A magnetic field measurement device based on total reflection evanescent field

Abstract

A magnetic field measurement device based on total reflection evanescent field is beneficial for providing technical support for the development of next-generation chip-level magnetometers by using microscopic evanescent light fields as pump light and detection light to act on alkali metal atomic gas cells. It is characterized by comprising an alkali metal atomic gas cell with a first refractive index n1 and an optical path dielectric device with a second refractive index n2 forming a bonding interface therewith, n1<n2. Incident light of the optical path dielectric device forms a microscopic evanescent field on the bonding interface. The evanescent field acts as pump light and detection light acting on the alkali metal atomic gas cell, causing the reflected light intensity and polarization degree of the incident light to change. The reflected light is detected by a differential detection device, thereby realizing magnetic field measurement.

Description

Technical Field

[0001] The present invention relates to the technical field of atomic magnetometers, and in particular to a magnetic field measurement device based on a total reflection evanescent field. The device is advantageous in that it uses a microscopic evanescent light field as pump light and detection light to act on an alkali metal atomic gas chamber, thereby providing technical support for the development of next-generation chip-level magnetometers. Background Art

[0002] With the development of quantum sensing technology, spin-exchange relaxation-free (SERF) magnetometers based on atomic spin effects have developed rapidly. With their ultra-high sensitivity, the fact that they do not require refrigeration equipment compared to superconducting quantum interference devices, and the advantages of being miniaturized, they have played a great role in the field of extremely weak magnetic field measurement and have been used in fields such as geological exploration and biomagnetic measurement. Although miniaturized magnetometers have reached the centimeter level, chip-scale magnetometers have always been a hot topic of research. The evanescent field at the wavelength level has applications in many fields, such as scanning microscopes and high-sensitivity sensors. The purpose of this invention is to explore the usefulness of the evanescent field in the development of chip-scale atomic magnetometers. Summary of the Invention

[0003] In response to the deficiencies in the prior art, the present invention provides a magnetic field measurement device based on total reflection evanescent field. This device is advantageous in that it uses microscopic evanescent light fields as pumping light and detection light to act on an alkali metal atomic gas chamber, thereby providing technical support for the development of next-generation chip-level magnetometers.

[0004] The technical solutions of the present invention are as follows:

[0005] A magnetic field measurement device based on total reflection evanescent field is characterized by comprising an alkali metal atom gas chamber having a first refractive index n1 and an optical path dielectric device having a second refractive index n2 forming a bonding interface therewith, n1<n2, and incident light of the optical path dielectric device forms a microscopic-scale evanescent field on the bonding interface. The evanescent field acts as pump light and detection light acting on the alkali metal atom gas chamber, causing the intensity and polarization degree of the reflected light of the incident light to change. The reflected light is detected by a differential detection device, thereby realizing magnetic field measurement.

[0006] The wave function of the evanescent field is expressed as follows:

[0007]

[0008] k′ z =-k z i

[0009] in Represents the complex form of the wave function, E0 is the amplitude, e is the natural constant, i is the imaginary unit, k z is the z-axis component of the wave vector, z is the z-axis coordinate, k′ z k z plural form of k x is the x-axis component of the wave vector, x is the x-axis coordinate, ω is the angular frequency, and t is the time;

[0010] The field intensity of the evanescent field decays exponentially in the z-axis direction, and the penetration depth d of the evanescent field is expressed as follows:

[0011]

[0012] Where λ0 is the wavelength of the incident light, i1 is the angle of incidence, and the corresponding parameters are substituted into the calculated penetration depth of the evanescent field, which is on the nanometer level.

[0013] The optical path dielectric device is a right-angle prism, the hypotenuse of the right-angle prism forms a bonding interface with the bottom edge of the alkali metal atom gas chamber, the angle between the normal line of the first right-angle side of the right-angle prism and the incident light is α, and the angle between the normal line of the first right-angle side and the incident light of the hypotenuse is α. t The angle between the normal line of the hypotenuse and the incident light of the hypotenuse is i1, and the angle between the normal line of the hypotenuse and the reflected light is the total reflection angle i c , i1=i c , the reflected light is emitted from the second right-angle side of the right-angle prism to the differential detection device, and the relevant parameters are calculated according to the following formula to ensure that the incident light beam is totally reflected on the oblique surface of the right-angle prism:

[0014] α t +i1=45°

[0015]

[0016] sinα=n2sinα t

[0017]

[0018] The alkali metal atom gas cell is a cubic gas cell lacking one side, and the oblique surface of the right-angle prism is bonded to the lacking side of the alkali metal atom gas cell by epoxy resin glue.

[0019] The differential detection device includes a first photodetector and a second photodetector respectively connected to a phase-locked amplifier, the first photodetector is connected to the transmission end of a polarization beam splitter, the second photodetector is connected to the reflection end of the polarization beam splitter, the input end of the polarization beam splitter is connected to the reflected light output side of the optical path medium device through a 1 / 2 wave plate and a reflector in sequence, and the phase-locked amplifier is connected to a computer.

[0020] The incident light of the optical path medium device comes from a laser, and the laser is connected to the optical path medium device through a collimator, a polarizer and a quarter wave plate in sequence.

[0021] A non-magnetic electric heating device is provided on the periphery of the alkali metal atom gas chamber to increase the atomic number density in the gas chamber by heating the alkali metal atom gas chamber.

[0022] The alkali metal atom gas chamber and the optical path dielectric device are both located in a magnetic compensation coil, and the magnetic compensation coil is located in a magnetic shielding barrel.

[0023] The alkali metal atom gas chamber includes any one of potassium, rubidium, and cesium alkali metal atoms, and also contains quenching gas nitrogen and buffer gas helium. The laser wavelength of the incident light is at the center of the alkali metal atom D1 line, and the incident light is elliptically polarized light.

[0024] The optical path medium device is a nanometer-scale waveguide or a nanometer-scale grating or a micrometer-scale optical fiber.

[0025] The technical effects of the present invention are as follows: The present invention is a magnetic field measurement device based on total reflection evanescent field, which combines an alkali metal atom gas chamber with an optical path dielectric device, and is conducive to using a microscopic evanescent light field as pump light and detection light to act on the alkali metal atom gas chamber, thereby providing technical support for the development of the next generation of chip-level magnetometers.

[0026] The present invention offers advantages over existing technologies: existing magnetic field measurement devices based on the atomic spin effect typically use macroscopic pump and detection light to polarize and detect alkali metal atoms. While some methods, such as modifying the optical path, can reduce the size of the measurement device, this approach is still some distance away from achieving a chip-based magnetometer. The present invention utilizes the microscopic evanescent field as both pump and detection light, technically demonstrating the feasibility of this approach. Besides being obtainable through total internal reflection at the surface of a medium, the evanescent field can also be obtained in nanoscale waveguides and gratings, as well as micrometer-scale optical fibers. This lays the foundation for subsequent research into chip-based magnetometers. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a schematic structural diagram of a magnetic field measurement device based on total reflection evanescent field.

[0028] Figure 2 yes Figure 1 Schematic diagram of the interaction between the evanescent field at the interface between the right-angle prism 8 and the alkali metal atom gas cell 7 and the atoms in the gas cell. Figure 2 The horizontal arrows at the bottom of the middle gas chamber represent the interface evanescent field (serving as pump light and probe light), the upper left arrow is the incident light, and the lower right arrow is the totally reflected light.

[0029] Figure 3 It is a schematic diagram of the light path propagation when the incident light undergoes total internal reflection. Figure 3 The horizontal solid line in the figure is the interface, the vertical dotted line is the normal, the black solid arrow is a schematic diagram of the light propagation path at the macro level, and the black dotted arrow is a schematic diagram of the propagation of the evanescent field (as pump light and detection light) at the micro level. n1 and n2 represent the refractive indices of the alkali metal atom gas chamber 7 and the right-angle prism 8, respectively, and n1<n2.

[0030] Figure 4 is a schematic diagram of the incident light angle. Figure 3 Where i1 is the incident angle of the inclined surface of the right angle prism 8, i1=i c ,i c is the total reflection angle, α is the incident angle of the right angle side of the incident right angle prism 8 that needs to be calculated, α t is the angle between the reflected light and the normal of the incident light at the right angle side, n1 is the refractive index of the alkali metal atom gas cell 7, and n2 is the refractive index of the right angle prism 8.

[0031] The reference numerals are listed as follows: 1-laser; 2-collimator; 3-polarizer; 4-1 / 4 wave plate; 5-magnetic shielding barrel; 6-non-magnetic electric heating device; 7-alkali metal atom gas chamber; 8-right-angle prism; 9-magnetic compensation coil; 10-reflector; 11-1 / 2 wave plate; 12-polarization beam splitter; 13-first photodetector; 14-second photodetector; 15-phase-locked amplifier; 16-computer; 17-elliptically polarized light. DETAILED DESCRIPTION

[0032] Below is the attached figure ( Figures 1-4 ) and Examples illustrate the present invention.

[0033] Figure 1 The present invention is a schematic structural diagram of a magnetic field measurement device based on total reflection evanescent field. Figure 2 yes Figure 1 Schematic diagram of the interaction between the evanescent field at the interface between the right-angle prism 8 and the alkali metal atom gas cell 7 and the atoms in the gas cell. Figure 3 It is a schematic diagram of the light path propagation when the incident light undergoes total internal reflection. Figure 4 is a schematic diagram of the incident light angle. Figures 1 to 4As shown, a magnetic field measuring device based on total reflection evanescent field is characterized in that it includes an alkali metal atom gas chamber 7 with a first refractive index n1 and an optical path dielectric device (such as a right-angle prism 8) with a second refractive index n2 forming a bonding interface therewith, n1<n2, the incident light of the optical path dielectric device forms a microscopic-scale evanescent field on the bonding interface, the evanescent field serves as pump light and detection light acting on the alkali metal atom gas chamber, so that the intensity and polarization degree of the reflected light of the incident light are changed, and the reflected light is detected by a differential detection device, thereby realizing magnetic field measurement.

[0034] The wave function of the evanescent field is expressed as follows:

[0035]

[0036] k′ z =-k z i

[0037] in Represents the complex form of the wave function, E0 is the amplitude, e is the natural constant, i is the imaginary unit, k z is the z-axis component of the wave vector, z is the z-axis coordinate, k′ z k z plural form of k x is the x-axis component of the wave vector, x is the x-axis coordinate, ω is the angular frequency, and t is the time;

[0038] The field intensity of the evanescent field decays exponentially in the z-axis direction, and the penetration depth d of the evanescent field is expressed as follows:

[0039]

[0040] Where λ0 is the wavelength of the incident light, i1 is the angle of incidence, and the corresponding parameters are substituted into the calculated penetration depth of the evanescent field, which is on the nanometer level.

[0041] The optical path dielectric device is a right-angle prism 8, the hypotenuse of the right-angle prism 8 forms a bonding interface with the bottom edge of the alkali metal atom gas chamber 7, the angle between the normal line of the first right-angle side of the right-angle prism 8 and the incident light is α, and the angle between the normal line of the first right-angle side and the incident light of the hypotenuse is α. t The angle between the hypotenuse normal and the incident light is i1, and the angle between the hypotenuse normal and the reflected light is the total reflection angle ic, i1=ic. The reflected light is emitted from the second right-angled side of the right-angle prism 8 to the differential detection device. The relevant parameters are calculated according to the following formula to ensure that the incident light beam is totally reflected on the oblique surface of the right-angle prism 8:

[0042] α t +i1=45°

[0043]

[0044] sinα=n2sinα t

[0045]

[0046] The alkali metal atom gas cell 7 is a cubic gas cell with one side missing. The oblique surface of a right-angle prism 8 is bonded to the missing side of the alkali metal atom gas cell 7 using epoxy resin glue. The differential detection device includes a first photodetector 13 and a second photodetector 14, each connected to a lock-in amplifier 15. The first photodetector 13 is connected to the transmission end of a polarization beam splitter 12, and the second photodetector 14 is connected to the reflection end of the polarization beam splitter 12. The input end of the polarization beam splitter 12 is connected to the reflected light output side of the optical path dielectric device via a half-wave plate 11 and a reflector 10. The lock-in amplifier 15 is connected to a computer 16. The incident light for the optical path dielectric device comes from a laser 1, which is connected to the optical path dielectric device via a collimator 2, a polarizer 3, and a quarter-wave plate 4. A non-magnetic electric heating device 6 is provided around the periphery of the alkali metal atom gas cell 7 to increase the atomic number density within the gas cell by heating the alkali metal atom gas cell 7. The alkali metal atom gas chamber 7 and the optical path dielectric device are both located within a magnetic compensation coil 9, which is located within a magnetic shielding barrel 5. The alkali metal atom gas chamber 7 contains alkali metal atoms of any one of potassium, rubidium, and cesium, as well as nitrogen as a quenching gas and helium as a buffer gas. The laser wavelength of the incident light is at the center of the alkali metal atom D1 line, and the incident light is elliptically polarized light 17. The optical path dielectric device is a nanoscale waveguide, a nanoscale grating, or a micrometer-scale optical fiber.

[0047] The present invention relates to a magnetic field measurement device based on total reflection evanescent field, comprising a laser 1, a collimator 2, a polarizer 3, a quarter-wave plate 4, a magnetic shielding barrel 5, a non-magnetic electric heating device 6, an alkali metal atom gas chamber 7, a right-angle prism 8, a magnetic compensation coil 9, a reflector 10, a half-wave plate 11, a polarization beam splitter 12, a first photodetector 13, a second photodetector 14, a lock-in amplifier 15, a computer 16, and elliptically polarized light 17. The present invention is characterized by using an evanescent field at the wavelength level as pump light and detection light, providing enhanced technical support for the development of next-generation chip-scale magnetometers.

[0048] A magnetic field measurement device based on total reflection evanescent field comprises a laser 1, a collimator 2, a polarizer 3, a quarter-wave plate 4, a magnetic shielding barrel 5, a non-magnetic electric heating device 6, an alkali metal atom gas chamber 7, a right-angle prism 8, a magnetic compensation coil 9, a reflector 10, a half-wave plate 11, a polarization beam splitter 12, a first photodetector 13, a second photodetector 14, a lock-in amplifier 15, a computer 16, and elliptically polarized light 17. The present invention uses a beam of elliptically polarized light 17 to be totally reflected by the right-angle prism 8. The evanescent field generated on the interface on one side of the alkali metal atom gas chamber 7 serves as pump light and detection light for the alkali metal atoms. After the evanescent field interacts with the atoms, the evanescent wave is completely returned to the reflected light, affecting the intensity and polarization state of the reflected light. When an external magnetic field is present, the polarization plane of the reflected light is deflected by the evanescent field. The deflection angle is called the optical rotation angle. The reflected light passes through the polarization beam splitter 12 and is detected by the first photodetector 13 and the second photodetector 14 respectively, and then is demodulated by the lock-in amplifier 15 and displayed on the computer 16.

[0049] The alkali metal atom gas chamber 7 is a gas chamber lacking one side, and is bonded to the oblique surface of the right-angle prism 8 by epoxy resin glue.

[0050] The magnetic shielding barrel 5 is made of high magnetic permeability material Permalloy and has a 5-layer cylindrical structure for shielding external magnetic fields.

[0051] The atoms in the alkali metal atom gas chamber 7 are alkali metal atoms, which may be any one of potassium, rubidium, and cesium, and also contain quenching gas nitrogen and buffer gas helium.

[0052] The wavelength of the laser emitted by the laser 1 is at the center of the alkali metal atom D1 line.

[0053] The elliptically polarized light 17 is incident on the right angle side of the right angle prism 8 at a near specific angle α.

[0054] The half wave plate 11 is used to precisely adjust the bias of the differential detection system so that the intensities of the two beams output by the polarization beam splitter 12 are precisely equal.

[0055] The non-magnetic electric heating device 6 is used to heat the alkali metal atom gas chamber to increase the atomic number density in the gas chamber.

[0056] The magnetic shielding barrel 5 is used to shield the external environmental magnetic field, and the magnetic compensation coil 9 is used to compensate for the residual magnetic field in the magnetic shielding barrel, so as to ensure a weak magnetic field environment. The non-magnetic electric heating device 6 is used to heat the alkali metal atom gas chamber 7 to provide the high-density conditions required for the atomic spin-free exchange state. The right-angle prism 8 is used to cause total reflection when the light is incident at the critical total reflection angle. The circular polarization component in the elliptically polarized evanescent field generated at the interface between the gas chamber and the prism is used to pump the alkali metal atoms, and the linear polarization component is used to detect the atomic spin precession signal. After the elliptically polarized light 17 is totally reflected by the right-angle prism 8, the evanescent field interacts with the gas chamber. When an external magnetic field exists, the spin direction of the alkali metal atoms will change, thereby affecting the evanescent field and the deflection of the polarization plane of the reflected light. The deflection angle is the light rotation angle. The reflected light passes through a reflector 10 and a half-wave plate 11, which adjust the intensity of the light received by the two photodetectors. The optical rotation angle signal is converted into an electrical signal by a first photodetector 13 and a second photodetector 14. Differential detection is used to reduce noise. The signal is then demodulated by a lock-in amplifier 15 and displayed on a computer 16. Magnetic field information is obtained by understanding the proportional relationship between the optical rotation angle and the magnetic field.

[0057] The elliptically polarized light 17 is adjusted by adjusting the angle between the optical axis of the quarter wave plate and the optical axis of the polarizer 3 to be π / 8.

[0058] The non-magnetic electric heating device comprises a boron nitride ceramic oven, a non-magnetic electric heating plate, a thermistor, and a high-temperature resistant housing. The alkali metal atom gas chamber 7 is a chamber with one side missing. It is bonded to the oblique surface of a right-angle prism 8 with epoxy resin. Both are fixed to an optical rotation adjustment mount with adjustable angles to ensure that incident light enters the prism surface at the critical total reflection angle. The magnetic compensation coil 9 is used to generate three orthogonal magnetic fields to ensure that the magnetic field within the gas chamber is compensated to a zero magnetic field environment.

[0059] Depend on Figure 1 It can be seen that the device of the present invention includes a laser 1, a collimator 2, a polarizer 3, a quarter-wave plate 4, a magnetic shielding barrel 5, a non-magnetic electric heating device 6, an alkali metal atom gas chamber 7, a right-angle prism 8, a magnetic compensation coil 9, a reflector 10, a half-wave plate 11, a polarization beam splitter 12, a first photodetector 13, a second photodetector 14, a lock-in amplifier 15, a computer 16, and an elliptically polarized light 17. In the device, the magnetic shielding barrel 5 is used to shield the earth's magnetic field and the ambient magnetic field, the magnetic compensation coil 9 is used to compensate for the residual magnetic field and magnetic field gradient in the magnetic shielding barrel, and the non-magnetic electric heating device 6 is used to heat the alkali metal atom gas chamber 7, so that the alkali metal atom density reaches about 10 per cubic centimeter. 14In order to meet the conditions of extremely weak magnetic field environment and high atomic number density required for alkali metal atoms to realize the state of no spin exchange. The magnetic compensation coil 9 is used to generate three orthogonal magnetic fields to compensate the magnetic field inside the gas chamber to a close to zero magnetic field environment, thereby reducing atomic relaxation. The alkali metal atom gas chamber 7 is filled with a specific proportion of alkali metal atoms, helium and nitrogen. Helium is used as a buffer gas to reduce bubble wall collision relaxation, and nitrogen is used as a quenching gas to eliminate the radiation capture effect. The alkali metal atom gas chamber 7 lacks one side, which is bonded to the right-angle prism 8 by epoxy resin glue to form an integrated body. The integrated body is placed on the optical rotation adjustment frame to ensure that the incident light enters the surface of the right-angle prism 8 at the critical total reflection angle. The specific incident angle calculation is shown in Figure 3 .

[0060] The wavelength of the laser emitted by the laser 1 is at the center of the alkali metal D1 line. After being collimated by the collimator 2, the beam passes through the polarizer 3 and the 1 / 4 wave plate 4. The 1 / 4 wave plate 4 forms an angle of π / 8 with the optical axis of the polarizer 3. After passing through the 1 / 4 wave plate 4, the beam becomes elliptically polarized light. The beam is incident from the right angle side of the right angle prism 8 and is totally reflected at the oblique surface of the right angle prism 8. An evanescent field is generated on the interface on one side of the alkali metal atom gas chamber 7. The alkali metal atoms are polarized by the circular polarization component in the evanescent field, and the linear polarization component is detected. When there is microscopic light from the outside, the evanescent field is generated. When the weak magnetic field changes, the polarization plane of the light beam will produce an angular change, that is, the optical rotation angle will change. The change of the evanescent field will cause the polarization plane of the reflected light to change. The light beam passes through the 1 / 2 wave plate 11 and the polarization beam splitter 12 and is differentially detected by the first photodetector 13 and the second photodetector 14 respectively. The optical signal is converted into an electrical signal by the photodetector and sent to the phase-locked amplifier 15, thereby extracting the atomic spin precession signal. The phase-locked amplifier 15 is connected to the computer 16, and the computer 16 is used to display and store the signal size extracted by the phase-locked amplifier 15.

[0061] Figure 2 Schematic diagram of the interaction between the evanescent field at the interface between the right-angle prism 8 and the alkali metal atom gas cell 7 and the atoms in the gas cell. The wave function of the evanescent field can be expressed as:

[0062]

[0063] k′ z =-k z i

[0064] in represents the complex form of the wave function, E0 is the amplitude, k z is the z-axis component of the wave vector, k′ z k z plural form of k xis the x-axis component of the wave vector, ω is the angular frequency, and t is the time. From the amplitude, it can be seen that the field strength of the evanescent field decays exponentially in the z-axis direction. The penetration depth of the evanescent field is:

[0065]

[0066] Where λ0 is the wavelength of the incident light, i1 is the incident angle, n1 and n2 are the refractive indices of the alkali metal atom gas cell 7 and the right-angle prism 8, respectively. Substituting the corresponding parameters, it can be calculated that the penetration depth of the evanescent field is on the nanometer level.

[0067] Figure 3 The figure shows the optical path propagation of the incident light undergoing total internal reflection, where the dotted line is the normal, the black solid arrow is a schematic diagram of the light propagation path at the macroscopic level, and the black dotted arrow is a schematic diagram of the propagation of the evanescent field at the microscopic level. n1 and n2 represent the refractive indices of the alkali metal atom gas chamber 7 and the right-angle prism 8, respectively (n1 < n2). When the incident light goes from a denser medium to a less dense medium, and the angle of incidence is greater than the angle of total internal reflection, the incident light wave will all return to the denser medium, i.e., total internal reflection occurs. For total internal reflection of light, the propagation path of the incident light should be to penetrate from the denser medium into the less dense medium, propagate forward a small distance, and then return to the less dense medium. That is, the center of mass of the reflected light beam at the medium interface does not coincide with the center of mass of the incident light beam, and the intensity of the transmitted light will exponentially decay with increasing distance from the interface, which is called the evanescent field. The present invention utilizes the evanescent field under the total internal reflection phenomenon as the pump light and detection light for atomic polarization. When the evanescent wave interacts with the atoms, the intensity and polarization degree of the reflected light will change. The reflected light is then detected by differential detection, thereby realizing magnetic field measurement.

[0068] Figure 4 Schematic diagram of the incident light angle. To ensure that the incident light beam is totally reflected on the oblique surface of the right-angle prism 8, it is necessary to calculate the incident angle of the light when it enters the right-angle side of the right-angle prism 8. This requirement is met by adjusting the optical rotation adjustment frame. The calculation method is as follows:

[0069] α t +i1=45°

[0070]

[0071] sinα=n2sinα t

[0072]

[0073] Where i1 is the incident angle of the inclined surface of the right angle prism 8, i c is the total reflection angle, α is the incident angle of the right angle side of the incident right angle prism 8 that needs to be calculated, α tIt is the angle between the reflected ray of the incident ray from the right angle side and the normal.

[0074] Any content not described in detail in this specification is prior art known to those skilled in the art. It should be noted that the above description is intended to help those skilled in the art understand the present invention, but does not limit the scope of protection of the present invention. Any equivalent substitution, modification, improvement, and / or simplification of the above description that does not depart from the essence of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A magnetic field measuring device based on total reflection evanescent field, characterized in that: The invention comprises an alkali metal atom gas cell having a first refractive index n1 and an optical path dielectric device having a second refractive index n2 forming a bonding interface therewith, wherein n1 is less than n2. Incident light from the optical path dielectric device forms a microscopic evanescent field on the bonding interface. The evanescent field acts as pump light and detection light acting on the alkali metal atom gas cell, causing the intensity and polarization degree of the reflected light of the incident light to change. The reflected light is detected by a differential detection device, thereby realizing magnetic field measurement. The optical path dielectric device is a right-angle prism, the hypotenuse of the right-angle prism forms a bonding interface with the bottom edge of the alkali metal atom gas chamber, the angle between the normal line of the first right-angle side of the right-angle prism and the incident light is α, and the angle between the normal line of the first right-angle side and the incident light of the hypotenuse is α. t The angle between the normal line of the hypotenuse and the incident light of the hypotenuse is i1, and the angle between the normal line of the hypotenuse and the reflected light is the total reflection angle i c , i1=i c , the reflected light is emitted from the second right-angle side of the right-angle prism to the differential detection device, and the relevant parameters are calculated according to the following formula to ensure that the incident light beam is totally reflected on the oblique surface of the right-angle prism: α t +i1＝45° sinα=n2sinα t 2. The magnetic field measuring device based on total reflection evanescent field according to claim 1, characterized in that: The wave function of the evanescent field is expressed as follows: k′ z =-k z i in Represents the complex form of the wave function, E0 is the amplitude, e is the natural constant, i is the imaginary unit, k z is the z-axis component of the wave vector, z is the z-axis coordinate, k′ z k z plural form of k x is the x-axis component of the wave vector, x is the x-axis coordinate, ω is the angular frequency, and t is the time; The field intensity of the evanescent field decays exponentially in the z-axis direction, and the penetration depth d of the evanescent field is expressed as follows: Where λ0 is the wavelength of the incident light, i1 is the angle of incidence, and the corresponding parameters are substituted into the calculated penetration depth of the evanescent field, which is on the nanometer level.

3. The magnetic field measuring device based on total reflection evanescent field according to claim 1, characterized in that: The alkali metal atom gas cell is a cubic gas cell lacking one side, and the oblique surface of the right-angle prism is bonded to the lacking side of the alkali metal atom gas cell by epoxy resin glue.

4. The magnetic field measuring device based on total reflection evanescent field according to claim 1, characterized in that: The differential detection device includes a first photodetector and a second photodetector respectively connected to a phase-locked amplifier, the first photodetector is connected to the transmission end of a polarization beam splitter, the second photodetector is connected to the reflection end of the polarization beam splitter, the input end of the polarization beam splitter is connected to the reflected light output side of the optical path medium device through a 1 / 2 wave plate and a reflector in sequence, and the phase-locked amplifier is connected to a computer.

5. The magnetic field measuring device based on total reflection evanescent field according to claim 1, characterized in that: The incident light of the optical path medium device comes from a laser, and the laser is connected to the optical path medium device through a collimator, a polarizer and a quarter wave plate in sequence.

6. The magnetic field measuring device based on total reflection evanescent field according to claim 1, characterized in that: A non-magnetic electric heating device is provided on the periphery of the alkali metal atom gas chamber to increase the atomic number density in the gas chamber by heating the alkali metal atom gas chamber.

7. The magnetic field measuring device based on total reflection evanescent field according to claim 1, characterized in that: The alkali metal atom gas chamber and the optical path dielectric device are both located in a magnetic compensation coil, and the magnetic compensation coil is located in a magnetic shielding barrel.

8. The magnetic field measuring device based on total reflection evanescent field according to claim 1, characterized in that: The alkali metal atom gas chamber includes any one of potassium, rubidium, and cesium alkali metal atoms, and also contains quenching gas nitrogen and buffer gas helium. The laser wavelength of the incident light is at the center of the alkali metal atom D1 line, and the incident light is elliptically polarized light.

9. The magnetic field measuring device based on total reflection evanescent field according to claim 1, characterized in that: The optical path medium device is a nanometer-scale waveguide or a nanometer-scale grating or a micrometer-scale optical fiber.

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