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2003 May Issue 3

RLE Pursues the Optical Clock
Erich P. Ippen at the New Limits of Precision

Multidisciplinary Initiative
the DoD MURI program and RLE

Rising Stars
Oxenham and Sugiyama

Students at the Forefront
The Helen Carr Peake Research Prize

Computational Prototyping
an interview with Jacob K. White

Introducing a New Professor
Luca Daniel joins RLE

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RLE pursues the optical clock
Erich P. Ippen at the New Limits of Precision
2003 May Issue 3

Erich P. Ippen
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.

Such a clock might gain or lose a second in four billion years. That is keeping good time.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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Erich P. Ippen is the Elihu Thomson Professor of Electrical Engineering and Professor of Physics at MIT. He is one of the leaders of RLE's Optics and Quantum Electronics Group. Ippen received the SB in Electrical Engineering from the Massachusetts Institute of Technology in 1962, and then attended the University of California, Berkeley where he received his MS in 1965 and PhD in 1968 in Electrical Engineering. He was a member of the technical staff at Bell Laboratories from 1968 to 1980 where he was one of the founders of the field of femtosecond optics. He joined the MIT faculty in 1980. Ippen is a member of both the National Academy of Sciences and the National Academy of Engineering, and is also a fellow of the American Academy of Arts and Sciences. His many honors include being named the 2001-2002 recipient of MIT's James R. Killian, Jr. Faculty Achievement Award in recognition of his extraordinary contributions to his fields and to the Institute. Ippen and his group continue to pioneer important new areas of optics, particularly in the areas of femtosecond science and ultra-highspeed devices, inventing new methods for generating extremely short bursts of light using lasers, innovating techniques to exploit the time resolution such pulses provide, and using these new techniques to probe ultrafast phenomena in materials.
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