| Issue |
EPL
Volume 139, Number 3, August 2022
|
|
|---|---|---|
| Article Number | 35001 | |
| Number of page(s) | 5 | |
| Section | Atomic, molecular and optical physics | |
| DOI | https://doi.org/10.1209/0295-5075/ac7dfa | |
| Published online | 01 August 2022 | |
Frequency changes during the propagation of a light beam
1 Université de Rennes 1 - Campus de Beaulieu, F-35000 Rennes, France
2 Université de Rennes 1 - CNRS IPR UMR 6251, F-35000 Rennes, France
(a) olivier.emile@univ-rennes.fr (corresponding author)
Received: 13 April 2022
Accepted: 4 July 2022
The energy and therefore the frequency of electromagnetic fields are quantities which are generally considered to be conserved in free space propagation. However, we observe here a frequency varying optical wave in free space propagation. The light comes from an Arago spot. Its frequency changes due to the rotational Doppler effect. More precisely, the light diffracted by a two-dimensional asymmetric object carries orbital angular momentum that varies with distance. As the object rotates, the frequency of the diffracted light experiences different rotational Doppler shifts along propagation. It varies in a discrete quantized way as it propagates. It can be adjusted, without violation of the conservation of energy. Since this phenomenon is deeply rooted in the diffraction process, it sheds some new light on this still open issue.
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