Laser Physics.1
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Transcript of Laser Physics.1
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Laser Physics
lecture WS 2007/2008
Thomas Halfmann
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