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Searching for exoplanets using a microresonator astrocomb


Orbiting planets induce a weak radial velocity (RV) shift in the host star that provides a powerful method of planet detection. Importantly, the RV technique provides information about the exoplanet mass, which is unavailable with the complementary technique of transit photometry. However, RV detection of an Earth-like planet in the ‘habitable zone’1 requires extreme spectroscopic precision that is only possible using a laser frequency comb (LFC)2. Conventional LFCs require complex filtering steps to be compatible with astronomical spectrographs, but a new chip-based microresonator device, the Kerr soliton microcomb3,4,5,6,7,8, is an ideal match for astronomical spectrograph resolution and can eliminate these filtering steps. Here, we demonstrate an atomic/molecular line-referenced soliton microcomb for calibration of astronomical spectrographs. These devices can ultimately provide LFC systems that would occupy only a few cubic centimetres9,10, thereby greatly expanding implementation of these technologies into remote and mobile environments beyond the research lab.

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Fig. 1: Concept of a microresonator astrocomb.
Fig. 2: Experimental schematic and atomic/molecular line-referenced soliton microcomb.
Fig. 3: Data from testing at Keck II.
Fig. 4: Arc lamp data for absolute wavelength calibration.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request.


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We gratefully acknowledge J. Schlieder, A. Howard, F. Hadaegh and the support of the entire Keck summit team. We thank D. Carlson and H. Timmers for preparing the HNLF. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. The data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and NASA. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. This paper made use of data available in the NASA Exoplanet Archive and the Keck Observatory Archive. S.D. and S.P. acknowledge support from NIST. K.V., M.-G.S., X.Y. and Y.-H.L. thank the Kavli Nanoscience Institute and NASA for support under KJV.JPLNASA-1-JPL.1459106. This research was carried out at JPL and the California Institute of Technology under a contract with NASA and funded through the JPL Research and Technology Development Program.

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Authors and Affiliations



M.-G.S., S.L., G.V., M.P.F., D.M., S.B.P., S.A.D., C.B. and K.V. conceived the experiments. All co-authors designed and performed experiments. M.-G.S. and X.Y. built the soliton microcomb set-up and EO comb set-up with S.L., I.S.G., S.A.D., S.B.P. and Y.-H.L. providing assistance. G.D. managed operations and the experimental interface of the Keck II telescope. E.C.M., J.W. and C.B. analysed NIRSPEC data. C.B. and K.V. supervised the experiment. M.-G.S., C.B. and K.V. prepared the manuscript with input from all co-authors.

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Correspondence to C. Beichman or Kerry Vahala.

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Suh, MG., Yi, X., Lai, YH. et al. Searching for exoplanets using a microresonator astrocomb. Nature Photon 13, 25–30 (2019).

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