JP2012047573A - Cell unit and magnetism measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the capacity of a cell.SOLUTION: A cell unit has: a first cell; a second cell disposed in a first direction when viewed from the first cell; a first optical system for outputting light outputted from a first light source as a beam array including a plurality of beams aligned in a second direction vertical to the first direction; a second optical system having a first plane for reflecting light in the second direction made incident from the first optical system, in the first direction and making the light incident to the first cell; a third optical system having a first plane for reflecting light in the second direction made incident from the first optical system, in the first direction and making the light incident to the second cell and a second plane for reflecting light in the first direction reflected by the first plane of the second optical system and passed through the first cell, in the second direction; and a fourth optical system having a second plane for reflecting light in the first direction reflected by the first plane of the third optical system and passed through the second cell, in the second direction.

Description

  The present invention relates to a cell unit and a magnetic measurement device.

  A SQUID (Superconducting Quantum Interference Device) is known as a magnetic sensor for measuring a magnetic field generated by a living body. Further, as a technique that does not use SQUID, an optical pumping type magnetic sensor is known. Non-Patent Document 1 shows the operating principle of an optically pumped magnetic sensor. Non-Patent Document 2 discloses a demonstration of magnetocardiography using a multi-channel optical pumping magnetic sensor. Patent Document 1 discloses a technique for simultaneously irradiating a plurality of regions with a laser beam.

JP 2004-354130 A

K. Kominis, 3 others, “A subfemtotesla multichannel atomic magnetometer”, Nature, (UK), Nature Publishing Group, April 10, 2003, 422, p. 596-599 G. Bison, 7 others, “A room temperature 19-channel magnetic field mapping device for cardiac signals”, Applied Journal of Applied Physics (Applied Physics Letters), (USA), American Institute of Physics, June 29, 2009, vol. 95, p. 173701

One way to increase the sensitivity of an optically pumped magnetic sensor is to increase the internal volume of the cell. However, in the technique described in Patent Document 1, since the space used for the propagation of light is large, there is a problem that when the internal volume of the cell is increased, the entire apparatus becomes large.
The present invention provides a technique that enables an increase in the capacity of a cell.

The present invention includes a first cell that operates by light incident from the outside, a second cell that is disposed in the first direction as viewed from the first cell and operates by light incident from the outside, and an output from the first light source. A first optical system that outputs the emitted light as a beam array including a plurality of beams aligned in a second direction perpendicular to the first direction, and in a direction opposite to the first direction as viewed from the first cell A second optical system disposed and having a first surface that reflects the light in the second direction incident from the first optical system in the first direction and enters the first cell; and from the second cell A first surface disposed in a direction opposite to the first direction and reflecting the light in the second direction incident from the first optical system in the first direction and entering the second cell; and Reflected by the first surface of the second optical system and passing through the first cell. A third optical system having a second surface for reflecting the light in the first direction in the second direction; and disposed in the first direction as viewed from the second cell; and by the first surface of the third optical system. And a fourth optical system having a second surface that reflects the light in the first direction reflected and passed through the second cell in the second direction.
According to this cell unit, the capacity of the cell can be increased as compared with the case where the above configuration is not provided.

In a preferred aspect, the first cell and the second cell are operated by light in the first direction and light in a third direction perpendicular to both the first direction and the second direction, and the first optical system Outputs the light output from the second light source as a beam array including a plurality of beams aligned in the second direction, and the cell unit has a direction opposite to the third direction as viewed from the first cell. A fifth optical system that is disposed in the second light source and that reflects the light in the second direction incident from the second light source through the first optical system in the third direction and is incident on the first cell; The second cell is disposed in a direction opposite to the third direction as viewed from two cells, and reflects the second direction light incident from the second light source through the first optical system in the third direction. You may have the 6th optical system which injects into a cell.
According to this cell unit, the capacity of the cell can be increased as compared with the case where the above configuration is not provided.

In a preferred embodiment, the first cell and the second cell have an internal space, and atoms that are spin-polarized by circularly polarized light are enclosed in the internal space and are incident on the first cell and the second cell. The light in the first direction is linearly polarized light, the light in the third direction incident on the first cell and the second cell is circularly polarized light, and is reflected by the second surface of the third optical system. A detection means including a first detection element for detecting a polarization plane rotation angle of the reflected light and a second detection element for detecting a polarization plane rotation angle of the light reflected by the second surface of the fourth optical system; May be.
According to this cell unit, the capacity of the cell in which atoms that are spin-polarized by circularly polarized light are enclosed can be increased.

In another preferred embodiment, the cell unit is disposed in the third direction as viewed from the first cell, and operates with the light in the first direction and the light in the third direction incident from the outside. , Disposed in a direction opposite to the third direction when viewed from the third cell, and reflects the light in the second direction incident from the fifth optical system in the third direction and enters the third cell. And a seventh optical system.
According to this cell unit, the capacity of the two-dimensionally arranged cells can be increased.

The present invention also provides a magnetic measurement apparatus comprising the cell unit and a measurement unit that measures the strength of the magnetic field in the second direction using the polarization plane rotation angle detected by the detection unit. .
According to this magnetometer, the sensitivity can be increased compared to the case where the above configuration is not provided.

1 is a diagram illustrating a configuration of a magnetic measurement device 1. FIG. 2 is a schematic diagram showing a cross-sectional structure of the array sensor 10. FIG. 2 is a diagram illustrating a structure of a cell array 13. FIG.

  FIG. 1 is a diagram illustrating a configuration of a magnetic measurement apparatus 1 according to an embodiment. The magnetic measurement device 1 includes an array sensor 10, a signal processor 20, a light source 30, and a light source 40. The magnetic measurement device 1 is a magnetocardiograph, for example, and is a device that observes the state of the heart of a living body by magnetism. Although details will be described later, the magnetic field is measured using light (probe light) output from the light source 30 (an example of the first light source) and light (pump light) output from the light source 40 (an example of the second light source). Done. The magnetic measurement device 1 is an optical pumping type magnetic sensor. The light source 30 and the light source 40 are, for example, tunable lasers.

  FIG. 2 is a schematic diagram showing a cross-sectional structure of the array sensor 10. The array sensor 10 includes an array illuminator 11, an array illuminator 12, a cell array 13, and a light detection layer 14. For the sake of explanation, the coordinate axes are defined as follows. In the figure, the x-axis (an example of the first direction) is directed to the right, the y-axis (an example of the third direction) is perpendicular to the page and directed from the page to the reader, and the z-axis is an upward direction in the figure (an example of the second direction). Take.

  The array illuminator 11 repeatedly reflects the probe light incident from the light source 30 to split the beam, thereby forming a two-dimensional beam array. That is, the array illuminator 11 is an example of a first optical system that outputs the probe light output from the light source 30 as a beam array including a plurality of beams aligned in the z-axis direction. The array illuminator 11 includes a diffraction grating 111, an optical coupler 112, and a light guide 113. The probe light output from the light source 30 is guided to the array illuminator 11 by transmission means such as an optical fiber and is optically coupled via the optical coupler 112. The light guided to the array illuminator 11 becomes a branched beam (light beam) by being repeatedly reflected by the surfaces of the diffraction grating 111 and the light guide 113, and forms a two-dimensionally expanded beam array. This beam array includes a plurality of beams aligned in the z-axis direction. The probe light is linearly polarized light.

  The array illuminator 12 repeatedly reflects the pump light incident from the light source 40 to split the beam, thereby forming a two-dimensional beam array. That is, the array illuminator 12 is an example of a first optical system that outputs the pump light output from the light source 40 as a beam array including a plurality of beams aligned in the z-axis direction. The array illuminator 12 includes a diffraction grating 121, an optical coupler 122, and a light guide 123. The pump light output from the light source 40 is guided to the array illuminator 12 by transmission means such as an optical fiber and is optically coupled via the optical coupler 122. The pump light guided to the array illuminator 12 becomes a branched beam by being repeatedly reflected by the surfaces of the diffraction grating 121 and the light guide 123, and a beam array spreading two-dimensionally. This beam array includes a plurality of beams aligned in the z-axis direction. The pump light is converted into circularly polarized light before being incident on the optical coupler 122 by a λ / 4 plate (quarter wavelength plate) (not shown) or the like. In order to prevent the drawing from becoming complicated, pump light is not shown in FIG.

  The cell array 13 includes a plurality of cells 131, a plurality of mirrors 132, and a plurality of mirrors 133 (not shown in FIG. 2). The plurality of cells 131 are arranged in a matrix along the x-axis direction and the y-axis direction on a plane having a constant z-axis coordinate. In the example of FIG. 2, eight cells 131 and nine mirrors 132 are arranged in the x-axis direction.

  FIG. 3 is a diagram showing the structure of the cell array 13. In FIG. 3, the right direction is the x-axis direction, the downward direction is the y-axis direction, and the direction perpendicular to the paper surface and facing the reader is the z-axis direction. Here, in order to distinguish and describe each of the cells 131, they are described using an array such as a cell 131 (x, y). The array index is assigned in order from the upstream in the coordinate axis direction. For example, in the x-axis direction, indexes 1, 2, 3,..., 8 are assigned in order from the left in FIG. The same applies to the mirror 132 and the mirror 133.

  The cell 131 is operated by probe light in the x-axis direction and pump light in the y-axis direction. The cell 131 is formed of a material that transmits pump light and probe light, such as glass or plastic, and has an internal space. In this internal space, gaseous alkali metal atoms (potassium (K), rubidium (Rb), cesium (Cs), etc.) are enclosed. When the alkali metal atoms are irradiated with pump light in the y-axis direction, they are spin-polarized along the y-axis and become magnetized. This magnetization vector precesses at an angular frequency corresponding to the magnetic field in the z-axis direction to be measured. The magnetization vector is constantly tilted with respect to the y-axis in balance with the precession relaxation effect. Due to this inclination, the magnetization vector has a component in the x-axis direction. Probe light in the x-axis direction is incident on the cell 131 from the outside. When the probe light passes through the cell 131, its polarization plane is rotated by the Faraday effect. The polarization plane rotation angle is proportional to the strength of the magnetic field in the z-axis direction.

  Here, cell 131 (1, 1) (an example of the first cell), cell 131 (2, 1) (an example of the second cell), and cell 131 (1, 2) (an example of the third cell) 3 One cell, mirror 132 (1, 1) (an example of the second optical system), mirror 132 (2, 1) (an example of the third optical system), and mirror 132 (3, 1) (an example of the fourth optical system) Three mirrors (example), mirror 133 (1, 1) (example of fifth optical system), mirror 133 (2, 1) (example of sixth optical system), and mirror 133 (1, 2) (first example) The structure of the cell array 13 will be described using the three mirrors of (example 7 optical system) as an example. The cell 131 (2, 1) is arranged in the x-axis direction when viewed from the cell 131 (1, 1). The mirror 132 (1, 1) is disposed in a direction opposite to the x-axis direction (x-axis negative direction) when viewed from the cell 131 (1, 1). The mirror 132 (2, 1) is arranged in the x-axis direction when viewed from the cell 131 (1, 1) (that is, the direction opposite to the x-axis direction when viewed from the cell 131 (2, 1)). The mirror 132 (3, 1) is arranged in the x-axis direction when viewed from the cell 131 (2, 1). The mirror 133 (1, 1) is arranged in a direction opposite to the y-axis direction (y-axis negative direction) when viewed from the cell 131 (1, 1). The mirror 133 (2, 1) is arranged in the direction opposite to the y-axis direction when viewed from the cell 131 (2, 1). The mirror 133 (1, 2) is disposed in a direction opposite to the y-axis direction when viewed from the cell 131 (2, 1) (y-axis direction when viewed from the cell 131 (2, 1)). The positional relationship among other cells 131, mirrors 132, and mirrors 133 is the same as this.

  Refer to FIG. 2 again. The mirror 132 includes a surface 1321 (an example of a first surface) that reflects the probe light in the z-axis direction incident from the array illuminator 11 in the x-axis direction, and the x-axis that has passed through the cell 131 after being reflected by the surface 1321. And a surface 1322 (an example of a second surface) that reflects the probe light in the direction in the z-axis direction. The surfaces 1321 and 1322 are surfaces that totally reflect incident light. In this example, the mirror 132 has a plate shape, and the surface 1321 and the surface 1322 are in a relationship between the front surface and the back surface. The mirror 132 is inclined 45 ° with respect to the x-axis and the z-axis, but is not inclined with respect to the y-axis.

  The positional relationship between the mirror 133 and the cell 131 is equal to the relationship obtained by rotating the mirror 132 and the cell 131 by 90 ° along the z axis. The mirror 133 is a surface that reflects the z-axis pump light incident from the array illuminator 12 in the y-axis direction, and a surface that reflects the y-axis pump light that has been reflected by this surface and then passed through the cell 131. And have. The former surface is a surface that totally reflects incident light. In this example, the mirror 133 has a plate shape, and the above-mentioned two surfaces are in a relationship between the front surface and the back surface. The mirror 133 is inclined 45 ° with respect to the y-axis and the z-axis, but is not inclined with respect to the x-axis.

  The light detection layer 14 includes a PBS (Polarizing Beam Splitter) 141, a PD (Photo Detector) array 142, and a coaxial cable 143. The PBS 141 divides the incident probe light into two orthogonal polarization components (for example, an x-axis component and a y-axis component) and outputs them. The PD array 142 includes PD1421 and PD1422 photodetectors. The PD 1421 and the PD 1422 detect light components of the components separated by the PBS 141, that is, the x-axis component and the y-axis component. The coaxial cable 143 is a multi-channel transmission line that transmits a signal indicating the detected light amount. The coaxial cable 143 is connected to the signal processor 20. The signal processor 20 calculates the polarization plane rotation angle from the difference in the amount of light indicated by the input signal. That is, the PD array 142 is an example of a detection element that detects the polarization plane rotation angle of the probe light reflected by the surface 1322 of the mirror 132. The PD array 142 and the cell 131 have a one-to-one correspondence. The PD array 142 is arranged in a matrix like the cells 131. A set of the plurality of PD arrays 142 is an example of a detection unit that detects a polarization plane rotation angle in the plurality of cells 131. The PD array 142 is fixed to a highly rigid support (for example, plastic or glass).

  The signal processor 20 includes a processing unit 21 and a display unit 22. The processing unit 21 (an example of a measurement unit) includes a processor and a memory. The processing unit 21 calculates the strength of the magnetic field in the z-axis direction for each of the cells 131 using a signal input via the coaxial cable 143. The display unit 22 includes a display device such as a CRT (Cathode Ray Tube) or an LCD (Liquid Crystal Display). The display unit 22 displays characters or images indicating the calculated magnetic field strength.

  The magnetic measurement apparatus 1 measures the magnetic field of a living body using the above configuration. The measurement of the magnetic field is generally performed as follows. Prior to the measurement, the power sources of the light source 30 and the light source 40 are turned on. When the measurement of the magnetic field is instructed by a switch or the like (not shown), the signal processor 20 measures the magnetic field using the signal output from the array sensor 10 and displays the measurement result.

  According to the magnetic measurement apparatus 1, the ratio of the area occupied by the optical system (mirror 132 and mirror 133) to the cell 131 can be reduced as compared with the case where the array illuminator 11 and the array illuminator 12 are not used. The capacity of the cell 131 can be increased (that is, the sensitivity can be increased) and the density can be increased (that is, the spatial resolution can be increased).

  The present invention is not limited to the above-described embodiment, and various modifications can be made. Hereinafter, some modifications will be described. Two or more of the following modifications may be used in combination.

  The optical system for forming the pump light beam array and the optical system for forming the probe light beam array may be the same. In the above-described embodiments, the example in which the array illuminator 11 forms a probe light beam array and the array illuminator 12 forms a pump light beam array has been described. However, for example, the array illuminator 11 may have a configuration in which a beam array of pump light and a beam array of probe light are formed. The diffraction grating for forming the beam array does not necessarily have to be provided on the entire surface of the light guide (substrate), and it is sufficient if it is formed in a region where the beam is to be reflected. Therefore, for example, on the lower surface of the array illuminator 11, a diffraction grating in the x-axis direction may be formed in a region where the pump light is to be reflected, and a diffraction grating in the y-axis direction may be formed in a region where the probe light is to be reflected. .

  The optical system that forms the beam array in the array illuminator 11 is not limited to the diffraction grating 111. A dielectric multilayer film configured to branch the beam may be used as an optical system for forming the beam array. This optical system has any configuration as long as the laser beam traveling straight is branched while being bent in a crank shape and is output as a plurality of beams aligned in a certain direction (z-axis direction in the embodiment). May be used. The same applies to the array illuminator 12.

  The number of light sources of the magnetic measurement device 1 is not limited to two. The magnetic measurement device 1 may have only a single light source. In this case, the magnetic measurement apparatus 1 may use non-linear optical rotation (NMOR) or an optical double resonance method. According to these methods, one beam serves as both pump light and probe light.

  In addition to the alkali metal gas, the cell 131 may be filled with a rare gas such as helium (He) or argon (Ar) or a nonmagnetic gas such as nitrogen (N) as a buffer gas. Further, the alkali metal atom is not necessarily gasified at all times, and may be gasified when measuring the magnetic field. For example, a structure that is solid when not measured and gasified by heating at the time of measurement may be used. Further, the gas used as the magnetic medium in the cell 131 is not limited to alkali metal. Any atom may be used as long as it is spin-polarized by pump light.

  The back surface of the mirror 133 (the surface on which the pump light in the y-axis direction that has passed through the cell 131 is incident) is not limited to the one that absorbs the pump light. It may reflect pump light. In this case, for example, in order to increase the efficiency of optical pumping, the back surface of the mirror 133 may reflect incident pump light in the negative y-axis direction. According to this configuration, since the pump light passes through the cell 131 twice, the pumping efficiency is improved as compared with the case where the light passes only once. Further, as an optical system replacing the mirror 132 or the mirror 133, an air gap (air layer) configured to satisfy the total reflection condition may be used.

The arrangement of the cells 131 in the cell array 13 is not limited to a two-dimensional arrangement. A configuration in which the cells 131 are arranged one-dimensionally, that is, on a straight line may be used.
The x axis and the y axis do not have to be orthogonal.
The pump light only needs to include a circularly polarized component, and may include a linearly polarized component instead of 100% circularly polarized light. The same applies to the probe light.
In the above-described embodiment, the example in which the cell array 13 is applied to the magnetic measurement device has been described. However, the cell array 13 may be used for devices other than the display device and the magnetic measurement device. When used in an apparatus other than the magnetic measurement apparatus, the cell 131 does not have an alkali metal gas inside. In this case, the cell 131 only needs to be operated by light incident from the outside.

DESCRIPTION OF SYMBOLS 1 ... Magnetic measuring apparatus, 10 ... Array sensor, 11 ... Array illuminator, 12 ... Array illuminator, 13 ... Cell array, 14 ... Photodetection layer, 20 ... Signal processor, 21 ... Processing part, 22 ... Display part, 30 DESCRIPTION OF SYMBOLS ... Light source, 40 ... Light source, 111 ... Diffraction grating, 112 ... Optical coupler, 113 ... Light guide, 121 ... Diffraction grating, 122 ... Optical coupler, 123 ... Light guide, 131 ... Cell, 132 ... Mirror, 133 ... Mirror , 141 ... PBS, 142 ... PD array, 143 ... coaxial cable, 1321 ... face, 1322 ... face, 1421 ... PD, 1422 ... PD

Claims (5)

A first cell that operates by light incident from the outside;
A second cell disposed in a first direction as viewed from the first cell and operated by light incident from the outside;
A first optical system that outputs light output from the first light source as a beam array including a plurality of beams aligned in a second direction perpendicular to the first direction;
The second cell is disposed in a direction opposite to the first direction as viewed from the first cell, and reflects the light in the second direction incident from the first optical system in the first direction and enters the first cell. A second optical system having one surface;
The second cell is disposed in a direction opposite to the first direction as viewed from the second cell, and reflects the light in the second direction incident from the first optical system in the first direction and enters the second cell. A third optical system having a first surface and a second surface that reflects the light in the first direction reflected by the first surface of the second optical system and passed through the first cell in the second direction;
The first cell is disposed in the first direction when viewed from the second cell, and is reflected by the first surface of the third optical system and reflects the light in the first direction that has passed through the second cell in the second direction. And a fourth optical system having two surfaces. The first cell and the second cell are operated by light in the first direction and light in a third direction perpendicular to both the first direction and the second direction;
The first optical system outputs light output from a second light source as a beam array including a plurality of beams aligned in the second direction,
The second cell is disposed in a direction opposite to the third direction when viewed from the first cell, and reflects light in the second direction incident from the second light source through the first optical system in the third direction. A fifth optical system incident on the first cell;
The second cell is disposed in a direction opposite to the third direction as viewed from the second cell, and reflects light in the second direction incident from the second light source through the first optical system in the third direction. The cell unit according to claim 1, further comprising: a sixth optical system incident on the second cell. The first cell and the second cell have an internal space,
In the internal space, atoms that are spin-polarized by circularly polarized light are enclosed,
The light in the first direction incident on the first cell and the second cell is linearly polarized light,
The light in the third direction incident on the first cell and the second cell is circularly polarized,
A first detection element for detecting a polarization plane rotation angle of light reflected by the second surface of the third optical system and a polarization plane rotation angle of light reflected by the second surface of the fourth optical system The cell unit according to claim 1, further comprising a detection unit including a second detection element. A third cell disposed in the third direction as viewed from the first cell and operated by the light in the first direction and the light in the third direction incident from the outside;
The second cell is disposed in a direction opposite to the third direction as viewed from the third cell, and reflects the light in the second direction incident from the fifth optical system in the third direction and enters the third cell. The cell unit according to claim 1, comprising: 7 optical systems. The cell unit according to claim 3,
A magnetic measurement apparatus comprising: a measurement unit that measures the intensity of the magnetic field in the second direction using the polarization plane rotation angle detected by the detection unit.

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