INTRODUCTION TO LASERS

TECHNOLOGY EDUCATION

SCARSDALE MIDDLE SCHOOL

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Many of the pictures for this “LASER” presentation camefrom www.howstuffworks.com.

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LASER

• Originally LASER was an acronym for Light Amplification by the Stimulated Emission of Radiation.

• Now laser is a word used to identify this type of equipment or the light it produces.

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The Atom

Different electron orbits represent different energy levels.

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The Electron

Applying energy to an electron causes it to jumpto a higher orbit.

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The Photon

When the electron drops back to its original orbit itreleases a particle called a photon. Light is made up of photons.

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Wavelength of Light

Light moves in waves that are similarto ripples in water.

Light is an example of electromagnetic radiation: It doesn’trequire a medium to pass through

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Wavelength of Light1 CYCLE

Wavelength (): The distance the wave travels in one cycle.

Frequency (f): The number of times a cyclerepeats in one second (Hertz,formerley cycles/second).

= c f

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Wavelength of Light HERTZ ENERGY

~ 400 nanometers

~ 700 nanometers

HIGHER

FREQUENCY

LESS

ENERGY

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1 NANOMETER IS ONE BILLIONTH OF A METER

A human hair is about 80,000nanometers in diameter.

That’s about 115 times the wavelength () of red light.

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Light BulbLight is not focused

Light is made up of many colors (wavelengths)

Light is not coherent

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White LightLight From A Light Bulb

•All colors (wavelengths).

•More longer wavelengths.

•Light is notcoherent.

•Light is notfocused.

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Laser Light Light is very focused

Light is made up of one color (wavelength)

Light is coherent

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Laser LightLight From A Laser

•One color (wavelength).

•Light is coherent.

•Light is focused.

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Theodore MaimanFirst Ruby Laser

1960

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How a Laser Works

ATOM

PHOTONS

PHOTONS FROM EXTERNALSOURCE STRIKE ATOMSIN THE ROD.

ATOMS RELEASE MORE PHOTONS(STIMULATED EMISSION OF RADIATION)WHICH STRIKE OTHER ATOMS CONTINUING THE PROCESS (AMPLIFICATION).

MANY PHOTONS ARE REFLECTEDBACK AND FORTH BY THE MIRRORSAT EACH END OF THE ROD.

COHERENT, FOCUSED PHOTONS LEAVE THE ROD THROUGH A SLIT IN THE MIRROR.

MIRROR

MIRROR

SLIT

LIGHT AMPLIFICATION BY THE STIMULATED EMISSION OF RADIATION

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Ruby Laser

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Types of LasersBased on the Material Used in the Laser

Classes of LasersBased on the Biological Damage the Laser

Can Cause

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Laser Type Wavelength (nm)

•Argon fluoride (UV) 193•Krypton fluoride (UV) 248•Nitrogen (UV) 337•Argon (blue) 488•Argon (green) 514•Helium neon (green) 543•Helium neon (red) 633•Rhodamine 6G dye (tunable) 570 - 650•Ruby (CrAlO3) (red) 694•Nd:Yag (NIR) 1064•Carbon dioxide (FIR) 10600

Typical Lasers and Their Emission Wavelengths

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Optical Damage Threshold TestNASA Research Center

The Optical Damage Threshold test station at NASA Langley Research Center has three lasers: a high-energy pulsed ND:Yag laser,a Ti:sapphire laser and an alignment HeNe laser.

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Classes of LasersBased on the Biological Damage the Laser Can

CauseClass I: Lasers that don’t produce any harmful

radiation.Class II: Lasers that are harmful if viewed for

long periods of time. (The assumption is that people wouldn’t let this happen.)

Class III: Lasers that are dangerous for short exposure. (Many laser pointers are class III lasers!)

Class IV: Lasers that can blind or burn after a very brief exposure. These can only be used under very controlled conditions.

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LASER WEAPONS“Do you expect me to talk Goldfinger?”“No Mr. Bond, I expect you to die.”

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Laser Gun Sights

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Multiple Integrated Laser Engagement SystemMILES (2000)

“Laser Tag” for Soldiers

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Laser Targeting SystemAircraft Mounted

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Laser Guided Bomb(“Smart” Bomb)

Optical sensor

Guidance system

Control surfaces

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Laser Targeting

1. Laser targetingsystem “paints”target.

2. Laser guided weapon tracks

laser spot ontarget.

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Laser Targeting SystemGround Based

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Laser Targeting CountermeasuresAN/VVR-1 Laser Warning Receiver System

System detectsthe targetinglaser.

Countermeasuresinclude smoke,brighter laserbeam, maneuvering,etc.

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Laser Guided MissileHellfire laser guided missiles mounted on a US Army Apache helicopter gunship.

Newer variation (Hellfire II) replaces laser guidancewith radar guidance to penetrate smoke and cloud cover.

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ABLAirborne LaserAntimissile Weapon

United States Air Force

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ABLNose Turret

CO2 Targeting Laser

LASERS IN MANUFACTURING

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Punch Press

Punch Press Problems•Dangerous to operate.•Required long runs to be profitable.

Typical Stamped Parts

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Laser Cutter

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Computer Controlof Laser Cutter Equipment

•No human contactwith the part during operation.

•Computer programcan be loaded quickly. Shorter runs are nowprofitable.

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Laser Welding

Welded Parts

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Laser WeldingWelded car door panel made from three types of steel.

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Laser Stereolithography(SLA)

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Part Produced by

SLA

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LASERS IN MEDICINE

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Laser Eye SurgeryLAser in SItu Keratomileusis (Lasik)

1. Tiny flap of outercornea folded back.

2. Laser removes tissuefrom remaining corneato change its shape.

3. Flap of outercornea thenreattached.

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Laser Tattoo Removal(Doesn’t always work!)

The laser beam breaks up the pigments in the tattoointo small particles. Then the body’s immune systemattacks and destroys them.

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Laser Dentistry

Laser

Water jet

•Major advantage is no “drilling sound”.•Can’t be used on existing metal fillings.

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LASER TESTING AND MEASURING

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Laser Bar Code Scanning

Universal Product Code (UPC) Label

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Barcode on a UPS Label

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Barcode Scanner

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Railroad Car SortingUsing Barcode Scanning

Labels were often too dirty for thescanners to read.

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Laser Surface Roughness Tester

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Laser Level

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Laser Speed MeasurementNew York State Police

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Telescope Calibration Lick Observatory

The adaptive optics system at the Shane 3 meter telescope utilizes a 20-watt sodium laser to put a false star in the sky. The system uses the star to compensate for atmospheric disturbances, creating sharper, clearer images of the objects observed.

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LASER COMMUNICATION

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Laser Printer

Corona Wire Discharge Lamp

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Laser DiskPit

Land

Beam reflects:logical 1.

Beam doesn’t reflect:logical 0.

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Laser Disk Drive

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MODULATIONSuperimposing a weak signal

on a strong one

MODULATOR: Combines audio signal and laser beam.

DEMODULATOR: Removes audio signal from the modulated laser beam.

MODULATED LASER BEAM: Changes in the beam representinformation in the audio signal.Audio

Laser Carrier

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FIBER OPTICSTransparent “Pipe” for Light to Travel Through

Advantages:• Very high capacity.• Can’t be tapped into.• Not affected by electromagnetic (EM) interference.• Allows light to travel around corners.

Disadvantages:• Expensive.• Can be difficult to install.

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Fiber OpticsCenter fiber optic cable has greater capacity

than any of these bundles of cable.