Abstract
We report the transverse-mode dynamics of electrically-biased multi-transverse mode vertical-cavity surface-emitting lasers (VCSELs) after resonant femtosecond optical pulse injection. In addition to a multiresonance relaxation-oscillation response at high injection levels, we observe picosecond oscillations in the VCSEL emission due to transverse mode beating. These oscillations persist at injection powers that are lower than those required for inducing observable relaxation oscillations and are caused by locking of the transverse modes to the injected optical pulse.