  Injection-locked semiconductor lasers can be brought to a neuron-like
excitable regime when parameters are set close to the unlocking transition.
Here we study experimentally the response of this system to repeated optical
perturbations and observe the existence of a refractory period during which
perturbations are not able to elicit an excitable response. The results are
analyzed via simulations of a set of dynamical equations which reproduced
adequately the experimental results.
