Introduction to Lasers Video Lecture - Civil Engineering (CE)

[Music]
introduction to laces at the end of this
lesson you will be able to we find the
characteristics of laser on comparison
with ordinary light explain the basic
principle and conditions for working of
laser explained absorption spontaneous
and stimulated emission in a two-level
system list the properties of laser the
field for darkness vanished when man
discovered fire till then man knew only
the natural sources of light later light
sauce evolved into different artificial
forms physicists had work to create
devices for producing powerful beam of
light this resulted in the invention of
lasers lasers are an important milestone
in the field of engineering in science
from a barcode scanner to include a
detection in high-security areas from a
projection pointer to Printers from
optical tweezers for handling delicate
matter to cutting off eye strength
materials from removing body art or
complicated I searchable lasers are
simply everywhere lasers have unique
characteristics different from ordinary
light this enables to produce highly
intense light focus to a small point
next let us discuss the basic principles
characteristics and working of a laser
the term laser is an acronym of light
amplification by stimulated emission of
radiation it is a device which produces
an intense beam of monochromatic and
coherent light
invention has some history so indeed
lasers
the basic principle of laser is based on
the einstein's theory of light proposed
in 1916 which was later developed by god
and gold in 1957 in 1960 the order may
man invented the first working Ruby
laser which was also the first optical
laser apart from solids such as Ruby
researchers have analyzed that some
materials like xenon helium or
semiconductors can also be used as laser
mediums different types of lasers have
been developed which enhanced the scope
of their applications the working and
principle of the laser is based on some
important features let us discuss about
them
the working principle of lasers is based
on spontaneous absorption spontaneous
emission stimulated emission and
population inversion absorption an atom
consists of different energy states let
us consider two different states of an
electron such as ground state he not an
excited state e^x electromagnetic energy
falls on an atom in the form of photon
of frequency is from the principle of
conservation of energy the
electromagnetic energy is given as the
difference of e^x and e not when the
photon energy falls on the electron it
jumps from the ground inor to the
excited state eh by absorbing the energy
this process of absorbing energy from
photons is known as absorption of
radiation spontaneous emission it is
known that electron absorbs energy and
moves from lower energy level e not to
the higher energy level e X but the
excited electrons that had jumped to the
higher energy state does not remain in
the same state for a long period and
comes back to its original ground state
he not by losing its energy in the form
of photons these photons are considered
as in coherent light as they do have any
correlation in phase thus the electrons
in the excited atoms are released on
their own from their higher energy state
to the ground state emitting photons
this is called as spontaneous emission
the mean life or lifetime of the excited
atom is the time for which it stays in
that state this is about 10 to the power
minus eight seconds the for spontaneous
emission
however the mean life for some excited
states is 10 to the power of five times
longer and such states are called as
metastable state and they play an
important role in laser operation
stimulated emission in this process the
atomists initially present in its
excited state e^x a photon of energy H s
can stimulate the atom to move to its
ground state he not
during this process the atom emits an
additional photon with the same energy
HF this process is called as stimulated
emission as it is triggered by an
external photon population inversion
generally in any atomic system the
number of atoms in the ground state is
more than that in the excited state this
is because of the tendency of electrons
to stay in the ground state but in order
for more photon to be emitted there
should be more electrons in the excited
state this process is achieved through
optical pumping and this occurrence is
known as population inversion the
transition electrons do not stay in an
excited state for a longer time but in
some systems the electrons remain in an
excited state for longer period these
systems are called as active systems or
media generally these active systems are
compounds or mixtures of different
elements
consider the ecosystem containing a
large number of atoms in thermal
equilibrium condition at a temperature T
before the system is subjected to any
radiation there are n naught number of
atoms present in their ground state with
energy e naught and a number and X are
in a state of higher energy X according
to Ludwig Boltzmann annex can be given
in terms of and not Y and X is equal to
n naught into e to the power of minus of
e X minus T naught divided by K T as the
temperature increases due to thermal
agitation mode number of atoms move to
the higher energy state e^x since X is
greater than T naught the Boltzmann
equation requires NX to be lesser than
and naught means there will be less
number of atoms in the excited state
compared to the ground state thus only
by thermal agitation the populations of
e^x can exceed that of Enoch suppose the
atoms are flooded with the photons of
energy X minus T naught then by
absorption by ground state atoms the
photons will disappear and atoms move
through excited state leading to
population inversion thus through
stimulated emission of excited state
atoms most number of photons will be
generated
showed that the probability is per
attend for absorption and stimulated
emission processes are identical thus
the net if it will be absorption of
photons when more atoms are in the
ground state when stimulated emission
dominates that is when more photons are
emitted than the absorbed photons the
laser light is produced the lasers have
certain unique characteristics that
enable the laser light to be focused
hundred times better than the ordinary
light these characteristics are mono
chromaticity coherence directionality
and sharp focus
let us discuss these in detail laser
lights are highly monochromatic it means
the laser beam is made up of a single
color or a single wavelength in contrast
the ordinary white light from an
incandescent light bulb is a combination
of many colors or wavelengths and is
certainly not monochromatic the laser is
highly coherent means a wavelength of
the laser light is in phase in space in
time this is because of the orderly
electronic transitions that take place
in laser
the laser-light can travel several
hundred kilometers long in space without
any destruction
whereas the corresponding coherence
length for wave trains emitted by
ordinary light is typically less than a
meter laser emits light that are highly
directional which means the light
emitted by the laser are relatively a
narrow beam in a specific direction
without dispersion
moreover the laser beam spreads very
little and thus can be focused sharply
but if you observe the ordinary light
bulb it emits light in many directions
away from the source
thus lasers with a unique
characteristics illuminate investigate
repaired transfer here and we take
certainly it is interesting to know
about the fundamentals of laser
technology as always you could connect
it in some form of application in
day-to-day life
this lesson we have learned laser or
light amplification by stimulated
emission of radiation is a device which
produces an intense beam of
monochromatic light the working of
lasers is based on absorption
spontaneous emission stimulated emission
and population inversion
crystals of lasers are mono chromaticity
coherence directionality and sharp focus