Simultaneous laser frequency stabilization to an optical cavity and an iodine frequency reference

Abstract

In this Letter, we demonstrate a method to combine a molecular iodineabsolute frequency reference with a high-finesse optical cavity in asingle laser to take advantage of the frequency stability propertiesof both systems at different time scales. The result is a laser exhibiting the long-term and short-term stability levels of the iodinefrequency reference and optical cavity, respectively. The method usesfrequency offset side-band locking and an acousto-optical modulatordriven ac-coupled servo-loop to correct the iodine's short-termfrequency fluctuations. Experimental results show cavity-limited stability above 1 Hz of 10^(-15) 1/rtHz and iodine stability below 10 mHz of 10^(-13) 1/rtHz. In terms of the Allan deviation, this corresponds to stability levels close to the 10^(-15) at 1 s and 10^(-14) for observation times >100 s.