Giovannini, D., Romero, J., Potoček, V., Ferenczi, G., Speirits, F., Barnett, S. , Faccio, D. and Padgett, M. (2015) Spatially structured photons that travel in free space slower than the speed of light. [Data Collection]
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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 wavevectors 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 of 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 the order of 1 m. Our work highlights that, even in free space, the invariance of the speed of light only applies to plane waves.
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| College / School: | College of Science and Engineering > School of Physics and Astronomy |
| Date Deposited: | 02 Apr 2015 09:28 |
| Enlighten Publications URL: | http://eprints.gla.ac.uk/102869/ |
| URI: | https://researchdata.gla.ac.uk/id/eprint/157 |
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