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Lasers
Introduction to
Lecture Contents
•
•
•
•
•
•

Laser Applications
Definition of lasers
Population Inversion
Materials used for semiconducting laser
Quantum dot devices
Laser Safety
Intro to

lasers
Intro to

lasers

Laser Applications
TELECOMMUNICATION

10 Gbits /s
FLAG network
From UK to Japan
(Fiber-optic Link Around the Globe)
28OOOKM

Flag Network owned by

Reliance Globecom -UK
Flag Network Collaboration In India

Reliance Communications
Another Typical Application of

Laser – Fibre Optics

• An example of application is for the light source for fibre

optics communication.

• Light travels down a fibre optics glass at a speed, = c/n, where
n = refractive index.
• Light carries with it information
• Different wavelength travels at different speed.
• This induce dispersion and at the receiving end the light is
observed to be spread. This is associated with data or
information lost.
• The greater the spread of information, the more loss
• However, if we start with a more coherent beam then loss can
be greatly reduced.

Intro to

lasers
Laser Applications
MEDICINAL PURPOSE

#

Intro to

lasers

Fiber optic
Endoscopeto
Detect ulcers
in the intestines.

Lasers are used extensively
in the treatment of
eye-diseases ,particularly to
reattach a detached retina.

Bloodless Surgery.

# The liver and lung diseases could be
treated using lasers.
Laser Applications
MEDICINAL PURPOSE

Intro to

lasers

• To destroy cancerous and precancerous cells; at the same
time, the heat seal off capillaries,

To break up gallstones and
kidney stones

To remove plaque clogging
human arteries
Laser Applications
INDUSTRIAL PURPOSES

Intro to

lasers

#

lasers are used now for cutting, drilling and
welding of metals and other materials.

Laser light is used to collect the
information about the prefixed prices of
various products in shops and
business establishments from the barcode printed on the product.

• LIDAR –Light Detection & Ranging (Mines)
• Leveling of Ceramic Tile Floor
# For precision measurements & leveling
Laser Applications
INDUSTRIAL PURPOSES

PC-board CAD tools s

3D printers

Latching tool

Intro to

lasers

Milling tool

A variety of 3D printing techniques have appeared in the last few years.
SLA: Stereolithography: laser curing of liquid plastic.
SLS: Selective Laser Sintering: similar, laser fuses powder.
LOM: Layered Object Modeling: laser cuts paper one layer at a time.
FDM: Fused Deposition Modeling: a thread of plastic is melted through a
moving head.
Laser Applications
DEFENCE & SECURITY

Intro to

lasers

#
LASTEC- HPL Researches
(Laser Science & Technology Centre) # In sniper guns, for target acquisition & locking
Dragunov SVD – Semi Automatic Sniper gun
Under DRDO
(Defence Research & Development Organisation)

Indian ARM industry :- OFB (Ordinance Factories Board )
MILITARY USES
THERMAL IMAGING

THERMAL IMAGING

• Laser guided munitions
– Designated from air or ground
Intro to

lasers

• Thermal homing missiles
• Optical Guidance
• Night Vision
Lasers – Military Applications
• Targeting tool
– Absorbed by target – thermal radiator
– Reflected by target – selective radiator

• Modulated
– Different lasers of the same frequency to be deconflicted and
limits enemy interference

• Weapon Systems: Hellfire, Maverick, Rockeye
• Laser Range finders, Beam riders, and laser target
designators (LTD)
• THEL & MHEL - Tactical High Energy Laser (Shoot down
incoming)
@ www.gizmag.com/millitarygadgets

Intro to

lasers
Intro to

lasers

Laser Applications
HOLOGRAPHY

• Holography is the production of holograms by the use of laser.
@ www.pranavmistry.com
Laser Applications
HOLOGRAPHY

• Possible medical applications using the technology
– Surgical procedures (using tracking capabilities)
– Rehabilitation techniques & Gaming

Intro to

lasers
Typical Application of

Laser

The detection of the binary data stored in the form of pits on
the compact disc is done with the use of a semiconductor
laser. The laser is focused to a diameter of about 0.8 mm at
the bottom of the disc, but is further focused to about 1.7
micrometers as it passes through the clear plastic substrate
to strike the reflective layer. The reflected laser will be
detected by a photodiode. Moral of the story: without
optoelectronics there will no CD player!

Intro to

lasers
BASIC LASER
Light
Amplification by
Stimulated
Emission of
Radiation
Intro to

lasers
Definition of

laser

• A laser is a device that generates light by a process
called STIMULATED EMISSION.
• The acronym LASER stands for Light Amplification
by Stimulated Emission of Radiation
• Semiconducting lasers are multilayer semiconductor
devices that generates a coherent beam of
monochromatic light by laser action. A coherent
beam resulted which all of the photons are in
phase.
Intro to

lasers
Electromagnetic Spectrum
Gamma Rays

10-13

10-12

10-11

X-Rays

10-10

10-9

Ultra- Visible
violet

Infrared

10-8

10-5

10-7

10-6

Microwaves

10-4

10-3

10-2

Radar
waves

10-1

TV
waves

1

10

Radio
waves

102

Wavelength (m)

LASERS

Retinal Hazard Region
Ultraviolet

200

300

Visible

400

500

600

Near Infrared

700

800

900

1000

1100

Far Infrared

1200

1300

1400

1500

10600

Wavelength (nm)
ArF
193

XeCl
308
KrF
248

Ar
488/515

HeNe Ruby
633 694
2w
Alexandrite GaAs
Nd:YAG
755
905
532

Nd:YAG
1064

Communication CO2
10600
Diode
1550

Lasers operate in the ultraviolet, visible, and infrared.

Intro to

lasers
Properties of Laser Light
• Monochromaticity
– Laser light is concentrated in a narrow range of wavelengths

• Coherence
– All the emitted photons bear a constant phase relationship with
each other in both time and phase

• Directionality
– laser light is usually low in divergence

• High Irradiance
– Power of EM radiation Incident per unit area
Intro to

lasers
Types of LASERS

LASERS
Semiconductor

Diode Laser

Solid state

Liquid

Gas Lasers

Solid state

Liquid

Neodymium Yag Laser
Ruby laser

Gaseous

Intro to

lasers
Market demand of QD lasers
( QUANTUM DOT )
Microwave/Millimeter wave
transmission with optical fibers

Datacom
network

Telecom
network

QD Lasers

High speed QDL
Directly Modulated Quantum
Dot Lasers

•Datacom

Mode-Locked Quantum Dot
Lasers

Optics

Advantages

•Short

InP Based Quantum Dot
Lasers

•Low

@ www.fibers.org
Intro to

lasers

application
•Rate of 10Gb/s
optical pulses
•Narrow spectral width
•Broad gain spectrum
•Very low α factor-low chirp

emission wavelength
•Wide temperature range
•Used for data transmission
DEFINITION OF MPE

The level of laser light to which a person may be
exposed without risk of injury.
Intro to

lasers
Mechanisms of Light Emission
For 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
 It is an important process for laser action

Therefore 3 process of
light emission:

1. Absorption
2. Spontaneous Emission
3. Stimulated Emission
Stimulated Emission
•It is pointed out by Einstein that:
“Atoms in an excited state can be stimulated to jump to a
lower energy level when they are struck by a photon of incident light
whose energy is the same as the energy-level difference involved in
the jump. The electron thus emits a photon of the same wavelength as
the incident photon. The incident and emitted photons travel away
from the atom in phase.”
Intro to
This process is called stimulated emission.

lasers
Intro to

lasers

Stimulated Emission
Emitted
photon

Incident
photon

Excited
electron

Incident
photon

Unexcited
electron

Before emission

After emission
Intro to

lasers
In order to obtain the coherent light from stimulated emission,
two conditions must be satisfied:
1. The atoms must be excited to the higher state. That is, an
inverted population is needed, one in which more atoms are
in the upper state than in the lower one, so that emission of
photons will dominate over absorption.
Unexcited system

Excited system

E3
E2

E3
E2

E1

E1
Metastable State

Intro to

lasers

2. The higher state must be a metastable state – a state in which the
electrons remain longer than usual so that the transition to the
lower state occurs by stimulated emission rather than
spontaneously.

E3
Metastable state

E3

E2

E2
Incident photon

Photon of energy E 2  E1

E1
Metastable system

E1

Emitted photon

Stimulated emission
Common Laser System

Intro to

lasers
Intro to

lasers

BASIC LASER COMPONENTS

ACTIVE MEDIUM

Optical Resonator

Solid (Crystal)
Gas
Semiconductor (Diode)
Liquid (Dye)
EXCITATION
MECHANISM
Optical
Electrical
Chemical

OPTICAL
RESONATOR
HR Mirror and
Output Coupler

Active
Medium
High Reflectance
Mirror (HR)

Output
Beam

Output Coupler
Mirror (OC)

Excitation
Mechanism

The Active Medium contains atoms which can emit light
by stimulated emission.
The Excitation Mechanism is a source of energy to
excite the atoms to the proper energy state.
The Optical Resonator reflects the laser beam through
the active medium for amplification.
Laser Wavelength Linewidth

Intro to

lasers
CDRH CLASS WARNING LABELS

Laser Radiation
Do Not Stare Into Beam
Helium Neon Laser
1 milliwatt max/cw
CLASS II LASER PRODUCT

Class II
Class IIIa with expanded beam

VISIBLE LASER RADIATIONAVOID EYE OR SKIN EXPOSURE TO
DIRECT OR SCATTERED RADIATION

Argon Ion
Wavelength: 488/514 nm
Output Power 5 W
CLASS IV Laser Product

Class IIIa with small beam
Class IIIb
Class IV

Intro to

lasers
INTERNATIONAL LASER WARNING LABELS
INVISIBLE LASER RADIATION
AVOID EYE OR SKIN EXPOSURE
TO DIRECT OR SCATTERED RADIATION
CLASS 4 LASER PRODUCT

WAVELENGTH
MAX LASER POWER
EN60825-1

Symbol and Border: Black
Background: Yellow

10,600 nm
200 W
1998

Legend and Border: Black
Background: Yellow

Intro to

lasers
Intro to

NEODYMIUM YAG LASER

lasers

Courtesy of Los Alamos National Laboratory

Rear Mirror
Adjustment Knobs

Safety Shutter Polarizer Assembly (optional)
Coolant
Beam
Tube

Adjustment
Knob
Output
Mirror
Beam

Q-switch
(optional)

Beam Tube

Nd:YAG
Laser Rod
Flashlamps

Pump
Cavity
Laser Cavity
Harmonic
Generator (optional)

Medium :- Neodymium-Doped Yttrium Aluminum Garnet Crystal
State :- Solid
Excitation :- Diode Laser
Beam :- 1064 nm infrared
Uses :- Cataract ,Glaucoma , Gingivectomy surgeries
Intro to

lasers

Light Absorption

• Dominant interaction
– Photon absorbed
– Electron is excited to CB
– Hole left in the VB

• Depends on the energy
band gap (similar to
lasers)
• Absorption (a) requires
the photon energy to be
larger than the material
band gap

hc

 Eg


hc
1.24
 m )


E g E g eV )
LASER HAZARD CLASSES
Lasers are classified according to the level of laser radiation that
is accessible during normal operation.

Intro to

lasers
CLASS 1

• Safe during normal use

• Incapable of causing injury
• Low power or enclosed beam

CLASS I Laser Product

Label not required

Nd:YAG Laser Marker

May be higher class during
maintenance or service
CLASS 2
•
•
•
•

Staring into beam is eye hazard
Eye protected by aversion response
Visible lasers only
CW maximum power 1 mW

Laser Scanners

Laser Radiation
Do Not Stare Into Beam

Helium Neon Laser
1 milliwatt max/cw
CLASS II LASER PRODUCT
CLASS 3R (Formerly 3a)
• Aversion response may not provide
adequate eye protection
• CDRH includes visible lasers only
• ANSI includes invisible lasers
• CW maximum power (visible) 5 mW

Expanded Beam

Laser Pointers
Laser RadiationDo Not Stare Into Beam or View
Directly With Optical Instruments

Helium Neon Laser
5 milliwatt max/cw
CLASS IIIa LASER PRODUCT

LASER RADIATIONAVOID DIRECT EYE EXPOSURE

ND:YAG 532nm
5 milliwatts max/CW
CLASS IIIa Laser Product

Small Beam
CLASS 3B
DPSS Laser with cover removed

• Direct exposure to beam is eye hazard
• Visible or invisible
• CW maximum power 500 mW

LASER RADIATIONAVOID DIRECT EXPOSURE TO BEAM
2w ND:YAG Wavelength: 532 nm
Output Power 80 mW
CLASS IIIb Laser Product

Courtesy of Sam’s Laser FAQ, www.repairfaq.org/sam/lasersam.htm, © 1994-2004
CLASS 4
• Exposure to direct beam and scattered
light is eye and skin hazard
• Visible or invisible
• CW power >0.5 W
• Fire hazard

VISIBLE LASER RADIATIONAVOID EYE OR SKIN EXPOSURE TO
DIRECT OR SCATTERED RADIATION

Photo: Keith Hunt - www.keithhunt.co.uk
Copyright: University of Sussex, Brighton (UK)

2w Nd:YAG
Wavelength: 532 nm
Output Power 20 W
CLASS IV Laser Product
TYPES OF LASER EYE EXPOSURE
INTRABEAM
VIEWING
EYE

LASER

SPECULAR
REFLECTION
LASER

DIFFUSE
REFLECTION

LASER

REFLECTED
BEAM
MIRROR

SCATTERED
LIGHT
ROUGH
SURFACE

Intro to

lasers
VISIBLE and/ or INVISIBLE LASER
RADIATION-AVOID EYE OR SKIN
EXPOSURE TO DIRECT OR
SCATTERED RADIATION.
ND:YAG 1064 nm
100 Watts Max. Average Power

CLASS 4 LASER
Controlled Area Warning Sign
Intro to

lasers

LABORATORY DOOR INTERLOCK
Intro to

lasers

ENTRYWAY WARNING LIGHTS
Intro to

lasers

LASER PROTECTIVE BARRIERS
Intro to

lasers

CURBS ON OPTICAL TABLE
Intro to

lasers

BEAM CONTROL
Intro to

lasers

COMPUTERS IN RESEARCH LABS

Allowing a direct view
from a computer
workstation into a laser
experimental setup
increases the risk of eye
exposure to reflected
beams.
Laser-Professionals.com
LASER SAFETY EYEWEAR

Intro to

lasers
EYEWEAR LABELS

Intro to

lasers
All eyewear must be labeled with wavelength and optical density.
Visit www.ignitedmindsv2.tk

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Introduction to Lasers

  • 2. Lecture Contents • • • • • • Laser Applications Definition of lasers Population Inversion Materials used for semiconducting laser Quantum dot devices Laser Safety Intro to lasers
  • 3. Intro to lasers Laser Applications TELECOMMUNICATION 10 Gbits /s FLAG network From UK to Japan (Fiber-optic Link Around the Globe) 28OOOKM Flag Network owned by Reliance Globecom -UK Flag Network Collaboration In India Reliance Communications
  • 4. Another Typical Application of Laser – Fibre Optics • An example of application is for the light source for fibre optics communication. • Light travels down a fibre optics glass at a speed, = c/n, where n = refractive index. • Light carries with it information • Different wavelength travels at different speed. • This induce dispersion and at the receiving end the light is observed to be spread. This is associated with data or information lost. • The greater the spread of information, the more loss • However, if we start with a more coherent beam then loss can be greatly reduced. Intro to lasers
  • 5. Laser Applications MEDICINAL PURPOSE # Intro to lasers Fiber optic Endoscopeto Detect ulcers in the intestines. Lasers are used extensively in the treatment of eye-diseases ,particularly to reattach a detached retina. Bloodless Surgery. # The liver and lung diseases could be treated using lasers.
  • 6. Laser Applications MEDICINAL PURPOSE Intro to lasers • To destroy cancerous and precancerous cells; at the same time, the heat seal off capillaries, To break up gallstones and kidney stones To remove plaque clogging human arteries
  • 7. Laser Applications INDUSTRIAL PURPOSES Intro to lasers # lasers are used now for cutting, drilling and welding of metals and other materials. Laser light is used to collect the information about the prefixed prices of various products in shops and business establishments from the barcode printed on the product. • LIDAR –Light Detection & Ranging (Mines) • Leveling of Ceramic Tile Floor # For precision measurements & leveling
  • 8. Laser Applications INDUSTRIAL PURPOSES PC-board CAD tools s 3D printers Latching tool Intro to lasers Milling tool A variety of 3D printing techniques have appeared in the last few years. SLA: Stereolithography: laser curing of liquid plastic. SLS: Selective Laser Sintering: similar, laser fuses powder. LOM: Layered Object Modeling: laser cuts paper one layer at a time. FDM: Fused Deposition Modeling: a thread of plastic is melted through a moving head.
  • 9. Laser Applications DEFENCE & SECURITY Intro to lasers # LASTEC- HPL Researches (Laser Science & Technology Centre) # In sniper guns, for target acquisition & locking Dragunov SVD – Semi Automatic Sniper gun Under DRDO (Defence Research & Development Organisation) Indian ARM industry :- OFB (Ordinance Factories Board )
  • 10. MILITARY USES THERMAL IMAGING THERMAL IMAGING • Laser guided munitions – Designated from air or ground Intro to lasers • Thermal homing missiles • Optical Guidance • Night Vision
  • 11. Lasers – Military Applications • Targeting tool – Absorbed by target – thermal radiator – Reflected by target – selective radiator • Modulated – Different lasers of the same frequency to be deconflicted and limits enemy interference • Weapon Systems: Hellfire, Maverick, Rockeye • Laser Range finders, Beam riders, and laser target designators (LTD) • THEL & MHEL - Tactical High Energy Laser (Shoot down incoming) @ www.gizmag.com/millitarygadgets Intro to lasers
  • 12. Intro to lasers Laser Applications HOLOGRAPHY • Holography is the production of holograms by the use of laser. @ www.pranavmistry.com
  • 13. Laser Applications HOLOGRAPHY • Possible medical applications using the technology – Surgical procedures (using tracking capabilities) – Rehabilitation techniques & Gaming Intro to lasers
  • 14. Typical Application of Laser The detection of the binary data stored in the form of pits on the compact disc is done with the use of a semiconductor laser. The laser is focused to a diameter of about 0.8 mm at the bottom of the disc, but is further focused to about 1.7 micrometers as it passes through the clear plastic substrate to strike the reflective layer. The reflected laser will be detected by a photodiode. Moral of the story: without optoelectronics there will no CD player! Intro to lasers
  • 16. Definition of laser • A laser is a device that generates light by a process called STIMULATED EMISSION. • The acronym LASER stands for Light Amplification by Stimulated Emission of Radiation • Semiconducting lasers are multilayer semiconductor devices that generates a coherent beam of monochromatic light by laser action. A coherent beam resulted which all of the photons are in phase. Intro to lasers
  • 17. Electromagnetic Spectrum Gamma Rays 10-13 10-12 10-11 X-Rays 10-10 10-9 Ultra- Visible violet Infrared 10-8 10-5 10-7 10-6 Microwaves 10-4 10-3 10-2 Radar waves 10-1 TV waves 1 10 Radio waves 102 Wavelength (m) LASERS Retinal Hazard Region Ultraviolet 200 300 Visible 400 500 600 Near Infrared 700 800 900 1000 1100 Far Infrared 1200 1300 1400 1500 10600 Wavelength (nm) ArF 193 XeCl 308 KrF 248 Ar 488/515 HeNe Ruby 633 694 2w Alexandrite GaAs Nd:YAG 755 905 532 Nd:YAG 1064 Communication CO2 10600 Diode 1550 Lasers operate in the ultraviolet, visible, and infrared. Intro to lasers
  • 18. Properties of Laser Light • Monochromaticity – Laser light is concentrated in a narrow range of wavelengths • Coherence – All the emitted photons bear a constant phase relationship with each other in both time and phase • Directionality – laser light is usually low in divergence • High Irradiance – Power of EM radiation Incident per unit area Intro to lasers
  • 19. Types of LASERS LASERS Semiconductor Diode Laser Solid state Liquid Gas Lasers Solid state Liquid Neodymium Yag Laser Ruby laser Gaseous Intro to lasers
  • 20. Market demand of QD lasers ( QUANTUM DOT ) Microwave/Millimeter wave transmission with optical fibers Datacom network Telecom network QD Lasers High speed QDL Directly Modulated Quantum Dot Lasers •Datacom Mode-Locked Quantum Dot Lasers Optics Advantages •Short InP Based Quantum Dot Lasers •Low @ www.fibers.org Intro to lasers application •Rate of 10Gb/s optical pulses •Narrow spectral width •Broad gain spectrum •Very low α factor-low chirp emission wavelength •Wide temperature range •Used for data transmission
  • 21. DEFINITION OF MPE The level of laser light to which a person may be exposed without risk of injury. Intro to lasers
  • 22. Mechanisms of Light Emission For 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  It is an important process for laser action Therefore 3 process of light emission: 1. Absorption 2. Spontaneous Emission 3. Stimulated Emission
  • 23. Stimulated Emission •It is pointed out by Einstein that: “Atoms in an excited state can be stimulated to jump to a lower energy level when they are struck by a photon of incident light whose energy is the same as the energy-level difference involved in the jump. The electron thus emits a photon of the same wavelength as the incident photon. The incident and emitted photons travel away from the atom in phase.” Intro to This process is called stimulated emission. lasers
  • 25. Intro to lasers In order to obtain the coherent light from stimulated emission, two conditions must be satisfied: 1. The atoms must be excited to the higher state. That is, an inverted population is needed, one in which more atoms are in the upper state than in the lower one, so that emission of photons will dominate over absorption. Unexcited system Excited system E3 E2 E3 E2 E1 E1
  • 26. Metastable State Intro to lasers 2. The higher state must be a metastable state – a state in which the electrons remain longer than usual so that the transition to the lower state occurs by stimulated emission rather than spontaneously. E3 Metastable state E3 E2 E2 Incident photon Photon of energy E 2  E1 E1 Metastable system E1 Emitted photon Stimulated emission
  • 28. Intro to lasers BASIC LASER COMPONENTS ACTIVE MEDIUM Optical Resonator Solid (Crystal) Gas Semiconductor (Diode) Liquid (Dye) EXCITATION MECHANISM Optical Electrical Chemical OPTICAL RESONATOR HR Mirror and Output Coupler Active Medium High Reflectance Mirror (HR) Output Beam Output Coupler Mirror (OC) Excitation Mechanism The Active Medium contains atoms which can emit light by stimulated emission. The Excitation Mechanism is a source of energy to excite the atoms to the proper energy state. The Optical Resonator reflects the laser beam through the active medium for amplification.
  • 30. CDRH CLASS WARNING LABELS Laser Radiation Do Not Stare Into Beam Helium Neon Laser 1 milliwatt max/cw CLASS II LASER PRODUCT Class II Class IIIa with expanded beam VISIBLE LASER RADIATIONAVOID EYE OR SKIN EXPOSURE TO DIRECT OR SCATTERED RADIATION Argon Ion Wavelength: 488/514 nm Output Power 5 W CLASS IV Laser Product Class IIIa with small beam Class IIIb Class IV Intro to lasers
  • 31. INTERNATIONAL LASER WARNING LABELS INVISIBLE LASER RADIATION AVOID EYE OR SKIN EXPOSURE TO DIRECT OR SCATTERED RADIATION CLASS 4 LASER PRODUCT WAVELENGTH MAX LASER POWER EN60825-1 Symbol and Border: Black Background: Yellow 10,600 nm 200 W 1998 Legend and Border: Black Background: Yellow Intro to lasers
  • 32. Intro to NEODYMIUM YAG LASER lasers Courtesy of Los Alamos National Laboratory Rear Mirror Adjustment Knobs Safety Shutter Polarizer Assembly (optional) Coolant Beam Tube Adjustment Knob Output Mirror Beam Q-switch (optional) Beam Tube Nd:YAG Laser Rod Flashlamps Pump Cavity Laser Cavity Harmonic Generator (optional) Medium :- Neodymium-Doped Yttrium Aluminum Garnet Crystal State :- Solid Excitation :- Diode Laser Beam :- 1064 nm infrared Uses :- Cataract ,Glaucoma , Gingivectomy surgeries
  • 33. Intro to lasers Light Absorption • Dominant interaction – Photon absorbed – Electron is excited to CB – Hole left in the VB • Depends on the energy band gap (similar to lasers) • Absorption (a) requires the photon energy to be larger than the material band gap hc  Eg  hc 1.24  m )   E g E g eV )
  • 34. LASER HAZARD CLASSES Lasers are classified according to the level of laser radiation that is accessible during normal operation. Intro to lasers
  • 35. CLASS 1 • Safe during normal use • Incapable of causing injury • Low power or enclosed beam CLASS I Laser Product Label not required Nd:YAG Laser Marker May be higher class during maintenance or service
  • 36. CLASS 2 • • • • Staring into beam is eye hazard Eye protected by aversion response Visible lasers only CW maximum power 1 mW Laser Scanners Laser Radiation Do Not Stare Into Beam Helium Neon Laser 1 milliwatt max/cw CLASS II LASER PRODUCT
  • 37. CLASS 3R (Formerly 3a) • Aversion response may not provide adequate eye protection • CDRH includes visible lasers only • ANSI includes invisible lasers • CW maximum power (visible) 5 mW Expanded Beam Laser Pointers Laser RadiationDo Not Stare Into Beam or View Directly With Optical Instruments Helium Neon Laser 5 milliwatt max/cw CLASS IIIa LASER PRODUCT LASER RADIATIONAVOID DIRECT EYE EXPOSURE ND:YAG 532nm 5 milliwatts max/CW CLASS IIIa Laser Product Small Beam
  • 38. CLASS 3B DPSS Laser with cover removed • Direct exposure to beam is eye hazard • Visible or invisible • CW maximum power 500 mW LASER RADIATIONAVOID DIRECT EXPOSURE TO BEAM 2w ND:YAG Wavelength: 532 nm Output Power 80 mW CLASS IIIb Laser Product Courtesy of Sam’s Laser FAQ, www.repairfaq.org/sam/lasersam.htm, © 1994-2004
  • 39. CLASS 4 • Exposure to direct beam and scattered light is eye and skin hazard • Visible or invisible • CW power >0.5 W • Fire hazard VISIBLE LASER RADIATIONAVOID EYE OR SKIN EXPOSURE TO DIRECT OR SCATTERED RADIATION Photo: Keith Hunt - www.keithhunt.co.uk Copyright: University of Sussex, Brighton (UK) 2w Nd:YAG Wavelength: 532 nm Output Power 20 W CLASS IV Laser Product
  • 40. TYPES OF LASER EYE EXPOSURE INTRABEAM VIEWING EYE LASER SPECULAR REFLECTION LASER DIFFUSE REFLECTION LASER REFLECTED BEAM MIRROR SCATTERED LIGHT ROUGH SURFACE Intro to lasers
  • 41. VISIBLE and/ or INVISIBLE LASER RADIATION-AVOID EYE OR SKIN EXPOSURE TO DIRECT OR SCATTERED RADIATION. ND:YAG 1064 nm 100 Watts Max. Average Power CLASS 4 LASER Controlled Area Warning Sign
  • 45. Intro to lasers CURBS ON OPTICAL TABLE
  • 47. Intro to lasers COMPUTERS IN RESEARCH LABS Allowing a direct view from a computer workstation into a laser experimental setup increases the risk of eye exposure to reflected beams. Laser-Professionals.com
  • 49. EYEWEAR LABELS Intro to lasers All eyewear must be labeled with wavelength and optical density.