Journal Article

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

Walsworth, Ronald L, Li, Chih-Hao, Sasselov, Dimitar, Phillips, David F, Benedick, Andrew J, Szentgyorgyi, Andrew, Kaertner, Franz X, Glenday, Alexander G, Fendel, Peter

2008

Overview

Searches for extrasolar planets using the periodic Doppler shift of stellar spectral lines have recently achieved a precision of 60 cm s super(-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 approx5 cm s super(-1) is necessary. The combination of a laser frequency comb with a Fabry-Perot filtering cavity has been suggested as a promising approach to achieve such Doppler shift resolution via improved spectrograph wavelength calibration, with recent encouraging results. Here we report the fabrication of such a filtered laser comb with up to 40-GHz (approx1-Aa) 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 super(-1) in astronomical radial velocity measurements.