Versatile Molecular Vibrations of Soliton Pairs in an Ultrafast Fiber Laser

Time-stretched spectroscopy based real-time measurement serves as an efficient access to the frontier research on the internal motions of soliton molecules, akin to matter molecules. A considerable question is raised of how far the light-matter analogy would reach. Here, we unveil this analogy from the aspect of molecular vibration, highlighting the versatile internal motions within soliton molecules in a near-zero-dispersion fiber oscillator. Assisted with real-time spectral interferometry, molecular vibration based composite internal motions are resolved towards extended degrees of freedom of dynamical soliton molecules. The relative intensity difference and the total energy fluctuation of the soliton pairs are presented to unveil the intrinsic mechanisms of internal motions. All these findings enrich the knowledge towards versatile internal motions of dual-pulse structures, further promoting the research on the analogy between optical soliton molecules and matter molecules.