Polarisation

Electromagnetic Waves

H Field

E Field

Direction of Propagation

H Lines

E Lines

• Electromagnetic waves consist of E (electric) fields and H (magnetic) fields

They form an ORTHOGONAL Set

H Field

E Field

Direction of Propagation

H Lines

E Lines

• That is, in linear media, they are all at right angles to each other.

We always use the E field as our reference

H Field

E Field

Direction of Propagation

H Lines

E Lines• Because E (electric) fields

are easy to measureeasy to measure.

Waves and Vectors

• The wave can be described by a ROTATING VECTOR.

Any general E field can be represented by two components, Ex and Ey.

• They are always oriented in space at right angles to each other

But Ex and Ey need not stay in phase.

The resulting E field will have one of three polarisations

• Linear

• Circular

• Elliptic

• Both elliptic and circular polarisations are referred to as random polarisation.

Linear Polarisation

Both Ex and Ey are present with equal magnitude and they stay in phase The resultant E wave describes a straight line, fixed in space as it propagates.

Circular Polarisation

Both Ex and Ey are present with equal magnitude and 90 degrees phase difference. The resultant E wave describes a circle as it propagates.

Elliptical Polarisation

Both Ex and Ey are present They may have:equal magnitude and do not stay in phase orunequal magnitude and do not stay in phase.The resulting E wave describes an ellipse as it propagates.

Action of a Polariser.

• Only one polarisation of the wave is allowed through. All others are stopped.

Polarising elements in a confocal microscope system.

• Brewster windows

• Phase plates

• Beam splitters

• Dichroics

• Prisms

• Diffraction gratings

• Coated mirrors

• Polaroid filters

Some Applications

Sun Glasses

Pockels Cell

Brewster windows

• The refracted wave does not suffer any loss in the window.

Liquid crystal displays