Reply to comment on "Observation of subluminal twisted light in vacuum"
  Recently, we showed experimentally that light carrying orbital angular momentum experiences a slight subluminality under free-space propagation [1]. We thank Saari [2] for pointing out an apparent discrepancy between our theoretical results and the well-known results for the simple case of Laguerre-Gauss modes. In this reply, we note that the resolution of this apparent discrepancy is the distinction between Laguerre-Gauss modes and Hypergeometric-Gauss modes, which were used in our experiment and in our theoretical analysis, which gives rise to different subluminal effects. 
Fr\'ed\'eric Bouchard, Robert W. Boyd, and Ebrahim Karimi
physics.optics