The document provides an overview of lasers, including: 1. It defines what a laser is, describing the acronym LASER and how lasers emit a useful form of light energy. 2. It discusses the history and development of lasers, including milestones such as the first laser built in 1960 and early medical uses starting in 1963. 3. It describes the key principles and components of how lasers work, including stimulated emission, the pumping system, and optical cavity that contains the lasing medium.

1. Principle and Application
of
LASER

2. Presentation Layout
•Introduction
•History
•Laser action
•Principle
•Types of Laser
•Applications

3. What is Laser?
LASER is an acronym for:
L : Light
A : Amplification (by)
S : Stimulated
E : Emission (of)
R : Radiation
Term coined by Gordon Gould.
Laser means to absorb energy in one form and to emit a new
form of light energy which is more useful.

4. LASER history
• 1917 -Sir Albert Einstein created the foundations for the
laser.
• 1958 - C.H. Townes, A.L. Schawlow: Theoretical basis for
lasers.

5. 1960 –dr. Theodore Maiman : Built first laser
by using a ruby crystal medium .

6. •1963 - C. Zweng: First medical
laser trial (retinal coagulation).
• 1965 - W.Z. Yarn: First clinical
laser surgery.
•1970- The excimer laser was
invented in by Nikolai Basov
• 1971 -Neodymium yttrium
aluminum garnet
(Nd.YAG) and Krypton
laser developed.

7. LASER Vs. LIGHT
LASER
Stimulated emission
Monochromatic.
Highly energized
Parallelism
Coherence
Can be sharply focussed.
LIGHT
Spontaneous emission.
Polychromatic.
Poorly energized.
Highly divergence
Not coherent
Can not be sharply
focussed.

8. LASER PHYSICS
• Light as electromagnetic waves, emitting radiant energy
in tiny package called ‘quanta’/photon. Each photon has
a characteristic frequency and its energy is proportional
to its frequency.
• Three basic ways for photons and atoms to interact:
Absorption
Spontaneous Emission
Stimulated Emission

9. Mechanisms of Light Emission
Atomic systems in thermal equilibrium with their
surrounding, the emission of light is the result of:
Absorption
And subsequently, spontaneous emission of energy
There is another process whereby the atom in an upper
energy level can be triggered or stimulated in phase with
the an incoming photon. This process is:
Stimulated emission
Is an important process for laser action
1. Absorption
2. Spontaneous Emission
3. Stimulated Emission
Therefore 3 process
of light emission:

10. Absorption
E1
E2

11. Spontaneous Emission

12. Stimulated Emission

13. Metastable state
•Energy states having mean life time
(average time for which the excited
atom stays in it’s excited state) for
more than 10-3 seconds.
•Population Inversion:
It is the state at which the atom
in excited state(metastable state) is
higher in no. than the ground state.

15. Characteristics of LASER
• Lasers are concentrated beams of light which can
very precisely cut, seal and even vaporize tissue.
1. Monochromatic
2. Collimated
3. Directional
4. Coherence

16. 1.Monochromatic

17. 2.Collimated

18. 3.Directional

19. 4.Coherence

20. General construction of LASER
•Laser consists of three major components:
1. Lasing material: solid,liquid or gas
2. A pumping system: optical,electric or chemical
Provides energy required to lase the material
3.Optical cavity: contains lasing materials bounded
by mirrors at each end of cavity

22. Contd…
• Totally reflecting(100%)
• Partially reflecting(99%)
• Coherent light escape from the cavity, return
back after reflection and produce more
stimulated emission
• Leads to amplification
• Laser beam is emitted through partially reflecting
mirror

23. CLASSIFICATION OF LASER
• Solid State
Ruby
Nd.Yag
Erbium.YAG
• Gas
Ion
Argon
Krypton
He-Neon
CO2
• Metal Vapour
Cu
Gold
 Dye
Rhodamine
 Excimer
Argon Fluoride
Krypton Fluoride
Krypton Chloride
 Diode
Gallium-Aluminum
Arsenide (GaAlAs)

25. LASER TISSUE INTERACTION
LASER
TISSUE
Thermal
Effect
Photo-
chemical
Ionizing
Effect
 Photocoagulation  Photoradation
 Photodisruption  Photoablation
 Photovaporization

26. Thermal effect
(1) Photocoagulation:
Laser Light

Target Tissue

Generate Heat

Denatures Proteins
(Coagulation)
Rise in temperature of about 10 to 20 0C will cause
coagulation of tissue.

27. Contd…
(2) Photodisruption:
Mechanical Effect:
• Laser Light

Optical Breakdown

Vapor

Quickly Collapses

Acoustic Shockwaves

Tissue Damage

28. 3.Photovaporization
• Vaporization of tissue to CO2 and water occurs
when its temperature rise 60—100 0C or greater.
• Commonly used CO2

Absorbed by water of cells

Visible vapor (vaporization)
 
Heat Cell disintegration
 
Cauterization Incision

29. Photochemical effect
1. PHOTORADIATION (PDT):
• Also called Photodynamic Therapy
• Photochemical reaction following visible/infrared
light particularly after administration of exogenous
chromophore.
• Commonly used photosensitizers:
 Hematoporphyrin
 Benzaporphyrin Derivatives
e.g. Treatment of ocular tumour and CNV

30. Photon + Photosensitizer in ground state (S)

3S (high energy triplet stage)

Energy Transfer
 
Molecular Oxygen Free Radical
S + O2 (singlet oxygen) Cytotoxic
Intermediate
 
Cell Damage, Vascular Damage , Immunologic
Damage

31. Contd…
2.PHOTOABLATION:
Breaks the chemical bonds that hold
tissue together essentially vaporizing the tissue,
e.g. Photorefractive Keratectomy, Argon Fluoride
(ArF) Excimer Laser.
Usually -
Visible Wavelength : Photocoagulation
Ultraviolet Yields : Photoablation
Infrared : Photodisruption
Photocoagulation

32. IONISING EFFECT
• Highly energized focal laser beam is delivered on tissue over a
period of nanosecond or picoseconds and produce plasma in
target tissue.
• Q Switching Nd.Yag

Ionization (Plasma formation)

Absorption of photon by plasma

Increase in temperature and
expansion of supersonic velocity

Shock wave production  Tissue Disruption

33. MODES OF LASER OPERATION
• Continuous Wave (CW) Laser:
It deliver their energy in a continuous stream
of photons.
• Pulsed Lasers:
Produce energy pulses of a few tens of micro to few mili
second.
• Q Switches Lasers:
Deliver energy pulses of extremely short duration (nano
second).

34. Contd…
• A Mode-locked Lasers: Emits a train of short
duration pulses (picoseconds).
• Fundamental System: Optical condition in which
only one type of wave is oscillating in the laser
cavity.
• Multimode system: Large number of waves, each
in a slight different direction ,oscillate in laser
cavity.

35. LASER TISSUE
INTERACTION
LASER VARIABLE:
 Wavelength
 Spot Size
 Power
 Duration
TISSUE VARIABLE:
 Transparency
 Pigmentation
 Water Content

36. LASER IN ANTERIOR SEGMENT
CORNEA:
Laser in Keratorefractive Surgery:
• Photo Refractive Keratectomy (PRK)
• Laser in situ Keratomileusis (LASIK)
• Laser Subepithelial Keratectomy (LASEK)
• Epi Lasik
Laser Thermal Keratoplasty
Corneal Neovascularization
Retrocorneal Pigmented Plaques
Laser Asepsis

37. •Laser in lens:
•Posterior capsulotomy(YAG)
•Laser phacoemulcification
•Phacoablation
•Laser in vitreous:
•Vitreous membranes
•Vitreous traction bands

38. LASER IN GLAUCOMA
Laser Iridotomy,
Laser Iredectomy
Laser
Trabeculoplasty
(LT)
Selective Laser
Trabeculoplasty

39. LASER TREATMENT OF
FUNDUS DISORDERS
Diabetic Retinopathy
Retinal Vascular Diseases
Choroidal Neovascularization (CNV)
Clinical Significant Macular Edema (CSME)
Central Serous Retinopathy (CSR)
Retinal Break/Detachment
Tumour

40. COMPLICATION OF LASER
TREATMENT
 Pain
 Seizure
 Choroidal & retinal
detachment
 Foveal Burn
Increased IOP
Corneal Damage
Iris Burn
Cataract
InternalOphthalmoplegia

41. LASER HAZARDS
EYE
• Small lesion to extensive hemorrhage
• Disruption of retina and choroid
• Immediate loss of vision
• Epi-retinal membrane formation
• Macular hole, gliosis

42. Complications of Laser treatment in Eye
•Lids and adnexae: Ecchymosis, retrobulbar and
subconjunctival haemorrhage
•Cornea: punctate erosion, edema, corneal burns,
opacification
•Iris: sphincter damage, haemorrhage
rupture
•Lens: opacification

43. Contd…
•Viterous: opacification, hemorrhage, choroidal
neo-vascularization
•Retina: hemorrhage, receptor layer and nerve
fibre damage
•Optic nerve: neuritis, nerve fibre damage

44. PREVENTION OF LASER HAZARDS
Engineering Control Measure:
laser housing
filters and shutter for
safe observer viewing
Personal protective devices,
like protective eye wear or
goggles with side shields,
protective clothes may be
included.

45. Other uses of LASER
•Cosmetic Sugery
•Removing tattoos, scars, stretch marks,
sunspots, wrinkles,birthmarks
•Laser hair removal

46. Dentistry
•caries removal
•endodontic/periodontic
procedures
•tooth whitening
•oral surgery
•laser scalpel

47. In Industry
•To drill tiny holes in hard
materials
•For welding and machining
•For lining up equipments
precisely
•To measure the distance of
tunnel

48. In everyday life
•To be used as bar code
readers
•To be used in compact
disc players
•To produce short pulses
of light used in digital
communication

49. Holography
•Is the production of holograms by
the use of laser
Hologram is a 3D image recorded in
a special photographic plate.
The image appears to float in
space and to move when viewer
moves
Research:
Used to measure the speed of light
in a laboratory

51. MCQS
1) Which is not a characteristics of
LASER light?
A) stimulated emission
B) spontaneous emission
C) collimated
D) monochromatic

52. 2) ND: YAG Capsulotomy is done by
LASER having wavelength …
A) 1064 nm
B) 555 nm
C) 193 nm
D) 1 micron

53. 3) In metastable state excited electron
stays for a time about…
A) 0.1 sec
B)0.01 sec
C)0.001 sec
D) 0.0001 sec

54. 4) In photoablation, temperature of a
tissue increases by…degree Celsius
A) 10-20
B) 60-100
C) upto 2000
D) zero

55. 5) Iridotomy is done for…
A) cosmetic purpose
B) treat ACG
C) to dilate pupillary area
D) to relax accommodation

56. References
•Clinical procedures in optometry
•Optics
A.H. Tunacliffe
•Environmental Vision
Donald G. Pitts
Robert N. Kleinstein
•Internet