Describing som properties of physical optics and microwaves.

1. Measurement of Physical Optics and
Microwaves
Presented by:
Subhasis Shit
Roll: 15PH40040

2. Introduction
In physics, physical optics, or wave optics, is the branch of optics which studies
interference, diffraction, polarization, and other phenomena for which the ray approximation
of geometric optics is not valid. Actually it is an intermediate method between geometric
optics, which ignores wave effects, and full wave electromagnetism, which is a precise
theory. The word "physical" means that it is more physical than geometric or ray optics and
not that it is an exact physical theory. In this context we study the wave nature of light
through Photoconductivity, Interference, Diffraction and Polarization.
Beside light wave here we also use microwaves which is a form of electromagnetic
radiation with wavelengths ranging from one meter to one millimetre; with frequencies
between 300 MHz (100 cm) and 300 GHz (0.1 cm), to observe the diffraction pattern.

3. Interferometer
In physics, interference is a phenomenon in which two waves
superpose to form a resultant wave of greater, lower, or the same
amplitude. Interference usually refers to the interaction of
waves that are correlated or coherent with each other, either
because they come from the same source or because they have
the same or nearly the same frequency. Interference effects can
be observed with all types of waves, for example, light, radio,
acoustic, surface water waves or matter waves.
Types of Interference:
1. Division of wavefront (Young’s double slit)
2. Division of amplitude (Michelson Interferometer)

4. Michelson Interferometer with laser
The Michelson interferometer is an important example of this
second class. Here the two beams obtained by amplitude
division are sent in quite different directions against plane
mirrors, whence they are brought together again to form
interference fringes.
Now if the wavelength of the source is λ and D be the
separation distance between two mirrors that occurs for ‘n’
fringes to collapse or evolve then
𝜆 =
2𝐷
𝑛
Now if a glass plate is introduced in that path then the optical
path lengths will change. It also changes the interference
pattern. The refractive index of the glass plate will be
Schematic diagram of Michelson Interferometer
cos
1
2 (1 cos )
n
t
 


 


5. Aim of the Experiment and results
 Aim:
• Measurement of Wavelength of laser
• Refractive index of the glass plate
 Results:
• The wavelength of the laser source: 771 nm
• Refractive index of the glass plate: 1.54
Experimental set up

6. Diffraction
Diffraction refers to various phenomena which occur when a wave encounters an obstacle
or a slit. It is defined as the bending of light around the corners of an obstacle or aperture
into the region of geometrical shadow of the obstacle. In classical physics, the diffraction
phenomenon is described as the interference of waves according to the Huygens–Fresnel
principle. These characteristic behaviours are exhibited when a wave encounters an
obstacle or a slit that is comparable in size to its wavelength.
Wave propagation from sources forming secondary wavefront and producing
diffraction pattern on the screen.

7. Classification of Diffraction:
 Fresnel Diffraction:
In Fresnel diffraction, either the source or the point of
observation or both are at finite distances from the
diffraction obstacle or opening. Here, incident wavefront is
divergent.
 Fraunhofer Diffraction:
In Fraunhofer diffraction, either the source or the point of
observation or both are at effectively infinite distances from
the diffraction obstacle or opening. Here, incident
wavefront is plane.

8. Microwave Diffraction (Fresnel Diffraction):
Experimental set-up
 Principle:
Microwaves impinge on a slit and the edge of a
screen. The diffraction pattern is determined on the
basis of diffraction at these obstacle.
 Tasks:
Determination of the diffraction pattern of the
microwave intensity
1. behind the edge of a screen.
2. after passing through a slit.
3. behind a slit of variable width with a fixed
receiving point.

9. Intensity Distribution in the diffraction of the microwaves at the edge of a screen

10. Intensity Distribution in the diffraction of the microwaves at the slit as a function of the position of the
detector

11. Intensity Distribution in the diffraction of the microwaves at the slit as a function of the slit width

12. Laser Diffraction (Fraunhofer Diffraction):
 Aim of the Experiment:
• Plot the intensity distribution of the Fraunhofer
diffraction pattern by an aperture.
• Measure the dimension of aperture.
 Theory:
If a beam of light of wavelength λ falls normally on surface of
an aperture of dimension (axb) diffraction pattern is observed
on the screen. The intensity of the diffraction pattern is given
by
where,
And θ is the angle between the diffracted ray and the normal
to the aperture.
𝐼(𝜃) = 𝐼0
sin2
𝛼
𝛼2
×
sin2
𝛽
𝛽2
𝛼 =
𝜋𝑎sin𝜃
𝜆
𝛽 =
𝜋𝑏sin𝜃
𝜆

13. Intensity Distribution of the diffraction pattern(Capacitive grid)

14. Intensity Distribution of the diffraction pattern(Inductive grid)

15. Calculation of the dimension of the
aperture:
 Capacitive Grid:
Length along X-axis: 0.376mm
Length along Y-axis: 0.377mm
 Inductive Grid:
Length along X-axis: 0.360mm
Length along Y-axis: 0.335mm

16. Photoconductivity
 Principle:
The photo resistor is exposed to light from a halogen lamp.
The irradiance at the position of photo resistor is being
varied by means of two polarization filters which are placed
one behind the other.
 Aim of the Experiment:
• To measure Variation of photocurrent ‘I’ as a
function of the voltage ‘V’ at constant irradiance.
• To measure Variation of photocurrent ‘I’ as a
function of the irradiance at constant voltage.
Photoconductivity is a optical phenomenon in which material becomes more electrically
conductive due to absorption of electromagnetic radiation.

17. Variation of photocurrent ‘I’ as a function of
the voltage ‘V’ at constant irradiance
Variation of photocurrent ‘I’ as a function of
irradiance at constant voltage ‘V’

18. Polarization of light
A electromagnetic wave is said to be polarized if the plane of vibration is confined in a definite
direction. The phenomenon of polarization which for its explanation requires that the light must be
a transverse wave. In e.m theory light is considered as transverse wave consisting of vibrating
electric vectors and magnetic vectors at right angles to each other and also at right angles to the
direction of propagation.
Polarised wave with its vibration perpendicular to the direction of propagation
There are so many process to produce the polarised light
1. By reflection
2. By refraction
3. By selective absorption
4. By double refraction

19. Some types of Polarization:
1. Linearly Polarised light: 2. Circularly Polarised light:
3. Elliptically Polarised light:

20. Malus’s law
According to Malus, when completely plane polarized light is incident on the analyzer,
the intensity I of the light transmitted by the analyzer is directly proportional to the square
of the cosine of angle between the transmission axes of the analyzer and polarizer.
If E0 is the amplitude of the electric vector transmitted
by the polarizer, then intensity I0 of the light incident
on the analyzer is
Therefore, it proves the law of Malus.
2
cosI 

21. Verification of Malus law

22. Polar representation of elliptically polarised light

23. Variation of photocurrent with cos2θ for Elliptically polarised light
(a2-b2)= 12.9243
b2= 3.93783
a= 2.998
a/b= 1.51

24. Bibliography:
 Optics: A.Ghatak
 A text book on Light: B.Ghosh
 Optics: E.Hecht
 Wikipedia
 Google

25. Thank You