arXiv subjects

Nishkarsh Kumar

Publications and source records attributed to Nishkarsh Kumar.

3 recordsLinked to original sources

arXiv2026

Geometry Driven Spin Polarization Effects in Waveguiding Plasmonic Crystal

We investigated the modulation in the polarization-dependent optical behaviour of the waveguiding plasmonic crystal by varying the illumination and detection geometry. We employed the finite element method-based COMSOL simulation and Jones-Mueller formalisms to probe the variations in optical parameters by systematically varying the angle of incidence and azimuthal angle of the incident plane wave source, thereby quantifying the variations in the polarization anisotropy parameters. The enhancement of optical properties at various resonances and the tunability of the hybridized modes are discussed. Importantly, our study reveals that despite the system being perfectly inversion-symmetric and achiral, it exhibits circular polarization anisotropy effects for non-zero finite azimuthal angles, manifested in the off-block-diagonal elements of the constructed Mueller matrices. The origin of this intriguing circular anisotropy effect is unravelled using the sequential linear birefringence and linear diattenuation effects arising from geometrical polarization transformation. Its implications in the spin-orbit interaction of light in the plasmonic crystal system are discussed.

physics.optics↗

arXiv2025

Spin-Split Dispersion of Leaky Surface plasmons in Inversion- Symmetric System

Spin-dependent dispersion and Rashba effect are manifestations of universal spin orbit interaction associated with the breaking of the spatial inversion symmetry in condensed matter and in optical systems. In sharp contrast to this, we report a spin-split dispersion effect of leaky surface plasmons in an inversion-symmetric one dimensional plasmonic grating system. In our system, the signature of spin-momentum locking and the resulting spin-polarization dependent splitting of dispersion of the surface plasmons are observed through the leakage radiation detected in a Fourier (momentum) domain optical arrangement. The setup enables single-shot recording of the full polarization-resolved dispersion (frequency vs transverse momentum (k)) of the leaky surface plasmons. Momentum domain polarization analysis identified a transverse momentum (k) dependent linear birefringence-linear dichroism effect (referred to as the geometric LB-LD effect) responsible for the observed spin-split dispersion. This unconventional SOI effect is reminiscent of the recently reported LB-LD effect resulting in giant chirality in centrosymmetric crystal, albeit with geometric origin. It is demonstrated that the interplay of the geometrical polarization transformation in focused polarized light and subsequent interaction of the structured field polarization with the plasmonic grating leads to the evolution of strong geometrical phase gradient or spin(circular polarization)-dependent transverse momentum of light resulting in spin-split dispersion. Our study offers a new paradigm of spin-based dispersion engineering and spin-enabled nano-optical functionalities in simple symmetric metasurfaces using geometric LB-LD effect.

physics.optics↗

arXiv2023

Mueller matrix based characterization of Cervical tissue sections: A quantitative comparison of Polar and Differential decomposition methods

Detection of cervical intraepithelial Neoplasia (CIN) at the early stage enables prevention of cervical cancer, which is one of the leading cause of cancer deaths among women. Recently there is a great interest to use the optical polarimetry as a non-invasive diagnosis tool to characterize the cervical tissues. In this context, it is crucial to validate the performance of various Mueller matrix decomposition techniques, that are utilized to extract the intrinsic polarization properties of complex turbid media, such as biological tissues. The aim of the work is to quantitatively compare the performance of polar and differential MM decomposition methods for probing the polarization properties in various complex optical media. Complete polarization responses of the cervical tissue sections, and other media are recorded by preparing a home-built Mueller matrix imaging set up with a spatial resolution of 400 nm. The Mueller matrices are then processed with the polar and differential decomposition methods to separate, and quantify the individual polarization parameters. ronounced differences in the extracted polarization properties are observed for different CIN grades with both the decomposition methods. Our results indicate that the differential decomposition of MM have certain advantages over the polar decomposition method to extract the intrinsic polarization properties of a complex tissue medium. The quantified polarization parameters obtained through the decomposition methods can be used as useful metrics to distinguish between the different grades of CIN, and to describe the healing efficiency of a self-healing organic crystal. Thus the Mueller matrix polarimetry shows great potential as an label-free, non-invasive diagnostic and imaging tool with potential applications in biomedical clinical research, and in various other disciplines.

physics.optics↗