In this Slide describe abot the LASER,FIBER OPTICS & ULTRASONIC……

3. Characteristics of laser
 Coherence:
The wave trains which are identical in phase and direction are called
coherent waves
 High intensity:
Cue to the coherent nature of laser,it has the ability to focus over a
small area of 10-6 cm2
 High directionality:
an ordinary light source emits light in all possible direction. but, since
laser travels as a parallel beam it can travel over a long distance
without spreading.
 high monochromaticity:
The ligh from a normal monochromatic source spreads over a range of
wavelength of the order. But, the spread of the order of 1nm for laser.

4. Induced absorption
Let the atom
initially in the lower
state E1. if a photon
of energy hv is
incident on the
atom in the lower
state, the atom
absorbs the incident
photon and gets
excited to the higher
energy state E2. this
process is called
induced absorption.

5. Spontaneous emission
•It is a process in which there is an
emission of a photon whenever an
atom transits from a higher energy
state to a lower energy state without
the aid of any external agency.
For this process to take place ,
the atom has to be in the excited
state . Since, the higher energy level
is an unstable one, the excited atom
in the higher energy level E2
spontaneously returns to the lower
energy level E1 with the emission of
a photon of energy hv=E2-E1 .

6. Stimulated Emission
for this process also, the
atom should be already in the
excited states. Let a photon
having energy hv=E2-E1
Interact with an atom in the
excited states. Under such
interaction, the incident
photon stimulates the excited
atom in the level E2 to
transmit to the lower energy
level E1, resulting in the
emission of a photon of
energy.

7. Active medium:
This is a four- level solid state laser system.
Yttrium aluminium garnet(Y3 Al5 O12),commonly
known as YAG, doped with neodymium ions Nd3+ is
the active medium. The active medium is taken in the
form of a crystal and is drawn into a rod. The
neodymium ions Nd3+ are the active center.
Resonator cavity:
The end faces of the Nd: YAG rod are ground
polished and silvered to act as the optical resonator
mirrors, or the optical cavity can be formed by using
two external reflecting mirrors M1 and M2.

8. Optical pumping
 A xenon flash lamp or a krypton flash lamp is
used as a pumping source.
Construction:
 The schematic diagram of a Nd: YAG laser is
shown in figure .
 A Nd: YAG rod and a krypton flash lamp are
enclosed inside an ellipsoidal reflector. In order to
make the entire flash radiation to focus on the laser
rod, the Nd: YAG rod is placed at one focal axis and the
flash lamp at the other focal axis of the ellipsoidal
reflector.

10. Working………
 Any of the spontaneously emitted photon will make
the excited Nd3+ ions to undergo a transition between
E2-E1 state. Thus,during this transition the stimulated
photon is generated.
 The photons travelling parallel to the resonator axis
experience multiple reflections at the mirrors. As a
result, the transition E2-E1 yields an intense and
coherent laser beam of wavelength 1.064mum. These
lasers give beam continuously. The Nd3+ ions then
make a transition beteeen E1-Eo, which is a non-
radiative transition.

11.  Only a part of the energy emitted by the flash lamp is
used to excite the Nd3+ ions,while the rest heats up
the crystal. Thus,the system can be cooled by either air
or water circulation.

12. APPLICATION OF LASER
 (A) In industries, laser are applied to a
large extent for the following processes:
 (1) for welding and melting.
 (2) for cutting and drilling holes.
 (3) to test the quality of the materials.
 (4) for the heat treatment of metallic and non-metallic
materials.

13. (B) In medicine
 (1) used for the treatment of detached retinas.
 (2) used in performing micro and bloodless surgery.
 (3) used for the treatment of human and animal cancer
and skin tumours

14. (C) Military applications
 (1) the laser beam can serve as a war weapon,i.e., a
powerful laser beam can be used to destroy in a few
seconds, the big size objects like aeroplanes, missiles
etc.,by pointing the laser beam on to them. For this
reason, it can be even called as death ray.
 (2) the laser beam can be used to determine
precisely the distance, velocity and direction as well
as the size and from of distant objects by means of
the reflected signal.it is known as LIDAR.

15.  (D) science and engineering
applications
 (1)it is used in fiber optic communication.
 (2) communication between planets is possible with
laser.
 (3) it is used in holography.
 (4) it is used in underwater communication vetween
submarines, as they are not easily absorbed by water.
 (5) it is used to accelerate some chemical reactions.
 (6) it is used to create new chemical compound by
destroying atomic bonds between molecules.
 (7)it is uses to drill minute holes in cell walls without
damaging the cell itself.

16. Introduction about fiber optics…
 You hear about fiber-optic cables whenever
people talk about the telephone system, the
cable TV system or the Internet.
 Fiber-optic lines are strands of optically
pure glass as thin as a human hair that carry
digital information over long distances.
 They are also used in medical imaging and
mechanical engineering inspection.

17. What are Fiber Optics?
 If you look closely at a single optical fiber, you will
see that it has the following parts:
 Core - Thin glass center of the fiber where the
light travels
 Cladding - Outer optical material surrounding
the core that reflects the light back into the core
 Buffer coating - Plastic coating that protects
the fiber from damage and moisture

18. Fiber Optics….
plastic jacketglass or plastic
claddingfiber core
TOTAL INTERNAL REFLECTION

19. How Does an Optical Fiber Transmit
Light?
 The light in a fiber-optic cable travels through the
core (hallway) by constantly bouncing from the
cladding (mirror-lined walls), a principle called
total internal reflection.
 Because the cladding does not absorb any light
from the core, the light wave can travel great
distances.
 However, some of the light signal degrades within
the fiber, mostly due to impurities in the glass. The
extent that the signal degrades depends on the
purity of the glass and the wavelength of the
transmitted light

20. How Does an Optical Fiber Transmit Light?

21. Types of Fiber Optics….
* Single-mode fibers have small cores (about 3.5 x 10-
4 inches or 9 microns in diameter) and transmit
infrared laser light (wavelength = 1,300 to 1,550
nanometers).
* Multi-mode fibers have larger cores (about 2.5 x 10-3
inches or 62.5 microns in diameter) and transmit
infrared light (wavelength = 850 to 1,300 nm) from
light-emitting diodes (LEDs).

22. Advantages of Fiber Optics…..
Less expensive .
Thinner
Higher carrying capacity
Less signal degradation Light
signals Low power Digital signals
Non-flammable
Lightweight
Flexible Medical imaging

28. PH0101 UNIT 1 LECTURE 6 28
Piezo Electric Generator or
Oscillator……
Principle : Inverse piezo electric effect
 If mechanical pressure is applied to one pair of
opposite faces of certain crystals like quartz, equal
and opposite electrical charges appear across its
other faces.This is called as piezo-electric effect.
 The converse of piezo electric effect is also true.
 If an electric field is applied to one pair of faces,
the corresponding changes in the dimensions of
the other pair of faces of the crystal are
produced.This is known as inverse piezo electric
effect or electrostriction.

29. PH0101 UNIT 1 LECTURE 6 29
Construction
The circuit diagram is shown in Figure
Piezo electric oscillator

30. PH0101 UNIT 1 LECTURE 6 30
 The quartz crystal is placed between two metal
plates A and B.
 The plates are connected to the primary (L3) of a
transformer which is inductively coupled to the
electronics oscillator.
 The electronic oscillator circuit is a base tuned
oscillator circuit.
 The coils L1 and L2 of oscillator circuit are taken
from the secondary of a transformer T.
 The collector coil L2 is inductively coupled to base
coil L1.
 The coil L1 and variable capacitor C1 form the tank
circuit of the oscillator.

31. PH0101 UNIT 1 LECTURE 6 31
Working…..
 When H.T. battery is switched on, the oscillator produces high
frequency alternating voltages with a frequency.
 Due to the transformer action, an oscillatory e.m.f. is induced in the coil
L3. This high frequency alternating voltages are fed on the plates A and
B.
 Inverse piezo-electric effect takes place and the crystal contracts
and expands alternatively.The crystal is set into mechanical
vibrations.
 The frequency of the vibration is given by
n =
112
1
CL
f



Y
l
P
2
where P = 1,2,3,4 … etc. for fundamental,
first over tone, second over tone etc.,
Y = Young’s modulus of the crystal and
ρ = density of the crystal.

32. PH0101 UNIT 1 LECTURE 6 32
 The variable condenser C1 is adjusted such
that the frequency of the applied AC voltage
is equal to the natural frequency of the
quartz crystal, and thus resonance takes
place.
 The vibrating crystal produces longitudinal
ultrasonic waves of large amplitude.

33. PH0101 UNIT 1 LECTURE 6 33
Advantages
 Ultrasonic frequencies as high as 5 x 108Hz or 500
MHz can be obtained with this arrangement.
 The output of this oscillator is very high.
 It is not affected by temperature and humidity.
Disadvantages
 The cost of piezo electric quartz is very high
 The cutting and shaping of quartz crystal are very
complex.

34. PH0101 UNIT 1 LECTURE 6 34
(7) SONAR
 SONAR is a technique which stands for Sound
Navigation and Ranging.
 It uses ultrasonics for the detection and
identification of under water objects.
 The method consists of sending a powerful beam of
ultrasonics in the suspected direction in water.
 By noting the time interval between the emission
and receipt of beam after reflection, the distance of
the object can be easily calculated.
 The change in frequency of the echo signal due to
the Dopper effect helps to determine the velocity of
the body and its direction.

36. PH0101 UNIT 1 LECTURE 6 36
 Measuring the time interval (t) between the transmitted
pulses and the received pulse, the
distance between the transmitter and the remote
object is determined using the formula., where v is the
velocity of sound in sea water.
 The same principle is used to find the depth of the sea.
2
tv
d 
Applications of SONAR
1. Sonar is used in the location of shipwrecks and submarines
on the bottom of the sea.
2. It is used for fish-finding application .
3. It is used for seismic survey.