SOME BASICS

OF

LASERS

L LightA Amplification byS StimulatedE Emission of R Radiation

A laser is a device that transforms light of

various frequencies into a chromatic radiation in the visible, infrared, and ultraviolet regions with all the waves in phase capable of mobilizing

immense heat and power when focused at

close range.

WHAT IS A LASER ?

• Light beam is composed of packets of energy known as PHOTONS

• Ground State – Atoms are normal position

• Atoms are excited by an energy source and move to a higher energy

• As it reverts back to its ground state, energy is emitted – Spontaneous Emission

• Results without external interference and forms waves that are in phase

HOW COHERENT AND INCOHERENT LIGHT WAVES

DIFFERS ?

• Is a part of a process that occurs inside the laser

• An optical cavity is at the center of the laser device & the core is comprised of chemical elements, molecules or compounds – “Active Medium”

• Lasers are generically named for the material of the active medium

• Gas, Crystals or Semi-Conductors

AMPLIFICATION

• Gas – Co2 & Argon

• Solid state semi conductors :– With metals like – Gallium, Aluminum, Indium,

Arsenic– With solid rods of garnet crystal growth with

various combinations of Yytrium, Aluminum, Scandium, Gallium and then doped with elements of Chromium, Neodynium or Erbium.

AMPLIFICATION

• The crystal or gas is excited to emit photons of a characteristic wavelength

• These ware amplified and filtered to make a coherent beam

• The effect of this energy depends on whether or not the WL of the energy is absorbed by the surface or not

AMPLIFICATION

STIMULATED EMISSION

• Quantum theory of Max Planck & Neils Bohr

• Smallest unit of energy

• It can be absorbed by electrons, cause brief excitation and then the quatum is released – Process called as Spontaneous Emission

• Refers to light waves produced by the laser as electromagnetic energy

• EM Spectrum – entire range Wavelength’s

.Within the visible or invisible infrared non-ionizing EM range & emit thermal radiation

.The dividing line between ionizing and non-ionizing portion is on the junction of ultraviolet and visible violet light

RADIATION

Laser consists of a lasing medium contained with an optical cavity, with an external energy source to maintain a population inversion so that stimulated emission of a specific wavelength can occur, producing monochromatic, collimated and coherent beam of light

• Active medium – Gas, liquid or solid

• Contained in glass or ceramic tubes

• Energy – Electric current

• Mirrors are added to each end to increase the back and forth movement of photons

• Thus increasing the stimulation of emission of radiation

• Two delivery systems that are employed

1. Hollow Waveguide or Tube

2. Glass fiber optic cable

LASER DELIVERY SYSTEMS

• Has an interior finish mirror

• Laser energy is reflected along this tube and exits through a hand piece

• Strikes the tissue in a non-contact manner

• An accessory tip of sapphire or hollow metal can be connected

1. FLEXIBLE HOLLOW WAVEGUIDE (TUBE)

• More flexible than waveguide

• Less weight and less resistance in movement

• Smaller diameter (200-600 μm)

• Glass component is encased in a resilient sheath

• Fragile & can’t be bent in sharp angles

• Used in contact and non-contact mode

2. GLASS FIBER OPTIC CABLE

Glass Fiber (Flexible)

Waveguide (Tube)

Argon Er

Diode Cr:YSGG

Nd:YAG Er:YAG

CO2

Fiber Optic

WAVEGUIDE TUBE

Level of applied power (Power

Density)

Total energy to

be delivered (Energy density)

Rate & Duration

of exposure(Pulse

Repetition)

Mode of energy delivery

WHAT DOES THE OPERATOR CONTROL?

Light Amplification by

Stimulated

Emission of RadiationSpontaneous emission Stimulated emission

• The possible energies which electrons in the atom can have is depicted in an energy level diagram.

ENERGY LEVEL DIAGRAM

E1

E2

E3

E4

LASER

The operation of the Laser

E1

E2

E3

E4

absorption

The operation of the Laser

E1

E2

E3

E4

Spontaneous emission

The operation of the Laser

E1

E2

E3

E4

Spontaneous emission

1. Incoherent light

2. Accidental direction

The operation of the Laser

The operation of the Laser

E1

E2

E3

E4

Stimulated emission

The operation of the Laser

E1

E2

E3

E4

Light: Coherent, polarized

The stimulating and emitted. photons have the same:

Frequency,

Phase,

Direction.

The operation of the Laser

TWO LEVEL SYSTEM

absorption Spontaneous emission

Stimulated emission

hn hnhn

E1

E2

E1

E2

h n =E2-E1

TYPES OF LASER 1. Based on the mode of operation

(i) Pulsed Laser systems(ii) High power Q-switched systems(iii) Continuous wave Laser systems

2.Based on the mechanism in which Population Inversion is achieved

(i) Three level lasers(ii) Four level lasers

3.Based on state of active medium used(i) Gas Laser(ii) Solid state Laser(iii) Semiconductor Laser(iv) Tunable dye Laser

THE ELECTROMAGNETIC SPECTRUM

LASER FUNDAMENTALS The light emitted from a laser is monochromatic, that is, it

is of one color/wavelength. In contrast, ordinary white light is a combination of many colors (or wavelengths) of light.

Lasers emit light that is highly directional, that is, laser light is emitted as a relatively narrow beam in a specific direction. Ordinary light, such as from a light bulb, is emitted in many directions away from the source.

The light from a laser is said to be coherent, which means that the wavelengths of the laser light are in phase in space and time. Ordinary light can be a mixture of many wavelengths.

These three properties of laser light are what can make it more hazardous than ordinary light. Laser light can deposit a lot of energy within a small area.

INCANDESCENT VS LASER LIGHT

1. Many wavelengths

2. Multidirectional

3. Incoherent

1. Monochromatic

2. Directional

3. Coherent

Common Components of all Lasers1. Active Medium

The active medium may be solid crystals such as ruby or Nd:YAG, liquid dyes, gases like CO2 or Helium/Neon, or semiconductors such as GaAs. Active mediums contain atoms whose electrons may be excited to a metastable energy level by an energy source.

2. Excitation Mechanism

Excitation mechanisms pump energy into the active medium by one or more of three basic methods; optical, electrical or chemical.

3. High Reflectance Mirror

A mirror which reflects essentially 100% of the laser light.

4. Partially Transmissive Mirror

A mirror which reflects less than 100% of the laser light and transmits the remainder.

LASER COMPONENTS

Gas lasers consist of a gas filled tube placed in the laser cavity. A voltage (the external pump source) is applied to the tube to excite the atoms in the gas to a population inversion. The light emitted from this type of laser is normally continuous wave (CW).

Factors affecting Laser classification level

6 main factors to consider:

- Wavelength

- Continuous Wave or Pulsed Operation

- Power or Pulse Energy

- Repetition Rate (PRF)

- Beam Diameter & Profile

- Beam Divergence

1. Energy is applied to a medium raising electrons to an unstable energy level.

2. These atoms spontaneously decay to a relatively long-lived, lower energy, metastable state.

3. A population inversion is achieved when the majority of atoms have reached this metastable state.

4. Lasing action occurs when an electron spontaneously returns to its ground state and produces a photon.

5. If the energy from this photon is of the precise wavelength, it will stimulate the production of another photon of the same wavelength and resulting in a cascading effect.

6. The highly reflective mirror and partially reflective mirror continue the reaction by directing photons back through the medium along the long axis of the laser.

7. The partially reflective mirror allows the transmission of a small amount of coherent radiation that we observe as the “beam”.

8. Laser radiation will continue as long as energy is applied to the lasing medium.

LASING ACTION

Lasing Action Diagram

En

erg

y

Intr

od

ucti

on

Ground State

Excited State

Metastable State

Spontaneous Energy Emission

Stimulated Emission of Radiation

WAVELENGTHS OF MOST COMMON LASERS

Argon fluoride (Excimer-UV)Krypton chloride (Excimer-UV)Krypton fluoride (Excimer-UV)Xenon chloride (Excimer-UV)Xenon fluoride (Excimer-UV)Helium cadmium (UV)Nitrogen (UV)Helium cadmium (violet)Krypton (blue)Argon (blue)Copper vapor (green)Argon (green)Krypton (green)Frequency doubled      Nd YAG (green)Helium neon (green)Krypton (yellow)Copper vapor (yellow)

0.1930.2220.2480.3080.3510.3250.3370.4410.4760.4880.5100.5140.5280.532

0.5430.5680.570

Helium neon (yellow)Helium neon (orange)Gold vapor (red)Helium neon (red)Krypton (red)Rohodamine 6G dye (tunable)Ruby (CrAlO3) (red)

Gallium arsenide (diode-NIR)Nd:YAG (NIR)Helium neon (NIR)Erbium (NIR)Helium neon (NIR)Hydrogen fluoride (NIR)Carbon dioxide (FIR)Carbon dioxide (FIR)

0.5940.6100.6270.6330.647

0.570-0.6500.6940.8401.0641.15  1.5043.392.709.6  

10.6   

Key:      UV   =   ultraviolet (0.200-0.400 µm)              VIS   =   visible (0.400-0.700 µm)              NIR   =   near infrared (0.700-1.400 µm)

Wavelength (mm)Laser Type

                                              

Laser OutputContinuous Output (CW) Pulsed Output (P)

                       

watt (W) - Unit of power or radiant flux (1 watt = 1 joule per second).

Joule (J) - A unit of energy

Energy (Q) The capacity for doing work. Energy content is commonly used to characterize the output from pulsed lasers and is generally expressed in Joules (J).

Irradiance (E) - Power per unit area, expressed in watts per square centimeter.

En

erg

y (W

atts

)

TimeE

ner

gy

(Jo

ule

s)Time

WAVE NATURE OF LIGHT

Light is an electromagnetic wave.

Different wavelengths in the visible spectrum are seen by the eye as different colors.

lWavelength

Red: l = 700 nm

Blue: l = 400 nm

Radio

Long Wavelength

Short Wavelength

Gamma Ray

X-ray Ultraviolet

Infrared Microwaves

Visible

ELECTROMAGNETIC SPECTRUM

Lasers operate in the ultraviolet, visible, and infrared.

Radio

RedBlue YellowGreen

STIMULATED EMISSIONIncident Photon

Excited Atom

Stimulated Photon same wavelength same direction in phase

Incident Photon

CHARACTERISTICS OF LASER LIGHT

MONOCHROMATIC

DIRECTIONAL

COHERENT

The combination of these three properties makes laser light focus 100 times better than ordinary light

HELIUM-NEON GAS LASER

SIMPLE EXAMPLE

OF LASER :

APPLICATIONS OF

LASERS

APPLICATION OF LASERMany scientific, military, medical and commercial laser applications have been developed since the invention of the laser in 1958. The coherency, high monochromaticity, and ability to reach extremely high powers are all properties which allow for these specialized applications.

SCIENTIFIC In science, lasers are used in

many ways, including: A wide variety of interferometric

 techniques Raman spectroscopy Laser induced breakdown spectr

oscopy Atmospheric remote sensing Investigating nonlinear optics

 phenomena

Holographic techniques employing lasers also contribute to a number of measurement techniques.

Laser based LIght Detection And Ranging (LIDAR) technology has application in geology, seismology, remote sensing and atmospheric physics.

Lasers have been used aboard spacecraft such as in the Cassini-Huygens mission.

In astronomy, lasers have been used to create artificial laser guide stars, used as reference objects for adaptive optics telescopes.

Lasers may also be indirectly used in spectroscopy as a micro-sampling system, a technique termed Laser ablation (LA), which is typically applied to ICP-MS apparatus resulting in the powerful LA-ICP-MS.

The principles of laser spectroscopy are discussed by Demtröder and the use of tunable lasers in spectroscopy are described in Tunable Laser Applications.

 ).

DOPPLER EFFECT

Definition:- There is an apparent change in frequency of the sound waves emitted from the source, when there is a relative motion between the source and the observer. This effect is called Doppler effect and the shift in frequency is called as doppler shift.

DOPPLER SHIFT

RED SHIFT BLUE SHIFT

GRAVITATIONAL COSMOLOGICAL

LASER COOLING The use of Lasers to

achieve extremely low temperatures has advanced to the temperatures of 10e-9 K.

These laser cooling can be used for transmitting power without any loss from power station to sub station without the help of power transformers.

COMMUNICATION AT PRESENT

The speed of the communication is high,

But still the communication with the outer world is still lagging.

IN FUTURE

Using LASER the communication to other galaxy is possible.

COMPUTING SPEEDS

At present the computing speed ranges from 256 kilobits per

second to 1 gigabit per second, which is slow for the present

world. The ability to achieve a speed of 25 gigabits

per second can be done with the use of laser chips.

Lasers are already used to transmit high volumes of computer data over longer distances — for example, between offices, cities and across oceans — using fibre-optic cables. In computer chips, data moves at great speed over the wires inside, then slows when it is sent chip-to-chip inside a computer.

MILITARY DEFENCE

1.Find TargetAn infrared camera on the laser continuously scans a 6 to 10-mile radius around the airport for suspicious heat emissions. When it finds a plume, it relays the coordinates to an identification and tracking system, which is also on the unit.

2.Confirm ThreatThe onboard computer checks the object’s heat signature against a data bank, confirms that it’s a missile (and not a bird or a plane), and activates the laser.

3.Prepare to FireReactive gases in the laser’s fuel tanks are funneled through a vacuum tube to heat up atoms and send them cascading through resonator mirrors. This produces a tightly focused, high-energy beam.

4.Destroy MissileThe laser-beam cannon emits a burst of intense light aimed at the missile’s most vulnerable spot, usually the explosives compartment. Simultaneously, it sends a signal to airport control tower to give authorities a fix on the origin of the rocket.

MILITARYMilitary uses of lasers include applications such as target designation and ranging, defensive countermeasures, communications and directed energy weapons.

METEOROIDS ATTACKS The concept which was

used for military defence can be used to destroy the meteoroids coming towards earth.

These incoming meteoroids can be shattered into pieces, thus saving our earth from any major destruction.

A group of strong laser beams are focused together to the target and the target is shattered off.

LASER IN AUTOMOBILES

We are proposing our own idea for the use of laser light in automobiles. All automobiles have ball bearings in there wheels, these bearings wear off while use and this may cause accidents. To prevent these accidents we use a laser beam to detect the position of the shaft in the wheels, on one end there will be a laser and the other end a sensor is kept, when the ball bearing malfunctions the shaft position is moved from the original position, now the sensor is activated. This sensed signal is sent to the user. Now the user should take necessary actions to prevent accidents due to a ball bearing.

MATERIAL PROCESSINGLaser cutting, laser welding, laser brazing, laser bending, laser engraving or marking, laser cleaning, weapons etc. When the material is exposed to laser it produces intense heat, thus the material is heated and melted.

LASER COOLING A technique that has recent success

is laser cooling. This involves atom trapping, a method where a number of atoms are confined in a specially shaped arrangement of electric and magnetic fields. Shining particular wavelengths of laser light at the ions or atoms slows them down, thus cooling them. As this process is continued, they all are slowed and have the same energy level, forming an unusual arrangement of matter known as a Bose-Einstein condensate.

MEDICAL Cosmetic surgery (removing tattoos,

scars, stretch marks, sunspots, wrinkles, birthmarks, and hairs): see laser hair removal. Laser types used indermatology include ruby (694 nm), alexandrite (755 nm), pulsed diode array (810 nm), Nd:YAG (1064 nm), Ho:YAG (2090 nm), and Er:YAG (2940 nm).

Eye surgery and refractive surgery

Soft tissue surgery: CO2, Er:YAG laser

Laser scalpel (General surgery, gynecological, urology, laparoscopic)

Photobiomodulation (i.e. laser therapy)

"No-Touch" removal of tumors, especially of the brain and spinal cord.

In dentistry for caries removal, endodontic/periodontic  procedures, tooth whitening, and oral surgery

CURIOSITY USING ITS ‘LASER DEVICE ‘ IN ITS

MISSION

OTHER APPLICATIONS Cutting and peening of metals and other

material, welding, marking, etc.

Laser drilling Guidance systems (e.g., ring laser gyroscopes) Rangefinder / surveying, LIDAR / pollution monitoring,

Laser cladding, a surface engineering process applied to mechanical components for reconditioning, repair work or hardfacing

Laser accelerometers

INDUSTRIAL AND COMMERCIALLevelling of ceramic tiles floor

with a laser device

LASERS USED FOR VISUAL EFFECTS DURING

A MUSICAL PERFORMANCE. (A LASER LIGHT SHOW.)

Laser line levels are used in surveying and construction. Lasers are also used for guidance for aircraft.

Extensively in both consumer and industrial imaging equipment. In laser printers: gas and diode lasers play a key role in

manufacturing high resolution printing plates and in image scanning equipment.

Diode lasers are used as a lightswitch in industry, with a laser beam and a receiver which will switch on or off when the beam is interrupted, and because a laser can keep the light intensity over larger distances than a normal light, and is more precise than a normal light it can be used for product detection in automated production.

Laser alignment Additive manufacturing In consumer electronics, telecommunications, and 

data communications, lasers are used as the transmitters in optical communications over optical fiber and free space.

To store and retrieve data in optical discs Laser lighting displays (pictured) accompany many music

concerts.

Digital minilabsBarcode readersLaser engraving of printing plateLaser bonding of additive marking materials for decoration and identification,

LASER POINTERS:

Holography Bubblegrams Photolithography Optical communications (over 

optical fiber or in free space) Optical tweezers Writing subtitles onto motion picture 

films.[18]

Space elevator, a possible solution transfer energy to the climbers by laser or microwave power beaming

3D laser scanners for accurate 3D measurement.

IS LASER

DANGER ?

Laser-Professionals.com

LASER BEAM INJURIES

High power lasers can cause skin burns.

Lasers can cause severe eye injuriesresulting in permanent vision loss.

SKIN BURN FROM CO2 LASER EXPOSURE

Accidental exposure to partial reflection of 2000 W CO2 laser beam

from metal surface during cutting

Class 4 Unsafe for eyesUnsafe for skin

0.5W Class 3B Unsafe for eyesGenerally safe for skin

5mW Class 3R Safe with (0.25 s.) aversion response no viewing aids

0.5W Class 2MVisible wavelengths only

Safe with no viewing aids

1mW Class 2Visible wavelengths only

Safe with (0.25 s.) aversion response including viewing aids

0.5W Class 1M Safe with no viewing aids

220μW to 0.4μW

Class 1 No precautions required

LASER CLASSIFICATION SYSTEM

App

rox.

Pow

er L

imits

for

CW

Vis

ible

Wav

elen

gths

Onl

y

OLD LASER CLASSIFICATION SYSTEM

Class 4 Unsafe for eyesUnsafe for skin

0.5 W Class 3B Unsafe for eyesGenerally safe for skin

5 mW Class 3A Safe with (0.25 s.) aversion response no viewing aids

1 mW Class 2Visible wavelengths only Safe with (0.25 s.) aversion

response including viewing aids

220μW to 0.4μW

Class 1 No precautions required

App

rox.

Pow

er L

imits

for

CW

Vis

ible

Wav

elen

gths

Onl

y

LASER SAFETY PRECAUTIONS

BY CLASSIFICATIONClass 1 Lasers : - Safe

Class 1M Lasers: - No viewing aids

Class 2 Lasers : - Safe with aversion response

(No staring)

Class 2M Lasers: - Safe with aversion response

(No staring); No viewing aids

Class 3R Lasers : - No Staring, No viewing aids,

(also old Class 3A lasers) Unsafe outside visible range

LASER SAFETY PRECAUTIONS

BY CLASSIFICATION, CONTINUE…….

Class 3B Lasers : - Unsafe for eyes, generally safe for skin

Class 4 Lasers : - Unsafe for eyes, unsafe for

skin

A NOTE ABOUT EYE SAFE LASERS

.Lasers with emission wavelengths longer than 1400nm are often labelled as ‘eye-safe’ because wavelengths greater than 1400nm are strongly absorbed in the cornea & lens of the eye rather than the relatively more sensitive retina.

.High powered or pulsed lasers at these wavelengths will still burn the cornea and cause severe eye damage. Corneal injuries are very painful.

A laser labelled eye-safe should be treated the same as any other laser – with extreme caution. NEVER stare at a laser beam.

LASER CONTROLS

PPEThe main form of protective equipment is protective eyewear, but when using Class 4 lasers protective clothing and footwear must also be worn

GENERAL LASER LAB SAFETY, CONT.

Clothing: Long sleeve clothing should be worn to protect skin. Wear enclosed footwear in labs.

Jewelry: watches & rings which could reflect beams should not be worn.

Viewing Aids: Never use microscopes, telescopes, magnifying glasses etc to view laser beams

General Laser Lab Safety

Never directly view a laser beam.

Never point a laser pointer at a person.

Never over-ride interlocks

Never remove covers from equipment without approval from supervisors – laser, high voltages and other hazards are present.

THANK YOU

REFERENCES