“Coherent Sources" A pedestrian guide

Credit: www.national.com

Experimental Methods in [2011-2012]

J-D Ganiere EPFL - SB - ICMP - IPEQ CH - 1015 Lausanne

IPEQ - ICMP - SB - EPFL Station 3 CH - 1015 LAUSANNE jeudi, 1 décembre 2011 The context Optical

coherent light light light light sample sourcesource analyzer detector

Lasers

J-D Ganiere 2 MEP/2011-2012 jeudi, 1 décembre 2011 Bibliography

For the curious or the beginners Introduction aux Daniel O’Shea, W. Callen, W.T. Rhode, Eyrolles 1977

For people interested in the domain, but who do not like too much the theory ... Principles of lasers Orazio Svelto, D.C. Hanna, Plenum Press 1982

For those who love the theory ... and the lasers Physics M. Sargent, M. Scully, W. Lamb Addison-Wesley 1974

On the Internet Wikipedia Encyclopedia of Laser Physics and Technology - http://www.rp-photonics.com/

J-D Ganiere 3 MEP/2011-2012 jeudi, 1 décembre 2011 Content

Introduction • history • principle, intuitive aspects, characteristics • what we can learn from the 2 levels system, NH3 Laser • - absorption, linewidth • 3-4 levels models • Optical feedback, threshold conditions • Single line, single frequency operating modes • pulsed lasers (Q-switched, mode-locked lasers) Examples + • He-Ne, CO2, Ar , Nd:YAG, Ti:saph, semiconductor lasers

J-D Ganiere 4 MEP/2011-2012 jeudi, 1 décembre 2011 • history • principle, intuitive aspects, Lasers characteristics • 2 levels systems

1917 A. Einstein, stimulated emission

Iy Iy & & stimulated emission & & Iy

1950 C.H. Townes, Maser (Microwave Amplification of Stimulated Emission of Radiation)

The Inventor, The Nobel Laureates, and the Thirty-Year Patent War

1957 G. Gould 1958 C.H. Townes - A.-L.Shawlow 1960 T.H. Maiman, First laser ()

J-D Ganiere 5 MEP/2011-2012 jeudi, 1 décembre 2011 • history Introduction • principle, historyintuitive aspects, Lasers ... patent war characteristics • 2 levels systems

Charles H. Townes The Nobel Prize in Physics 1964 Production of Coherent Radiation by Atoms and Molecules

Arthur L. Schawlow The Nobel Prize in Physics 1981 Spectroscopy in a New Light

Gordon Gould Born Jul 17 1920 - Died September 16, 2005

Optically Pumped Laser Amplifiers; Light Amplifiers Employing Collisions to Produce a Laser

Patent Number(s) 4,053,845; 4,704,583

J-D Ganiere 6 MEP/2011-2012 jeudi, 1 décembre 2011 • history Introduction • principle, historyintuitive aspects, Laser ... the first one characteristics • 2 levels systems

Ruby crystal

Al2O3::Cr

Howard HUGHES

T.H. Maiman

J-D Ganiere 7 MEP/2011-2012 jeudi, 1 décembre 2011 • history Introduction characteristics• principle, intuitive aspects, Lasers ... spectral domain characteristics • 2 levels systems

Texte spectral domain

Texte

Texte

Texte

J-D Ganiere 8 MEP/2011-2012 jeudi, 1 décembre 2011 • history • principle, intuitive aspects, Laser ... the principle characteristics • 2 levels systems

Back Output Lasing medium coupler (100%) gaz, liquid, solid (95%)

Laser Brightness Active medium beam

Excitation mechanism Monochromaticity

power supply, flash lamp, laser, … Directivity

Coherence

J-D Ganiere 9 MEP/2011-2012 jeudi, 1 décembre 2011 • history • principle, intuitive aspects, Lasers ... the active medium characteristics • 2 levels systems

liquids gaz rhodamine Argon + ... Nitrogen Texte ...

solids Nd: YAG How to choose the Cr:Al2O3 TexteTi:Al2O3 active medium ? GaAs GaN ...

J-D Ganiere 10 MEP/2011-2012 jeudi, 1 décembre 2011 • history • principle, intuitive aspects, Lasers ... pumping mechanism characteristics • 2 levels systems

Pumping mechanism

Ruby Nd:YAG

Ti:Al2O3 Dye ...

electrical discharge Argon Krypton Helium Neon Nitrogen ...

electrical injection Semiconductors ....

J-D Ganiere 11 MEP/2011-2012 jeudi, 1 décembre 2011 • history • principle, intuitive aspects, Laser emission ... energy conservation characteristics • 2 levels systems

blue absorption energy conservation 4F1 2F2 green absorption

4F2 stockes-shift

2E R2 = 694.3 nm optical pumping

R1 = 692.7 nm

crystal field splitted levels of the first crystal field splitted levels excited state of Cr 3+ of the fundamental state of Cr 3+ Absorption band Emission band Ruby laser

radiative transitions between discret Emission and absorption energy levels 450 500 550 600 Wavelength [nm]

J-D Ganiere 12 MEP/2011-2012 jeudi, 1 décembre 2011 • history • principle, intuitive aspects, Lasers ... the optical cavity characteristics • 2 levels systems

Ti:Helium Al2O3 - Neonmodel-locked laser laser VCSEL bragg

cleaved facets

J-D Ganiere 13 MEP/2011-2012 jeudi, 1 décembre 2011 • history • principle, intuitive aspects, Laser ... characteristics characteristics • 2 levels systems

Sun

Luminance = 1,5 x 105 lm/cm2·sr

Spectral luminance at 633 nm = 500 lm/cm2·sr·nm

Multimode He-Ne laser

(1 mW, Ø = 1 mm, divergence = 10-3 rad)

Luminance = 2,0 x 107 lm/cm2·sr

Spectral luminance at 633 nm = 108 lm/cm2·sr·nm

Spectral luminance of laser = 106 Spectral luminance of sun

J-D Ganiere 14 MEP/2011-2012 jeudi, 1 décembre 2011 • history Characteristics monochromaticity• principle, intuitive aspects, Laser ... monochromaticity characteristics • 2 levels systems

The spectral purity of the laser is a direct consequence of the fact that a laser is an oscillator, i.e. formed of an optical cavity + an active material.

Δνemission line >> Δνcavity mode

Example: He-Ne laser (single frequency)

Δνemission line = 1600 MHz

Δνcavity mode < 1 MHz

Laser sun 6i100 Hz

14 6i10 Hz

Spectral emission band of the sun and a laser

J-D Ganiere 15 MEP/2011-2012 jeudi, 1 décembre 2011 • history Characteristics directionality• principle, intuitive aspects, Laser ... directivity characteristics • 2 levels systems

The divergence of a laser beam is limited by the diffraction. Because bouncing back between mirrored ends of the laser cavity, those paths which sustain amplification must pass between the mirrors many times and be nearly perpendicular to the mirrors. As a result, laser beams are very narrow and do not spread very much.

iE laser

m id . D

J-D Ganiere 16 MEP/2011-2012 jeudi, 1 décembre 2011 • history Characteristics • principle, intuitive aspects, Lasers ... coherence characteristics • 2 levels systems

Spatial coherence

Spatial coherence describes the ability for two points in space, x1 and x2, in the extent of a wave to interfere (from wikipedia)

Temporal coherence Temporal coherence is the measure of the average correlation between the value of a wave at any pair of times, separated by delay τ (from wikipedia)

In practice, the coherence is measured using an interferometer. The visibility of the interference fringes is given by:

Intensitymax - Intensitymin C = Intensitymax + Intensitymin

and is a direct measure of the coherence

J-D Ganiere 17 MEP/2011-2012 jeudi, 1 décembre 2011 • history • principle, intuitive aspects, Lasers ... characteristics characteristics • 2 levels systems

Brigthness, coherence, directivity and monochromaticity are not independent !

1 lc xc = = Do c

where τc and lc are, respectively, the temporal coherence and the spatial coherence of the light source.

J-D Ganiere 18 MEP/2011-2012 jeudi, 1 décembre 2011 • history • principle, intuitive aspects, Lasers ... stimulated emission characteristics • 2 levels systems

Iy & & absorption

& &

Iy Iy & & stimulated emission & & Iy

& & Iy spontaneous emission & &

J-D Ganiere 19 MEP/2011-2012 jeudi, 1 décembre 2011 • history • principle, intuitive aspects, Laser ... spontaneous emission characteristics • 2 levels systems

The numbers of atoms which spontaneously pass, by unit of time, from the state “1” in the state “0” is given by:

spon dN1 " 0 dt = A10 $ N1

A10 is known under the name of Einstein coefficient for spontaneous emission: 1 x10 = A10

τ10 is the lifetime of the state "1"

J-D Ganiere 20 MEP/2011-2012 jeudi, 1 décembre 2011 • history • principle, intuitive aspects, Laser ... absorption characteristics • 2 levels systems

The numbers of atoms which pass, by unit of time, from the state “0” in the state “1”, when the system is illuminated with an EM wave, characterized by a spectral energy density, ρν , is given by:

dNabs 0 " 1 = dt t o $ B01 $ N0

B01 is known under the name of Einstein coefficient for absorption

J-D Ganiere 21 MEP/2011-2012 jeudi, 1 décembre 2011 • history • principle, intuitive aspects, Laser ... stimulated emission characteristics • 2 levels systems

The numbers of atoms which pass, by unit of time, from the state “1” in the state “0”, when the system is illuminated with an EM wave, characterized by a spectral energy density, ρν , is given by:

dNstim 1 " 0 = dt t o $ B10 $ N1

B10 is known under the name of Einstein coefficient for stimulated emission.

J-D Ganiere 22 MEP/2011-2012 jeudi, 1 décembre 2011 • history • principle, intuitive aspects, Laser ... Einstein coefficients characteristics • 2 levels systems

B01 = B10 Relationships between the 3 8ro10 Einstein coefficients A10 = $ B10 c3

At optical frequencies, spontaneous emission is an important factor of noise

J-D Ganiere 23 MEP/2011-2012 jeudi, 1 décembre 2011 • history • principle, intuitive aspects, Laser ... thermal equilibrium characteristics • 2 levels systems

thermodynamical equilibrium with a bath at temperature T

N0 = Ni + Nj

E - i Ni = N0 $ e kT Boltzmann statistics

J-D Ganiere 24 MEP/2011-2012 jeudi, 1 décembre 2011 • history Optical and/or microwave frequencies 2 levels • principle, intuitive aspects, Laser ... population characteristics • 2 levels systems

(Ei -Ej) Ni - = e kT Nj

optical frequencies radiofrequencies (500 nm, 10 14 Hz) (1,25 cm, 24·10 9 Hz)

ΔE >> kT ➞ Nj / Ni = 0 ΔE << kT ➞ Nj / Ni = 1

Only the fundamental the two levels are level is populated equally populated

J-D Ganiere 25 MEP/2011-2012 jeudi, 1 décembre 2011 • history • principle, intuitive aspects, Laser ... population inversion characteristics • 2 levels systems

Population Nj 2 Ni (also known as negative temperature) inversion

Energy Energy

/ & / &

/ / & & &  &  F L5 F L5

Population density Population density

J-D Ganiere 26 MEP/2011-2012 jeudi, 1 décembre 2011 • history • principle, intuitive aspects, The NH3 Maser characteristics • 2 levels systems

The transition which interests us in the case of the

NH3 is a transition between two vibrational levels of the molecule.

The difference of energy between these two levels is 24 GHz (what corresponds to a wavelength of 1,25 cm).

The dipole moment of the molecule is not the same in both states. We can realize an inversion of population by separating physically molecules by making the gas flowing through a zone presenting a gradient of electric field.

J-D Ganiere 27 MEP/2011-2012 jeudi, 1 décembre 2011 • history The NH3 Maser • principle, 2 levelsintuitive aspects, The NH3 Maser characteristics • 2 levels systems

&

&

NH3 source & / focalisation Texte microwave (quadrupole) emission (24 GHz) 7  7

 7 7 TUBUF & & TUBUF & 

&

& /

J-D Ganiere 28 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Laser ... absorption and gain •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

I

o z

Beer’s law

In usual cases the absorption coefficient , α(ν) , is positive and will have units of cm -1

J-D Ganiere 29 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Laser ... gain coefficient •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

If the coefficient of absorption is negative, the light beam is amplified, we speak then about coefficient of gain, β, defined by:

In the case of a 2 levels system:

J-D Ganiere 30 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Laser ... •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

Active material

2 levels system with Nj > Ni

We can use the stimulated emission to build up an optical amplifier ... We only need an active material where the population is inverted ... we don’t need to put it in an optical cavity ...

The only problem is the noise .... which is proportionnal to ν3 ... !

J-D Ganiere 31 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Laser ... weak signal gain •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

Gain - weak signal

hoij b(o) = Bij $ 6Nj - Ni@$ c $ g(o)

g(ν) = line profile, in an ideal case:

hoij g(o) = d (o - oij) b = Bij $ 6Nj - Ni@$ c

J-D Ganiere 32 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Laser ... Line profile •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

A line extends over a range of frequencies, not a single frequency. There are several reasons for this broadening.

Natural broadening (intrinsic line width) The uncertainty principle relates the life of an excited state with the precision of the energy ... This broadening effect is described by a Lorentzian profile

Thermal Doppler broadening The atoms in a gas which are emitting radiation will have a distribution of velocities. Each photon emitted will be shifted by the Doppler effect. This broadening effect is described by a Gaussian profile.

Pressure broadening The collision of other particles with the emitting particle iinterrupts teh emission process.This broadening effect id described by a Lorentian profile.

J-D Ganiere 33 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Laser ... linewidth broadening •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

Natural broadening

1 g(o) = 2 4r $ (o - oij) 1 + < c F

Lorentzian profile ( γ is related to the lifetime of the transition : γ =1/τ)

J-D Ganiere 34 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth Broadening of the transitions •3-4 levels models •Optical feedback, threshold conditions Laser ... linewidth broadening •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

Natural broadening of the emission line

J-D Ganiere 35 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth Broadening of the transitions •3-4 levels models •Optical feedback, threshold conditions Laser ... linewidth broadening •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

Impact pressure broadening

1 g(o) = 2 4r $ (o - oij) 1 + > 2 H T2

Lorentzian profile ( T2 is the duration between two collisions)

J-D Ganiere 36 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth Broadening of the transitions •3-4 levels models •Optical feedback, threshold conditions Laser ... linewidth broadening •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

Thermal Doppler broadening

2 2 Mc (o - oij) gdoppler = exp<- $ 2 F 2kT oij

Gaussian profile ( M is the mass of the atom or molecule)

J-D Ganiere 37 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Laser ... linewidth broadening •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

Homogeneous broadening

If every atom emits with the same central frequency and with the same line profile, the broadening is said homogeneous and the line profile is lorenzian.

Examples:

• Natural linewidth (homogeneous broadening)

• Impact pressure broadening (homogeneous broadening)

J-D Ganiere 38 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth Broadening of the transitions •3-4 levels models •Optical feedback, threshold conditions Laser ... linewidth broadening •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

Inhomgeneous broadening

If there are different classes of atoms emitting at different wavelengths or profiles, the broadening is said inhomogeneous and the linewidth is gaussian

Example:

• Thermal Doppler broadening gaussian

oJK o

J-D Ganiere 39 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth Optical pumping • 3-4 levels 2 modelslevels •Optical feedback, threshold conditions Laser ... back to the 2 levels system •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

Iy Iy & & stimulated emission & & Iy

You want to build up a laser with a 2 levels system ... It is a joke !

J-D Ganiere 40 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Laser ... 3 levels - Optical pumping •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

blue absorption

4F1 2F2 green absorption The ruby laser is based on a 3 levels 4F2 system.

2E R2 = 694.3 nm

optical pumping It is working only in pulsed mode !

R1 = 692.7 nm Why ... any idea ? crystal field splitted levels of the first crystal field splitted levels excited state of Cr 3+ of the fundamental state of Cr 3+

Ruby laser

J-D Ganiere 41 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth Optical pumping • 3-4 levels 4 modelslevels •Optical feedback, threshold conditions Optical pumping - 4 levels system •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

&

& fast decay

& Lifetime engineering is important ! * transition

& fast decay

& /

J-D Ganiere 42 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Rate equations •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

J-D Ganiere 43 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Laser •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

rate equations

To invert the population between levels

1 and 2, we must have A21 < A10 A21 R;1 - E A10 N2 - N1 = I A21 + B21 $ : D the lifetime of the upper level should be c greater than the lifetime of the final state

J-D Ganiere 44 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Laser •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

A21 ;1 - E > A10 H c Ioutput . R $ - 1 $ $ A21 A21 $ DNth B21

ΔN Ιoutput

There is a saturation of the gain above the R threshold ! th R (pompage)

J-D Ganiere 45 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Laser = oscillator •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

a laser is an oscillator ...

optical feedback is needed

Milieu actif

optical feedback

= mirror 100 % mirror 95 % optical cavity

pompage pumping

J-D Ganiere 46 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Laser = active medium + cavity •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

L

active medium

R1 R2

J-D Ganiere 47 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Net gain per round trip •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

L

active medium

losses gain (intrinsic) R1 R2

Intensity after one round trip g ==-RR12$$exp 2 ba $ l I0 6 ^ h @

Steady state operation : g = 1

the optical gain is exactly balanced by the sum of all the losses

J-D Ganiere 48 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Cavity •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

The optical cavity is nothing else than o  D a Perot-Fabry interferometer ... ! -

o  D -

o  D - Only frequences, νmnq , corresponding to

o  D the optical modes of cavities are authorized: -

-

with: l l g1 = 1 - g2 = 1 - r1 r2 ☛

J-D Ganiere 49 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Cavity ... longitudinal modes •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

For a perfect cavity (100% reflectivity for the mirrors, g1= g2 =1). The longitudinal modes (m=n=0) are separated by c/2L

2

D -

o

J-D Ganiere 50 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions ... optical modes •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

spatial distribution of the intensity for different radial and angular modes

The modes are denoted TEMpl where p and l are integers labeling the radial and angular mode orders

J-D Ganiere 51 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Unstable / stable •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

l l g1 = 1 - g2 = 1 - r1 r2

stability condition

0 # g1 $ g2 # 1

J-D Ganiere 52 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Laser ... all-lines •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

laser He-Ne

Helium Neon A laser can work in a multi-line 21

 mode !  4 T 3.39 !m * Q 20   4  T * 632.8 nm 19 To get only one single line, one  collisions 1.15* !m Q Q must introduce in the cavity an

18 element which induces losses for fast decay on the different wavelengths except strong visible transitions Energy [eV] (0.54 - 0.73 !m) one ... 17

T A dispersive element inside the cavity can force the laser to   0 4  Q work on a single line

J-D Ganiere 53 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Laser ... single line operation • Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

Single line operation

Idea: Introduce some losses at the different wavelengths except at λ2

m m m m

m Argon laser

m

This configuration is known as the Littrow configuration ... (i.e. the wavelength λ2 is reflected back on the same axis ...)

J-D Ganiere 54 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Laser ... multimode operation •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

gain curve (closely related to the line width profile)

optical cavity modes

We observe experimentally that the laser tends to work on several wavelengths ... This is a bit paradoxical, because of the gain saturation ...

J-D Ganiere 55 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Laser ... multimode operation •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

There is a saturation of the gain above the threshold ... only one mode should lase !

Why does the laser work on several modes ?

Hole burning (spatial and spectral)

J-D Ganiere 56 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Laser ... spatial hole burning •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

spatial hole burning

The different modes use different parts of the active material

J-D Ganiere 57 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Laser ... spectral hole burning •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

spectral hole burning In the case of an inhomogeneous broadening

J-D Ganiere 58 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Laser ... single-frequency mode •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

J-D Ganiere 59 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Laser ... single-frequency operation •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

To force the laser to work in a single-frequency mode, we can choose two different options:

• Ultra-short cavity + etalon • Conventionnal cavity

J-D Ganiere 60 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions lasers •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

In many cases, unidirectional operation (where light propagates only in one of the two possible directions) is enforced by introducing an element into the resonator which leads to different losses for the propagation directions; this can be, e.g., a Faraday rotator combined with a polarizing element (e.g. a Brewster surface of the laser crystal ). If unidirectional operation is achieved, there is no standing-wave interference pattern in the laser gain medium (except near reflection points), and consequently no spatial hole burning. Therefore, single-frequency-operation, is easily achieved. Particularly for solid-state bulk lasers, unidirectional ring laser designs can be considered as a standard approach to obtain stable single- frequency emission.

from RP photonics

J-D Ganiere 61 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Dye lasers •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

A is a laser which uses an organic dye as the lasing medium, usually as a liquid solution. A dye laser consists of an organic dye mixed with a solvent, which may be circulated through a dye cell, or streamed through open air using a dye jet. A high energy source of light is needed to "pump" the liquid beyond its . The dyes used in these lasers contain rather large organic molecules which fluoresce when exposed to the proper frequency of light. Dyes will emit stimulated radiation when the molecules are in their singlet state. In this state, the molecules emit light via fluorescence, and the dye is quite clear to the lasing wavelength. Within a microsecond, or less, the molecules will change to their triplet state . In the triplet state, light is emitted via phoosphorescence , and the molecules begin to absorb the lasing wavelength, making the dye opaque, the dye must be circulated at high speeds to keep the triplet molecules out of the beam path.

J-D Ganiere 62 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Dye lasers •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

due to the lifetime of the triplet states, the laser does not work in CW regime ....

J-D Ganiere 63 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Les lasers accordables (dye lasers) •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

J-D Ganiere 64 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Q-switched laser •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

Q-switching, sometimes known as giant pulse formation, is a technique used to produce a pulsed output beam. Compared to modelocking, Q-switching leads to much lower pulse repetition rates, much higher pulse energies, and much longer pulse durations. Q-switching is achieved by putting some type of variable attenuator, called "Q- switched" inside the optical resonator . When the attenuator is functioning, that's correspond to a decrease in the Q factor of the optical resonator .

Active Q-switching Here, the Q-switch is an externally-controlled variable attenuator. This may be a mechanical device such as a shutter, chopper wheel, or spinning mirror/prism placed inside the cavity, or (more commonly) it may be some form of modulator such as an acousto-optic device or an electro-optic device — a Pockels cell or Kerr cell.

Passive Q-switching In this case, the Q-switch is a saturable absorber, a material whose transmission increases when the intensity of light exceeds some threshold. The material may be an ion-doped crystal like Cr:YAG, which is used for Q- switching of Nd:YAG lasers, a bleachable dye, or a passive semiconductor device.

from Wikipedia

J-D Ganiere 65 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Q-switched lasers •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

mirror angle

laser used to probe 0° the angular position time detector end mirror of the Output (100%) Flash lamp coupler (pumping) pumping time intensity

Active medium Q cavity time

Gain time

detector Output time power

time

The output coupler is mounted on a rotating holder. Lasing is obtained only when there is no loss, e.g. when the output coupler is perfectly aligned with the end mirror.

J-D Ganiere 66 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Q-switched lasers •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

end mirror laser crystal cut at polarzation selector output coupler (100 %) bewster angle Electro-optic crystal

The laser crystal is cut at the brewster angle and only one can propagate without loss. The Q-switching is simply achieved using a Pockels cell (electro-optic crystal which can rotate the polarization ...).

J-D Ganiere 67 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Mode-locked lasers •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

Mode-locking is a technique in by which a laser can be made to produce pulses of light of extremely short duration, on the order of picoseconds (10−12s) or femtoseconds (10−15s). The basis of the technique is to induce a fixed phase relationship between the modes of the laser's resonant cavity. The laser is then said to be phase-locked or mode-locked. Interference between these modes causes the laser light to be produced as a train of pulses. Depending on the properties of the laser, these pulses may be of extremely brief duration, as short as a few femtoseconds. In a simple laser, each of these modes will oscillate independently, with no fixed relationship between each other, in essence like a set of independent lasers all emitting light at slightly different frequencies. The individual phase of the light waves in each mode is not fixed, and may vary randomly due to such things as thermal changes in materials of the laser. In lasers with only a few oscillating modes, interference between the modes can cause brating effects in the laser output, leading to random fluctuations in intensity; in lasers with many thousands of modes, these interference effects tend to average to a near-constant output intensity, and the laser operation is known as a c.w. or .

J-D Ganiere 68 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Mode-locked lasers •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

If instead of oscillating independently, each mode operates with a fixed phase between it and the other modes, the laser output behaves quite differently. Instead of a random or constant output intensity, the modes of the laser will periodically all constructively interfere with one another, producing an intense burst or pulse of light. Such a laser is said to be mode-locked orphase-locked. These pulses occur separated in time by τ = 2L/c, where τ is the time taken for the light to make exactly one round trip of the laser cavity. This time corresponds to a frequency exactly equal to the mode spacing of the laser, Δν = 1/τ. The duration of each pulse of light is determined by the number of modes which are oscillating in phase (in a real laser, it is not necessarily true that all of the laser's modes will be phase-locked). If there are N modes locked with a frequency separation Δν, the overall mode-locked bandwidth is NΔν, and the wider this bandwidth, the shorter the pulse duration from the laser. In practice, the actual pulse duration is determined by the shape of each pulse, which is in turn determined by the exact amplitude and phase relationship of each longitudinal mode. 044. time bandwidth product: Dt = N $ Do

J-D Ganiere 69 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Mode-locked lasers •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

laser gain bandwidth

cavity longitudinal modes

c 6i = 2L

laser output spectrum

N modes intensity

frequency

22 It()max = E0 $ N 1 Dt p = Dy $ N

J-D Ganiere 70 MEP/2011-2012 jeudi, 1 décembre 2011 •gain - absorption, linewidth •3-4 levels models •Optical feedback, threshold conditions Mode-locked lasers •Single line, single frequency operating modes •pulsed lasers (Q-switched, mode-locked lasers)

ν0 + Δν

ν0

ν0 - Δν

J-D Ganiere 71 MEP/2011-2012 jeudi, 1 décembre 2011 Laser safety

J-D Ganiere 72 MEP/2011-2012 jeudi, 1 décembre 2011 Wavelengths of common lasers used at IPEQ

J-D Ganiere 73 MEP/2011-2012 jeudi, 1 décembre 2011 •Argon laser, CO2 laser, He-Ne laser •Semiconductor laser Argon laser • laser, •Nd:YAG laser, Ti:saph laser

3p44p levels 4p 488 nm lasing A=7.8 107/sec

3p44s

72.3 nm 73.1 nm A=23 108/sec A=4.5 108/sec levels 4s

3 0 P 1/2 3p5 3 0 P 3/2

J-D Ganiere 74 MEP/2011-2012 jeudi, 1 décembre 2011 •Argon laser, CO2 laser, He-Ne laser •Semiconductor laser Argon laser •, chemical laser •Nd:YAG laser, Ti:saph laser

The upper laser levels (there are several, clumped tightly together) are about 20 eV above the ground state of the argon ion or nearly 36 eV above the ground state of the argon atom. Obviously, this is a very high energy which will require a large pump energy to build-up a high population of ions in that high-energy state. The dynamics of the argon ion are good for CW laser action in that the lifetime of the lower level is very short compared to the upper level. This allows population inversion to be maintained so long as a large pump energy is available (and all argon lasers need large pump energies - most have between 10 to 70A continuously through the discharge !). The short lifetime of the lower lasing level lead to another problem though in that ions in that energy state (i.e. having just emmitted a coherent photon) drop rapidly to the ground state of argon ion. This is a large jump and results in the spontaneous emission of a 74-nm extreme- photon (the energy had to go somewhere, right ?). From an efficiency standpoint, this means an excited ion at the upper lasing level loses about 2 eV of energy in producing the coherent photon then loses 18 eV in spontaneous emission of that UV photon. These dynamics limit efficiency severely. As well the extreme UV light from that emission can damage many optical materials so mirrors and windows in an argon laser must be built to withstand such punishment!

There are three major mechanisms which raise the argon ion to the upper laser levels. One is energy transfer from an electron to a ground-state argon ion. Another is collisional transfer of energy from an electron to the argon ion in an excited metastable state similar to the way in which helium pumps neon's levels in the HeNe laser. The third is decay of higher levels produced by electron excitation. All three effects combine to pump the argon ions to the upper levels for lasing.

from Pofessor Mark Csele's Homebuilt Lasers Page

J-D Ganiere 75 MEP/2011-2012 jeudi, 1 décembre 2011 •Argon laser, CO2 laser, He-Ne laser •Semiconductor laser •Excimer laser, chemical laser Argon laser •Nd:YAG laser, Ti:saph laser

J-D Ganiere 76 MEP/2011-2012 jeudi, 1 décembre 2011 •Argon laser, CO2 laser, He-Ne laser •Semiconductor laser Argon laser ... single mode •Excimer laser, chemical laser •Nd:YAG laser, Ti:saph laser

J-D Ganiere 77 MEP/2011-2012 jeudi, 1 décembre 2011 •Argon laser, CO2 laser, He-Ne laser •Semiconductor laser He-Ne laser •Excimer laser, chemical laser •Nd:YAG laser, Ti:saph laser

A 1400 V high voltage, DC power supply Helium Neon 21

 maintains a glow discharge or plasma in a  4 T 3.39 !m tube containing an optimal mixture * Q 20   4  (typically 5:1 to 7:1) of helium and neon gas. T * 632.8 nm The discharge current is limited to about 5 19  collisions 1.15* !m Q mA by a 91 kW ballast resistor. Energetic Q

electrons accelerating from the cathode to 18 fast decay on the anode collide with He and Ne atoms in strong visible transitions Energy [eV] (0.54 - 0.73 !m) the laser tube, producing a large number of 17 neutral He and Ne atoms in excited states. He and Ne atoms in excited states can T deexcite and return to their ground states

  by spontaneously emitting light. This light 0 4  Q makes up the bright pink-red glow of the plasma that is seen even in the absence of laser action.

http://community.middlebury.edu/~PHManual/heliumneon.html

J-D Ganiere 78 MEP/2011-2012 jeudi, 1 décembre 2011 •Argon laser, CO2 laser, He-Ne laser •Semiconductor laser Helium-Neon laser •Excimer laser, chemical laser •Nd:YAG laser, Ti:saph laser

J-D Ganiere 79 MEP/2011-2012 jeudi, 1 décembre 2011 •Argon laser, CO2 laser, He-Ne laser •Semiconductor laser He-Ne laser •Excimer laser, chemical laser •Nd:YAG laser, Ti:saph laser

J-D Ganiere 80 MEP/2011-2012 jeudi, 1 décembre 2011 •Argon laser, CO2 laser, He-Ne laser •Semiconductor laser Excimer laser •Excimer laser, chemical laser •Nd:YAG laser, Ti:saph laser

The term excimer is short for 'excited dimer', while exciplex is short for 'excited complex'. An excimer laser typically uses a combination of an inert gas (Ar, Kr, or Xe) and a reactive gas (fluorine or chlorine). Under the appropriate conditions of electrical stimulation, a pseudo-molecule called an excimer (or in case of noble gas halides, exciplex) is created, which can only exist in an energized state and can give rise to laser light in the UV range. Laser action in an excimer molecule occurs because it has a bound (associative) excited state, but a repulsive (disassociative) ground state. This is because noble gases such as Xe and Kr are highly inert and do not usually form chemical compound. However, when in an excited state (induced by an electrical discharge or high- energy electron beams, which produce high energy pulses), they can form temporarily-bound molecules with themselves (dimers) or with halogens (complexes) such as Fl and Cl. The excited compound can give up its excess energy by undergoing spontaneous or stimulated emission, resulting in a strongly-repulsive ground state molecule which very quickly (on the order of a picosecond) dissociates back into two unbound atoms. This forms a population inversion between the two states.

J-D Ganiere 81 MEP/2011-2012 jeudi, 1 décembre 2011 •Argon laser, CO2 laser, He-Ne laser •Semiconductor laser Le laser excimer ArF, KrF, ... •Excimer laser, chemical laser •Nd:YAG laser, Ti:saph laser

J-D Ganiere 82 MEP/2011-2012 jeudi, 1 décembre 2011 •Argon laser, CO2 laser, He-Ne laser •Semiconductor laser Excimer laser •Excimer laser, chemical laser •Nd:YAG laser, Ti:saph laser

Excimer Wavelength Relative Power (mW)

Ar2 126 nm

Kr2 146 nm

F2 157 nm 10

Xe2 172 and 175 nm

ArF 193 nm 60

KrF 248 nm 100

XeBr 282 nm

XeCl 308 nm 50

XeF 351 nm 45

KrCl 222 nm 25

Cl2 259 nm

N2 337 nm 5

J-D Ganiere 83 MEP/2011-2012 jeudi, 1 décembre 2011 •Argon laser, CO2 laser, He-Ne laser •Semiconductor laser Chemical laser •Excimer laser, chemical laser •Nd:YAG laser, Ti:saph laser

A chemical laser is a laser that obtains its energy from a Chemical lasers can achieve CW output with power reaching to MW levels. They are used in industry for cutting and drilling. Common examples of chemical lasers are the chemical oxygen iodine laser (COIL), all gas-phase iodine laser (AGIL), and the HF laser and deuterium fluoride laser, both operating in the mid- region.

Origin of the CW chemical HF/DF laser Very quickly, deuterium was dropped in favor of hydrogen, since it is far less costly and more readily available. However, later it was realized that HF produces infrared radiation in the 2.6 to 3.1 μm waveband, a region of the spectrum absorbed by water vapor in the atmosphere. Interest was renewed in DF, which produces radiation in the 3.7 to 4.2 μm band, which passes easily through the atmosphere.

J-D Ganiere 84 MEP/2011-2012 jeudi, 1 décembre 2011 •Argon laser, CO2 laser, He-Ne laser •Semiconductor laser Chemical laser •Excimer laser, chemical laser •Nd:YAG laser, Ti:saph laser

J-D Ganiere 85 MEP/2011-2012 jeudi, 1 décembre 2011 •Argon laser, CO2 laser, He-Ne laser •Semiconductor laser Chemical laser •Excimer laser, chemical laser •Nd:YAG laser, Ti:saph laser

Texte

Texte

Texte

Texte

J-D Ganiere 86 MEP/2011-2012 jeudi, 1 décembre 2011 •Argon laser, CO2 laser, He-Ne laser •Semiconductor laser CO2 laser •Excimer laser, chemical laser •Nd:YAG laser, Ti:saph laser

The laser (CO2 laser) was one of the earliest gas lasers to be developed (invented by Kumar Patel of in 1964), and is still one of the most useful. Carbon dioxide lasers are the highest-power continuous wave lasers that are currently available. CO2 lasers are also quite efficient: the ratio of output power to pump power can be as large as 20%.

The CO2 laser produces a beam of infrared light with the principal wavelength bands centering around 9.4 and 10.6 micrometers .

J-D Ganiere 87 MEP/2011-2012 jeudi, 1 décembre 2011 •Argon laser, CO2 laser, He-Ne laser •Semiconductor laser CO2 Lasers •Excimer laser, chemical laser •Nd:YAG laser, Ti:saph laser

Nitrogen N2 Carbon Dioxyde CO2 O C O

Asymmetric Symmetric Bending CO2 molecule strech strech

O C O 0.3 [ R10 ] 9.6 !m Laser asymmetric stretch mode * transitions collisions [ P10 ] * C 10.6 !m O O

0.2 bending mode collisions

Fast decay O C O Pumping symmetric stretch mode

0.1

Fast decay

Ground level 0.0

J-D Ganiere 88 MEP/2011-2012 jeudi, 1 décembre 2011 •Argon laser, CO2 laser, He-Ne laser •Semiconductor laser CO2 laser •Excimer laser, chemical laser •Nd:YAG laser, Ti:saph laser

Because of the high power levels available (combined with reasonable cost for the laser),

CO2 lasers are frequently used in industrial applications for cutting and welding, while lower power level lasers are used for . They are also very useful in surgical procedures because water (which makes up most biological tissue) absorbs this frequency of light very well. Some examples of medical uses are , skin resurfacing ("laser facelifts") (which essentially consist of burning the skin to promote collagen formation), and dermabrasion. Also, it could be used to treat certain skin conditions by removing embarrassing or annoying bumps, podules, etc.

Researchers are experimenting with using CO2 lasers to weld human tissue, as an alternative to traditional sutures.

J-D Ganiere 89 MEP/2011-2012 jeudi, 1 décembre 2011 •Argon laser, CO2 laser, He-Ne laser •Semiconductor laser YAG lasers •Excimer laser, chemical laser •Nd:YAG laser, Ti:saph laser

Nd:YAG (neodymium-doped yttrium aluminium garnet; Nd:Y3Al5O12) is a crystal that is used as a lasing medium for solid state laser [DPSS - Diode-Pumped Solid- State]. The dopant, triply ionized neodynium, typically replaces yttrium in the crystal structure of the yttrium aluminium garnet (YAG), since they are of similar size. Generally the crystalline host is doped with around 1% neodymium by atomic percent. Laser operation of Nd:YAG was first demonstrated by Geusic et al. at Bell Laboratories in 1964.

Nd:YAG lasers are optically pumped using a flashlamp or laser diodes . They are one of the most common types of laser, and are used for many different applications. Nd:YAG lasers typically emit light with a wavelength of 1064 nm. Nd:YAG lasers operate in both pulsed and continuous mode. Pulsed Nd:YAG lasers are typically operated in the so called Q-switching mode.

Ref.: Wikipedia

J-D Ganiere 90 MEP/2011-2012 jeudi, 1 décembre 2011 •Argon laser, CO2 laser, He-Ne laser •Semiconductor laser YAG laser •Excimer laser, chemical laser •Nd:YAG laser, Ti:saph laser

Pumping bands

nonradiative decay

  ' 

1.06 !m laser transition Pumping   * 

nonradiative decay   *  ground state

J-D Ganiere 91 MEP/2011-2012 jeudi, 1 décembre 2011 •Argon laser, CO2 laser, He-Ne laser •Semiconductor laser Ti:sapphire laser •Excimer laser, chemical laser •Nd:YAG laser, Ti:saph laser

Ti:sapphire lasers (also known as Ti:Al2O3 lasers, titanium-sapphire lasers, or simply Ti:sapphs) are tunable lasers which emit red and near-infrared light in the range from 650 to 1100 nanometers. These lasers are mainly used in scientific research because of their tunability and their ability to generate ultrashort pulses . Lasers based on Ti:sapphire were first constructed in 1982.

Titanium-sapphire refers to the lasing medium , a crystal of sapphire (Al2O3) that is doped with titanium ions . A Ti:sapphire laser is usually pumped with another laser with a wavelength of 514 to 532 nm, for which argon-ion lasers (514.5 nm) and frequency-doubled Nd:Yag, Nd:YLF, and Nd:YVO lasers (527-532 nm) are used. Ti:sapphire lasers operate most efficiently at wavelengths near 800 nm.

J-D Ganiere 92 MEP/2011-2012 jeudi, 1 décembre 2011 •Argon laser, CO2 laser, He-Ne laser •Semiconductor laser Ti:sapphire laser •Excimer laser, chemical laser •Nd:YAG laser, Ti:saph laser

 collisonal & relaxation

tunable * laser * output

optical pumping *

 collisonal 5 relaxation

J-D Ganiere 93 MEP/2011-2012 jeudi, 1 décembre 2011 •Argon laser, CO2 laser, He-Ne laser •Semiconductor laser Semiconductor laser •Excimer laser, chemical laser •Nd:YAG laser, Ti:saph laser

J-D Ganiere 94 MEP/2011-2012 jeudi, 1 décembre 2011 Medical applications of lasers

✓ Cosmetic surgery (removing tattoos, scars, stretch marks, sunspots, wrinkles, birthmarks, and hairs): see . Laser types used in dermatology 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 (Excimer laser)

✓ 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

from wikipedia: http://en.wikipedia.org/wiki/List_of_applications_for_lasers

J-D Ganiere 95 MEP/2011-2012 jeudi, 1 décembre 2011 Industrial and commercial applications of lasers I

✓ Cutting and peening of metals and other material, welding, marking, etc. ✓ Guidance systems (e.g., ring laser gyroscopes) ✓ Rangefinder / surveying, ✓ / pollution monitoring, ✓ Digital minilabs ✓ Barcode readers ✓ of printing plate ✓ of additive marking materials for decoration and identification, ✓ Laser pointers ✓ Laser accelerometers ✓ Holography ✓ Bubblegrams ✓ Photolithography

from wikipedia: http://en.wikipedia.org/wiki/List_of_applications_for_lasers

J-D Ganiere 96 MEP/2011-2012 jeudi, 1 décembre 2011 Industrial and commercial applications of lasers I

J-D Ganiere 97 MEP/2011-2012 jeudi, 1 décembre 2011 Industrial and commercial applications of lasers II

✓ Optical communications (over optical fiber or in free space) ✓ ✓ 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. ✓ 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 from wikipedia: http://en.wikipedia.org/wiki/List_of_applications_for_lasers

J-D Ganiere 98 MEP/2011-2012 jeudi, 1 décembre 2011 J-D Ganiere 99 MEP/2011-2012 jeudi, 1 décembre 2011 Temporal coherence

J-D Ganiere 100 MEP/2011-2012 jeudi, 1 décembre 2011 Spatial coherence

J-D Ganiere 101 MEP/2011-2012 jeudi, 1 décembre 2011 Cavité P-F

J-D Ganiere 102 MEP/2011-2012 jeudi, 1 décembre 2011 Cavité P-F

J-D Ganiere 103 MEP/2011-2012 jeudi, 1 décembre 2011 Cavité P-F

J-D Ganiere 104 MEP/2011-2012 jeudi, 1 décembre 2011 Lamb dip

J-D Ganiere 105 MEP/2011-2012 jeudi, 1 décembre 2011