Reply to comment on "Observation of subluminal twisted light in vacuum"

TL;DR

This paper clarifies the difference in subluminal light propagation effects observed in experiments using Hypergeometric-Gauss modes versus Laguerre-Gauss modes, resolving previous theoretical discrepancies.

Contribution

It highlights the importance of mode choice in analyzing light's subluminal behavior and clarifies the theoretical understanding of these effects in different mode types.

Findings

Hypergeometric-Gauss modes exhibit subluminal propagation.

Laguerre-Gauss modes have different propagation characteristics.

Theoretical and experimental results are consistent when mode differences are considered.

Abstract

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.