Microscopic modeling of transverse mode instabilities in mode-locked vertical external-cavity surface-emitting lasers

The generation and control of higher order transverse modes within a mode-locked vertical external-cavity surface-emitting laser with a semiconductor saturable absorber mirror are studied using a numerical solver for the two dimensional Maxwell Semiconductor Bloch Equations. In this work, the complex spatiotemporal evolution of the pulse toward a mode-locked state depends sensitively on the pumping level and pump to pulse spot size ratio. Microscopic physics sourced effects such as kinetic hole burning and filling, occurring on femtosecond timescales, play a central role. In particular, unsaturated charge carriers, both spectrally and transversally, initiate the development of asymmetric pulse profiles that transform over various characteristic time scales in a carrier chasing behavior.