title: Optical frequency metrology.
abstract: Extremely narrow optical resonances in cold atoms or single trapped ions can be measured with high resolution. A laser locked to such a narrow optical resonance could serve as a highly stable oscillator for an all-optical atomic clock. However, until recently there was no reliable clockwork mechanism that could count optical frequencies of hundreds of terahertz. Techniques using femtosecond-laser frequency combs, developed within the past few years, have solved this problem. The ability to count optical oscillations of more than 1015 cycles per second facilitates high-precision optical spectroscopy, and has led to the construction of an all-optical atomic clock that is expected eventually to outperform today's state-of-the-art caesium clocks.
authors.affiliation: Max-Planck-Institut für Quantenoptik, Garching, Germany. thomas.udem@mpq.mpg.de
authors.forename: Th
authors.initials: T
authors.lastname: Udem
authors.forename: R
authors.initials: R
authors.lastname: Holzwarth
authors.forename: T W
authors.initials: TW
authors.lastname: Hänsch