Optical excitation magnetic sensor and brain magnetic instrument

Abstract

The invention provides an optical excitation magnetic sensor and a brain magnetic instrument. The optical excitation magnetic sensor includes: a unit; a pump light incidence section that causes pump light to enter a plurality of sensitivity regions inside the cell in a first direction; a probe light incidence unit that causes probe light to enter the plurality of sensitivity regions in a direction intersecting the first direction; a bias magnetic field coil that applies a bias magnetic field to the inside of the cell to determine the resonance frequency of the electron spin; an electron spin tilting unit that tilts the rotation axis direction of electron spin; a light sensor for detecting the probe light that has passed through the sensitivity region; and a magnetic field measurement unit that measures the magnetic field intensity of the sensitivity regions, and the bias magnetic field coil applies a plurality of bias magnetic fields having mutually different intensities to each of the plurality of sensitivity regions.

Description

Technical Field

[0001] The invention relates to a light-excited magnetoelectric sensor and a magnetoencephalometer comprising the light-excited magnetoelectric sensor. Background Art

[0002] There are known optically excited magnetic sensors that can measure weak external magnetic fields (for example, see U.S. Patent Publication No. 2022 / 0091200 and U.S. Patent No. 10,782,368). In the optically excited magnetic sensor, pump light is used to excite alkali metal atoms inside a cell, and a light sensor is used to measure probe light irradiated to the cell in a manner intersecting with the pump light, and the intensity of the external magnetic field is detected based on the output of the light sensor. Summary of the invention

[0003] Regarding the above-mentioned optically excited magnetic sensor, it is sometimes desirable to measure the magnetic field strength in a multi-channel manner. However, in such a case, the structure of the optical system tends to become complicated. Therefore, the technical problem of the present invention is to provide a multi-channel optically excited magnetic sensor and a magnetoencephalometer that can measure the magnetic field strength with a simple structure.

[0004] A light-induced magnetization sensor according to one aspect of the present invention is [1] "a light-induced magnetization sensor comprising: a cell in which alkali metal vapor is sealed; a pump light incident portion, which causes pump light to be incident on a plurality of sensitive regions inside the cell along a first direction, the pump light being used to excite alkali metal atoms constituting the alkali metal vapor; a probe light incident portion, which causes probe light to be incident on the plurality of sensitive regions along a direction intersecting the first direction, the probe light being used to detect changes in electron spins in an excited state of the alkali metal atoms; a bias magnetic field coil, which applies a bias magnetic field along the first direction to the inside of the cell to determine a resonance frequency of the electron spin; an electron spin tilting portion, which tilts the rotation axis direction of the electron spin in a direction perpendicular to the first direction; a light sensor, which detects the probe light after passing through the sensitive region; and a magnetic field measuring portion, which measures the magnetic field strength of the sensitive region based on an output of the light sensor, the bias magnetic field coil applying a plurality of bias magnetic fields having different strengths to each of the plurality of sensitive regions."

[0005] In this optically excited magnetic sensor, the intensity of the bias magnetic field can be changed for each of a plurality of sensitive regions, and the magnetic field intensity of a plurality of sensitive regions can be obtained using a single probe light. That is, multi-channel measurement of magnetic field intensity can be realized with a simple structure.

[0006] The light-excited magnetic sensor of one aspect of the present invention may also be [2] "the light-excited magnetic sensor described in [1], wherein the plurality of sensitivity regions include at least a first sensitivity region and a second sensitivity region, and the bias magnetic field coil includes: a first coil corresponding to the first sensitivity region; and a second coil corresponding to the second sensitivity region." In this case, it is possible to specifically change the intensity of the bias magnetic field for each of the plurality of sensitivity regions.

[0007] The optically excited magnetic sensor of one aspect of the present invention may also be [3] "the optically excited magnetic sensor described in [2], comprising a substrate on which the first coil and the second coil are provided, and a through hole for the pump light to pass through is formed in the substrate." In this case, the bias magnetic field coil can be specifically installed without hindering the incidence of the pump light on the unit.

[0008] The optically excited magnetic sensor of one aspect of the present invention may also be [4] "the optically excited magnetic sensor described in [2] or [3], wherein the first sensitive region is present at the end of the unit, and the bias magnetic field coil includes an outer coil of the unit that is arranged to be separated from the unit and adjacent to the first coil when viewed from the first direction." In this case, the outer coil of the unit can be used to more appropriately ensure the strength of the bias magnetic field applied to the first sensitive region on the end side of the unit.

[0009] The photoexcitation magnetic sensor of one aspect of the present invention may also be [5] "the photoexcitation magnetic sensor described in [1], wherein the plurality of sensitive regions include a first sensitive region, a second sensitive region adjacent to the first sensitive region, a third sensitive region adjacent to the second sensitive region, and a fourth sensitive region adjacent to the third sensitive region, and the bias magnetic field coil includes: a pair of first coils, which are arranged in a manner of sandwiching the first sensitive region in the first direction and formed with a first number of turns in the first rotation direction; a pair of second coils, which are arranged in a manner of sandwiching the second sensitive region in the first direction and formed with a second number of turns in the first rotation direction; a pair of third coils, which are arranged in a manner of sandwiching the third sensitive region in the first direction and formed with the second number of turns in the second rotation direction opposite to the first rotation direction; and a pair of fourth coils, which are arranged in a manner of sandwiching the fourth sensitive region in the first direction and formed with the first number of turns in the second rotation direction." In such a case, it is possible to specifically change the intensity of the bias magnetic field for each plurality of sensitive regions.

[0010] The optically excited magnetic sensor of one aspect of the present invention may also be [6] "the optically excited magnetic sensor described in any one of [1] to [5], wherein the plurality of sensitive regions include 1st to N sensitive regions (N is an integer greater than 2), the bias magnetic field coil applies 1st to N bias magnetic fields to the 1st to N sensitive regions respectively, so that the resonant frequencies of the 1st to N sensitive regions are 1st to N resonant frequencies, the magnetic field measuring unit obtains a mixed waveform of free induction decay containing components of the 1st to N resonant frequencies based on the output of the optical sensor, filters the mixed waveform using a bandpass filter, obtains 1st to N waveforms of free induction decay in each frequency band of the 1st to N resonant frequencies, derives each frequency of the 1st to N waveforms, and obtains the magnetic field strength of the 1st to N sensitive regions based on each frequency of the derived 1st to N waveforms." In such a case, the magnetic field strength of the 1st to N sensitive regions can be specifically measured.

[0011] The optically excited magnetic sensor according to one aspect of the present invention may be [7] "the optically excited magnetic sensor according to any one of [1] to [6], wherein the electron spin tilting unit irradiates an RF signal having the same frequency as the resonance frequency." In this case, the RF signal can be used to tilt the rotation axis of the electron spin.

[0012] The photoexcited magnetic sensor according to one aspect of the present invention may be [8] "the photoexcited magnetic sensor described in any one of [1] to [6], wherein the electron spin tilting unit irradiates pulsed light." In this case, the pulsed light can be used to tilt the rotation axis of the electron spin.

[0013] The optically excited magnetic sensor of one aspect of the present invention may also be [9] "the optically excited magnetic sensor described in any one of [1] to [8], wherein the magnetic field measuring unit measures the magnetic field strength based on the difference in output of the optical sensor corresponding to the two adjacent sensitivity regions." In this case, the common mode noise existing in the two sensitivity regions can be removed, and the measurement of weak magnetic field strength can be achieved.

[0014] A magnetoencephalometer according to one aspect of the present invention is

[10] "a magnetoencephalometer comprising a light-excited magnetoencephalometer as described in any one of [1] to [9], wherein the light-excited magnetoencephalometer is configured to be arranged around the head of a subject to measure the intensity of a magnetic field emitted by the subject."

[0015] In this magnetoencephalometer, since the optically excited magnetoencephalometer sensor is provided, the above-mentioned effect of enabling multi-channel measurement of magnetic field intensity with a simple structure can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a perspective view showing the structure of a light-excited magnetic sensor according to an embodiment.

[0017] Figure 2 From the -x axis Figure 1 A top view of the first optical system and the second optical system.

[0018] Figure 3 Yes means Figure 1 A timing diagram showing the generation timings of pump light, RF signal, and probe light when the external magnetic field measurement process is performed by a readout circuit.

[0019] Figure 4 It means by Figure 1 A graph showing the FID variation over time obtained by the read circuit.

[0020] Figure 5 Yes means Figure 1 A three-dimensional diagram of the bias magnetic field coil.

[0021] Figure 6 (a) in the formula indicates Figure 1 A top view of the bias magnetic field coil. Figure 6 (b) in the formula indicates Figure 1 Side view of the bias field coil.

[0022] Figure 7 It is a graph showing the magnetic field strength of the bias magnetic field generated by the bias magnetic field coil.

[0023] Figure 8 Yes means Figure 1 A functional block diagram of the processing of the read circuit.

[0024] Fig. 9 (a) is a graph showing the output waveform. Fig. 9 (b) is a graph showing the waveform of the FID in the frequency band of the first resonance frequency.

[0025] Fig.10 It is a perspective view showing the structure of the light-excited magnetic sensor according to the first modified example.

[0026] Fig.11 It is a top view showing the structure of the magnetoencephalometer according to the embodiment.

[0027] Fig.12 : is a functional block diagram showing the processing of the reading circuit according to the modification. DETAILED DESCRIPTION

[0028] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description, the same reference numerals are used for the same elements or elements having the same functions, and repeated descriptions are omitted.

[0029] Figure 1 1 is a perspective view showing the structure of the optically excited magnetic sensor 1 of the embodiment. The optically excited magnetic sensor 1 is a device that uses optical pumping to measure the external magnetic field. In this embodiment, although the optically excited magnetic sensor 1 is described as being used for brain magnetometry, its use is not limited to this. In one example, the optically excited magnetic sensor 1 measures the brain magnetic field. For the sake of convenience, Figure 1 In the y-axis, the direction along the magnetic field direction of the measured object is the y-axis, and the two axes perpendicular to the y-axis and mutually perpendicular axes constituting the three-dimensional coordinate system together with the y-axis are the x-axis and the z-axis. In the following description, the positive direction and negative direction along the x-axis are respectively recorded as the +x-axis direction and the -x-axis direction, the positive direction and negative direction along the y-axis are respectively recorded as the +y-axis direction and the -y-axis direction, and the positive direction and negative direction along the z-axis are respectively recorded as the +z-axis direction and the -z-axis direction. The y-axis direction corresponds to the first direction.

[0030] like Figure 1 As shown, the optical excitation magnetization sensor 1 includes a unit 2, a heater 3, a pump laser 4, a detection laser 5, a first optical system 6, a second optical system 7, an optical sensor group 8, a third optical system 9, a reading circuit 10, bias magnetic field coils 11, 15 and a tilting coil (electron spin tilting unit) 14. The optical excitation magnetization sensor 1 is an axial sensor. The structural elements of the optical excitation magnetization sensor 1 are described in detail below.

[0031] Unit 2 is a container for sealing alkali metal vapor. Unit 2 is arranged along the z-axis direction. Two units 2 are arranged in the x-axis direction. Unit 2 is roughly rectangular and has a bottomed cylindrical shape with a surface roughly parallel to the xz plane. The cross section of unit 2 in a direction perpendicular to the long side direction of unit 2 (along the xy plane) is, for example, square. Unit 2 can be composed of materials such as quartz, sapphire, silicon, Kovar glass, borosilicate glass, etc. Unit 2 is light-transmissive to the pump light and probe light described later. Heaters 3 and the like are installed on the opposite sides of each of the two units 2. On the side of unit 2 in the -y-axis direction, the magnetic field Bm of the measurement object generated from the measurement object is incident in the +y-axis direction.

[0032] The alkali metal constituting the alkali metal vapor sealed in the unit 2 may be, for example, at least one of lithium (Li), sodium (Na), potassium (K), rubidium (Rb) and cesium (Cs). For example, the alkali metal may be potassium and rubidium, or may be only potassium. The spin-destruction collision relaxation rate of potassium is relatively small among the alkali metals used by the photoexcitation magnetic sensor. The spin breakdown collision relaxation rate of potassium is, for example, smaller than that of cesium and rubidium. Therefore, in the case of using a single alkali metal, the photoexcitation magnetic sensor using only potassium is more sensitive than the photoexcitation magnetic sensor using only cesium or only rubidium.

[0033] In addition, the cell 2 contains a sealed gas. The sealed gas suppresses the relaxation of the spin polarization of the alkali metal vapor. In addition, the sealed gas protects the alkali metal vapor and suppresses noise emission. The sealed gas can be, for example, an inert gas such as helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), nitrogen (N2), etc. The sealed gas can be, for example, helium and nitrogen.

[0034] As described above, the unit 2 is provided with a heater 3. The heater 3 generates heat in accordance with the current supplied from the heater power supply (not shown). The heater 3 controls the vapor density of the alkali metal by controlling the internal temperature of the unit 2. For example, when potassium is stored in the unit 2 as the alkali metal, the heater 3 heats the unit 2 so that the internal temperature is 120°C.

[0035] The pump laser 4 emits pump light for exciting alkali metal atoms in the -y axis direction. That is, the pump laser 4 emits linearly polarized pump light, which is converted into circularly polarized light by the 1 / 4 wavelength plates 27a to 27d. The alkali metal atoms contained in the unit 2 are excited by the pump light in a polarized state of circular polarization, generating 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). For example, when the atoms constituting the alkali metal vapor are potassium, the wavelength of the pump light is set to 770.11nm, which is consistent with the resonance line of potassium. When the alkali metal atoms contained in the unit 2 are potassium and rubidium, the pump laser 4 can also emit pump light for exciting rubidium atoms and transferring the spin polarization of the rubidium atoms to the potassium atoms. In this case, the rubidium atoms are in an excited state due to the pump light. Furthermore, due to the spin exchange interaction between potassium and rubidium, the spin polarization of the rubidium atom is transferred to the potassium atom, and the potassium atom becomes excited.

[0036] The pump light from the pump laser 4 is incident on the cell 2 via the first optical system 6. Figure 1 and Figure 2As shown, the first optical system 6 includes a lens 21, a half wavelength plate 22, polarization beam splitters 23a, 23b, 23c, half wavelength plates 24a, 24b, a total reflection mirror 25, and quarter wavelength plates 27a, 27b, 27c, 27d.

[0037] The lens 21 is disposed adjacent to the pump laser 4 in the -y axis direction to focus the pump light emitted from the pump laser 4. The 1 / 2 wavelength plate 22 is disposed adjacent to the lens 21 in the -y axis direction to rotate the polarization plane by the polarization beam splitter 23a so that the power of the pump laser 4 is distributed in a 1:3 ratio.

[0038] The polarization beam splitter 23a is disposed adjacent to the 1 / 2 wavelength plate 22 in the -y axis direction, and separates two linear polarization light components perpendicular to each other from the polarization component of the pump light that has passed through the 1 / 2 wavelength plate 22, and transmits one linear polarization light component in the -y axis direction, and reflects the other linear polarization light component in the -z axis direction. The polarization beam splitters 23b, 23c and the total reflection mirror 25 are disposed side by side in sequence in the -z axis direction relative to the polarization beam splitter 23a. The polarization beam splitters 23b, 23c separate two linear polarization light components perpendicular to each other from the pump light that has passed through the polarization beam splitters 23a, 23b, respectively, and transmit one linear polarization light component in the -z axis direction, and reflect the other linear polarization light component in the -y axis direction. The total reflection mirror 25 reflects the linear polarization pump light that has passed through the polarization beam splitter 23c in the -y axis direction.

[0039] The 1 / 2 wavelength plate 24a is disposed between the polarization beam splitter 23a and the polarization beam splitter 23b, and rotates the polarization plane of the linearly polarized pump light reflected by the polarization beam splitter 23a. Thus, the polarization beam splitter 23b can be used to separate the pump light into two polarization components of linearly polarized light. The 1 / 2 wavelength plate 24b is disposed between the polarization beam splitter 23b and the polarization beam splitter 23c, and rotates the polarization plane of the linearly polarized pump light that has passed through the polarization beam splitter 23b. Thus, the polarization beam splitter 23c can be used to separate the pump light into two polarization components of linearly polarized light.

[0040] The quarter wavelength plate 27a is disposed adjacent to the polarization beam splitter 23a in the -y axis direction. The quarter wavelength plate 27a changes the polarization state of the pump light that has passed through the polarizer 26a into circularly polarized light, and transmits it in the -y axis direction as the pump light PLa. The quarter wavelength plates 27b, 27c, and 27d are disposed adjacent to the polarization beam splitters 23b, 23c and the total reflection mirror 25 in the -y axis direction, respectively. The functions of the quarter wavelength plates 27b, 27c, and 27d are the same as those of the quarter wavelength plate 27a, and the pump lights PLb, PLc, and PLd are transmitted in the -y axis direction.

[0041] The first optical system 6 of the above-mentioned structure adopts a structure in which four systems of pump light PLa to PLd transmitted through four 1 / 4 wavelength plates 27a, 27b, 27c, and 27d can be incident on the sensitivity areas ARa to ARd inside the unit 2, respectively. Such a pump laser 4 and the first optical system 6 constitute a pump light incident part that allows the pump light PLa to PLd to be incident on the sensitivity areas ARa to ARd along the -y axis direction.

[0042] The detection laser 5 emits a detection light for detecting the precession motion of the spin when the electron spin in the excited state of the alkali metal atom is tilted by 90 degrees. That is, the detection laser 5 emits a detection light of linear polarization. When the detection light passes through the alkali metal vapor, it is affected by the state of the spin polarization of the alkali metal atom, and the magneto-optical rotation angle changes. By detecting the change in the magneto-optical rotation angle, the state of the precession motion of the spin can be derived. The wavelength of the detection light is set according to the type of atoms constituting the alkali metal vapor (more specifically, the wavelength of the absorption line). For example, in the case where the unit 2 contains only potassium as an alkali metal, the wavelength of the detection light is detuned from the wavelength of the pump light (for example, 770.11nm), for example, to about 770.05nm. By detuning the wavelength of the detection light from the wavelength of the pump light, the absorption of the detection light by potassium is suppressed.

[0043] In the case where potassium and rubidium are contained in the cell 2 as alkali metals, the detection laser 5 can also emit detection light for detecting the change of the magneto-optical rotation angle caused by the spin polarization of the potassium atoms in the excited state. The density of rubidium used in the excitation is set to be smaller than the density of potassium used in the detection. In the case where the density of rubidium is smaller than the density of potassium, the attenuation of the pump light caused by the excitation is suppressed. As a result, the optically excited magnetic sensor 1 can obtain uniform sensitivity in the cell 2.

[0044] The probe light from the probe laser 5 is incident on the unit 2 via the second optical system 7. The second optical system 7 includes a lens 35, a 1 / 2 wavelength plate 36, a polarization beam splitter 38, and total reflection mirrors 37a to 37c. The polarization beam splitter 38 is disposed adjacent to the 1 / 2 wavelength plate 36 in the -y axis direction, and separates two linearly polarized light components perpendicular to each other from the polarization component of the probe light that has passed through the 1 / 2 wavelength plate 36, and transmits one linearly polarized light component in the -y axis direction, and reflects the other linearly polarized light component in the +x axis direction. The total reflection mirror 37a reflects the linearly polarized light component of the probe light that has passed through the polarization beam splitter 38 in the -z axis direction, and is incident on one unit 2 along its long side direction. The total reflection mirrors 37b and 37c reflect the linearly polarized light component of the probe light reflected by the polarization beam splitter 38 in the -y axis direction and the -z axis direction continuously, and are incident on the other unit 2 along its long side direction. The two probe lights QL of the second optical system 7 having such a structure are arranged in the longitudinal direction (z-axis direction) inside the cell 2 and are incident on four sensitive areas ARa to ARd intersecting with the pump light.

[0045] The sensitivity regions ARa to ARd are regions arranged at intervals in the longitudinal direction inside the cell 2. The sensitivity regions ARa to ARd are regions intersecting with the pumping lights PLa to PLd inside the cell 2. The sensitivity regions ARa to ARd are intersection regions where the probe light QL intersects with the pumping lights PLa to PLd. Such a probe laser 5 and the second optical system 7 constitute a probe light incident portion that causes the probe light QLa to QLd to be incident on the sensitivity regions ARa to ARd along the x-axis direction.

[0046] The bias magnetic field coils 11 and 15 are coils for applying a bias magnetic field By along the y-axis direction to the inside of the cell 2, and determine the resonance frequency of the electron spins of the alkali metal atoms excited inside the cell 2. The bias magnetic field coil 11 applies a reference bias magnetic field in the same direction as the incident direction of the pump light with respect to the sensitive areas ARa to ARd to the inside of the cell 2. As a result, the rotation axes of the electron spins of the alkali metal atoms excited inside the cell 2 are aligned in the y-axis direction.

[0047] The bias magnetic field coil 15 is linked with the bias magnetic field coil 11 to apply a plurality of bias magnetic fields By of different strengths to each of the sensitivity areas ARa to ARd inside each unit 2. The bias magnetic field coil 15 generates bias magnetic fields By of different magnetic field strengths in a stepwise manner in the four sensitivity areas ARa to ARd inside each unit 2. The details of the bias magnetic field coil 15 will be described later. When the magnetic field strength of the bias magnetic field applied by the bias magnetic field coils 11 and 15 is 14 μT and the alkali metal atom is potassium, the resonance frequency of the electron spin becomes 100 kHz. 14 μT is a magnetic field strength that can be easily formed.

[0048] The tilting coil 14 generates and irradiates an RF signal Rf in order to tilt the rotation axis direction of the electron spin of the alkali metal atom excited inside the cell 2 in a direction perpendicular to the incident direction of the pump light. Specifically, the tilting coil 14 generates an RF signal Rf having the same frequency as the resonance frequency of the electron spin generated by the bias magnetic field coil 11 (100 kHz when the intensity of the reference bias magnetic field generated by the bias magnetic field coil 11 is 14 μT and the alkali metal atom is potassium), and irradiates the RF signal Rf in the -z axis direction with the intensity and length required to tilt the electron spin by 90°. In addition, instead of the tilting coil 14, a technical means for irradiating other pulsed pump light from a direction perpendicular to the incident direction of the pump light may be provided as an electron spin tilting unit for tilting the direction of the electron spin.

[0049] The third optical system 9 includes a total reflection mirror 46, a 1 / 2 wavelength plate 47, a polarization beam splitter 48, and a total reflection mirror 49. The total reflection mirror 46 reflects the probe light passing through the unit 2 in the -z axis direction in the +y axis direction. The 1 / 2 wavelength plate 47 rotates the polarization plane of the probe light reflected by the total reflection mirror 46. The 1 / 2 wavelength plate 47 is supported so as to be rotatable around an axis along the y axis so that the rotation angle of the polarization plane of the probe light can be adjusted. The polarization beam splitter 48 separates the probe light transmitted through the 1 / 2 wavelength plate 47 into two linear polarization light components perpendicular to each other, transmits one linear polarization light component in the +y axis direction and enters the optical sensor group 8, and reflects the other linear polarization light component in the +z direction. The total reflection mirror 49 reflects the other linear polarization light component reflected by the polarization beam splitter 48 in the +y axis direction and enters the optical sensor group 8. Two third optical systems 9 are provided corresponding to two units 2.

[0050] The optical sensor group 8 is an element group that detects the polarization plane angle of the detection light QL after passing through the sensitivity areas ARa to ARd, and includes two optical sensor pairs (optical sensors) 43a and 43b corresponding to the two units 2, respectively. The optical sensor pair 43a has two photodiodes 44a and 45a. The photodiode 44a outputs a detection signal for detecting the intensity of the component of the other linear polarized light of the detection light QL, and the photodiode 45a outputs a detection signal for detecting the intensity of the component of the one linear polarized light of the detection light QL. Similarly, the optical sensor pair 43b has two photodiodes.

[0051] The reading circuit 10 is electrically connected to the two optical sensor pairs 43a and 43b constituting the optical sensor group 8, and is a processing circuit that processes the detection signals output from the two optical sensor pairs 43a and 43b. That is, the reading circuit 10 includes: a reading unit that reads the detection signals output from the two optical sensor pairs 43a and 43b (outputs of the optical sensor pairs 43a and 43b); and a measuring unit that performs measurement processing of the external magnetic field of the sensitivity area ARa to ARd based on the detection signals. However, the measuring unit may be provided outside the optical excitation magnetic sensor 1, and perform measurement processing based on the detection signals output from the optical excitation magnetic sensor 1. The reading circuit 10 constitutes a magnetic field measuring unit.

[0052] The reading circuit 10 physically includes a memory such as RAM, ROM, a processor such as CPU (calculation circuit), a communication interface, a hard disk, an auxiliary storage device such as a semiconductor memory, etc. The reading circuit 10 can be implemented by, for example, a personal computer, a cloud server, a smart phone, a tablet terminal, etc. The function of the reading circuit 10 is implemented by the CPU of the computer system executing a program stored in the memory.

[0053] Reference Figure 3 and Figure 4 , the function of the external magnetic field measurement processing performed by the measuring unit of the reading circuit 10 is described. Figure 3 The diagram shows the reading timing of the pump light, RF signal and probe light when the reading circuit 10 performs the measurement processing of the external magnetic field, wherein part (a) shows the generation timing of the pump light, part (b) shows the generation timing of the RF signal, and part (c) shows the reading timing of the probe light. Figure 4 This is a graph showing the temporal change of FID (Free Induction Decay) obtained by the reading circuit 10 .

[0054] When the external magnetic field is measured by the reading circuit 10, the control circuit (not shown) controls the pump light to be repeatedly turned on and off in a pulsed manner. Figure 5 (a) of the figure shows that the RF signal is irradiated in a pulsed manner immediately after the pump light is turned off. Figure 5 (b) of the embodiment), the detection light is read during a predetermined relaxation time after the RF signal is irradiated ( Figure 5 (c) of FIG. 1 ). In such a control state, the reading circuit 10 obtains the detection signals output from the two light sensor pairs 43a and 43b during the relaxation time. Then, the reading circuit 10 obtains the time-dependent change of the FID by obtaining the difference in the detection signals of the two photodiodes 44a and 45a constituting the light sensor pair 43a (refer to FIG. Figure 4) Similarly, the reading circuit 10 obtains the temporal change of FID by obtaining the difference between the detection signals of the two photodiodes of the photosensor pair 43b.

[0055] The waveform of the FID obtained in the present embodiment is a mixed waveform containing components of the 1st to 4th resonance frequencies corresponding to the sensitivity areas ARa to ARd. Therefore, if the waveform of the FID containing the resonance frequency components corresponding to the sensitivity area ARa in the mixed waveform of the FID is taken as an example, the FID represents the situation where the electron spin of the alkali metal atom is relaxed, and the frequency of the precession motion of the electron spin changes in accordance with the change of the external magnetic field in the sensitivity area ARa, thereby the frequency of the vibration changes according to the change of the external magnetic field. For example, when the resonance frequency of the electron spin is 100kHz and the external magnetic field changes from 0pT to 1pT, the frequency of the precession motion changes by about 0.007Hz. The reading circuit 10 uses this property to fit the waveform of the FID in the early stage of the relaxation time by using the function V shown in the following formula (in the following formula, t represents the time, and a0, a1, and a2 represent specified parameters.),

[0056] [Number 1]

[0057]

[0058] The frequency a1 of the vibration of the FID is derived and acquired as the measured value of the external magnetic field in the sensitive area ARa. The reading circuit 10 repeatedly performs this operation at a frequency of 100 to 1000 Hz, thereby acquiring time series data of the measured values.

[0059] like Figure 5 and Figure 6 As shown, the bias magnetic field coil 15 includes a first coil 15a, a second coil 15b, a third coil 15c, a fourth coil 15d, and unit external coils 16a and 16b. The first coil 15a is a coil corresponding to the sensitive area (first sensitive area) ARa existing at the end of each unit 2 in the +z-axis direction, and a pair of the first coils 15a is arranged in a manner of sandwiching the sensitive area ARa in the y-axis direction. The first coil 15a is formed with a first number of turns in one rotation direction (first rotation direction). The first coil 15a is provided in a manner of bridging a pair of units 2 when viewed from the y-axis direction. The first coil 15a is formed in a manner of surrounding the sensitive area ARa of each unit 2. The first number of turns is, for example, 3.

[0060] The second coil 15b is a coil corresponding to the sensitivity region (second sensitivity region) ARb of each unit 2, and is configured in a pair in a manner that sandwiches the sensitivity region ARb in the y-axis direction. The second coil 15b is formed with a second number of turns in one rotation direction. The second coil 15b is provided in a manner that bridges a pair of units 2 as viewed from the y-axis direction. The second coil 15b is formed in a manner that surrounds the sensitivity region ARb of each unit 2 as viewed from the y-axis direction. The second number of turns is, for example, 1.

[0061] The third coil 15c is a coil corresponding to the sensitivity region (third sensitivity region) ARc of each unit 2, and a pair of coils are arranged in a manner sandwiching the sensitivity region ARc in the y-axis direction. The third coil 15c is formed with a second number of turns in another rotation direction (second rotation direction) opposite to the one rotation direction. The third coil 15c is provided in a manner bridging a pair of units 2 as viewed from the y-axis direction. The third coil 15c is formed in a manner surrounding the sensitivity region ARc of each unit 2 as viewed from the y-axis direction.

[0062] The fourth coil 15d is a coil corresponding to the sensitive area (fourth sensitive area) ARd existing at the end of each unit 2 in the -z-axis direction, and is arranged in a pair so as to sandwich the sensitive area ARd in the y-axis direction. The fourth coil 15d is formed with the first number of turns in the other rotation direction. The fourth coil 15d is provided so as to bridge a pair of units 2 as viewed from the y-axis direction. The fourth coil 15d is formed so as to surround the sensitive area ARd of each unit 2 as viewed from the y-axis direction.

[0063] The unit external coil 16a is configured to be separated from the pair of units 2 in the +z-axis direction as viewed from the y-axis direction. A pair of unit external coils 16a are provided at intervals in the y-axis direction. One unit external coil 16a is adjacent to the first coil 15a in the +z-axis direction and is located at the same position in the y-axis direction. Another unit external coil 16a is adjacent to the other first coil 15a in the +z-axis direction and is located at the same position in the y-axis direction. The unit external coil 16b is configured to be separated from the pair of units 2 in the -z-axis direction as viewed from the y-axis direction. A pair of unit external coils 16b are provided at intervals in the y-axis direction. One unit external coil 16b is adjacent to one fourth coil 15d in the -z-axis direction and is located at the same position in the y-axis direction. Another unit external coil 16b is adjacent to another fourth coil 15d in the -z-axis direction and is located at the same position in the y-axis direction.

[0064] The first to fourth coils 15a to 15d are as follows Figure 7As shown, a bias magnetic field By that varies in a step-like manner is generated inside each unit 2. The bias magnetic field By has a (flat) intensity range F1 to F4 of constant values ​​with different intensities at each z-axis position corresponding to the four sensitivity areas ARa to ARd. The bias magnetic field By varies in a symmetrical step-like manner with respect to the reference bias magnetic field α.

[0065] For example, by passing a predetermined current through the first to fourth coils 15a to 15d, the bias magnetic field By adds 0.14 μT to the reference bias magnetic field α in the first coil 15a, adds 0.07 μT to the reference bias magnetic field α in the second coil 15b, subtracts 0.07 μT from the reference bias magnetic field α in the third coil 15c, and subtracts 0.14 μT from the reference bias magnetic field α in the fourth coil 15d. By using the bias magnetic field coil 15 as described above, the resonance frequencies of the electron spins in the four sensitive regions ARa to ARd can be made to be the first to fourth resonance frequencies that are different from each other. For example, when the alkali metal atom is potassium, the first resonance frequency is 98.5 kHz, the second resonance frequency is the above-mentioned 99.5 kHz, the third resonance frequency is 100.5 kHz, and the fourth resonance frequency is 101.5 kHz.

[0066] like Figure 5 and Figure 6 As shown, a substrate 17 is arranged on one side and the other side of each unit 2 in the y-axis direction. The substrate 17 is a printed substrate with the y-axis direction as the thickness direction. The substrate 17 is a rectangular shape that is long in the z-axis direction. The substrate 17 is arranged in a manner that bridges a pair of units 2 in the x-axis direction.

[0067] A first coil 15a, a second coil 15b, a third coil 15c, a fourth coil 15d, a unit outer coil 16a, and a unit outer coil 16b are provided on one side of the substrate 17. Another first coil 15a, another second coil 15b, another third coil 15c, another fourth coil 15d, another unit outer coil 16a, and another unit outer coil 16b are provided on the other side of the substrate 17.

[0068] The substrate 17 is provided with a through hole 19 through which the pump light passes. The through hole 19 is in the shape of a track with the x-axis direction as the long side direction. Four through holes 19 are formed corresponding to the sensitivity areas ARa to ARd. The four through holes 19 are located inside each of the first to fourth coils 15a to 15d. The four through holes 19 are arranged so as to overlap with the sensitivity areas ARa to ARd of each unit 2 as viewed from the y-axis direction, so that the sensitivity areas ARa to ARd of each unit 2 are exposed. The through hole 19 only needs to be formed on the substrate 17 arranged on the incident surface side or the exit surface side of the pump light in the unit 2.

[0069] As described above, the reading circuit 10 obtains a mixed waveform of FID including components of the first to fourth resonance frequencies, which are the resonance frequencies of the electron spins in the sensitivity regions ARa to ARd, as an output waveform based on the outputs of the optical sensor pairs 43a and 43b. Figure 8 As shown, the reading circuit 10 filters the obtained output waveform WI using the bandpass filter BF, and obtains the waveforms (first to fourth waveforms) WO of the FID in the respective frequency bands of the first to fourth resonance frequencies.

[0070] As an example, the readout circuit 10 obtains an output waveform WI which is a mixed waveform including a plurality of frequency components reflecting the different bias magnetic fields By in the sensitivity regions ARa to ARd (see Fig. 9 (a)). The output waveform WI is the sum of waveforms containing components of the first to fourth resonance frequencies that are different from each other. The reading circuit 10 applies a bandpass filter BF of a frequency band (fi±Δf) corresponding to the first to fourth resonance frequencies of each sensitivity region ARa to ARd. Thus, the reading circuit 10 extracts the waveform WO of FID in each frequency band of the first to fourth resonance frequencies (refer to Fig. 9 (b)).

[0071] Then, the reading circuit 10 performs fitting on the waveform WO of each FID using the above-mentioned function V, and derives the frequency a1 of the waveform WO of each FID. The derived frequency a1 is obtained as the measured value of the external magnetic field in the sensitivity areas ARa to ARd. Fig. 9 The waveform of the FID shown in (b) is a waveform of the frequency band of the first resonance frequency (e.g., 98.2kHz to 98.8kHz), and the fitting result indicates the magnetic field intensity corresponding to the sensitivity area ARa. The width of the frequency band can be fully measured at 0.6kHz when the measured magnetic field is less than 100pT, for example, without being confused with adjacent frequencies.

[0072] In the above-described optically excited magnetic sensor 1, pump light is emitted to each unit 2 in which alkali metal vapor is sealed, thereby generating (exciting) the electron spin of the alkali metal atom. Detection light QL is emitted to the sensitive regions ARa to ARd inside each unit 2, and the polarization plane angle of the detection light QL after passing through the sensitive regions ARa to ARd is detected by the optical sensor pairs 43a and 43b. At this time, a bias magnetic field By that changes in a stepwise manner is generated inside each unit 2 by the bias magnetic field coil 15, and the resonance frequency of the electron spin in the sensitive regions ARa to ARd becomes the first to fourth resonance frequencies that are different from each other.

[0073] The output waveform WI, which is a mixed waveform of FID including components of the first to fourth resonance frequencies for each unit 2, is obtained by the reading circuit 10 based on the outputs of the optical sensor pairs 43a and 43b. The output waveform WI is filtered by the reading circuit 10 to obtain waveforms WO of FID in each frequency band of the first to fourth resonance frequencies. The waveform WO of each FID is fitted using a function V by the reading circuit 10 to obtain a frequency a1 of each FID as a measured value of the magnetic field Bm in the -y axis direction of the sensitivity regions ARa to ARd.

[0074] As described above, in this embodiment, the intensity of the bias magnetic field By can be changed for each of the multiple sensitivity regions ARa to ARd, and the magnetic field intensity of the multiple sensitivity regions ARa to ARd can be obtained using one probe light QL. That is, the multi-channel measurement of the magnetic field intensity can be realized with a simple structure. In other words, by changing the intensity of the bias magnetic field By for each of the multiple sensitivity regions ARa to ARd, although one probe light QL is used, multi-channel measurement of the magnetic field Bm can be performed. This embodiment, which reduces the number of probe lights QL, is very important in miniaturization.

[0075] In this embodiment, the bias magnetic field coil 15 includes first to fourth coils 15a to 15d corresponding to the sensitivity regions ARa to ARd, respectively. In this case, it is possible to specifically change the intensity of the bias magnetic field for each sensitivity region ARa to ARd.

[0076] This embodiment includes a substrate 17 provided with first to fourth coils 15a to 15d, and a through hole 19 through which pump light passes is formed in the substrate 17. In this case, the bias magnetic field coil 15 can be mounted specifically without hindering the incidence of pump light to the cell 2.

[0077] In this embodiment, the bias magnetic field coil 15 includes unit external coils 16a and 16b that are adjacent to the sensitivity regions ARa and ARd at the ends of the unit 2 and are separated from the unit 2 when viewed in the y-axis direction. In this case, the existence of the unit external coils 16a and 16b can appropriately maintain the strength of the bias magnetic field By applied to the sensitivity regions ARa and ARd at one end and the other end of the unit 2. Specifically, Figure 7 In the example of the bias magnetic field By shown in the figure, for the flat intensity range F1 located closest to the +z-axis direction, it is possible to suppress the -z-axis direction side from decreasing (decreasing and becoming non-flat). In addition, for the flat intensity range F4 located closest to the -z-axis direction, it is possible to suppress the +z-axis direction side from increasing (increasing and becoming non-flat).

[0078] In this embodiment, the first coil 15a is formed with the first number of turns in one rotation direction, the second coil 15b is formed with the second number of turns in one rotation direction, the third coil 15c is formed with the second number of turns in the other rotation direction, and the fourth coil 15d is formed with the first number of turns in the other rotation direction. In this case, it is possible to specifically change the strength of the bias magnetic field for each sensitivity region ARa to ARd. It is possible to realize a bias magnetic field By having different magnetic field strengths in a step-like manner in the four sensitivity regions ARa to ARd in the unit 2.

[0079] In this embodiment, the reading circuit 10 obtains the mixed waveform of the FID including the components of the first to fourth resonance frequencies, that is, the output waveform WI, and filters the output waveform WI using the bandpass filter BF to obtain the waveform WO of each FID in each frequency band of the first to fourth resonance frequencies. In addition, the reading circuit 10 obtains the magnetic field strength of the sensitivity area ARa~ARd based on the frequency of the waveform WO of each FID. In this case, the magnetic field strength of the sensitivity area ARa~ARd can be specifically measured.

[0080] In this embodiment, a bias magnetic field coil 11 is provided for applying a bias magnetic field in the same direction as the pump light and determining the resonance frequency of the electron spin, and a tilting coil 14 is provided for tilting the direction of the electron spin in a direction perpendicular to the pump light. In this case, by measuring the intensity of the external magnetic field based on the frequency of the change in the polarization plane angle of the probe light detected using the detection signal, the measurement sensitivity of the external magnetic field can be ensured without being affected by the ambient magnetic field.

[0081] In the present embodiment, a tilting coil 14 is used that irradiates an RF signal of the same frequency as the resonance frequency. In this case, the RF signal can be used to tilt the rotation axis direction of the electron spin. The external magnetic field can be measured by simple technical means based on the frequency of the change in the polarization plane angle of the detection light. In addition, in the present embodiment, a light source that irradiates pulsed light can also be used. In this case, the pulsed light can be used to tilt the rotation axis direction of the electron spin. The external magnetic field can be measured by simple technical means based on the frequency of the change in the polarization plane angle of the detection light.

[0082] In the present embodiment, there are sensitivity areas ARa to ARd divided into four parts in the z-axis direction. Therefore, the common mode noise can be removed by obtaining the difference in the measured values ​​of the external magnetic field obtained with respect to two adjacent sensitivity areas in the sensitivity areas ARa to ARd divided into four parts. That is, in the present embodiment, there are more than two sensitivity areas, and the reading circuit 10 can measure the magnetic field strength based on the difference in the output of the optical sensor corresponding to the two adjacent sensitivity areas. In this case, the common mode noise coexisting in the two adjacent sensitivity areas can be removed, and the measurement of the weak magnetic field strength can be achieved, which can further improve the sensitivity of the magnetic field strength. This effect of improving the sensitivity is particularly significant in the absence of magnetic shielding. For example, the detection limit of 20pT / rHz can be reduced by about 2 orders of magnitude to below 300ft / rHz.

[0083] In this embodiment, it is important to expand the sensitivity area ARa~ARd in order to improve the sensitivity. In this regard, the inner diameter of the unit 2 is preferably 10×10 mm, and the beam diameter of the pump light is preferably 4 mm, and the beam diameter of the probe light is preferably 3 mm. In addition, when four sensitivity areas are set at intervals of 10 mm, due to the size limitation of the polarization beam splitters 23a, 23b, and 23c that branch the pump light, it is preferred to shape the pump light into a roughly rectangular shape (for example, 10 mm×4 mm), increase the area of ​​intersection with the probe light, and limit the pump light in the direction orthogonal thereto.

[0084] Although various embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and may be modified or applied to other aspects within the scope of the gist of each technical solution.

[0085] Fig.10 1 is a perspective view showing the structure of the optical excitation magnetization sensor 1A of the first variant. In the optical excitation magnetization sensor 1A, the incident direction of the detection light directed to the unit 2 is the -z axis direction, the application direction of the bias magnetic field By is the +x axis direction, and the irradiation direction of the RF signal Rf is the -y axis direction, which is different from the optical excitation magnetization sensor 1. In the following, only the structure that is different from the optical excitation magnetization sensor 1 is described. In addition, in Fig.10 In the figure, for convenience of explanation, the heater 3, the bias magnetic field coil 11, and the tilting coil 14 are omitted.

[0086] The first optical system 6 includes a total reflection mirror 29. The total reflection mirror 29 reflects the pump light transmitted through the half-wave plate 22 in the -z axis direction and enters the polarization beam splitter 23a. The first optical system 6 adopts a structure that allows four systems of pump light transmitted through four quarter-wave plates 27a, 27b, 27c, and 27d to enter the sensitive areas ARa to ARd inside the unit 2 along the x-axis direction.

[0087] The optically excited magnetic sensor 1A replaces the bias magnetic field coil 15 (refer to Figure 1 ) is provided with a bias magnetic field coil 115. The bias magnetic field coil 115 has the same function as the bias magnetic field coil 15, and generates a bias magnetic field with different magnetic field strengths in a step-like manner in the four sensitivity areas ARa to ARd in each unit 2. The bias magnetic field coil 115 includes the first to fourth coils 115a to 115d respectively provided in the two units 2.

[0088] The first coil 115a is a coil corresponding to the sensitivity area ARa, and a pair of coils are arranged so as to sandwich the sensitivity area ARa in the x-axis direction. The first coil 115a is formed so as to surround the sensitivity area ARa as seen from the x-axis direction. The second coil 115b is a coil corresponding to the sensitivity area ARb, and a pair of coils are arranged so as to sandwich the sensitivity area ARb in the x-axis direction. The second coil 115b is formed so as to surround the sensitivity area ARb as seen from the x-axis direction. The third coil 115c is a coil corresponding to the sensitivity area ARc, and a pair of coils are arranged so as to sandwich the sensitivity area ARc in the x-axis direction. The third coil 115c is formed so as to surround the sensitivity area ARc as seen from the x-axis direction. The fourth coil 115d is a coil corresponding to the sensitivity area ARd, and a pair of coils are arranged so as to sandwich the sensitivity area ARd in the x-axis direction. The fourth coil 115d is formed so as to surround the sensitivity area ARd as seen from the x-axis direction.

[0089] In the optically excited magnetic sensor 1A, it is also possible to obtain a magnetic field Bm in the −y-axis direction for the sensitive regions ARa to ARd (see Figure 2 ) measured value. In the optical excitation magnetometry sensor 1A, the above-mentioned effect of multi-channel measurement of magnetic field intensity can also be obtained with a simple structure. In the optical excitation magnetometry sensor 1A, pump light can be irradiated in a manner that crosses multiple units 2, so that multiple units 2 can be excited at the same time. For example, when a multi-channel module structure such as 4x4 is adopted (a structure in which four sensitivity areas are set in two units 2 respectively), the branching of pump light can be controlled to a minimum and the structure can be simplified, thereby realizing the miniaturization of the optical excitation magnetometry sensor 1A.

[0090] Fig.111 is a top view showing the structure of a magnetoencephalometer 100 according to an embodiment. The magnetoencephalometer 100 includes a plurality of optically excited magnetoencephalometer sensors 1 or optically excited magnetoencephalometer sensors 1A that can be arranged around a head (subject) S of a subject. In the illustrated example, the plurality of optically excited magnetoencephalometer sensors 1 or optically excited magnetoencephalometer sensors 1A provided by the magnetoencephalometer 100 are arranged so as to be opposed to each other in the y-axis direction across the head S, and so as to be opposed to each other in the x-axis direction across the head S. A pair of optically excited magnetoencephalometer sensors 1 or optically excited magnetoencephalometer sensors 1A that are opposed to each other in the y-axis direction are configured such that two units 2 are arranged in the y-axis direction with the x-axis direction being the long side direction. A pair of optically excited magnetoencephalometer sensors 1 or optically excited magnetoencephalometer sensors 1A that are opposed to each other in the x-axis direction are configured such that two units 2 are arranged in the x-axis direction with the y-axis direction being the long side direction.

[0091] In addition, the bias magnetic field coil 11, the bias magnetic field gradient correction coils 12 and 13, and the tilting coil 14 are shared between the plurality of optically excited magnetic sensors 1 and the plurality of optically excited magnetic sensors 1A. The bias magnetic field By is applied in the x-axis direction by the bias magnetic field coil 11. The optically excited magnetic sensors 1 and 1A measure the intensity of the magnetic field emitted by the head S.

[0092] The magnetoencephalometer 100 with the above structure can obtain the measured value of the weak magnetic field from the head S. Specifically, Fig.11 In the configuration example, the measured values ​​of the magnetic field in the x-axis direction of 8×4=32 sensitive areas can be obtained. In addition, by obtaining the difference between the measured value of the sensitive area close to the head S and the measured value of the sensitive area adjacent to the sensitive area on the outside of the head S, it is possible to measure weak brain magnetism without common mode noise.

[0093] In addition, in the magnetoencephalometer 100, it is also possible to apply a structure in which the optical excitation magnetometry sensor 1 and the optical excitation magnetometry sensor 1A are only arranged at a position close to the head S, rather than arranged in parallel. In this case, by obtaining the difference in the measurement values ​​of two adjacent sensitivity areas of one optical excitation magnetometry sensor 1, 1A, it is possible to measure weak brain magnetism with common mode noise removed. In the magnetoencephalometer 100, since it is provided with the optical excitation magnetometry sensors 1, 1A, it is also possible to obtain the above-mentioned effect of multi-channel measurement of magnetic field strength with a simple structure.

[0094] In the above embodiment, the reading circuit 10 obtains the waveform WO of FID in each of the first to fourth resonant frequency bands by filtering the obtained output waveform WI using the bandpass filter BF, but the present invention is not limited thereto, and for example, the following signal processing steps using quadrature phase detection may be adopted. That is, the reading circuit 10 may be configured as follows: Fig.12As shown in FIG. 1 , a mixed waveform including a plurality of frequency components reflecting different bias magnetic fields By of each sensitivity region ARa to ARd, namely, an output waveform WI is obtained. The reading circuit 10 generates a reference signal (a sine wave or a cosine wave of a predetermined frequency) and performs a multiplication operation with the output waveform WI. The reading circuit 10 applies a low-pass filter LF of a cutoff frequency. Thus, a waveform WT after orthogonal phase detection, which is a waveform FID reflecting the frequency difference with the reference signal, is obtained. The waveform WT after orthogonal phase detection is fitted to obtain the frequency difference with the reference signal in each frequency band of the 1st to 4th resonance frequencies.

[0095] In the above embodiment, there are four sensitive regions ARa to ARd, but it can also be changed to a structure with two sensitive regions. In this case, the detection accuracy after removing the common mode noise can be improved by obtaining the difference in the measured values ​​of the two sensitive regions. In the above embodiment, the sensitive regions can also be provided with one, three or five or more. In other words, the plurality of sensitive regions can also include the 1st to Nth sensitive regions (N is an integer greater than 2). In such a case, the bias magnetic field coils 15 and 115 can also apply the 1st to Nth bias magnetic fields to the 1st to Nth sensitive regions, respectively, so that the resonance frequencies of the 1st to Nth sensitive regions become the 1st to Nth resonance frequencies. The reading circuit 10 can also obtain a mixed waveform of FID containing components of the 1st to Nth resonance frequencies, and filter the obtained mixed waveform of FID to obtain the 1st to Nth waveforms of FID in each frequency band of the 1st to Nth resonance frequencies, derive each frequency of the 1st to Nth waveforms, and obtain the magnetic field strength of the 1st to Nth sensitivity regions based on each frequency of the derived 1st to Nth waveforms.

[0096] The above embodiment includes two units 2, but may include one or more than three units 2. In the above embodiment, if two units 2 can be sufficiently heated by one heater 3, one heater 3 may be used. In such a case, the two units 2 may be arranged close to each other, for example, the interval between the two units 2 may be 15 mm.

[0097] In the above embodiment, when the gradients of the bias magnetic field By in the x-axis direction and the z-axis direction are small, high sensitivity can be achieved, so it is preferred. Therefore, for example, by providing a bias magnetic field gradient correction coil such as a parallel four-wire coil, the gradient of the bias magnetic field By can be corrected to improve the uniformity of the bias magnetic field By. In this case, the bias magnetic field gradient correction coil can also correct the gradient in a manner that prolongs the relaxation time of the FID in each frequency band of the 1st to 4th resonance frequencies. In the above embodiment, linearly polarized light is sometimes converted into circularly polarized light for use, but it is also possible to use circularly polarized light from the beginning without performing this conversion.

[0098] The present invention can provide a multi-channel optically excited magnetoencephalometer and a magnetoencephalometer that can measure magnetic field intensity with a simple structure.

Claims

1. A light-excited magnetic sensor, comprising: A cell enclosed with alkali metal vapor; a pump light incident portion for causing pump light to be incident along a first direction onto a plurality of sensitive regions inside the cell, wherein the pump light is used to excite alkali metal atoms constituting the alkali metal vapor; a probe light incident portion for causing a probe light to be incident on the plurality of sensitive regions along a direction intersecting the first direction, the probe light being used to detect a change in the electron spin in an excited state of the alkali metal atom; a bias magnetic field coil for applying a bias magnetic field along the first direction to the interior of the unit to determine the resonance frequency of the electron spin; an electron spin tilting portion for tilting the rotation axis direction of the electron spin in a direction perpendicular to the first direction; a light sensor that detects the detection light after passing through the sensitivity region; and a magnetic field measuring unit that measures the magnetic field intensity of the sensitive area based on the output of the optical sensor, The bias magnetic field coil applies a plurality of bias magnetic fields having different intensities to each of the plurality of sensitive regions.

2. The optically excited magnetic sensor according to claim 1, wherein: The plurality of sensitivity regions include at least a first sensitivity region and a second sensitivity region, The bias magnetic field coil comprises: a first coil corresponding to the first sensitivity area; and A second coil corresponding to the second sensitive area.

3. The optically excited magnetic sensor according to claim 2, wherein: comprising a substrate provided with the first coil and the second coil, The substrate has a through hole formed therein for allowing the pump light to pass therethrough.

4. The optically excited magnetic sensor according to claim 2, wherein: The first sensitive area exists at the end of the unit. The bias magnetic field coil includes a unit outer coil which is arranged to be separated from the unit when viewed from the first direction and is adjacent to the first coil.

5. The optically excited magnetic sensor according to claim 1, wherein: The plurality of sensitivity regions include a first sensitivity region, a second sensitivity region adjacent to the first sensitivity region, a third sensitivity region adjacent to the second sensitivity region, and a fourth sensitivity region adjacent to the third sensitivity region. The bias magnetic field coil comprises: a pair of first coils arranged so as to sandwich the first sensitive region in the first direction and formed with a first number of turns in the first rotation direction; a pair of second coils arranged so as to sandwich the second sensitive region in the first direction and formed with a second number of turns in the first rotation direction; a pair of third coils arranged so as to sandwich the third sensitive region in the first direction and formed with the second number of turns in a second rotation direction opposite to the first rotation direction; and A pair of fourth coils are arranged so as to sandwich the fourth sensitive region in the first direction and are formed with the first number of turns in the second rotation direction.

6. The optically excited magnetic sensor according to claim 1, wherein: The plurality of sensitivity regions include first to N sensitivity regions, wherein N is an integer greater than or equal to 2, The bias magnetic field coil applies first to N bias magnetic fields to the first to N sensitive regions respectively, so that the resonance frequencies of the first to N sensitive regions are the first to N resonance frequencies. The magnetic field measuring unit, acquiring a mixed waveform of free induction decay including components of the first to Nth resonance frequencies based on the output of the optical sensor, The mixed waveform is filtered by a bandpass filter to obtain the first to N waveforms of free induction attenuation in the respective frequency bands of the first to N resonance frequencies, and the respective frequencies of the first to N waveforms are derived. The magnetic field intensities of the first to N sensitive regions are obtained based on the derived frequencies of the first to N waveforms.

7. The optically excited magnetic sensor according to claim 1, wherein: The electron spin tilting unit irradiates an RF signal having the same frequency as the resonance frequency.

8. The optically excited magnetic sensor according to claim 1, wherein: The electron spin tilting unit irradiates pulsed light.

9. The optically excited magnetic sensor according to claim 1, wherein: The magnetic field measurement unit measures the magnetic field intensity based on a difference between outputs of the optical sensors corresponding to two adjacent sensitivity regions.

10. A magnetoencephalometer, comprising the optically excited magnetoencephalometer according to claim 1, wherein the optically excited magnetoencephalometer is configured to be arranged around the head of a subject and measures the intensity of the magnetic field emitted by the subject.

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