RLE
pursues the optical clock
Erich P. Ippen at the New
Limits of Precision
2003 May Issue 3
Erich P. Ippen
The shortest pulse, the brightest light, and the coldest atom are
all coming together in a major new $5M research program directed
by RLE's Erich P. Ippen that
enters MIT into the world-wide race to revolutionize the science
of optical metrology and to create a new generation of ultraprecise
optical clocks.
Ippen's
project is sponsored by the Office of Naval Research through the
Department of Defense’s Multidisciplinary Research Program
of the University Research Initiative, or MURI (see related article
in this issue). Ippen has assembled an extraordinary interdisciplinary
team of RLE researchers from four MIT academic departments and laboratories:
RLE's Director Jeffrey H. Shapiro
and Associate Director Daniel Kleppner,
as well as RLE's Yoel Fink,
Thomas J. Greytak, Franz
X. Kärtner, Leslie A.
Kolodziejski, and Franco
N. C. Wong.
All clocks require two components. First, there must be a regular,
periodic event or occurrence, such as the swing of a pendulum. Second,
there must be a way of accumulating or recording the events, such
as the step by step movement of gears attached to the minute hands
of a watch. Ippen's project will attempt to use the oscillations
of ultracold atoms as the "pendulum," and the pulse of
femtosecond lasers—pulsing at a thousandth of a trillionth
of a second—as the "gears and hands" to count the
oscillations. Such a clock might gain or lose a second in four billion
years. That is keeping good time.
The opportunity to greatly increase timing precision arises from
recent advances in ultrashort-pulse modelocked lasers and in ultracold
atom and ion physics, fields in which RLE researchers are leaders.
A major feature of the program is the close integration of research
efforts to apply femtosecond comb technology to ultraprecise atom
spectroscopy, in a sense, creating a femtosecond comb bridge between
the microwave domain and the optical domain.
The optical transition frequencies of single ions or collections
of laser-cooled atoms are emerging as the most stable and accurate
frequency sources. Their high frequencies, however, make it difficult
to count cycles as required for comparisons to the current cesium
microwave standard. Now, femtosecond technology provides a promising
means for making this difficult connection. Recent developments
in RLE open the opportunity of building optical clocks with accuracies
superior to the current microwave standard—which dates back
fundamentally to 1967—by several orders of magnitude. Such
improved clocks would find widespread applications in measurements
of the highest precision and should greatly improve the resolution
of today’s guidance and global positioning systems.
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