Real-time spectral transient dynamics measurement of mode-locked semiconductor disk lasers with DFT

Abstract

The real-time measurement of transient dynamics of a semiconductor disk laser (SDL) was demonstrated using the dispersive Fourier transform (DFT) technology. Operating in a stable mode-locking state with a repetition rate of 425 MHz and a pulse width of 2.18 ps, the SDL exhibits significant changes in both spectral shape and pulse profile in the process of the establishment and extinction of mode locking. The pulse-resolved spectral evolution was captured, which includes relaxation oscillation, Q-switched oscillation and mode-locking states. Notably, we observed a progressive shift in the central wavelength—from 983.8 nm during initial mode-locking to 982.5 nm in the stabilization phase, and finally to 980 nm at extinction. The shift of mode locked wavelength can be attributed to thermal effect. To the best of our knowledge, this is the first time to observe the mode-locked dynamics in SDLs using a DFT technology.