WAVEPLATES

PLATE RETARDERS

A wave plate or retarder is an optical device that alters the

polarization state of a light wave traveling through it.

Waveplate (Retarders)

•Full Wave Plate

•Half Wave Plate

•Quarter Wave Plate

0 et n n

Optical path length

Phase difference

00

2et n n

Quarter wave, Half wave and Full wave

4

2

2

2

Half-Wave Plate

Desired Result Method

Change linear polarization to circular polarization

.

Change circular

polarization to linear

Change the handedness of

circular polarization

Rotate linear polarization to

a more desirable orientation

Insert a λ/4 plate with axis at 45° to the input polarization

Insert a λ/4 plate with axis at

45° to the desired output

polarization.

Insert a λ/2 plate – orientation

unimportant.

Insert a λ/2 plate with axis at ½

the desired rotation.

Interference of polarized light

Fresnel-Arago laws

1. Two coherent rays polarised at right angles do not interfere

2. Two parallel coherent polarised rays will interfere in the same way as will ordinary light

Optical Activity

The two hands are "non-superimposable mirror images".

An optically active compound and its mirror image are called enantiomers or optical isomers

Optically active medium

Polarimetry

Sugar, Glucose and Fructose

Sugar (Sucrose or Cane sugar)

Glucose-D ( Dextrose or Grape sugar)

Fructose (Levulose or Fruit sugar)

Specific rotation

52.7

66.47

- 92

o

o

o

112212 OHC

6126 OHC

6126 OHC

Half Shade plate

A OO´

E´EQ´ Q

PolarizingSunglass

Antiglare screen

Problem

Unpolarized light of intensity I0 is incident normally on three

polaroid sheets P1, P2 and P3 all arranged in series. The pass

axis of each polaroid sheet makes an angle of 450 with the

earlier sheet.

(i) What is the intensity of the transmitted beam?

(ii) What is the intensity of the transmitted beam if the Polaroid

sheet P2 is replaced with a quarter wave plate Q2 with its

optic axis along the pass axis of P2?