High-sensitivity single light vector atom magnetometer based on Herriott multi-reflection cavity

Abstract

The invention discloses a high-sensitivity single-light vector atomic magnetometer based on a Herriott multi-reflection cavity, an internal reflection rectangular prism in the center of the Herriott multi-reflection cavity can bend entering light by 90 degrees and divide the light into two directions perpendicular to each other, and for light in one direction, if a magnetic field perpendicular to the light exists, the light in the other direction can be reflected by the Herriott multi-reflection cavity. Therefore, the polarization of the atoms deviates from the previous direction, and the absorption of the atoms to light changes, so that the magnetic field can be measured. And the two beams of circularly polarized light in the mutually vertical direction work simultaneously to obtain three-axis magnetic field vector information. According to the invention, the complexity of the vector atomic magnetometer is simplified, the experimental device is simpler, the required resources are fewer, and the miniaturization is maintained.

Description

Technical Field

[0001] The invention belongs to the field of atomic devices for quantum precision measurement, and in particular relates to a high-sensitivity single-light vector atomic magnetometer based on a Herriott multi-reflection cavity. Background Art

[0002] Atomic magnetometers have been applied in many fields due to their high sensitivity to magnetic field detection. In order to achieve high sensitivity detection in the SERF state of near-zero magnetic field, a high temperature is usually required to maintain a high atomic density, and a film is coated in the atomic gas chamber to reduce atomic relaxation caused by collision. In the development of SERF atomic magnetometers, there are generally two working modes: dual-light and single-light. Among them, the single-light SERF atomic magnetometer completes magnetic field measurement under the drive of a non-resonant radio frequency field, and the optical path is simple, requiring fewer resources, so it is easy to miniaturize and practical. The typical working principle of the single-light SERF atomic magnetometer is: when the external magnetic field is zero, the polarization of the rubidium atoms is consistent with the pumping light, and the transmittance of the pumping light is the largest after passing through the atomic gas chamber. The magnetic field perpendicular to the pumping light will cause the polarization of the rubidium atoms to deviate from the direction of the light, resulting in a decrease in transmittance, so that the external magnetic field can be measured, but the atomic magnetometer is insensitive to the magnetic field along the direction of the pumping light. In this way, there is a blind spot for detection, and three-axis vector magnetic field detection cannot be achieved. If another beam of light is added and the two groups of light are perpendicular to each other, each beam of light can measure the magnetic field in two directions. In this way, the use of two groups of orthogonal light perpendicular to each other can achieve the purpose of complementary blind spots in single-axis detection and realize three-axis vector detection of spatial magnetic fields. However, the use of two beams of light will inevitably make the structure of the atomic magnetometer more complicated and larger in size. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a high-sensitivity single-light vector atomic magnetometer based on the Herriott multi-reflection cavity. A right-angle prism is placed in the middle of the Herriott multi-reflection cavity through the anode bonding technology, and the light is bent 90° in the atomic gas chamber to obtain two mutually perpendicular directions of light. For the light in one direction, in the presence of a modulated magnetic field perpendicular to the direction of the light, the signal contains the first-order and second-order harmonic components of the modulation frequency, and the amplitude of the first-order harmonic signal is proportional to the offset field in the direction of the oscillation field, thereby obtaining the value of the magnetic field. The light in another direction can similarly obtain the size of the magnetic field, and each beam of light can measure the magnetic field in two directions perpendicular to it, so that three-axis vector magnetic field detection is achieved using the light in two directions in the atomic gas chamber. The Herriott multi-reflection cavity introduced in the atomic gas chamber can improve the sensitivity. The light is emitted after 14 reflections in the multi-reflection cavity. The right-angle prism bends the light 90° in the atomic gas chamber to obtain light in two directions perpendicular to each other. The detection light is received by a photodetector and then demodulated by a phase-locked amplifier. The first-order harmonic components of different modulation frequencies on the three axes are demodulated respectively to obtain the amplitude output, based on which the magnetic field direction information in the three directions is obtained respectively.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0005] A high-sensitivity single-light vector atomic magnetometer based on a Herriott multi-reflection cavity, the magnetometer comprising a Herriott multi-reflection cavity, the Herriott multi-reflection cavity comprising a front cavity mirror, a rear cavity mirror and a right-angle prism, wherein:

[0006] The main axes of the front cavity mirror and the rear cavity mirror have a relative rotation angle of 39.3°, the respective axes of the front cavity mirror and the rear cavity mirror can intersect along the direction of the relative rotation angle, and the sum of the distances from the respective axes to the intersection point is 26.3 mm;

[0007] The right-angle prism is located within the relative rotation angle range of the main axes of the front cavity mirror and the rear cavity mirror, and is used to bend the light incident from the front cavity mirror by 90° and emit it from the front cavity mirror after multiple reflections.

[0008] Furthermore, the front cavity mirror and the rear cavity mirror are cylindrical mirrors with the same curvature.

[0009] Furthermore, the front and rear cavity mirrors and the right-angle prism are all precisely positioned using anodic bonding technology.

[0010] Furthermore, the front cavity mirror includes a small hole with a central size of 2.5 mm, the light spot diameter is 1 mm and is incident into the multi-reflection cavity from the 2.5 mm small hole at a horizontal angle of 7°.

[0011] Furthermore, the incident light is bent 90 degrees and then continues to be emitted toward the rear cavity mirror, and finally is emitted from the 2.5 mm small hole on the front cavity mirror after 14 reflections.

[0012] Furthermore, the incident light resonates with the transition frequency of the D1 line of the Rb87 atom, and after being converted into circularly polarized light by a quarter-wave plate, the light path is precisely incident in the 3D printed positioning device.

[0013] Furthermore, when performing three-axis vector magnetic field detection of the magnetometer, a modulated magnetic field signal is applied to each direction of X, Y, and Z. The magnetometer signal is demodulated by a phase-locked amplifier to obtain a first harmonic signal. The closed-loop operation of the magnetometer is realized through a feedback loop composed of a PID controller and an adder, and the atomic magnetometer signal is measured from the output end of the PID controller.

[0014] The beneficial effects of the present invention are:

[0015] The present invention adds an internal reflection right-angle prism in the center of a complex atomic gas chamber containing a Herriott multi-reflection cavity, and only one beam of light is introduced to realize three-axis vector magnetic field detection by relying on the light in two directions in the atomic gas chamber, which can simplify the complexity of the vector atomic magnetometer, make the experimental device simpler, require fewer resources and maintain miniaturization; and effectively improve the sensitivity of the vector atomic magnetometer, because the introduction of the Herriott multi-reflection cavity can effectively increase the optical path and enhance the absorption of atoms, and high-sensitivity measurement can be realized under the condition that the heating temperature of the atomic gas chamber does not need to be too high, and under typical conditions, the three-axis magnetic field sensitivity of the magnetometer is better than 50 fT / Hz1 / 2.

[0016] The vector atomic magnetometer has a large magnetic field measurement range. An active magnetic compensation coil is introduced to offset the interference of the external magnetic field. It can work within a magnetic field range of 500 nT. Due to the presence of two mutually perpendicular lasers, three-axis detection without blind spots can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the Herriott multi-reflection cavity made using a mechanical mold;

[0018] Figure 2 A schematic diagram of the optical path of using a beam of light to form two mutually perpendicular directions of light in a multi-reflection cavity;

[0019] Figure 3 Schematic diagram of the use of an atomic gas chamber containing a Herriott multi-reflection cavity in conjunction with a 3D printing platform;

[0020] Figure 4 The present invention is an implementation block diagram of a high-sensitivity single-light vector atomic magnetometer based on a Herriott multi-reflection cavity.

[0021] Reference numerals:

[0022] 1. Front cavity mirror, 2. Back cavity mirror, 3. Right-angle prism, 4. Mechanical mold, 5. Incident light, 6. Outgoing light, 7. Incident light plug, 8. 3D printing platform, 9. Atomic gas chamber. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0024] As mentioned above, the present invention provides a high-sensitivity single-light vector atomic magnetometer based on the Herriott multi-reflection cavity. The internal reflection right-angle prism at the center of the Herriott multi-reflection cavity can bend the incoming light by 90° into two mutually perpendicular directions. The light in each direction is circularly polarized light that resonates with the D1 line transition of the alkali metal atom Rb87, and can spin polarize the atom. Then, a photodiode is used to detect the intensity of the light after passing through the atomic gas chamber. The alkali metal atom Rb87 is filled in the atomic gas chamber, and two mutually perpendicular circularly polarized lights work simultaneously. A radio frequency field is applied in a direction perpendicular to the laser for modulation. The signal after the laser passes through the atomic gas chamber contains the first-order harmonic component and the second-order harmonic component of the non-resonant modulation magnetic field frequency. Among them, the amplitude of the first-order harmonic signal is proportional to the bias magnetic field along the direction of the excitation magnetic field. Under weak magnetic field conditions, the polarization of the atom is consistent with the propagation direction of the light, and the atom absorbs the least light. When there is a magnetic field perpendicular to the light, this will cause the polarization of the atom to deviate from the previous direction, and the atom's absorption of light will change. The demodulated signal from the phase-locked amplifier is used to complete the closed-loop negative feedback through a PID controller and an adder. After the closed-loop is locked, the feedback signal output from the PID controller represents the magnetic field information measured by the single-light vector atomic magnetometer. The magnitude of the magnetic field can be obtained based on the locked modulation magnetic field frequency, and similarly, the three-axis magnetic field vector information can be obtained from two mutually perpendicular lights.

[0025] Specifically, a complex atomic gas chamber containing a Herriott multi-reflection cavity is manufactured. The multi-reflection cavity used here adds a right-angle prism to bend the light path 90° inside the atomic gas chamber into light in two perpendicular directions in order to complete vector magnetic field detection. The front and rear cavity mirrors and the right-angle prism are precisely positioned using anode bonding technology, and then the multi-reflection cavity and the atomic gas chamber are completed. The front and rear cavity mirrors of the Herriott multi-reflection cavity are cylindrical mirrors with a diameter of 12.7 mm, a thickness of 2.5 mm, and a curvature radius of 60 mm. The distance between the two cylindrical mirrors is 26.3 mm, as shown in FIG. Figure 1As shown, the front and rear cavity mirrors are placed on the two right-angled sides of the right triangle. The spacing of 26.3 mm here refers to the sum of the distances from the center of the front and rear cavity mirrors to the right-angled vertices. The main axis has a relative rotation angle of 39.3°. A small hole with a diameter of 2.5 mm is opened in the center of the front cavity mirror. The light spot diameter is 1 mm and is incident from the small hole into the multi-reflection cavity at a horizontal angle of 7°. The light path is first bent 90° by a right-angle prism. The bent light will continue to shoot toward the rear cavity mirror, and finally emerge from the same small hole on the front cavity mirror after 14 reflections. The length, width and height of the atomic gas chamber are 29 mm×29 mm×15 mm, which is filled with Rb87 atoms and 250 torr buffer gas N2.

[0026] Construct the optical path of the atomic magnetometer. Adjust the laser frequency to make it resonate with the transition frequency of the D1 line of the Rb87 atom. After being converted into circularly polarized light by a quarter-wave plate, the optical path is precisely incident in the 3D printed positioning device, and is shot into the multi-reflection cavity in the atomic gas chamber at a horizontal angle of 7°. First, the light enters from the front cavity mirror and then shoots to the right-angle prism, and then is reflected to the rear cavity mirror. In this way, it is repeated 14 times between the front cavity mirror, the rear cavity mirror, and the right-angle prism before being emitted ( Figure 2 Approximate light path diagram with 14 reflections), using a photodetector to receive the final outgoing light.

[0027] Data acquisition and processing. The temperature of the atomic gas chamber is heated to 75 °C. Taking the laser in one direction as an example, a modulated magnetic field is applied perpendicular to the direction of the laser beam. The laser beam signal contains the 1st and 2nd harmonics of the modulation frequency. The amplitude of the 1st harmonic signal is proportional to the residual magnetic field along the direction of the modulated magnetic field. The same measurement steps can be carried out for magnetic fields in three directions. Here, taking the X direction as an example, a modulated magnetic field signal (ωx=1.795 kHz, amplitude of 44nT) is applied along the X direction. The atomic magnetometer signal is demodulated by a phase-locked amplifier to obtain the 1st harmonic signal, and then the closed-loop operation of the atomic magnetometer is realized through a feedback loop composed of a PID controller and an adder, and the atomic magnetometer signal is measured from the PID output. By analogy, the three-axis vector magnetic field detection of the atomic magnetometer is completed.

[0028] Example

[0029] like Figure 1As shown, the front cavity mirror 1, the rear cavity mirror 2 and the right-angle prism 3 constituting the Herriott multi-reflection cavity are precisely positioned with the assistance of the mechanical mold 4. Only after their positions are determined can the multi-reflection cavity be prepared by the anodic bonding technology. The front cavity mirror 1 and the rear cavity mirror 2 are cylindrical mirrors with the same curvature, with a diameter of 12.7 mm, a thickness of 2.5 mm, and a curvature radius of 60 mm. The two cavity mirrors must also ensure the correct angle of the optical axis of 39.3° and the stability of the mutual distance of 26.3 mm. Under these parameter conditions, light is injected from the center hole of the front cavity mirror 1 at a specific incident angle, bent 90° by the right-angle prism to form light in two perpendicular directions, and emitted from the same center hole after multiple reflections.

[0030] Figure 2 The Herriott multi-reflection cavity is shown with a given reflection number of 14 and the focal lengths of the front and rear cavity mirrors. =30 mm, according to the calculation method of ABCD matrix, the appropriate angle between the optical axes of the front cavity mirror 1 and the rear cavity mirror 2 is 39.3°, and the mutual distance between them is 26.3 mm. The incident light 5 enters the multi-reflection cavity through the small hole with a size of 2.5 mm in the center of the front cavity mirror 1. Due to the action of the right-angle prism 3, the light path is bent by 90°, which means that only one beam of light can exist in two vertical directions. At the same time, the multi-reflection cavity with 14 reflections finally changes from the same small hole to the outgoing light 6 after repeating this step many times.

[0031] Figure 3 It shows that the atomic gas chamber 9 containing the Herriott multi-reflection cavity is placed in the 3D printing platform 8, where 3D printing can ensure the accuracy of the optical path and avoid the tedious work of adjusting the optical path. The output light of the laser is introduced by the optical fiber, and after passing through the collimating lens, it is integrated into the incident light plug 7, which is plug-and-play on the 3D printing platform 8, and can easily introduce light into the entire atomic magnetometer experimental system. The incident light 5 passes through the quarter-wave plate and becomes circularly polarized light, which hits the atomic gas chamber 9. The laser frequency is equal to the D1 line transition frequency of Rb87, which is used to measure the intensity change of light and atoms under the action of the magnetic field.

[0032] Figure 4The complete working process of a highly sensitive single-light vector atomic magnetometer based on a Herriott multi-reflection cavity is demonstrated. The assembled 3D printing platform 8 is placed in a 5-layer Permalloy magnetic shielding tube, and the atomic gas chamber 9 is heated to approximately 75 °C and maintained, and then the magnetic field measurement is started. In a weak magnetic field, the polarization of the Rb87 atom is consistent with the direction of circularly polarized light, and the light can be transmitted to the photodetector through the atom to the maximum extent. However, the magnetic field perpendicular to the light beam will cause the atomic polarization to deviate from the polarization direction, which will cause a significant decrease in light transmittance. Therefore, the magnitude of the magnetic field can be measured by light transmittance. In the multi-reflection cavity of the present invention, the right-angle prism 3 is bent 90° to produce light in two directions perpendicular to each other, which means that three-axis vector magnetic field measurement can be achieved. Taking any one of the magnetic field directions, the Z axis, as an example, a modulated magnetic field signal is applied along the Z axis direction, and an adder is used to add it to the output of the PID controller. The atomic magnetometer signal passes through a phase-locked amplifier, a PID controller and an adder to realize a closed feedback loop. The atomic magnetometer signal is measured from the PID output. In the modulated magnetic field ωz perpendicular to the direction of the light beam, the signal of the photodetector contains the 1st and 2nd harmonics of the modulation frequency ωz. The amplitude of the 1st harmonic signal is proportional to the offset magnetic field along the Z axis of the modulation magnetic field direction, thus realizing the Z-axis magnetic field measurement. Similarly, the three-axis magnetic field vector detection can be realized simultaneously.

[0033] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-sensitivity single-light vector atomic magnetometer based on Herriott multi-reflection cavity, characterized in that: The magnetometer comprises a Herriott multi-reflection cavity, and the Herriott multi-reflection cavity comprises a front cavity mirror, a rear cavity mirror and a right-angle prism, wherein: The main axes of the front cavity mirror and the rear cavity mirror have a relative rotation angle of 39.3°, the respective axes of the front cavity mirror and the rear cavity mirror can intersect along the direction of the relative rotation angle, and the sum of the distances from the respective axes to the intersection point is 26.3 mm; The right-angle prism is located within the relative rotation angle range of the main axes of the front cavity mirror and the rear cavity mirror, and is used to bend the light incident from the front cavity mirror by 90° and emit it from the front cavity mirror after multiple reflections.

2. The high-sensitivity single-light vector atomic magnetometer based on the Herriott multi-reflection cavity according to claim 1, characterized in that: The front cavity mirror and the rear cavity mirror are cylindrical mirrors with the same curvature.

3. The high-sensitivity single-light vector atomic magnetometer based on the Herriott multi-reflection cavity according to claim 1, characterized in that: The front and rear cavity mirrors and the right-angle prism are all precisely positioned using anodic bonding technology.

4. The high-sensitivity single-light vector atomic magnetometer based on the Herriott multi-reflection cavity according to claim 1, characterized in that: The front cavity mirror includes a small hole with a center size of 2.5 mm, the light spot diameter is 1 mm and is incident into the multi-reflection cavity from the 2.5 mm small hole at a horizontal angle of 7°.

5. The high-sensitivity single-light vector atomic magnetometer based on the Herriott multi-reflection cavity according to claim 1, characterized in that: The incident light is bent 90° and then continues to travel toward the rear cavity mirror, and finally exits from a 2.5 mm small hole on the front cavity mirror after 14 reflections.

6. The high-sensitivity single-light vector atomic magnetometer based on Herriott multi-reflection cavity according to claim 1, characterized in that: The incident light resonates with the transition frequency of the D1 line of the Rb87 atom, and after being converted into circularly polarized light by a quarter-wave plate, the light path is precisely incident in the 3D printed positioning device.

7. The high-sensitivity single-light vector atomic magnetometer based on Herriott multi-reflection cavity according to claim 1, characterized in that: When performing three-axis vector magnetic field detection of the magnetometer, a modulated magnetic field signal is applied to each direction of X, Y, and Z. The magnetometer signal is demodulated by a phase-locked amplifier to obtain a first harmonic signal. The closed-loop operation of the magnetometer is realized through a feedback loop composed of a PID controller and an adder, and the atomic magnetometer signal is measured from the output end of the PID controller.

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