  We report on the experimental study of an optically driven multimode
semiconductor laser with 1~m cavity length. We observed a spatiotemporal regime
where real time measurements reveal very high intensity peaks in the laser
field. Such a regime, which coexists with the locked state and with stable
phase solitons, is characterized by the emergence of extreme events which
produce a heavy tail statistics in the probability density function. We
interpret the extreme events as collisions of spatiotemporal structures with
opposite chirality. Numerical simulations of the semiconductor laser model,
showing very similar dynamical behavior, substantiate our evidences and
corroborate the description of such interactions as collisions between phase
solitons and transient structures with different phase rotations.
