JP2013108833A - Magnetic field measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a magnetic field while suppressing influence of a disturbance magnetic field existing in a direction other than a magnetic field direction to be measured.SOLUTION: A magnetic field measuring apparatus 9 includes an irradiation part 1, a gas cell 2, a measurement part (a polarization separator 3, a light receiving part 4 and a signal processing circuit 5), and a tracking mechanism 7. The gas cell 2 encloses gas atoms in its inside. An adjustment part 72 in the tracking mechanism 7 moves and adjusts a conversion part 12 so that a disturbance magnetic field direction detected by the detection part 71 is coincident with a vibration direction of a magnetic field of linearly polarized light included in irradiation light radiated to the gas cell 2 through the conversion part 12. The measurement part is irradiated with irradiation light from the irradiation part 1 and measures a rotation angle of a polarization plane of irradiation light transmitted through the gas atom.

Description

  The present invention relates to a magnetic field measuring apparatus using light.

A magnetic field measurement device using light measures a minute magnetic field generated from a living body such as a magnetic field from the heart (magnetomagnetic field) or a magnetic field from the brain (magnetomagnetic field). Expected. For the measurement of the magnetic field, an element in which a gas such as an alkali metal atom is enclosed is used. By irradiating this element with pump light, the energy of atoms in the element is excited according to the magnetic field, and the polarization plane of the probe light transmitted through this element is rotated by the magneto-optic effect. The magnetic field measuring apparatus measures the rotation angle of this polarization plane as magnetic field information.
Research has been conducted to improve the sensitivity of these magnetic field measuring devices. Patent Document 1 discloses an optical pumping magnetometer that enables more sensitive magnetic field detection by increasing the detection signal intensity.

JP 2009-236599 A

  However, the magnetometer disclosed in Patent Document 1 has a problem in that the sensitivity decreases when a magnetic field that causes disturbance in a direction other than the magnetic field direction to be measured (hereinafter also referred to as a disturbance magnetic field) exists. Also, the direction of the disturbing magnetic field may not be predictable and may vary during the measurement of the magnetic field.

  An object of this invention is to measure a magnetic field according to the disturbance magnetic field so that the influence of the disturbance magnetic field which exists in directions other than the magnetic field direction which should be measured may be suppressed.

In order to solve the above-described problem, the magnetic field measurement apparatus according to the present invention is configured to determine a gas cell in which gas atoms are sealed and irradiation light including linearly polarized light with respect to the gas atoms sealed in the gas cell. An irradiating unit that irradiates along the measuring direction, a detecting unit that detects a direction in which the magnetic field is the strongest among directions perpendicular to the measuring direction, a direction detected by the detecting unit, and a vibration direction of the electric field of the linearly polarized light And an adjustment unit that adjusts the irradiation light, and a measurement unit that measures the rotation angle of the polarization plane of the irradiation light irradiated by the irradiation unit and transmitted through the gas atoms, To do.
According to this configuration, the magnetic field can be measured according to the disturbance magnetic field so as to suppress the influence of the disturbance magnetic field existing in a direction other than the magnetic field direction to be measured.

Preferably, the irradiation unit may guide the irradiation light to the gas cell by an optical fiber.
According to this configuration, restrictions on the size and arrangement of the irradiation unit can be reduced as compared with the case where the irradiation light is not guided to the gas cell by the optical fiber.

The magnetic field measurement apparatus according to the present invention includes a gas cell in which gas atoms are enclosed, a detection unit that detects a direction in which the magnetic field is strongest among directions perpendicular to a predetermined measurement direction, and a circularly polarized light component. A pump light irradiating unit for irradiating a gas atom enclosed in the gas cell along a direction perpendicular to the measurement direction, and a gas enclosed in the gas cell with a probe light containing linearly polarized light. A probe light irradiating unit that irradiates atoms along a direction perpendicular to both the measurement direction and the direction in which the pump light is irradiated, and is irradiated by the probe light irradiating unit and transmitted through the gas atoms A measurement unit that measures the rotation angle of the polarization plane of the probe light, and the pump light irradiation unit and the probe light irradiation unit so that the pump light is irradiated along the direction detected by the detection unit. And characterized by comprising an adjusting unit for adjusting the respective positions of the measuring unit.
According to this configuration, the magnetic field can be measured according to the disturbance magnetic field so as to suppress the influence of the disturbance magnetic field existing in a direction other than the magnetic field direction to be measured.

Preferably, the pump light irradiation unit guides the pump light to the gas cell by an optical fiber, and the probe light irradiation unit guides the probe light to the gas cell by an optical fiber.
According to this configuration, restrictions on the size and arrangement of the pump light irradiation unit and the probe light irradiation unit can be reduced as compared with the case where the pump light and the probe light are not guided to the gas cell by the optical fiber.

The magnetic field measuring apparatus according to the present invention includes a gas cell in which gas atoms are enclosed, a detection unit that detects a direction in which the magnetic field is strongest as a detection direction, and irradiation light including linearly polarized light, which is enclosed in the gas cell. The irradiation unit that irradiates the gas atoms along a measurement direction that is perpendicular to the detection direction detected by the detection unit, and the polarization of the irradiation light that is irradiated by the irradiation unit and transmitted through the gas atoms Adjusting the irradiation light so that the measurement unit for measuring the rotation angle of the surface matches the detection direction and the vibration direction of the electric field of the linearly polarized light, and positions of the gas cell, the irradiation unit, and the measurement unit And an adjusting unit for adjusting.
According to this configuration, it is possible to determine the direction that is not easily affected by the disturbance magnetic field as the magnetic field direction to be measured, and measure the magnetic field.

The magnetic field measuring apparatus according to the present invention encloses a gas cell in which gas atoms are enclosed, a detection unit that detects a direction in which the magnetic field is strongest as a detection direction, and pump light including a circularly polarized component in the gas cell. A pump light irradiating unit for irradiating the emitted gas atoms and a probe light including linearly polarized light along a direction perpendicular to the direction in which the pump light is applied to the gas atoms sealed in the gas cell. Along with the detection direction detected by the detection part detected by the probe light irradiation part to irradiate, the measurement part which measures the rotation angle of the polarization plane of the probe light irradiated by the probe light irradiation part and transmitted through the gas atom An adjustment unit that adjusts each position of the pump light irradiation unit, the probe light irradiation unit, and the measurement unit so as to be irradiated with the pump light is provided.
According to this configuration, it is possible to determine the direction that is not easily affected by the disturbance magnetic field as the magnetic field direction to be measured, and measure the magnetic field.

It is a figure which shows the whole structure of the magnetic field measuring apparatus which concerns on 1st Embodiment. It is a figure which shows the external appearance of a magnetic shield. It is a figure for demonstrating the principle which measures a magnetic field with the measuring apparatus of a one beam system. It is a figure for demonstrating the measurement of the magnetic field by the measuring apparatus which does not have the characteristic of the magnetic field measuring apparatus which concerns on 1st Embodiment. It is a figure for demonstrating the measurement of the magnetic field by the magnetic field measuring apparatus which concerns on 1st Embodiment. It is a figure which shows the whole structure of the magnetic field measuring apparatus which concerns on 2nd Embodiment. It is the figure which showed a mode that positions, such as a pump light irradiation part, were adjusted so that pump light may be irradiated along a disturbance magnetic field direction. It is a figure for demonstrating the principle which measures a magnetic field with the measuring apparatus of a two beam system. It is a figure explaining the locus | trajectory of the magnetization vector which concerns on 2nd Embodiment. It is a figure for demonstrating the measurement of the magnetic field by the measuring apparatus which does not have the characteristic of the magnetic field measuring apparatus which concerns on 2nd Embodiment. It is a figure for demonstrating the measurement of the magnetic field by the magnetic field measuring apparatus which concerns on 2nd Embodiment.

1. First embodiment 1-1. Configuration FIG. 1 is a diagram showing an overall configuration of a magnetic field measurement apparatus 9 according to a first embodiment of the present invention. The magnetic field measuring device 9 is a so-called one-beam type measuring device that combines irradiation with pump light by irradiation with probe light. The irradiation unit 1 includes a light source 11 and a conversion unit 12. The light source 11 is a laser generator that generates a laser having a frequency corresponding to a transition of an ultrafine structure level of atoms sealed in a gas cell 2 described later. The conversion unit 12 includes a polarizing plate and converts the laser generated by the light source 11 into irradiation light having a linearly polarized light component in a predetermined direction. Irradiation light generated by the light source 11 and converted by the conversion unit 12 is guided by, for example, an optical fiber and irradiated to the gas cell 2. Note that the above-described irradiation light may be directly irradiated from the irradiation unit 1 or the like without passing through an optical fiber or the like, but there are few restrictions on the size or arrangement of the irradiation unit 1 by guiding the irradiation light by the optical fiber or the like. Become.

  The gas cell 2 is a glass cell (element) in which alkali metal atoms such as potassium (K) and cesium (Cs) are enclosed. The gas cell 2 transmits the above-described irradiation light irradiated from the irradiation unit 1. The above-mentioned irradiation light transmitted through the gas cell 2 is guided to the polarization separator 3 by an optical fiber or the like. The material of the gas cell 2 is not limited to glass, and may be a resin or the like as long as the material transmits the irradiation light. Moreover, the above-mentioned irradiation light which permeate | transmitted the gas cell 2 may be directly irradiated from the irradiation part 1 etc., without passing through an optical fiber etc.

  The polarization separator 3 separates the above-described irradiation light transmitted through the gas cell 2 based on the polarization direction. Specifically, the polarization separator 3 transmits the linearly polarized light component in the same direction as the above-mentioned linearly polarized light component included in the irradiation light before being converted by the conversion unit 12, and is perpendicular to the polarization direction of the linearly polarized light component. Reflects light having a polarization component in any direction.

  The light receiving unit 4 includes a transmitted light receiving element 41 and a reflected light receiving element 42. The transmitted light that has passed through the polarization separator 3 is received by the transmitted light receiving element 41, and the reflected light that has reflected from the polarization separator 3 is received by the reflected light receiving element 42. Each of the transmitted light receiving element 41 and the reflected light receiving element 42 generates a signal corresponding to the amount of received light and supplies it to the signal processing circuit 5. The signal processing circuit 5 receives the above signals from the transmitted light receiving element 41 and the reflected light receiving element 42, respectively. Then, based on each received signal, the signal processing circuit 5 rotates the linearly polarized light component included in the irradiation light irradiated by the irradiation unit 1 through the gas cell 2, that is, the rotation angle of the polarization plane. Measure. The polarization separator 3, the light receiving unit 4, and the signal processing circuit 5 function as a measurement unit that measures the rotation angle of the polarization plane of the irradiation light irradiated by the irradiation unit 1 and transmitted through the gas atoms. The magnetic field measuring device 9 measures the magnetic field in the determined direction inside the gas cell 2 based on the rotation angle measured by the measuring unit. This direction is called “measurement direction”. The display device 6 is a display device using liquid crystal or the like, and displays the rotation angle of the polarization plane measured by the signal processing circuit 5.

  The follow-up mechanism 7 includes a detection unit 71 that detects a disturbance magnetic field, and an adjustment unit 72 that moves the conversion unit 12 according to the detection result of the detection unit 71. The detection unit 71 is a magnetic sensor using a fluxgate method, a magnetoresistive effect method, a magnetic impedance method, or the like. The detection unit 71 may be an optical pumping type magnetic sensor or the like separately provided with the same configuration as the irradiation unit 1, the gas cell 2, the polarization separator 3, the light receiving unit 4, and the signal processing circuit 5 described above. . The detection unit 71 detects the direction in which the magnetic field is the strongest among the directions perpendicular to the measurement direction measured by the magnetic field measuring device 9 as the direction of the disturbance magnetic field (hereinafter referred to as the disturbance magnetic field direction).

  The adjustment unit 72 controls the conversion unit 12 so that the disturbance magnetic field direction detected by the detection unit 71 matches the vibration direction of the linearly polarized electric field included in the irradiation light irradiated to the gas cell 2 through the conversion unit 12. Move to adjust. The conversion unit 12 includes a polarizing plate arranged perpendicular to the laser irradiated from the light source 11, and the polarizing plate passes through the polarizing plate while maintaining its orientation with respect to the laser. Is rotated by the adjusting unit 72 so that the plane of polarization of the light follows the direction of the disturbance magnetic field. In addition, the position of each structure of the magnetic field measuring apparatus 9 represented in FIG. 1 does not indicate their actual arrangement.

  FIG. 2 is a diagram illustrating the appearance of the irradiation unit 1, the gas cell 2, and the detection unit 71. Hereinafter, in order to explain the arrangement of each component of the magnetic field measuring apparatus 9, the space in which each component is arranged is represented as an xyz right-handed coordinate space. Also, among the coordinate symbols shown in the figure, a symbol in which a black circle is drawn in a circle with a white inside represents an arrow heading from the back side to the near side. A symbol depicting two line segments intersecting in a white circle on the inside represents an arrow from the front side to the back side of the page. A direction along the x-axis in space is referred to as an x-axis direction. Of the x-axis directions, the direction in which the x component increases is referred to as + x direction, and the direction in which the x component decreases is referred to as -x direction. Similarly, for the y and z components, the y-axis direction, + y direction, -y direction, z-axis direction, + z direction, and -z direction are defined.

  In the following description, a direction along a certain axis includes a case where the “certain direction” is completely parallel to the “certain axis”, but is not limited thereto. If the same effect is produced, the case where it can be regarded as parallel is also included. The case where it can be regarded as parallel is, for example, the case where the angle formed by both falls within a range of ± 2 degrees.

  As shown in FIG. 2, the direction in which light is irradiated from the irradiation unit 1 toward the gas cell 2 is the + x direction. Therefore, the measurement direction of the magnetic field in the gas cell 2 measured by the magnetic field measurement device 9 is the + x direction. And the detection part 71 detects the direction where a magnetic field is the strongest as a disturbance magnetic field direction among the directions perpendicular | vertical to + x direction which is a measurement direction. Therefore, the disturbance magnetic field direction is a direction along the yz plane and has no component in the x-axis direction.

  In this magnetic field measuring device 9, the conversion unit 12 is adjusted so that the disturbance magnetic field direction detected by the detection unit 71 matches the vibration direction of the linearly polarized electric field included in the irradiation light irradiated by the irradiation unit 1. It has a feature in that.

1-2. Operation FIG. 3 is a diagram for explaining the principle of measuring a magnetic field by a so-called one-beam type measuring apparatus. In a one-beam measurement device, when linearly polarized light is irradiated to gas atoms enclosed in a gas cell, the probability distribution of the magnetic moment that occurs when the gas atoms are optically pumped and the energy changes is a spherically symmetric origin distribution. Change from. For example, at the energy transition of the hyperfine structure level F → F ′ = F−1, the probability distribution of the magnetic moment of the gas atom has a shape corresponding to the region R ₁ extending along the direction of vibration of the linearly polarized light. Become. This probability distribution is called alignment. That is, as shown in FIG. 3 (a), for example, a linearly polarized light oscillation direction of the electric field is along the parallel arrows D ₀ direction + y direction, is irradiated toward the + x-direction, the gas which the linearly polarized light passes through Alignment distributed in the region R ₁ along the y-axis direction occurs in the atoms. When passing through gas atoms, the plane of polarization of linearly polarized light rotates due to linear dichroism. FIG. 3B shows the rotation angle α of the polarization plane when the vibration direction of the linearly polarized electric field is viewed in the −x direction. Since the rotation angle α is correlated with the strength of the magnetic field in the + x direction, the strength of the magnetic field in the x-axis direction inside the gas cell 2 is measured by measuring the rotation angle α. That is, in Wanbimu scheme, arrow D _M direction showing the measurement direction is the direction (in FIG. 3 + x direction) for emitting light.

Here, in order to explain the above-described characteristics of the magnetic field measurement apparatus 9 according to the present invention, the operation of the measurement apparatus not having this characteristic will be described. FIG. 4 is a diagram for explaining the measurement of the magnetic field by the measuring device that does not have the characteristics of the magnetic field measuring device 9. Although this measuring apparatus has a configuration common to the magnetic field measuring apparatus 9, the conversion unit 12 is not adjusted, and therefore the vibration direction of the electric field of linearly polarized light included in the irradiation light does not match the disturbance magnetic field direction. For example, in this measuring apparatus, the direction of the arrow D _E that is the disturbance magnetic field direction is the + y direction shown in FIG. Furthermore, since the arrow D _M direction is the measurement direction is the + x direction, irradiation light having a linear polarization component is emitted toward the + x direction. The irradiation direction of the linearly polarized light is such that the vibration direction of the electric field does not match the disturbance magnetic field direction (+ y direction). Specifically, the vibration direction of the above are the arrow D ₀ direction shown in FIG. 4, which is parallel to the z-axis direction. Therefore, alignment occurs in the region Ra indicated by a broken line in FIG. 4A in the gas atoms in the gas cell. This alignment has a substantially rotationally symmetric shape about the z-axis, and extends along the z-axis direction.

When receiving the disturbance magnetic field along the disturbance magnetic field direction, the above-described alignment generated in the gas atoms in the gas cell rotates around an axis extending in the disturbance magnetic field direction. That is, the alignment rotates and assumes a posture corresponding to the region Rb indicated by the solid line in FIG. FIG. 4B shows the alignment viewed in the + y direction. Thus, originally, the alignment that occurred in the region Ra is affected by the disturbance magnetic field in the + y-direction, and rotated in the arrow D ₄ direction and orientation in accordance with the region Rb.

FIG. 4C shows the alignment when the side where the gas atoms are present, that is, the side in the −x direction is seen from the side receiving the irradiation light transmitted through the gas atoms, that is, the side in the + x direction. Has been. When viewed in the −x direction, the region Rb indicating the shape of the alignment after the rotation by the disturbance magnetic field is shorter than the region Ra indicating the shape of the alignment before the rotation. That is, the length of the region Ra in the z-axis direction is L ₀ , while the length of the region Rb in the z-axis direction is L ₁ shorter than L ₀ . Therefore, in this measuring apparatus, the alignment viewed from the side receiving the irradiation light transmitted through the gas atoms is affected by the disturbance magnetic field and becomes small. As a result, the sensitivity of this measuring device is reduced due to the influence of a disturbance magnetic field.

On the other hand, FIG. 5 is a figure for demonstrating the measurement of the magnetic field by the magnetic field measuring apparatus 9 which concerns on this invention. In the magnetic field measurement device 9, the conversion unit 12 is adjusted by the adjustment unit 72 so that the vibration direction of the electric field of linearly polarized light included in the irradiation light matches the disturbance magnetic field direction. Since the measurement direction of arrow D _M direction is the + x direction, irradiation light including a linearly polarized light component is emitted toward the + x direction. The direction of vibration of the linearly polarized light irradiated is the direction of arrow D ₀ shown in FIG. This arrow D ₀ direction is adapted to the arrow D _E direction (+ y direction) which is the disturbance magnetic field direction. Therefore, alignment occurs in the region R ₁ shown in FIG. 5A in the gas atoms in the gas cell. This alignment has a substantially rotationally symmetric shape about the y-axis, and extends along the y-axis direction. Note that this alignment has a llama rotation about the x axis, and therefore the rotational symmetry is deviated from the y axis. However, since the displacement is small compared to the magnitude of the disturbance magnetic field, this alignment can be regarded as a shape that is substantially rotationally symmetric about the y-axis.

When the above-described alignment generated in the gas atoms in the gas cell 2 receives a disturbance magnetic field along the disturbance magnetic field direction, the alignment rotates around an axis extending in the disturbance magnetic field direction. That is, the alignment is rotated in the arrow D ₅ direction shown in Figure 5 (a). FIG. 5B shows the alignment viewed in the + y direction. As described above, the alignment generated in the region R ₁ is substantially rotationally symmetric about the y-axis and extends along the y-axis direction, so the arrow along the arc trajectory centered on the y-axis be rotated to D ₅ direction, the shape is hardly changed. Therefore, as shown in FIG. 5C, the length of the alignment shape hardly changes before and after being rotated by the disturbance magnetic field when viewed in the −x direction. That is, the alignment length L ₀ before rotation is substantially the same as the alignment length L ₁ after rotation. Therefore, the sensitivity of the magnetic field measuring device 9 is hardly affected by the disturbance magnetic field.

  In the first embodiment described above, the disturbance magnetic field direction does not have a measurement direction component, but the disturbance magnetic field direction may have a measurement direction component. In this case, for example, the measurement direction itself may be changed so that the disturbance magnetic field direction does not have a component of the measurement direction. In this case, the irradiation unit 1 and the measurement unit of the magnetic field measurement device 9 may be moved, and an object (for example, a human body that is a measurement target) measured by the magnetic field measurement device 9 may be moved.

2. Second embodiment 2-1. Configuration FIG. 6 is a diagram showing an overall configuration of a magnetic field measurement apparatus 9A according to the second embodiment of the present invention. The magnetic field measuring device 9A is a so-called two-beam measuring device in which the pump light irradiation device and the probe light irradiation device are separated. The magnetic field measuring device 9A includes a probe light irradiation unit 1A instead of the irradiation unit 1, a tracking mechanism 7A, and a pump light irradiation unit 8. Unlike the magnetic field measuring apparatus 9 of one embodiment, other configurations are common. Note that the positions of the respective components of the magnetic field measurement apparatus 9A shown in FIG. 6 do not indicate the actual arrangement thereof.
Hereinafter, differences of the magnetic field measuring apparatus 9A from the magnetic field measuring apparatus 9 will be mainly described.

  The probe light irradiation unit 1A includes a light source 11A and a conversion unit 12A. The light source 11A may be the light source 11 and the conversion unit 12A may be the conversion unit 12, but the wavelength of the probe light irradiated by the probe light irradiation unit 1A is the gas cell 2 in order to avoid unnecessary pumping. It is desirable to be away from the resonance frequency of the gas atoms enclosed in. Further, it is desirable that the component contained in the probe light is higher as the proportion of linearly polarized light in all components increases. However, the probe light may contain other polarization components as long as it has a linear polarization component. The probe light generated by the light source 11A and converted by the conversion unit 12A is guided by, for example, an optical fiber and irradiated on the gas cell 2. Note that the probe light may be directly applied to the gas cell 2 without using an optical fiber or the like.

  The pump light irradiation unit 8 includes a light source 81 and a conversion unit 82. The light source 81 is a laser generator that generates a laser having a frequency corresponding to the transition of the hyperfine structure level of atoms enclosed in the gas cell 2. That is, the light source 81 generates a laser that is tuned to a wavelength that can excite gas atoms enclosed in the gas cell 2. The conversion unit 82 includes a circular polarization filter and converts the laser generated by the light source 81 into pump light having a circular polarization component. The pump light generated by the light source 81 and converted by the conversion unit 82 is guided by, for example, an optical fiber and applied to the gas cell 2. The pump light is irradiated so as to intersect the probe light inside the gas cell 2. The pump light may be directly applied to the gas cell 2 without using an optical fiber or the like.

  The follow-up mechanism 7A includes a detection unit 71A that detects a disturbance magnetic field, and the irradiation direction of the probe light emitted from the probe light irradiation unit 1A and the pump that is emitted from the pump light irradiation unit 8 according to the detection result by the detection unit 71A. Adjustment for adjusting the positions of the probe light irradiation unit 1A, the pump light irradiation unit 8, the polarization separator 3 and the light receiving unit 4 so that the light irradiation direction and the light receiving direction of the polarization separator 3 and the light receiving unit 4 are determined. 72A.

  71 A of detection parts detect the direction where a magnetic field is the strongest from the directions perpendicular | vertical to the measurement direction measured by the magnetic field measuring apparatus 9A as a disturbance magnetic field direction. The detection unit 71 </ b> A may be configured in common with the detection unit 71.

  72 A of adjustment parts are each positions of the probe light irradiation part 1A, the pump light irradiation part 8, the polarization separator 3, and the light-receiving part 4 so that pump light may be irradiated along the disturbance magnetic field direction detected by the detection part 71A. Adjust. FIG. 7 is a diagram showing the state of this adjustment. In FIG. 7, the irradiation direction of the probe light by the probe light irradiation unit 1A is the + x direction, and the irradiation direction of the pump light by the pump light irradiation unit 8 is the + y direction.

Here, in the right-hand system represented by the right hand with the thumb, index finger, and middle finger bent at right angles, the two-beam method is used when the pump light irradiation direction is aligned with the thumb direction and the probe light irradiation direction is aligned with the index finger direction. In this measuring apparatus, the magnetic field in the direction of the middle finger is measured. That measurement direction here is the arrow D _M direction as shown in FIG. 7 (-z direction), the pump light is irradiated to a + y-direction in a direction perpendicular to the measuring direction of the probe light is the Is irradiated in the + x direction perpendicular to both the measurement direction (−z direction) and the direction in which the pump light is irradiated (+ y direction).

  Then, the detection unit 71A detects the direction in which the magnetic field is strongest from the directions perpendicular to the −z direction as the measurement direction as the disturbance magnetic field direction. Therefore, the disturbance magnetic field direction is a direction along the xy plane and does not have a component in the z-axis direction.

In this case, the adjustment unit 72A, not shown, the gas cell 2, the light source 11A, the conversion unit 12A, the light source 81, converting unit 82, the polarization separator 3, the transmitted light receiving element 41 and the reflected light receiving element 42, the arrow D ₇ direction Rotate along. As a result, the irradiation direction of the pump light by the pump light irradiation unit 8 is rotated and approaches the disturbance magnetic field direction detected by the detection unit 71A. Arrow D ₇ direction is the direction of rotation about the z axis is along the xy plane. That is, the arrow D ₇ direction is the direction along the xy plane perpendicular to the arrow D _M direction (-z direction).

  When the pump light or the probe light is guided to the gas cell 2 by an optical fiber or the like, or the probe light transmitted through the gas cell 2 is guided by the optical fiber or the like and received by the polarization separator 3, these optical fibers are , The probe light irradiation unit 1A, the pump light irradiation unit 8, and the polarization separator 3. In this case, the adjustment unit 72A may adjust the position, direction, posture, and the like of the portion of these optical fibers facing the gas cell 2. In short, the adjustment unit 72A adjusts the position of the configuration included in the magnetic field measurement device 9A so that the pump light is irradiated along the disturbance magnetic field direction detected by the detection unit 71A, and the irradiation direction of the pump light, The irradiation direction of the probe light and the light receiving direction of the probe light may be adjusted.

  In this magnetic field measuring apparatus 9A, the irradiation direction of the pump light, the irradiation direction of the probe light, and the light receiving direction of the probe light are adjusted so that the pump light is irradiated along the disturbance magnetic field direction detected by the detection unit 71A. Characterized by points.

2-2. Operation FIG. 8 is a diagram for explaining the principle of measuring a magnetic field by a so-called two-beam type measuring apparatus. In a two-beam type measurement device, when pump light is irradiated to gas atoms enclosed in a gas cell, the probability distribution of the magnetic moment that occurs when the gas atoms are optically pumped and the energy changes depends on the incident direction of the pump light. The shape corresponds to the region R ₂ extending along the line. This probability distribution is called orientation. A vector (hereinafter referred to as a magnetization vector M) representing the direction of magnetization generated by the orientation is the orientation direction. In this case, the irradiation direction of the pump light is the direction of the magnetization vector M.

As shown in FIG. 8, for example, is irradiated toward the pump light having the arrow D ₈ direction of the circularly polarized light component of arrow D _p direction (+ y direction), the gas atoms that the pump light is transmitted, extending in the + y direction An orientation distributed in the region R ₂ is formed, and a magnetization vector M in the + y direction is generated. When the probe light having a linearly polarized component whose electric field vibration direction is along the arrow D ₀ direction is irradiated in the arrow D _r direction (+ x direction), the arrow D _p direction (+ y direction) and the arrow _Dr orientation mainly direction (+ x direction) respectively perpendicular arrow D _M direction (-z direction) Rama rotated. As a result, the magnetization vector M rotates about the z-axis, and at this time, the following two phenomena occur.

[Phenomenon a] A phenomenon of trying to return the orientation (magnetization vector M) to the direction of pump light.
[Phenomenon b] A phenomenon in which the orientation is relaxed to be spherically symmetrical before the optical pumping.
Thereby, the magnetization vector M draws a spiral locus on the xy plane. FIG. 9 is a diagram illustrating the locus of the magnetization vector M. For example, in the configuration shown in FIG. 8, the magnetization vector M draws a trajectory T _M shown in FIG. 9A on the xy plane viewed in the arrow D _M direction (−z direction). The polarization plane of the probe light described above rotates through the orientation due to the Faraday effect. Thus, by measuring the rotation angle of the polarization plane, it is determined magnetic flux density of the arrow D _M direction (-z direction) inside of the gas cell 2.

For example, when the magnetization vector M draws a locus T _M shown in FIG. 9A, the expected value <M _X > of the magnetization in the + x direction appears as a specific value. When the horizontal axis represents the magnetic flux density B and the vertical axis represents the expected magnetization <M _X >, an output waveform as shown in FIG. 9B is obtained. The magnetic flux density B to be measured can be determined by reading the output of the linearly changing portion (the range of ΔB in the figure) near the origin in this waveform.
The relational expression between the expected magnetization <M _X > and the magnetic flux density B is as follows.

ここで、Γ_gは緩和速度であり、緩和時間Ｔの逆数で与えられる。そして緩和時間Ｔは、縦緩和時間Ｔ₁および横緩和時間Ｔ₂により、１／Ｔ＝１／Ｔ₁＋１／Ｔ₂で表される。また、ラーモア角周波数をω_L［ｒａｄ／ｓ］とし、磁気回転比をγ［ｒａｄ／ｓＴ］とし、磁束密度をＢ［Ｔ］とすると、ω_L＝γＢが成り立つ。磁化Ｍは、磁気モーメントの単位体積あたりの総和であるから比例定数Ｃは原子密度ｎに比例するパラメータと考える。

Here, Γ _g is the relaxation rate and is given by the reciprocal of the relaxation time T. The relaxation time T is expressed by 1 / T = 1 / T ₁ + 1 / T ₂ by the longitudinal relaxation time T ₁ and the lateral relaxation time T ₂ . Further, when the Larmor angular frequency is ω _L [rad / s], the magnetic rotation ratio is γ [rad / sT], and the magnetic flux density is B [T], ω _L = γB is established. Since the magnetization M is the sum of the magnetic moment per unit volume, the proportionality constant C is considered as a parameter proportional to the atomic density n.

Here, in order to explain the above-described feature of the magnetic field measurement device 9A according to the present invention, the operation of the measurement device that does not have this feature will be explained. FIG. 10 is a diagram for explaining the measurement of the magnetic field by the measuring device that does not have the characteristics of the magnetic field measuring device 9A. The measuring device is provided with the same configuration as the magnetic field measuring device 9A, arrow D _p direction is the incident direction of the pumping light, the position of such as a pump light irradiating unit 8 to match the disturbance magnetic field direction is not adjusted . For example, in this measuring apparatus, the direction of the arrow D _E that is the direction of the disturbance magnetic field is along the + y direction shown in FIG. 10, but the pump light having a circularly polarized component is irradiated toward the −x direction. That is, the arrow D _p direction is the incident direction of the pumping light to be irradiated (-x direction), so as not fit disturbance magnetic field direction (+ y direction). Therefore, the orientation of the gas atoms in the gas cell is generated in the region Rc indicated by the broken line in FIG. This orientation has a substantially rotationally symmetric shape about the x axis and extends along the −x direction. Incidentally, the pump light is irradiated in an arrow D _p direction (-x direction), because the probe light is irradiated in an arrow D _r direction (+ y direction), the measurement direction, the arrow D _M direction (-z direction) It has become.

When the above-described orientation generated in the gas atoms in the gas cell receives a disturbance magnetic field along the disturbance magnetic field direction, the orientation rotates around an axis extending in the disturbance magnetic field direction. That is, the orientation rotates and takes a posture corresponding to the region Rd indicated by the solid line in FIG. FIG. 10B shows an orientation viewed in the + y direction. Thus, originally, orientation that occurred in the area Rc indicated by a broken line, is affected by the disturbance magnetic field in the + y-direction, and rotated in the arrow D ₁₀ direction and orientation in accordance with the region Rd.

In the example shown in FIG. 10, in order to measure the magnetic flux density of the arrow D _M direction (-z direction) is irradiated with probe light to the arrow D _r direction (+ y direction). That is, the probe light is irradiated from the −y direction of the gas cell, and the rotation angle of the polarization plane of the probe light transmitted in the + y direction of the gas cell is measured by the measurement unit (polarization separator 3, light receiving unit 4, signal processing circuit 5). The As shown in FIG. 10B, when viewed along the + y direction, the orientation receives a disturbance magnetic field along the y-axis direction and rotates from the region Rc to the region Rd, so the magnetization vector M is also in the −z direction. It is rotating. Therefore, the magnetization vector M draws a different locus from that of FIG. 9A described above, and the expected value of magnetization is also different, so that the output waveform is a waveform that takes into account the influence of the disturbance magnetic field. Therefore, the measurement in this case is easily affected by the disturbance magnetic field.

On the other hand, FIG. 11 is a figure for demonstrating the measurement of the magnetic field by the magnetic field measuring apparatus 9A based on this invention. In the magnetic field measuring apparatus 9A, the disturbance magnetic field direction is along the y-axis direction shown in FIG. 11, and the pump light having a circularly polarized component is irradiated toward the + y direction. That is, the arrow _Dp direction (+ y direction) that is the incident direction of the pump light is adapted to the arrow _DE direction (+ y direction) that is the disturbance magnetic field direction. Therefore, orientation occurs in the region R ₂ shown in FIG. 11A in the gas atoms in the gas cell. This orientation has a substantially rotationally symmetric shape about the y-axis, and extends along the y-axis direction. Here, an arrow D probe light to the _r direction (+ x direction) is irradiated, the magnetic field of an arrow D _M direction (-z direction) is measured.

When the above-mentioned orientation generated in the gas atoms in the gas cell 2 receives a disturbance magnetic field along the disturbance magnetic field direction, the orientation rotates around an axis extending in the disturbance magnetic field direction. That is, the orientation is rotated in the arrow D ₉ direction shown in FIG. 11 (a). FIG. 11B shows the orientation viewed in the + y direction. As described above, the orientation generated in the region R ₂ has a substantially rotationally symmetric shape around the y-axis and extends along the y-axis direction. Therefore, the arrow along the arc trajectory around the y-axis be rotated in the D ₁₁ direction, the shape is hardly changed. Accordingly, as shown in FIG. 11 (c), on the xy plane as seen in the arrow D _M direction (-z direction), the direction of magnetization vector M caused by the formation of orientation, before and after orientation is rotated by the disturbance magnetic field does not change. Therefore, in this case, when the probe light having a linearly polarized light component is irradiated in the direction of the arrow _Dr (+ x direction), the magnetization vector M draws a locus as shown in FIG. 9A, and the magnetic flux density is obtained. That is, the sensitivity of the magnetic field measuring device 9A is hardly affected by the disturbance magnetic field.

  In the second embodiment described above, the disturbance magnetic field direction has no measurement direction component, but the disturbance magnetic field direction may have a measurement direction component. In this case, the measurement direction itself may be changed by adjusting the position of the object to be measured so that the disturbance magnetic field direction does not have a component of the measurement direction.

DESCRIPTION OF SYMBOLS 1 ... Irradiation part, 1A ... Probe light irradiation part, 11, 11A ... Light source, 12, 12A ... Conversion part, 2 ... Gas cell, 3 ... Polarization separator, 4 ... Light receiving part, 41 ... Transmitted light receiving element, 42 ... Reflection Light receiving element, 5 ... signal processing circuit, 6 ... display device, 7, 7A ... tracking mechanism, 71, 71A ... detection unit, 72 ... adjustment unit, 72A ... adjustment unit, 8 ... pump light irradiation unit, 81 ... light source, 82 ... Conversion unit, 9 ... Magnetic field measurement apparatus (first embodiment), 9A ... Magnetic field measurement apparatus (second embodiment).

Claims (6)

A gas cell with gas atoms sealed inside;
An irradiation unit that irradiates irradiation light including linearly polarized light along a predetermined measurement direction with respect to gas atoms sealed in the gas cell;
A detection unit for detecting a direction in which the magnetic field is strongest from directions perpendicular to the measurement direction;
An adjustment unit that adjusts the irradiation light so that the direction detected by the detection unit matches the vibration direction of the electric field of the linearly polarized light;
A magnetic field measurement apparatus comprising: a measurement unit that measures a rotation angle of a polarization plane of irradiation light irradiated by the irradiation unit and transmitted through the gas atoms. The magnetic field measurement apparatus according to claim 1, wherein the irradiation unit guides the irradiation light to a gas cell by an optical fiber. A gas cell with gas atoms sealed inside;
A detection unit that detects the direction in which the magnetic field is the strongest among the directions perpendicular to the determined measurement direction;
A pump light irradiating unit that irradiates pump light including a circularly polarized component along a direction perpendicular to the measurement direction with respect to gas atoms sealed in the gas cell;
A probe light irradiation unit configured to irradiate probe light including linearly polarized light along a direction perpendicular to both the measurement direction and the direction in which the pump light is irradiated with respect to gas atoms sealed in the gas cell;
A measurement unit that measures the rotation angle of the polarization plane of the probe light irradiated by the probe light irradiation unit and transmitted through the gas atoms;
An adjustment unit that adjusts each position of the pump light irradiation unit, the probe light irradiation unit, and the measurement unit so that the pump light is irradiated along the direction detected by the detection unit. Magnetic field measuring device characterized by. The pump light irradiation unit guides the pump light to a gas cell by an optical fiber,
The magnetic field measurement apparatus according to claim 3, wherein the probe light irradiation unit guides the probe light to a gas cell using an optical fiber. A gas cell with gas atoms sealed inside;
A detection unit that detects the direction in which the magnetic field is strongest as the detection direction;
Irradiation unit that irradiates irradiation light including linearly polarized light along a measurement direction that is a direction perpendicular to a detection detection direction detected by the detection unit with respect to gas atoms sealed in the gas cell;
The measurement unit that measures the rotation angle of the polarization plane of the irradiation light irradiated by the irradiation unit and transmitted through the gas atoms, and the irradiation light is adjusted so that the detection direction matches the vibration direction of the electric field of the linearly polarized light And an adjusting unit that adjusts the position of the gas cell, the irradiation unit, and the measuring unit. A gas cell with gas atoms sealed inside;
A detection unit that detects the direction in which the magnetic field is strongest as the detection direction;
A pump light irradiating unit that irradiates a gas atom enclosed in the gas cell with pump light including a circularly polarized component;
A probe light irradiation unit configured to irradiate probe light including linearly polarized light along a direction perpendicular to a direction in which the pump light is irradiated to gas atoms sealed in the gas cell;
A measurement unit that measures the rotation angle of the polarization plane of the probe light irradiated by the probe light irradiation unit and transmitted through the gas atoms;
An adjustment unit that adjusts each position of the pump light irradiation unit, the probe light irradiation unit, and the measurement unit so that the pump light is irradiated along the detection direction detected by the detection unit. Magnetic field measuring apparatus characterized by the above.

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