Abstract
The existing methods for measuring the orbital-angular-momentum (OAM) spectrum suffer from issues such as poor efficiency, strict interferometric stability requirements, and too much loss. Furthermore, most techniques inevitably discard part of the field and measure only a post-selected portion of the true spectrum. Here, we propose and demonstrate an interferometric technique for measuring the true OAM spectrum of optical fields in a single-shot manner. Our technique directly encodes the OAM-spectrum information in the azimuthal intensity profile of the output interferogram. In the absence of noise, the spectrum can be fully decoded using a single acquisition of the output interferogram, and, in the presence of noise, acquisition of two suitable interferograms is sufficient for the purpose. As an important application of our technique, we demonstrate measurements of the angular Schmidt spectrum of the entangled photons produced by parametric down-conversion and report a broad spectrum with the angular Schmidt number 82.1.
Highlights
The existing methods for measuring the orbital-angular-momentum (OAM) spectrum suffer from issues such as poor efficiency, strict interferometric stability requirements, and too much loss
A way to bypass the interferometric stability requirement is by measuring the angular coherence function[33, 34] using angular double-slits[39]. This method requires a series of measurements and since in this method only a very small portion of the incident field is used for detection, it is not suitable for very low-intensity fields such as the fields produced by parametric down-conversion (PDC)
We demonstrate an interferometric technique for measuring the true OAM spectrum in a single-shot manner, that is, by acquiring only one image of the output interferogram using a multi-pixel camera
Summary
The existing methods for measuring the orbital-angular-momentum (OAM) spectrum suffer from issues such as poor efficiency, strict interferometric stability requirements, and too much loss. As an important application of our technique, we demonstrate measurements of the angular Schmidt spectrum of the entangled photons produced by parametric down-conversion and report a broad spectrum with the angular Schmidt number 82.1 It was shown by Allen et al that a photon in a light beam can have orbital-angular-momentum (OAM) values in the integer multiples of ħ1. A way to bypass the interferometric stability requirement is by measuring the angular coherence function[33, 34] using angular double-slits[39] This method requires a series of measurements and since in this method only a very small portion of the incident field is used for detection, it is not suitable for very low-intensity fields such as the fields produced by parametric down-conversion (PDC). Since our method is interferometric, the efficiency is very high, and since it involves only single-shot measurements, the interferometric stability requirements are much less stringent
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have