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

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 similar to 5 cm s(-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(2-4), with recent encouraging results(5). Here we report the fabrication of such a filtered laser comb with up to 40-GHz ( similar to 1-angstrom ) line spacing, generated from a 1-GHz repetition- rate source, without compromising long- term stability, reproducibility or spectral resolution. This wide- linespacing 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.