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 alternating magnetic fields which have the same cycle and different phases to the gas cell 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 X axis and Y axis components A x and A y of the alternating magnetic fields, 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 in which a first direction, a second direction, and a third direction are perpendicular to each other and which 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, a first magnetic field generator that applies a magnetic field in the first direction to the medium, and a second magnetic field generator that applies a magnetic field in the second direction to the medium, the method comprising:
causing the first magnetic field generator to generate a first alternating magnetic field;
causing the second magnetic field generator to generate a second alternating magnetic field which has the same cycle as a cycle of the first alternating magnetic field and has δ as a phase difference relative to the first alternating magnetic field; and
calculating the magnetic field of the measurement region using a detection result from the photodetector, the first alternating magnetic field, and the second alternating magnetic field.
2. The magnetic field measurement method according to claim 1 ,
wherein the calculating of the magnetic field of the measurement region includes calculating a magnetization value indicating a component in the first direction of a magnetization vector of the medium when the first alternating magnetic field and the second alternating magnetic field are generated, or a value corresponding to the magnetization value, on the basis of the detection result from the photodetector.
3. The magnetic field measurement method according to claim 2 ,
wherein the calculating of the magnetic field of the measurement region is performed using three or more different combinations of the first alternating magnetic field and the second alternating magnetic field.
4. The magnetic field measurement method according to claim 3 , wherein the calculating of the magnetic field of the measurement region is performed by applying the following Equation 1 to each of the combinations:
M
x
=
c
a
·
C
x
C
y
+
C
x
A
20
f
(
ω
t
+
δ
)
+
C
y
A
10
f
(
ω
t
)
+
A
10
f
(
ω
t
)
A
20
f
(
ω
t
+
δ
)
+
a
C
z
a
2
+
C
x
2
+
C
y
2
+
C
z
2
+
2
C
x
A
10
f
(
ω
t
)
+
2
C
y
A
20
f
(
ω
t
+
δ
)
+
A
10
2
f
(
ω
t
)
2
+
A
20
2
f
(
ω
t
+
δ
)
2
(
1
)
wherein, in the equation, the magnetic field of the measurement region is expressed by C=(Cx, Cy, Cz); x, y, and z respectively indicate spatial coordinates in the first direction, the second direction, and the third direction; Mx indicates the magnetization value; a and c are constants; A10f(ωt) indicates the first alternating magnetic field; and A20f(ωt+δ) indicates the second alternating magnetic field, in which δ is the phase difference, ω is an angular frequency of the first alternating magnetic field and the second alternating magnetic field, and t is time.
5. The magnetic field measurement method according to claim 1 ,
wherein the phase difference is π/2.
6. The magnetic field measurement method according to claim 1 ,
wherein the first alternating magnetic field and the second alternating magnetic field comprise trigonometric function waves.
7. The magnetic field measurement method according to claim 1 ,
wherein the first alternating magnetic field and the second alternating magnetic field comprise triangular waves.
8. The magnetic field measurement method according to claim 1 ,
wherein the first alternating magnetic field and the second alternating magnetic field comprise rectangular waves.
9. A magnetic field measurement method of measuring a magnetic field of a measurement region in a magnetic field measurement apparatus in which a first direction, a second direction, and a third direction are perpendicular to each other and which 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, a first magnetic field generator that applies a magnetic field in the first direction to the medium, a second magnetic field generator that applies a magnetic field in the second direction to the medium, and a third magnetic field generator that applies a magnetic field in the third direction to the medium, the method comprising:
causing the first magnetic field generator to generate a first alternating magnetic field;
causing the second magnetic field generator to generate a second alternating magnetic field which has the same cycle as a cycle of the first alternating magnetic field and has δ as a phase difference relative to the first alternating magnetic field;
a first procedure of calculating the magnetic field of the measurement region as an original magnetic field using a detection result from the photodetector, the first alternating magnetic field, and the second alternating magnetic field;
a second procedure of disposing a measurement target object in the measurement region;
a third procedure of causing the first magnetic field generator, the second magnetic field generator, and the third magnetic field generator to generate a magnetic field corresponding to a difference between a target magnetic field which is desired to be formed in the measurement region and the original magnetic field; and
a fourth procedure of measuring a magnetic field generated by the measurement target object using the detection result from the photodetector in a period in which the third procedure is being performed and the second procedure is completed.
10. A magnetic field measurement method of measuring a magnetic field of a measurement region in a magnetic field measurement apparatus in which a first direction, a second direction, and a third direction are perpendicular to each other and which 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, a first magnetic field generator that applies a magnetic field in the first direction to the medium, a second magnetic field generator that applies a magnetic field in the second direction to the medium, and a third magnetic field generator that applies a magnetic field in the third direction to the medium, the method comprising:
causing the first magnetic field generator to generate a first alternating magnetic field;
causing the second magnetic field generator to generate a second alternating magnetic field which has the same cycle as a cycle of the first alternating magnetic field and has δ as a phase difference relative to the first alternating magnetic field;
a first procedure of calculating the magnetic field of the measurement region as an original magnetic field using a detection result from the photodetector, the first alternating magnetic field, and the second alternating magnetic field;
a second procedure of disposing a measurement target object in the measurement region;
a third procedure of causing the first magnetic field generator to generate a third alternating magnetic field in which a first direction component of a magnetic field corresponding to a difference between a target magnetic field which is desired to be formed in the measurement region and the original magnetic field is added to the first alternating magnetic field, causing the second magnetic field generator to generate a fourth alternating magnetic field in which a second direction component of the magnetic field corresponding to the difference is added to the second alternating magnetic field, and causing the third magnetic field generator to generate a magnetic field having a third direction component of the magnetic field corresponding to the difference; and
a fourth procedure of measuring a magnetic field generated by the measurement target object using the detection result from the photodetector, the third alternating magnetic field, and the fourth alternating magnetic field in a period in which the third procedure is being performed and the second procedure is completed.
11. 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 is arranged to emit light;
a medium through which the light is arranged to pass in the third direction and that is arranged to change optical characteristics depending on a magnetic field of a measurement region;
a photodetector that is arranged to detect the optical characteristics;
a first magnetic field generator that is arranged to apply a magnetic field in the first direction to the medium;
a second magnetic field generator that is arranged to apply a magnetic field in the second direction to the medium; and
a calculation controller that is arranged to cause the first magnetic field generator to generate a first alternating magnetic field, is arranged to cause the second magnetic field generator to generate a second alternating magnetic field which has the same cycle as a cycle of the first alternating magnetic field and has δ as a phase difference relative to the first alternating magnetic field, and is arranged to calculate the magnetic field of the measurement region using a detection result from the photodetector, the first alternating magnetic field, and the second alternating magnetic field.