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Science 5 September 2008:
Vol. 321. no. 5894, pp. 1335 - 1337
DOI: 10.1126/science.1161030
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Reports

Laser Frequency Combs for Astronomical Observations

Tilo Steinmetz,1,2 Tobias Wilken,1 Constanza Araujo-Hauck,3 Ronald Holzwarth,1,2 Theodor W. Hänsch,1 Luca Pasquini,3 Antonio Manescau,3 Sandro D'Odorico,3 Michael T. Murphy,4 Thomas Kentischer,5 Wolfgang Schmidt,5 Thomas Udem1*

A direct measurement of the universe's expansion history could be made by observing in real time the evolution of the cosmological redshift of distant objects. However, this would require measurements of Doppler velocity drifts of ~1 centimeter per second per year, and astronomical spectrographs have not yet been calibrated to this tolerance. We demonstrated the first use of a laser frequency comb for wavelength calibration of an astronomical telescope. Even with a simple analysis, absolute calibration is achieved with an equivalent Doppler precision of ~9 meters per second at ~1.5 micrometers—beyond state-of-the-art accuracy. We show that tracking complex, time-varying systematic effects in the spectrograph and detector system is a particular advantage of laser frequency comb calibration. This technique promises an effective means for modeling and removal of such systematic effects to the accuracy required by future experiments to see direct evidence of the universe's putative acceleration.

1 Max-Planck Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching, Germany.
2 Menlo Systems GmbH, Am Klopferspitz 19, D-82152 Martinsried, Germany.
3 European Southern Observatory, Karl-Schwarzschild-Strasse 3, D-85748 Garching, Germany.
4 Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Mail H39, Post Office Box 218, Victoria 3122, Australia.
5 Kiepenheuer-Institut für Sonnenphysik, Schöneckstr. 6, D-79104 Freiburg, Germany.

* To whom correspondence should be addressed. E-mail: thu{at}mpq.mpg.de

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
10-GHz Self-Referenced Optical Frequency Comb.
A. Bartels, D. Heinecke, and S. A. Diddams (2009)
Science 326, 681
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