Applied Optics. Dr D. Arun Kumar Assistant Professor Department of Physical Sciences Bannari Amman Institute of Technology Sathyamangalam

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1 Applied Optics Dr D. Arun Kumar Assistant Professor Department of Physical Sciences Bannari Amman Institute of Technology Sathyamangalam

2 LIGHT AS A WAVE Light has dual nature. It has both particle nature and wave nature but it cannot act as a wave and particle simultaneously. Light is also having the properties such as reflection, refraction, interference, diffraction, polarization. Light is also having two most famous effects like photoelectric effect and Compton Effect.

3 LIGHT AS A WAVE To explain the properties like interference diffraction and polarization we need to adopt wave nature for light. Light is a transverse wave. The first person to advance a convincing wave theory for light was DUTCH PHYSICIST CHRISTIAN HUYGENS, in 1678.

4 Representation of Light wave Whose displacement is given b y=asinωt Where ' a' is amplitude of wave. 'ωt' is Phase, Which gives the position and direction of wave at a time 't'

5 PHASE DIFFERENCES: The angular separation between two points of wave is called Phase difference. It is measured in radians or degrees.

6 PATH DIFFERENCE: The linear separation between two points of wave is called Path Difference It is measured in mm or cm.

7 RELATION BETWEEN PHASE DIFFERENCE AND PATH DIFFERENCE:

8 INTERFERENCE: Interference is the optical phenomenon in which brightness and darkness are produced by the combination of two similar light waves.

9 INTERFERENCE: When two light waves of same frequency having constant phase difference coincide in space and time. There is modification in the intensity of light. This modification in the intensity is due to superposition of two light waves are called Interference. And the pattern dark and bright fringes produced are called Interference pattern.

10 TYPES OF INTERFERENCE: Interference is of two types. Constructive interference / constructive superposition Destructive interference / destructive superposition

11 CONSTRUCTIVE INTERFERENCE: When crust of one light wave falls on the crust of another wave then the resultant intensity increases

12 DESTRUCTIVE INTERFERENCE: When crust of one light wave falls on the trough of another wave then the resultant intensity decreases.

13 Conditions for sustained or Good interference pattern : We require two monochromatic light sources. These two sources must be coherent i.e., they constant phase difference. The frequency must be the same. The amplitude must be the same. They must travel in the same directions. The two sources must be the same These two sources must be as near as possible and the screen must be as far from them as possible.

14 Interference at a wedge shaped films

15 Determination of thickness of a paper or wire Two optically plane glass plates are placed one over the other and tied at one end. The given wire is introduced near the other end, so that an air wedge is formed. The distance between the wire and the tied end (L) is measured using a scale. Light from a sodium vapour lamp is incident on a plane glass plate inclined at 45 to the horizontal. The reflected light from the plane glass plate is incident normally on the optically plane glass plates forming the air wedge and reflected back.

16 Determination of thickness of a paper or wire The reflected light from the air-wedge is viewed through the eye-piece of a microscope. The microscope is moved up and down and adjusted for clear interference fringes of alternate dark and bright. The microscope is fixed so that the vertical cross-wire coincides with the dark band (say nth band) and the reading is noted. The microscope is moved across the fringes and readings are noted when the vertical cross-wire coincides with the (n+5)th, (n+10)th.. dark bands.

17 Determination of thickness of a paper or wire The observed readings are tabulated and the band width ( ) is calculated. The thickness of the given wire/thin-sheet is calculated using the formula. t = L /2 (m)

18 Determination of thickness of a paper or wire Order of Fringes Microscope reading Width for 5 MSR (10-2 m) VC (div) TR (10-2 m) fringes (10-2 m) Fringe width (10-2 m)

19 Testing of flatness of a surface