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A laser frequency comb that enables radial velocity measurements with a precision of 1 cm s-1

Nature volume 452, pages 610–612 (2008)Cite this article

Abstract

Searches for extrasolar planets using the periodic Doppler shift of stellar spectral lines have recently achieved a precision of 60 cm s-1 (ref. 1), which is sufficient to find a 5-Earth-mass planet in a Mercury-like orbit around a Sun-like star. To find a 1-Earth-mass planet in an Earth-like orbit, a precision of ∼5 cm s-1 is necessary. The combination of a laser frequency comb with a Fabry–Pérot filtering cavity has been suggested as a promising approach to achieve such Doppler shift resolution via improved spectrograph wavelength calibration2,3,4, with recent encouraging results5. Here we report the fabrication of such a filtered laser comb with up to 40-GHz (∼1-Å) line spacing, generated from a 1-GHz repetition-rate source, without compromising long-term stability, reproducibility or spectral resolution. This wide-line-spacing comb, or ‘astro-comb’, is well matched to the resolving power of high-resolution astrophysical spectrographs. The astro-comb should allow a precision as high as 1 cm s-1 in astronomical radial velocity measurements.

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Figure 1: Block diagram of the astro-comb.
Figure 2: Example astro-comb output spectrum with 37-GHz line spacing.
Figure 3: Suppression of extraneous source-comb lines for the astro-comb.

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Acknowledgements

This project is supported by the Harvard University Origins of Life Initiative, the Smithsonian Institution, and DARPA.

Author contributions D.S., A.S. and R.L.W. initiated the project. C.-H.L., D.F.P. and R.L.W. designed the comb filtering strategy. C.-H.L. and D.F.P. designed the Fabry–Pérot stabilization strategy. R.L.W. supervised the project. C.-H.L. constructed the comb filtering system and acquired the filtered-comb data. A.J.B., P.F. and F.X.K. provided the 1-GHz laser comb and assisted C.-H.L. in its integration with the comb filtering system. C.-H.L. performed the initial data analysis. C.-H.L., A.G.G., F.X.K., D.F.P., D.S., A.S. and R.L.W. interpreted the data and assessed systematic effects. D.S. and A.S. advised on the astrophysical relevance of the data.

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Authors and Affiliations

  1. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge,,

    Chih-Hao Li, Alexander G. Glenday, David F. Phillips, Dimitar Sasselov, Andrew Szentgyorgyi & Ronald L. Walsworth

  2. Department of Physics, Harvard University, 17 Oxford Street, Cambridge, Massachusetts 02138, USA,

    Chih-Hao Li, Alexander G. Glenday & Ronald L. Walsworth

  3. Department of Electrical Engineering and Computer Science and Research Laboratory for Electronics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA,

    Andrew J. Benedick, Peter Fendel & Franz X. Kärtner

  4. MenloSystems Inc., 69 Stickles Pond Road, Newton, New Jersey 07860, USA ,

    Peter Fendel

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  1. Chih-Hao Li
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Correspondence to Ronald L. Walsworth.

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Li, CH., Benedick, A., Fendel, P. et al. A laser frequency comb that enables radial velocity measurements with a precision of 1 cm s-1. Nature 452, 610–612 (2008). https://doi.org/10.1038/nature06854

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