arXiv subjects

Maruthi M. Brundavanam

Publications and source records attributed to Maruthi M. Brundavanam.

12 recordsLinked to original sources

arXiv2026

Contest between diverging k-vectors and astigmatism in an aberrated randomly scattered light

The impact of astigmatism on randomly scattered light, here speckles which are generated from a ground glass (GG) plate, is investigated by studying the change in the shape of the intensity correlation function (ICF) of the speckles for different amount of astigmatism introduced to it by rotating a lens at different angles. It is observed that the shape of the ICF, which reflects the average shape of the speckles, changes from circular to elliptical with the change of the tilt angle of the lens (theta), and the variation of length of two axes of the ICF with theta is completely different in nature. It is shown that these different natures are observed due to a contest between the diverging k-vectors of the speckles and the astigmatism introduced by the tilted lens system. It is also found that the diverging k-vectors resist the effect of astigmatism on the speckles, and after a certain theta, the impact of astigmatism becomes prominent. The contest between the diverging k-vectors and astigmatism in an aberrated speckle pattern are confirmed by further experimental studies and are discussed in detail. This study will surely be helpful in designing different imaging systems, where scattered light plays an important role.

physics.optics↗

arXiv2026

Engineering of Tunable Topological Texture Transformation in Optical Skyrmions and Bimerons using Enantiomeric Excess

Optical skyrmions, which are the topologically protected quasiparticles and characterized by the nontrivial polarization textures, have emerged as a promising candidate due to their potential applications in optical communication, data storage, and particle manipulation. In this article, we propose and experimentally demonstrate an efficient and tunable approach for the dynamic transformation of generalized optical skyrmionic textures through the interaction of structured vector vortex beams with chiral media. By controlling the enantiomeric excess of an optically active material, we achieve on-demand conversion among Bloch, Neel or any intermediate skyrmionic states, extending also to optical bimerons. The topological conservation of the skyrmion number proves its robustness towards even higher-order textures. While maintaining a common path and stable setup, the proposed methodology provides an efficient and cost-effective approach towards the flexible manipulation of the topological textures, paving the way towards the understanding of topological transformation and engineering optical skyrmions for information processing or particle manipulation.

physics.optics↗

arXiv2024

Anomalous Lasing Behavior in a Nonlinear Plasmonic Random Laser

An unprecedented double-threshold lasing behavior has been observed in a plasmonic random laser composed of Au nanoislands decorated on vertically standing ZnO nanorods, infiltrated with dye-doped polymer matrix. The strong coupling of random laser modes to plasmonic nanocavities results in a dominant absorption of the random laser emission, leading to the first unusual lasing threshold. At higher pump fluences, the nonlinear optical behavior of the Au nanoislands induces a second lasing threshold. Various statistical tools have been employed to analyze the intensity fluctuations of the random laser modes, validating this unique lasing behavior.

physics.optics↗

arXiv2022

Tracking nanoscale perturbation in active disordered media

The disorder induced feedback makes random lasers very susceptible to any changes in the scattering medium. The sensitivity of the lasing modes to perturbations in the disordered systems have been utilized to map the regions of perturbation. A tracking parameter, that takes into account the cumulative effect of changes in the spatial distribution of the lasing modes of the system has been defined to locate the region in which a scatterer is displaced by a few nanometers. We show numerically that the precision of the method increases with the number of modes. The proposed method opens up the possibility of application of random lasers as a tool for monitoring locations of nanoscale displacement which can be useful for single particle detection and monitoring.

physics.optics↗

arXiv2021

Measuring obscured OAM spectrum using Stokes fluctuations

A novel technique to measure the orbital angular momentum (OAM) spectrum of the beam obscured by a complex random media is proposed and experimentally demonstrated. This is realized by measuring the complex correlation polarization function (CPCF) with the help of a two-point Stokes fluctuations correlation of the random light. The OAM spectrum analysis is implemented by projecting a complex field of the CPCF into spiral harmonics. A detailed theoretical framework is developed to measure complex amplitude and to decompose different integer OAM states of the obscured beam. The developed theoretical framework is verified by numerical simulation and tested by experimental demonstration of OAM mode compositions of the fractional optical vortex (FOV) beam.

physics.optics↗

arXiv2020

Tracking the rotation of a birefringent crystal from speckle shift measurement

The random intensity distribution observed due to the propagation of a coherent beam of light through a scattering medium is known as a speckle pattern. The interaction of the speckles with a birefringent crystal, here, YVO4 results in the e-ray and o-ray speckles. It is observed that the e-ray and o-ray speckles experience an angular shift with the rotation of the crystal and the shift depends on the rotation angle of the crystal. It is also found that the rate of the shift is different for e-ray and o-ray speckles, and is independent of the topological charge of the beam incident on the scattering medium. The observed rate of shift of the speckle pattern is found to be same as that of the e-ray and o-ray beams. It is experimentally demonstrated that the rotation of a birefringent crystal can be tracked very accurately from the speckle shift measurement.

physics.optics↗

arXiv2019

Polarization based intensity correlation of polarization speckle

A new, different kind of intensity correlation, denoted as polarization based intensity correlation, is proposed and investigated to study the correlation between different polarization components of polarization speckle, which has non-uniform spatial polarization distribution. It is shown both theoretically and experimentally that the range of the polarization based intensity correlation for a particular polarization component of the polarization speckle depends on the spatial average intensity of the speckles corresponding to that particular polarization component. The experimentally determined nature of the change of range of the intensity correlation for different polarization components, due to variation in the average intensity, is found to be matching well with the theoretical prediction. The existence of non-zero correlation between two orthogonally polarized speckle patterns, filtered from a partially depolarized speckle pattern, is also observed. This study may be useful in exploiting the polarization based intensity correlation for different applications such as speckle cryptography etc.

physics.optics↗

arXiv2019

Common-path generation of stable cylindrical perfect vector vortex beams with arbitrary order

A Highly flexible and efficient method of generating stable radially and Azimuthally polarized perfect optical vortex beams and all higher-order cylindrical vector vortex beams are proposed and demonstrated. The method is the most convenient implementation of the superposition of two orthogonally circularly polarized optical vortex beams of arbitrary integer topological charges. By simply controlling the relative amplitude and phase between vertical and horizontal polarization component of an input perfect vortex beam on a phase-sensitive Spatial Light Modulator (SLM) and using a common-path interferometry, all arbitrary order Poincaré beams are prepared. Calibration curve of relative phase vs grey-scale of the phase function on the SLM is drawn to facilitate the determination of required phase-offset using pre-calculated grey-scale colour-map. Generated beams states of polarization are uniformly distributed throughout the beam cross-section. The interference pattern of the two-beam in a projected linear polarization state also gives the cylindrically symmetric petal beams with control over the number and orientation of petals.

physics.optics↗

arXiv2019

Geometric phase associated with Poincaré beams due to unfolding of fractional optical vortex beams

Optical vortex beam of fractional order is generated by the diffraction of a Gaussian beam using computer generated hologram embedded with mixed screw-edge dislocation. Unfolding of the generated fractional vortex beam into eigen-polarization components inside a birefringent crystal results in the conversion of scalar phase singularity to vector polarization singularities in the beam cross-section. The evolution of the singularities of the ellipse field namely C-points (points of undefined major axis) and L-lines (lines of undefined handedness) across the beam quantifies the transformation. The effect of the phase morphology dictated by the fractional order of the dislocation, transverse spatial separation and longitudinal relative phase of the two eigen-polarization components on determining the complex transverse polarization structure is investigated. The nature of the generated Poincaré beam is also indicated by projecting the states of polarization on to the Poincaré sphere. With increasing order of dislocation from 0.0 to 1.0 in fractional steps and increasing relative phase, the partial Poincaré beam is transformed to a full Poincaré beam. The transformation of the local structure around the C-points is measured through the geometric phase due to the Poincaré sphere contour around the C-points for different dynamic phase difference of the unfolded FOV beams. This study can be useful for different geometric phase based application of optical vortex beams.

physics.optics↗

arXiv2018

Non-invasive tracking of polarization rotation from speckle contrast measurement

A technique based on speckle contrast measurement is proposed and demonstrated to track the polarization rotation of an optical beam behind a scattering layer. It is shown that with the help of a reference speckle pattern with a known linear polarization, it is possible to track the polarization rotation behind a scattering layer in a non-invasive manner by measuring the contrast of the resultant speckle pattern. Working principle and experimental demonstration are presented, and results are compared with the theoretically known results in certain cases. Performance of the proposed technique is quantitatively evaluated by determining the polarization vector rotation behind the scattering layer for two different cases, namely polarization rotation by a half wave plate and sugar solution of different concentrations, and good match are found between the experimental results and theoretical prediction. Issues like resolution of determination of the polarization vector rotation and sugar solution concentration are also discussed in the context of the recovered results. The proposed technique can have potential application in non-invasive sensing and biomedical imaging.

physics.optics↗

arXiv2017

Effect of average number of reference speckles on the SNR of object retrieved using off-axis holographic technique

The propagation of coherent light through a random scattering medium generates speckle pattern. Although the speckle is random in nature, the object information is scrambled into it. The scrambled object information can be retrieved using off-axis holographic technique where the retrieval is made from coherence hologram which is constructed from the interferogram formed by object speckle and a tilted reference speckle. It is shown that the SNR of the object retrieved from the coherence hologram, calculated from the far-field intensity correlation of the interferogram, depends on the average number of reference speckles. The effect of average number of reference speckles on the SNR of the retrieved object in off-axis holographic technique is investigated experimentally by changing the reference speckle while keeping the object speckle unchanged. The experimental observations are presented in this paper.

physics.optics↗

arXiv2017

Controlled Modulation of Depolarization in Laser Speckle

A new technique based on superposition of two speckle patterns is proposed and demonstrated for controlled modulation of the spatial polarization distribution of the resultant speckle. It is demonstrated both theoretically and experimentally that controlled modulation of the spatial polarization distribution of laser speckle can be achieved by proper choice of the polarization states as well as the average spatial intensity of the constituent speckles. It is also shown that the proposed technique is useful to generate different speckle patterns with sinusoidal variation in their degree of polarization, which can be tuned from zero to unity. This technique can find applications in sensing, biomedical studies, and in determining the rotation of the electric field vector after passing through a scattering medium.

physics.optics↗