Operation of a broadband visible-wavelength astro-comb with a high-resolution astrophysical spectrograph

Searches for Earth-like exoplanets using the periodic Doppler shift of stellar absorption lines require 10 cm/s precision in the measurement of stellar radial velocity (RV) over timescales of years. Current techniques have led to the discovery of short-period exoplanets that induce RV wobbles as small as approximate to 1 m/s on their parent stars. It has been suggested that order-of-magnitude improved RV precision may be achievable using an astro-comb, a laser frequency comb optimized for astrophysical spectrograph wavelength calibration. Here we report the development of a broadband visible-wavelength astro-comb and its operation with the HARPS-N spectrograph at the Telescopio Nazionale Galileo in the Canary Islands. This green astro-comb has > 7000 narrow (< 1 MHz) spectral lines spaced by 16 GHz with relatively uniform line power from 500 to 620 nm. The line frequencies are locked to GPS, enabling us to realize HARPS-N wavelength calibration with RV measurement precision and stability < 10 cm/s. (C) 2015 Optical Society of America.