We present the temporal and spectral evolution of stimulated emission from In0.2Ga0.8As/GaAs microcavity laser samples at 20 K after femtosecond optical excitation. Both, linewidth and chirp become smaller when the cavity resonance is at shorter wavelengths within the gain spectrum of the quantum well: The linewidth is reduced from &Dgr;&lgr;=0.41 nm at 923 nm, where the threshold is lowest, to &Dgr;&lgr;=0.26 nm at 884 nm. Comparison with a phenomenological model yields linewidth enhancement factors &agr; of 2 and 5 for emission wavelengths of 884 and 925 nm, respectively. A time‐bandwidth product of 0.68 is obtained at the shorter wavelength. ©1995 American Institute of Physics.