Experimental evidence of selection and stabilization of spatial patterns in a CO2 laser by means of spatial perturbations

We report on experimental evidence of selection and stabilization of unstable patterns by means of spatial perturbations. Thin metallic wires, with a diameter comparable to the laser wavelength, are inserted into a laser cavity to realize the selection and stabilization process. We studied the effects of small displacement of a single wire on the fundamental and annular patterns. The observed phenomena can be explained considering the diffractive effects of the wire inside the optical cavity. By using more wires instead of a single wire, square and hexagonal patterns are obtained. (C) 1998 Elsevier Science B.V.