Topological light bullets supported by spatio-temporal gain
  We reveal that the competition between diffraction, cubic nonlinearity, two-photon absorption, and gain localized in both space and time results in arrest of collapse, suppression of azimuthal modula-tion instabilities for spatiotemporal wavepackets, and formation of stable three-dimensional light bul-lets. We show that Gaussian spatiotemporal gain landscapes support bright, fundamental light bullets, while gain landscapes featuring a ring-like spatial and a Gaussian temporal shapes may support stable vortex bullets carrying topological phase dislocations. 
Valery E. Lobanov, Olga. V. Borovkova, Yaroslav V. Kartashov, Victor   A. Vysloukh, and Lluis Torner
physics.optics nlin.PS