Response to comments on “Slowing of Bessel light beam group velocity”

Peeter Saari

Robert R. Alfano, Daniel A. Nolan

Chih-Shiang Chou, Ming-Feng Shih

We find theoretically that modulation instability in a non-instantaneous medium could be used to achieve slow light. We use the beam propagation method to simulate slow light and use Fourier decomposition of the light pulse to predict the reduced group velocity in such a medium. This method of achieving slow light can be used in any self-focusing medium with non-instantaneous nonlinear response. It also provides an easy way to adjust the group velocity of the light in the medium.

J.T. Lunardi

Daniel Giovannini, Jacquiline Romero, Václav Potoček +5 more

That the speed of light in free space is constant is a cornerstone of modern physics. However, light beams have finite transverse size, which leads to a modification of their wave vectors resulting in a change to their phase and group velocities. We study the group velocity of single photons by measuring a change in their arrival time that results from changing the beam's transverse spatial structure. Using time-correlated photon pairs, we show a reduction in the group velocity of photons in both a Bessel beam and photons in a focused Gaussian beam. In both cases, the delay is several micrometers over a propagation distance of ~1 meter. Our work highlights that, even in free space, the invariance of the speed of light only applies to plane waves.

Mark A. Newbold, Gregory J. Salamo