Characterization Setup of a Molecular Iodine Based Optical Clock: Long-term Optical Frequency Generation for Time and Frequency Transfer Experiments

Abstract

Summary — In this mansucript we present a setup and first results for long-term operation of an optical clock based on an existing Doppler-free iodine vapor cell spectroscopy unit [1] acting as an optical frequency reference system and an optical frequency comb. The combination of comb and optical frequency reference represents an ultra-stable radiofrequency source, as the comb is transferring the stability of the optical frequency reference to the radiofrequency regime. The radiofrequency is therefore generated directly from the pulse train of the optical frequency comb. The frequency comb is optically phase locked to the optical frequency reference based on molecular iodine, resulting in a full optical-to-radiofrequency chain. We will present the phase and amplitude noise performance of this radiofrequency source, i.e. an optical clock. The short-term stability in terms of Allan deviation is determined in an optical comparison measurement with a cavity stabilized laser system with a sub-Hz linewidth via the frequency comb. However, our main focus lies on the investigation of the long-term stability of the clock chain in the radiofrequency domain in comparison to the UTC realization of the German Aerospace Center (represented by the Galileo Competence Center) and the continuous operation of an optical clock.