Internal motion within ultrafast asynchronous dual wavelength mode-locked lasers

Real-time spectroscopy access to ultrafast fiber lasers provides new opportunities for exploring complex soliton interaction dynamics. In this study, we employ a time-stretch technique that enables real-time access to both spectral and temporal dynamics, revealing rich nonlinear processes in asynchronous dual wavelength mode-locked pulses in an ultrafast fiber laser. Due to the different group velocities of the two wavelengths, the mode-locked solitons centered at different wavelengths periodically collide with each other. We recorded the entire process of soliton establishment, stabilization, and disappearance, shedding light on the mystery of stable transmission of dual-wavelength mode-locked pulses. These processes were observed for the first time in an ultrafast fiber laser, and the experimental evidence provides important insights into the understanding of nonlinear dynamics in fiber lasers, as well as the potential for improving laser performance for application in dual-comb spectroscopy.