Spatiotemporal Dynamics of Lasers with a Large Fresnel Number

We measure the local intensity and the intensity cross-correlation function of patterns emitted by a CO₂ laser with a Fresnel number around 60 and find evidence of weak turbulence. We show theoretically that the spatiotemporal dynamics of such a laser can be governed by two fields. One leads to a "turbulent" state principally through phase fluctuations, whereas the other yields a periodic modulation in space and time of the intensity. This can explain why the intensity of the laser is locally chaotic but the time-averaged intensity pattern retains the global symmetry of the system.