Geoscience Reference
In-Depth Information
2. Principle — Faraday Effect
The interaction between the light and the atmosphere is caused by
scattering (Mie, Rayleigh, Raman), and also by the magneto-optical effect
and electro-optical effect. The magneto-optical effect (Faraday effect)
is associated with the lightning discharge. It has been reported as an
optical measurement method for magnetic confinement fusion reactor.
5
The
polarization plane of a beam propagating parallel to the magnetic flux is
rotated in a partially ionized atmosphere (plasma) (Fig. 1). The rotation
angle is proportional to the product of the ionization electron density
n
e
and the magnetic flux density
B
along the beam propagation path. The
linearly polarized beam can be regarded as a combination of the clockwise
and the counterclockwise circularly polarized beams. The refractive indices
of the ionized atmosphere for each circularly polarized beam are as follows:
n
±
=
1
1
/
2
ω
pe
ω
2
ω
ω ± ω
ce
−
,
e
2
n
e
ε
0
m
e
eB
m
e
ω
pe
=
ω
ce
=
(1)
where
ω
pe
,
ω
ce
are the plasma and electron cyclotron frequencies, respect-
ively,
e
is the fundamental charge,
m
e
is the electron mass, and
ε
0
is the
permittivity of free space. Therefore, the rotation angle of polarization of
Rotation Angle
δ
Partially Ionized
Atmosphere/Cloud
Magnetic Flux
Density B
Linearly
Polarized Beam
Fig. 1.
Faraday effect.
