Spatial and temporal characterization of a Bessel beam produced using a   conical mirror
  We experimentally analyze a Bessel beam produced with a conical mirror, paying particular attention to its superluminal and diffraction-free properties. We spatially characterized the beam in the radial and on-axis dimensions, and verified that the central peak does not spread over a propagation distance of 73 cm. In addition, we measured the superluminal phase and group velocities of the beam in free space. Both spatial and temporal measurements show good agreement with the theoretical predictions. 
K. B. Kuntz, B. Braverman, S. H. Youn, M. Lobino, E. M. Pessina, A. I.   Lvovsky