Browsing by Author "Akanksha Gautam"

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Detecting topological index of randomly scattered V-point singularities using Stokes correlations
(Optica Publishing Group (formerly OSA), 2024) Akanksha Gautam; Gauri Arora; P. Senthilkumaran; Rakesh Kumar Singh
Topological defects in vector fields constitute polarization singularities that have numerous applications in classical and quantum optics. These beams are inhomogeneously polarized and are shown to self-heal under symmetric amplitude perturbations. Polarization singular beams are characterized using a singularity index that can be detected using Stokes polarimetry or other interferometric and diffraction approaches. However, the information about the singularity index is lost when these beams travel through random scattering media; this results in a spatially fluctuating polarization pattern known as polarization speckle. This paper proposes and experimentally demonstrates a new method to detect the topological index of these randomly scattered V-point singularities using higher-order Stokes correlations in a lensless condition. A detailed theoretical basis is developed, and the performance of the technique is demonstrated by retrieving the signature of polarization singularities with Poincaré–Hopf index |η| = 1 and |η| = 2. We also demonstrate that by studying the intensity–intensity correlations of the polarization speckle, it is possible to differentiate between different vector beams having the same magnitude as the Poincaré–Hopf index. © 2024 OSA - The Optical Society. All rights reserved.
Folded interferometer to measure coherence–polarization matrix
(Optica Publishing Group (formerly OSA), 2024) Sourav Chandra; Akanksha Gautam; Rakesh Kumar Singh
We present and experimentally demonstrate a new, to the best of our knowledge, technique to quantitatively measure coherence–polarization (BCP) matrix with correlations of only two Stokes fluctuations. The BCP matrix is a square matrix with four elements that involves two-point correlations among orthogonal polarization components. A theoretical framework of the technique is developed, and its viability is demonstrated by a proof of principle experiment. Experimental tests and measurement of the elements of the BCP matrix of statistically stationary beams are demonstrated. © 2024 Optica Publishing Group.
Phase retrieval in inverse ghost diffraction using Sagnac interferometer
(Institute of Physics, 2024) Akanksha Gautam; Sourav Chandra; Rakesh Kumar Singh
Ghost diffraction (GD) involves the use of non-local spatial correlations to image objects with light, which has not interacted with them. Here, we propose and experimentally demonstrate a new technique for first-order correlation measurement and retrieval of two-dimensional phase objects in the GD from inversion of the experimentally measured two-point complex correlation function in a first order interferometer. The GD scheme is experimentally implemented by a specially designed experimental setup wherein one of the orthogonal polarization components of the transversely polarized light interacts with the object and the other polarization component of the light remains intact and directly reaches the detector. The Fourier spectrum of the object is encoded into the two-point spatial correlation of these two orthogonal polarization components which is experimentally detected in an interferometer with a radial shearing in the Sagnac geometry. We experimentally demonstrated imaging of spatially varying phase objects and results are presented for three different cases. © 2024 IOP Publishing Ltd.