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

TL;DR

This paper reports the development of a laser frequency comb, called 'astro-comb', capable of achieving 1 cm/s precision in radial velocity measurements, significantly improving exoplanet detection capabilities.

Contribution

The creation of a stable, wide-line-spacing laser comb suitable for high-resolution spectrographs, enabling ultra-precise astronomical radial velocity measurements.

Findings

Fabricated a 40-GHz line spacing astro-comb from a 1-GHz source.

Demonstrated the astro-comb's compatibility with high-resolution spectrographs.

Projected radial velocity measurement precision of 1 cm/s.

Abstract

Searches for extrasolar planets using the periodic Doppler shift of stellar spectral lines have recently achieved a precision of 60 cm/s (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 Earthlike orbit, a precision of 5 cm/s 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 (1-A) 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 in astronomical radial velocity measurements.