EM waves are periodic changes of electric and magnetic fields in space

and time. EM waves is transverse waves.

• EM waves velocity

Directionof EM wave propagation

Electric and magnetic fields are produced by charges and currents, but these fields also extend into surrounding regions of empty space.

Polarization (also polarisation) is a property of waves that

describes the orientation of their oscillations. If the vector of the electric field (measured at a fixed point

of space) oscillates along a straight line then the waves are called linearly polarized waves. The following animation

presents a wave that is plane-polarized in a vertical plane.

The intersecting plane looked at from the front.

The following animation presents a wave that is plane-polarized in a horizontal plane.

The intersecting plane looked at from the front.

Superposition of plane-polarized waves 1.When two electromagnetic waves plane-polarized in two perpendicular planes are present simultaneously

then the electric fields are added according to the rules

of vector addition, 'parallelogram rule' (superposition) .

The intersecting plane looked at from the front.

Superposition of plane-polarized waves 2.The superposition of two waves that have the same amplitude and wavelength and are polarized in two

perpendicular planes but there is a phase difference of 90 degrees between them. A phase difference of 90° means

that when one wave is at its peak then the other one is just crossing the zero line. Right polarization.

The intersecting plane looked at from the front.

• Unfortunately, two opposing historical conventions exist. In physics, astronomy, and optics. In physics, astronomy the polarization is defined as seen from the receiver, such as a telescope or radio telescope (the

source of EM waves).

• By this definition, if you could stop time and look at the electric field along the beam, it would trace a helix which is the same shape as the same-handed screw.

http://www.its.bldrdoc.gov/fs-1037/dir-031/_4609.htm

• right-hand (or clockwise) polarized wave: An elliptically or circularly polarized wave, in which the electric field vector, observed in any fixed plane, normal to the direction of propagation, while looking in the direction of propagation, rotates with time in a right-hand or clockwise direction. Synonym clockwise polarized wave.

Superposition of plane-polarized waves 3.The following animation shows what happens when

the two waves shown on the previous page are added with a phase difference of -90 degrees

The intersecting plane looked at from the front.

Circularly polarized wavesThe animations presenting the two types of circularly

polarized light are shown together so that you can compare

them more easily. •

Superposition of circularly polarized waveswhen a left circularly polarized wave and a right

circularly polarized wave are added.

• As we see, the result of superposing two circularly polarized waves is a plane-polarized wave.

The intersecting plane looked at from the front.

The interaction of EM waves and matter

• If EM waves enters matter (material), EM waves properties may change. Namely, its intensity (amplitude), polarization, velocity, wavelength, etc. may alter. The two basic phenomena of the interaction of light and matter are absorption (or extinction) and a decrease in velocity.

• The decrease in velocity (i.e. the slowdown) of EM wavest in matter is caused by the fact that all materials have a refraction index (refractive index) n=c/vph

=sqrt(eps*mu), which means that the velocity of EM waves is smaller in material than in vacuum. The refraction index is the ratio of the velocities of light measured in vacuum and in the given material.

Plane-polarized waves in an absorbing medium

The refraction index is 1 (n=c/vph =sqrt(eps*mu)

the intersecting planes looked at from the front.

The intersecting planes looked at from the front.

Circularly polarized waves in an absorbing mediumThe circularly polarized EM wave traverses a light-absorbing

medium (the refraction index is n=c/vph =sqrt(eps*mu)=1

• If the absorption in a dichroic material is different for different linear states of polarization, the material is termed linear dichroic. If it is different for right and left circularly polarized light, it is termed circular dichroic. Similarly, there can be elliptically dichroic crystals.

Plane-polarized waves in a refracting medium(1#2) A plane-polarized wave

traverses a non-absorbing medium with

refraction index greater than 1.0

Its frequency does not change, therefore its wavelength decreases (the product of the frequency and the wavelength should be equal to the velocity of light f*Labda=c). In these animations, we used a refraction index n=2.2. This means that the velocity of EM wave in the medium is vp=(1/2.2)*c=0.4545*c, and its wavelength also decreases to (1/2.2) times the original value. When the light exits the material, its velocity and wavelength are restored to their original (vacuum) values. Since the material does not absorb light, the intensity of the EM wave does not decrease.

Plane-polarized waves in a refracting medium(2#2) with refraction index

n=c/vp=sqrt(EPS*MU)=2.2The distance between the intersecting planes in front of and behind the piece of material is exactly 8 times the vacuum wavelength of the EM wave. The two field vectors at the intersecting planes do not oscillate in the same phase any longer.

The two field vectors at the intersecting planes do not oscillate in the same phase any longer.

Circularly polarized waves in a refracting medium

A circularly polarized wave traverses a non-absorbing

medium with a refraction index greater than 1.0.

Plane-polarized waves in a medium showing circular dichroism. They absorb left circularly polarized light to

a different extent than right circularly polarized light.

• circular dichroism makes plane-polarized light elliptically polar.

Plane-polarized waves in a medium showing circular birefringence

(characterized by double refraction)

• materials having another special property: their refraction index is different for left and right circularly polarized light

circular birefringence rotates the plane of polarization of plane-polarized light

Plane-polarized waves in a medium showing both circular dichroism and circular

birefringence

 Optical Activity of the chiral substance and EM waves Polarization. Optical rotation.

http://www.nsm.buffalo.edu/~jochena/research/opticalactivity.html

• Chiral molecules are molecules that do not have a plane of symmetry, an inversion center, or so-called improper rotation symmetry axes. For example, the water molecule has a plane of symmetry but sugar molecules don't. Sugar, amino acids, and most other bio-molecules come in two forms that are mirror images of each other and that are not the same.