laser physics.1

8/6/2019 Laser Physics.1

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Laser Physics

lecture WS 2007/2008

Thomas Halfmann

[email protected]

www.quantumcontrol.de


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Contents of the lecture :

1. Introduction & Motivation

(Laser applications, particular properties of laser radiation, laser-related

Nobel prizes, history of laser developments, references)

2. Basics of laser operation

(A quick guide to lasers; Maxwells wave equation, photons, Plancks law,

photon statistics : Bose-Einstein distribution, Poisson distribution, spatial

and temporal coherence, correlation functions, diffraction-limitedfocussing, laser speckles)

3. Light amplification(Interaction of light with a two-level quantum system, spectral lines,

absorption & refraction, saturation, population rate equations, conditions

for light amplification, population inversion, losses in a laser resonator,

dynamics of a two-level laser, laser oscillations, relaxation oscillations &

spiking, three-level laser scheme, four-level laser-scheme)


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6. Nonlinear optics & frequency conversion

(Maxwells wave equation in matter, nonlinear polarization, slowly

varying envelope approximation, 2nd order NLO processes, sum frequency

mixing, difference frequency mixing, parametric amplification, optical

parametric amplifiers, optical Kerr effect, self focussing, Manley-Rowe

relations, phase matching, 3rd order NLO processes, third harmonicgeneration, four wave mixing, Raman scattering, coherent anti-Stokes

Raman scattering, optical phase conjugation)


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1. Introduction & Motivation

(Laser applications, particular properties of laser radiation, laser-related

Nobel prizes, history of laser developments, references)


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Motivation : (1) Laser applications (definitly incomplete)


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Motivation : (2) Particular properties of laser radiation

large spatial and temporal coherence : fixed phase relation between

spatially and temporally separated parts of a laser pulse large interferometric resolution becomes possible

highly monochromatic : small spectral bandwidth

large spectral resolution possible ( = 1 Hz at 1015 Hz)

large intensity :

Lawrence Livermore National Laboratory (USA) : 500 TWPHELIX at GSI (still in setup) : 1000 TW ?

large temporal resolution :

shortest radiation pulse up-to-date (INFM, Milano, 2007) : = 130 as investigation of ultra-fast phys. & chem. processes possible

(comp. : time scale of molecular vibrations ~ 100 fs

time scale of electronic motion ~ 100 as)


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1960 1970 1980 1990 2000 20101E-16

1E-15

1E-14

1E-13

1E-12

1E-11

1E-10

1E-9

Ramangeneration

high-order

harmonic

generation

pulse

compression

mode-locked

Ti:Sapphire

cw mode-locked dye

colliding pulsemode-locked dye lasers

flashlamp dye

Nd:Glass

mode-locked ruby

pulse

duration

year

conventional techniques (1) :

generation of short radiation pulses in a

laser resonator

conventional techniques (2) :

compression of short laser pulses

techniques, Verfahren, based on the

interaction between ultra-shortradiation pulses and molecular media :

generation and superposition of Raman

sidebands

techniques, based on nonlinear optical

interaction between ultra-short

radiation pulses and atomic media :

generation and superposition of high-

order harmonics in the regime of

extreme-ultraviolet radiation

e.g. rapid developments in the

field of laser physics : increasing

temporal resolution

M i i (3) N b l i f l d l li i


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C.H. Townes N.G. Basov A.M. Prokhorov

Nobel prize 1964 : quantum electronics, maser & laser

N. Bloembergen A.L. Schawlow K.M. Siegbahn

Nobel prize 1981 :

laser spectroscopy &

electron spectroscopy

Motivation : (3) Nobel prizes for lasers and laser applications

A. Kastler

Nobel prize 1966 :

optical spectroscopy


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S. Chu W.D. Phillips C. Cohen-

Tannoudji

Nobel price 1997 :

laser cooling

Nobel prize (chemistry) 1999 :femtosecond spectroscopy

of chemical reactions

A. Zewail


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E.A. Cornell C.E. Wieman W. Ketterle

Nobel prize 2001 :

Bose-Einstein condensation

R.J. Glauber J.L. Hall T.W. Hnsch

Nobel prize 2006 :quantum coherence &

high-precision spectroscopy

h k f l li i


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some other guys known for laser applications

History of laser developments


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History of laser developments

1917 A. Einstein quantum mech. of radiation (spont. & stim. emission)

1928 R Ladenburg et al. exp. dem. of stim. emission in gas discharges

1954 C. H. Townes et al. first maser, implemented with NH3 molecules1954 N. G. Basov & A. M. Prokhorov maser theory

1958 A. L. Schawlow & Ch. H. Townes laser theory

1959 G. Gould laser patent

LASER : Light Amplification by Stimulated Emission ofRadiation


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1960 T. H. Maiman first laser, made from a ruby crystal

1961 A. Javan et al. first gas laser (HeNe)

1961 E. Snitzer Nd3+:glass - laser (1.06 m)

1962 several authors GaAs diode laser (840 nm)

1964 C. K. N. Patel CO2

- laser (10 m)

1964 J. E. Geusic et al. Nd3+: YAG-Laser (Y3Al5O12, 1.06 m)

1964 W. B. Bridges Ar+ ion laser

1965 J. V. V. Kasper & G. C. Pimentel chemical laser (HCl, 3.8 m)1966 P. P. Sorokin & J. R. Lankard dye laser

1971 N. G. Basov et al. Xe2+ - excimer laser

1984 P.F. Moulton Ti-Sapphire laser (Ti3+:Al2O3)


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1961 R. J. Collins Q-switching

1965 H. W. Mocker & R. J. Collins passive modelocking in a ruby laser

1968 D. J. Bradley & A. J. F. Durrant synchroneous pumping

1971 H. Kogelnik & C. V. Shank distributed feedback(DFB) - dye laser

1984 W. H. Knox et al. pulse compression1985 D. Strickland & G. Mourou chirped pulse amplification

1991 D. E. Spence et al. Kerr lens modelocking

and many recent developments :

e.g. single-cycle laser pulses,THz pulses,

pulse shaping,

generation of attosecond pulses,

laser-based nuclear fusion,


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references :

P.W. Milonni & J.H. Eberly LasersA.E. Siegman Lasers

F.K. Kneubhl & M.W. Sigrist Laser

W. Demtrder Laser Spectroscopy

H. Haken & H.C. WolfAtom- und QuantenphysikA. Yariv Quantum Electronics

M.V. Klein & T.E. FurtakOptik

R.W. Boyd Nonlinear Optics

P.N. Butcher & D. Cotter The Elements of Nonlinear Optics


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2. Basics of laser operation

(A quick guide to lasers; Maxwells wave equation, photons, Plancks law,

photon statistics : Bose-Einstein distribution, Poisson distribution, spatialand temporal coherence, correlation functions, diffraction-limited

focussing, laser speckles)

A quick guide to lasers


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A quick guide to lasers

essential components of a laser:

(1) medium (quantum system, capable to permit population inversion,e.g. gas, liquid, solid,)

(2) pumping process (optical, electron impact, current, chemical,)

(3) resonator (i.e. mirrors)aims : feedback, mode selection, energy concentration in few modes

(i) Basic setup of a laser

(ii) Amplification by stimulated emission


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(ii) Amplification by stimulated emission

consider the interaction of a two-level quantum system with radiation :

(1) stimulated absorption attenuation

(2) stimulated emission amplification (correlated)

(3) spontaneous emission fluorescence (uncorrelated)iikki

sp

iik

ki

stim

kkiik

stim

NAP

wNBP

wNBP

=

=

=

population distribution

due to Boltzmann law :

kTE

eEN/

)(

with Einstein coefficients Aik, Bik, Bki and field energy density w

laser physics.1

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