Noise Performance of the Carrier-Envelope Offset in Passively Stabilized Frequency Combs

Frequency metrology and high-field physics heavily depend on reliable stabilization of the carrier-envelope offset frequency <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(f_{\text{ceo}})$</tex> of optical combs. To this end, passively stabilized frequency combs are particularly appealing as they promise zero offset frequency [1]. However, this theoretical expectation has never been put to a thorough test yet. Here we demonstrate an f-2f interferometer with additional frequency shift for a long term measurement of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$f_{\text{ceo}}$</tex> [2]. In particular, our analysis provides an indication for a non-deterministic shift of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$f_{\text{ceo}}$</tex> in passively stabilized frequency combs. Our method can easily be adapted for the analysis of other passively stabilized optical sources, e.g., parametric or difference frequency generated mid- IR combs.