Magnetic field measurement method and magnetic field measurement device for measuring and offsetting original magnetic field
A light source unit irradiates a gas cell disposed in a measurement region with linearly polarized light in which the direction of travel is a z-axis direction and the vibration direction of an electric field is a y-axis direction. A polarimeter detects optical characteristics of light passing through the gas cell. A magnetic field generator applies an artificial magnetic field, capable of varying an x-axis component, a y-axis component, and a z-axis component, to the measurement region. A calculation control unit generates a plurality of artificial magnetic fields, calculates a magnetization value or a value corresponding to the magnetization value on the basis of the detection results of the polarimeter, and calculates an original magnetic field present in the measurement region, using an artificial magnetic field when the magnetization value or the value corresponding to the magnetization value satisfies a condition for external value.
1. A magnetic field measurement method of measuring a magnetic field of a measurement region in a magnetic field measurement device, the magnetic field measurement device including (i) a light source unit that emits linearly polarized light in which a first direction, a second direction and a third direction are orthogonal to each other, (ii) a medium, disposed in the measurement region, which changes optical characteristics of the linearly polarized light in accordance with a magnetic field, and that is irradiated along the third direction with the linearly polarized light of which a vibration direction of an electric field of the linearly polarized light is the second direction, (iii) an optical detector that detects the optical characteristics, and (iv) a magnetic field generator that applies an artificial magnetic field to the measurement region, the method comprising:
generating and applying to the measurement region a plurality of artificial magnetic fields, obtained by changing an artificial magnetic field component in the third direction and one artificial magnetic field component in the first direction and the second direction, in the magnetic field generator, in a state where the other artificial magnetic field component in the first direction and the second direction is set to a fixed value in each of the plurality of artificial magnetic fields;
calculating a magnetization value that is a component of a magnetization vector of the medium in the first direction or a value corresponding to the magnetization value based on detection results of the optical detector for each of the plurality of artificial magnetic fields; and
calculating an original magnetic field present in the measurement region, based on a selected artificial magnetic field of the plurality of artificial magnetic fields when the magnetization value in the selected artificial magnetic field or the value corresponding to the magnetization value in the selected artificial magnetic field satisfies a condition for external value.
2. The magnetic field measurement method according to claim 1 , wherein the calculating of the original magnetic field includes calculating using:
a first magnetic field that is an artificial magnetic field when the magnetization value or value corresponding to the magnetization value satisfies a maximum value condition; and
a second magnetic field that is an artificial magnetic field when the magnetization value or value corresponding to the magnetization value satisfies a minimum value condition.
3. The magnetic field measurement method according to claim 2 , wherein the one artificial magnetic field component is an artificial magnetic field component in the first direction, and the other artificial magnetic field component is an artificial magnetic field component in the second direction, and
the calculating of the original magnetic field includes calculating using the following Expressions (4) to (6):
C
x
=
-
A
py
+
A
vy
2
-
A
fx
(
4
)
C
y
=
A
py
-
A
vy
2
(
5
)
C
z
=
-
A
pz
+
A
vz
2
(
6
)
where, A py is a component of the first magnetic field in the second direction, A vy is a component of the second magnetic field in the second direction, A pz is a component of the first magnetic field in the third direction, A vz is a component of the second magnetic field in the third direction, A fx is the fixed value, C x is a component of the original magnetic field in the first direction, C y is a component of the original magnetic field in the second direction, and C z is a component of the original magnetic field in the third direction.
4. The magnetic field measurement method according to claim 1 , wherein the one artificial magnetic field component is an artificial magnetic field component in the second direction, and the other artificial magnetic field component is an artificial magnetic field component in the first direction, and
the calculating of the original magnetic field includes calculating using the following Expressions (1) to (3):
C
x
=
-
A
px
+
A
vx
2
(
1
)
C
y
=
A
px
-
A
vx
2
-
A
fy
(
2
)
C
z
=
A
pz
+
A
vz
2
(
3
)
where, A px is a component of the first magnetic field in the first direction, A vx , is a component of the second magnetic field in the first direction, A pz is a component of the first magnetic field in the third direction, A vz is a component of the second magnetic field in the third direction, A fy is the fixed value, C x is a component of the original magnetic field in the first direction, C y is a component of the original magnetic field in the second direction, and C z is a component of the original magnetic field in the third direction.
5. The magnetic field measurement method according to claim 1 , wherein the fixed value is zero.
6. The magnetic field measurement method according to claim 1 , further comprising:
generating a magnetic field of a difference in the original magnetic field with respect to a target magnetic field, in the magnetic field generator;
disposing a measuring object in the measurement region; and
measuring a magnetic field which is radiated by the measuring object, using the detection results of the optical detector while the magnetic field of the difference is generated.