Quasi-instantaneous transverse patterns have been measured in a broad-aperture class A laser, using an ultrafast camera. The evolution from order to fully developed turbulence is observed as the Fresnel number increases up to 110. In the turbulent regime, two very different spatial scales coexist, one order of magnitude apart. The linear analysis allows us to interpret most of the features of the experiment.

• Received 15 October 2001

DOI:https://doi.org/10.1103/PhysRevA.66.023820