Single-shot measurement of the orbital angular momentum spectrum of light


Abstract: The existing methods for measuring the orbital-angular-momentum (OAM) spectrum suffer from issue such as poor efficiency, strict interferometric stability requirements, and toomuch loss. Furthermore, most techniques inevitably discard part of thefield and measureonly a post-selected portion of the true spectrum. Here, we propose and demonstrate aninterferometric technique for measuring the true OAM spectrum of opticalfields in a single-shot manner. Our technique directly encodes the OAM-spectrum information in the azi-muthal intensity profile of the output interferogram. In the absence of noise, the spectrumcan be fully decoded using a single acquisition of the output interferogram, and, in thepresence of noise, acquisition of two suitable interferograms is sufficient for the purpose. Asan important application of our technique, we demonstrate measurements of the angularSchmidt spectrum of the entangled photons produced by parametric down-conversion andreport a broad spectrum with the angular Schmidt number 82.1

Nature Communications 8 1054 (2017)

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