Interferometric Measurements of Phase Singularities in the Output of a Visible Laser

Abstract We report the use of a simple interferometric technique which allows direct identification of phase singularities in laser fields. Phase singularities are observed in families of optical patterns formed via cooperative frequency mode locking in a continuous single longitudinal mode Na2 ring laser. The interferometric technique complements a previously reported astigmatic imaging method, and is superior in that it can be used to elucidate the structure of the higher order stationary patterns.