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WAVES AND OPTICS PHYSICS-C IV unit 7

Wave Optics
Author of this note Mr
...
Prasad BSc from University of Calicut, MSc from
university of Delhi, and M
...
A from IGNOU Delhi
These notes were prepared during my teaching session for under graduate
students (11 Th and 12 Th class) of my school physics department

This note is helpful for under graduate students and junior level graduates

I declare that these notes are my original works based on my knowledge in
physics and the books mentioned below are the reference books I used for
preparing these notes

Table of contents
(1) Electromagnetic wave nature of light
...
Definition

(10)Types of wave front
(11)What are coherent sources?
(12)Temporal coherence
(13)Spatial coherence
(14)Young’s double slit experiment
(15)Huygens Principle
(16)Huygens Principle of Secondary Wavelets
(17)Advantages and Disadvantages of Huygens Principle
(18)Temporal and spatial coherence
Reference Books
Vibrations and Waves, A
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French, 1stEdn
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Waves: Berkeley Physics Course, vol
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Fundamentals of Optics, F
...
Jenkins and H
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White, 1981,
McGraw-Hill
Principles of Optics, Max Born and Emil Wolf, 7th Edn
...

Optics, Ajoy Ghatak, 2008, Tata McGraw Hill
The Physics of Vibrations and Waves, H
...
Pain, 2013, John Wiley
and Sons
...
K
...

Fundamental of Optics, A
...
R
...
R
...
ChandPublications
Optics, Eugene Hecht, 4thEdn
...

Electromagnetic wave nature of light
Newton’s corpuscular theory of light
In 1672, Newton's gave the corpuscular hypothesis of light which expresses that
light is comprised of little discrete particles called "corpuscles" (little particles)
which travel in an orderly fashion with a limited speed
...


Huygens wave theory of light
In 1678, Christian Huygens gave the wave hypothesis of light
...

Thomas Young and Augustine Jean Fresnel disproved Newton's corpuscular
theory
...

Electromagnetic wave travels through space at a constant speed of 3
...
Visible light is a little portion of the electromagnetic radiation
...

Quantum theory of light
Quantum hypothesis lets us know that Light is made out of small particles called
photon which have wavelike properties related with them it is called as WaveParticle Duality of Light
Photons are only discrete bundle of energy E=h where h is the Planck's constant
and f is the frequency of light radiation
Huygens's wave theory
Huygens suggested that each point source makes unnecessary influences in ether
medium and produce spherical wave which goes with same speed toward all path
in a homogenous, isotropic medium
Each point in the spherical wave goes about as a source of secondary waves which
travel with the same speed
...
A wave generally goes toward a path normal to the
wave front
...
A wavefront is the arrangement of all areas
in a medium where the wave is at a similar phase
...

Types of wave front:

Plane wave front
Spherical wave front
Cylindrical wave front
When the source is a point source then the wave front is called spherical wave
front
...

When the loci of points of constant phase lie on a plane, then the wave front is
called as plane wave front
...

What are coherent sources?
Two sources are supposed to be coherent when the waves discharged from them
have a similar frequency, amplitude and constant phase difference
...


Coherence is a fundamental condition for interference of
Light waves
...
Temporal coherence
ii
...

The most significant length of time period for which a similar wave pulse keep on
going through a space point is called coherence time
...

Temporal coherence can be explained by Michelson Morley experiment

Temporal coherence
Spatial coherence
Spatial coherence is the stage connection between two space points in a specific
moment of time
...

At the point when the shape of a source is gradually expanded then horizontal
element of the source over which the radiation remains coherent decides the
spatial coherence
Young’s double slit experiment

Spatial coherence
In above figure S and S1 are two sources isolated by a distance ro
...

Mathematically it can be proved that ro=λR/2 l
...
Good
interference pattern will be obtained only when
ro<< λR/ l
l << λR/ ro
l << λ/Ɵ where Ɵ= R/ ro
If the distance between the two holes increases the interference fringes
decreases
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Huygens Principle
Huygens Principle is otherwise called the Huygens-Fresnel Principle
...
A technique for examination applies to issues of wave propagation
both in the near field and far-field limit and in close field diffraction and reflection
Huygens' Principle Statement is that each point on a wavefront is itself the source
of circular wavelets and the optional wavelets emerging from various focuses
commonly interfere
...

In the year 1678, Huygens stated that each point which a glowing vibration comes
to turns into a source of a round wave, and in this manner, the amount of these
optional waves assists us with deciding the type of the wave at any resulting time
...

Huygens Principle is utilized to give a subjective clarification of both rectilinear
and spherical wave spread, and to infer the laws of reflection and refraction
utilizing the Huygens Principle of secondary wavelets rule, yet couldn't make
sense of the rectilinear propagation that happen when light encounters edges,
gaps, and screens, generally known as impacts of diffraction
...
B
...

The goal is that the source is a dipole, i
...
, not the mono pole according to the
suppositions of Huygens that drops in the reflected direction
Huygens Principle of Secondary Wavelets
Huygens principle of secondary wavelets expresses that each point on a given
wavefront is a secondary wavelet/disturbance
...

At the instant, a common tangent had drawn on the wavelets in the forward
direction points to the new wavefront
...

In conclusion, Huygen’s principle is a comprehensive method of analysis that we
can use to understand the problems of wave propagation both in diffraction and
reflection
...

The concepts like diffraction of light, as well as interference of light, were proved
by Huygens
...

Huygens principle failed to explain the photoelectric effect
...
This was proved to be false in the
20th century
...

Temporal coherence gives the measurement of how monochromatic a source is
...

Spatial coherence
Spatial coherence describes the ability for two points in space in the extent of a
wave to interfere when averaged over time
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