Principle and Application of

LASER

Presentation Layout

•Introduction

•History

•Laser action

•Principle

•Types of Laser

•Applications

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.

LASER history

• 1917 -Sir Albert Einstein created the foundations for the laser.

• 1958 - C.H. Townes, A.L. Schawlow: Theoretical basis for lasers.

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

•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.

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.

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

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:

Absorption

E1

E2

Spontaneous Emission

Stimulated Emission

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.

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

1.Monochromatic

2.Collimated

3.Directional

4.Coherence

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

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

CLASSIFICATION OF LASER

• Solid StateRubyNd.YagErbium.YAG

• GasIonArgonKryptonHe-NeonCO2

• Metal VapourCuGold

DyeRhodamine

ExcimerArgon FluorideKrypton FluorideKrypton Chloride

DiodeGallium-AluminumArsenide (GaAlAs)

LASER TISSUE INTERACTIONLASER

TISSUE

Thermal Effect

Photo-chemical

Ionizing Effect

Photocoagulation Photoradation

Photodisruption Photoablation

Photovaporization

Thermal effect

(1) Photocoagulation:Laser Light

Target Tissue

Generate Heat

Denatures Proteins

(Coagulation)

Rise in temperature of about 10 to 20 0C will causecoagulation of tissue.

Contd…

(2) Photodisruption:Mechanical Effect:

• Laser Light

Optical Breakdown

Vapor

Quickly Collapses

Acoustic Shockwaves

Tissue Damage

3.Photovaporization

• Vaporization of tissue to CO2 and water occurswhen its temperature rise 60—100 0C or greater.

• Commonly used CO2

Absorbed by water of cells

Visible vapor (vaporization)

Heat Cell disintegration

Cauterization Incision

Photochemical effect

1. PHOTORADIATION (PDT):

• Also called Photodynamic Therapy

• Photochemical reaction following visible/infraredlight particularly after administration of exogenouschromophore.

• Commonly used photosensitizers:

Hematoporphyrin

Benzaporphyrin Derivatives

e.g. Treatment of ocular tumour and CNV

Photon + Photosensitizer in ground state (S)

3S (high energy triplet stage)

Energy Transfer

Molecular Oxygen Free RadicalS + O2 (singlet oxygen) Cytotoxic

Intermediate

Cell Damage, Vascular Damage , Immunologic Damage

Contd…

2.PHOTOABLATION:

Breaks the chemical bonds that holdtissue together essentially vaporizing the tissue,e.g. Photorefractive Keratectomy, Argon Fluoride(ArF) Excimer Laser.

Usually -

Visible Wavelength : Photocoagulation

Ultraviolet Yields : Photoablation

Infrared : PhotodisruptionPhotocoagulation

IONISING EFFECT

• Highly energized focal laser beam is delivered on tissue over aperiod of nanosecond or picoseconds and produce plasma intarget 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

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).

Contd…

• A Mode-locked Lasers: Emits a train of shortduration pulses (picoseconds).

• Fundamental System: Optical condition in whichonly one type of wave is oscillating in the lasercavity.

• Multimode system: Large number of waves, eachin a slight different direction ,oscillate in lasercavity.

LASER TISSUE INTERACTION

LASER VARIABLE:

Wavelength

Spot Size

Power

Duration

TISSUE VARIABLE:

Transparency

Pigmentation

Water Content

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

•Laser in lens:

•Posterior capsulotomy(YAG)

•Laser phacoemulcification

•Phacoablation

•Laser in vitreous:

•Vitreous membranes

•Vitreous traction bands

LASER IN GLAUCOMA

Laser Iridotomy,Laser Iredectomy

LaserTrabeculoplasty(LT)

Selective LaserTrabeculoplasty

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

COMPLICATION OF LASER TREATMENT

Pain

Seizure

Choroidal & retinal detachment

Foveal Burn

Increased IOP

Corneal Damage

Iris Burn

Cataract

InternalOphthalmoplegia

LASER HAZARDS

EYE

•Small lesion to extensive hemorrhage

•Disruption of retina and choroid

• Immediate loss of vision

•Epi-retinal membrane formation

•Macular hole, gliosis

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

Contd…

•Viterous: opacification, hemorrhage, choroidalneo-vascularization

•Retina: hemorrhage, receptor layer and nerve fibre damage

•Optic nerve: neuritis, nerve fibre damage

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.

Other uses of LASER

•Cosmetic Sugery

•Removing tattoos, scars, stretch marks, sunspots, wrinkles,birthmarks

•Laser hair removal

Dentistry

•caries removal

•endodontic/periodonticprocedures

•tooth whitening

•oral surgery

• laser scalpel

In Industry

•To drill tiny holes in hard materials

•For welding and machining

•For lining up equipmentsprecisely

•To measure the distance of tunnel

In everyday life

•To be used as bar code readers

•To be used in compact disc players

•To produce short pulsesof light used in digitalcommunication

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

MCQS1) Which is not a characteristics of LASER light?

A) stimulated emission

B) spontaneous emission

C) collimated

D) monochromatic

2) ND: YAG Capsulotomy is done by LASER having wavelength …

A) 1064 nm

B) 555 nm

C) 193 nm

D) 1 micron

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

4) In photoablation, temperature of a tissue increases by…degree Celsius

A) 10-20

B) 60-100

C) upto 2000

D) zero

5) Iridotomy is done for…

A) cosmetic purpose

B) treat ACG

C) to dilate pupillary area

D) to relax accommodation

References

•Clinical procedures in optometry•Optics

A.H. Tunacliffe

•Environmental VisionDonald G. Pitts

Robert N. Kleinstein

•Internet