  Speckle is a wave interference phenomenon that has been studied in various
fields, including optics, hydrodynamics and acoustics. Speckle patterns contain
spectral information of the interfering waves, and of the scattering medium
that generates the pattern. Here we study experimentally the speckle patterns
generated by the light emitted by two types of semiconductor lasers:
conventional laser diodes, where we induce low-coherence emission by optical
feedback or by pump current modulation, and coupled nanolasers. In both cases
we analyze the intensity statistics of the respective speckle patterns to
inspect the degree of coherence of the light. We show that that speckle
analysis provides a non-spectral way to assess the coherence of semiconductor
laser light.
