Chapter XIX Polarization of light

Interference and diffraction of light are arguments for wavecharactiristics of light.We know that there are two types of wave processes: transverse &longitutional waves →to what are light waves belong ?Study of polarization of light makes clear thatThis conclusion is in according to the concept that light waves areelectromagnetic waves with a definte band of frequencies. Recall thatelectromagnetic waves are transervse waves in which e-vectors &m-vectors oscillate in such follwing directions...
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Chapter XIX Polarization of light GENERAL PHYSICS III Optics & Quantum Physics Chapter XIX Polarization of light§1. Natural and polarized light. Malus’s law§2. Polarization in reflection and refraction§3. Polarization by birefringent§4. Rotation of polarizing planeInterference and diffraction of light are arguments for wave charactiristics of light.We know that there are two types of wave processes: transverse & longitutional waves → to what are light waves belong ?Study of polarization of light makes clear that light waves is transverse wavesThis conclusion is in according to the concept that light waves are electromagnetic waves with a definte band of frequencies. Recall that electromagnetic waves are transervse waves in which e-vectors & m-vectors oscillate in such follwing directions x z y§1. Natural and polarized light: 1.1 Definitions:• Light waves emmitted from naturalsources are from excited moleculesor atoms.• The light waves emitted by anyindividual molecule can be linearly Natural (unpolarized) light raypolarized (definite in direction),but any natural light source consists of a very large number of moleculeswith random orientation → natural light is a random mixture of linearlypolarized waves with all possible transvere directions.• Definitons:Polarized light → light waves that have oscillation direction oriented in any definite wayLinearly (or planely) polarized light → oscillation of light vector ( E ) is in one plane only Oscillation Light rayOscillation plane → the plane in which plane the light vector E oscillates PolarizationPolarization plane → the plane that plane is perpendicular to osc. plane (it is used rarely) 1.2 Polarizer: How can make a polarized light beam from natural light ? → using a polarizer There are some crystal materials that have dichroism, that is, a selective absorption: one of components of the light vector is absorbed much more strongly than the other Polarizing axis Polarizing axis a) b)Therefore if a polarizer (polaroid) is illuminated by natural light →after polarizer there will be a linearly polarized light.The direction of E vector of transmitted light is parallel to thedirection called polarizing axis of polarizer. A||=A.cos 1.3 Malus’s law: ANow we are interested in the light intensity after a polarizer, Polarizer if the incident light is natural:• Before P → I ~ A2• After P → I’ = < I cos2> = I/2 (the average over all equi-probability direction) ( : the angle between the incident and transmitted light vectors) If we rotate the polarizer around the propagation direction → wedon’t observe any variation in light intensity.What happens when the Ilinearly polarized light I0emerging from a polarizerpasses through a secondpolaroid ? Analyzer Then I = I0 cos2 Polarizer This is Malus’s law Intensity of the  the angle between : transmitted light two polarizing axises Intensity of the incident linearly polarized light of polarizer and analyzer• Rotate the second polaroid → varies → variation of light intensity Iis observed.• The second polaroid helps us know about is the incident light eithernatural or polarized → it is called analyzer.1.4 Partially polarized light: We have known about linearly polarized light in which the light vector E oscillates in one definite direction. There is the case of polarized light in which the light vector E oscillates in different directions (that are all, of course, perpendicular to the propagation direction), but one direction predominates over all other → it is called partially polarized light. It can be considered as a mixing of natural and linearly polarized light. When a partially polarozed lighi transmits through an analyzer → the light intensity varies from Imax to Imin . One cycle of analyzer rotation the intensity has twice got maximum anf twice got minimum. It is useful to introduce the degree of polarization P : Imax - Imin P= Imax + Imin The limit cases: Natural light → Imax = Imin → P = 0; Linear polarized light → Imin = 0 → P = 11.5 Cicular and elliptical polarization: Consider two coherent linearly polarized waves, and their oscillation directions are perpendicular each to other: the first is along x-axis, the second – y-axis (xOy plane  the ray) We have The composition of two such waves is the vector E whose arrowhead draws an ellipse. → then we have a polarized light wave in which the oscilation plane rotates around the propagation direction, and the head end of the light vector moves describes an ellipse. This light is called elliptically polarized.Some limit cases: • When phase difference equals m.→ the ellipse collapses to a straight line, we have a linearly polarized light • When  ...