MOTION OF PHASE SINGULARITIES IN A CLASS-B LASER

We investigate the circling motion of phase singularities in a small F resnel number CO2-laser. This occurs whenever modes with singly or mul tiply charged phase singularities are simultaneously excited with rota tionally symmetric modes. From the helical bistability of modes contai ning phase singularities follows bistability of the circling motion. U p to three simultaneously circling singularities are demonstrated. The slowly relaxing inversion of class-B lasers has as a consequence the nonstationarity of phase singularities which results in motion even wh en all mode frequencies are equal. Evidence of this nonstationarity, w hich relates class-B lasers to excitable chemical systems, is given.