Optical pumping magnetometer and magnetic sensing method

Patent metadata

Field	Value
Publication number	US-9244137-B2
Application number	US-201414258817-A
Country	US
Kind code	B2
Filing date	Apr 22, 2014
Priority date	Apr 25, 2013
Publication date	Jan 26, 2016
Grant date	Jan 26, 2016

Abstract

An optical pumping magnetometer is provided that is capable of improving the response of the magnetometer with respect to a magnetic field that varies with a period shorter than the transverse relaxation time of electron spin of an alkali metal atom.

First claim

What is claimed is:

1. An optical pumping magnetometer for measuring a magnetic field with variation in Larmor frequency, the optical pumping magnetometer comprising:
a unit configured to irradiate a cell with circularly polarized pumping light, to produce the cell containing an alkali metal atoms and spin polarization of the alkali metal atoms in the cell;
a unit configured to emit linearly polarized probe light for reading spin of the alkali metal atoms;
a probe light detection system configured to detect a rotational displacement of a plane of polarization of the linearly polarized probe light;
a static magnetic field application coil configured to apply a static magnetic field to the alkali metal atoms;
an oscillating magnetic field application coil configured to apply an oscillating magnetic field for causing a rotational motion around the spin of the alkali metal atoms; and
a unit configured to detect information including a phase difference between an output signal from the probe light detection system and a driving current input into the oscillating magnetic field application coil,
wherein detuning as a difference between Larmor frequency determined from the static magnetic field and a frequency of the driving current input into the oscillating magnetic field application coil is configured to be set within a predetermined range with respect to a measured magnetic field by adjusting the static magnetic field or the oscillating magnetic field, so as to improve response of the optical pumping magnetometer.

2. The optical pumping magnetometer according to claim 1 , wherein the static magnetic field is adjusted by adjusting a value of a current input into the static magnetic field application coil.

3. The optical pumping magnetometer according to claim 1 , wherein the oscillating magnetic field is adjusted by adjusting a frequency of a current input into the oscillating magnetic field application coil.

4. The optical pumping magnetometer according to claim 1 , wherein the detuning is set within a range of ±20% with respect to the measured magnetic field.

5. The optical pumping magnetometer according to claim 1 , wherein the period of the varying measured magnetic field is shorter than transverse relaxation time of electron spin of an alkali metal atom.

6. The optical pumping magnetometer according to claim 5 , wherein the varying measured magnetic field is a weak magnetic field generated from a head of a subject.

7. An optical pumping magnetometer comprising more than one optical pumping magnetometer according to claim 1 , wherein respective detuning in the optical pumping magnetometers with respect to the measured magnetic field differs from each other within a predetermined range.

8. A magnetic sensing method for measuring a magnetic field with variation in Larmor frequency, the method comprising:
carrying out circularly polarized optical pumping for producing a cell containing an alkali metal atoms and spin polarization of the alkali metal atoms in the cell;
reading spin of the alkali metal atoms;
applying a static magnetic field to the alkali metal atoms;
applying an oscillating magnetic field for causing a rotational motion of the spin of the alkali metal atoms around the static magnetic field;
detecting information including a phase difference between an output signal obtained in the step of reading the spin of the alkali metal atoms and an input signal for generating the oscillating magnetic field in the step of applying oscillating magnetic field; and
setting detuning as a difference between Larmor frequency determined from the static magnetic field and a frequency of a driving current input into a coil to which the oscillating magnetic field is applied, within a predetermined range with respect to a measured magnetic field by adjusting the static magnetic field or the oscillating magnetic field, so as to improve response of the optical pumping magnetometer.

9. The magnetic sensing method according to claim 8 , wherein the static magnetic field is adjusted by adjusting a value of a current input into the static magnetic field application coil.

10. The magnetic sensing method according to claim 8 , wherein the oscillating magnetic field is adjusted by adjusting a frequency of a current input into the oscillating magnetic field application coil.

11. The magnetic sensing method according to claim 8 , wherein the detuning is set within a range of ±20% with respect to the measured magnetic field.

12. The magnetic sensing method according to claim 8 , wherein the measured magnetic field is a magnetic field varying with a period shorter than transverse relaxation time of electron spin of an alkali metal atom.

13. The magnetic sensing method according to claim 12 , wherein the magnetic field varying with the shorter period is a weak magnetic field generated from a head of a subject.

14. A non-transitory computer storage medium storing thereon a program configured to cause a computer to execute the magnetic sensing method according to claim 8 .

Assignees

• Canon Kk

Inventors

• Kobayashi Tetsuo
• Terao Akira

Classifications

• G01R33/26 Primary

  using optical pumping · CPC title