Optically pumped magnetometer

Abstract

This optically pumped magnetometer comprises: a laser unit including a laser element; a cell unit including a cell in which an alkali metal is sealed; a photodetector; a polarization unit which is disposed on an optical path of laser light from the laser element to the cell and which includes a polarization element that emits incident laser light as circularly polarized light; and a support member supporting the polarization unit. The polarization unit and the support member are shaped so that the polarization unit can rotate about the optical axis of the polarization element as a central axis with respect to the support member while the polarization unit is supported by the support member, and are fixed to each other while the polarization unit is supported by the support member.

Description

Optically Pumped Magnetic Sensor

[0001] The present disclosure relates to an optically pumped magnetic sensor.

[0002] An optically pumped magnetic sensor including a laser unit including a laser element that emits laser light, a cell unit including a cell filled with an alkali metal, and a photodetector that detects the laser light emitted from the laser element and passing through the cell is known (see, for example, Patent Document 1).

[0003] U.S. Patent No. 10,955,495

[0004] In the optically pumped magnetic sensor as described above, the detection sensitivity of the magnetic field may decrease due to some cause.

[0005] An object of the present disclosure is to provide an optically pumped magnetic sensor capable of suppressing a decrease in the detection sensitivity of a magnetic field.

[0006] The optically pumped magnetic sensor according to one aspect of the present disclosure is [1] "a laser unit including a laser element that emits laser light, a cell unit including a cell filled with an alkali metal, a photodetector that detects the laser light emitted from the laser element and passing through the cell, a polarization unit including a polarization element disposed on an optical path of the laser light from the laser element to the cell and emitting the incident laser light as circularly polarized light, and a support member that supports the polarization unit, wherein the polarization unit and the support member have a shape in which the polarization unit is rotatable about the optical axis of the polarization element with respect to the support member in a state where the polarization unit is supported by the support member, and are fixed to each other in a state where the polarization unit is supported by the support member", an optically pumped magnetic sensor.

[0007] In the above-described optically excited magnetic sensor, the polarization unit and support member are shaped such that the polarization element can rotate around the optical axis of the polarization element while the polarization unit is supported by the support member. This allows the rotation angle of the polarization element in the circumferential direction around the optical axis of the polarization element to be adjusted during the manufacturing of the optically excited magnetic sensor so that the laser light incident on the cell as circularly polarized light approaches ideal circular polarization. As a result, an optically excited magnetic sensor can be obtained in which the polarization unit and support member are fixed to each other while laser light approaching ideal circular polarization is incident on the cell. When ideal circular polarization is incident on the cell, alkali metal atoms in the cell are appropriately excited. Therefore, the above-described optically excited magnetic sensor can suppress a decrease in magnetic field detection sensitivity.

[0008] One aspect of the present disclosure is an optically excited magnetic sensor, which may also be [2] "the optically excited magnetic sensor according to [1], further comprising the laser unit, the cell unit, the photodetector, and a support that supports the support member." With this optically excited magnetic sensor, the support member and the support can be individually designed in a manner suitable for each other during the manufacturing of the optically excited magnetic sensor.

[0009] One aspect of the present disclosure is an optically excited magnetic sensor [3] "an optically excited magnetic sensor according to [1] or [2] above, further comprising a mirror that reflects the laser light and is arranged on the optical path of the laser light from the laser element to the cell, and the polarization unit is arranged on the optical path of the laser light from the mirror to the cell." With this optically excited magnetic sensor, since the mirror is arranged on the optical path of the laser light from the laser element to the cell, the laser unit, the cell unit and the photodetector can be arranged efficiently. In addition, since the polarization unit is arranged on the optical path of the laser light from the mirror to the cell, the optical path length from the laser light emitted as circularly polarized light from the polarizing element to the cell can be shortened, and the distortion of circular polarization due to an increase in the optical path length can be suppressed.

[0010] One aspect of the present disclosure is an optically excited magnetic sensor [4] "the optically excited magnetic sensor according to [3] above, further comprising a collimating lens arranged on the optical path of the laser light from the laser element to the mirror, and collimating the laser light." With this optically excited magnetic sensor, the spreading of the laser light emitted from the laser element is suppressed, so that the laser light with suppressed spreading can be appropriately directed to the photodetector via the polarizing element and the cell.

[0011] One aspect of the present disclosure is an optically excited magnetic sensor according to any one of [1] to [4] above, which is further comprising a coil that is arranged along the outer surface of the cell unit and generates a corrective magnetic field, wherein at least a portion of the coil is arranged between the polarization unit and the cell unit. The optically excited magnetic sensor makes it easy to adjust the rotation angle of the polarizing element in the polarization unit.

[0012] One aspect of the present disclosure is the photo-excited magnetic sensor according to any one of [1] to [5] above, wherein the polarizing unit further includes a holding member that holds the polarizing element, the holding member and the support member are engaged with each other and the holding member has a shape that allows the holding member to rotate with respect to the support member with respect to the optical axis of the polarizing element as the center line, and they are fixed to each other in an engaged state. With this photo-excited magnetic sensor, the holding member can be stably rotated with respect to the optical axis of the polarizing element as the center line during the manufacture of the photo-excited magnetic sensor, so that the rotation angle of the polarizing element can be easily and reliably adjusted in the circumferential direction with respect to the optical axis of the polarizing element as the center line.

[0013] One aspect of the present disclosure is the photo-excited magnetic sensor described in [6] above, which includes: [7] "the holding member having a first recess on which the polarizing element is disposed, and a first light-passing hole opening to the bottom surface of the first recess, the support member having a second recess on which the holding member is disposed, and a second light-passing hole opening to the bottom surface of the second recess, each of the first recess and the second recess opening to the side opposite to the cell unit, and the first light-passing hole and the second light-passing hole overlapping each other when viewed from a direction parallel to the optical axis of the polarizing element." With this photo-excited magnetic sensor, when the cell in the cell unit is heated by a heater, the polarizing element is less susceptible to heat, thus suppressing a decrease in the polarization characteristics of the polarizing element caused by heat.

[0014] According to this disclosure, it is possible to provide an optically excited magnetic sensor that can suppress the decrease in magnetic field detection sensitivity.

[0015] Figure 1 is a perspective view of an example of a photo-excited magnetic sensor. Figure 2 is another perspective view of the photo-excited magnetic sensor shown in Figure 1. Figure 3 is a cross-sectional view of the photo-excited magnetic sensor shown in Figure 1. Figure 4 is a cross-sectional view of the photo-excited magnetic sensor along the line IV-IV shown in Figure 3. Figure 5 is a perspective view of the polarizing unit and support member shown in Figure 1. Figure 6 is an exploded perspective view of the polarizing element, holding member and support member shown in Figure 5. Figure 7 is a plan view of the polarizing unit and support member of the first modified example. Figure 8 is an exploded perspective view of the polarizing element, holding member and support member shown in Figure 7. Figure 9 is a plan view of the polarizing unit and support member of the second modified example. Figure 10 is an exploded perspective view of the polarizing element, holding member and support member shown in Figure 9. Figure 11 is another exploded perspective view of the polarizing element, holding member and support member shown in Figure 9. Figure 12 is a plan view of the polarizing unit and support member of the third modified example. Figure 13 is an exploded perspective view of the polarizing element, holding member and support member shown in Figure 12. Figure 14 is a plan view of the polarization unit of the fourth modified example. Figure 15 is an exploded perspective view of the polarizing element and holding member shown in Figure 14.

[0016] An example of this disclosure will be described in detail below with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and redundant explanations are omitted. [Configuration of the optically excited magnetic sensor]

[0017] As shown in Figures 1 to 4, the optically excited magnetic sensor 1 comprises a laser unit 2, a lens unit 3, a mirror 4, a polarizing unit 5, a cell unit 6, a photodetector 7, a unit support member (support member) 8, and a support body 9. The laser unit 2 includes a laser element 21. The lens unit 3 includes a collimating lens 31. The polarizing unit 5 includes a polarizing element 51. The cell unit 6 includes a cell 61. The unit support member 8 supports the polarizing unit 5. The support body 9 supports the laser unit 2, the lens unit 3, the mirror 4, the cell unit 6, the photodetector 7, and the unit support member 8. The support body 9 supports the polarizing unit 5 via the unit support member 8.

[0018] In the optically excited magnetic sensor 1, the laser light L emitted from the laser element 21 of the laser unit 2 passes through the collimating lens 31 of the lens unit 3, is reflected by the mirror 4, and then sequentially passes through the polarizing element 51 of the polarizing unit 5 and the cell 61 of the cell unit 6 before entering the photodetector 7. In other words, in the optically excited magnetic sensor 1, the lens unit 3, mirror 4, and polarizing unit 5 are arranged in this order on the optical path P of the laser light L from the laser element 21 to the cell 61. The lens unit 3 is located on the optical path P1 from the laser element 21 to the mirror 4. The polarizing unit 5 is located on the optical path P2 from the mirror 4 to the cell 61.

[0019] Hereinafter, the direction parallel to the optical path P1 will be referred to as the Z-axis direction, the direction parallel to the optical path P2 which is perpendicular to the optical path P1 will be referred to as the X-axis direction, and the direction perpendicular to the optical paths P1 and P2 will be referred to as the Y-axis direction. The Z-axis direction is parallel to the optical axis A1 of the laser element 21. The X-axis direction is parallel to the optical axis A2 of the polarizing element 51. The optical path P1 is coaxial with the optical axis A1, and the optical path P2 is coaxial with the optical axis A2. In the optically excited magnetic sensor 1, laser light L is emitted from the laser element 21 to one side in the Z-axis direction, and the laser light L is reflected by the mirror 4 to one side in the X-axis direction.

[0020] The support 9 includes a first portion 91 and a second portion 92. The first portion 91 and the second portion 92 are integrally formed from a non-magnetic resin (for example, a heat-resistant resin such as PPS or PEEK as a base material and free of magnetic materials, or a flame-retardant resin such as ABS or POM as a base material and free of magnetic materials). In other words, the support 9 is made of resin. The first portion 91 has a rectangular plate shape, for example, with the Y-axis direction as the thickness direction. The second portion 92 has a rectangular plate shape, for example, with the Z-axis direction as the thickness direction. The first portion 91 is located on one side of the second portion 92 in the Z-axis direction. The second portion 92 protrudes on one side of the main surface 91a of the first portion 91 in the Y-axis direction. The main surface 91a is the main surface on one side in the Y-axis direction. A recess 93 is formed in the second portion 92. The recess 93 opens into the main surface 92a of the second portion 92. The main surface 92a is the main surface on the other side in the Z-axis direction. The recess 93 extends to one side of the second portion 92 in the Y-axis direction and the other side in the X-axis direction.

[0021] A recess 94 is formed in the support 9. The recess 94 opens into the main surface 91a of the first portion 91. The recess 94 includes a plurality of housing portions 95, 96, 97, 98, and 99. A lens unit 3 is arranged in housing portion 95. A mirror 4 is arranged in housing portion 96. A unit support member 8 supporting a polarization unit 5 is arranged in housing portion 97 so as to intersect perpendicularly with the optical path P2. A cell unit 6 is arranged in housing portion 98. A photodetector 7 is arranged in housing portion 99. The recess 94 is formed as a continuous structure so that the optical path of the laser light L from the laser element 21 to the photodetector 7 can be located within the recess 94. Housing portion 95 opens to the bottom surface of the recess 93 via the second portion 92. As a result, the support 9 defines a space S in which the portion Pa of the optical path P on the laser element 21 side is located.

[0022] The laser unit 2 includes a laser element 21, a laser support member 22, a rigid wiring board 23, a flexible wiring board 24, and a submount 25. The laser support member 22 is made of a non-magnetic resin (for example, a heat-resistant resin such as PPS or PEEK as the base material and free of magnetic materials, or a flame-retardant resin such as ABS or POM as the base material and free of magnetic materials). The laser support member 22 has a rectangular plate shape, for example, with the Z-axis direction as the thickness direction. The laser support member 22 has a first surface 22a which is a plane perpendicular to the optical axis A1 of the laser element 21. The first surface 22a is one end face in the Z-axis direction. A groove 26 is formed in the laser support member 22. The groove 26 opens to the first surface 22a. The groove 26 extends in the Y-axis direction, and one end 26a of the groove 26 reaches one region of the side surface of the laser support member 22 in the Y-axis direction.

[0023] One end 24a of the flexible wiring board 24 is electrically and physically connected to the rigid wiring board 23. The rigid wiring board 23 and one end 24a of the flexible wiring board 24 are fixed on the bottom surface of the groove 26. The flexible wiring board 24 extends outside the groove 26 via one end 26a of the groove 26. The submount 25 is fixed on the rigid wiring board 23 within the groove 26. The laser element 21 is fixed on the submount 25 within the groove 26. In this way, the laser element 21, the rigid wiring board 23, one end 24a of the flexible wiring board 24, and the submount 25 are housed within the groove 26. The laser element 21 is electrically connected to the rigid wiring board 23 via wiring (not shown) provided on the submount 25 and a wire (not shown) stretched between the wiring and the rigid wiring board 23. The laser element 21 emits linearly polarized laser light L to one side in the Z-axis direction. The laser element 21 is, for example, a vertical-cavity surface-emitting laser element. As described above, in the laser unit 2, the rigid wiring board 23 supports the laser element 21 while being electrically connected to it, and is fixed to the laser support member 22. In other words, in the laser unit 2, the laser element 21 is supported by the laser support member 22.

[0024] The laser support member 22 is positioned within a recess 93 of the support body 9 and is fixed to the second surface 9a, which is the bottom surface of the recess 93. The second surface 9a is perpendicular to the optical axis A1 of the laser element 21. In the optically excited magnetic sensor 1, the laser support member 22 and the support body 9 are fixed to each other by a plurality of bolts 27, with the first surface 22a of the laser support member 22 and the second surface 9a of the support body 9 in contact with each other. With the laser support member 22 and the support body 9 fixed to each other, the laser element 21 is exposed to the space S defined by the support body 9. In the optically excited magnetic sensor 1, during manufacturing, the position of the optical axis A1 of the laser element 21 is adjusted in a direction perpendicular to the optical axis A1 of the laser element 21 (i.e., "any direction perpendicular to the optical axis A1", including the X-axis and Y-axis directions), and with this position adjusted, the laser support member 22 and the support body 9 are fixed to each other by a plurality of bolts 27. Each bolt 27 is made of a non-magnetic resin (for example, a heat-resistant resin such as PPS or PEEK as the base material and free of magnetic materials, or a flame-retardant resin such as ABS or POM as the base material and free of magnetic materials).

[0025] The lens unit 3 includes a collimating lens 31 and a cylindrical holder 32. The collimating lens 31 is positioned inside the holder 32 and fixed to the inner surface of the holder 32 by adhesive. The collimating lens 31 collimates the laser light L emitted from the laser element 21. In the optically excited magnetic sensor 1, the holder 32 and the support 9 are fixed to each other by adhesive, with the outer surface 32a of the holder 32 and the inner surface 95a of the housing 95 in contact with each other. In the optically excited magnetic sensor 1, during manufacturing, the position of the collimating lens 31 is adjusted in the direction of extension of the optical path P1 of the laser light L (i.e., the Z-axis direction), and in that state, the holder 32 and the support 9 are fixed to each other by adhesive. The holder 32 is made of a non-magnetic resin (for example, a heat-resistant resin such as PPS or PEEK as the base material and not containing magnetic materials, or a flame-retardant resin such as ABS or POM as the base material and not containing magnetic materials).

[0026] The mirror 4 reflects the laser light L, which has been collimated by the collimating lens 31, to one side in the X-axis direction. In the optically excited magnetic sensor 1, the mirror 4 is fixed to the housing 96 with adhesive, with the mirror surface 4a of the mirror 4 forming a 45-degree angle with the Z-axis direction and the Y-axis direction, respectively, and parallel to the Y-axis direction.

[0027] The polarization unit 5 includes a polarizing element 51 and a holding member 52. The polarizing element 51 is held by the holding member 52 by being fixed to the holding member 52 with an adhesive. The polarizing element 51 emits the laser light L reflected by the mirror 4 as circularly polarized light to one side in the X-axis direction. As an example, the polarizing element 51 is a quarter-wave plate that converts the incident laser light L from linearly polarized to circularly polarized light and emits it. In the optically excited magnetic sensor 1, the holding member 52 and the unit support member 8 are engaged with each other and fixed to each other with an adhesive, and the unit support member 8 is fixed to the housing 97 with an adhesive. In the optically excited magnetic sensor 1, during manufacturing, the orientation of the polarization axis (i.e., the fast axis and the slow axis) of the polarizing element 51 is adjusted by rotating the holding member 52 with respect to the unit support member 8 with respect to the optical axis A2 of the polarizing element 51 as the center line, and in that state, the holding member 52 and the unit support member 8 are fixed to each other with an adhesive. Furthermore, the holding member 52 and the unit support member 8 are each made of a non-magnetic resin (for example, a heat-resistant resin such as PPS or PEEK as the base material and free of magnetic materials, or a flame-retardant resin such as ABS or POM as the base material and free of magnetic materials).

[0028] The unit support member 8 has a light-passing hole 8a, and the holding member 52 has a light-passing hole 52a (see Figure 4). The laser light L emitted from the polarizing element 51 passes through the light-passing hole 52a and the light-passing hole 8a in sequence.

[0029] The cell unit 6 includes a cell 61, a heater 62, a plurality of heat insulating members 63, and a cell case 64. The cell 61 is made of a material that is light-transmitting to laser light L (for example, glass, sapphire, etc.). Parts of the cell 61 that do not require light transmission to laser light L may be made of a material that is impermeable to laser light L (for example, silicon, etc.). The cell 61 is sealed with an alkali metal and an inert gas. As an example, the alkali metal is at least one of potassium, lithium, sodium, rubidium, and cesium, and the inert gas is at least one of helium, neon, argon, krypton, xenon, nitrogen, and hydrogen.

[0030] The heater 62 is positioned along the outer surface of the cell 61. In the photo-excited magnetic sensor 1, the heater 62 is positioned along the other surface of the outer surface of the cell 61 in the Y-axis direction. The heater 62 heats the cell 61 so that the alkali metals inside the cell 61 vaporize. As an example, the heater 62 is a sheet-like member containing a heating wire that generates heat when an electric current is applied. Multiple heat insulating members 63 cover the cell 61 and the heater 62. The cell case 64 houses the cell 61, the heater 62, and the multiple heat insulating members 63. In the photo-excited magnetic sensor 1, the cell case 64 includes a box-shaped main body 65 that opens on one side in the Y-axis direction, and a lid 66 that closes the opening of the main body 65. The main body 65 and the lid 66 are each made of a non-magnetic resin (for example, a heat-resistant resin such as PPS or PEEK as the base material and free of magnetic materials, or a flame-retardant resin such as ABS or POM as the base material and free of magnetic materials). In the photo-excited magnetic sensor 1, the main body 65 is fixed to the housing 98 with adhesive.

[0031] Multiple heat insulating members 63 have a pair of light-passing holes 63a and 63b facing each other in the X-axis direction, and the main body 65 has a pair of light-passing holes 65a and 65b facing each other in the X-axis direction (see Figure 4). The laser light L emitted from the polarizing element 51 passes sequentially through the light-passing hole 65a, the light-passing hole 63a, the cell 61, the light-passing hole 63b, and the light-passing hole 65b.

[0032] The photodetector 7 detects the laser light L emitted from the laser element 21 of the laser unit 2 and passing through the cell 61 of the cell unit 6. The photodetector 7 is configured to include, for example, a photodetector such as a photodiode. The photodetector 7 is fixed to the housing 99 with adhesive.

[0033] The photo-excited magnetic sensor 1 further comprises a coil 11, a control board 12, a connector 13, and a case 14. The coil 11 is arranged along the outer surface 6a of the cell unit 6. In the photo-excited magnetic sensor 1, the coil 11 is arranged along one surface in the Y-axis direction and both surfaces in the X-axis direction of the outer surface of the cell case 64. A portion of the coil 11 is arranged between the polarization unit 5 and the cell unit 6. The coil 11 generates a correction magnetic field, for example, so that the influence of magnetic fields other than the magnetic field being measured on the cell 61 approaches zero. As an example, the coil 11 is a sheet-like member that includes wiring that generates a magnetic field when energized.

[0034] The control board 12 is mounted on the main surface 92a of the second portion 92 of the support 9, spaced apart from the laser unit 2, so as to cover the recess 93 from the other side in the Z-axis direction. The other end 24b of the flexible wiring board 24 of the laser unit 2 is electrically and physically connected to the control board 12. In other words, the flexible wiring board 24 is stretched between the rigid wiring board 23 of the laser unit 2 and the control board 12. The control board 12 is electrically connected via wiring to the laser element 21 of the laser unit 2, as well as to the heater 62 and photodetector 7 of the cell unit 6. The connector 13 is mounted on the control board 12. External wiring for inputting and outputting electrical signals to and from the control board 12 is electrically and physically connected to the connector 13.

[0035] Case 14 houses the various parts of the photo-excited magnetic sensor 1. In the photo-excited magnetic sensor 1, case 14 includes a box-shaped main body 15 that opens to the other side in the Z-axis direction, and a lid 16 that closes the opening of the main body 15. Both the main body 15 and the lid 16 are made of a non-magnetic resin (for example, a heat-resistant resin such as PPS or PEEK as the base material and free of magnetic materials, or a flame-retardant resin such as ABS or POM as the base material and free of magnetic materials). In the photo-excited magnetic sensor 1, the control board 12 can be accessed by removing the lid 16 from the main body 15. Note that the case 14 is not shown in Figures 1 and 2.

[0036] The optically excited magnetic sensor 1, configured as described above, is used, for example, in the following way when measuring the magnetic field of a target object. First, with the external wiring electrically and physically connected to the connector 13, the optically excited magnetic sensor 1 is placed near the target object. Next, with the cell 61 heated by the heater 62, and alkali metal vaporized inside the cell 61, linearly polarized laser light L is emitted from the laser element 21. The linearly polarized laser light L emitted from the laser element 21 is collimated by the collimating lens 31 and reflected by the mirror 4. The laser light L reflected by the mirror 4 is converted into circularly polarized light by the polarizing element 51. The circularly polarized laser light L emitted from the polarizing element 51 passes through the cell 61 and is detected by the photodetector 7.

[0037] At this time, the alkali metal vaporized in the cell 61 is excited by irradiation with circularly polarized laser light L, resulting in a spin-polarized state. Here, the spin-polarized state of the alkali metal changes according to the magnetic field of the object being measured, and the intensity of the laser light L incident on the photodetector 7 changes according to the spin-polarized state of the alkali metal. Therefore, it becomes possible to measure the magnetic field of the object being measured based on the intensity of the laser light L detected by the photodetector 7.

[0038] Furthermore, the sensitivity of the photodetector 7 in detecting the laser light L decreases if the circular polarization of the laser light L emitted from the polarizing element 51 deviates from ideal circular polarization. In order to bring the laser light L incident on the cell 61 closer to ideal circular polarization, for example, the angle between the polarization direction of the linearly polarized laser light L incident on the polarizing element 51 and the polarization axis of the polarizing element 51 must be an ideal value (for example, 45°). In the photo-excited magnetic sensor 1, for example, if the angle between the polarization direction of the linearly polarized laser light L and the polarization axis of the polarizing element 51 deviates from the ideal value during the manufacturing of the photo-excited magnetic sensor 1, the rotation angle of the polarizing element 51 is adjusted with the optical axis A2 of the polarizing element 51 as the center line so that the angle approaches the ideal value, thereby suppressing the deviation of the laser light L incident on the cell 61 from ideal circular polarization. [Configuration of polarizing unit and support member]

[0039] As shown in Figures 5 and 6, the polarizing unit 5 and the unit support member 8 are shaped such that the polarizing element 51 can rotate around the optical axis A2 of the polarizing element 51 when the polarizing unit 5 is supported by the unit support member 8. In the optical excitation magnetic sensor 1, the holding member 52 and the unit support member 8 are shaped such that the holding member 52 can rotate around the optical axis A2 when they are engaged with each other. The holding member 52 includes a main body 521 and a plurality of protrusions 522. In the holding member 52, the plurality of protrusions 522 function as engaging parts that engage with the unit support member 8. The main body 521 has a circular shape centered on the optical axis A2 when viewed, for example, from the X-axis direction. The plurality of protrusions 522 project from the outer edge of the main body 521 toward the opposite side of the optical axis A2, which is the center of the main body 521. The plurality of protrusions 522 are provided at equal intervals along the outer edge of the main body 521. Gaps are formed between adjacent protrusions 522. In the example shown in Figure 5, the protrusions 522 are provided along the outer edge of the main body 521 at approximately 30° intervals.

[0040] A recess (second recess) 8b is formed in the unit support member 8. A retaining member 52 is positioned within the recess 8b. The recess 8b defines a cylindrical space for receiving the retaining member 52. When viewed from the X-axis direction, the recess 8b has a circular shape centered on the optical axis A2. In the unit support member 8, the recess 8b functions as an engaging portion that engages with the retaining member 52. The recess 8b has a bottom surface 8d that includes a planar portion extending in a direction perpendicular to the optical axis A2. The recess 8b has a circular side surface along the outer edge of the main body portion 521. The planar portion of the bottom surface 8d is in contact with the planar portion of the back surface 52d of the retaining member 52, which will be described later, and the tips of the multiple protrusions 522 are in contact with the side surface of the recess 8b. As a result, the retaining member 52 engages with the unit support member 8. In this state, the multiple protrusions 522 slide against the side surface of the recess 8b around the optical axis A2, causing the holding member 52 to rotate while maintaining a state in which the optical axis A2 and the polarizing element 51 intersect perpendicularly with respect to the optical axis A2 as the center line. In other words, the holding member 52 rotates while maintaining a state in which the polarizing element 51 extends in a direction perpendicular to the optical axis A2 (optical path P2).

[0041] A recess (first recess) 52b is formed in the holding member 52. The recess 52b defines a space for receiving the polarizing element 51, and the polarizing element 51 is placed in that space. In the example of Figure 6, the polarizing element 51 is rectangular parallelepiped, and the recess 52b defines a rectangular parallelepiped space for receiving the polarizing element 51 and has a bottom surface 52e including a planar portion extending in a direction perpendicular to the optical axis A2. The depth of the recess 52b is, for example, greater than the thickness of the polarizing element 51. However, the depth of the recess 52b should be such that the polarizing element 51 does not interfere with other members when the polarizing element 51 is placed in the recess 52b, and the depth of the recess 52b may be the same as the thickness of the polarizing element 51, or it may be shallower than the thickness of the polarizing element 51. If the depth of the recess 52b is the same as the thickness of the polarizing element 51, the surface of the polarizing element 51 on the side into which the laser light L is incident may be flush with the surface 52c of the holding member 52 when the polarizing element 51 is placed in the recess 52b. Also, if the depth of the recess 52b is shallower than the thickness of the polarizing element 51, the surface of the polarizing element 51 on the side into which the laser light L is incident may be located on the side of the surface 52c of the holding member 52 that is into which the laser light L is incident. The surface 52c is the surface of the holding member 52 opposite to the bottom surface 8d of the recess 8b, and the back surface 52d is the surface of the holding member 52 on the side of the bottom surface 8d of the recess 8b. Both the surface 52c and the back surface 52d have planar portions that extend in a direction perpendicular to the optical axis A2. When viewed from a direction parallel to the optical axis A2, the outer edge of the recess 52b may coincide with, for example, the outer edge of the polarizing element 51, or it may be larger than the outer edge of the polarizing element 51. An injection port for injecting adhesive to fix the retaining member 52 and the polarizing element 51 may be provided on a part of the side surface of the recess 8b. In the example of Figure 6, when viewed from a direction parallel to the optical axis A2, multiple injection ports are provided at the corners of the recess 52b.

[0042] The light-passing hole 52a (first light-passing hole) opens into the bottom surface 52e of the recess 52b. The light-passing hole 52a communicates with the recess 52b in a direction parallel to the optical axis A2. The center of the light-passing hole 52a and the center of the recess 52b coincide on the optical axis A2. The recess 52b and the light-passing hole 52a penetrate the holding member 52 in a direction parallel to the optical axis A2. When viewed from a direction parallel to the optical axis A2, the outer edge of the light-passing hole 52a is smaller than the outer edge of the recess 52b and the outer edge of the polarizing element 51. This prevents the polarizing element 51 from slipping through the holding member 52 when it is placed in the recess 52b. The recess 52b opens on the opposite side of the cell unit 6 from the light-passing hole 52a in a direction parallel to the optical axis A2. As a result, when the polarizing element 51 is positioned in the recess 52b, the polarizing element 51 is located on the opposite side of the light passage hole 52a from the cell unit 6.

[0043] The light-passing hole (second light-passing hole) 8a opens into the bottom surface 8d of the recess 8b. The light-passing hole 8a communicates with the recess 8b in a direction parallel to the optical axis A2. The center of the light-passing hole 8a and the center of the recess 8b coincide on the optical axis A2. The recess 8b and the light-passing hole 8a penetrate the unit support member 8 in a direction parallel to the optical axis A2. When viewed from a direction parallel to the optical axis A2, the outer edge of the light-passing hole 8a is smaller than the outer edge of the recess 8b. This prevents the retaining member 52 from slipping through the unit support member 8 when the retaining member 52 is positioned in the recess 8b and the multiple protrusions 522 are in contact with the side surface of the recess 8b. When viewed from a direction parallel to the optical axis A2, the outer edge of the light-passing hole 8a may coincide with the outer edge of the light-passing hole 52a. With the holding member 52 positioned in the recess 8b, the light-passing hole 52a communicates with the light-passing hole 8a in a direction parallel to the optical axis A2. The light-passing holes 52a and 8a overlap when viewed from a direction parallel to the optical axis A2 of the polarizing element 51. In the example of Figure 5, the outer edges of the light-passing hole 52a and the outer edges of the light-passing hole 8a coincide when viewed from a direction parallel to the optical axis A2 of the polarizing element 51.

[0044] The concave portion 8b opens on the side opposite to the cell unit 6 with respect to the light passage hole 8a in the direction parallel to the optical axis A2. That is, in the state where the holding member 52 is disposed in the concave portion 8b, the holding member 52 is positioned on the side opposite to the cell unit 6 with respect to the light passage hole 8a. The laser beam L passes through the polarization element 51, passes through the light passage hole 52a and the light passage hole 8a, and then enters the cell unit 6.

[0045] A notch 8c is formed in the unit support member 8. As shown in FIG. 5, the notch 8c is formed so as to notch a part of the unit support member 8 from the concave portion 8b to one end surface of the unit support member 8 in the Y-axis direction. The notch 8c forms a groove connecting the concave portion 8b and one end surface of the unit support member 8 in the Y-axis direction. The width (length in the Z-axis direction) of the notch 8c is smaller than the diameter of the concave portion 8b. The width of the notch 8c may be a length including at least two protruding portions 522. As shown in FIG. 1 and the like, the height (length in the Y-axis direction) of the unit support member 8 is higher than the depth of the housing portion 97. Therefore, when the unit support member 8 supports the polarization unit 5 and is housed in the housing portion 97, the notch 8c and a part of the polarization unit 5 are exposed from the housing portion 97. The state where a part of the polarization unit 5 is exposed means, for example, a state where at least a part of a plurality of protruding portions 522 is exposed. The polarization unit 5 may be rotated with respect to the unit support member 8 around the optical axis A2 due to the gap between adjacent protruding portions in a part of the plurality of exposed protruding portions 522. In this way, the direction of the polarization axis of the polarization element 51 is adjusted, and in that state, the holding member 52 and the unit support member 8 may be fixed to each other by an adhesive. [Operation and Effect]

[0046] In the above-described photoexcitation magnetic sensor 1, the polarization unit 5 and the unit support member 8 are shaped such that the polarization element 51 can rotate about the optical axis A2 of the polarization element 51 as the center line while the polarization unit 5 is supported by the unit support member 8. As a result, during the manufacture of the photoexcitation magnetic sensor 1, the rotation angle of the polarization element 51 can be adjusted in the circumferential direction with the optical axis A2 of the polarization element 51 as the center line so that the laser light L incident on the cell 61 as circularly polarized light approaches an ideal circularly polarized light. As a result, a photoexcitation magnetic sensor 1 can be obtained in which the polarization unit 5 and the unit support member 8 are fixed to each other with the laser light L that has approached an ideal circularly polarized light incident on the cell 61. When an ideal circularly polarized light is incident on the cell 61, the alkali metal atoms in the cell 61 are appropriately excited. Therefore, according to the photoexcitation magnetic sensor 1, a decrease in the detection sensitivity of the magnetic field can be suppressed.

[0047] The photoexcitation magnetic sensor 1 further includes a support 9 that supports the laser unit 2, the cell unit 6, the photodetector 7, and the unit support member 8. According to this, during the manufacture of the photoexcitation magnetic sensor 1, the unit support member 8 and the support 9 can be individually designed in a state suitable for each.

[0048] The photoexcitation magnetic sensor 1 further includes a mirror 4 disposed on the optical path P of the laser light L from the laser element 21 to the cell 61 for reflecting the laser light L, and the polarization unit 5 is disposed on the optical path P of the laser light L from the mirror 4 to the cell 61. According to this, since the mirror 4 is disposed on the optical path P of the laser light L from the laser element 21 to the cell 61, the laser unit 2, the cell unit 6, and the photodetector 7 can be efficiently arranged. Further, since the polarization unit 5 is disposed on the optical path P of the laser light L from the mirror 4 to the cell 61, the optical path length until the laser light L emitted as circularly polarized light from the polarization element 51 is incident on the cell 61 can be shortened, and the breakdown of the circularly polarized light due to an increase in the optical path length can be suppressed.

[0049] The optically excited magnetic sensor 1 is positioned on the optical path P of the laser beam L from the laser element 21 to the mirror 4, and further includes a collimating lens 31 that collimates the laser beam L. This suppresses the spreading of the laser beam L emitted from the laser element 21, allowing the laser beam L, with its spread suppressed, to be properly directed to the photodetector 7 via the polarizing element 51 and the cell 61.

[0050] The photo-excited magnetic sensor 1 is positioned along the outer surface of the cell unit 6 and further includes a coil 11 that generates a corrective magnetic field, with a portion of the coil 11 positioned between the polarization unit 5 and the cell unit 6. This allows for easy adjustment of the rotation angle of the polarizing element 51 in the polarization unit 5. Furthermore, compared to the case where the coil 11 is positioned to surround both the cell unit 6 and the polarization unit 5, the corrective magnetic field can be applied more directly to the cell 61.

[0051] The polarizing unit 5 further includes a holding member 52 that holds the polarizing element 51. The holding member 52 and the unit support member 8 are engaged with each other, and the holding member 52 is rotatable relative to the unit support member 8 with respect to the optical axis A2 of the polarizing element 51 as its centerline. They are fixed to each other while engaged. This allows the holding member 52 to be stably rotated with respect to the optical axis A2 of the polarizing element 51 as its centerline during the manufacturing of the optical excitation magnetic sensor 1. As a result, the rotation angle of the polarizing element 51 in the circumferential direction with respect to the optical axis A2 of the polarizing element 51 as its centerline can be easily and reliably adjusted.

[0052] The holding member 52 has a recess 52b in which the polarizing element 51 is arranged, and a light-passing hole 52a opening in the bottom surface 52e of the recess 52b. The unit support member 8 has a recess 8b in which the holding member 52 is arranged, and a light-passing hole 8a opening in the bottom surface 8d of the recess 8b. Each of the recesses 52b and 8b opens on the side opposite to the cell unit 6, and the light-passing holes 52a and 8a overlap each other when viewed from a direction parallel to the optical axis A2 of the polarizing element 51. With this configuration, when the cell 61 in the cell unit 6 is heated by the heater 62, the heat is less likely to be transferred to the polarizing element 51, thereby suppressing the deterioration of the polarization characteristics of the polarizing element 51 caused by heat. [First Modified Example]

[0053] Referring to Figures 7 and 8, the first modified polarization unit 5A and unit support member 8A will be described. As shown in Figure 7(b) and Figure 8, the holding member 52A of the polarization unit 5A differs from the polarization unit 5 in that it further includes an annular projection 523 that engages with the unit support member 8A. The projection 523 has a predetermined width in the radial direction of the main body 521 and is erected in the thickness direction of the holding member 52A (parallel to the optical axis A2). The projection 523 is formed around the light passage hole 52a. When viewed from a direction parallel to the optical axis A2, the inner edge of the projection 523 coincides with the outer edge of the light passage hole 52a, and the outer edge of the projection 523 is smaller than the outer edge of the main body 521. In the polarization unit 5A, the projection 523 functions as an engaging portion that engages with the unit support member 8A.

[0054] As shown in Figure 7(a), the unit support member 8A differs from the unit support member 8 of the embodiment in the shape of the recess 8b. In the example of Figure 7(a), when viewed from the X-axis direction, the recess 8b is integrated with the notch 8c to form a U-shape. The width of the recess 8b is, for example, the same as the width of the notch 8c. The width of the recess 8b and the width of the notch 8c may be constant from the recess 8b through the notch 8c to one end face in the Y-axis direction of the unit support member 8A.

[0055] In the unit support member 8A, the light-passing hole 8a functions as an engaging portion that engages with the polarizing unit 5A. The protrusion 523 is positioned in the light-passing hole 8a, as shown in Figure 7. In this position, the outer surface of the protrusion 523 is in contact with the side surface of the light-passing hole 8a. This allows the holding member 52A to engage with the unit support member 8A. Note that the tips of the multiple protrusions 522 do not necessarily have to be in contact with the side surface of the recess 8b. With the outer surface of the protrusion 523 in contact with the side surface of the light-passing hole 8a, the polarizing unit 5A becomes rotatable relative to the unit support member 8A with respect to the optical axis A2. For example, when the unit support member 8A is housed in the housing portion 97 with the polarizing unit 5A supported, the gaps between adjacent protrusions in some of the exposed multiple protrusions 522 may cause the polarizing unit 5A to rotate relative to the support member 7A with respect to the optical axis A2. In this process, the annular protrusion 523 slides around the optical axis A2 relative to the side surface of the circular light-passing hole 8a. In this way, the orientation of the polarization axis of the polarizing element 51 is adjusted, and in this state, the holding member 52A and the unit support member 8A may be fixed to each other with adhesive. The photo-excited magnetic sensor 1 equipped with the polarization unit 5A and unit support member 8A of the first modified example can also suppress the decrease in magnetic field detection sensitivity. [Second Modified Example]

[0056] Referring to Figures 9 to 11, a second modified example of the polarizing unit 5B and unit support member 8B will be described. As shown in Figure 11, the polarizing unit 5B differs from the polarizing unit 5 in that the holding member 52B includes an annular groove 52f that engages with the unit support member 8B. The polarizing unit 5B also differs from the polarizing unit 5 in the shape of the multiple protrusions 522 on the holding member 52B. The groove 52f has a predetermined width in the radial direction of the main body 521. The groove 52f is also recessed from the back surface 52d in a direction parallel to the optical axis A2. The groove 52f is formed around the light passage hole 52a. When viewed from a direction parallel to the optical axis A2, the inner edge of the groove 52f is larger than the outer edge of the light passage hole 52a. In the polarizing unit 5B, the groove 52f functions as an engaging portion that engages with the unit support member 8B. In the example shown in Figure 11, the protrusions 522 are provided at 90° intervals along the outer edge of the main body 521. At both ends of the protrusions 522, notches 524 are formed where the retaining member 52B is cut out from its outer edge toward the optical axis A2. These notches 524 serve as a starting point for, for example, the rotation of the polarizing unit 5B relative to the unit support member 8B.

[0057] The unit support member 8B differs from the unit support member 8A of the first modification in that, as shown in Figure 10, it includes an annular projection 81 that engages with the groove 52f. The projection 81 has a predetermined width that matches the width of the groove 52f and is erected in a direction parallel to the optical axis A2. The height of the projection 81 should be such that it does not hinder the polarization unit 5B from rotating relative to the unit support member 8B, and the height of the projection 81 may match the depth of the groove 52f or may be different from the depth of the groove 52f. The projection 81 is formed around the light-passing hole 8a. When viewed from a direction parallel to the optical axis A2, the size of the inner edge of the projection 81 should be such that it does not hinder the polarization unit 5B from rotating relative to the unit support member 8B, and the size of the inner edge of the projection 81 may be larger than the size of the outer edge of the light-passing hole 8a or may match the size of the outer edge of the light-passing hole 8a.

[0058] In the unit support member 8B, the protrusion 81 functions as an engaging portion that engages with the polarizing unit 5B. As shown in Figure 11, the protrusion 81 is positioned in the groove 52f. In this position, the outer surface of the protrusion 81 is in contact with the outer surface of the groove 52f, and the inner surface of the protrusion 81 is in contact with the inner surface of the groove 52f. This allows the holding member 52B to engage with the unit support member 8B. Note that the tips of the multiple projections 522 do not need to be in contact with the side surface of the recess 8b. With the protrusion 81 in contact with the groove 52f, the polarizing unit 5B becomes rotatable relative to the unit support member 8B with respect to the optical axis A2. For example, when the unit support member 8B is housed in the housing 97 with the polarizing unit 5B supported, the notches 524 formed at both ends of the exposed projections 522 may act as a trigger, causing the polarizing unit 5B to rotate relative to the unit support member 8B with respect to the optical axis A2. In this process, the annular protrusion 81 slides relative to the annular groove 52f around the optical axis A2. In this way, the orientation of the polarization axis of the polarizing element 51 is adjusted, and in this state, the holding member 52B and the unit support member 8B may be fixed to each other with adhesive. The optical excitation magnetic sensor 1 equipped with the polarization unit 5B and unit support member 8B of the second modified example can also suppress the decrease in magnetic field detection sensitivity. [Third Modified Example]

[0059] Referring to Figures 12 and 13, a third modified example of the polarizing unit 5C and unit support member 8C will be described. As shown in Figures 12(a) and 12(b), the holding member 52C of the polarizing unit 5C differs from the polarizing unit 5 in that it does not include a plurality of protrusions 522, includes a plurality of projections 525 on the surface 52c side, includes a plurality of projections 526 on the back surface 52d side, and has a polygonal shape when viewed from the X-axis direction. It also differs from the polarizing unit 5 in that the polarizing element 51 is cylindrical, and the recess 52b defines a cylindrical space for receiving the polarizing element 51. Because the holding member 52C has a polygonal shape, it further has a plurality of side surfaces 52g. The plurality of projections 525 are erected from the surface 52c in the X-axis direction. In the example shown in Figure 12(a), the multiple protrusions 525 are formed along the outer edge of the holding member 52C, corresponding to each side surface 52g. The number of side surfaces 52g and the number of protrusions 525 may be the same. The multiple protrusions 525 are, for example, the parts that initiate rotation of the polarizing unit 5C relative to the unit support member 8C.

[0060] As shown in Figures 12(b) and 13, the multiple protrusions 526 are formed around the light-passing hole 52a and are arranged along the outer circumference of the light-passing hole 52a. The multiple protrusions 526 are erected from the back surface 52d in the X-axis direction (parallel to the optical axis A2). The number of protrusions 526 may be the same as or different from the number of protrusions 525. In the examples of Figures 12(b) and 13, three protrusions 526 are provided along the outer circumference of the light-passing hole 52a at 120° intervals. In the polarizing unit 5C, the multiple protrusions 526 function as engaging parts that engage with the unit support member 8C.

[0061] The unit support member 8C differs from the unit support member 8A of the first modification in that, as shown in Figures 12(a) and 12(b), it includes a pair of legs 82 on the other end face in the Y-axis direction of the unit support member 8. The pair of legs 82 are formed on the end face opposite to the notch 8c with respect to the polarizing unit 5C. The pair of legs 82 function to stably support the unit support member 8C when it is placed in the housing 97, for example.

[0062] In the unit support member 8C, similar to the unit support member 8A, the light-passing hole 8a functions as an engaging portion that engages with the polarizing unit 5C. As shown in Figures 12(a) and 12(b), the multiple protrusions 526 are positioned in the light-passing hole 8a. In this position, the multiple protrusions 526 are in contact with the side surface of the light-passing hole 8a. This causes the holding member 52C to engage with the unit support member 8C. Note that the multiple side surfaces 52g do not necessarily have to be in contact with the side surface of the recess 8b. With the multiple protrusions 526 in contact with the side surface of the light-passing hole 8a, the polarizing unit 5C becomes rotatable relative to the unit support member 8C with the optical axis A2 as its centerline. For example, when the unit support member 8C is positioned in the housing 97 supporting the polarizing unit 5C, the exposed multiple protrusions 525 may act as a trigger, causing the polarizing unit 5C to rotate relative to the unit support member 8C with the optical axis A2 as its centerline. In this process, the multiple protrusions 526 slide around the optical axis A2 relative to the side surface of the circular light-passing hole 8a. In this way, the orientation of the polarization axis of the polarizing element 51 is adjusted, and in this state, the holding member 52C and the unit support member 8C may be fixed to each other with adhesive. The optical excitation magnetic sensor 1 equipped with the polarization unit 5C and unit support member 8C of the third modified example can also suppress the decrease in magnetic field detection sensitivity. [Fourth Modified Example]

[0063] The polarizing unit does not necessarily have to be placed in the housing 97 while being supported by a support member. For example, the polarizing unit may be placed directly in the housing 97 without a support member. In this case, the housing 97 may function as a support member.

[0064] Referring to Figures 14 and 15, a fourth modified example of the polarizing unit 5D will be described. The polarizing unit 5D differs from the polarizing unit 5 in that it does not include a plurality of protrusions 522, includes a plurality of through holes 52h that penetrate the surface 52c and back surface 52d of the holding member 52D, and the holding member 52D has a polygonal shape when viewed from the X-axis direction. It also differs from the polarizing unit 5 in that the polarizing element 51 is cylindrical, and the recess 5b defines a cylindrical space for receiving the polarizing element 51. Because the holding member 52D has a polygonal shape, it further has a plurality of side surfaces 52g. In the example of Figures 14 and 15, the plurality of through holes 52h are formed along the outer edge of the holding member 52D so as to correspond to each side surface 52g. The number of side surfaces 52g and the number of through holes 52h may be the same. The plurality of through holes 52h are, for example, parts that serve as a starting point when the polarizing unit 5D is rotated relative to the housing 97. Alternatively, instead of multiple through holes 52h, multiple recesses may be formed along the outer edge of the retaining member 52D. These multiple recesses are, for example, non-through holes formed in the X-axis direction from the surface 52c. These multiple recesses may also serve as triggers for the rotation of the polarization unit 5D.

[0065] In the polarization unit 5D, multiple sides 52g function as engaging parts that engage with the housing 97. When the polarization unit 5D is positioned in the housing 97, at least a portion of the multiple sides 52g are in contact with the inner wall of the housing 97. Also, at least a portion of the multiple through holes 52h are exposed from the housing 97. For example, when the polarization unit 5D is positioned in the housing 97, the exposed portion of the multiple through holes 52h may cause the polarization unit 5D to rotate relative to the housing 97 with the optical axis A2 as the centerline. In this case, the multiple sides 52g slide relative to the housing 97 around the optical axis A2. In this case, at least a portion of the multiple sides 52g are in contact with the inner wall of the housing 97, which prevents the polarization unit 5D from rotating more than necessary. In this way, the orientation of the polarization axis of the polarizing element 51 is adjusted, and in this state, the holding member 52D and the housing 97 may be fixed to each other with an adhesive. The optical excitation magnetic sensor 1 equipped with the polarization unit 5D of the fourth modified example can also suppress the decrease in magnetic field detection sensitivity. [Variations]

[0066] This disclosure is not limited to the examples described above. In the examples described above, the polarizing element 51 may be directly supported by a support member or housing 97 without being held by a holding member. For example, consider a case where the polarizing element 51 is supported by a unit support member 8 without being held by a holding member 52. In this case, the polarizing element 51 and the unit support member 8 are engaged with each other and have a shape that allows the polarizing element 51 to rotate around the optical axis A2 of the polarizing element 51 as the center line. For example, the polarizing element 51 may include a main body and a plurality of protrusions. The plurality of protrusions may function as engaging parts that engage with the unit support member 8. The polarizing element 51 may also have a shape other than a rectangular parallelepiped or cylindrical shape. For example, the polarizing element 51 may have a triangular prism shape. The recess 52b may define a space that matches the shape of the polarizing element 51. In the examples described above, a part of the coil 11 is arranged between the polarizing unit 5 and the cell unit 6, but it is sufficient that at least a part of the coil 11 is arranged between the polarizing unit 5 and the cell unit 6. Furthermore, the light-passing holes 52a and 8a only need to overlap when viewed from a direction parallel to the optical axis A2 of the polarizing element 51, and the outer edges of the light-passing holes 52a and 8a do not need to coincide when viewed from a direction parallel to the optical axis A2 of the polarizing element 51.

[0067] Any combination is possible in each of the above examples. In the first modified example, the holding member 52A may include a plurality of through holes that penetrate the surface 52c and back surface 52d of the holding member 52A, instead of the plurality of protrusions 522. Then, some of the plurality of through holes may act as a trigger to rotate the polarization unit 5A with respect to the unit support member 8A with respect to the optical axis A2 as the center line. Alternatively, the unit support members 8, 8A, and 8B may include a pair of legs 82.

[0068] 1...Optical excitation magnetic sensor, 2...Laser unit, 4...Mirror, 5, 5A, 5B, 5C, 5D...Polarization unit, 6...Cell unit, 6a...Outer surface, 7...Photodetector, 8, 8A, 8B, 8C...Unit support member (support member), 8a...Optical passage hole (second optical passage hole), 8b...Recess (second recess), 9...Support, 11...Coil, 21...Laser element, 31...Collimating lens, 51...Polarization element, 52, 52A, 52B, 52C, 52D...Holding member, 52a...Optical passage hole (first optical passage hole), 52b...Recess (first recess), 61...Cell, 62...Heater, A2...Optical axis, L...Laser light.

Claims

1. An optically excited magnetic sensor comprising: a laser unit including a laser element that emits laser light; a cell unit including a cell containing an alkali metal; a photodetector that detects the laser light emitted from the laser element and passing through the cell; a polarizing unit including a polarizing element arranged on the optical path of the laser light from the laser element to the cell and emitting the incident laser light as circularly polarized light; and a support member that supports the polarizing unit, wherein the polarizing unit and the support member are shaped such that the polarizing unit can rotate with respect to the support member with respect to the optical axis of the polarizing element as the center line when the polarizing unit is supported by the support member, and the polarizing unit is fixed to each other when the polarizing unit is supported by the support member.

2. The photo-excited magnetic sensor according to claim 1, further comprising a support that supports the laser unit, the cell unit, the photodetector, and the support member.

3. The optically excited magnetic sensor according to claim 1 or 2, further comprising a mirror disposed on the optical path of the laser light from the laser element to the cell, the polarization unit being disposed on the optical path of the laser light from the mirror to the cell.

4. The optically excited magnetic sensor according to claim 3, further comprising a collimating lens disposed on the optical path of the laser light from the laser element to the mirror, for collimating the laser light.

5. The photo-excited magnetic sensor according to claim 1 or 2, further comprising a coil disposed along the outer surface of the cell unit for generating a corrective magnetic field, wherein at least a portion of the coil is disposed between the polarization unit and the cell unit.

6. The optically excited magnetic sensor according to claim 1 or 2, wherein the polarizing unit further includes a holding member that holds the polarizing element, and the holding member and the support member are engaged with each other and the holding member has a shape that allows the holding member to rotate with respect to the support member about the optical axis of the polarizing element as the center line, and are fixed to each other in an engaged state.

7. The optically excited magnetic sensor according to claim 6, wherein the holding member has a first recess in which the polarizing element is arranged and a first light-passing hole opening to the bottom surface of the first recess, the support member has a second recess in which the holding member is arranged and a second light-passing hole opening to the bottom surface of the second recess, each of the first recess and the second recess opens to the side opposite to the cell unit, and the first light-passing hole and the second light-passing hole overlap each other when viewed from a direction parallel to the optical axis of the polarizing element.

Images