Chapter 3_laser [Compatibility Mode]

7/27/2019 Chapter 3_laser [Compatibility Mode]

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LASER

Dr. Satyam Shinde

Assistant Professor in Physics, School of Technology

Pandit Deendayal Petroleum University, Gandhinagar


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What is LASER?

Stands for

Light Amplification by Stimulated Emission of

Radiation

It is a quantum physical phenomenona in which highly

concentrated, highly intense, highly monochromatic andpowerful light wave is produced through process of

population inversion and stimulated emission.


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Where LASER is used?


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1916:

Albert Einstein can be considered the fatherof the laser.

He established photons and postulated stimulated

emission.

History of Lasers

1958:

. . c aw ow an . . ownes pu s e t e r paper"Infrared and optical masers" on the possibility of laser

action in the infrared and visible spectrum.

1960:

T.H. Maiman constructed at Hughes Laboratory in Malibu

(California) the first successful laser. His laser consisted

of a ruby rod, with its ends silvered to reflect light, which

he placed inside a spring-shaped flashlight.


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Normal Light Wave Vs LASER

Opposite to LASER, normal light wave is highly incoherent i.e. it is

formed as a result of superposition of millions of photons which are

having different phase, freqency, energy and direction.

As a result the normal light wave has less intensity, large divergence

and hence can not travel a longer distance.

The main reasons for this ro erties of normal li ht wave is due to

following:

1. We do not have any control on which atom will absorb which

photon and when

2. We do not have any control on time for which atom remain in

excited state

3. We do not have control on steps of deexcitation

4. We do not have any control on direction in which photon will be

emitted


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E1

What happens in a LASER?

1. Quantum Absorption:

E2

Excitation

Life Time of an electron or atom in excited state (~ 10-8 Sec)


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2. Spontaneous Emission

The emission of photon from excited state to ground state within 10-8

Sec without any external force byitself is known as spontaneous

emission.


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1. Energy is applied to a medium raising electrons to an unstable energylevel. These atoms spontaneously decay to a relatively long-lived, lowerenergy, metastable state.

2. As process is continued more and more atoms will accumulated in the statecalled metastable state and condition is achieved when no. of atoms inexcited state becomes higher than no. of atoms in lower state, resulting in astate called population inversion.

Stimulated Emission:

8

3. Lasing action occurs when any one of the excited electron spontaneouslyreturns to its ground state and produces a photon. If the energy from thisphoton is of the precise wavelength, it will stimulate the another atom tode-excite and produces another photon of the same wavelength and

resulting in a cascading effect.

4. This forceful emission of an electron from metastable state is known asstimulated emission.


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ntroduction

Excited State

Metastable State

Non radiative Spontaneous

Energy Emission

Energy

I

Ground State

Stimulated Emission

of Radiation

Lasing Action

*2h A h + +


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The critical detail of stimulated emission is that the induced photon has the

same frequency and phase as the incident photon. In other words, the twophotons are coherent. It is this property that allows optical amplification, and

the production of a laser system. During the operation of a laser, all three

light-matter interactions described above are taking place. Few important

features of stimulated emission are as follows:

The emitted photon is exactly identical to the incident photon in allrespects. The process is controllable from outside.

Photons are multiplied in this process. One photon induces an atom toemit a second photon, these two traveling along the same direction to de-

excite two atoms in their path and producing four photons which in turn

stimulate eight photons and so on.

The constructive interference of many waves traveling in the samedirection with same frequency and phase produces an intense coherent lightbeam. The net amplitude of wave is proportional to the number of atoms that

contributed to it and the net intensity is proportional to the square of the

number of atoms.


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Population Inversion and Thermal Equilibrium

Under thermal equilibrium condition, N1 and N2 are fixed by the

Boltzmann factor. The population ratio is given by

( )2 12

1

E EkTN

eN

=

The negative exponent indicates N2 < N1 at equilibrium. When the

external radiation incident to the N1 atoms having E1 energy sate then

they will make transition to upper energy level E2 by absorbing thephotons energy. Then they de excite to E1 once again. In order to maintain

N1 and N2 constant, the number of upward and downward transitions

must be same.

ab sp st N N N= +

12 1 21 2 21 2B N Q A N B N Q= +

The coefficients A12, B21 and B12 are calledEinstein coefficients.


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Conditions for light amplification

At thermal equilibrium, the ratio of the stimulated to spontaneoustransitions is generally very small and the stimulated emission is negligible.

The ratio is given by

21 2 21

21 2 21tan

B N Q Bstimulated transitionsQ

spon eous transition A N A= =

The ratio of stimulated to absorption transitions is given by

21 2 2

12 1 1

B N Q Nstimulated transition

absorption transition B N Q N= =

Above eq.(7.9) indicates that in order to enhance the number ofstimulated transitions, the radiation density Q is to be made larger.

Here, B12=B21 as the probability of stimulated transition must be equal

to the probability of absorption transition.


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Mode of Pumping

Pumping is the process by which the atoms are energized from the ground

state to the excited state. Some of these atoms decay via spontaneous

emission, releasing incoherent light as photons of frequency, . These

photons are fed back into the laser medium, usually by an optical resonator.Some of these photons are absorbed by the atoms in the ground state, and the

photons are lost to the laser process. However, some photons cause

stimulated emission in excited-state atoms, releasing another coherent

p o on. n e ec , s resu s n op ca mp ca on. e num er o

photons being amplified per unit time is greater than the number of photons

being absorbed, then the net result is a continuously increasing number of

photons being produced; the laser medium is said to have a gain of greater

than unity.

Recall from the descriptions of absorption and stimulated emission above

that the rates of these two processes are proportional to the number of atoms

in the ground and excited states, N1 and N2, respectively.


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If the ground state has a higher population than the excited state (N1 >N2), the process of absorption dominates and there is a net attenuation of

photons.

If the populations of the two states are the same (N1 = N2), the rate of

absorption of light exactly balances the rate of emission; the medium isthen said to be optically transparent.

If the higher energy state has a greater population than the lower energy

state (N1 < N2), then the emission process dominates, and light in thesystem undergoes a net increase in intensity.

It is thus clear that to produce a faster rate of stimulated emissions than

absorptions, it is required that the ratio of the populations of the two

states is such that N2/N1 > 1.

In other words, a population inversion is must for laser operation.


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Commonly used pumping techniques are:

Optical pumping is used in solid state lasers in which light source suchas flash discharge tube is used.

Electrical discharge uses the electric field which causes ionization of

medium and raises it to an excited state. This technique is used in gas

lasers.

Direct conversion causes conversion of electrical energy to light energy

.


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Optical Resonator

The arrangement consist of active medium between two mirrors: one

semitransparent and other 100% reflecting mirror is known as optical

resonator.

Three practical requirements has to be satisfied:

Positive feedback must be employed

Directional selectivity

Optical amplification


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17


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Stage 1: In an equilibrium condition, all atoms are in ground state and active

medium is placed in between two mirrors to form optical resonator.

Stage 2: When am energy is supplied to the system through proper pumping,

atoms are excited to normal higher state. Spontaneous emission takes

place from higher state to ground state and to metastable state. The

photons emitted are highly incoherent.

Stage 3: Here, photons emitted in a direction other than along optical axis or

parallel to optic axis are removed from the system. The photons emitted

n a rec on a ong op c ax s are re ec e rom e er sem ransparen

mirror or 100% reflecting mirror. In their path they de-excite other

atoms and thus such coherent photons increases their number.

Stage 4: So, on one side number of incoherent photons decreases and on other

side number of highly coherent photons increases. During this repeatedprocess these coherent photons super impose multiple times and slowly

optical intensity is amplified.

Stage 5: When enough intensity is build up within the system, the laser beam will

emerged from the opening provided.


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In order to ensure that optical intensity is build up quickly, we keep the

length of an optical resonator such that it satisfy the following conditions forformation of standing waves:

Where m is number of modes of waves.

Thus photons which are highly coherent and satisfies this condition of

2

mm

L

=

,

those photons which are coherent but does not support standing waves willgradually eliminated from the system.


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LASER Characteristics

Coherence:

The coherence length emitted by normal light wave is coherent for

about few millimeters, whereas in case of lasers normally it is up to

kilometers. The relation for coherence length is,

where c = L/C is coherence tome.

Directionality:cohr cl c=

Divergence: Divergence or angular spread of the laser beam is given as,

Intensity:

Monochromaticity:

1.22d d

=


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The ruby mineral (corundum) is aluminum oxide with a small amount(about0.05%) of chromium which gives it its characteristic pink or red color byabsorbing green and blue light. The ruby laser is The ruby laser is used as apulsed laser, producing red light at 694.3 nm. After receiving a pumping flashfrom the flash tube, the laser light emerges for as long as the excited atoms

persist in the ruby rod, which is typically about a millisecond.

RUBY LASER


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For a ruby laser, a crystal of ruby is formed into a cylinder. The rod'sends had to be polished with great precision, such that the ends of the rod

were flat to within a quarter of a wavelength of the output light, and parallelto each other within a few seconds of arc. The finely polished ends of the rod

were silvered: one end completely, the other only partially. The rod with its

reflective ends then acts as a Fabry-Prot etalon. A xenon lamp is rolled over

ruby rod and is used for pumping ions to excited state.


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High-voltage electricity causes the quartz

flash tube to emit an intense burst of light,

exciting some of Cr3+ in the ruby crystal tohigher energy levels.

At a specific energy level, some Cr3+ emit

photons. At first the photons are emitted

in all directions. Photons from one Cr3+

stimulate emission of photons from other

Cr3+ and the light intensity is rapidly

amplified.


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Mirrors at each end reflect the

photons back and forth, continuingthis process of stimulated emission

and amplification.

The photons leave through the

partially silvered mirror at one

end. This is laser light.


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Ruby lasers have declined in use with the discovery of

better lasing media. They are still used in a number of

applications where short pulses of red light are required.

Heliographers around the world produce holographic

portraits with ruby lasers, in sizes up to a meter squared.

ApplicationApplicationApplicationApplication

Many non-destructive testing labs use ruby lasers to

create holograms of large objects such as aircraft tires to

look for weaknesses in the lining.

Ruby lasers were used extensively in tattoo and hair

removal.


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He-Ne LASER

Gas lasers usually employs a mixture of two gases, say A and B. Atoms of

kind A are excited through impact of electron and then they transfer theirenergy to atoms of kind B which are actually plays the role of active centers.

The gas laser uses gases like He, Ne, argon etc and excited normallythrough electric discharge pumping.


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Construction of He-Ne laser

The setup consists of a discharge tube of length 80 cm and bore diameter of1.5cm. The gain medium of the laser, as suggested by its name, is a mixture

of helium and neon gases, in a 5:1 to 20:1 ratio, contained at low pressure(an average 50 Pa per cm of cavity length ) in a glass envelope.

discharge of around 1000 volts through an anode and cathode at each endof the glass tube. A current of 5 to 100 mA is typical for CW operation.

The optical cavity of the laser typically consists of a plane, high-reflecting

mirror at one end of the laser tube, and a concave output coupler mirror ofapproximately 1% transmission at the other end. HeNe lasers are normally

small, with cavity lengths of around 15 cm up to 0.5 m, and optical output

powers ranging from 1 mW to 100 mW.


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Working of He-Ne laser

AA descriptiondescription ofof thethe ratherrather complexcomplex HeNeHeNe excitationexcitation processprocess cancan bebe givengiveninin termsterms ofof thethe followingfollowing fourfour stepssteps::

WhenWhen thethe powerpower isis switchedswitched on,on, AnAn energeticenergetic electronelectron collisionallycollisionally excitesexcitesaa HeHe atomatom toto thethe statestate labeledlabeled 2211SS .. AsAs electronelectron hashas smallersmaller massmass itit cancan bebe

acceleratedaccelerated easilyeasily comparedcompared toto heavyheavy NeNe atomsatoms..

TheThe excitedexcited He*(He*(2211S)S) atomatom collidescollides withwith anan unexcitedunexcited NeNe atomatom andand thetheatomsatoms exchangeexchange internalinternal energy,energy, withwith anan unexcitedunexcited HeHe atomatom andand excitedexcited NeNe

atom,atom, writtenwritten Ne*(Ne*(33ss22),), resultingresulting.. ThisThis energyenergy exchangeexchange processprocess occursoccurs

withwith highhigh probabilityprobability onlyonly becausebecause ofof thethe accidentalaccidental nearnear equalityequality ofof thethe

twotwo excitationexcitation energiesenergies ofof thethe twotwo levelslevels inin thesethese atomsatoms.. Thus,Thus, thethe purposepurpose

ofof populationpopulation inversioninversion isis fulfilledfulfilled..

WhenWhen thethe excitedexcited NeNe atomatom passespasses fromfrom metastablemetastable state(state(33s)s) toto lowerlowerlevel(level(22p),p), itit emitsemits photonphoton ofof wavelengthwavelength 632632 nmnm..


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ThisThis photonphoton travelstravels throughthrough thethe gasgas mixturemixture parallelparallel toto thethe axisaxis ofof tube,tube, itit isisreflectedreflected backback andand forthforth byby thethe mirrormirror endsends untiluntil itit stimulatesstimulates anan excitedexcited NeNe

atomatom andand causescauses itit toto emitemit aa photonphoton ofof 632632nmnm withwith thethe stimulatingstimulating photonphoton..

TheThe stimulatedstimulated transitiontransition fromfrom ((33s)s) levellevel toto ((22p)p) levellevel isis laserlaser transitiontransition..ThisThis processprocess isis continuedcontinued andand whenwhen aa beambeam ofof coherentcoherent radiationradiation becomesbecomes

sufficientlysufficiently strong,strong, aa portionportion ofof itit escapeescape throughthrough partiallypartially silveredsilvered endend..

TheThe NeNe atomatom passespasses toto lowerlower levellevel 11ss emittingemitting spontaneousspontaneous emissionemission.. andand

andand undergoesundergoes radiationradiation lessless transitiontransition..

ApplicationApplication::

TheThe NarrowNarrow redred beambeam ofof HeHe--NeNe laserlaser isis usedused inin supermarketssupermarkets toto readread barbar

codescodes..

TheThe HeHe-- NeNe LaserLaser isis usedused inin HolographyHolography inin producingproducing thethe 33DD imagesimages ofofobjectsobjects..

HeHe--NeNe laserslasers havehave manymany industrialindustrial andand scientificscientific uses,uses, andand areare oftenoften usedused inin

laboratorylaboratory demonstrationsdemonstrations ofof opticsoptics


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Introduction to Fibre Optics

Communication:

The term communication may be defined as the transfer of informationfrom source to destination.

Need : Efficient communication system.

Problem: loss of signal during communication process, distortion and

attenuation.

This problem was taken up by the engineers in the early 1970 with fabrication

of low loss optical fibers and semiconductor lasers, which led us torevolutionary concept of optical fiber communication systems. The

applications of optical fibers are now ever-increasing with proliferation of

internet along with in the areas of telecommunication, sensors and many more.


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Basically the communication system has three parts: (i) transmitter;which transmits the signal (either diode laser or LED) (ii) transmission

channel or carrier guide and (iii) receiver which is photo detector,

detects it and signal is electronically processed to retrieve the signal.

What is in it?


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How it is done?

@ If we need to transmit a signal or information over a longer

distance, the information or signal is modulated on the

electromagnetic wave such as radio wave or microwave.

@ Then it is transmitted by the transmitter through a channel and it

is received by the receiver at other end. This modulated information

is then demodulated and converted into the required information.


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Why laser based fibre optic system?

@ With development of lasers which provides reliable and powerful

coherent radiation, possibility of use of electromagnetic waves having

optical range of frequency is also being explored.

@ There are two reasons due to which it is natural to use light for

communication purpose:

(ii) more information carrying capacity compared to conventional

radio and microwave carriers.

@ However as light waves can not travel a longer distance because of

high dissipation rate of energy in the open atmosphere, it requires some

kind of guiding channel just in case of electric current the metallic wire is

needed. In case of light waves for communication optical fiber provides

crucial wave guide for light.


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Thus, fiber optics is a technology related to transportation of

optical energy in guiding media specifically glass fibers. This

communication system is known as fiber-optic communication system.

Principle of the Optical Fiber: Total internal reflection

sin

sin

ci

r=

1sinci

=


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Construction of an optical fibre cable

@ We can use the principle of total internal reflection to construct an optical

fiber, which can guide the light wave up to long distance. However we

have to keep two important conditions in our mind: first the refractive

index of the inner medium must be greater than outer surface and

second the light wave must reach the wall of the optical fiber at anangle of incidence greater than critical angle, otherwise gradual loss of

energy will take place and light wave will be attenuated.


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@ As shown in the above figure an optical fiber consists of an inner

cylinder generally made up of dielectric glass of refractive index 1known as core and this core surrounded by another cylindrical shellhaving refractive index lower than the core known as cladding. This

cladding helps to keep the light wave within the core through the

phenomenon of total internal reflection. In addition to this, to protect the

fiber from external mechanical influences the cladding is covered withsoft plastic coating (primary coating) which is often followed by another

coating (secondary coating).

A t l


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Acceptance angle

@ Acceptance angle of the fiber is defined as the maximum value of theangle of incidence at the entrance end of the fiber, at which the angle of

incidence at the core-cladding interface is equal to critical angle of the

core medium.

@ Now it is clear that the rays which will incident at an angle less than

critical angle c at interface will suffer partial reflection and may be leaked out

of the fiber. However the ray, which will incident at an angle greater than

critical angle c will undergo total internal reflection. Thus, this max for

which total internal reflection takes place is called acceptance angle and

respective cone is known as acceptance cone.


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02

1sin sin (90 ) cosc r r

n

n = = =

2 2

1

max 1

0

0

max

1

1 sin

sin, ( ' )sin

sin sin

r

r

r

n

n

nnow from Snell s Lawn

n

n

=

=

=

1

2 2 2sinn n

22 2

0 max 2

2

1 1

22 2 2 2

0 max 2 1 2

2 2

1 1 1

2 2

2 1 2

sin1

sin1

n n

n n

n n n n

n n n

n n

=

= =

2

1 1

22 2

0 max 2

2

1 1

sin1

n n

n n

n n

=

=

( )

ma x 2

0

1

2 2 21 2

ma x

0

sin

n

n n

n

=

The quantity n0sin

max is known as numerical aperture and we can obtain lightgathering capacity of the system can be achieved by squaring the NA.

( )1

2 2 21 2

NA = n n( )2 21 21

max

0

sinn n

n

=

Numerical Aperture

Acceptance angle

T f O ti l fib


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Now question may be arise in ones mind: what criteria should we considerfor an optical fiber if we want to use it as a replacement of metallic cables in

a communication system?

We can include following factors among many for this case:

@ It should be long lasting with invariable optical and transmission

characteristics

Types of Optical fiber

@ It must be possible to fabricate optical fibers with different characteristics

such as relative refractive index, size, operating frequencies etc.

@ The connections between fibers should be such that produces least loss.

In reference to above facts, we can broadly classify the fibers in three

categories:

(i) Based on the materials

(ii) The mode of propagation and

(iii) The refractive index.

B d th t i l


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Based on the materials

@ We need two compatible transparent materials with different operatingfrequency. In addition they must have relative difference in refractive index and

must be able to transform in long, thin and flexible fibers.

@ In this present scenario our choice of materials for fabrication of opticalfibers are limited to either glass or plastic. However as plastic exhibits high

attenuation, the best choice for fibers is glass.

ere are t ree cruc a c aracter st cs w c ma es g ass most su ta e:

i. It gradually becomes stiffer with temperature variation and this helps

to transform into thin fiber of desired thickness

ii. Pure silica exhibits extremely low loss and up to 96 % transparency

iii. Great intrinsic mechanical strength. To create difference in refractiveindex between the core and cladding, either fluorine or oxides are

added such as TiO2, Al2O3, GeO2, P2O5 etc, in silica with silicon

dioxide.

Plastic core with Plastic cladding Glass core with Plastic cladding Glass core with Glass cladding


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Based on mode of propagation

@ Before we discuss the different types of fibers on the basis of mode of

propagation, let is define two more terms: (i) index profile (ii) step index

fiber and (iii) Graded index fiber.

@ From the basic knowledge of fiber, we know that the refractive index ofcore and that of cladding are different. However, cladding itself must have

uniform refractive index, while the refractive index of core may not or may

.

@ The curve representing variation of refractive index of core with respect

to the radial distance from the axis of the fiber is termed as index profile.

There are two types of index profile:

(i) Step index Profile or Step index fiber

(ii) Graded index profile or graded index fiber


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St I d fib


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Step Index fibre

Single Mode Step Index fibre Multi Mode Step Index fibre

Core diameter narrow-only one

mode will propagate

Small core and sin le li ht wave

Core diameter larger- many mode

will propagate

Different modes travels different

Less distortion due to less

overlapping

Least attenuation and highest

transmission speed

results in distances in different time

Grouping at the end results in

spreading

Less information carrying capacity &

used for short distance transmission


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@ As shown in figure (a), step index fiber the core has uniform refractive

index through out the core radius and undergoes an abrupt change at core-cladding interface. As at the interface, the index profile is a step function,

this type of fiber is referred as step index fiber. There are two type of step

index fiber: single mode step index fiber and multimode step index fiber.

@ Single Mode Fiber with a relatively narrow diameter, through which

only one mode will propagate typically of 1310 or 1550 nm. Single-mode

fiber has a much smaller core than multimode. The small core and single

light-wave virtually eliminate any distortion that could result from

overlapping light pulses, providing the least signal attenuation and thehighest transmission speeds of any fiber cable type.

@ The second type of step index fiber is multimode step index fiber in

which fiber has relatively large core of diameter of 50-100 micrometerwith cladding diameter in a range of 100-250 micrometer as shown in

figure (b). As a result, some of the light rays that make up the digital

pulse may travel a direct route, whereas others zigzag as they bounce off

the cladding.


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@ These alternative pathways cause the different groupings of light rays,

referred to as modes, to arrive separately at a receiving point. The pulse, an

aggregate of different modes, begins to spread out, losing its well-defined

shape. The need to leave spacing between pulses to prevent overlapping

limits bandwidth that is, the amount of information that can be sent.

Consequently, this type of fiber is best suited for transmission over short

distances, in an endoscope, for instance.

@ The multimode graded index fiber contains a core in which the

refractive index diminishes raduall from the center axis out toward the

cladding as shown in figure (c). The higher refractive index at the center

makes the light rays moving down the axis advance more slowly than those

near the cladding. Also, rather than zigzagging off the cladding, light in the

core curves helically because of the graded index, reducing its travel

distance. The shortened path and the higher speed allow light at the

periphery to arrive at a receiver at about the same time as the slow butstraight rays in the core axis. The result is less dispersion for digital pulses.

These fibers can handle higher bandwidths and provides longer lengths of

transmission.


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Graded Index fibre

Multi Mode graded Index fibreCore diameter larger and refractive

index decreases gradually from

centre to interface

Light ray travels slowly near axisLight ray travels helically

Shortened path and higher

speed results in

Can handle larger bandwidth

and longer transmission

Grouping at the end at same time

Less dispersion for digital pulses


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Multimode fiber offers

several advantages

over the single modefibers such as easy

connecting procedure,

low ower source

such as LED and

therefore less

expensive compared

to single mode fibers.

What is holography?


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What is holography?

Green 3-D image of Yoda and many images in star wars wereactually a hologram

@ Holography was invented in 1947 by Hungarian physicist Dennis Gabor.

@ Did not really advance until the invention of LASER in 1960.

@ He received the Nobel Prize in physics in 1971.

What happens when a photo is taken:


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What happens when a photo is taken:

@ The shutter opens.

@ Light passes through a lens and hits

the photographic emulsion on a piece of

film.

@ Silver halide reacts with the light andrecords its amplitude as it reflects off of

the scene.

.

@ It is a point-to-point recording of the intensity of light rays that make up

an image. Each point on the photograph records just the intensity of the light

wave that illuminates that particular point.

@ When we develop the film and make a print of the picture, our brain

interprets the light that reflects from the picture as a representation of the

original image.


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1. Laser: Red lasers, usually helium-neon

lasers, are common in holography.

2. Lenses: Holography is often referred to

as "lensless photography," but holography

does require lenses. However, a camera's

lens focuses light, while the lenses used inholography cause the beam to spread out.

3. A beam splitter: This is a device that

of light into two beams.4. Mirrors: These direct the beams of

light to the correct locations. Along with

the lenses and beam splitter, the mirrors

have to be absolutely clean. Dirt andsmudges can degrade the final image.

5. Holographic film: Holographic film can record light at a very high resolution,

which is necessary for creating a hologram. It's a layer of light-sensitive

compounds on a transparent surface, like photographic film


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SecurityAnd many more

Holography

Display

Medical


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Holography in Medicine Holographic technique is also used in

various medical applications. (eg. CATscans, X-ray, MRI, Ultrasound)

Future Applications of Holographic


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Technology

@ Future liquid crystal displays (LCDs) are expected to be brighterand whiter.

@ Holographic computers will be able to transfer trillions of bits ofinformation faster than the latest computers.

@ Currently, holographic security methods use a mostly mass-produced hologram. In the future, we are more likely to see aunique encrypted signature whose validity can only be checked

.

@ Holograms can also replace disc drives, microfilm and even flashmemory as a data recording medium due to holography'sintrinsically higher memory storage capacity.

Key features of laser cutting


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Key features of laser cuttingincludes:

Application to a wide range ofmaterials

Narrow width

Non contact

Good edge quality (square ,cleanand no burrs)

Very narrow HAZ, low heat input

Very high repeatability and

reliability

Virtually any material can be cut

L M ki


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Laser Marking

Laser marking the worlds largest laser

applicationRelevant to all sectors

Virtually any material can be laser marked

to produce robust images, texts and codes

An example of a plastic keypad laser

marked

Applications include part marking and serialisation, asset tracking, etc.

Applying brand logos and emergency info on moulded components

Marking of fabrics (e.g. faded jeans)and seat coverings

Welding


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g

A 10 kW fibre laser used in

shipbuilding

A hybrid laser welding system

Drilling


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CleaningEmerging process, particularly driven by

art and monument restoration (I.e.

National Museums and Galleries on

Merseyside (NMGM) conservation

centre.

Engineering applications are being

identified dry cleaning of metal

components prior to welding and PCBs

and component leads prior to soldering.

Documents

Chapter 3_laser [Compatibility Mode]