Stabilizing a Fabry-Perot etalon peak to 3 cm s⁻¹ for spectrograph calibration

We present a method of frequency stabilizing a broadband etalon that can serve as a high-precision wavelength calibrator for an echelle spectrograph. Using a laser to probe the Doppler-free saturated absorption of the rubidium D₂ line, we stabilize one etalon transmission peak directly to the rubidium frequency. The rubidium transition is an established frequency standard and has been used to lock lasers to fractional stabilities of < 10⁻¹², a level of accuracy far exceeding the demands of radial velocity (RV) searches for exoplanets. The stabilized bandwidth depends on the dispersion characteristics of the etalon. We describe a simple setup designed specifically for use at an observatory and demonstrate that we can stabilize the etalon peak to a relative precision of < 10⁻¹⁰; this is equivalent to 3 cm s⁻¹ RV precision.10 page(s