Magnetic field measurement method based on ultrashort pulse laser pumping of atomic spins with adjustable repetition rate

Abstract

A magnetic field measurement method based on ultrashort pulse laser pumping of atomic spins with adjustable repetition rate can improve the uniformity and stability of polarizability of alkali metal atoms by adopting ultrashort pulse laser with adjustable repetition rate as a pumping light source, and is characterized in that, in a pumping system of an atomic magnetic field measurement device, a beam of light emitted by an ultrashort pulse laser is optimized from a pulse time interval t to nt, where n is an integer greater than 1, and a beam of light with a pulse time interval nt is changed into three beams of light with a pulse time interval of nt / 3 passing through a gas chamber, and by optimizing the repetition frequency of the ultrashort pulse laser, the relaxation rate and polarizability distribution of the alkali metal atoms in the gas chamber are stabilized to an optimal value, thereby maximizing the amplitude output of the response signal.

Description

Technical Field

[0001] The present invention relates to the technical field of atomic magnetic field measurement, and in particular to a magnetic field measurement method based on ultrashort pulse laser pumping of atomic spins with adjustable repetition frequency. The uniformity and stability of polarizability of alkali metal atoms can be improved by using ultrashort pulse laser with adjustable repetition frequency as a pumping light source. Background Art

[0002] In recent years, the development of ultrashort pulse lasers has promoted people's understanding of the interaction mechanism between light and matter. The emergence of ultrashort and ultra-intense pulse lasers has made the nonlinear effect of the interaction between light and atoms more significant, making the manipulation of atomic states by ultrashort pulse lasers more precise. This advanced technology has brought new possibilities and application prospects to many fields.

[0003] In magnetic field measurement based on atomic spin effect, the use of ultrashort pulse lasers to polarize alkali metal atoms (such as potassium, rubidium, cesium, etc.) has significant advantages. Compared with traditional continuous lasers, the peak power of ultrashort pulse lasers is much greater than the saturation absorption power of alkali metal atoms, and can efficiently pump the ground state atoms inside the gas chamber to the excited state uniformly, reducing the influence of uneven polarizability distribution on the sensitivity of the atomic magnetic field measurement device, thereby improving the sensitivity of the magnetic field measurement device and overcoming the problem of strong absorption of pumping light in traditional methods, which leads to the formation of a large atomic polarization gradient along the pumping direction.

[0004] The present invention replaces the continuous light pumping laser in the pumping system with an ultrashort pulse laser with adjustable repetition frequency, adjusts the repetition frequency of the pulse laser through the information of atomic polarizability and relaxation rate, and precisely regulates the atoms through the ultrashort pulse laser to stabilize the atomic polarizability in the gas chamber at a desired value, thereby reducing the influence of uneven polarizability distribution on the sensitivity of the atomic magnetic field measuring device. This innovation is conducive to improving the sensitivity of the SERF atomic magnetic field measuring device (SERF, spin-exchange relaxation free, no spin exchange relaxation), and fills the gap in the current application of ultrashort pulse laser pumping methods with adjustable repetition frequency in magnetic field measuring devices based on atomic spins. Summary of the invention

[0005] The present invention aims at the defects or deficiencies of the prior art and provides a magnetic field measurement method based on ultrashort pulse laser pumping atomic spins with adjustable repetition frequency. The ultrashort pulse laser precisely polarizes alkali metal atoms. Under the action of an external magnetic field, the polarized atoms will precess, and the magnetic field measurement is achieved by detecting the atomic spin precession signal. Since the average power of the ultrashort pulse laser is 20mW, the pulse width is 100fs, and the repetition frequency is 80MHz, its peak power significantly exceeds the saturation absorption power of the alkali metal atoms, so that the ultrashort pulse laser can uniformly polarize the alkali metal atoms at various locations in the gas chamber, avoiding the polarization rate gradient caused by the large optical depth in continuous laser pumping, reducing the negative impact of uneven polarization rate distribution on the sensitivity of the atomic magnetic field measurement device, and improving the sensitivity of the measurement device.

[0006] The technical solution of the present invention is as follows:

[0007] The magnetic field measurement method based on ultrashort pulse laser pumping of atomic spins with adjustable repetition rate is characterized in that it includes optimizing a beam of light emitted by an ultrashort pulse laser from a pulse time interval t to nt in the pumping system of the atomic magnetic field measurement device, where n is an integer greater than 1, and converting the beam of light with a pulse time interval nt into three beams of light with a pulse time interval of nt / 3 passing through the gas chamber, and by optimizing the repetition frequency of the ultrashort pulse laser, stabilizing the relaxation rate and polarizability distribution of the alkali metal atoms in the gas chamber to an optimal value, thereby maximizing the amplitude output of the response signal.

[0008] t=1*10 -8 Seconds~1.25 *10 -8 Second.

[0009] n=30~50.

[0010] The ultrashort pulse laser emitted by the ultrashort pulse laser is connected to the first depolarizing beam splitter prism through an optical isolator, a first polarizer, a Pockels cell and a first analyzer in sequence. The Pockels cell is connected to a Pockels cell controller. The Pockels cell controller applies a voltage to the electrodes of the Pockels cell to change the refractive index of the crystal, thereby changing the polarization state of the laser. The polarizer and the analyzer are then used to control the passage or blocking of the ultrashort pulse laser so that the pulse time interval t becomes nt, and a beam of light with a pulse time interval nt is transmitted to the first depolarizing beam splitter prism.

[0011] The x-axis transmission side of the first depolarizing beam splitter is connected to the first reflector through the second depolarizing beam splitter, the z-axis reflection side of the second depolarizing beam splitter is connected to the second absorption mirror, the inverse z-axis reflection side of the second depolarizing beam splitter is connected to the first absorption mirror, the inverse z-axis reflection side of the first depolarizing beam splitter is connected to the second reflector through the third depolarizing beam splitter, the inverse x-axis reflection side of the third depolarizing beam splitter is connected to the third reflector, the x-axis side of the third depolarizing beam splitter is connected to the third absorption mirror, and the z-axis side of the first depolarizing beam splitter passes three beams of light with a pulse time interval of nt / 3 through the gas chamber to uniformly and efficiently pump the ground state atoms inside the gas chamber to an excited state.

[0012] The first reflector is mounted on a first displacement platform, the second reflector is mounted on a second displacement platform, the third reflector is mounted on a third displacement platform, and the first displacement platform, the second displacement platform and the third displacement platform are connected to a host computer via a displacement platform controller respectively.

[0013] The air chamber is located in a non-magnetic electric heating system, the non-magnetic electric heating system is located in a three-axis compensation coil, the three-axis compensation coil is located in a shielding barrel, and the three-axis compensation coil is connected to a signal generator.

[0014] The detection system of the atomic magnetic field measuring device comprises a detection laser, which is connected to a host computer via a second polarizer, a photoelastic modulator, a quarter wave plate, an air chamber, a second polarizer, a photodetector and a lock-in amplifier in sequence.

[0015] The average power of the ultrashort pulse laser in the pumping system is 20 mW, the pulse width is 100 fs, the repetition frequency is 80 MHz, and the peak power thereof significantly exceeds the saturation absorption power of the alkali metal atoms.

[0016] The technical effects of the present invention are as follows: The present invention is based on a magnetic field measurement method for pumping atomic spins with an ultrashort pulse laser with an adjustable repetition rate. By using an ultrashort pulse laser with an adjustable repetition rate as a pumping light source, the uniformity and stability of the polarizability of alkali metal atoms can be improved. By optimizing the repetition frequency of the ultrashort pulse laser, the relaxation rate and polarizability distribution of the alkali metal atoms are stabilized to the optimal value, thereby maximizing the amplitude output of the response signal. The average power of the ultrashort pulse laser of the device is 20mW, the pulse width is 100fs, and the repetition frequency is 80MHz, and its peak power significantly exceeds the saturation absorption power of the alkali metal atoms. This enables the ultrashort pulse laser to uniformly polarize the alkali metal atoms in various locations in the gas chamber, avoiding the polarizability gradient caused by the large optical depth in continuous laser pumping, reducing the negative impact of the uneven polarizability distribution on the sensitivity of the atomic magnetic field measurement device, and improving the sensitivity of the measurement device.

[0017] The advantages of the present invention compared with the prior art are:

[0018] (1) Compared with the traditional atomic magnetic field measurement device, the problem of uneven and unstable distribution of atomic polarizability in the atomic magnetic field measurement device is solved.

[0019] (2) Using ultrashort pulse lasers, since the average power of ultrashort pulses is 20 mW, the pulse width is 100 fs, and the repetition frequency is 80 MHz, the random spontaneous relaxation process of alkali metal atoms caused by spontaneous radiation and other uniform broadening mechanisms can be ignored within the interaction time of femtoseconds. In addition, the peak power of ultrashort pulse lasers significantly exceeds the saturation absorption power of alkali metal atoms, which enables the ultrashort pulse lasers to uniformly polarize alkali metal atoms throughout the gas chamber, thereby achieving uniformity and stability of the polarization rate of alkali metal atoms in the atomic magnetic field measurement device and reducing pumping optical noise.

[0020] (3) The adjustable repetition rate ultrashort pulse pumping system optimizes the repetition frequency of the ultrashort pulse laser, stabilizes the relaxation rate and polarizability distribution of the alkali metal atoms to the optimal value, and improves the amplitude output of the magnetic field measurement signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The present invention is a schematic structural diagram of an atomic magnetic field measuring device involved in the magnetic field measuring method based on ultrashort pulse laser pumping of atomic spins with adjustable repetition frequency.

[0022] The reference numerals are as follows: 1-ultra-short pulse laser (for pumping); 2-optical isolator; 3-first polarizer; 4-Pockels cell; 5-first analyzer; 6-first depolarizing beam splitter; 7-second depolarizing beam splitter; 8-first absorption mirror; 9-first reflection mirror; 10-first displacement stage; 11-second absorption mirror; 12-third depolarizing beam splitter; 13-second reflection mirror; 14-second displacement stage; 15-third absorption mirror; 16-third reflection mirror; 17-third displacement stage; 1 8-detection laser; 19-second polarizer; 20-photoelastic modulator; 21-quarter wave plate; 22-non-magnetic electric heating system; 23-gas chamber; 24-three-axis compensation coil; 25-shielding barrel; 26-second polarizer; 27-photodetector; 28-phase-locked amplifier; 29-host computer; 30-signal generator; 31-translation stage controller; 32-Pockels cell controller; xyz-three axes of rectangular coordinate system (i.e., x-axis, y-axis, and z-axis); t-pulse time interval (t=1*10 -8 Seconds~1.25 *10 -8 seconds), n-the optimal value of the pulse time interval during the experiment (n=30~50, take an integer). DETAILED DESCRIPTION

[0023] Below is the attached figure ( Figure 1 ) and examples illustrate the present invention.

[0024] Figure 1 The structure diagram of the atomic magnetic field measuring device involved in the magnetic field measuring method based on adjustable repetition frequency ultrashort pulse laser pumping atomic spins of the present invention. Figure 1 As shown, the magnetic field measurement method based on ultrashort pulse laser pumping atomic spin with adjustable repetition frequency includes optimizing a beam of light emitted by an ultrashort pulse laser from a pulse time interval t to nt in the pumping system of the atomic magnetic field measurement device, where n is an integer greater than 1, and converting a beam of light with a pulse time interval nt into three beams of light with pulse time intervals of nt / 3 passing through the gas chamber. By optimizing the repetition frequency of the ultrashort pulse laser, the relaxation rate and polarizability distribution of the alkali metal atoms in the gas chamber are stabilized to the optimal value, thereby maximizing the amplitude output of the response signal. t=1*10 -8 Seconds~1.25 *10 -8 Seconds. n=30~50.

[0025] The ultrashort pulse laser 1 is connected to the first depolarizing prism 6 via the optical isolator 2, the first polarizer 3, the Pockels cell 4 and the first analyzer 5 in sequence; the Pockels cell 4 is connected to the Pockels cell controller 32; the Pockels cell controller 32 applies a voltage to the electrodes of the Pockels cell 4 to change the refractive index of the crystal, thereby changing the polarization state of the laser; and the use of the polarizer and the analyzer is combined to control the passage or blocking of the ultrashort pulse laser to realize the change of the pulse time interval t to nt, and transmit a beam of light with a pulse time interval nt to the first depolarizing prism 6.

[0026] The x-axis transmission side of the first depolarizing beam splitter 6 is connected to the first reflector 9 through the second depolarizing beam splitter prism 7, the z-axis reflection side of the second depolarizing beam splitter prism 7 is connected to the second absorption mirror 11, the inverse z-axis reflection side of the second depolarizing beam splitter prism 7 is connected to the first absorption mirror 8, the inverse z-axis reflection side of the first depolarizing beam splitter prism 6 is connected to the second reflector 13 through the third depolarizing beam splitter prism 12, the inverse x-axis reflection side of the third depolarizing beam splitter prism 12 is connected to the third reflector 16, the x-axis side of the third depolarizing beam splitter prism 12 is connected to the third absorption mirror 15, and the z-axis side of the first depolarizing beam splitter prism 6 passes three beams of light with a pulse time interval of nt / 3 through the gas chamber 23, so as to uniformly and efficiently pump the ground state atoms inside the gas chamber 23 to an excited state.

[0027] The first reflector 9 is mounted on the first displacement stage 10, the second reflector 13 is mounted on the second displacement stage 14, the third reflector 16 is mounted on the third displacement stage 17, and the first displacement stage 10, the second displacement stage 14 and the third displacement stage 17 are connected to the host computer 29 through the displacement stage controller 31 respectively. The gas chamber 23 is located in the non-magnetic electric heating system 22, the non-magnetic electric heating system 22 is located in the three-axis compensation coil 24, the three-axis compensation coil 24 is located in the shielding barrel 25, and the three-axis compensation coil 24 is connected to the signal generator 30. The detection system of the atomic magnetic field measurement device includes a detection laser 18, and the detection laser 18 is connected to the host computer 29 through the second polarizer 19, the photoelastic modulator 20, the quarter-wave plate 21, the gas chamber 23, the second polarizer 26, the photodetector 27 and the phase-locked amplifier 28 in sequence.

[0028] The average power of the ultrashort pulse laser in the pumping system is 20 mW, the pulse width is 100 fs, the repetition frequency is 80 MHz, and the peak power thereof significantly exceeds the saturation absorption power of the alkali metal atoms.

[0029] refer to Figure 1 As shown, a method and device for ultrashort pulse laser pumping with adjustable repetition frequency for an atomic magnetic field measuring device comprises an ultrashort pulse laser pumping system with adjustable repetition frequency, wherein the relaxation rate and polarizability distribution of alkali metal atoms are stabilized to an optimal value by optimizing the repetition frequency of the ultrashort pulse laser in the pumping system, thereby maximizing the amplitude output of the response signal. The ultrashort pulse laser (1) in the pumping system emits an average power of 20 mW, a pulse width of 100 fs, and a repetition frequency of 80 MHz, and its peak power significantly exceeds the saturation absorption power of the alkali metal atoms. This enables the ultrashort pulse laser to uniformly polarize the alkali metal atoms at various locations in the gas chamber, avoids the polarizability gradient caused by the large optical depth in continuous laser pumping, reduces the negative impact of uneven polarizability distribution on the sensitivity of the atomic magnetic field measuring device, and is conducive to improving the sensitivity of the measuring device.

[0030] The adjustable repetition frequency ultrashort pulse laser pumping system comprises an ultrashort pulse laser (1), wherein the ultrashort pulse laser (1) emits an ultrashort pulse pumping laser which passes through an optical isolator (2), a polarizer (3), a Pockels cell (4), and an analyzer (5) in sequence, and a voltage is applied to the electrodes of the Pockels cell (4) through a Pockels cell controller (32) to change the refractive index of the crystal, thereby changing the polarization state of the laser. In combination with the polarizer (3) and the analyzer (5), the passing or blocking of the pulse laser is controlled, and during this process, the pulse time interval t is precisely controlled to become nt (n is the optimal value of the pulse time interval optimized during the experiment), and then the pulse laser continues to pass through the first depolarizing beam splitter prism (6), and the transmission beam of the first depolarizing beam splitter prism (6) passes through the second depolarizing beam splitter prism (7), and the transmission beam of the second depolarizing beam splitter prism (7) passes through the first reflector (9), returns to the original path through the first depolarizing beam splitter prism (6), and is refracted into the alkali in the magnetic shielding barrel (25). The metal atom gas chamber (23) is provided. The refracted beam of the first depolarizing beam splitter (6) passes through the third depolarizing beam splitter (12), and the transmitted beam of the third depolarizing beam splitter (12) passes through the second reflector (13) and returns to the first depolarizing beam splitter (6) and is then transmitted into the alkali metal atom gas chamber (23) in the magnetic shielding barrel (25). The refracted beam of the third depolarizing beam splitter (12) passes through the third reflector (16) and returns to the first depolarizing beam splitter (6) and is then refracted into the alkali metal atom gas chamber (23) in the magnetic shielding barrel (25). The refracted beam that passes through the second depolarizing beam splitter (7) for the first time is absorbed by the first absorption mirror (8), and the refracted beam that passes through the second depolarizing beam splitter (7) for the second time is absorbed by the second absorption mirror (11), so as to prevent the pulse laser from causing harm to the laboratory and the experimental personnel. Through this process, the pulse is changed from one beam to three beams, which enter the magnetic shielding barrel in sequence, and the pulse time interval nt is changed to nt / 3. The repetition frequency of the pulse is the inverse of the time interval, and the repetition frequency of the pulsed laser can be changed through this process. A non-magnetic electric heating system (22), a three-axis magnetic compensation coil (24) and a magnetic shielding barrel (25) are sequentially arranged around the alkali metal gas chamber (23) from the inside to the outside, and the three-axis magnetic compensation coil (24) is connected to a signal generator (30). The detection system includes a detection laser (18), and the detection laser (18) is sequentially connected to a photodetector (27) through a second polarizer (19), a photoelastic modulator (20), a quarter-wave plate (21), the alkali metal gas chamber (23) and a second polarizer (26). The photodetector (27) is connected to a host computer (29) through a phase-locked amplifier (28).

[0031] The first reflector (9) is attached with a first displacement stage (10), and the first displacement stage (10) is connected to a host computer (29) via a displacement stage controller (31); the second reflector (13) is attached with a first displacement stage (14), and the second displacement stage (13) is connected to the host computer (29) via a displacement stage controller (35); the third reflector (16) is attached with a third displacement stage (17), and the third displacement stage (17) is connected to the host computer (29) via a displacement stage controller (31).

[0032] The present invention provides a magnetic field measurement method and device based on ultrashort pulse laser pumping atomic spins with adjustable repetition frequency. The pulse laser emitted by an ultrashort pulse laser (1) passes through a pulse repetition frequency adjustment optical path (polarizer (3), Pockels cell (4), analyzer (5), depolarizing beam splitter prism ((6), (7), (12)) and movable reflector ((9), (16), (13)) and then enters an alkali metal gas chamber. The high peak power of the ultrashort pulse and the appropriate pulse repetition frequency are used to stabilize the polarization rate at a desired value.

[0033] A magnetic field measurement method and device based on ultrashort pulse laser pumping of atomic spins with adjustable repetition frequency, characterized by comprising two parts: an atomic magnetic field measurement system and a control system.

[0034] The SERF atomic magnetic field measurement system comprises: an alkali metal gas chamber (23), a non-magnetic electric heating system (22), a three-axis magnetic compensation coil (24), a magnetic shielding barrel (25), a function generator (30), and a phase-locked amplifier (28), wherein the magnetic shielding barrel (25) is used to provide the alkali metal gas chamber with a weak magnetic field environment required by the SERF magnetic field measurement device, the non-magnetic electric heating system (22) heats the alkali metal gas chamber to achieve a sufficiently high alkali metal atomic number density, the three-axis magnetic field compensation coil (24) is connected to the function generator (or signal generator 30) to compensate for the residual magnetic field felt by the atoms in the shielding barrel, and the phase-locked amplifier (28) is used to collect the optical signal The pumping optical path of the SERF atomic magnetic field measurement system is in the Z direction. The ultrashort pulse pumping laser (1) emits a pumping laser beam along the X axis. The pumping laser passes through the optical isolator (2), the first polarizer (3), the Pockels cell (4), the first analyzer (5), and the first depolarizing beam splitter prism (6) in sequence. The transmission beam of the first depolarizing beam splitter prism (6) passes through the second depolarizing beam splitter prism (7). The refracted beam of the second depolarizing beam splitter prism (7) is absorbed by the first absorption mirror (8). The transmission beam of the second depolarizing beam splitter prism (7) passes through the first reflection mirror (9), returns along the original path, and passes through the second depolarizing beam splitter prism (7) again. The refracted beam The refracted beam of the first depolarizing beam splitter (6) passes through the third depolarizing beam splitter (12), and the transmitted beam of the third depolarizing beam splitter (12) returns to the original path through the second reflecting mirror (13) and enters the alkali metal gas chamber (23) in the magnetic shielding barrel (25); the refracted beam of the third depolarizing beam splitter (12) passes through the third reflecting mirror (16), and enters the third depolarizing beam splitter (12) again through the third reflecting mirror (16), and the projected beam is absorbed by the third absorbing mirror (15), and the refracted beam enters the magnetic shielding barrel (25). ) in the alkali metal gas chamber (23), thereby realizing the polarization of the alkali metal atoms; the detection optical path of the SERF atomic magnetic field measurement system is in the X direction, the detection laser (18) emits a detection laser beam along the X axis, which is changed into linearly polarized light after passing through the second polarizer (19), and then modulated by the photoelastic modulator (20) and the quarter-wave plate (21), and enters the alkali metal gas chamber (23) in the magnetic shielding barrel (25). The transmitted light beam is affected by the precession of the atomic spin, and the polarization axis of the linearly polarized light is deflected. Then, the transmitted light beam is converted into an electrical signal after passing through the second polarizer (26) and the photodetector (27), and then input into the phase-locked amplifier (28) for demodulation.

[0035] The SERF atomic magnetic field control system comprises: a first displacement stage (10), a second displacement stage (14), a third displacement stage (17), and a displacement stage controller (31), which is used to adjust the positions of the first reflector (9), the second reflector (13), and the third reflector (16); and a host computer (29) connected to the phase-locked amplifier (28) and the displacement stage controller (31), which is used to calculate polarizability information and control the movement of the displacement stage.

[0036] The alkali metal atom in the alkali metal gas chamber is one of potassium, rubidium and cesium.

[0037] The alkali metal gas chamber (23) contains buffer gas nitrogen and quenching gas helium, the nitrogen pressure is not less than 1 atm, and the helium pressure is about 50 Torr.

[0038] The working principle of the ultrashort pulse laser pumping device used in the atomic magnetic field measurement device is as follows:

[0039] After the ultrashort pulse pumping laser enters the alkali metal gas chamber (23), since its peak power is much greater than the saturation absorption power of the alkali metal atoms, it can efficiently and evenly pump the ground state atoms inside the gas chamber to the excited state. The ultrashort pulse pumping system can adjust the repetition frequency of the pulsed laser according to the relaxation rate of the atoms in the gas chamber to stabilize the atomic polarizability at the desired value.

[0040] In the atomic magnetic field measurement system, after the linearly polarized detection light passes through the alkali metal gas chamber (23), its linear polarization plane is deflected to generate an optical rotation angle θ, which is proportional to the electronic polarizability of the alkali metal atoms. The optical rotation angle information is converted into an electrical signal by the photoelectric detector (28), and the polarizability is calculated by the host computer (29). The polarizability value is continuously monitored. If the polarizability changes, the host computer gives a control signal to control the displacement stage controller (31) to drive the first displacement stage (10), the second displacement stage (14) and the third displacement stage (17) to change the pulse time interval. Then repeat this process until the atomic polarizability in the alkali metal gas chamber no longer changes.

[0041] A magnetic field measurement method and device based on ultrashort pulse laser pumping atomic spins with adjustable repetition frequency, including a pumping system, in which the relaxation rate and polarizability distribution of alkali metal atoms are stabilized to an optimal value by optimizing the repetition frequency of the ultrashort pulse laser, thereby maximizing the amplitude output of the response signal. The average power of the ultrashort pulse laser in the pumping system is 20mW, the pulse width is 100fs, and the repetition frequency is 80MHz, and its peak power significantly exceeds the saturation absorption power of the alkali metal atoms. This enables the ultrashort pulse laser to uniformly polarize alkali metal atoms everywhere in the gas chamber, avoiding the polarizability gradient caused by the large optical depth in continuous laser pumping, reducing the negative impact of uneven polarizability distribution on the sensitivity of the atomic magnetic field measurement device, and improving the sensitivity of the measurement device.

[0042] The pumping system includes an ultrashort pulse laser, which emits an ultrashort pulse pumping laser that passes through an optical isolator, a polarizer, a Pockels cell, and an analyzer in sequence. A voltage is applied to the electrodes of the Pockels cell through a Pockels cell controller to change the refractive index of the crystal, thereby changing the polarization state of the laser. In combination with the use of a polarizer and an analyzer, the passage or blocking of the pulse laser is controlled. In this process, the pulse time interval t is precisely controlled to become nt (n is the optimal value of the pulse time interval optimized during the experiment). After that, the pulse laser continues to pass through the first depolarization beam splitter prism, and the transmission beam of the first depolarization beam splitter prism passes through the second depolarization beam splitter prism. The transmission beam of the second depolarization beam splitter prism passes through the first reflector, returns to the first depolarization beam splitter prism, and is refracted into the alkali metal atom gas chamber in the magnetic shielding barrel; the refracted beam of the first depolarization beam splitter prism passes through the third depolarization beam splitter prism, and the transmission beam of the third depolarization beam splitter prism passes through the second reflector and returns to the first depolarization beam splitter prism, and is transmitted into the alkali metal atom gas chamber in the magnetic shielding barrel; the refracted beam of the third depolarization beam splitter prism passes through the third reflector and returns to the first depolarization beam splitter prism, and is refracted into the alkali metal atom gas chamber in the magnetic shielding barrel. Through this process, the pulse is changed from one beam to three beams, which enter the magnetic shielding barrel in sequence, and the pulse time interval nt is changed to nt / 3. The repetition frequency of the pulse is the inverse of the time interval. Through this process, the repetition frequency of the pulsed laser can be changed.

[0043] The invention comprises a detection laser, wherein the detection laser is connected to a photodetector through a polarizer, a photoelastic modulator, a quarter wave plate, the alkali metal gas chamber and a polarizer in sequence, and the photodetector is connected to a host computer through a phase-locked amplifier.

[0044] The alkali metal atom gas chamber is provided with a non-magnetic electric heating system, a three-axis magnetic compensation coil and a magnetic shielding barrel in sequence from the inside to the outside, and the three-axis magnetic compensation coil is connected to the signal generator.

[0045] The first reflector is equipped with a first displacement stage, which is connected to a host computer via a displacement stage controller; the second reflector is equipped with a second displacement stage, which is connected to a host computer via a displacement stage controller; the third reflector is equipped with a first displacement stage, which is connected to a host computer via a displacement stage controller.

[0046] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. It is pointed out here that the above description helps those skilled in the art to understand the invention, but does not limit the protection scope of the invention. Any equivalent replacement, modification and / or simplification of the above description without departing from the essence of the invention falls within the protection scope of the invention.

Claims

1. A magnetic field measurement method based on ultrashort pulse laser pumping of atomic spins with adjustable repetition rate, characterized in that: The method comprises optimizing a beam of light emitted by an ultrashort pulse laser from a pulse time interval t to nt in a pumping system of an atomic magnetic field measuring device, wherein n is an integer greater than 1, and converting a beam of light with a pulse time interval nt into three beams of light with pulse time intervals of nt / 3 passing through a gas chamber, and stabilizing the relaxation rate and polarizability distribution of alkali metal atoms in the gas chamber to an optimal value by optimizing the repetition frequency of the ultrashort pulse laser. After that, the magnetic field to be measured will cause the precession of polarized atoms. After a beam of linearly polarized detection light passes through the gas chamber, its polarization direction will rotate due to the interaction with the atomic spin. The magnetic field is measured by detecting the light rotation angle. Since the pumping light determines the polarizability of the atom, which in turn affects the magnetometer signal, the amplitude output of the response signal can be maximized by optimizing the polarizability of the alkali metal atom. The average power of the ultrashort pulse laser in the pumping system is 20 mW, the pulse width is 100 fs, the repetition frequency is 80 MHz, and the peak power thereof significantly exceeds the saturation absorption power of the alkali metal atoms.

2. The magnetic field measurement method based on ultrashort pulse laser pumping of atomic spins with adjustable repetition rate according to claim 1, characterized in that: t=1*10-8 seconds~1.25*10-8 seconds.

3. The magnetic field measurement method based on ultrashort pulse laser pumping of atomic spins with adjustable repetition rate according to claim 1 is characterized in that: n=30～50。 4. The magnetic field measurement method based on ultrashort pulse laser pumping of atomic spins with adjustable repetition rate according to claim 1 is characterized in that: The ultrashort pulse laser emitted by the ultrashort pulse laser is connected to the first depolarizing beam splitter prism through an optical isolator, a first polarizer, a Pockels cell and a first analyzer in sequence. The Pockels cell is connected to a Pockels cell controller. The Pockels cell controller applies a voltage to the electrodes of the Pockels cell to change the refractive index of the crystal, thereby changing the polarization state of the laser. The polarizer and the analyzer are then used to control the passage or blocking of the ultrashort pulse laser so that the pulse time interval t becomes nt, and a beam of light with a pulse time interval nt is transmitted to the first depolarizing beam splitter prism.

5. The magnetic field measurement method based on ultrashort pulse laser pumping of atomic spins with adjustable repetition rate according to claim 4 is characterized in that: The x-axis transmission side of the first depolarizing beam splitter is connected to the first reflector through the second depolarizing beam splitter, the z-axis reflection side of the second depolarizing beam splitter is connected to the second absorption mirror, the inverse z-axis reflection side of the second depolarizing beam splitter is connected to the first absorption mirror, the inverse z-axis reflection side of the first depolarizing beam splitter is connected to the second reflector through the third depolarizing beam splitter, the inverse x-axis reflection side of the third depolarizing beam splitter is connected to the third reflector, the x-axis side of the third depolarizing beam splitter is connected to the third absorption mirror, and the z-axis side of the first depolarizing beam splitter passes three beams of light with a pulse time interval of nt / 3 through the gas chamber to uniformly and efficiently pump the ground state atoms inside the gas chamber to an excited state.

6. The magnetic field measurement method based on ultrashort pulse laser pumping of atomic spins with adjustable repetition rate according to claim 5 is characterized in that: The first reflector is mounted on a first displacement platform, the second reflector is mounted on a second displacement platform, the third reflector is mounted on a third displacement platform, and the first displacement platform, the second displacement platform and the third displacement platform are respectively connected to a host computer via a displacement platform controller.

7. The magnetic field measurement method based on ultrashort pulse laser pumping of atomic spins with adjustable repetition rate according to claim 1 is characterized in that: The air chamber is located in a non-magnetic electric heating system, the non-magnetic electric heating system is located in a three-axis compensation coil, the three-axis compensation coil is located in a shielding barrel, and the three-axis compensation coil is connected to a signal generator.

8. The magnetic field measurement method based on ultrashort pulse laser pumping of atomic spins with adjustable repetition rate according to claim 1 is characterized in that: The detection system of the atomic magnetic field measuring device comprises a detection laser, which is connected to a host computer via a second polarizer, a photoelastic modulator, a quarter wave plate, an air chamber, a second polarizer, a photodetector and a lock-in amplifier in sequence.

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