Experimental observation of topological defects in a laser

Abstract

Recently, it was proposed that topological defects are the cause of the symmetry breaking in transverse intensity distribution of lasers.1 We use a CO2 laser with variable Fresnel number to study experimentally the transition from symmetric to asymmetric patterns. This process of spontaneous symmetry breaking leads to the appearance of standing and traveling waves in the azimuthal direction.2 Here, we show experimentally that the symmetry breaking process is followed by the appearance of topological defects moving around the center of the beam. We detect defects both by intensity measurements and interferometric techniques. Interferometric techniques allow the observation of the position of the defect and the phase of the field around the defect. We also discuss the effects of the presence of defects on intensity and field cross-correlation measurements, and how they induce different length scales in the system.