Optically pumped magnetometer module

Abstract

An OPM module (1) comprises: a glass cell (10) that has encapsulated therein two types of alkali metals which are Rb and K; a pump light source (20) that irradiates the glass cell (10) with pump light (22) for exciting the alkali metals; a probe light source (30) that irradiates the glass cell (10) with probe light (32) in a direction orthogonal to the pump light (22); a magnetic field coil (40) that applies, to the glass cell (10), RF pulses in a direction intersecting the pump light (22); a detector (60) that detects the probe light (32) that has passed through the glass cell (10); and a measurement device (100) that measures a magnetic field acting on the glass cell (10), on the basis of the detection result from the detector (60). The glass cell (10) is continuously irradiated with the pump light (22).

Description

Optical Pumping Magnetic Sensor Module

[0003]

[0001] The present disclosure relates to an optical pumping magnetic sensor module.

[0002] Conventionally, an optically pumped magnetometer (hereinafter also referred to as "OPM") is known as a sensor capable of measuring a weak magnetic field. The OPM includes a cell in which gas atoms (excited species) are enclosed, and a light source that irradiates the cell with pump light for exciting the gas atoms in the cell. The OPM measures a weak magnetic field by utilizing the phenomenon that the energy levels of gas atoms excited by the pump light respond sensitively to the ambient magnetic field due to the Zeeman effect.

[0003] As the gas atoms enclosed in the cell, the vapor of alkali metal atoms may be used. Also, as a method for increasing sensitivity, a hybrid cell in which two types of alkali metal atoms are enclosed in the cell has been proposed.

[0004] Also, as a signal detection method of the OPM, there is a two-axis orthogonal type in which, in addition to the pump light, a probe light in a direction orthogonal to the pump light is irradiated to the cell to measure the change in polarization. In the measurement mode of the two-axis orthogonal type, there is a mode called a scalar mode that can be measured even under geomagnetism. Conventionally, in the scalar mode of the two-axis orthogonal type, first, pump light is applied to the cell to cause spin polarization in the metal atoms in the cell. Spin polarization refers to the amount indicating the bias of the spins of the atomic ensemble, and it is a phenomenon in which the direction of the macroscopic magnetization indicated by the ensemble of polarized spins is biased in one direction. Then, the pump light is turned off, and an alternating magnetic field pulse (RF pulse) in a direction intersecting the pump light immediately after the pump light is turned off is applied to the cell to tilt the spin polarization of the metal atoms in the direction of the RF pulse. Then, after turning off the alternating magnetic field pulse, the magnitude of the magnetic field is measured by reading with the probe light the state in which the spin polarization of the metal atoms converges in the direction of the magnetic field while performing a precession motion.

[0005] Yosuke Ito et al, “Development of an optically pumped atomic magnetometer using a K-Rb hybrid cell and its application to magnetocardiography”, AIP Advances 2, 032127 (2012), JULY 31 2012

[0006] As mentioned above, in conventional two-axis orthogonal scalar mode, the pump light was turned off before the RF pulse was applied to the cell. This required a separate dedicated device and control system to instantly switch the pump light on and off, resulting in a complex overall module configuration.

[0007] This disclosure was made to solve these problems, and its purpose is to simplify the configuration of a two-axis orthogonal optical pumping magnetic sensor module capable of scalar mode measurement.

[0008] The optical pumping magnetic sensor module according to this disclosure comprises a cell containing two or more alkali metals, a first light source that irradiates the cell with pump light to excite the alkali metals, a second light source that irradiates the cell with probe light in a direction perpendicular to the pump light, an application device that applies an alternating magnetic field pulse to the cell in a direction intersecting the pump light, a detector that detects the probe light that has passed through the cell, and a measuring device that measures the magnetic field acting on the cell based on the detection result of the detector. The pump light is continuously irradiated onto the cell.

[0009] According to this disclosure, the configuration of a two-axis orthogonal optical pumping magnetic sensor module capable of scalar mode measurement can be simplified.

[0010] This is a schematic diagram (1) showing an example of the overall configuration of an OPM module. This is a schematic diagram showing the principle of measurement in scalar mode. This is a schematic diagram showing the waveform of the command output by the measuring device in scalar mode. This is a diagram (1) showing the results of a verification experiment of measurement in scalar mode. This is a diagram (2) showing the results of a verification experiment of measurement in scalar mode. This is a schematic diagram (2) showing an example of the overall configuration of an OPM module. This is a schematic diagram (3) showing an example of the overall configuration of an OPM module.

[0011] This embodiment will be described in detail below with reference to the drawings. In the following description, the same or corresponding parts in the drawings will be denoted by the same reference numerals, and their descriptions will not be repeated.

[0012] <Overall Configuration> Figure 1 is a schematic diagram showing an example of the overall configuration of the optical pumping magnetic sensor (OPM) module 1 according to this embodiment. The OPM module 1 can be used to measure weak magnetic fields such as brain magnetic fields and cardiac magnetic fields.

[0013] The OPM module 1 according to this embodiment is a so-called two-axis orthogonal type that measures the change in polarization by irradiating the cell with pump light and probe light in a direction perpendicular to the pump light. The OPM module 1 comprises a glass cell 10, a pump light source 20 (first light source), a probe light source 30 (second light source), polarizing elements 21, 31, a magnetic field coil 40 (applying device), an AC power supply 50, a detector 60, and a measuring device 100.

[0014] The pump light source 20 is a light source that emits laser light, which is the source of the pump light 22, in response to a pump command from the measuring device 100. The laser light emitted by the pump light source 20 passes through the polarizing element 21 and then irradiates the glass cell 10. The polarizing element 21 is equipped with an element that converts the input light into a circularly polarized wave. Therefore, the pump light 22 that passes through the polarizing element 21 and irradiates the glass cell 10 is a circularly polarized wave.

[0015] The probe light source 30 is a light source that emits laser light, which is the source of the probe light 32, in response to a probe command from the measuring device 100. The laser light emitted by the probe light source 30 passes through the polarizing element 31 and then irradiates the glass cell 10. The polarizing element 31 is equipped with an element that converts the input light into a linearly polarized wave. Therefore, the probe light 32 that passes through the polarizing element 31 and irradiates the glass cell 10 is a linearly polarized wave.

[0016] The pump light 22 and probe light 32 irradiated onto the glass cell 10 are orthogonal to each other. Hereinafter, the direction of travel of the pump light 22 will be referred to as the Z-axis direction, the direction of travel of the probe light 32 as the X-axis direction, and the direction perpendicular to the Z-axis and X-axis will be referred to as the Y-axis direction.

[0017] The glass cell 10 is sealed with light-transmitting glass. The glass cell 10 is a hybrid glass cell in which two types of alkali metal atoms are sealed inside. In this embodiment, an example will be described in which rubidium Rb is used as the pump target and potassium K is used as the probe target as the two types of alkali metal atoms sealed inside the glass cell 10. Although not shown in Figure 1, the glass cell 10 is separately equipped with a heater for heating and vaporizing the alkali metal atoms inside.

[0018] The wavelength of the laser light emitted by the pump light source 20 is set to the resonance wavelength of rubidium Rb (for example, about 795 nm), one of the two alkali metal atoms (Rb, K) in the glass cell 10. As a result, when the pump light 22 is irradiated onto the glass cell 10, rubidium Rb is efficiently excited. On the other hand, since the resonance wavelength of potassium K is different from that of rubidium Rb, potassium K is not affected by the pump light 22.

[0019] The wavelength of the laser light emitted by the probe light source 30 is set to a wavelength that makes it easy to measure the signal change due to the spin polarization of potassium K, one of the two alkali metal atoms (Rb, K) in the glass cell 10. Specifically, the wavelength of the laser light emitted by the probe light source 30 is a value different from the resonance wavelength of rubidium Rb, and is set to a value slightly shifted from the resonance wavelength of potassium K (for example, about 770 nm) so that the probe light 32 does not reach the detector 60 due to excessive absorption by potassium K. This ensures sufficient detection intensity of the probe light 32 by the detector 60, making it easier to measure the signal change due to the spin polarization of potassium K.

[0020] The detector 60 is a polarimeter that detects probe light 32 that has passed through the glass cell 10. The detection result from the detector 60 is transmitted to the measuring device 100 as a measurement signal.

[0021] The AC power supply 50 responds to the RF pulse command from the measuring device 100 and supplies AC current to the magnetic field coil 40 for the duration of the RF pulse command.

[0022] The magnetic field coil 40 is supplied with alternating current from the AC power supply 50, and applies an alternating magnetic field pulse 41 to the glass cell 10 in a direction intersecting the pump light 22 (in the example shown in Figure 1, the X-axis direction). Hereinafter, the alternating magnetic field pulse 41 applied by the magnetic field coil 40 to the glass cell 10 will also be referred to as the "RF pulse 41". The magnetic field coil 40 in this embodiment has a Helmholtz coil shape, including a pair of coils arranged at both ends of the glass cell 10 in the X-axis direction. However, the magnetic field coil 40 is not necessarily limited to having a Helmholtz coil shape.

[0023] <Scalar Mode Measurement Principle> The OPM module 1 according to this embodiment can measure the magnetism acting on the glass cell 10 in scalar mode.

[0024] Figure 2 schematically illustrates the principle by which the OPM module 1 measures the target magnetic field Bm in scalar mode. Although Figure 2 shows an example where the target magnetic field Bm acts in the positive Z-axis direction, the direction of the target magnetic field Bm is not limited to the positive Z-axis direction.

[0025] First, by irradiating a glass cell 10 containing alkali metals (Rb, K) with pump light 22, spin polarization is induced in the alkali metal atoms within the glass cell 10. That is, the spin polarization of the alkali metal atoms becomes aligned with the direction of the pump light 22 (Z-axis direction).

[0026] Subsequently, by applying an RF pulse 41 to the glass cell 10 in a direction intersecting the pump light 22 (X-axis direction), the spin polarization of the alkali metal atoms is tilted. Figure 2 shows an example in which the spin polarization of the alkali metal atoms is tilted in the direction of the RF pulse 41 (X-axis direction) when the pump light 22 is turned off.

[0027] Subsequently, the RF pulse 41 is turned off. This causes the spin polarization of the alkali metal atoms to precess and gradually converge in the direction of the magnetic field (in the example shown in Figure 2, the direction of the target magnetic field Bm). The rotational frequency of this precession is called the Larmor frequency, and its value is proportional to the magnitude of the external magnetic field acting in the direction of spin polarization convergence. In other words, if the Larmor frequency is determined, the magnitude of the external magnetic field is also determined. This phenomenon is used to measure the magnitude of the target magnetic field Bm from the time change of the signal frequency detected by the detector 60. Specifically, the magnitude of the target magnetic field Bm is measured from the spectral density of the frequency of the FID (Free Induction Decay) signal detected by the detector 60.

[0028] <Continuous Irradiation of Pump Light 22> Conventionally, during measurements in scalar mode, the pump light 22 was irradiated intermittently. Specifically, the irradiation of the pump light 22 was stopped immediately before applying the RF pulse 41 to the glass cell 10, and the process of irradiating with the pump light 22 again after a predetermined time had elapsed was repeated. This was because there was a concern that if the pump light 22 continued to irradiate after the application of the RF pulse 41, the alkali metal atoms would continue to be excited by the pump light 22, causing the spin polarization to converge prematurely in the direction of the pump light 22, making it impossible to detect the FID signal for a long time and resulting in insufficient data necessary for frequency analysis.

[0029] Thus, conventional scalar mode measurements require intermittent irradiation of the pump light 22, which necessitates the separate control of a dedicated device such as an AOM (Acousto-Optic Modulator) to instantly switch the pump light 22 on and off (irradiation / non-irradiation), resulting in a complex overall module configuration.

[0030] Furthermore, while conventional scalar mode can measure the magnitude of the target magnetic field Bm, it has the drawback of not being able to determine the direction in which the measured magnetic field is acting.

[0031] Therefore, in the OPM module 1 according to this embodiment, the pump light 22 is continuously irradiated during measurement in scalar mode. This eliminates the need for a dedicated device and its control for instantaneously switching the pump light 22 on and off, thereby simplifying the overall configuration of the module. Furthermore, in the OPM module 1 according to this embodiment, since the pump light 22 is irradiated even after the RF pulse 41 is turned off, the direction of spin polarization convergence can be made to the direction of the pump light 22. As a result, the magnitude of the magnetic field can be measured based on the rotation frequency (Larmor frequency) when the spin polarization of alkali metal atoms converges in the direction of the pump light 22 while precessing. As a result, it becomes possible to identify that the measured magnitude of the magnetic field is acting in the direction of the pump light 22.

[0032] Figure 3 schematically shows the waveforms of commands (pump command, probe command, and RF pulse command) output by the measuring device 100 in scalar mode. The upper part of Figure 3 shows a command equivalent to a conventional device as a comparative example, and the lower part of Figure 3 shows the command according to this embodiment (present disclosure).

[0033] In the comparative example shown in the upper part of Figure 3, after irradiating with pump light 22 by pump command, the pump command is turned off to stop the irradiation of pump light 22, and then RF pulse 41 is applied by RF pulse command. The probe command is output continuously, and the probe light 32 is continuously irradiated.

[0034] Thus, in the comparative example, the pump command is output intermittently, and in order to instantly turn the pump light 22 on and off as commanded, a dedicated device and its control are required separately, making the overall configuration of the module complicated.

[0035] In contrast, in the present disclosure shown in the lower part of Figure 3, a pump command is output continuously, and the pump light 22 is continuously irradiated. That is, the measuring device 100 according to this embodiment controls the pump light source 20, probe light source 30, and AC power supply 50 to intermittently apply RF pulses 41 to the glass cell 10 while the pump light 22 and probe light 32 are continuously irradiated. The measuring device 100 according to this embodiment then measures the magnitude of the magnetic field acting on the glass cell 10 based on the time change in the frequency of the output signal, which depends on the magnitude of the rotation angle of the linear polarization plane of the probe light 32 detected by the detector 60 during the period when the RF pulse 41 is not applied to the glass cell 10. As a result, after the RF pulse 41 is turned off, the magnitude of the magnetic field can be measured based on the time change in the rotation frequency (Larmor frequency) when the spin polarization of the alkali metal atoms in the glass cell 10 precesses and converges in the direction of the pump light 22.

[0036] Thus, in this embodiment, during measurement in scalar mode, both probe commands and pump commands are output continuously, and the probe light 32 and pump light 22 are continuously irradiated. Therefore, a dedicated device and its control for instantaneously switching the pump light 22 on and off is not required, and the overall configuration of the module can be simplified.

[0037] Furthermore, in this embodiment, since the pump light 22 is continuously irradiated even after the RF pulse 41 is turned off, the spin polarization of the alkali metal atoms will converge towards the direction of the pump light 22 while precessing. Therefore, the rotational frequency (Larmor frequency) of the precession of the alkali metal atoms after the RF pulse 41 is turned off will be a value proportional to the magnitude of the magnetic field in the direction of the pump light 22. Thus, it can be determined that the measured magnitude of the magnetic field is acting in the direction of the pump light 22.

[0038] Conventionally, as described above, continuous irradiation with the pump light 22 caused the spin polarization to converge prematurely towards the pump light 22 after the RF pulse 41 was turned off, raising concerns that there would be insufficient data for frequency analysis. However, verification experiments conducted by the inventors of the present invention confirmed that even with continuous irradiation with the pump light 22, the spin polarization did not converge so quickly, and sufficient data for frequency analysis could be obtained.

[0039] Figures 4 and 5 show the results of a verification experiment of measurement in scalar mode according to this embodiment. In this verification experiment, a test magnetic field of 10 pT and 10 Hz was applied to the glass cell 10, and it was verified whether or not the test magnetic field could be measured.

[0040] Figure 4 is a graph showing an example of the waveforms of the signals (measured signal, RF pulse 41 command, and RF pulse 41 signal) obtained in the verification experiment. In Figure 4, the horizontal axis represents time (unit: s), and the vertical axis represents voltage (unit: V) which represents the signal level. In the scalar mode according to this embodiment, the pump light 22 is continuously irradiated as described above, but even in this case, as shown in Figure 4, the measured signal is gradually attenuated, and it was confirmed that a sufficient amount of FID signal (attenuated signal) necessary for frequency analysis can be obtained.

[0041] Figure 5 is a graph showing the result of converting the spectral density, analyzed from the FID signal included in the measurement signal in Figure 4, into a magnetic field. In Figure 5, the horizontal axis shows frequency (unit: Hz) on a logarithmic scale, and the vertical axis shows the magnetic field conversion result (unit: pT / √Hz) on a logarithmic scale. Note that "√Hz" represents the square root of the frequency (Hz). From Figure 5, it can be seen that the noise level is suppressed to about 500 fT / √Hz. It can also be seen that the magnetic field conversion result of the 10 Hz peak corresponds to a value of 10 pT. The magnetic field conversion results in Figure 5 are consistent with the strength of the test magnetic field applied in this verification experiment, suggesting that the magnetic field can be directly converted from the spectral density value even without prior knowledge of the magnitude of the magnetic field.

[0042] Furthermore, even when the pump light 22 is continuously irradiated, sufficient data necessary for frequency analysis can be obtained mainly due to the following two factors.

[0043] The first factor is that the intensity of the pump light 22 is not so strong. That is, because the intensity of the pump light 22 is not so strong, even if the pump light 22 remains irradiated after the RF pulse 41 is turned off, the spin polarization does not converge early in the direction of the pump light 22, but converges at a slow speed such that a sufficient amount of attenuation signal data necessary for frequency analysis can be obtained.

[0044] The second factor is that two types of alkali metal atoms, rubidium Rb and potassium K, are enclosed inside the glass cell 10. That is, rubidium Rb is spin-polarized by the pump light 22, while potassium K is not much affected by the pump light 22. On the other hand, what is detected by the probe light 32 is the behavior of potassium K that is not much affected by the pump light 22. Therefore, it is considered that even in a state where the pump light 22 is continuously irradiated, the state of the precession motion of potassium K can be detected by the probe light 32.

[0045] As described above, the OPM module 1 according to the present embodiment includes a glass cell 10 in which two types of alkali metals (Rb, K) are enclosed, a pump light source 20 that irradiates the glass cell 10 with pump light 22 for exciting the alkali metal, a probe light source 30 that irradiates the glass cell 10 with probe light 32 in a direction orthogonal to the pump light 22, a magnetic field coil 40 that applies an RF pulse 41 in a direction intersecting the pump light 22 to the glass cell 10, a detector 60 that detects the probe light 32 that has passed through the glass cell 10, and a measuring device 100 that measures the magnetic field acting on the glass cell 10 based on the detection result of the detector 60. The pump light 22 is continuously irradiated to the glass cell 10.

[0046] In the OPM module 1 according to the present embodiment, by having the above-described configuration, during measurement in a biaxial orthogonal scalar mode, a dedicated device for instantaneously switching the on / off of the pump light 22 and its control become unnecessary. As a result, the configuration of the OPM module 1 can be simplified.

[0047] Furthermore, in the OPM module 1 according to the present embodiment, after the RF pulse 41 is turned off, the magnitude of the magnetic field is measured based on the rotational frequency (Larmor frequency) when the spin polarization of the alkali metal atoms converges in the direction of the pump light 22. Therefore, it is possible to specify that the measured magnitude of the magnetic field acts in the direction of the pump light 22.

[0048] <Modification Example 1> In the OPM module 1 shown in FIG. 1 described above, an example in which the RF pulse 41 is applied in the X-axis direction is shown. However, the direction in which the RF pulse 41 is applied may be any direction that intersects the pump light 22, and is not necessarily limited to the X-axis direction.

[0049] FIG. 6 is a diagram schematically showing an example of the overall configuration of the OPM module 1A according to the present Modification Example 1. The OPM module 1A in FIG. 6 is obtained by changing the magnetic field coil 40 of the OPM module 1 in FIG. 1 to a magnetic field coil 40A.

[0050] The magnetic field coil 40A has a Helmholtz coil shape including a pair of coils respectively arranged at both ends in the Y-axis direction of the glass cell 10. When a current is supplied from the AC power supply 50 to the magnetic field coil 40A, an RF pulse 41 in the Y-axis direction is applied to the glass cell 10. Thus, the direction in which the RF pulse 41 is applied may be the Y-axis direction.

[0051] <Modification Example 2> FIG. 7 is a diagram schematically showing an example of the overall configuration of the OPM module 1B according to the present Modification Example 2. The OPM module 1B in FIG. 7 is obtained by adding an angle changing mechanism 200 to the OPM module 1A in FIG. 6.

[0052] The angle changing mechanism 200 is configured to change the irradiation direction of the pump light 22 to the glass cell 10 in response to a command from the measuring device 100, while maintaining the positional relationship of the components other than the glass cell 10 and the measuring device 100 (pump light source 20, probe light source 30, polarizing elements 21, 31, magnetic field coil 40A, AC power supply 50, detector 60). Figure 7 shows the state in which the components other than the glass cell 10 and the measuring device 100 have been rotated by a predetermined angle counterclockwise when viewed from the positive direction of the Y axis. This makes it possible to rotate the irradiation direction of the pump light 22 relative to the glass cell 10 by a predetermined angle around the Y axis.

[0053] By providing such an angle-changing mechanism 200, the direction of irradiation of the pump light 22 to the glass cell 10 can be arbitrarily changed. This makes it possible to measure the magnitude of the magnetic field acting on the glass cell 10 in any direction.

[0054] <Modification 3> In the above-described embodiment, an example was given in which rubidium Rb and potassium K are used as the two types of alkali metal atoms sealed inside the glass cell 10.

[0055] However, the glass cell 10 only needs to contain a first type of alkali metal that is excited by the pump light 22 and a second type of alkali metal that is not excited or is difficult to excited by the pump light 22, and is not necessarily limited to rubidium Rb and potassium K. For example, the two types of alkali metal atoms sealed inside the glass cell 10 may be any two of rubidium Rb, potassium K, and cesium Cs. Furthermore, there may be three or more types of alkali metal atoms sealed inside the glass cell 10.

[0056] In either case, the inclusion of two types of alkali metals inside the glass cell 10 makes it easier to secure the amount of data necessary for frequency analysis, even when the pump light 22 is continuously irradiated.

[0057] [Embodiments] The embodiments and their modifications described above will be understood by those skilled in the art to be specific examples of the following embodiments.

[0058] (Section 1) The optical pumping magnetic sensor module according to this disclosure comprises a cell containing two or more alkali metals, a first light source that irradiates the cell with pump light to excite the alkali metals, a second light source that irradiates the cell with probe light in a direction perpendicular to the pump light, an application device that applies an alternating magnetic field pulse to the cell in a direction intersecting the pump light, a detector that detects the probe light that has passed through the cell, and a measuring device that measures the magnetic field acting on the cell based on the detection result of the detector. The pump light is continuously irradiated onto the cell.

[0059] According to the optical pumping magnetic sensor module described in paragraph 1, during measurement in scalar mode with two axes orthogonal, the pump light is continuously irradiated onto the cell. Therefore, a dedicated device and its control for instantaneously switching the pump light on and off is unnecessary. As a result, the configuration of a two-axis orthogonal optical pumping magnetic sensor module capable of measurement in scalar mode can be simplified.

[0060] (Section 2) In the optical pumping magnetic sensor module described in Section 1, the measuring device measures the magnitude of the magnetic field in the direction of the pump light based on the time change of the signal frequency detected by the detector.

[0061] According to the optical pumping magnetic sensor module described in paragraph 2, it is possible to determine that the measured magnetic field magnitude is acting in the direction of the pump light.

[0062] (Section 3) In the optical pumping magnetic sensor module described in Section 1, the measuring device controls the first light source, the second light source, and the application device to intermittently apply an AC magnetic field pulse to the cell while the cell is continuously irradiated with pump light and probe light, and measures the magnetic field acting on the cell based on the time change of the signal frequency detected by the detector during the period when the AC magnetic field pulse is not applied to the cell.

[0063] According to the optical pumping magnetic sensor module described in Section 3, the magnitude of the magnetic field can be measured based on the time change of the rotation frequency (Larmor frequency) when the spin polarization of alkali metal atoms in the cell precesses and converges in the direction of the pump light after the AC magnetic field pulse is turned off.

[0064] (Clause 4) In the optical pumping magnetic sensor module described in paragraph 1, the alkali metal includes a first type of alkali metal that is excited by the pump light and a second type of alkali metal that is less excited by the pump light than the first type of alkali metal.

[0065] According to the optical pumping magnetic sensor module described in Section 4, it is possible to easily secure the amount of data necessary for frequency analysis even when the pump light is continuously irradiated.

[0066] (Clause 5) The optical pumping magnetic sensor module described in Clause 1 further comprises an angle changing mechanism that changes the direction of irradiation of the pump light to the cell while maintaining the positional relationship between the first light source, the second light source, the application device, and the detector.

[0067] According to the optical pumping magnetic sensor module described in Section 5, the direction of irradiation of the pump light onto the cell can be arbitrarily changed. This makes it possible to measure the magnitude of the magnetic field acting on the cell in any direction.

[0068] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope of the claims are intended to be included.

[0069] 1, 1A, 1B Optical pumping magnetic sensor (OPM) module, 10 Glass cell, 20 Pump light source, 21, 31 Polarizing element, 22 Pump light, 30 Probe light source, 32 Probe light, 40, 40A Magnetic field coil, 41 RF pulse (AC magnetic field pulse), 50 AC power supply, 60 Detector, 100 Measuring device, 200 Angle change mechanism.

Claims

1. An optical pumping magnetic sensor module comprising: a cell containing two or more alkali metals; a first light source that irradiates the cell with pump light to excite the alkali metals; a second light source that irradiates the cell with probe light in a direction perpendicular to the pump light; an application device that applies an alternating magnetic field pulse to the cell in a direction intersecting the pump light; a detector that detects the probe light that has passed through the cell; and a measuring device that measures the magnetic field acting on the cell based on the detection result of the detector, wherein the pump light is continuously irradiated onto the cell.

2. The optical pumping magnetic sensor module according to claim 1, wherein the measuring device measures the magnitude of the magnetic field in the direction of the pump light based on the time change of the signal frequency detected by the detector.

3. The optical pumping magnetic sensor module according to claim 1, wherein the measuring device controls the first light source, the second light source, and the application device to intermittently apply the AC magnetic field pulse to the cell while the pump light and the probe light are continuously irradiated to the cell, and measures the magnitude of the magnetic field acting on the cell based on the time change of the signal frequency detected by the detector during the period when the AC magnetic field pulse is not applied to the cell.

4. The optical pumping magnetic sensor module according to claim 1, wherein the alkali metal comprises a first type of alkali metal excited by the pump light and a second type of alkali metal less excited by the pump light than the first type of alkali metal.

5. The optical pumping magnetic sensor module according to claim 1, further comprising an angle changing mechanism that changes the direction of irradiation of the pump light to the cell while maintaining the positional relationship between the first light source, the second light source, the application device, and the detector.

Images