Pattern dynamics in a large Fresnel number laser close to threshold

A high Fresnel number laser close to threshold can be set at a detuning value where it displays only the first transverse pattern with zero intensity in its center. However, the availability of a large phase space gives rise to a new type of dynamics. Precisely, for this highly symmetric situation, the intensity pattern undergoes a transition between stable and oscillating superpositions of traveling and standing waves. Such a transition corresponds to the so-called Takens-Bogdanov bifurcation. We report experimental evidence of such a behavior.