Creating a self-induced dark spontaneous-force optical trap for neutral   atoms
  This communication describes the observation of a new type of dark spontaneous-force optical trap (dark SPOT) obtained without the use of a mask blocking the central part of the repumper laser beam. We observe that loading a magneto-optical trap (MOT) from a continuous and intense flux of slowed atoms and by appropriately tuning the frequency of the repumper laser is possible to achieve basically the same effect of the dark SPOT, using a simpler apparatus. This work characterizes the new system through measurements of absorption and fluorescence imaging of the atomic cloud and presents a very simple model to explain the main features of our observations. We believe that this new approach may simplify the current experiments to produce quantum degenerated gases. 
S. R. Muniz, K. M. F. Magalh\~aes, E. A. L. Henn, L. G. Marcassa and   V. S. Bagnato