Laser frequency combs for precision astrophysical spectroscopy

Searches for extrasolar planets using the periodic Doppler shift of stellar spectral lines resulting from the motion of the host star around the barycentre of an extrasolar system have recently achieved a precision of 60 cm/s. To find a 1-Earth-mass planet in an Earth-like orbit, a precision of 5 cm/s is necessary. The sensitivity of astrophysical spectroscopy is presently limited by its wavelength calibration sources. The combination of a laser frequency comb with a Fabry-Perot (FP) filter cavity has been suggested as a promising approach to improved sensitivity. The paper reports on the fabrication and tests of a filtered comb with up to 40-GHz (~ 1 Aring) line spacing, generated from a 1 - GHz repetition-rate source, without compromising long-term stability, reproducibility or spectral resolution. This 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 in astronomical radial velocity measurements.