Optically pumped magnetometer having reduced footprint

Patent metadata

Field	Value
Publication number	US-11619689-B2
Application number	US-202117346322-A
Country	US
Kind code	B2
Filing date	Jun 14, 2021
Priority date	Jun 16, 2020
Publication date	Apr 4, 2023
Grant date	Apr 4, 2023

Abstract

An optically pumped magnetometer 1 includes: a cell 2 ; a pump laser 7 that emits pump light; one or more pump light mirrors that cause the pump light guided in a first direction; a probe laser 8 that emits probe light; a splitting unit 12 that splits the probe light into multiple light components; one or more probe light mirrors that cause each of the probe light components guided in a second direction, which is a direction perpendicular to the first direction; a detection unit that detects each of the probe light components perpendicular to the pump light inside the cell 2 ; and a derivation unit that derives a magnetic field corresponding to a region where each of the probe light components and the pump light are perpendicular to each other based on a detection result of the detection unit.

First claim

What is claimed is:

1. An optically pumped magnetometer comprising:
a cell arranged along a measurement target and filled with vapor of an alkali metal;
a pump laser configured to emit pump light for exciting an atom of the alkali metal;
one or more pump light mirrors configured to reflect the pump light emitted from the pump laser and cause the pump light guided in a first direction along the measurement target to be incident on the cell;
a probe laser configured to emit probe light for detecting a change in a polarization angle caused by a magnetic field in an excited state of the alkali metal atom;
a splitting unit comprising beam splitters configured to split the probe light into multiple light components;
probe light mirrors configured to reflect the probe light components obtained as a result of the splitting by the splitting unit, and cause each of the probe light components guided in a second direction along the measurement target and perpendicular to the first direction, to be incident on the cell;
a detection unit configured to detect each of the probe light components perpendicular to the pump light inside the cell; and
a derivation unit configured to derive a change in the polarization angle corresponding to each of the probe light components based on a detection result of the detection unit and derive a magnetic field relevant to a measurement location of the measurement target corresponding to a region where each of the probe light components and the pump light are perpendicular to each other, from the change in the polarization angle corresponding to each of the probe light components,
wherein the splitting unit is arranged on a side opposite to the measurement target with the cell interposed therebetween,
the probe laser is arranged to emit the probe light so that the probe light is guided in a direction opposite to the first direction and is incident on the splitting unit,
the splitting unit outputs each of the split probe light components in a direction perpendicular to the first direction and along the measurement target, and
one of the two probe light mirrors reflects each of the probe light components obtained as a result of the splitting by the splitting unit, in a direction toward the measurement target, and the other one of the two probe light mirrors further reflects each of the probe light components reflected by the one probe light mirror in the second direction and causes each of the probe light components to be incident on the cell.

2. The optically pumped magnetometer according to claim 1 ,
wherein the probe laser emits probe light whose height is smaller than its width in cross-section.

3. The optically pumped magnetometer according to claim 1 ,
wherein the alkali metal is potassium and rubidium,
the pump laser excites an atom of the rubidium for spin polarization to be transferred to that of the potassium, and
the probe laser emits probe light for detecting a change in a polarization angle caused by a magnetic field in an excited state of the potassium atom.

4. The optically pumped magnetometer according to claim 1 ,
wherein the pump light and each of the probe light components are perpendicular to each other near a magnetic field incidence surface of the cell on which a magnetic field generated from the measurement target is incident.

5. The optically pumped magnetometer according to claim 1 ,
wherein at least one of the pump light mirrors and at least one of the probe light mirrors are bonded to the cell with an adhesive.

6. The optically pumped magnetometer according to claim 1 ,
wherein the pump laser emits the pump light in the same direction as an emission direction of the probe light from the probe laser.

7. The optically pumped magnetometer according to claim 1 ,
wherein the pump laser emits the pump light in a direction perpendicular to an emission direction of the probe light from the probe laser.

8. An optically pumped magnetometer, comprising:
a cell arranged along a measurement target and filled with vapor of an alkali metal;
a pump laser configured to emit pump light for exciting an atom of the alkali metal;
one or more pump light mirrors configured to reflect the pump light emitted from the pump laser and cause the pump light guided in a first direction along the measurement target to be incident on the cell;
a probe laser configured to emit probe light for detecting a change in a polarization angle caused by a magnetic field in an excited state of the alkali metal atom;
a splitting unit comprising beam splitters configured to split the probe light into multiple light components;
probe light mirrors configured to reflect the probe light components obtained as a result of the splitting by the splitting unit, and cause each of the probe light components guided in a second direction along the measurement target and perpendicular to the first direction, to be incident on the cell;
a detection unit configured to detect each of the probe light components perpendicular to the pump light inside the cell;
a derivation unit configured to derive a change in the polarization angle corresponding to each of the probe light components based on a detection result of the detection unit and derive a magnetic field relevant to a measurement location of the measurement target corresponding to a region where each of the probe light components and the pump light are perpendicular to each other, from the change in the polarization angle corresponding to each of the probe light components;
a first member for reference being filled with the alkali metal vapor and arranged on a side opposite to the measurement target with the cell interposed therebetween, the first member for reference being configured such that a first light for reference guided in the first direction is incident thereon in order to excite the alkali metal atom of the first member for reference, and multiple second light components for reference guided in the second direction are incident thereon in order to detect a change in the polarization angle caused by a magnetic field in the excited state of the alkali metal atom of the first member for reference; and
a second member for reference configured to detect the multiple second light components for reference perpendicular to the first light for reference inside the first member for reference, outside the first member for reference,
wherein each region where each of the probe light components and the pump light are perpendicular to each other in the cell overlaps a respective region where any of the second light components for reference and the first light for reference are perpendicular to each other in the first member for reference, in a direction perpendicular to the measurement target,
when deriving a change in the polarization angle corresponding to each of the probe light components detected by the detection unit, the derivation unit performs noise removal processing in consideration of a detection result of the detection unit with respect to each of the probe light components and a detection result of the second member for reference with respect to the multiple second light components for reference whose region overlaps each of the probe light components in the direction perpendicular to the measurement target, and
the optically pumped magnetometer is configured as a first-order differential axial gradiometer.

9. The optically pumped magnetometer according to claim 8 ,
wherein the probe laser emits probe light whose height is smaller than its width in cross-section.

10. The optically pumped magnetometer according to claim 8 ,
wherein the alkali metal is potassium and rubidium,
the pump laser excites an atom of the rubidium fo

Assignees

• Hamamatsu Photonics Kk
• Univ Kyoto

Inventors

• Saito Akinori
• Moriya Takahiro
• Oida Takenori
• Suyama Motohiro
• Kobayashi Tetsuo

Classifications

• G01R33/26 Primary

  using optical pumping · CPC title

• G01R33/032 Primary

  using magneto-optic devices, e.g. Faraday {or Cotton-Mouton effect} · CPC title

• A61B5/245

  specially adapted for magnetoencephalographic [MEG] signals · CPC title

• G01R33/0094

  Sensor arrays · CPC title