A Robust Green Astro-Comb for Earth-Like Exoplanet Searches

One technique for detecting exoplanets (i.e. planets outside our solar system) is the radial velocity method. This technique works by observing, in a star-exoplanet system, the periodic shifts in the star’s spectral lines caused by the gravitational influence of an orbiting planet. Detecting Earth-sized planets around Sun-like stars is very challenging as it requires extremely precise calibration and characterization the of astrophysical spectrographs used to make such measurements. To address this challenge, we employ a visible wavelength laser frequency comb as a wavelength calibration source. Our frequency comb calibrator, known as an astro-comb, is realized by spectrally broadening and shifting the output of a 1 GHz repetition rate modelocked Ti:sapphire laser using a photonic crystal fiber and then filtering the comb lines to create a coarse-toothed comb with 16 GHz line spacing. Our astro-comb system has been deployed at the TNG telescope on La Palma, Spain to calibrate the HARPS-N spectrograph. Here, we present improved spectral broadening techniques, a wider comb-spacing implementation for instrument profile characterization, and ongoing comb-calibrated astrophysical measurements, including measurements of solar radial velocities.