arXiv subjects

A. Vijayakumar

Publications and source records attributed to A. Vijayakumar.

6 recordsLinked to original sources

arXiv2019

A compact single channel interferometer to study vortex beam propagation

We propose and demonstrate a single channel interferometer that can be used to study how vortex beams propagate. The interferometer consists of a multifunctional diffractive optical element (MDOE) synthesized by the spatial random multiplexing of a Fresnel zone plate and a spiral Fresnel zone plate with different focal lengths. The MDOE generates two co-propagating beams, such that only the beam carrying orbital angular momentum is modulated by an annular stack of thin scatterers located at the focal plane of the Fresnel zone plate, while the other beam passes through the centre of the annulus without any modulation. The interference pattern is recorded at the focal plane of the spiral Fresnel zone plate. The scattering of vortex beams through stacks consisting of different number of thin scatterers was studied using the proposed optical setup. Conflicting results have been reported earlier on whether higher or lower charge beams suffer more deterioration. The proposed interferometer provides a relatively simple and compact means of experimentally studying propagation of vortex beams through scattering medium.

physics.optics↗

arXiv2019

SLM aided noninvasive imaging through thin scattering layers

We propose and demonstrate a new imaging technique to noninvasively see through scattering layers with the aid of a spatial light modulator (SLM). A relay system projects the incoherent light pattern emitting from the scattering layer onto the SLM. Two coded phase masks are displayed, one after another, on the SLM to modulate the projected scattered field. Two corresponding intensity patterns are recorded by a digital camera, and subtracted one from the other in the computer to obtain a bipolar matrix. A modified phase retrieval algorithm is used to retrieve the object information from this bipolar matrix.

physics.optics↗

arXiv2019

Implementation of a speckle correlation based optical lever (SC-OptLev) with extended dynamic range

A speckle correlation based optical lever (SC-OptLev) is constructed for the measurement of small changes in the angle of orientation of a surface. The dynamic range of SC-OptLev is found to be twice that of a conventional OptLev for the same experimental configurations. Different filtering mechanisms are implemented and the correlation results are compared. Two types of computer automated SC-OptLevs, open source based computing system with a low-cost image sensor and a commercial computing system, are presented with assistive computational modules.

physics.ins-det↗

arXiv2018

Structured light by discrete-phase orbital angular momentum holograms

Structured light has been created by a myriad of near- and far-field techniques and has found both classical and quantum applications. In the case of orbital angular momentum (OAM), continuous spiral phase patterns in dynamic or geometric phase are often employed with the phase patterns existing across the entire transverse plane. Here we exploit the uncertainty relation between OAM and angle to create structured OAM fields using multilevel OAM holograms. We show theoretically and experimentally that only a multilevel angular phase contour in the near-field is needed to create structured OAM light in the far-field, exploiting the reciprocal nature of angular momentum and angle. We use this approach to demonstrate exotic 3D structured light control to show the evolution of the Poynting vector in such fields and to highlight the physics underlying this phenomenon.

physics.optics↗

arXiv2017

Incoherent digital holograms acquired by interferenceless coded aperture correlation holography system without refractive lenses

We present a lensless, interferenceless incoherent digital holography technique based on the principle of coded aperture correlation holography. The acquired digital hologram by this technique contains a three-dimensional image of some observed scene. Light diffracted by a point object is modulated using a random-like coded phase mask (CPM) and the intensity pattern is recorded and composed as a point spread hologram (PSH). A library of PSH is created using the same CPM by moving the pinhole to all possible axial locations. Intensity diffracted through the same CPM from an object placed within the axial limits of the PSH library is recorded by a digital camera. The recorded intensity this time is composed as the object hologram. The image of the object at any axial plane is reconstructed by cross-correlating the object hologram with the corresponding component of the PSH library. The reconstruction noise attached to the image is suppressed by various methods. The reconstruction results of multi-plane and thick objects by this technique are compared with regular lens-based imaging.

physics.optics↗

arXiv2015

Generalized power domination in WK-Pyramid Networks

The notion of power domination arises in the context of monitoring an electric power system with as few phase measurement units as possible. The $k-$power domination number of a graph $G$ is the minimum cardinality of a $k-$power dominating set ($k-$PDS) of $G$. In this paper, we determine the $k-$power domination number of WK-Pyramid networks, $WKP_{(C,L)}$, for all positive values of $k$ except for $k=C-1, C \geq 2$, for which we give an upper bound. The $k-$propagation radius of a graph $G$ is the minimum number of propagation steps needed to monitor the graph $G$ over all minimum $k-$PDS. We obtain the $k-$propagation radius of $WKP_{(C,L)}$ in some cases.

math.CO↗