Stable and Controllable High-Order Pulse Cluster VECSELs

High-order pulse clusters was demonstrated from passively mode-locked VECSELs. The highest order reached to 13 sub-pulses. The master pulse cluster exhibited a repetition rate of 108.67 MHz, while sub-pulses achieving a maximum repetition rate of 3.2 GHz. A minimum pulse width of 14.5 ps was achieved within these higher-order pulse clusters. The output of pulse clusters of different orders can be controlled by adjusting the cavity symmetry parameters (CSP) and pump light intensity. The influence of the pulse cluster order on the transient mode-locking stability was investigated by the time stretching dispersion Fourier transform technique. The results reveal that the interplay between the cavity geometry, the slow carrier dynamics of the gain medium, and the non-instantaneous recovery of the SESAM plays a crucial role in enabling and stabilizing high-order pulse clusters.