Observation of azimuthal modulational instability and formation of patterns of optical solitons in a quadratic nonlinear crystal Petrov, Dmitri V. ; Torner, Lluis ; Martorell, Jordi ; Vilaseca, Ramon ; Torres, Juan P. ; Cojocaru, Crina Abstract Publication: Optics Letters Pub Date: September 1998 DOI: 10.1364/OL.23.001444 Bibcode: 1998OptL...23.1444P