A new type of alkali metal optical pumping magnetometer

Abstract

The present invention discloses a novel alkali metal optical pumping magnetometer, which relates to the field of magnetic measurement. The present invention creatively designs a single-wavelength reflection cavity, thereby realizing self-locking of the pump light wavelength and single-axis bidirectional pumping. The optical pumping magnetometer probe has a strong optical pumping effect, and its magnetic resonance signal is higher than that of the traditional structure magnetometer probe, and the magnetometer has higher sensitivity. At the same time, the present structure simplifies the structure of the optical pumping magnetometer pump lamp and the atomic absorption chamber, realizing the integration of the pump source and the atomic absorption chamber. Without reducing the performance of the magnetometer, the optical pumping probe structure and the auxiliary circuits are simplified, which is conducive to the miniaturization of the optical pumping probe. The present invention has the advantages of low technical difficulty and low production cost, can meet the actual requirements of miniaturization of the optical pumping probe, and is practical.

Description

Technical Field

[0001] The invention relates to the field of magnetic measurement, and in particular to a novel alkali metal optical pump magnetometer. Background Art

[0002] In geological structures, due to the differences in density, elasticity, conductivity, magnetism, radioactivity, and thermal conductivity of different rock layers in the crust, the local geophysical field changes. By measuring the distribution and change characteristics of these physical fields, the geological structure is analyzed and the geological properties are inferred. The main task of geophysical exploration is to measure the conductivity, radioactivity, magnetism, gravity and other parameters of the local crust, provide reference information for geological analysis, and facilitate future mineral exploration and mining. In order to collect geological magnetic parameters, geophysical exploration personnel conduct magnetic exploration by operating various magnetic exploration equipment to collect crustal magnetic parameters.

[0003] There are a lot of paramagnetic materials such as iron, chromium and nickel in the earth's crust. Under the strong magnetic field of the earth, paramagnetic materials have strong magnetism after magnetization. Due to their good structural strength, material properties and abundant reserves, paramagnetic materials of iron, chromium and nickel are widely used in daily production and life and military purposes. Unexploded objects UXO, unidentified objects on the ground and underwater cause changes in the surrounding earth's magnetic field because they have a lot of magnetic bodies. Their magnetic properties are often used as a detection target. Magnetic detection equipment is the main detection and positioning equipment.

[0004] The optical pumping magnetometer is a highly sensitive magnetic detection device. Its working principle is that specific atoms in the magnetic field undergo magnetic resonance under the action of optical pumping, and the external magnetic field is tracked and measured through the tracking loop of the deorientation effect or the self-excitation loop of Larmor magnetic resonance frequency. Due to its high sensitivity, the optical pumping magnetometer has become the main equipment for high-precision and high-performance magnetic exploration and magnetic anomaly detection for military and civilian use. The new alkali metal optical pumping magnetometer adopts a self-excited magnetometer. Only when the Larmor signal amplitude in the self-excitation tracking loop is large enough and the phase meets the self-excitation condition, the optical pumping probe generates self-excited oscillation of the Larmor signal. By measuring the Larmor frequency, the external magnetic field value can be calculated. In order to realize the optical pumping effect, the pump lamp and the atomic absorption chamber in the traditional optical pumping magnetometer adopt a separated structure. The independent pump lamp produces an optical pumping effect on the atoms in the atomic absorption chamber, and the atoms in the atomic absorption chamber undergo magnetic resonance. In this method, the pumping effect is a unidirectional pumping, and the pumping probability of alkali metal atoms is limited. To ensure sufficient pump light intensity, technicians will apply high-power high-frequency excitation to the pump lamp. At the same time, due to the wide spectrum of the pump lamp, the light waves outside the pump light will introduce optical noise. If a laser is used as a pump source, its structure is more complicated, with many supporting circuits, and the laser pump magnetometer is technically difficult and expensive to produce. In addition, in order to ensure the metal vapor concentration in the alkali metal pump lamp and the alkali metal atomic absorption chamber, designers usually use two sets of circuits to heat and insulate the lamp and chamber respectively. Therefore, the traditional optical pump probe has a complicated structure, large size, and complex circuit. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a novel alkali metal optical pumping magnetometer, which has the advantages of self-locking pump light wavelength, uniaxial bidirectional pumping, simple structure, less technical difficulty and low production cost.

[0006] The objective of the present invention is achieved through the following technical solutions: this new alkali metal optical pump magnetometer includes a probe, a magnetometer host and a magnetic sensor, the probe is electrically connected to the magnetometer host through a cable; the probe includes a probe cover, the inner cavity of the probe cover is placed with a magnetic sensor, a coil is arranged around the outer periphery of the magnetic sensor, the coil is electrically connected to the magnetometer host through a cable, and is used to apply a Larmor signal radio frequency field to the magnetic sensor; the magnetic sensor is a tubular structure with closed ends, the magnetic sensor is filled with alkali metal, a heating wire is evenly wound on the outer wall of the magnetic sensor, and is used to heat the alkali metal to a gaseous state, and the heating wire is electrically connected to the cable to realize power supply. One end of the electrode is connected to a cable, and the other end of the electrode is inserted into the magnetic sensor, which is used to high-frequency excite alkali metal vapor to make the alkali metal vapor emit light; a polarizer is installed in the magnetic sensor to convert alkali metal light into pump light; reflectors are installed at both ends of the magnetic sensor to form a bidirectional reflection channel in the inner cavity of the magnetic sensor, and the pump light repeatedly pumps the alkali metal vapor atoms along the bidirectional reflection channel to produce an optical pumping effect; a photodetector is fixed at one end of the magnetic sensor close to the magnetometer host, which is used to detect optical signals containing Larmor frequencies and convert them into electrical signals, which are transmitted to the magnetometer host through cables to achieve measurement of external magnetic fields.

[0007] As a further technical solution, a heat-insulating layer is filled between the outer wall of the magnetic sensor and the inner wall of the probe cover.

[0008] As a further technical solution, the tubular structure is a glass outer sleeve, which is sleeved on the outer circumference of the magnetic resonance glass tube; the magnetic resonance glass tube has a pear-shaped end and a cylindrical end; one end of the glass outer sleeve is welded and sealed to the outer wall of the pear-shaped end of the magnetic resonance glass tube, and the other end of the glass outer sleeve is welded and sealed to the cylindrical end portion of the magnetic resonance glass tube.

[0009] As a further technical solution, a spherical reflector is sealed and welded to the pear-shaped end of the magnetic resonance glass tube, and a plane reflector is welded and sealed to the cylindrical end portion of the magnetic resonance glass tube.

[0010] As a further technical solution, the polarizer is fixed in the magnetic resonance glass tube, and the photodetector is fixed on the plane reflector; the magnetic resonance glass tube is filled with alkali metal and buffer gas to form a magnetic resonance cavity in the magnetic resonance glass tube.

[0011] As a further technical solution, the magnetometer host is electrically connected to an external device via an external interface module to achieve power supply and communication.

[0012] As a further technical solution, the magnetometer host also includes a high-frequency excitation module, one end of which is electrically connected to the external interface module, and the other end of which is connected to the electrode via a cable to provide tunable, high-frequency excitation power.

[0013] As a further technical solution, the magnetometer host also includes a signal processing module and a main control module. One end of the signal processing module is electrically connected to the photodetector through a cable for receiving the Larmor frequency electrical signal, and the other end of the signal processing module is electrically connected to the main control module for outputting an analog or TTL frequency signal; the main control module converts the received signal into a magnetic field value and outputs it to the external interface module.

[0014] As a further technical solution, the magnetometer host also includes a temperature control module, one end of which is electrically connected to the coil and the heating wire through cables, so as to control the heating temperature of the heating wire and the current of the coil, and the other end of the temperature control module is electrically connected to the external interface module.

[0015] The beneficial effects of the present invention are:

[0016] 1. The pump light wavelength self-locking technology solution can overcome the shortcomings of wide pump source spectrum, weak optical pump effect and large optical noise in the optical pump probe of optical pump magnetometer;

[0017] 2. The use of optical axis bidirectional pumping can increase the pumping probability of alkali metal atoms, which can overcome the shortcomings of reduced size of magnetic sensors, decreased magnetic resonance signals, and decreased performance of magnetometers;

[0018] 3. The integrated design of optical pump source and atomic absorption chamber will help simplify the structure of optical pump probe and its auxiliary circuits;

[0019] 4. It has the advantages of small size and high sensitivity, and can be widely used in magnetic measurement tasks in various fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of the present invention.

[0021] Figure 2 This is a schematic diagram of the probe structure.

[0022] Figure 3 Schematic diagram of the structure of the magnetic sensor.

[0023] Figure 4 This is a structural diagram of the magnetometer host.

[0024] Explanation of the accompanying drawings: probe 1, cable 2, magnetometer host 3, magnetic sensor 4, coil 5, electrode 6, insulation layer 7, heating wire 8, spherical reflector 9, polarizer 10, magnetic resonance glass tube 11, glass outer sleeve 12, plane reflector 13, photodetector 14, high-frequency excitation module 15, signal processing module 16, temperature control module 17, main control module 18, external interface module 19, probe cover 20. DETAILED DESCRIPTION

[0025] The present invention will be described in detail below with reference to the accompanying drawings:

[0026] Example: As attached Figures 1 to 4 As shown, this novel alkali metal optical pump magnetometer comprises a probe 1, a magnetometer host 3 and a magnetic sensor 4, wherein the probe 1 is electrically connected to the magnetometer host 3 via a cable 2; the probe 1 comprises a probe cover 20, wherein the magnetic sensor 4 is placed in the inner cavity of the probe cover 20, a coil 5 is arranged around the outer periphery of the magnetic sensor 4, and the coil 5 is electrically connected to the magnetometer host 3 via a cable 2, and is used to apply a Larmor signal radio frequency field to the magnetic sensor 4; the magnetic sensor 4 is a tubular structure with closed ends, the magnetic sensor 4 is filled with alkali metal, a heating wire 8 is evenly wound on the outer wall of the magnetic sensor 4, and is used to heat the alkali metal to a gaseous state, and the heating wire 8 is electrically connected to the cable 2 to realize power supply; an electrode 6 One end of the electrode 6 is connected to the cable 2, and the other end of the electrode 6 is inserted into the magnetic sensor 4, which is used to high-frequency excite the alkali metal vapor to make the alkali metal vapor emit light; a polarizer 10 is installed in the magnetic sensor 4, which is used to convert the alkali metal light into pumping light; both ends of the magnetic sensor 4 are installed with reflectors, so as to form a bidirectional reflection channel in the inner cavity of the magnetic sensor 4, and the pumping light repeatedly pumps the alkali metal vapor atoms along the bidirectional reflection channel to produce an optical pumping effect; a photodetector 14 is fixed at one end of the magnetic sensor 4 close to the magnetometer host 3, which is used to detect the optical signal containing the Larmor frequency, and convert it into an electrical signal, which is transmitted to the magnetometer host 3 through the cable 2 to achieve the measurement of the external magnetic field.

[0027] Furthermore, if Figure 3 As shown, the tubular structure is a glass outer sleeve 12, which is sleeved on the outer periphery of a magnetic resonance glass tube 11; the magnetic resonance glass tube 11 has a pear-shaped end and a cylindrical end; one end of the glass outer sleeve 12 is welded and sealed to the outer wall of the pear-shaped end of the magnetic resonance glass tube 11, and the other end of the glass outer sleeve 12 is welded and sealed to the cylindrical end portion of the magnetic resonance glass tube 11. A spherical reflector 9 is welded and sealed to the pear-shaped end of the magnetic resonance glass tube 11, and a plane reflector 13 is welded and sealed to the cylindrical end portion of the magnetic resonance glass tube 11. A polarizer 10 is fixed in the magnetic resonance glass tube 11, and a photodetector 14 is fixed on the plane reflector 13; an alkali metal and a buffer gas are filled in the magnetic resonance glass tube 11 to form a magnetic resonance cavity in the magnetic resonance glass tube 11.

[0028] Furthermore, if Figure 4As shown, the magnetometer host 3 is electrically connected to the external device through the external interface module 19 to realize power supply and communication. The magnetometer host 3 also includes a high-frequency excitation module 15, a signal processing module 16, a temperature control module 17 and a main control module 18. One end of the high-frequency excitation module 15 is electrically connected to the external interface module 19, and the other end of the high-frequency excitation module 15 is connected to the electrode 6 through a cable 2 to provide tunable, high-frequency excitation power. One end of the signal processing module 16 is electrically connected to the photodetector 14 through a cable 2 to receive the Larmor frequency electrical signal, and the other end of the signal processing module 16 is electrically connected to the main control module 18 to output an analog or TTL frequency signal; the main control module 18 converts the received signal into a magnetic field value and outputs it to the external interface module 19. One end of the temperature control module 17 is electrically connected to the coil 5 and the heating wire 8 through a cable 2, respectively, to control the heating temperature of the heating wire 8 and the current of the coil 5, and the other end of the temperature control module 17 is electrically connected to the external interface module 19.

[0029] Preferably, refer to the attached Figure 2 The outer wall of the magnetic sensor 4 (i.e. the glass outer sleeve 12) and the inner wall of the probe cover 20 are filled with a heat preservation layer 7 to prevent the internal heating of the magnetic sensor 4 from being transmitted to the outside and avoid being affected by the external temperature.

[0030] Working principle of the present invention: The present invention is a self-excited alkali metal optical pump magnetometer. Under the influence of slow-filling gas and high-frequency excitation, the alkali metal in the magnetic resonance glass tube 11 emits light, and under the action of the polarizer 10, polarized light pumping light is formed. The pumping light pumps the alkali metal atoms (taking cesium atoms as an example) back and forth between the spherical reflector 9 and the plane reflector 13. When the frequency of the radio frequency field generated by the coil 5 on the periphery of the magnetic sensor 4 in the magnetic resonance glass tube 11 (i.e., the magnetic resonance cavity) is consistent with the Larmor frequency generated by the external magnetic field in the energy level transition of the cesium atom, under the action of the phase shifter, the cesium optical pump magnetometer optical pump probe generates a self-excitation phenomenon. Cesium atom generates magnetic resonance phenomenon in magnetic resonance cavity, and the Larmor frequency signal of atomic transition is collected and transmitted to magnetometer mainframe 3 by photoelectric detector 14, and signal processing module 16 of magnetometer mainframe 3 receives Larmor frequency electrical signal, and outputs analog or TTL frequency signal to main control module 18, and main control module 18 converts received signal into magnetic field value and outputs to external interface module 19. In actual use, magnetic resonance can be generated when the frequency generated by coil 5 is consistent with Larmor frequency, but self-excitation can not be formed. It is necessary to phase-shift the received Larmor frequency signal to realize self-excitation. At this point, by counting the Larmor frequency, substituting the relational formula of Larmor frequency and external magnetic field, the magnetic field value of the position of optical pump magnetometer can be derived.

[0031] It is understandable that, for those skilled in the art, any equivalent replacement or change to the technical solution and inventive concept of the present invention should fall within the protection scope of the claims attached to the present invention.

Claims

1. A novel alkali metal optical pumping magnetometer, characterized in that: The invention comprises a probe (1), a magnetometer host (3) and a magnetic sensor (4), wherein the probe (1) is electrically connected to the magnetometer host (3) via a cable (2); the probe (1) comprises a probe cover (20), the inner cavity of the probe cover (20) is provided with a magnetic sensor (4), a coil (5) is arranged around the outer periphery of the magnetic sensor (4), the coil (5) is electrically connected to the magnetometer host (3) via the cable (2), and is used to apply a Larmor signal radio frequency field to the magnetic sensor (4); the magnetic sensor (4) is a tubular structure with both ends closed, the magnetic sensor (4) is filled with an alkali metal, and the outer wall of the magnetic sensor (4) is uniformly provided with a magnetic field. A heating wire (8) is wound around the magnetic sensor (4) for heating the alkali metal to a gaseous state, and the heating wire (8) is electrically connected to the cable (2) to realize power supply; one end of the electrode (6) is connected to the cable (2), and the other end of the electrode (6) is inserted into the magnetic sensor (4) for high-frequency excitation of the alkali metal vapor to make the alkali metal vapor emit light; a polarizing plate (10) is installed in the magnetic sensor (4) for converting the alkali metal light into pumping light; both ends of the magnetic sensor (4) are installed with reflectors, so that a bidirectional reflection channel is formed in the inner cavity of the magnetic sensor (4), and the pumping light repeatedly pumps the alkali metal vapor atoms along the bidirectional reflection channel to generate an optical pumping effect; The photoelectric detector (14) is fixed to one end of the magnetic sensor (4) close to the magnetometer host (3) and is used to detect the optical signal containing the Larmor frequency and convert it into an electrical signal, which is transmitted to the magnetometer host (3) through the cable (2) to achieve the measurement of the external magnetic field; A heat-insulating layer (7) is filled between the outer wall of the magnetic sensor (4) and the inner wall of the probe cover (20); The tubular structure is a glass outer sleeve (12), which is sleeved on the outer circumference of the magnetic resonance glass tube (11); the magnetic resonance glass tube (11) has a pear-shaped end and a columnar end; one end of the glass outer sleeve (12) is welded and sealed to the outer wall of the pear-shaped end of the magnetic resonance glass tube (11), and the other end of the glass outer sleeve (12) is welded and sealed to the columnar end portion of the magnetic resonance glass tube (11); A spherical reflector (9) is sealed and welded to the pear-shaped end of the magnetic resonance glass tube (11), and a plane reflector (13) is welded and sealed to the cylindrical end portion of the magnetic resonance glass tube (11); The polarizing plate (10) is fixed in the magnetic resonance glass tube (11), and the photodetector (14) is fixed on the plane reflector (13); the magnetic resonance glass tube (11) is filled with alkali metal and buffer gas to form a magnetic resonance cavity in the magnetic resonance glass tube (11).

2. The novel alkali metal optical pumping magnetometer according to claim 1 is characterized in that: The magnetometer host (3) is electrically connected to an external device via an external interface module (19) to achieve power supply and communication.

3. The novel alkali metal optical pumping magnetometer according to claim 2 is characterized in that: The magnetometer host (3) further comprises a high-frequency excitation module (15), one end of the high-frequency excitation module (15) being electrically connected to the external interface module (19), and the other end of the high-frequency excitation module (15) being connected to the electrode (6) via a cable (2) for providing tunable, high-frequency excitation power.

4. The novel alkali metal optical pumping magnetometer according to claim 2 is characterized in that: The magnetometer host (3) further comprises a signal processing module (16) and a main control module (18); one end of the signal processing module (16) is electrically connected to the photodetector (14) via a cable (2) for receiving a Larmor frequency electrical signal; the other end of the signal processing module (16) is electrically connected to the main control module (18) for outputting an analog or TTL frequency signal; the main control module (18) converts the received signal into a magnetic field value and outputs it to the external interface module (19).

5. The novel alkali metal optical pumping magnetometer according to claim 2 is characterized in that: The magnetometer host (3) further comprises a temperature control module (17), one end of the temperature control module (17) being electrically connected to the coil (5) and the heating wire (8) respectively through the cable (2) for controlling the heating temperature of the heating wire (8) and the current of the coil (5), and the other end of the temperature control module (17) being electrically connected to the external interface module (19).

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