Laser Frequency Combs for Astronomical Observations

• Published in: Science (American Association for the Advancement of Science) Vol. 321; no. 5894; pp. 1335 - 1337
• Main Authors: Steinmetz, Tilo, Wilken, Tobias, Araujo-Hauck, Constanza, Holzwarth, Ronald, Hänsch, Theodor W, Pasquini, Luca, Manescau, Antonio, D'Odorico, Sandro, Murphy, Michael T, Kentischer, Thomas, Schmidt, Wolfgang, Udem, Thomas
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 05.09.2008; The American Association for the Advancement of Science
• Subjects: Astronomical cosmology; Astronomy; Astrophysics; Atomic clocks; Calibration; Cosmology; Earth, ocean, space; Exact sciences and technology; Frequencies; Laser modes; Lasers; Observational astronomy; Observational cosmology; Observational cosmology (including hubble constant, distance scale, cosmological constant, early universe, etc.); Red shift; Stellar systems. Galactic and extragalactic objects and systems. The universe; Telluric lines; Wavelengths; Universe expansion; Cosmology; Astronomical telescopes; Modelling; Cosmological redshift; Drift velocity
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1161030

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.