Table Of ContentLaser Physics at the Limits
Springer-Verlag Berlin Heidelberg GmbH
ONLINEL1BRARY
Physics and Astronomy
http://www.springer.de/phys/
Hartmut Figger Dieter Meschede
Claus Zimmermann (Eds.)
laser Physics
at the limits
With 245 Figures and9Tables
i
Springer
Dr.HartmutFigger ProfessorDr.Dieter Meschede
Max-Planck-InstitutfürQuantenoptik Universität Bonn
Hans-Kopfermann-Str.1 InstitutfürAngewandte Physik
85748Garehing Wegelerstr.8
Germany 53115Bonn
E-mail: [email protected] Germany
E-mail: [email protected]
Professor Dr.ClausZimmermann
UniversitätTübingen
PhysikalischesInstitut
AufderMorgensteIle14
72076Tübingen
Germany
E-mail: [email protected]
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Dedicated to Theodor W. Hänsch
on the Occasion of his 60th Birthday
A Passion for Physics
On the occasion of Professor Theodor W. Hänsch's
60th birthday
"A Passion for Precision" was thetitleofanessaywritten by DanielKleppner
12 years aga for the Reference Frame section of Physics Today. It describes
the intensely pleasurable sensation an experimentalist feels when measuring
something useful to umpteen significant figures. One of the most prominent
experimentalists in this context is Theodor Hänsch, who must have noticed
this sensation many times in his life. Indeed, the quest for attaining higher
and higher precision in fundamental-physicsexperiments isone ofthecentral
themes in the scientific work of Theodor Hänsch, a true pioneer in high
resolution laser spectroscopy, first at the University of Heidelberg in the
late 1960s, then at Stanford University, and since 19S6 at the Max-Planck
Institute for Quantum Optics in Garching and the Ludwig-Maximilians
University in Munich.
For example, he and his collaborators cultivated laser-saturated absorp
tion spectroscopy and two-photon Doppler-free absorption spectroscopy as
a brilliant means to suppress the first-order Doppler effect. Already in the
early 1970s,this made possible the measurement ofthe ultra-violet resonance
line of hydrogen with an unprecedented precision of a few parts in 108.
Some of his measurements from this time are now included in major atomic
physics textbooks. To reduce the second-order Doppler effect, he, together
with colleague and Nobel Prize winner Arthur Schawlow, had the ingenious
idea to cool a gas ofatoms by meansoflight pressure,nearly a decade before
its first experimental realisation in the mid-19S0s. Laser-cooled atoms are
now an essential part of the world's best atomic fountain clocks, operating
in the microwave domain with a remarkable accuracy ofa few parts in 1015.
To transfer such a precision into the optical domain without the need for
a sophisticated frequency chain, Hänsch and hisco-workers recently invented
thefrequency-comb generator. Providingmillionsofcloselyspaced and stable
reference frequencies ranging from the infrared regime across the optical
spectrum, this revolutionary device allowed him to count the frequency of
the fundamental lS-2S two-photon transition in atomic hydrogen with an
astonishing precision ofa fewparts in 1014 - a morethan 10-fold improvcmcnt
over previous measurements,which electrified thecommunity. Largelydue to
Hänsch's longlasting dedication to high-precision experiments, the Rydberg
constant is presently the best-known fundamental constant in physics, and
VIII A Passion for Physics
opticalatomicclockswitha potentialfor vast improvements in accuracyseem
to be realisable in the not-too-distant future.
Inadditionto precise laser spectroscopyandfundamental physics,Theodor
Hänsch has also pioneered the research field of laser cooling and trapping,
another exciting area of present-day physics already mentioned above. Here,
his widespread activities range from optical lattices to atom interferometers,
atomlasersandatomchips.Hisachievementsin this researchfield aretoo nu
merous to describe allofthem indetail, so that only a fewcan be highlighted.
For example, he and his co-workers were among the first to trap atoms in the
motionalground stateofa periodiclatticemadeofinterferinglight beams. In
atom interferometry, thewavenatureofatoms isused to explorefundamental
quantum physical phenomena and measure atomic properties like the mass
or the transition frequency with high precision. The atom laser realised in his
laboratory is a quasicontinuous and monochromatic source of atoms which
are ejected from a Bose-Einstein condensate as a highly collimated beam.
Last, but not least, the atom chip is the result of the group's more-than-a
decade long research program devoted to the magnetic trapping of atoms.
It employs an array of micron-sized current-carrying wires on the surface
of a chip to store and guide atoms in a strongly confining magnetic field.
Arguably the most spectacular result here is the recent achievement of Bose
Einstein condensation,which opens up the possibility to realise,for example,
a miniature atom interferometer.
Most of the spectacular experiments mentioned above would have been
impossible without a true "passion for precision". But the broad spectrum of
research activities would also have been impossible without a deep interest
in physics in general. Indeed, the laser wizard Theodor Hänsch has an ever
lasting passion forphysics.For more than 30 years now, he hasconstantly in
spiredquantum optics and laser spectroscopy researchers with exciting ideas,
novel techniques and fabulous experiments, sometimes originating in a small
semiprivate laboratory at the University of Munich. His way of uncovering
the secrets of physics reminds me of the way my children are discovering
the world: "simply" by asking questions nobody has expected. Many of his
achievements were believed to be impossible at the time they were proposed.
It is only due to his persistence and steadiness that theoretical visions could
become experimental reality.
It comes without saying that the Max-Planck Society is happy to have
a leadingscientist likeTheodor Hänsch among its scientific members.He and
his group make excellent use ofthe wonderful framework provided by the So
ciety,demonstrating in a spectacular way that basic research supported over
alongperiodoftimeisindeedagood investmentfor thefuture.Together with
my co-directors and all co-workers ofthe Max-Planck Institute for Quantum
Optics, it is a pleasure for me to wish hirn health and happiness, and many
more years of his remarkably great scientific creativity. Happy birthday!
Garching, October 2001 Gerhard Rempe
Preface
Laser physics has always beendriven by a genuinelyscientific quest to extend
existing limits, limits of physical knowledge and limits of physical methods.
Enhancing precision, sensitivity, and resolution has been an essential topic
of this evolution. Experiments and concepts oflaser physics have also earned
a central place in modern physics. More than 100years after the invention
of quantum physics, subtleties of light-matter interaction can be beautifully
illustrated through the application of lasers, an invaluable highlight of our
current presentation of modern microscopic physics.
The scientific advancement ofphysics is impossible without the ingenuity
of experimenters and oftheoreticians. Among those,Theodor Hänsch has oc
cupied a commandingposition formanydecades now,contributingnumerous
original and fundamental contributions to the fieldof laser physics.This vol
urne was thus initiated on the occasion of his 60th birthday. It demonstrates
the influence of his scientific activities at present and during the recent past.
Current developments in fields such as atomicelocks, precisionmeasurements
of fundamental constants, nonlinear optical effects, Bose-Einstein condensa
tion, and atomic quantum engineering underline the virtue of concepts and
results derived in his laboratories.
Authors were invited from among his present coworkers in Munich and
Florence, prominent collaborators and elosecolleagues from his time at Stan
ford University before 1986, and colleagues working on elosely related sub
jects. The authors were asked to write about their current research work and
also, if possible, to inelude recent as yet unpublished work and ideas. They
responded enthusiastically, and the result again proves the wide acceptance
and recognition of Theodor Hänsch's work in atomic and optical physics and
beyond.
We wish to thank all contributing authors for their fine artieles, which
had to be written in a rather short time, and for their warm response and
cooperation. We realise that their contributions in this volume well reflect
the present status in the fields mentioned above and the developments to be
expected in the near future relating to "Laser Physics at the Limits".
All three editors met Theodor Hänsch while working with hirn at the
Max-Planck-Institute für Quantenoptik in Munich, and the inspiration from
this time will not end. We benefited not only from the scientifically fruitful
