Observation of subluminal twisted light in vacuum: reply

Abstract

Recently, we showed experimentally that light carrying orbital angular momentum experiences a slight subluminality under free-space propagation. We thank Saari [Optica4, 204 (2017)10.1364/OPTICA.4.000204] 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.