The document discusses lasers, including their principle, construction, types, and uses. It begins by explaining that a laser works by stimulating electrons to produce coherent and monochromatic photons through population inversion. The key components of a laser are a pump source to cause excitation, a gain medium such as gas or solid, and an optical resonator with mirrors. Common medical lasers described include CO2, Nd:YAG, diode, and excimer lasers used for procedures like photocoagulation, photodisruption, and photoablation. Industrial and scientific uses as well as laser safety are also covered at a high level.

1. LASER
Raju Kaiti, M. Optom
consultant Optometrist
NEH

2. LASER (Principle, Nature & Application)
• LASER – acronym for
Light Amplification by Stimulated Emission of Radiation
• LASER coined – Gordon Gould
• Albert Einstein (1917) – explained basic physical process –
Stimulated Emission
• Theoddore Maiman (1960) – Built first LASER

4. Light – Photon (wave Packets)
Energy (E) = h * f
where, H is planck’s constant and f is the frequency
-Atom – nucleus at the center and electrons revolving round
round the specific orbits along with other empty orbits that
electron could potentially occupy
- Each orbit has specific energy level, so to jump from one
orbit to another an electron must gain or loose energy

5. Every atom always tends to remain in lowest Energy Level (ground
state)
Get energy- Excited state – Ground state by losing energy in the
form of photon

6. Stimulated emission

7. POPULATION INVERSION
• Precondition of laser action
• Electrons will normally reside
in lower available energy state
• Absorption lead to electrons
in the excited state
• No significant collection of
electrons in higher states due
to spontaneous emission

8. • Life time of typical excited =10-8
sec
• Material is induced to have majority of atoms
in the higher excited state i.e N2>N1

9. General construction of laser
• Population inversion is
necessary
• 3 principal parts
Pump source
Gain medium
Optical resonator

10. Pump source
• Can be
Chemical reaction
Electric discharge
Light from another laser
• Depend upon gain medium
• Chain of stimulation emission occur
• Excites lasing medium into population inversion

11. Gain Medium
• Solid: Crystall & glass
• Liquid :Organic solvent, Glycol
• Gases :CO2, Ar, Kr. He-Ne
• Semiconductor

12. Optical resonator
• Two mirrors are placed at each end of the cavity –
- totally reflecting (100%)
- Partially (99%)
- Coherent light escape from the cavity return back after
reflection and produce more stimulated emission.
• leads to Amplification
Small amount of light pass through partially reflecting mirror
-LASER

13. Contd..

14. Production

15. Charecteristics of laser light
1. Coherence : as the radiation is produced by the
single stimulus they have same phase difference,
importance in holography
2. Monochromatic :as the light of laser comes from
the same atom transition it has a single wavelength
,depends upon the type of material

16. • Collimated :because of bouncing of radiations between the
mirrors ,becomes perpendicular to the mirror and while
emerging from the cavity are collimated or parallel and not
much spreaded.
• Directional

17. Monochromatic

18. Collimated

19. Directional

20. Coherence

21. Types of Laser
• According to their sources:
• Gas Lasers
• Crystal Lasers
• Semiconductors Lasers
• Liquid Lasers
• According to the nature of emission:
• Continuous Wave
• Pulsed Laser
• According to their wavelength:
• Visible Region
• Infrared Region
• Ultraviolet Region

23. LASER-TISSUE INTERACTIONLASER-TISSUE INTERACTION
 PHOTORADIATIONPHOTORADIATION
 PHOTOCOAGULATIONPHOTOCOAGULATION
 PHOTOVAPORIZATIONPHOTOVAPORIZATION
 PHOTODISRUPTIONPHOTODISRUPTION
 PHOTOABLATIONPHOTOABLATION

24. PHOTORADIATION/ PhotodynamicsPHOTORADIATION/ Photodynamics
• Occurs when tissue temperature is raised from 37-380
c
• To treat tumors
• Uses photosensitizing agent
• Photosensitizing material causes light induced reaction
in molecule that doesn’t absorb light

25. PHOTOCOAGULATIONPHOTOCOAGULATION
•Occurs when tissue temperature is raised from
37-650
c
•Causes thermal damage that causes
denaturation of protein
•4 changes occur
– Scar- cause tissue to bind or adhere
– Tissue atrophy
– Collagen and smooth muscle contraction
– Blockage of blood vessels

26. • Ocular examples of photocoagulation
– Pan retinal photocoagulation
– Trabeculoplasty
– Peripheral iridectomy
– t/t of choroidal neovascular membrane
– Sealing of holes in RD

28. PhotovaporisationPhotovaporisation
• Occurs when tissue temperature is raised from 37-1000
c
• Target tissue is converted to water vapour and smoke
• Treat malignant tumor of choroid or retina

29. PHOTODISRUPTIONPHOTODISRUPTION
• Occurs when tissue
temperature is raised from
37-20,0000
c
• Cause transient shock wave
which cause tissue damage
due to mechanical stress
• Ocular example
– Nd- YAG capsulotomy

30. PHOTOABLATION
• Breaks intramolecular
bond by high energy
photon
• Affected tissue
disappear from affected
area
• Ocular examples
– Photorefractive
keratectomy
– LASIK

31. TYPES
A. SOLID
1)Ruby laser
•1st
type of laser
•Chromium ion is active ingredient
•As pulsed laser, red light=694.3nm
•3 energy levels
2) Nd-YAG
•4 energy levels
•Neodymium added to YAG
•1064nm,high powers

32. 3) Semiconductor lasers
• Diode laser
• Used in data processing and fibre optics
• Gallium arsenide-infrared fine for fibres
•
B. GAS LASERS:
1)He-Ne laser:
• Widely used
• 5 parts He and 1 part Ne pressure of 1 mm Hg
• Common and inexpensive
• 623nm, 543.5nm and 1523nm

33. 2) CO2 laser
• Continuous output
• IR frequencies
• N2 as pumping gas
• Cutting and Welding
3) Argon lasers
• Continuous output in 25 different wavelengths
• Much higher than He-Ne laser

34. C)Dye laser: mostly liquid laser
Widely used dye rhodamine 6G
Often combines with michelson interferometer
D)Excimer laser: excited dimer
Active medium is the diatomic molecule
In submarines
LASIK
E)free electron laser:
Wide range of frequencies
Types contd…..

36. Laser in ophthalmic Use
• Nd- YAG
• Semiconductor/Diode
• Argon
• Krypton
• Excimer

37. Nd- YAG LASER
• Principle: Photo disruption
• Wavelength:1063 nm
• Composition: Neodymium:Yttrium Aluminum Garnet
Use : YAG Capsulotomies

38. Argon laser
• Argon laser- 488nm and 514.5 nm
• Use:
Choroidal neovascular membranes
panretinal photocoagulation

39. Krypton Laser
• Wavelength:521, 568 , 647 nm
• Principle: photocoagulation
• Preferred for retinal problem

40. Excimer laser
• Excited dimer laser
• Xenon+Halogen-------Xe(halogen)8
• Emit photons of 193 nm under high pressure.
• Principle: Photoablation
• Used for
Photorefractive keratectomy
LASIK
Band keratopathies.

41. DIODE LASERS
• Use semi conductors
• Used in ocular oncology like
melanoma
retinoblastoma.

42. Three Basic Ways for Photon and Atom Interaction
• Absorption – Electron can absorb passing photon
to jump into higher energy level
• Spontaneous emission – Electron in high energy state
spontaneously drop down to lower energy state and create
photon.
E= energy difference betwn two orbits

43. Stimuated Emission-
Passing photon at the vicinity of atom stimulates the electron to drop
and emit photon
Excited atom is struck by photon of same
energy as the photon to be emitted
Frequency of stimulating photon and emitted photon is same along with
phase – Two Photons are coherent

44. How LASER - Produced
• Gases, liquid and solids – working materials
• Krypton and Argon – LASER for LASER surgery
• Working materials enclosed in a cylindrical tube – LASER Tube
• Most of the electrons are in their ground state – natural condition
• Few at excited state – spontaneous emission – photon – stimulated
emission as it pass thru other excited atom

45. But to sustain number of stimulated emission, the electrons in high energy state
must exceed electrons in low energy state – Population Inversion
- the gas in laser tube is pumped by electric discharge/powerful light
- Maintain the population inversion
- Few electrons – spontaneous emission – photons – Stimulate high energy level
electron- Stimulated emission – coherent photon
- Chain Rxn – two mirrors are placed at each end of the cavity –
- totally reflecting (100%)
- Partially (99%)
- Coherent light escape from the cavity return back after reflection and produce
more stimulated emission.
- Small amount of light pass thru partially reflecting mirror -LASER

46. Some LASERS
• Helium neon LASER – Red 632.8 nm
• Krypton – Red 647.1 nm
• Argon – Blue and blue green – 488 nm & 514.5 nm
• Nd: YAG – Continous 1065 nm

47. Contd…
• Treatment of
Macular degenaration
Microaneurysm
• Laser Iridotomy
• Laser trabeculoplasty
• Photorefractive keratectomy
• LASIK
• LASEK

48. Industrial and commercial
• Cutting & peening of metals and other
material
• welding

49. Clinical uses in Eye
• Treatment of lid papillomas
• Treatment of age related keratosis
• Photocoagulation of retina
• Photovaporisation of choroidal tumors
• Posterior capsulotomies

50. Contd..
• Treat peripheral retinal disorders
– Retinal breaks
– RD
– Retinal choroidal tumor
• Treat ocular vascular disease
– Sickle cell retinopathy
– Cauterization of vessels in BRVO and BRAO
• Treatment of
choroidal neovascular membrane
– Diabetic retinopathy
– Diabetic maculopathy

51. Laser applications
• 1 Scientific1 Scientific
• 2 Military2 Military
• 3 Medical3 Medical
• 4 Industrial and commercial4 Industrial and commercial

52. 1 Scientific
– Spectroscopy
– Lunar laser ranging
– Material processing
– Photochemistry
– Laser cooling
– Nuclear fusion
– Microscopy

53. Military
Defensive countermeasures
Targeting
Ranging
Target designator
Military/police applications
Laser sight
Eye-targeted lasers

54. • Cosmetic surgery
removing tattoos,
scars, stretch marks,
sunspots,
wrinkles,
birthmarks,
laser hair removal.

55. Dentistry
caries removal,
endodontic/periodontic procedures,
tooth whitening
oral surgery.
laser scalpel

56. USES
• Industry, Communication, Science, Engineering
• MEDCINE- OPhthalmology
• LASER treatment for different ocular diseases
- Photocoagulation, Photodisruption, Photoablation

57. APPLICATIONS OF LASER
• INDUSTRIAL
WELDING AND CUTTING
SURVEYING AND RANGING
CUTTING IN GARMENT
INDUSTRY
COMMUNICATION;FIBRE
OPTICS
HEAT TREATMENT
LASER PRINTING
LIGHT EFFECTS

58. MEDICAL USES
INCLUDES TREATMENT OF :
a)Retinal detachment
b)Diabetic retinopathy
c)Neovascularization
d)Posterior capsulotomies
e)Laser trabeculoplasty in open angle glaucoma
f)Laser iridotomy in acute angle closure glaucoma or chronic
angle closure glaucoma
g)Macular degeneration
h)Heavily pigmented tumours of the eye

59. LASER SAFETY
• Lasers are usually labeled with a safety class number, which
identifies how dangerous the laser is:
• Class I/1 is inherently safe, usually because the light is contained
in an enclosure, for example in cd players.
• Class II/2 is safe during normal use; the blink reflex of the eye will
prevent damage. Usually up to 1 mW power, for example laser
pointers.
• Class IIIa/3R lasers are usually up to 5 mW and involve a small risk
of eye damage within the time of the blink reflex. Staring into such
a beam for several seconds is likely to cause (minor) eye damage.

60. • Class IIIb/3B can cause immediate severe eye damage upon
exposure. Usually lasers up to 500 mW, such as those in cd
and dvd burners.
• Class IV/4 lasers can burn skin, and in some cases, even
scattered light can cause eye and/or skin damage. Many
industrial and scientific lasers are in this class.
• The indicated powers are for visible-light, continuous-wave
lasers. For pulsed lasers and invisible wavelengths, other
power limits apply. People working with class 3B and class 4
lasers can protect their eyes with safety goggles which are
designed to absorb light of a particular wavelength.

61. LASER SAFETY
If eyes are not protected adequately when working with laser
beams, severe damage can occur

62. Warning symbol for lasers