubidium mixed atoms, and the alkali metal atom gas chamber is filled with a buffer gas helium and a quenching gas nitrogen, wherein the pressures of the buffer gas and the quenching gas are determined when the gas chamber is filled, and the quenching gas pressures of the first alkali metal atom gas chamber to the fifth alkali metal atom gas chamber are 40 Torr, 45 Torr, 50 Torr, 55 Torr and 60 Torr, respectively, and the density of alkali metal atoms in each alkali metal atom gas chamber remains consistent.

4. The method for measuring the optimal quenching gas pressure of an alkali metal gas chamber based on the atomic fluorescence effect according to claim 1, characterized in that: Step 4 includes: if an increase in fluorescence intensity is detected, it indicates that the quenching gas is insufficient; if a decrease in fluorescence intensity is detected, it indicates that the quenching gas has effectively absorbed photons. The quenching gas absorbs photons released by spontaneous radiation transitions of alkali metal atoms to avoid photons being reabsorbed by alkali metal atoms and reducing the pumping efficiency, thereby avoiding reducing the intensity of the magnetic field measurement output response signal; if no fluorescence intensity is detected, it indicates that there is an excess of quenching gas, which will increase spin-destructive collision relaxation and reduce the sensitivity of the magnetic field measurement device.

5. The method for measuring the optimal quenching gas pressure of an alkali metal gas chamber based on the atomic fluorescence effect according to claim 4, characterized in that: Include the following expressions: , in is the spin-destroying collisional relaxation between the alkali metal atoms and the quenching gas nitrogen, is the quench gas nitrogen density, is the effective collision cross-sectional area of ​​quenching gas nitrogen, is the relative thermal motion rate of quenching gas nitrogen.

6. The method for measuring the optimal quenching gas pressure of an alkali metal gas chamber based on the atomic fluorescence effect according to claim 1, characterized in that: The atomic magnetic field measurement and fluorescence detection device includes a pumping laser, a first reflector, a first half-wave plate, a first polarization beam splitter, a first lens beam expansion system, a first aperture, a second half-wave plate, a second polarization beam splitter, a second reflector, a first quarter-wave plate, an alkali metal gas chamber, an integrating sphere, a multimode optical fiber and a fluorescence spectrometer connected in sequence. The alkali metal gas chamber is located in an oven, the oven is located in a three-axis magnetic compensation coil, the three-axis magnetic compensation coil is located in a thermal insulation layer, and the thermal insulation layer is located in a shielding barrel.

7. The method for measuring the optimal quenching gas pressure of an alkali metal gas chamber based on the atomic fluorescence effect according to claim 1, characterized in that: The atomic magnetic field measurement and fluorescence detection device includes a detection laser, a third reflector, a third half-wave plate, a third polarization beam splitter prism, a second lens beam expansion system, a second aperture, a fourth half-wave plate, a fourth polarization beam splitter prism, a first Glan-Taylor prism, a photoelastic modulator, a second quarter-wave plate, an alkali metal gas chamber, a second Glan-Taylor prism, a convex lens and a photodetector, which are connected in sequence. The third polarization beam splitter prism is connected to a wavelength meter, and the third polarization beam splitter prism and the wavelength meter are used to determine the wavelength of the detection light for detection of different alkali metal atoms.

8. The method for measuring the optimal quenching gas pressure of an alkali metal gas chamber based on the atomic fluorescence effect according to claim 1, characterized in that: Step 1 includes the following expressions: , in is the quenching gas nitrogen density, P is the quenching gas pressure, k B is the Boltzmann constant, and T is the temperature of the gas chamber.

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