Magnetic sensor module and method for determining operating conditions for magnetic sensor module

Abstract

To enhance measurement sensitivity according to a state change of a cell.SOLUTION: A magnetic sensor module 1 comprises: a cell 2; a pump laser light source 4; a photodiode 13 for detecting intensity of pump light; a probe laser light source 5; a photodiode element 9a for detecting intensity of probe light; a differential amplifier 16 for generating a magnetism detection signal on the basis of the probe light passed through the cell 2; and a control circuit 17 that carries out at least one of first determination processing for determining a driving condition of the light source 4 on the basis of the intensity of the pump light as detected by the photodiode 13 while performing wavelength sweeping of the pump light by controlling the light source 4 and second determination processing for determining a driving condition of the light source 5 on the basis of the intensity of the probe light as detected by the photodiode element 9a while performing wavelength sweeping of the probe light by controlling the light source 5.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] One aspect of the embodiment relates to a magnetic sensor module and a method for determining an operating condition of the magnetic sensor module. [Background technology]

[0002] Optically pumped magnetometers have been used to measure magnetic fields (see Patent Document 1 below). An optically pumped magnetometer includes a cell containing an alkali metal, a light source that irradiates pump light into the cell, a light source that irradiates probe light into the cell so that the probe light intersects with the pump light, and a detection means that detects a signal reflecting the rotation angle of the polarization plane of the probe light. An optically pumped magnetometer with this configuration can measure weak magnetic fields by using the spin polarization of the alkali metal excited by optical pumping. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-50837 Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional optically pumped magnetometers such as those described above, it is important to adjust the operating conditions of the light source to ensure the sensitivity of magnetic field measurement. It is desirable to adjust the operating conditions of the light source in response to changes in the cell's internal temperature, cell pressure, etc., but it has tended to be difficult to achieve adjustments that respond to changes in the cell's state.

[0005] Therefore, one aspect of the embodiment has been made in consideration of such problems, and its objective is to provide a magnetic sensor module and a method for determining the operating conditions of a magnetic sensor module that can increase measurement sensitivity in response to changes in the state of the cell. [Means for solving the problem]

[0006] a signal output unit that detects a change in the polarization plane of the probe light based on the probe light passing through the cell, and generates an output signal related to the magnetism in the cell; and a control unit that performs at least one of a first determination process that controls the first light source to sweep the wavelength of the pump light and determines drive conditions for the first light source based on the intensity of the pump light detected by the first detector, and a second determination process that controls the second light source to sweep the wavelength of the probe light and determines drive conditions for the second light source based on the intensity of the probe light detected by the second detector.

[0007] Alternatively, a method for determining operating conditions of a magnetic sensor module according to a second aspect of the embodiment is a method for determining operating conditions of a magnetic sensor module including: a cell in which an alkali metal is sealed; a first light source that emits pump light for exciting atoms of the alkali metal; a first detector that detects the intensity of the pump light; a second light source that emits probe light for detecting changes in the magnetic rotation angle caused by spin polarization in the excited state of the atoms; a second detector that detects the intensity of the probe light; and a signal output unit that detects changes in the polarization plane of the probe light based on the probe light that has passed through the cell, and generates an output signal related to the magnetism in the cell, wherein the method performs at least one of a first determination process for determining operating conditions of the first light source based on the intensity of the pump light detected by the first detector while controlling the first light source to sweep the wavelength of the pump light; and a second determination process for determining operating conditions of the second light source based on the intensity of the probe light detected by the second detector while controlling the second light source to sweep the wavelength of the probe light.

[0008] According to the first or second aspect, the intensity of pump light emitted from a first light source toward the cell is detected by a first detector, the intensity of probe light emitted from a second light source toward the cell is detected by a second detector, and an output signal related to magnetism is generated based on the probe light that has passed through the cell. Furthermore, the magnetic sensor module performs either a process of determining drive conditions for the first light source based on the intensity of the pump light while sweeping the wavelength of the pump light, or a process of determining drive conditions for the second light source based on the intensity of the probe light while sweeping the wavelength of the probe light. This allows the light source to be set to an appropriate drive condition even if a change occurs in the state of the cell, thereby improving measurement sensitivity in response to the change in the state of the cell.

[0009] In the first aspect, it is preferable that the first determination process is a process of determining the drive conditions of the first light source so that the intensity of the pump light becomes a minimum value, thereby enabling the drive conditions of the first light source to be set so that the spin polarization of the alkali metal is increased, thereby reliably improving the measurement sensitivity.

[0010] It is also preferable that the second determination process is a process of measuring the wavelength characteristics of the probe light intensity, calculating the wavelength characteristics of the output signal from the wavelength characteristics, and determining the drive conditions of the second light source so that the wavelength characteristics of the output signal have a maximum value. In this case, the drive conditions of the second light source can be set so that the output signal of the signal output unit becomes large, thereby reliably improving the measurement sensitivity.

[0011] Furthermore, it is also preferable to further include a magnetic field correction coil for correcting the magnetic field in the space where the cell exists, and the control unit further performs processing to control the correction by the magnetic field correction coil based on the intensity of the pump light. In this way, residual magnetic fields such as geomagnetism in the cell can be corrected, and measurement sensitivity can be further improved.

[0012] Furthermore, it is also preferable that the control unit controls the correction by the magnetic field correction coil so that the intensity of the pump light becomes an extreme value. In this way, correction can be made to cancel out residual magnetic fields such as geomagnetism in the cell, thereby further improving measurement sensitivity.

[0013] Preferably, the control unit performs both the first determination process and the second determination process, which allows both the first light source and the second light source to be set to appropriate driving conditions, thereby reliably improving measurement sensitivity in response to changes in the cell state. [Effects of the Invention]

[0014] According to any aspect of the present invention, it is possible to improve measurement sensitivity in response to changes in the state of the cell. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic configuration diagram of a magnetic sensor module 1 according to an embodiment. [Figure 2] 10 is a graph showing a change in the probe light intensity signal with respect to a change in the supply current to the coil 10a. [Figure 3] 10 is a graph showing a change in the probe light intensity signal with respect to a change in the supply current to the coil 10c. [Figure 4] 10 is a graph showing a change in the probe light intensity signal with respect to a change in the supply current to the coil 10b. [Figure 5] 10 is a graph showing a change in pump light intensity signal with respect to a change in wavelength of pump light. [Figure 6] 10 is a graph showing the characteristics of the absorption cross section σ(ν) of an alkali metal and the polarization rotation angle θ with respect to the wavelength ν of the probe light, and the characteristics of the intensity of the magnetic detection signal with respect to the wavelength ν of the probe light. [Figure 7] 10 is a graph showing the relationship between the probe light intensity and the intensity value Sout of the magnetic detection signal, the noise value Nout of the magnetic detection signal, and the S / N value SNout of the magnetic detection signal. [Figure 8]1 is a flowchart illustrating a procedure of an operating condition determination method according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description, the same elements or elements having the same functions will be denoted by the same reference numerals, and redundant description will be omitted.

[0017] FIG. 1 is a schematic diagram of a magnetic sensor module 1 according to an embodiment. The magnetic sensor module 1 is a device that measures magnetic fields using optical pumping. The magnetic sensor module 1 is used for biological measurements such as magnetoencephalography and magnetospinography, or for material analysis such as NMR (Nuclear Magnetic Resonance), but is not limited to these uses. In FIG. 1, the y-axis is taken along the direction of incidence of pump light on a cell (described later), the x-axis is taken along the direction of incidence of probe light on the cell and perpendicular to the y-axis, and the z-axis is taken perpendicular to the y-axis and x-axis. In FIG. 1, the light propagation path is indicated by a dotted line, and the power and signal transmission paths are indicated by solid lines with arrows.

[0018] The magnetic sensor module 1 includes a cell 2, a heater 3, a pump laser light source (first light source) 4, a probe laser light source (second light source) 5, a half-wave plate 6, a quarter-wave plate 7, a polarizing beam splitter 8, a photodiode (detector) 9, a magnetic field correction coil 10, current sources 11 and 12, a photodiode (detector) 13, amplifiers 14 and 15, a differential amplifier (signal output unit) 16, and a control circuit (control unit) 17. Each component of the magnetic sensor module 1 will be described in detail below.

[0019] The cell 2 has, for example, a substantially rectangular parallelepiped, bottomed cylindrical shape and is made of a material that is optically transparent to the pump light and probe light described below. Examples of materials for the cell 2 include quartz, sapphire, silicon, Kovar glass, and borosilicate glass. The cell 2 contains an alkali metal and a filler gas. The alkali metal contained in the cell 2 may be, for example, at least one of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). The filler gas suppresses relaxation of the spin polarization of the alkali metal vapor. The filler gas also protects the alkali metal vapor and suppresses noise emission. The filler gas may be, for example, an inert gas such as helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), or nitrogen (N2).

[0020] The heater 3 is provided in the vicinity of the cell 2 and heats the inside of the cell 2. The heater 3 generates heat in response to a current supplied from a current source 11. Based on a measurement signal from a temperature sensor (not shown) that measures the internal temperature of the cell 2, the heater 3 controls the supply current of the current source 11 so that the internal temperature of the cell 2 reaches a predetermined temperature (e.g., 180°C), thereby vaporizing the alkali metal inside the cell 2 and controlling the vapor density.

[0021] The pump laser light source 4 emits linearly polarized pump light for exciting alkali metal atoms. The pump laser light source 4 may shape the pump light to any size. The alkali metal atoms contained in the cell 2 are excited by the pump light, and their spin directions become aligned (spin polarization). The wavelength of the pump light is set according to the type of atoms constituting the alkali metal vapor (more specifically, the wavelength of the absorption line). In this embodiment, the driving conditions of the pump laser light source 4 are determined by the control circuit 17, and the intensity and wavelength of the pump light emitted from the pump laser light source 4 can be adjusted by control of the control circuit 17 (details will be described later). To achieve such control, the pump laser light source 4 has a function that allows the oscillation wavelength to be controlled using an external resonator, or a configuration that allows the oscillation wavelength to be controlled by temperature control of the laser element.

[0022] The probe laser light source 5 emits linearly polarized probe light for detecting changes in the magnetic rotation angle caused by spin polarization of alkali metal atoms in an excited state. The probe laser light source 5 may shape the probe light to any size. When the probe light passes through the alkali metal vapor, it is affected by the spin polarization of the alkali metal atoms and causes magnetic rotation. By detecting changes in the polarization plane of the probe light due to this magnetic rotation, the state of spin polarization can be derived. The wavelength of the probe light is set according to the type of atoms constituting the alkali metal vapor (more specifically, the wavelength of the absorption line). In this embodiment, the control circuit 17 determines the driving conditions of the probe laser light source 5, and the intensity and wavelength of the probe light emitted from the probe laser light source 5 can be adjusted by control of the control circuit 17 (details will be described later). To achieve such control, the probe laser light source 5 has a function capable of controlling the oscillation wavelength using an external resonator or a configuration capable of controlling the oscillation wavelength by controlling the temperature of the laser element.

[0023] In this embodiment, the direction in which the pump light passes through the cell 2 (positive direction along the y-axis) and the direction in which the probe light passes through the cell 2 (positive direction along the x-axis) are set to be perpendicular to each other.

[0024] The half-wave plate 6 is an optical element fixed on the optical path of the probe light between the probe laser light source 5 and the cell 2, and rotates the polarization direction of the probe light. The half-wave plate 6 is provided together with the polarizing beam splitter 8, and functions as a beam splitter that can adjust the branching ratio of the probe light. The quarter-wave plate 7 is an optical element fixed on the optical path of the pump light between the pump laser light source 4 and the cell 2, and changes the polarization state of the pump light from linearly polarized to circularly polarized.

[0025] The polarizing beam splitter 8 separates the probe light that has passed through the cell 2 into a first light component having a first polarization plane and a second light component having a polarization plane orthogonal to the first light component. For example, the first polarization plane is tilted 45 degrees relative to the polarization plane of the probe light emitted from the probe laser light source 5. The second light component is tilted 90 degrees relative to the first polarization plane. Therefore, when no magnetic field is applied to the cell 2, the light intensities of the probe light having the first and second polarization planes are equal. On the other hand, when a magnetic field is applied to the cell 2, the spin polarization of the alkali metal atoms changes, and the polarization plane of the probe light changes as it passes through the cell 2. As a result, the balance of the light intensities changes depending on the strength of the magnetic field. In response to this balance, the polarizing beam splitter 8 outputs the first light component in the positive direction of the x-axis and the second light component in the positive direction of the y-axis.

[0026] The photodiode 9 includes two photodiode elements 9a and 9b, and is a detection unit that detects, outside the cell 2, the probe light that is orthogonal to the pump light inside the cell 2. The photodiode element 9a is arranged in the positive direction of the x-axis with respect to the polarizing beam splitter 8. A first light component that has passed through the polarizing beam splitter 8 is incident on the photodiode element 9a. The photodiode element 9a generates and outputs a signal corresponding to the intensity of the first light component. The photodiode element 9b is arranged in the positive direction of the y-axis with respect to the polarizing beam splitter. A second light component that has been reflected by the polarizing beam splitter 8 is incident on the photodiode element 9b. The photodiode element 9b generates and outputs a signal corresponding to the intensity of the second light component.

[0027] The differential amplifier 16 generates and amplifies a differential signal indicating the difference between the output signal of the photodiode element 9a and the output signal of the photodiode element 9b as a magnetic detection signal that detects a change in the polarization plane of the probe light that has passed through the cell 2, and outputs the signal to the control circuit 17. The voltage value of this magnetic detection signal indicates the strength of the magnetic field in the cell 2.

[0028] The amplifier 15 amplifies the output signal from the photodiode element 9a and generates a signal (probe light intensity signal) that detects the intensity of the probe light transmitted through the cell 2. The amplifier 15 outputs the amplified probe light intensity signal to the control circuit 17. Of the output signals from the photodiode element 9a, the amplifier 15 uses a voltage and the differential amplifier 16 uses a current, so that the photodiode element 9a can be shared, simplifying the configuration of the device.

[0029] The photodiode 13 is a detection unit that detects, outside the cell 2, the pump light that has passed through the inside of the cell 2. The photodiode 13 generates and outputs a signal (pump light intensity signal) that corresponds to the intensity of the pump light that has passed through the cell 2. The amplifier 14 amplifies the pump light intensity signal output from the photodiode 13 and outputs it to the control circuit 17.

[0030] The magnetic field correction coils 10 are a group of coils provided around the cell 2 to correct and cancel environmental magnetic fields, such as geomagnetism, in the space where the cell 2 exists in three axial directions: the x-axis, y-axis, and z-axis. The magnetic field correction coils 10 include, for example, three coils 10a, 10c, and 10b wound around the x-axis, y-axis, and z-axis. The three coils 10a, 10c, and 10b generate corrective magnetic fields along the x-axis, y-axis, and z-axis, respectively, by current supplied from a current source 12. The magnetic field correction coils 10 operate to cancel the environmental magnetic fields in the space where the cell 2 exists by controlling the current supplied from the current source 12 to the coils 10a, 10c, and 10b using a control circuit 17.

[0031] The control circuit 17 derives the magnetic field inside the cell 2 based on the magnetic detection signal from the differential amplifier 16, and outputs the derived result to the outside. The control circuit 17 also has a function of controlling the magnetic field correction by the magnetic field correction coil 10, and a function of determining the operating conditions (drive conditions) of the pump laser light source 4 and the probe laser light source 5.

[0032] That is, the control circuit 17, as a function of controlling magnetic field correction, adjusts the correction magnetic field by adjusting the current supplied to the coils 10a, 10b, and 10c based on the pump light intensity signal output from the amplifier 14. More specifically, the control circuit 17 observes the change in the pump light intensity signal while changing the current supplied to each of the coils 10a, 10b, and 10c, and adjusts the current supplied to each of the coils 10a, 10b, and 10c so that the change in the pump light intensity becomes an extreme value. In this way, the correction of the environmental magnetic field in the three axial directions is controlled.

[0033] A specific example of magnetic field correction control will be described with reference to FIGS. 2 to 4. FIGS. 2 to 4 are graphs showing changes in the pump light intensity signal with respect to changes in the supply current of each of the coils 10a, 10c, and 10b. As described above, when the correction magnetic field along the x-axis and z-axis is changed, the pump light intensity changes to a maximum value, and when the correction magnetic field along the y-axis is changed, the pump light intensity changes to a minimum value. The control circuit 17 adjusts the supply current to each of the coils 10a, 10c, and 10b to a value corresponding to these extreme values. The pump light intensity reaching an extreme value means that the environmental magnetic field is zero and there are few alkali atoms in the ground state in the cell 2. The control circuit 17 adjusts the correction magnetic field by utilizing this phenomenon.

[0034] Additionally, the control circuit 17 determines the operating conditions of the pump laser light source 4 by adjusting the wavelength of the pump light emitted from the pump laser light source 4 based on the pump light intensity signal. More specifically, the control circuit 17 changes the oscillation wavelength of the pump laser light source 4 to sweep the wavelength of the pump light while observing changes in the pump light intensity signal, and controls the pump laser light source 4 to achieve an oscillation wavelength (laser driving conditions such as laser driving temperature that indicate the oscillation wavelength) at which the change in pump light intensity is minimized. This makes it possible to determine the wavelength of the pump light without using a wavemeter.

[0035] A specific example of determining the operating conditions of the pump laser light source 4 will be described with reference to FIG. 5. FIG. 5 is a graph showing changes in the pump light intensity signal with respect to changes in the wavelength of the pump light. A minimum pump light intensity like this means that the wavelength of the pump light at that time corresponds to the absorption spectrum of the alkali metal atoms in the cell 2, and that the absorption of the pump light in the cell 2 is maximum at that wavelength of the pump light. In this case, the voltage value of the magnetic detection signal from the differential amplifier 16 also becomes maximum at that wavelength of the pump light. Taking advantage of this property, the control circuit 17 can correct the deviation of the oscillation wavelength of the pump laser light source 4 from the desired wavelength (the deviation between the set wavelength and the actual output wavelength) by adjusting it using the measurement result of the pump light intensity without using a wavemeter.

[0036] Furthermore, as a function of determining the operating conditions of the probe laser light source 5, the control circuit 17 determines the operating conditions of the probe laser light source 5 by adjusting the wavelength of the probe light emitted by the probe laser light source 5 based on the probe light intensity signal output from the amplifier 15.

[0037] A specific example of determining the operating conditions of the probe laser light source 5 will be described with reference to Fig. 6. Fig. 6 is a graph showing the characteristics of the absorption cross section σ(ν) of an alkali metal and the polarization rotation angle θ with respect to the wavelength ν of the probe light, and the characteristics of the intensity S of the magnetic detection signal with respect to the wavelength ν of the probe light. The absorption cross section σ(ν) of an alkali metal and the polarization rotation angle θ have the relationship expressed by the following theoretical formulas (1) and (2) with respect to the wavelength ν of the probe light.

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[0038] Using the above theoretical formula, the control circuit 17 measures the wavelength characteristics of the voltage value of the probe light intensity signal while sweeping the wavelength of the probe light, determines the above theoretical formula (1) that approximates the wavelength characteristics, and identifies the unknown parameter Γ in the obtained theoretical formula (1). The control circuit 17 then applies the identified Γ to the above theoretical formulas (2) and (3) to calculate the theoretical value of the wavelength characteristics of the intensity S. Furthermore, the control circuit 17 calculates the value of the absorption cross-section σ when the theoretical value of the calculated wavelength characteristics of the intensity S reaches a maximum value, and determines the operating conditions of the probe laser light source 5 so that the probe light intensity signal output from the amplifier 15 has a voltage value with an optical transmittance corresponding to the calculated value. This allows the wavelength of the probe light to be set to a state where the sensitivity of the magnetic detection signal is high, regardless of variations in the characteristics of the cell 2.

[0039] Furthermore, the control circuit 17 determines the operating conditions of the probe laser light source 5 by adjusting the intensity of the probe light emitted from the probe laser light source 5 based on the probe light intensity signal output from the amplifier 15. Figure 7 shows the relationship between the probe light intensity and the intensity value S of the magnetic detection signal. out , the noise value of the magnetic detection signal N out , and the signal-to-noise ratio value of the magnetic detection signal SN out 1 is a graph showing the relationship between the probe light intensity and the signal-to-noise ratio (SN ratio). As described above, when the probe light intensity becomes excessively strong, the signal-to-noise ratio (SN ratio) deteriorates in the output of the magnetic sensor module 1. The control circuit 17 controls the probe light intensity signal output from the amplifier 15 to a value (for example, 100 mW / cm) that does not deteriorate the signal-to-noise ratio. 2) is set to a voltage value corresponding to the value of the magnetic field intensity of the cell 2. This allows the probe light intensity to be set to a state where the quality of the magnetic detection signal is high, regardless of variations in the characteristics of the cell 2.

[0040] Hereinafter, with reference to FIG. 8, the procedure of the preparatory operation in the magnetic sensor module 1 will be described, and the operating condition determination method according to the embodiment will be described in detail.

[0041] First, when the operation of the magnetic sensor module 1 is started, the control circuit 17 controls the current supplied to the heater 3 to start a cell heating process so that the inside of the cell 2 reaches a predetermined temperature (step S1). Next, the control circuit 17 executes a function of determining the operating conditions of the probe laser light source 5 to adjust the wavelength of the probe light (step S2). Furthermore, the control circuit 17 executes a function of determining the operating conditions of the probe laser light source 5 to adjust the intensity of the probe light (step S3).

[0042] Thereafter, the control circuit 17 executes a function of determining the operating conditions of the pump laser light source 4, thereby adjusting the wavelength of the pump light (step S4). Next, the control circuit 17 executes a function of determining the operating conditions of the pump laser light source 4, thereby adjusting the intensity of the pump light (step S5). Furthermore, the control circuit 17 executes a function of controlling magnetic field correction, thereby controlling the magnetic field correction in the three axial directions by the magnetic field correction coil 10 (step S6). Finally, the control circuit 17 executes a process of quantifying the external output value of the magnetic detection signal while the magnetic reference signal is applied to the cell 2 (step S7).

[0043] In the above preparatory operation, the wavelengths of the probe light and the pump light are adjusted, followed by the intensities of the probe light and the pump light. This facilitates optimization of the operating conditions of the light source. Furthermore, the control of the correction magnetic field is performed after the probe light and the pump light are adjusted. This improves the accuracy of correction of the environmental magnetic field when the magnetic sensor module 1 actually detects a magnetic field.

[0044] The effects of the magnetic sensor module 1 according to the embodiment described above will be described.

[0045] According to the magnetic sensor module 1, the intensity of the pump light emitted from the pump laser light source 4 toward the cell 2 is detected by the photodiode 13, the intensity of the probe light emitted from the probe laser light source 5 toward the cell 2 is detected by the photodiode element 9a, and a magnetic detection signal related to magnetism is generated based on the probe light that has passed through the cell 2. Furthermore, the magnetic sensor module 1 performs both a process of determining the operating conditions of the pump laser light source 4 based on the intensity of the pump light while sweeping the wavelength of the pump light, and a process of determining the operating conditions of the probe laser light source 5 based on the intensity of the probe light while sweeping the wavelength of the probe light. This makes it possible to set both light sources to appropriate operating conditions even if a change occurs in the state of the cell, thereby improving measurement sensitivity in response to changes in the state of the cell.

[0046] The process of determining the operating conditions of the pump laser light source 4 is a process of determining the operating conditions of the first light source so that the intensity of the pump light becomes a minimum value. This allows the operating conditions of the light source to be set so that the spin polarization of the alkali metal is increased, thereby reliably improving the measurement sensitivity.

[0047] The process of determining the operating conditions of the probe laser light source 5 measures the wavelength characteristics of the probe light intensity, calculates the wavelength characteristics of the output signal from the wavelength characteristics, and determines the operating conditions of the second light source so that the wavelength characteristics of the output signal have a maximum value. In this case, the operating conditions of the light source can be set so that the magnetic detection signal becomes large, thereby reliably improving the measurement sensitivity.

[0048] The device further includes a magnetic field correction coil 10 that corrects the magnetic field in the space where the cell 2 exists, and the control circuit 17 further performs processing to control the magnetic field correction by the magnetic field correction coil 10 based on the intensity of the pump light. This allows for correction of residual magnetic fields such as geomagnetism in the cell, further improving measurement sensitivity. At this time, the control circuit 17 controls the correction by the magnetic field correction coil 10 so that the intensity of the pump light becomes an extreme value. This control allows for correction to cancel residual magnetic fields such as geomagnetism in the cell, further improving measurement sensitivity.

[0049] Various embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments, and may be modified or applied to other things within the scope that does not change the gist of the claims.

[0050] For example, in the above embodiment, either a process of determining the operating conditions of the pump laser light source 4 based on the intensity of the pump light while sweeping the wavelength of the pump light, or a process of determining the operating conditions of the probe laser light source 5 based on the intensity of the probe light while sweeping the wavelength of the probe light, may be performed. Even in this case, even if a change occurs in the state of the cell, one of the light sources can be set to an appropriate operating condition, and measurement sensitivity can be improved in response to the change in the state of the cell.

[0051] In the above embodiment, the amplifier that amplifies and outputs the probe light intensity signal may be a differential amplifier 16. In such a configuration, a shutter is provided that blocks the component of the probe light incident on either the photodiode element 9 a or the photodiode element 9 b, and the operation of the shutter is controlled to block the component of the probe light when the probe light intensity signal is output. [Explanation of symbols]

[0052] 1...magnetic sensor module, 2...cell, 4...pump laser light source (first light source), 5...probe laser light source (second light source), 9a...photodiode element (second detector), 13...photodiode (first detector), 10...magnetic field correction coil, 16...differential amplifier (signal output section), 17...control circuit (control section).

Claims

1. a cell in which an alkali metal is sealed; a first light source that emits pump light for exciting the alkali metal atoms; a first detector that detects the intensity of the pump light; a second light source that emits a probe light for detecting a change in the magnetic rotation angle caused by the spin polarization of the atoms in an excited state; a second detector for detecting the intensity of the probe light; a signal output unit that detects a change in the polarization plane of the probe light based on the probe light that has passed through the cell, and generates an output signal related to the magnetism in the cell; a control unit that performs at least one of a first determination process of determining a drive condition of the first light source based on the intensity of the pump light detected by the first detector while controlling the first light source to sweep the wavelength of the pump light, and a second determination process of determining a drive condition of the second light source based on the intensity of the probe light detected by the second detector while controlling the second light source to sweep the wavelength of the probe light; Equipped with the first determination process is a process of determining a driving condition of the first light source so that the intensity of the pump light becomes a minimum value; Magnetic sensor module.

2. A cell in which an alkali metal is sealed; a first light source that emits pump light for exciting the alkali metal atoms; a first detector that detects the intensity of the pump light; a second light source that emits a probe light for detecting a change in the magnetic rotation angle caused by the spin polarization of the atoms in an excited state; a second detector for detecting the intensity of the probe light; a signal output unit that detects a change in the polarization plane of the probe light based on the probe light that has passed through the cell, and generates an output signal related to the magnetism in the cell; a control unit that performs at least one of a first determination process of determining a drive condition of the first light source based on the intensity of the pump light detected by the first detector while controlling the first light source to sweep the wavelength of the pump light, and a second determination process of determining a drive condition of the second light source based on the intensity of the probe light detected by the second detector while controlling the second light source to sweep the wavelength of the probe light; Equipped with the second determination process is a process of measuring wavelength characteristics of the intensity of the probe light, calculating wavelength characteristics of the output signal from the wavelength characteristics, and determining drive conditions of the second light source such that the wavelength characteristics of the output signal have a maximum value. Magnetic sensor module.

3. A cell in which an alkali metal is sealed; a first light source that emits pump light for exciting the alkali metal atoms; a first detector that detects the intensity of the pump light; a second light source that emits a probe light for detecting a change in the magnetic rotation angle caused by the spin polarization of the atoms in an excited state; a second detector for detecting the intensity of the probe light; a signal output unit that detects a change in the polarization plane of the probe light based on the probe light that has passed through the cell, and generates an output signal related to the magnetism in the cell; a control unit that performs both a first determination process of determining a drive condition of the first light source based on the intensity of the pump light detected by the first detector while controlling the first light source to sweep the wavelength of the pump light, and a second determination process of determining a drive condition of the second light source based on the intensity of the probe light detected by the second detector while controlling the second light source to sweep the wavelength of the probe light; Equipped with Magnetic sensor module.

4. Further provided is a magnetic field correction coil for correcting a magnetic field in a space where the cell exists; the control unit further performs a process of controlling correction by the magnetic field correction coil based on the intensity of the pump light. The magnetic sensor module according to any one of claims 1 to 3.

5. the control unit controls the correction by the magnetic field correction coil so that the intensity of the pump light becomes an extreme value. The magnetic sensor module according to claim 4 .

6. 1. A method for determining operating conditions of a magnetic sensor module, comprising: a cell in which an alkali metal is sealed; a first light source that emits pump light for exciting atoms of the alkali metal; a first detector that detects the intensity of the pump light; a second light source that emits probe light for detecting a change in magnetic rotation angle caused by spin polarization in an excited state of the atoms; a second detector that detects the intensity of the probe light; and a signal output unit that detects a change in the polarization plane of the probe light based on the probe light that has passed through the cell, and generates an output signal related to magnetism in the cell, performing at least one of a first determination process of determining a driving condition of the first light source based on the intensity of the pump light detected by the first detector while controlling the first light source to sweep the wavelength of the pump light, and a second determination process of determining a driving condition of the second light source based on the intensity of the probe light detected by the second detector while controlling the second light source to sweep the wavelength of the probe light; the first determination process is a process of determining a driving condition of the first light source so that the intensity of the pump light becomes a minimum value; A method for determining operating conditions of a magnetic sensor module.

7. A method for determining operating conditions of a magnetic sensor module comprising: a cell in which an alkali metal is sealed; a first light source that emits pump light for exciting atoms of the alkali metal; a first detector that detects the intensity of the pump light; a second light source that emits probe light for detecting changes in the magnetic rotation angle caused by spin polarization in the excited state of the atoms; a second detector that detects the intensity of the probe light; and a signal output unit that detects changes in the polarization plane of the probe light based on the probe light that has passed through the cell, and generates an output signal related to magnetism in the cell, performing at least one of a first determination process of determining a driving condition of the first light source based on the intensity of the pump light detected by the first detector while controlling the first light source to sweep the wavelength of the pump light, and a second determination process of determining a driving condition of the second light source based on the intensity of the probe light detected by the second detector while controlling the second light source to sweep the wavelength of the probe light; the second determination process is a process of measuring wavelength characteristics of the intensity of the probe light, calculating wavelength characteristics of the output signal from the wavelength characteristics, and determining drive conditions of the second light source such that the wavelength characteristics of the output signal have a maximum value. A method for determining operating conditions of a magnetic sensor module.

8. A method for determining operating conditions of a magnetic sensor module comprising: a cell in which an alkali metal is sealed; a first light source that emits pump light for exciting atoms of the alkali metal; a first detector that detects the intensity of the pump light; a second light source that emits probe light for detecting changes in the magnetic rotation angle caused by spin polarization in the excited state of the atoms; a second detector that detects the intensity of the probe light; and a signal output unit that detects changes in the polarization plane of the probe light based on the probe light that has passed through the cell, and generates an output signal related to magnetism in the cell, performing both a first determination process of determining a driving condition of the first light source based on the intensity of the pump light detected by the first detector while controlling the first light source to sweep the wavelength of the pump light, and a second determination process of determining a driving condition of the second light source based on the intensity of the probe light detected by the second detector while controlling the second light source to sweep the wavelength of the probe light; A method for determining operating conditions of a magnetic sensor module.

9. A cell in which an alkali metal is sealed; a first light source that emits pump light for exciting the alkali metal atoms; a first detector that detects the intensity of the pump light; a control unit that performs a first determination process to determine a driving condition of the first light source based on the intensity of the pump light detected by the first detector while controlling the first light source to sweep the wavelength of the pump light; Equipped with the first determination process is a process of determining a driving condition of the first light source so that the intensity of the pump light becomes a minimum value; Magnetic sensor module.

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