Laser surazz
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Transcript of Laser surazz
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.
•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:
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
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