JP5764949B2 - Magnetic field measuring device - Google Patents

Description

  The present invention relates to a magnetic field measurement apparatus.

  A magnetic sensor using optical pumping is used in a biomagnetic measuring apparatus that detects a magnetic field emitted from a living heart or the like. As such a magnetic sensor, each cell in which a gas such as an alkali metal atom is sealed is irradiated with a pump light having a circularly polarized component and a probe light having a linearly polarized component perpendicular to each other and emitted from a living body. There is one that detects a magnetic field by probe light. Patent Document 1 below discloses such an optical pumping atomic magnetometer.

JP 2009-236599 A

By the way, the number of electrons of the alkali metal atom excited in the cell differs depending on the difference in the amount of atoms in the cell, the power for irradiating pump light, and the like. When measuring a wide range of a living body by arranging a plurality of cells, if there is a difference in the number of electrons excited in each cell, the spin polarization rate of the cell differs, and the magnetic field sensitivity of each cell varies.
The present invention provides a technique for improving the measurement accuracy of a magnetic field by controlling the amount of pump light in each cell in a magnetic field measurement apparatus that measures a magnetic field by arranging a plurality of cells.

  A magnetic field measurement apparatus according to the present invention includes a cell array having a plurality of cells including atomic groups composed of atoms excited by pump light, first irradiation means for irradiating each cell of the cell array with pump light, A second irradiating means for irradiating the cell with the probe light irradiated to the cell and the probe light so as to intersect within the cell; and receiving the probe light transmitted through the cells, respectively. Detection means for detecting a magnetic field in each cell, and a light amount provided for each cell, and adjusting the amount of light incident on the cell by the pump light emitted by the first irradiation means, according to the input control signal Adjusting means; storage means for storing the adjustment amount of the adjusting means for each cell; and the control signal based on the adjustment amount for each cell stored in the storage means. Characterized in that it comprises input means for inputting. According to this configuration, by storing in the storage means the adjustment amount for each cell that makes the spin polarization rate of the cell verified in advance uniform, the magnetic field sensitivity of each cell becomes uniform. The amount of pump light is controlled, and the measurement accuracy of the magnetic field can be improved.

  In the magnetic field measurement apparatus according to the present invention, in the magnetic field measurement apparatus, a constant magnetic field is applied to each cell, the control signal is changed and input to the adjustment unit, and the magnetic field detection unit The control signal when the detected value of the magnetic field of each cell to be detected becomes a predetermined reference value is specified for each cell, and the adjustment amount based on the specified control signal for each cell is stored in the memory It is good also as providing the specific means memorize | stored in a means. According to this configuration, since the adjustment amount for each cell can be set so that the spin polarization in each cell is uniform, the magnetic field sensitivity of each cell can be changed even when the installation environment of the magnetic field measurement device is changed or the cell is replaced. Can be made uniform.

  In the magnetic field measurement apparatus according to the present invention, in the magnetic field measurement apparatus, the first irradiation unit includes a light source of the pump light for a plurality of cells in the cell array, and the plurality of light sources from the light source It is good also as distributing and irradiating the said pump light with respect to a cell. According to this configuration, it is not necessary to provide a pump light source for each cell, and the apparatus can be downsized.

It is a figure which shows the structural example of the magnetic field measuring device which concerns on embodiment. It is a figure explaining the pump light and probe light which are irradiated with respect to the cell which concerns on embodiment. (A) is a figure explaining the 1st irradiation part and adjustment part which concern on embodiment. (B) is a figure explaining the 2nd irradiation part and detection part which concern on embodiment. It is the figure which illustrated the adjustment amount for every cell memorized by the storage part concerning an embodiment.

<Embodiment>
(Constitution)
FIG. 1 is a block diagram showing a configuration of a magnetic field measurement apparatus according to an embodiment of the present invention. The magnetic field measurement apparatus 1 includes a cell array 10, a pump light adjustment unit 20, a magnetic field detection unit 30, a control unit 40, an operation unit 50, and a storage unit 60.

  The cell array 10 is configured by arranging a plurality of cells (10a, 10b, 10c, 10d) in a line. Each cell is made of a material such as glass that transmits light, and each cell is an independent object having a cubic shape in which a group of atoms including predetermined atoms is included inside the cell. This predetermined atom is an atom that is excited by circularly polarized light and spin-polarized. For example, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr ) And the like. Each cell may contain a buffer gas such as helium (He) and nitrogen (N) in addition to alkali metal atoms. The alkali metal atoms may be in a gaseous state when detecting magnetism, and may not always be in a gaseous state. In the present embodiment, four cells of the cell array 10 are arranged in a line. However, the number of cells may be plural, and may be plural. In this embodiment, an example is used in which each cell is an independent object. However, for example, the cell may be formed by partitioning a rectangular parallelepiped so as not to be affected by the adjacent cell. Each cell may be communicated by a hole provided in a part of the partition between the cells so as not to be affected. In short, the cell array 10 only needs to have a plurality of partitioned spaces. Moreover, although the example of a cube shape is used for the shape of a cell, the shape of a cell is not restricted to this shape.

  The magnetic field detection unit 30 includes magnetic field detection units (30a, 30b, 30c, 30d) that detect magnetic fields in the cells (10a, 10b, 10c, 10d). Each magnetic field detection unit shares a first irradiation unit (not shown) that emits pump light for spin-polarizing atoms in each cell (10a, 10b, 10c, 10d) in the same direction. In addition, each magnetic field detection unit detects a magnetic field in each cell by detecting a second irradiation unit (not shown) that irradiates probe light for detecting the magnetic field in each cell and probe light transmitted through each cell. Each has a detector (not shown). In the present embodiment, the pump light is irradiated from the upper surface direction (z-axis direction) of each cell indicated by the broken line arrow in FIG. 2, and the probe light is irradiated from the side surface direction (y-axis direction) of each cell indicated by the solid line arrow in FIG. Irradiate. Details of the first irradiation unit, the second irradiation unit, and the detection unit will be described later.

  The pump light adjustment unit 20 has adjustment units (20a, 20b, 20c, 20d) provided corresponding to the cells (10a, 10b, 10c, 10d). Each adjustment unit is an example of an adjustment unit, and adjusts the amount of pump light incident on the corresponding cell. In the present embodiment, each adjustment unit is realized by, for example, a liquid crystal shutter, and changes the transmittance of the pump light according to a control signal input by the control unit 40 described later.

  FIG. 3A is a diagram illustrating the first irradiation unit 310, each cell illustrated in FIG. 2, and each adjustment unit. As illustrated in FIG. 3A, the first irradiation unit 310 is an example of a first irradiation unit, and includes a light source 311 and a distribution mechanism 312 that distributes light output from the light source 311. The light source 311 converts non-polarized laser light into pump light having a circularly polarized component by an optical member (not shown) such as a collimator lens, a polarizing plate, a quarter-wave plate, and the like, and outputs the pump light. The distribution mechanism 312 has a branch coupler that branches the pump light from the light source 311 by the number of cells and outputs the branched pump light from each output terminal. Each pump light branched and outputted by the branch coupler is irradiated to each corresponding adjustment unit via a medium for transmitting light such as an optical fiber.

FIG. 3B is a diagram illustrating each cell, each second irradiation unit (320a, 320b, 320c, 320d), and each detection unit (330a, 330b, 330c, 330d) illustrated in FIG. As shown in FIG.3 (b), each 2nd irradiation part and each detection part are provided corresponding to every cell. Each second irradiation unit is an example of a second irradiation unit, and includes a light source that outputs probe light having a linearly polarized light component.
Each light source converts unpolarized laser light into probe light having a linearly polarized component by an optical member (not shown) such as a collimator lens, a polarizing plate, and a half-wave plate, and outputs the probe light. The probe light output from each second irradiation unit is irradiated so as to be substantially orthogonal to the pump light irradiated to the cell corresponding to the second irradiation unit. The probe light irradiated to each cell is incident on each cell, and the plane of polarization is rotated according to the rotational force that the atoms in the cell have precessed due to the influence of the magnetic field in each cell, and passes through the cell. . In this embodiment, the pump light and the probe light are irradiated so that the pump light and the probe light incident on the cell are substantially orthogonal to each other. However, the pump light and the probe light intersect in the cell. If it does, it is not restricted to orthogonal.

  Each detection unit is an example of a detection unit, and the probe light transmitted through each cell is separated into a P-polarized component and an S-polarized component by a polarization beam splitter or the like, and the separated light is received by a photodetector. Each detection unit analyzes the electrical signal according to the light amount of the P-polarized component and S-polarized component output from the photodetector to determine the rotation angle of the polarization plane of the probe light, and detects the strength of the magnetic field according to the rotation angle To do. In this example, the magnetic field in the x-axis direction shown in FIG. 3B is detected.

  Returning to FIG. 1, the description of the configuration is continued. The control unit 40 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The CPU performs a calibration process and a magnetic field detection process for detecting a magnetic field emitted from the specimen by executing a control program stored in advance in the ROM.

  The control unit 40 switches between calibration processing and magnetic field detection processing in accordance with a user operation through the operation unit 50. The controller 40 uses a coil (not shown) provided for each cell as a calibration process, applies a constant magnetic field in the x-axis direction of FIG. In each cell (10a, 10b, 10c, 10d) by controlling the first irradiation unit 310, each second irradiation unit (320a, 320b, 320c, 320d), and each detection unit (330a, 330b, 330c, 330d). Detect magnetic field. The control unit 40 inputs, to the pump light adjustment unit 20, a control signal in which the transmittance of each adjustment unit is changed so that the detection result of the magnetic field in each cell becomes a predetermined reference value. The control signal of each adjustment unit when the detected value of the magnetic field of each detected cell becomes the reference value is specified, and the adjustment amount indicating the control signal of each specified adjustment unit is stored in the storage unit 60 for each cell. It has a function as a specifying means. In the present embodiment, a value corresponding to the magnetic field applied to the cell array 10 is used as an example of the reference value. The control unit 40 has a function as an input unit that inputs a control signal based on the adjustment amount of the adjustment unit for each cell stored in the storage unit 60 to the pump light adjustment unit 20 in the magnetic field detection process. The first irradiation unit 310, each second irradiation unit, and each detection unit are controlled to detect a magnetic field emitted from the specimen and output a detection result.

  The operation unit 50 has operation means such as an operation switch that accepts a calibration instruction operation and an operation switch that accepts a measurement instruction of a magnetic field emitted from a specimen, and sends an operation signal indicating the operated content to the control unit 40. . The storage unit 60 is an example of a storage unit, and is configured with a nonvolatile storage medium. The storage unit 60 stores the adjustment amount of each adjustment unit for each cell specified by the calibration process under the control of the control unit 40.

(Operation example)
Next, an operation example of the magnetic field measurement apparatus 1 will be described. When a user operation for instructing calibration processing is performed via the operation unit 50, the control unit 40 of the magnetic field measurement apparatus 1 emits pump light having a circularly polarized component from the first irradiation unit 310. At the same time, probe light having a linearly polarized light component is irradiated from each second irradiation unit (320a, 320b, 320c, 320d). And the control part 40 applies the fixed magnetic field of the direction orthogonal to pump light and probe light using the coil which is not shown in figure. In addition, the control unit 40 inputs a control signal in which the light transmittance in each adjustment unit is sequentially changed from a predetermined lower limit value to each adjustment unit, and changes the transmittance in each adjustment unit.

The pump light irradiated from the light source 311 of the first irradiation unit 310 is branched by the distribution mechanism 312 and irradiated toward the adjustment units (20a, 20b, 20c, 20d). The pump light irradiated to each adjustment unit is adjusted to a light amount corresponding to the transmittance in the adjustment unit and enters each cell. The atoms in each cell are excited according to the amount of incident pump light and spin-polarized in the same direction, and precess by changing the direction of the magnetic moment according to the applied magnetic field.
The probe light irradiated from each second irradiation unit and incident on each cell is transmitted through the cell by rotating the polarization plane according to the magnitude of the magnetic field received by the atoms in the cell. The probe light transmitted through each cell is received by the corresponding detector. Each detection unit (330a, 330b, 330c, 330d) analyzes the light amount of the received probe light to obtain the rotation angle of the polarization plane of the probe light, detects the magnetic field in the corresponding cell, and detects the detection result in the control unit 40. Is output.

  The control unit 40 inputs, to the adjustment unit, a control signal in which the transmittance of the adjustment unit corresponding to each cell is changed until the detected value detected for each cell becomes a value corresponding to the applied magnetic field. Detect magnetic field. And the control part 40 specifies the control signal of the adjustment part for every cell when the detected value of the magnetic field of each cell becomes a value equivalent to the applied magnetic field. As shown in FIG. 4, the control unit 40 uses a cell NO. And the adjustment amount indicating the control signal of each adjustment unit specified for each cell is stored in the storage unit 60 in association with each other.

  Next, an operation example in the case of performing a magnetic field measurement process for measuring a magnetic field emitted from a specimen will be described. When a user operation instructing magnetic field measurement processing is performed by the user via the operation unit 50, the control unit 40 reads the adjustment amount of each adjustment unit for each cell from the storage unit 60, and a control signal based on the read adjustment amount Is input to each adjustment unit. Each adjusting unit adjusts the light transmittance in the adjusting unit in accordance with the input control signal. And the control part 40 controls each magnetic field detection part (30a, 30b, 30c, 30d), detects the magnetic field emitted from a test substance, and outputs the detection result for every cell to an external apparatus etc.

  In the example of the above embodiment, in the calibration process, the amount of pump light incident on each cell can be adjusted so that the detection sensitivity of the magnetic field of each cell is uniform. When detecting the magnetic field from the specimen, the amount of pump light incident on each cell is adjusted according to the adjustment amount adjusted in the calibration process, so that the detection sensitivity of each cell is made uniform and the magnetic field is detected. Accuracy can be improved. In addition, after pump light having a circularly polarized component is distributed and output from the first irradiation unit 310, before the pump light enters each cell, the light amount of the pump light according to the characteristics of each cell is obtained. Since adjustment is performed by each adjustment unit, it is not necessary to provide a pump light source for each cell, and the apparatus can be downsized.

<Modification>
The present invention is not limited to the above-described embodiment, and may be carried out by being modified as follows. Further, the following modifications may be combined.

(1) In the above-described embodiment, the value corresponding to the magnetic field applied as the reference value in the calibration process has been described as an example. For example, in the calibration process, when the transmittance of the adjustment unit is maximized, the detection sensitivity A value equal to or lower than the maximum detection value of the lowest cell may be set as the reference value. In addition, the reference value may be a value having a certain width that is predetermined based on a value corresponding to the applied magnetic field, for example. That is, in the calibration process, if the detected value of the magnetic field of each cell is within the range of the reference value, the control value of the adjustment unit when the detected value is obtained may be specified.

(2) In the above-described embodiment, the example in which the first irradiation unit 310 branches and outputs the pump light by the number of cells using the branch coupler has been described, but for example, the first irradiation unit 310 in units of a plurality of cells. May be provided. In this case, the pump light is branched in each first irradiation unit 310 by the number of cells of the unit in which the first irradiation unit 310 is provided. Moreover, when providing the 1st irradiation part 310 for every cell, it irradiates without branching pump light.

(3) In the above-described embodiment, the magnetic field measurement apparatus 1 has been described with respect to the configuration for performing the calibration process and the magnetic field measurement process. However, the spin polarization rate in each cell at the time of manufacturing or shipping the magnetic field measurement apparatus 1. The adjustment amount of each adjustment unit verified in advance for each cell may be stored in the storage unit 60 so as to be uniform. In this case, the magnetic field measurement apparatus 1 may be configured to perform only the magnetic field measurement process similar to that of the embodiment.

(4) In the above-described embodiment, the example in which the calibration process and the magnetic field detection process are switched according to the user operation via the operation unit 50 has been described. However, the calibration process is started by a single user operation. In addition, the calibration process may be followed by a magnetic field detection process.

(5) In the above-described embodiment, an example in which a liquid crystal shutter is used as an example of the adjustment unit has been described. However, a lens shutter or the like may be used as long as the mechanism adjusts the amount of pump light.

(6) In the above-described embodiment, the example in which the pump light having the circularly polarized component output from the first irradiation unit 310 is incident on each adjustment unit has been described. A pump having a circularly polarized light component using an optical member such as a collimating lens, a polarizing plate, a quarter-wave plate, etc., using a laser beam that diverges and irradiates each adjusting unit and irradiates the laser beam through each adjusting unit It is also possible to convert the light into light and irradiate the cell with the pump light.

(7) In the above-described embodiment, an example in which a constant magnetic field is applied using a coil provided for each cell has been described. For example, a single set of coils supplies a magnetic field to the entire cell array 10. Alternatively, a constant magnetic field may be applied using a magnet or the like. In short, any configuration that can generate a predetermined magnetic field is not limited thereto.

  DESCRIPTION OF SYMBOLS 1 ... Magnetic field measuring device, 10 ... Cell array, 10a, 10b, 10c, 10d ... Cell, 20 ... Pump light adjustment unit, 20a, 20b, 20c, 20d ... Adjustment part, 30. .. Magnetic field detection unit, 30a, 30b, 30c, 30d ... Magnetic field detection unit, 40 ... Control unit, 301, 302, 303 ... Optical member, 310 ... First irradiation unit, 311 ... Light source, 312... Distribution mechanism, 320a, 320b, 320c, 320d... Second irradiation unit, 330a, 330b, 330c, 330d.

Claims (4)

A plurality of cell Le containing atomic excited by the pump light,
A first light source for outputting pump light to the front dress-le,
Over the previous xenon Le, a second light source for outputting probe light to cross in front Symbol pumping light and in the cell,
Detection means for detecting a magnetic field in the dress-le prior to receiving light of said probe light which has passed through the pre-xenon Le,
Provided for each front dress-le, control in accordance with control signals, and adjustment means for each cell to adjust the incoming Shako amount for the cell prior Symbol pump light,
Storage means for storing an adjustment amount of the incident light amount of the pump light for each cell;
The adjustment unit for each cell adjusts the amount of incident light of the pump light to the cell based on the adjustment amount. The magnetic field measurement apparatus according to claim 1, further comprising a distribution mechanism that distributes the pump light output from the first light source between the first light source and the adjustment unit for each cell . Between the adjustment means for each cell and the cell, a light conversion unit that converts the pump light output from the first light source so as to have a circularly polarized component is further provided.
The magnetic field measuring apparatus according to claim 1 or 2. A constant magnetic field is applied to each cell, and the control signal is changed and input to the adjustment unit for each cell, and a detection value of the magnetic field of each cell detected by the magnetic field detection unit is determined in advance. A control unit configured to specify, for each cell, the control signal when the reference value is set, and to store the adjustment amount based on the specified control signal for each cell in the storage unit. Item 2. The magnetic field measurement apparatus according to Item 1 .

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