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Laser 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] LibraryofCongressCataloging-in-PublicationDataapplied for. DieDeutscheBibliothek-CIP-Einheitsaufnahme Laserphysicsatthe limits;with9tables1HartmutFigger...(ed.).-Berlin;Heidelberg;NewYork; Barcelona;HongKong;London;Milan;Paris;Tokyo:Springer,2002 (Physicsandastronomyonlinelibrary) Thisworkissubject tocopyright. Allrights are reserved, whetherthe whole or partofthe material isconcerned,specificallytherights oftranslation,reprinting,reuseofillustrations,recitation,broad casting,reproduction on microfilm or inany otherway,and storage in data banks. Duplicationof thispublicationorparts thereofispermittedonlyundertheprovisionsoftheGermanCopyrightLaw ofSeptember 9,1965,initscurrentversion, and permission for use must alwaysbe obtained from Springer-Verlag.ViolationsareliableforprosecutionundertheGermanCopyrightLaw. http://www.springer.de ISBN 978-3-642-07627-5 ISBN 978-3-662-04897-9 (eBook) DOI 10.1007/978-3-662-04897-9 ©Springer-VerlagBerlinHeidelberg2002 OriginallypublishedbySpringer-VerlagBerlinHeidelbergNewYorkin2002. SoftcoverreprintofthehardcoverIstedition2002 Theuseofgeneral descriptive names,registered names,tradernarks,etc.inthis publicationdoes not imply,evenintheabsenceofaspecificstatement,that such namesareexempt from the relevant pro tectivelawsand regulationsandthereforefreeforgeneraluse. Typesetting:LE-TEX[elonek,Schmidt&VöcklerGbR,Leipzig Coverdesign:design&productionGmbH,Heidelbergusingapicturefrom©FrankOssenbrink Printedonacid-freepaper SPIN10848141 56/3141/di 54 3 210 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