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1. LASER AND APPLICATIONS
Submitted by:
ARUN T A
ROLL NO: 07
Dept. Instrumentation
CUSAT

2. INTRODUCTION
• Lasers have truly been the one of the greatest invention in 20th
century.
• They have found a variety of uses in electronics, computer
hardware, madicine, industry, military and experimental
science.
• In 1917, Albert Einstein first theorized about the process
which makes lasers possible called “stimulated emission”.
• The laser beam was invented by phycist Maiman in 1960.
• The laser stands for Light Amplification by Stimulated
Emission of radiation

3. CONTD….
• The basic operating principles of the laser were put forth by
Charles Townes and Arthur Schalow from the Bell Telephone
Laboratories in 1958, and the first actual laser, based on a pink
ruby crystal, was demonstrated in 1960 by Theodor Maiman at
Hughes Research Laboratories.
• Laser is a device that emits light through a process of optical
amplification based on the stimulated emission of
electromagnetic radiation.
• A laser differ from other sources of light beacause it emits
light coherently
• In coherent beam of electromagnetic energy, all the waves
have the same frequency and phase.

4. PROPERTIES OF LASER
• Monochromatic:
It means that it consist of one color or wavelength.
• Divergence and directionality:
it means that the beam is well collimated and travels long
distance with very little spread.
• Coherence:
it means that all the individual waves of light are moving
preciesly together through time and space.
• Brightness:
The radiance of laser is an important factor. It is defined as the
power emitted per unit surface area per unit solid angle.

5. Construction of laser
• A laser mainly requires three components for its operation: (a)
an active medium in the form of a laser rod, with energy levels
that can be selectively populated; (b) a pumping process to
produce population inversion between some of these energy
levels; and (c) a resonant cavity containing the active medium
which serves to store the emitted radiation and provides
feedback to maintain the coherence of the radiation.

6. CONTD….
• Pump light may be provided by flash lamp or by another laser.
• The most common type of laser uses feedback from an optical
cavity which is designed to internally reflect IR or UV waves
so they reinforces each other.
• At each end of the cavity, there is a mirror. One mirror is
totally reflective and other mirror is partially reflective.
• Depending the design of the cavity the light coming out of the
laser may spread out or form a narrow beam.

7. Principle of laser action
The principle of a laser is based on four separate features:
• Absorption
• Spontanious emission
• Stimulated emission
• Population inversion

8. Contd….
Absorption :
• In absorption an incoming photon excites the atomic system
from a lower energy state into higher energy state.
• It occurs when a photon strikes an atom with just exactly the
proper energy to induce an electronic transition between two
energy states.

9. Contd….
Spontanious emission:
• it takes place when an electron in a higher energy level drops
down to a lower energy level and a photon is emitted with an
energy equal to the energy difference between the two levels.

10. Contd….
Stimulated emission:
• It takes place when a photon with an energy equal to the
energy difference between two levels interacts with the
electron in the higher energy level

11. Population inversion
• population inversion is when more atoms are in an excited
state than in their ground state.
• It is necessery condition to sustain a laser beam, so that there
are enough excited atoms, that can be stimulated to emit more
photons.
• To achieve non-equilibrium conditions, an indirect method of
populating the excited state must be used which is done using
a three level laser and a four level laser.

12. Three level & four level laser
• Three level laser:

13. CONTD….
• Four level laser:

14. Types of laser
The most important and known types of laser are classified as:
• Solid state laser
• Gas laser
• Semiconductor laser
• Dye laser

15. SOLID STATE LASER
• Ruby laser
• Nd – YAG laser
• Nd – Glass laser

16. Ruby laser:
The important type of solid state laser is the ruby laser.
• Ruby laser is historically the first one to be discovered.
• It consist of a ruby rod , xenon flash tube, a suitable cavity to
reflect the light from flash tube to the ruby rod, and high
voltage power upply to give electrical energy to the flash tube.

17. Contd….
• The laser is a three level system only three energy levels are
involved in the process of stimulated emission.
• The population inversion is achieved by exciting the atoms
with intense light from a xenon flash lamp.
• Thus the atoms are excited from ground state to the upper state
by means of absorption.

18. Nd – YAG laser:

19. CONTD….
• YAG is formed from a mixed oxide system having a
composition of Y3Al5OI2.
• Using Czochralski method, the crystal is grown in a specially
designed furnace by dipping a rotating seed into a crucible of
molten material and withdrawing it at a constant speed.
• Iridium crucible is used because of high melting point of YAG
(1910-1970°C).
• the YAG host has the advantage of having a relatively high
thermal conductivity to dissipate the heat generated, thus
allowing these crystals to be operated at high repetition rates
of the order of many pulses per second. With a continuous
source of excitation like tungsten lamp or krypton arc lamp,
continuous laser output of about 1 kW power could be
obtained.

20. • Due to these excellent properties, Nd: YAG laser is
extensively used in many industrial applications like drilling of
holes in solid objects, welding of metals and alloys, etc, and
also in medical applications like eye surgery, treatment of
cancer, etc.

21. Nd – Glass laser:
• Nd: glass is an important laser material for high energy
applications.
• It affords considerable flexibility in size and shape and can be
obtained in large homogeneous spices. Glass is a compound of
oxides; the non-metal oxides, such silicon dioxide, phosphorus
pent oxide and boron oxides are its main constituents.
• The major disadvantage of glass is that it produces in
homogeneously broadened lines which are wider than those
found in crystals . This raises the threshold, as a larger
Inversion is required for the same gain.
• Another disadvantage of glass is its low thermal conductivity.

22. GAS LASERS
• It has gas or a mixture of gasese as their light amplifying
substance.
• It is much cheaper than solid state lasers and yields highly
coherent radiation required for many applications.
• The gas lasers are of continuous type and normally have high
coherence.
• He – Ne and carbon dioxide lasers are most widely used gas
lasers.

23. He – Ne laser:
• The helium-neon laser is the most widely used of all lasers
mainly because it is much cheaper than the solid-state lasers
and yields highly coherent radiation required for many
applications.

24. CONTD….
• In this system, an electrical discharge is given in helium
contained in a discharge tube at a pressure of about 1 torr with
an admixure of neon at about 0.1torr.
• The discharge excites the He atoms to their first excited level
above their ground state.
• Then the excited energy of the helium atom is transferred to
the Ne atoms by resonance transfer due to collision between
them.
• These excited states radiatively to lower energy neon state
giving rise to continuous laser beam

25. Carbon dioxide laser:
• It is a very important laser because of its high efficiency and
high power capacity.
• It is a molecular gas discharge with the laser action taking
place between two vibrational level of carbon dioxide gas.
• A suitable mixure of carbon dioxide, nitrogen, and helium
gases is taken in a gas discharge tube and excited electrically
with the help of a power supply.
• The nitrogen molecules are excited to their first excited the
lowervibrational levels giving rise to laser radiation.
• The helium gas helps to populate the upper state but also
assists to empty the lower state of carbon dioxide, thus
increasing the efficiency of carbon dioxide laser.

26. CONTD….
• The carbon dioxide laser is used for a wide variety of
applications, including eye and tissue surgery, welding, cutting
and heat treatment of materials, laser fusion, and beam
weapons. Rock sand granites crumble into pieces with a 1.2
kW carbon dioxide laser. One day, such a laser may be used to
drill underground tunnels.

27. Dye laser:
• Liquid lasers are similar to the solid-state lasers.
• Dyes exhibit a very high degree of fluorescence.
• Different dyes have different emission spectra or colors.
• Dye lasers cover a broad wavelength range from the ultraviolet
at320 nm to the infrared at about 1500 nm.
• The dye laser output can be a very narrow frequency beam.

28. CONTD….
• important application of dye lasers is for producing ultra short
optical pulses.
• The dye lasers are less expensive than the solid-state lasers and
are relatively easy to maintain for regular operation.

29. Semiconductor laser:
• It is based on the principle of electron hole recombination in a
direct band gap semiconductor which results in emission of
photons.
• It consists of a p-n junction in which p and n regions are
heavily doped. Each side of the laser is the order of 1 mm. the
width of p-n junction layer is 1 micrometer.

30. CONTD….

31. APPLICATION OF LASERS:
• Biomedical applications
• Industrial applications
• Other applications

32. Biomedical applications:
Flow cytometry:
• Flow cytometry is a technique used for measuring single cells.
• Not only is it a key research tool for cancer and immunoassay
disease research, but it is also used in the food industry for
monitoring natural beverage drinks for bacterial content or
other disease-causing microbes.

33. • In a basic cytometer, the cells flow, one at a time, through a
capillary or flow cell where they are exposed to a focused
beam of laser light.

34. CONTD….
• The cell then scatters the light energy onto a detector or array
of detectors. The pattern and intensity of the scattered energy
helps to determine the cell size, and shape.
• In many cases the cells are tagged with a variety of
fluorochromes designed to selectively adhere to cells or cell
components with specific characteristics.
• This is used in many systems to assist with separation or
sorting of cells or cellular components.
• The most popular lasers used in flow cytometry are the 488-
nm (blue) argon-ion laser and the 632-nm (red) and 594-nm
(yellow) He-Ne lasers. However, new violet, blue and red
diode lasers and a variety of new DPSS lasers are entering the
field.

35. Surgical Applications:
• Lasers are used in a variety of surgical and dental procedures
from cutting tissue, vaporizing tumors, removing tattoos,
removing plaque, removing cavities, removing hair and
follicles, resurfacing of skin and correcting vision.
• Ultraviolet excimer lasers are used for vision correction
because they can removing material from the lens of the eye
without causing thermal damage which could blur vision or
make the lens opaque.
• Ruby lasers are used for tattoo removal because many of the
dyes break down when exposed to 694-nm radiation, yet the
skin tissue is left undamaged.

36. CONTD….
• Cosmetic treatment of wrinkles, moles, warts, and
discolorations (birth marks) is often accomplished with near
infrared and infrared lasers.
• Lasers are also used to treat macular degeneration, an
overgrowth of veins and scar tissue in the retinal region, a
condition associated with advancing age. In this procedure, the
patient is injected with a selective dye, which enhances the
absorption of laser light by the blood in the blood vessels.
When the blood vessels absorb laser energy, they wither in
size, uncovering the active retina.
• A multi watt green DPSS laser is most commonly used for this
application because the green wavelength is not absorbed by
the lens or aqueous portion of the eye, which allows the laser
to affect only the targeted veins.

37. Industrial Applications:
• Laser Cutting
• Laser Drilling
• Laser Welding
• Laser glass decoration
• Laser marking

38. Laser cutting:
• Continuous wave lasers like carbon dioxide gas lasers are
extensively used for cutting a wide range of materials, such as
graphite, diamond, tungsten, carbide, all metallic foils,
ceramics, sapphire, and ferrite.
• In most cases, continuous cutting is carried out with assist
gases like oxygen, carbon dioxide, or air, which produces both
mechanical and chemical action intensifying the thermal
effects.
• This gas-assisted cutting is applicable to the metals of
thickness up to 5mmwith cut-widths down to 30 μm.
• The most promising field of laser cutting is the cutting of
steels of small thickness (several millimeters) and also of non-
metallic materials.
• Use of laser cutters in the garment industry, a new and very
useful application of the lasers, has been introduced recently in
the developed countries. With the aid of computers, lasers can
cut clothing many times faster than the tailors using old
techniques.

39. Laser Drilling:
• Laser drilling of metals is based on a face-heating
phenomenon.
• Laser enables drilling of a diamond die in a few minutes as
against 20 hours taken by conventional methods.
• Laser light energy is primarily applied in effecting micro
openings in rubies and diamonds.
• The plus point about laser drilling is that it does not cause any
damage to the diamond or any other processed material.

40. CONTD….
• For laser drilling, usually pulsed carbon dioxide, Nd:YAG or
alexandrite laser is used.

41. Laser Welding:
• This process utilizes mostly the continuous lasers of the
infraredCO2 spectrum and the Nd:YAG lasers, of a
wavelength of 10.6 nm and1.06 nm, respectively.
• The advantage of laser welding rests in the absence of physical
contact with the electrode, in localized heating and cooling, in
welding parts in a protective atmosphere or sealed into
optically transparent material .
• Lasers can weld, e.g., air-tight shields of miniature relays,
pacemakers, contacts in microelectronics, and metal sheets in
car or aircraft industry.

42. Laser glass decoration:
• It is a modification of laser cutting. At the spot focused laser
beam impinges upon the glass surface, the melted glass will
evaporate and cracks will appear on its surface. They will
diffuse light, producing thus a shiny effect of the lasered
ornament. Glass is decorated by lasers whose radiation is
easily absorbed by the glass, e.g., by the continousCO2 laser.

43. Laser Marking:
• It is based on local surface evaporation of the object material.
• In this case, the laser beam passes through a template with the
desired pattern.
• The depth of the marking usually ranges between fractions and
units of millimeters, the thickness being of the order of
micrometers.
• This technique is performed by the powerful pulse laser of
pulse energy up to tens of joules, or by the continuous laser,
i.e., the Nd:YAG or excimer laser.
• The advantage of laser marking is the non-contact process,
eliminating any possible stresses and strains in the lasered
material.

44. Other applications:
• Laser radar in ecology – LIDAR
• Laser Range Finder
• Ring Laser Gyroscope

45. Laser radar in ecology – LIDAR:
• Ground laser radars are used in ecology to measure air
pollution.
• In this case it is both reflection and scattering that are made
use of in measurements.
• Passing through the atmosphere, the laser pulse is scattered by
the molecules and aerosols present there, causing Mie,
Raleigh, or Raman scattering.
• Part of the radiation scattered backwards is concentrated by a
telescope, and passing through a filter detected by a photo
detector.
• The received signal, whose amplitude at any moment is
proportional to the intensity of the scattered radiation is
recorded as a function of time, due to which it is possible to
obtain also the distance of the scattering body, while the filter
width and/or the attached spectrometer determine the spectrum
of the received signal.

46. CONTD….
• LIDAR serves to monitor the distribution and direction of
smoke trails; to measure the bottom level and profile of clouds,
of atmospheric turbulence, distribution and areas of various
emissions in the atmosphere, etc.

47. Laser Range Finder:
• To knock down an enemy tank, it is necessary to range it very
accurately.
• Because of its high intensity and very low divergence even
after travelling quite a few kilometers, lasers ideally suited for
this purpose.
• The laser range finders using neodymium and carbon dioxide
lasers have become a standard item for artillery and tanks.
• These laser rangefinders are light weight and have higher
reliability and superior range accuracy as compared to the
conventional range finders. The laser range finder works on
the principle of radar.

48. CONTD….
• It makes use of the characteristic properties of the laser beam,
namely, monochromaticity, high intensity, coherency, and
directionality.
• A collimated pulse of the laser beam is directed towards a
target and the reflected 1ight from the target is received by an
optical system and detected.
• The time taken by the laser beam for the to and fro travel from
the transmitter to the target is measured. When half of the time
thus recorded is multiplied by the velocity of light, the product
gives the range, i.e., the distance of the target.

49. CONTD….
• The laser range finder is superior to microwave radar as the
former provides better collimation or directivity which makes
high angular resolution possible.
• The advantage of greater radiant brightness and the fact that
this brightness is highly directional even after travelling long
distances, the size of the emitting system is greatly reduced.
• The high monochromaticity permits the use of optical band
pass filter in the receiver circuit to discriminate between the
signal and the stray light noise.

50. Ring Laser Gyroscope:
• The ring laser gyroscope is an extremely useful instrument for
sensing and measuring very small angles of rotation of the
moving objects.
• The main advantages of the ring laser gyroscope are: (I) non-
existence of moving parts, (ii) high capability, and (iii) higher
reliability as compared to the mechanical gyroscope.
• the laser gyroscope is capable of wide dynamic range and
rapid reaction time, the characteristics required for missile
guidance.

52. • The ring laser gyroscope basically consists of a ring cavity
around which two laser light beams travel in opposite
directions. The operation of the ring laser gyroscopes is based
on the so called Signac effect by which rotation of an object is
sensed by an interferometric technique.
• In a triangular cavity of a quartz block, laser beam is split into
two light beams with the help of suitable mirrors. These two
light beam travel in opposite directions in the same path of the
cavity, one in the clockwise and the other in the anti-clockwise
direction.
• The two light beams then pass through a beam splitter and a
beam combiner, behind which a readout detector is placed.
• If the cavity which is acting as an interferometer is stationary,
the two light beams travel the same distance in the opposite
directions without any path difference and hence no
interference takes place.

53. CONTD….
• if the block is rotated clockwise about an axis through the
centre and perpendicular to the plane of the interferometer, the
beam travelling in the clockwise direction travels a path length
slightly more than the beam travelling in the anti-clockwise
direction.
• When these two light beams recombine at the beam combining
prism, interference takes place due to the path difference; the
interference fringes displaced in the field of view are
proportional to the amount of rotation of the block.
• The laser gyroscope uses a helium-neon gas laser to generate
monochromatic radiation in the two directions inside the
triangular quartz block.

54. CONTD….
• Two photo detectors sense the direction and the rate of
rotation. The output is proportional to the input angle. The
whole system is a single plane, rate integrating gyroscope and
is capable of measuring rotation rates of the order of 1/10,000
degree/hour.
• The main use of the ring laser gyroscope is for inertial
navigation. It is being used in inertial guidance of aircraft,
ships, and missiles; flight control; and gun-fire pointing.

55. CONCLUSION:
• A laser is a device that emits electromagnetic radiation through
a process of amplification based on the stimulated emission of
photons.
• The wavelength of laser light is extremely pure when
compared to other light sources and all of the photons that
make up the laser beam have a fixed phase relationship with
respect to one another.
• Laser is a powerful source of light having extraordinary
properties which are not found in the normal light sources like
tungsten lamps, mercury lamps etc.
• The unique property of laser is that its light waves travel very
long distances with very little divergence.

56. CONTD….
• More detailed attention has been paid here only to those fields
where lasers are used at present. Based on these laser
techniques, some new ones are being developed, as, e.g., for
the laser ranging device to be used in cars of the future: the
built-in laser radar plus automatic control will keep a safe
distance between cars. The spectrally defined laser interaction
with matter is made use of in art restorations to remove the dirt
from old paintings and statues, as well as in routine
maintenance and cleaning of the outer skin of ships and
aircraft. It is true that lasers have become irreplaceable and
research into their applications still continues.

57. THANK YOU