Asynchronous mutually-coherent dual-emission from a bidirectional mode-locked femtosecond Ti:Sapphire ring laser

Bidirectional Kerr-lens mode-locked (BD-KLM) Ti:Sapphire ring lasers were initially developed for rotation sensing based on the Sagnac effect. More recently, BD-KLM lasers have been shown to generate two free-running pulse trains with slightly different repetition rates while maintaining mutual coherence, enabling proof-of-principle molecular spectroscopy based on dual-comb spectroscopy. In this paper, we present a comprehensive characterization of this laser system and highlight the key properties of this unique cavity. Our experimental observations and analysis show that the observed asynchronicity is consistent with the differences in the central wavelengths of the two counter-propagating beams, as expected from the chromatic dispersion of the cavity. We also investigate the role of the self-steepening effect, as previously suggested in the literature, and show that its contribution is negligible in accounting for the observed asynchronicity in our system. These results represent a step forward in understanding the complex interplay between intracavity energy and the resulting asynchronicity in bidirectional KLM lasers. Fully elucidating this fundamental behavior requires a more advanced modeling framework, which lies beyond the scope of the present study.