The nature of electromagnetic radiation part2 Flashcards
The electric component of an electromagnetic plane wave can oscillate in
any direction normal to the direction of wave propagation (which is parallel to the k vector)
A represents
Electric field
B represents
Magnetic field
Suppose that the wave is propagating in the z direction. It follows that the
electric field can oscillate in any direction that lies in the x - y plane
The actual direction of oscillation determines the
polarization of the wave
The actual direction of oscillation determines the polarization of the wave. For instance,
a vacuum electromagnetic wave of angular frequency ω that is polarized in x direction has the associated electric field
a vacuum electromagnetic wave of angular frequency ω that is polarized in x direction has the associated electric field.
where ω=
ω=kc
where ω=kc. Likewise, a wave polarized in the y direction has the electric field
A represents
Horizontal linear polarization
B represent
Vertical linear polarization
Vertically polarized wave
is one for which the electric field lies only in the x-z plane
Horizontally polarized wave
is one for which the elecric field lies only in the y-z plane
(Vertical and horizontal polarized wave )These two waves are termed __________________
linearly polarized
These two waves are termed linearly polarized, since the
electric field vector oscillates in a straight-line
These two waves are termed linearly polarized, since the electric field vector oscillates in a straight-line. However,
other types of polarization are possible
, other types of polarization are possible. For instance, if we combine
two linearly polarized waves of equal amplitude, one polarized in the x direction, and one in the y direction, that oscillate π/2 radians out of phase, then we obtain a circularly polarized wave:
a circularly polarized wave
A represents
Left hand circular polarization
B represents
Right hand circular polarization
if the x and y components of the electric field in the previous two expressions have different ____________________ then we
(non-zero) amplitudes then we obtain right-hand and left-hand elliptically polarized waves, respectively.
(non-zero) amplitudes then we obtain right-hand and left-hand elliptically polarized waves, respectively. This nomenclature arises from
the fact that the tip of the electric field vector traces out an ellipse in the plane normal to the direction of wave propagation.
A represents
Linear
B represents
Circular
C represents
Elliptical
The Stokes parameters are
a set of values that describe the polarization state of electromagnetic radiation.
The Stokes parameters are a set of values that describe the polarization state of electromagnetic radiation. They were defined by George Gabriel Stokes in 1852, as a
mathematically convenient alternative to the more common description of incoherent or partially polarized radiation
a mathematically convenient alternative to the more common description of incoherent or partially polarized radiation in terms of
its total intensity (I), (fractional) degree of polarization (p), and the shape parameters of the polarization ellipse.
The Stokes parameters are often combined into
a vector, known as the Stokes vector:
Stokes Vector consists of four parameters (called Stokes parameters):
intensity I,
the degree of polarization Q,
the plane of polarization U,
the ellipticity V.
Stokes parmeters in terms of intensities
I = total intensity Q= I<sub>0</sub>-I<sub>90</sub> = differences in intensities between horizontal and vertical linearly polarized components; U = I<sub>+45</sub> –I<sub>-45</sub>= differences in intensities between linearly polarized components oriented at +45 and -45 V = I<sub>rcl</sub> –I<sub>lcr</sub>= differences in intensities between right and left circular polarized components.
For unpolarized light:
Q=U=V=0
The degree of polarization P of a light beam is defined as
P=(Q2+U2+V2)1/2/I
The degree of linear polarization LP of a light beam is defined by neglecting U and V
LP = -Q/I
Measurements of polarization are actively used in remote sensing in the
solar and microwave regions.
Polarization in the microwave – mainly due to
reflection from the surface
Polarization in the solar
– reflection from the surface and scattering by molecules and particulates.
Active remote sensing (e.g., ___________) commonly uses
RADAR
polarized radiation
