Pattern formation in the transverse section of a laser with a large fresnel number

We experimentally investigate pattern formation in a single-wavelength long laser cavity with a large Fresnel number. Near the laser threshold, we obs erve a single frequency spatially periodic structure corresponding to title d waves theoretically predicted by the Maxwell-Bloch equations. We also sho w the presence of secondary instabilities at other wavelengths and polariza tion instabilities at the same wavelength for different parameter values. [ S0031-9007(99)08512-9].