Miniaturized closed-loop FID scalar atom magnetometer and implementation method thereof

Abstract

The invention relates to a miniaturized closed-loop FID scalar atom magnetometer and an implementation method thereof, and belongs to the field of atom magnetic measurement. According to the method, the closed-loop working mode of the FID magnetometer is realized by utilizing a self-made electronics system, the modulation frequency of pumping light is corrected in real time, so that the magnetometer still keeps high sensitivity under a large magnetic field change rate, and the performance restriction between the dynamic range and the sensitivity of an open-loop FID magnetometer is broken through. The interaction between the self-made frequency meter and the time sequence control system is the core component of the closed loop of the magnetometer system. The device can measure a magnetic field with a large change rate at a high speed, is high in sensitivity and accuracy, and plays an important role in field magnetic measurement application.

Description

Technical Field

[0001] The present invention relates to the field of atomic devices and electronics, and in particular to a miniaturized closed-loop FID (Free-Induction-Decay) scalar atomic magnetometer and an implementation method thereof. Background Art

[0002] As a precision magnetic field measurement sensor, atomic magnetometers play an important role in basic physics research, geomagnetism research, and biomedical imaging. According to the working principle, atomic magnetometers can be divided into two categories: radio frequency modulation magnetometers and all-optical magnetometers. Compared with the former, the latter does not require additional application of a modulated magnetic field, avoiding the problem of the modulated magnetic field deteriorating the system noise. The FID magnetometer is an all-optical magnetometer, which avoids the optical frequency shift effect caused by the pumping light by separating the optical pumping stage and the optical detection stage in time domain. Therefore, the magnetic measurement accuracy is higher, and it is the mainstream solution in the field of atomic magnetometers.

[0003] Existing FID magnetometers use an open-loop working mode, and their pumping light is modulated at the Larmor precession frequency of atoms around the initial magnetic field to maximize the amplitude of the FID signal. However, there is a mutual constraint between the dynamic range and sensitivity performance of open-loop FID magnetometers. For example, a rubidium 87 atomic magnetometer with 200 Torr nitrogen in the atomic gas chamber: when the magnetic field to be measured changes by more than 50nT, the frequency difference between the pumping light modulation frequency and the atomic Larmor precession frequency will be greater than 350 Hz. At this time, the amplitude of the FID signal will decrease by about 10%, causing the sensitivity of the magnetometer system to be significantly reduced. Therefore, in practical applications, it is usually necessary to sacrifice the dynamic range to ensure the sensitivity of magnetic measurement, which is obviously not the best solution. Summary of the invention

[0004] The object of the present invention is to provide a miniaturized closed-loop FID scalar atomic magnetometer and a method for realizing the same.

[0005] According to a first aspect of the present invention, a miniaturized closed-loop FID scalar atomic magnetometer is provided, which is composed of a self-made miniaturized FID atomic magnetometer control circuit and a magnetic probe, wherein the magnetic probe integrates a small-volume atomic gas chamber, a first photodetector, a second photodetector, a third photodetector, and a fourth photodetector, and the self-made miniaturized FID atomic magnetometer control circuit comprises a pumping light source, a detection light source, a laser control unit, a pumping light modulation unit, a gas chamber heating unit, and a frequency meter unit, wherein the gas chamber heating unit is used to heat atoms in the small-volume atomic gas chamber, the first photodetector and the second photodetector are used to monitor the light intensity of the detection light and the pumping light respectively, and the third photodetector and the fourth photodetector are used to monitor the light intensity of the detection light after interacting with the atoms in the small-volume atomic gas chamber; the laser control unit is used to provide driving current for the pumping light source and the detection light source, the pumping light modulation unit is connected to the pumping light source, and the modulated pumping light is transmitted to the magnetic probe through an optical fiber; the detection light output by the detection light source is transmitted to the magnetic probe; the frequency meter unit calculates the FID signal frequency of the detection stage of the previous cycle and feeds it back to the pumping light modulation unit as the pumping light modulation frequency of the next cycle.

[0006] According to a second aspect of the present invention, a method for implementing an atomic magnetometer is provided, comprising:

[0007] The first step is to prepare a small-volume atomic gas chamber and fill the small-volume atomic gas chamber with rubidium 87 atoms and nitrogen;

[0008] The second step is to assemble the FID scalar atomic magnetometer: integrate a small-volume atomic gas chamber, a gas chamber heating unit, a first photodetector, a second photodetector, a third photodetector, and a fourth photodetector on the 3D-printed magnetic probe;

[0009] The third step is to control the gas chamber temperature of the small-volume atomic gas chamber at 90° C. by using a gas chamber heating unit, so that gaseous atoms with a stable atomic number density exist in the small-volume atomic gas chamber;

[0010] The fourth step is to use the laser control unit to drive the pumping light source and the detection light source to output the pumping light and the detection light respectively;

[0011] The fifth step is to perform closed-loop feedback signal processing of the FID scalar atomic magnetometer, wherein: the pumping light modulation unit outputs a trigger signal and frequency modulates the pumping light intensity during the pumping stage; the frequency meter unit calculates the FID signal frequency of the detection stage of the previous cycle and feeds it back to the pumping light modulation unit as the pumping light modulation frequency of the next cycle.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] 1) Based on the proposed self-made electronics system, the closed-loop working mode of the FID magnetometer is realized. By real-time correction of the modulation frequency of the pumping light, it can still have high sensitivity when measuring in a high dynamic range, breaking through the performance limitations of the dynamic range and sensitivity of the open-loop FID magnetometer, and giving it the ability to conduct on-site magnetic measurements;

[0014] 2) The large commercial instrument was replaced by a self-made highly integrated electronic system, achieving the miniaturization of the closed-loop FID magnetometer system;

[0015] 3) Use magnetic probes to achieve precise positioning of optical components, avoid tedious optical path adjustment processes, and facilitate miniaturization, integration, and application of magnetometer systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a block diagram of a miniaturized closed-loop FID scalar atomic magnetometer of the present invention;

[0017] Figure 2 It is a schematic diagram of the magnetic probe and its internal optical path in the present invention;

[0018] Figure 3 It is a closed-loop feedback signal processing flow chart and a signal processing timing chart of the FID scalar atomic magnetometer system of the present invention.

[0019] Reference numerals:

[0020] A self-made miniaturized FID atomic magnetometer control circuit 210, a magnetic probe 220, a small-volume atomic gas chamber 221, a first photodetector 222, a second photodetector 223, a third photodetector 224, a fourth photodetector 225, a pumping light source 211, a detection light source 212, a laser control unit 213, a pumping light modulation unit 214, a gas chamber heating unit 215, a frequency meter unit 216, and an operational amplifier 217;

[0021] Clamping head 1, first polarization beam splitter 2, first 1 / 2 glass slide 3, second polarization beam splitter 4, lens 5, 1 / 4 glass slide 7, first plano-convex lens 8, collimating head 9, linear polarizer 10, beam splitter 12, second plano-convex lens 13, second 1 / 2 glass slide 14, third polarization beam splitter 15. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0023] Figure 1 This is a block diagram of a miniaturized closed-loop FID scalar atomic magnetometer of the present invention. Figure 1As shown, the miniaturized closed-loop FID scalar atomic magnetometer is composed of a self-made miniaturized FID atomic magnetometer control circuit 210 and a magnetic probe 220, wherein the magnetic probe 220 integrates a small-volume atomic gas chamber 221, a first photodetector 222, a second photodetector 223, a third photodetector 224, and a fourth photodetector 225, and the self-made miniaturized FID atomic magnetometer control circuit 210 includes a pumping light source 211, a detection light source 212, a laser control unit 213, a pumping light modulation unit 214, and a gas chamber heating unit. 215, and a frequency meter unit 216, an operational amplifier 217, wherein the small-volume atomic gas chamber 221 may include a Herriott multi-reflection cavity, which may be a container for isotope rubidium 87 atoms and buffer gas nitrogen, the gas chamber heating unit 215 is used to heat the atoms in the small-volume atomic gas chamber 221, and may also be used to maintain the density of gaseous atoms stable, the first photodetector 222 and the second photodetector 223 are used to monitor the light intensity of the detection light and the pumping light, respectively, the third photodetector 224 and the fourth photodetector 2 25 is used to monitor the intensity of the detection light after the interaction with the atoms in the small-volume atomic gas chamber 221; the laser control unit 213 is used to provide driving current for the pumping light source 211 and the detection light source 212, and control the pumping light source 211 and the detection light source 212. The former can output a laser with a resonance frequency with the D1 transition line of the rubidium 87 atom, and the latter can output a laser far detuned from the D1 transition line of the rubidium 87 atom. The pumping light modulation unit 214 and the pumping light source 211 can be connected through an optical fiber to realize the modulation of the pumping light intensity or the laser frequency, and The modulated pumping light is transmitted to the magnetic probe through the optical fiber; the detection light output by the detection light source 212 can be directly transmitted to the magnetic probe 220 through the optical fiber; the frequency meter unit 216 calculates the FID signal frequency of the detection stage of the previous cycle and feeds it back to the pumping light modulation unit 214 as the pumping light modulation frequency of the next cycle; the frequency meter unit 216 is connected to an operational amplifier 217, and the operational amplifier 217 is used to convert the light intensity signal monitored by the third photodetector 224 and the fourth photodetector 225 into a voltage signal, and extract the corresponding FID signal.

[0024] In one embodiment, the small-volume atomic gas chamber 221 is made by an anodic bonding method. The magnetic probe 220 is made by 3D printing or machining, and is used for precise positioning and assembly of the atomic gas chamber and the photodetector, and should have sufficient manufacturing accuracy. The laser control unit 213 provides a driving current for the pumping light source and the detection light source through a constant current source circuit, and uses a proportional-integral control circuit to achieve temperature closed-loop locking, ensuring that the pumping light source and the detection light source generate pumping light and detection light with stable frequency and constant light intensity. The pumping light modulation unit 214 modulates the pumping light intensity or laser frequency generated by the pumping light source at a frequency f (f is the Larmor precession frequency of the atom around the external magnetic field). The frequency meter unit 216 calculates the frequency of the FID signal and calculates the magnetic field strength based on the gyromagnetic ratio of the rubidium 87 atom.

[0025] In one embodiment, the gas chamber heating unit 215 uses high-frequency alternating current to drive the non-magnetic heating sheet to heat the atoms in the small-volume atomic gas chamber 221, and stabilizes the density of gaseous atoms by controlling the heating temperature. The non-magnetic heating sheet is closely attached to the lower surface of the small-volume atomic gas chamber 221, and the small-volume atomic gas chamber 221 and the non-magnetic heating sheet are assembled together by designing a 3D printing structure inside the magnetic probe, and the assembly is wrapped with a heat-insulating material to reduce the heat exchange between the small-volume atomic gas chamber 221 and the external environment, thereby reducing the heating power consumption of the magnetometer.

[0026] The internal assembly and optical path of the magnetic probe are described below.

[0027] Figure 2 FIG. 1 is a schematic diagram of the atomic gas chamber assembly of the magnetic probe and its internal optical path in the present invention. Figure 2As shown, the atomic gas chamber assembly of the magnetic probe and its internal optical path are as follows: the pumping light is introduced into the magnetic probe through an optical fiber (fixed by a clamping head 1), and then polarized and purified by the first polarization beam splitter 2, and then divided into two parts of 12:1 by the first 1 / 2 glass slide 3 and the second polarization beam splitter 4. Among them, the light with an intensity of 1 / 13 is converged to the second photodetector 223 through the lens 5 for monitoring the pumping light intensity; the light with an intensity of 12 / 13 is converted into circularly polarized light through the 1 / 4 glass slide 7, and then passes through the first plano-convex lens 8 to uniformly polarize the rubidium 87 atoms in the atomic gas chamber. The detection light is introduced into the magnetic probe through an optical fiber (fixed by an optical fiber collimator 9). The optical fiber collimator 9 is a special 3D printed structure with a fixed plano-convex lens inside, which is used to collimate the detection light. The collimated detection light is polarized and purified by a linear polarizer 10, and then divided into two parts of 12:1 by a beam splitter 12. Among them, the light with a light intensity of 1 / 13 is received by the first photodetector 222 for detecting light intensity monitoring; the light with a light intensity of 12 / 13 is incident on the small-volume atomic gas chamber 221 and then emitted after interacting with the atoms. The emitted light is first converged by the second plano-convex lens 13, and then split by the second 1 / 2 glass slide 14 and the third polarization beam splitter 15 in a ratio of 1:1 to the third photodetector 224 and the fourth photodetector 225. Finally, the two parts of the detected light intensity are subtracted to obtain the FID signal.

[0028] At this point, the magnetic probe is used to assist in positioning the optical components of the main part of the magnetometer, avoiding the tedious process of adjusting the optical path and saving a lot of space.

[0029] Figure 3 The closed-loop feedback signal processing block diagram and signal processing timing diagram of the FID scalar atomic magnetometer of the present invention. Compared with the traditional open-loop FID magnetometer system, the introduction of the frequency meter unit and the pump light modulation unit realizes the closed loop of the FID magnetometer. Among them, the pump light modulation unit outputs a trigger signal to control the pump-detection process of the magnetometer and indicates the processing timing of the signal in the feedback system; the frequency meter unit calculates the FID signal frequency of the detection stage of the previous cycle and feeds it back to the pump light modulation unit as the pump light modulation frequency of the next cycle. With three pump-detection cycles ( , , ) as an example, the specific implementation steps of the above feedback system are:

[0030] Step a, cycle, the rising edge of the trigger signal output by the pump light modulation unit triggers the pump light modulation unit to Modulate the pump light, and the falling edge of the trigger signal output by the pump light modulation unit triggers the frequency meter unit to collect The periodic FID signal is recorded as ;

[0031] Step b, cycle, the rising edge of the trigger signal output by the pump light modulation unit triggers the pump light modulation unit to Modulate the pump light and trigger the frequency counter unit to calculate The frequency of the signal is denoted by The falling edge of the trigger signal output by the pump light modulation unit triggers the frequency meter unit to collect The periodic FID signal is recorded as , and Transmitted to the pump light modulation unit;

[0032] Step c, cycle, the rising edge of the trigger signal output by the pump light modulation unit triggers the pump light modulation unit to Modulate the pump light and trigger the frequency counter unit to calculate The frequency of the signal is calculated as The falling edge of the trigger signal output by the pump light modulation unit triggers the frequency meter unit to collect The periodic FID signal is recorded as , and Transmitted to the pump light modulation unit;

[0033] Step d: Repeating step c can continuously realize the closed loop of the FID scalar atomic magnetometer.

[0034] In one embodiment, the high level of the trigger signal lasts for 3 milliseconds, the low level lasts for 5 milliseconds, and the magnetic field sampling rate is 125 Hz.

[0035] According to an embodiment of the present invention, a method for implementing a miniaturized closed-loop FID scalar atomic magnetometer is provided, comprising:

[0036] The first step is to prepare a small-volume atomic gas chamber and fill the small-volume atomic gas chamber with rubidium 87 atoms and nitrogen;

[0037] The second step is to assemble the FID scalar atomic magnetometer: integrate a small-volume atomic gas chamber, a gas chamber heating unit, a first photodetector, a second photodetector, a third photodetector, and a fourth photodetector on a 3D-printed magnetic probe. In one embodiment, the 3D-printed magnetic probe is a platform with a precision of 0.05 mm.

[0038] The third step is to control the gas chamber temperature of the small-volume atomic gas chamber at 90° C. by using a gas chamber heating unit, so that gaseous atoms with a stable atomic number density exist in the small-volume atomic gas chamber;

[0039] The fourth step is to use the laser control unit to drive the pump light source and the detection light source to output pump light (the frequency resonates with the D1 transition line of the rubidium 87 atom) and detection light (the frequency deviates from the D1 transition line of the rubidium 87 atom by 80 GHz) respectively.

[0040] The fifth step is to perform closed-loop feedback signal processing of the FID scalar atomic magnetometer, wherein: the pumping light modulation unit outputs a trigger signal and frequency modulates the pumping light intensity during the pumping stage; the frequency meter unit calculates the FID signal frequency of the detection stage of the previous cycle and feeds it back to the pumping light modulation unit as the pumping light modulation frequency of the next cycle.

[0041] For the specific implementation process of the fifth step, please refer to the above Figure 3 Description.

[0042] The closed-loop working mode of the FID scalar atomic magnetometer can maintain high sensitivity at a large magnetic field change rate. Compared with the open-loop mode, this mode can respond to magnetic field changes of 2600 nT / s, which plays an important role in field magnetic measurements.

[0043] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0044] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A miniaturized closed-loop FID scalar atomic magnetometer, characterized in that: The invention is composed of a self-made miniaturized FID atomic magnetometer control circuit (210) and a magnetic probe (220), wherein the magnetic probe integrates a small-volume atomic gas chamber (221), a first photodetector (222), a second photodetector (223), a third photodetector (224), and a fourth photodetector (225); the self-made miniaturized FID atomic magnetometer control circuit comprises a pumping light source (211), a detection light source (212), a laser control unit (213), a pumping light modulation unit (214), a gas chamber heating unit (215), and a frequency meter unit (216); wherein the gas chamber heating unit (215) is used to heat the atoms in the small-volume atomic gas chamber (221). The first photodetector and the second photodetector are used to monitor the light intensity of the detection light and the pumping light respectively, and the third photodetector and the fourth photodetector are used to monitor the light intensity of the detection light after interacting with atoms in the small-volume atomic gas chamber; the laser control unit is used to provide driving current for the pumping light source and the detection light source; the pumping light modulation unit (214) is connected to the pumping light source (211) and transmits the modulated pumping light to the magnetic probe through the optical fiber; the detection light output by the detection light source (212) is transmitted to the magnetic probe (220); the frequency meter unit (216) calculates the FID signal frequency of the detection stage of the previous cycle and feeds it back to the pumping light modulation unit (214) as the pumping light modulation frequency of the next cycle.

2. The miniaturized closed-loop FID scalar atomic magnetometer according to claim 1, characterized in that: The small-volume atomic gas chamber (221) is manufactured by an anodic bonding method, and the magnetic probe (220) is manufactured by 3D printing or machining, and is used for accurate positioning and assembly of the small-volume atomic gas chamber (221) and the first photodetector (222), the second photodetector (223), the third photodetector (224), and the fourth photodetector (225).

3. The miniaturized closed-loop FID scalar atomic magnetometer according to claim 1, characterized in that: The laser control unit (213) provides driving current for the pumping light source and the detection light source through a constant current source circuit, and uses a proportional-integral control circuit to achieve temperature closed-loop locking, thereby ensuring that the pumping light source and the detection light source generate pumping light and detection light with stable frequency and constant power.

4. The miniaturized closed-loop FID scalar atomic magnetometer according to claim 1, characterized in that: The gas chamber heating unit (215) utilizes high-frequency alternating current to drive a non-magnetic heating sheet to heat atoms in the small-volume atomic gas chamber (221), and adjusts the heating current based on the temperature of the small-volume atomic gas chamber (221) measured by a thermocouple to stabilize the density of gaseous atoms.

5. The miniaturized closed-loop FID scalar atomic magnetometer according to claim 1, characterized in that: The non-magnetic heating plate is closely attached to the lower surface of the small-volume atomic gas chamber (221), and the thermocouple is closely attached to the side of the small-volume atomic gas chamber (221). The small-volume atomic gas chamber (221), the non-magnetic heating plate and the thermocouple are assembled together by designing a 3D printing structure inside the magnetic probe to form an assembly, and the assembly is wrapped with a thermal insulation material.

6. The miniaturized closed-loop FID scalar atomic magnetometer according to claim 1, characterized in that: The internal structure of the magnetic probe is as follows: The pumping light is introduced into the magnetic probe through the optical fiber, and then polarized and purified by the first polarization beam splitter (2), and then divided into two parts with a ratio of 12:1 by the first 1 / 2 glass plate (3) and the second polarization beam splitter (4), wherein the light with a light intensity of 1 / 13 is converged on the second photodetector (223) through the lens (5) for monitoring the pumping light intensity; the light with a light intensity of 12 / 13 is converted into circularly polarized light through the 1 / 4 glass plate (7), and then passes through the first plano-convex lens (8) to uniformly polarize the rubidium 87 atoms in the atomic gas chamber; the detection light is introduced into the magnetic probe through the optical fiber, and passes through the linear polarizer (10) is polarized and purified, and then the light is divided into two parts with a ratio of 12:1 by a spectroscope (12). The light with a ratio of 1 / 13 of the light intensity is received by a first photodetector (222) for detecting light intensity monitoring. The light with a ratio of 12 / 13 of the light intensity enters the atomic gas chamber and reacts with the atoms before being emitted. The emitted light is first converged by a second plano-convex lens (13), and then split by a second 1 / 2 glass slide (14) and a third polarization spectroscope (15) with a ratio of 1:1 to a third photodetector (224) and a fourth photodetector (225). Finally, the two detected light intensities are subtracted to obtain an FID signal.

7. A method for realizing an atomic magnetometer, for realizing a miniaturized closed-loop FID scalar atomic magnetometer according to any one of claims 1 to 6, characterized in that: include: The first step is to prepare a small-volume atomic gas chamber and fill the small-volume atomic gas chamber with rubidium 87 atoms and nitrogen; The second step is to assemble the FID scalar atomic magnetometer: integrate the small-volume atomic gas chamber, the non-magnetic heating plate and thermocouple required for the gas chamber heating unit, the first photodetector, the second photodetector, the third photodetector, and the fourth photodetector on the 3D printed magnetic probe; The third step is to control the gas chamber temperature of the small-volume atomic gas chamber at 90° C. by using a gas chamber heating unit, so that gaseous atoms with a stable atomic number density exist in the small-volume atomic gas chamber; The fourth step is to use the laser control unit to drive the pumping light source and the detection light source to output the pumping light and the detection light respectively; The fifth step is to perform closed-loop feedback signal processing of the FID scalar atomic magnetometer, wherein: the pumping light modulation unit outputs a trigger signal and frequency modulates the pumping light intensity during the pumping stage; the frequency meter unit calculates the FID signal frequency of the detection stage of the previous cycle and feeds it back to the pumping light modulation unit as the pumping light modulation frequency of the next cycle.

8. The method for realizing the atomic magnetometer according to claim 7, characterized in that: In the second step, the 3D printed magnetic probe is a platform with 0.05mm accuracy.

9. The method for realizing the atomic magnetometer according to claim 7, characterized in that: In the fourth step, the frequency of the pumping light resonates with the D1 transition line of the rubidium 87 atom, and the frequency of the detection light deviates from the D1 transition line of the rubidium 87 atom by 80 GHz.

10. The method for realizing an atomic magnetometer according to claim 7, characterized in that: The fifth step includes: Step a, first cycle The rising edge of the trigger signal output by the pump light modulation unit triggers the pump light modulation unit to generate a pulse at a frequency of Modulate the pump light, and the falling edge of the trigger signal output by the pump light modulation unit triggers the frequency meter unit to collect the first cycle The FID signal is recorded as ; Step b, second cycle The rising edge of the trigger signal output by the pump light modulation unit triggers the pump light modulation unit to generate a pulse at a frequency of Modulate the pump light and trigger the frequency counter unit to calculate The frequency of the signal is denoted by The falling edge of the trigger signal output by the pump light modulation unit triggers the frequency meter unit to collect the second cycle The FID signal is recorded as , and Transmitted to the pump light modulation unit; Step c, third cycle The rising edge of the trigger signal output by the pump light modulation unit triggers the pump light modulation unit to generate a pulse at a frequency of Modulate the pump light and trigger the frequency counter unit to calculate The frequency of the signal is calculated as The falling edge of the trigger signal output by the pump light modulation unit triggers the frequency meter unit to collect the third cycle The FID signal is recorded as , and Transmitted to the pumping light modulation unit; Step d, repeating step c, thereby continuously realizing the closed loop of the FID scalar atomic magnetometer.

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