Introduction to Lasers

Las rsIntroduction to

e

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• Laser Applications

• Definition of lasers

• Population Inversion

• Materials used for semiconducting laser

• Quantum dot devices

• Laser Safety

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Lecture Contents

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TELECOMMUNICATION

Laser Applications

FLAG network(Fiber-optic Link Around the Globe)

Flag Network Collaboration In India

Reliance Communications

10 Gbits /s

From UK to Japan

Flag Network owned by

Reliance Globecom -UK

28OOOKM

Another Typical Application of

• 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.

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Laser – Fibre Optics

lasersIntro toLaser Applications

# The liver and lung diseases could be

treated using lasers.

Lasers are used extensively

in the treatment of

eye-diseases ,particularly to

reattach a detached retina.

MEDICINAL PURPOSE

Bloodless Surgery.

Fiber optic

Endoscopeto

Detect ulcers

in the intestines.#


MEDICINAL PURPOSE

• To destroy cancerous and precancerous cells; at the same

time, the heat seal off capillaries,

To remove plaque clogging

human arteries

To break up gallstones and

kidney stones


# For precision measurements & leveling

Laser light is used to collect the

information about the prefixed prices of

various products in shops and

business establishments from the bar-

code printed on the product.

INDUSTRIAL PURPOSES

lasers are used now for cutting, drilling and

welding of metals and other materials.

#

• LIDAR –Light Detection & Ranging (Mines)

• Leveling of Ceramic Tile Floor


INDUSTRIAL PURPOSES

Milling tool3D printers Latching 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.

PC-board CAD tools s


# In sniper guns, for target acquisition & locking

Dragunov SVD – Semi Automatic Sniper gun

LASTEC- HPL Researches(Laser Science & Technology Centre)

Under DRDO

DEFENCE & SECURITY

Indian ARM industry :- OFB (Ordinance Factories Board )

(Defence Research & Development Organisation)

#

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• Laser guided munitions– Designated from air or ground

• Thermal homing missiles

• Optical Guidance

• Night Vision

MILITARY USES

THERMAL IMAGING THERMAL IMAGING

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)

lasersIntro to@ www.gizmag.com/millitarygadgets

• Holography is the production of holograms by the use of laser.

Laser ApplicationsHOLOGRAPHY

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@ www.pranavmistry.com

• Possible medical applications using the technology– Surgical procedures (using tracking capabilities)

– Rehabilitation techniques & Gaming

Laser ApplicationsHOLOGRAPHY

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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!

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Light

Amplification by

Stimulated

Emission of

Radiation

BASIC LASER

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• A laser is a device that generates light by a processcalled STIMULATED EMISSION.

• The acronym LASER stands for Light Amplificationby Stimulated Emission of Radiation

• Semiconducting lasers are multilayer semiconductordevices that generates a coherent beam ofmonochromatic light by laser action. A coherentbeam resulted which all of the photons are inphase.

Definition of

laser

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10-13 10-12 10-11 10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 1 10 102

LASERS

200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 10600

Ultraviolet Visible Near Infrared Far Infrared

Gamma Rays X-Rays Ultra- Visible Infrared Micro- Radar TV Radio

violet waves waves waves waves

Wavelength (m)

Wavelength (nm)

Nd:YAG

1064

GaAs

905

HeNe

633

Ar

488/515

CO2

10600

XeCl

308

KrF

248

2w

Nd:YAG

532

Retinal Hazard Region

ArF

193Communication

Diode

1550

Ruby

694

Alexandrite

755

Electromagnetic Spectrum

lasersIntro toLasers operate in the ultraviolet, visible, and infrared.

• 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

Properties of Laser Light

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Diode Laser

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Neodymium Yag Laser

Types of LASERS LASERS

Solid state Liquid Gas Lasers

Semiconductor

Solid state Liquid

Gaseous

Ruby laser

Market demand of QD lasers

QD Lasers

Microwave/Millimeter wave

transmission with optical fibers

Da

tac

om

ne

two

rk

Te

lec

om

ne

two

rk

Optics

( QUANTUM DOT )

High speed QDL Advantages

Directly Modulated Quantum Dot Lasers

•Datacom application

•Rate of 10Gb/s

Mode-Locked Quantum Dot Lasers

•Short optical pulses

•Narrow spectral width

•Broad gain spectrum

•Very low α factor-low chirp

InP Based Quantum Dot Lasers

•Low emission wavelength

•Wide temperature range

•Used for data transmissionlasersIntro to

@ www.fibers.org

DEFINITION OF MPE

The level of laser light to which a person may be

exposed without risk of injury.

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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:

Mechanisms 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.”

This process is called stimulated emission. lasersIntro to

Excited

electron

Unexcited

electron

Before emission After emission

Stimulated EmissionlasersIntro to

Incident

photon Incident

photon

Emitted

photon

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

1E

2E3E

Excited system

1E

2E3E

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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.

Metastable state

Photon of energy12 EE

1E

2E

3E

Metastable system

1E

2E

3E

Stimulated emission

Incident photon

Emitted photon

Metastable StatelasersIntro to

Common Laser System

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BASIC LASER COMPONENTSACTIVE MEDIUM

Solid (Crystal)

Gas

Semiconductor (Diode)

Liquid (Dye)

EXCITATION

MECHANISM

Optical

Electrical

Chemical

OPTICAL

RESONATOR

HR Mirror and

Output Coupler

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.

High ReflectanceMirror (HR)

Output CouplerMirror (OC)

ActiveMedium

Output

Beam

Optical Resonator

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Excitation Mechanism

Laser Wavelength Linewidth

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CDRH CLASS WARNING LABELS

CLASS II LASER PRODUCT

Laser RadiationDo Not Stare Into Beam

Helium Neon Laser

1 milliwatt max/cw

CLASS IV Laser Product

VISIBLE LASER RADIATION-

AVOID EYE OR SKIN EXPOSURE TO

DIRECT OR SCATTERED RADIATION

Argon Ion

Wavelength: 488/514 nm

Output Power 5 W

Class II

Class IIIa with expanded beam

Class IIIa with small beam

Class IIIb

Class IV

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INTERNATIONAL LASER WARNING LABELS

Symbol and Border: Black

Background: Yellow

Legend and Border: Black

Background: Yellow

INVISIBLE LASER RADIATION

AVOID EYE OR SKIN EXPOSURE

TO DIRECT OR SCATTERED RADIATION

CLASS 4 LASER PRODUCT

WAVELENGTH 10,600 nm

MAX LASER POWER 200 W

EN60825-1 1998

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Courtesy of Los Alamos National Laboratory

NEODYMIUM YAG LASERlasersIntro to

Rear Mirror

Adjustment Knobs

Safety Shutter Polarizer Assembly (optional)

CoolantBeamTube

AdjustmentKnob

OutputMirror

Beam

Beam Tube

HarmonicGenerator (optional)

Laser Cavity

PumpCavity

Flashlamps

Nd:YAGLaser Rod

Q-switch(optional)

Medium :- Neodymium-Doped Yttrium Aluminum Garnet Crystal

State :- Solid

Excitation :- Diode Laser

Beam :- 1064 nm infrared

Uses :- Cataract ,Glaucoma , Gingivectomy surgeries

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 gE

hc

) )m

eVEE

hc

gg

24.1

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LASER HAZARD CLASSES

Lasers are classified according to the level of laser radiation that

is accessible during normal operation.

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CLASS 1• Safe during normal use• Incapable of causing injury• Low power or enclosed beam

CLASS I Laser Product

Label not required

May be higher class duringmaintenance or service

Nd:YAG Laser Marker

CLASS 2

CLASS II LASER PRODUCT

Laser RadiationDo Not Stare Into Beam

Helium Neon Laser1 milliwatt max/cw

• Staring into beam is eye hazard

• Eye protected by aversion response

• Visible lasers only

• CW maximum power 1 mW

Laser Scanners

CLASS 3R (Formerly 3a)

Small Beam

Expanded Beam

CLASS IIIa Laser Product

LASER RADIATION-

AVOID DIRECT EYE EXPOSURE

ND:YAG 532nm

5 milliwatts max/CW

• Aversion response may not provide

adequate eye protection

• CDRH includes visible lasers only

• ANSI includes invisible lasers

• CW maximum power (visible) 5 mW

Laser Pointers

CLASS IIIa LASER PRODUCT

Laser Radiation-Do Not Stare Into Beam or ViewDirectly With Optical Instruments

Helium Neon Laser5 milliwatt max/cw

CLASS 3B

• Direct exposure to beam is eye hazard

• Visible or invisible

• CW maximum power 500 mW

CLASS IIIb Laser Product

LASER RADIATION-

AVOID DIRECT EXPOSURE TO BEAM

2w ND:YAG Wavelength: 532 nm

Output Power 80 mW

Courtesy of Sam’s Laser FAQ, www.repairfaq.org/sam/lasersam.htm, © 1994-2004

DPSS Laser with cover removed

CLASS 4

CLASS IV Laser Product

VISIBLE LASER RADIATION-

AVOID EYE OR SKIN EXPOSURE TO

DIRECT OR SCATTERED RADIATION

2w Nd:YAGWavelength: 532 nm

Output Power 20 W

• Exposure to direct beam and scattered

light is eye and skin hazard

• Visible or invisible

• CW power >0.5 W

• Fire hazard

Photo: Keith Hunt - www.keithhunt.co.uk

Copyright: University of Sussex, Brighton (UK)

http://www.keithhunt.co.uk/

TYPES OF LASER EYE EXPOSURE

EYE

INTRABEAM

VIEWING

LASER

DIFFUSE

REFLECTION

LASER

SCATTERED

LIGHT

MIRROR

SPECULAR

REFLECTION

LASER

REFLECTED

BEAM

ROUGH

SURFACE

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CLASS 4 LASER

ND:YAG 1064 nm

100 Watts Max. Average Power

VISIBLE and/ or INVISIBLE LASER

RADIATION-AVOID EYE OR SKIN

EXPOSURE TO DIRECT OR

SCATTERED RADIATION.

Controlled Area Warning Sign

LABORATORY DOOR INTERLOCKlasersIntro to

ENTRYWAY WARNING LIGHTSlasersIntro to

LASER PROTECTIVE BARRIERSlasersIntro to

CURBS ON OPTICAL TABLElasersIntro to

BEAM CONTROLlasersIntro to

COMPUTERS IN RESEARCH LABS

Laser-Professionals.com

Allowing a direct view

from a computer

workstation into a laser

experimental setup

increases the risk of eye

exposure to reflected

beams.

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LASER SAFETY EYEWEAR

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EYEWEAR LABELS

All eyewear must be labeled with wavelength and optical density.

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