Magnetic field measurement method and magnetic field measurement apparatus
In a magnetic field measurement apparatus, a light source irradiates a gas cell with linearly polarized light serving as pump light and probe light in a Z axis direction, and a magnetic field generator applies, to the gas cell, a magnetic field A x which is a time function f(t) having the amplitude A 0 taking n fixed values f i (where i=1, . . . , and n), and a magnetic field A y which is a time function g(t) having the amplitude A 0 taking m fixed values g j (where j=1, . . . , and m) in each of X axis and Y axis directions. A calculation controller calculates a magnetic field C (C x , C y , C z ) of a measurement region using the X axis and Y axis components A x and A y of an artificial magnetic field A, and a spin polarization degree M x corresponding to a measurement value W − from a magnetic sensor.
1. A magnetic field measurement method of measuring a magnetic field of a measurement region in a magnetic field measurement apparatus where a first direction, a second direction, and a third direction are perpendicular to each other, the magnetic field measurement apparatus includes a light source that emits light, a medium through which the light passes in the third direction and that changes optical characteristics depending on the magnetic field of the measurement region, a photodetector that detects the optical characteristics, and a first magnetic field generator that generates a magnetic field in the first direction in the measurement region, the method comprising:
causing the first magnetic field generator to generate a first-constant magnetic field, a second-constant magnetic field, and a third-constant magnetic field, as the magnetic field in the first direction; and
calculating the magnetic field of the measurement region using a detection result from the photodetector and the magnetic field in the first direction, wherein,
in the calculating of the magnetic field of the measurement region, a magnetization value indicating a component in the first direction of a magnetization vector of the medium is calculated on the basis of the detection result from the photodetector, and the magnetic field of the measurement region is calculated using a (1-1)-th magnetization value obtained when the constant magnetic field with the first level on the first direction side is generated, a (2-1)-th magnetization value obtained when the constant magnetic field with the second level on the first direction side is generated, a (3-1)-th magnetization value obtained when the constant magnetic field with the third level on the first direction side is generated, and the magnetic field in the first direction, and
in the calculating of the magnetic field of the measurement region, the following Equation 1 is applied to combinations of a constant magnetic field with an i-th level (where i=1, 2, and 3) on the first direction side, which is the magnetic field in the first direction, and a magnetization value obtained when the magnetic field in the first direction is generated:
M
xi
=
c
a
·
C
x
C
y
+
C
y
A
10
f
i
+
aC
z
a
2
+
C
x
2
+
C
y
2
+
C
z
2
+
2
C
x
A
10
f
i
+
(
A
10
f
i
)
2
(
1
)
in the equation, the magnetic field of the measurement region is expressed by C=(C x , C y , C z ); x, y, and z respectively indicate spatial coordinates in the first direction, the second direction, and the third direction; M xi indicates the magnetization value obtained when the constant magnetic field with the i-th level on the first direction side is generated; a and c are constants; and A 10 f i indicates the constant magnetic field with the i-th level on the first direction side.
2. The magnetic field measurement method according to claim 1 , wherein
at least one of the constant magnetic field with the first level on the first direction side, the constant magnetic field with the second level on the first direction side, and the constant magnetic field with the third level on the first direction side is a zero magnetic field.
3. A magnetic field measurement apparatus in which a first direction, a second direction, and a third direction are perpendicular to each other, the apparatus comprising:
a light source that emits light;
a medium through which the light passes in the third direction and that changes optical characteristics depending on a magnetic field of the measurement region;
a photodetector that detects the optical characteristics;
a first magnetic field generator that applies a magnetic field in the first direction to the measurement region; and
a calculation controller that causes the first magnetic field generator to generate a constant magnetic field with a first level on the first direction side, a constant magnetic field with a second level on the first direction side, and a constant magnetic field with a third level on the first direction side, as the magnetic field in the first direction, and calculates the magnetic field of the measurement region using a detection result from the photodetector and the magnetic field in the first direction, wherein,
in the calculating of the magnetic field of the measurement region, a magnetization value indicating a component in the first direction of a magnetization vector of the medium is calculated on the basis of the detection result from the photodetector, and the magnetic field of the measurement region is calculated using a (1-1)-th magnetization value obtained when the constant magnetic field with the first level on the first direction side is generated, a (2-1)-th magnetization value obtained when the constant magnetic field with the second level on the first direction side is generated, a (3-1)-th magnetization value obtained when the constant magnetic field with the third level on the first direction side is generated, and the magnetic field in the first direction, and
in the calculating of the magnetic field of the measurement region, the following Equation 1 is applied to combinations of a constant magnetic field with an i-th level (where i=1, 2, and 3) on the first direction side, which is the magnetic field in the first direction, and a magnetization value obtained when the magnetic field in the first direction is generated:
M
xi
=
c
a
·
C
x
C
y
+
C
y
A
10
f
i
+
a
C
z
a
2
+
C
x
2
+
C
y
2
+
C
z
2
+
2
C
x
A
10
f
i
+
(
A
10
f
i
)
2
(
1
)
in the equation, the magnetic field of the measurement region is expressed by C=(C x , C y , C z ); x, y, and z respectively indicate spatial coordinates in the first direction, the second direction, and the third direction; M xi indicates the magnetization value obtained when the constant magnetic field with the i-th level on the first direction side is generated; a and c are constants; and A 10 f i indicates the constant magnetic field with the i-th level on the first direction side.