arXiv subjects

Sivacarendran Balendhran

Publications and source records attributed to Sivacarendran Balendhran.

6 recordsLinked to original sources

arXiv2025

High Pixel Resolution Visible to Extended Shortwave Infrared Single Pixel Imaging with a black Phosphorus-Molybdenum disulfide (bP-MoS2) photodiode

High-resolution infrared imagers are currently more expensive than CMOS and CCD cameras, due to costly sensor arrays. Van der Waals (vdWs) materials present an opportunity for low-cost, room temperature infrared photodetectors. Although photodetectors based on vdWs materials show promising performance, creating a megapixel array is yet to be achieved. Imaging with a single vdWs photodetector typically relies on time-consuming mechanical scanning and suffers from low resolution. Single pixel imaging (SPI) offers an affordable alternative to achieve high-resolution imaging, utilizing only one photodetector and a spatial light modulator. Progress in SPI using vdWs material photodetectors has been limited, with only one prior demonstration in the near infrared range (64$\times$64 pixels). In this work, we demonstrate a high-resolution SPI system (1023$\times$768 for visible light and 512$\times$512 for extended shortwave infrared) using a black phosphorus-molybdenum disulfide (bP-MoS$_2$) photodiode, surpassing earlier vdWs material SPI implementations by a factor of 64 in pixel count. We introduce an easy-to-implement edge detection method for rapid feature extraction. We employ compressed sampling and reduce imaging time by a factor of four. Our compressed sampling approach is based on a cyclic S-matrix, which is derived from a Hadamard-based sequence, where each row is a circular shift of the first row. This enables efficient imaging reconstruction via circular convolution and Fourier transforms, allowing fewer measurements while preserving the key image features. Our method for SPI using a vdWs material photodetector presents the opportunity for inexpensive shortwave infrared and midwave infrared cameras, and thus may enable advances in gas detection, biomedical imaging, autonomous driving, security, and surveillance.

eess.IV↗

arXiv2025

Hopping of nanoparticles in optical tweezers governed by Mie resonances

Optical tweezers have become a standard tool for manipulating microscale and nanoscale particles and probing their local environments. However, complex particle dynamics under optical forces typically require structured light fields, multi-beam traps, or engineered environments. Here we achieve complex particle dynamics in a single Gaussian-beam optical tweezer. The effect originates from higher-order Mie resonances supported by wavelength-scale particles. In our optical tweezer, small particles in the regime of Rayleigh scattering or the lowest-order dipole-type Mie modes remain confined at the beam center. By contrast, particles within the range of sizes corresponding to quadrupole-type Mie modes exhibit more complex behavior. In a linearly polarized Gaussian beam, these particles are trapped in a potential with two off-axis equilibria. We observe thermally driven hopping between these equilibria, with the hopping frequency controlled by the laser power. In a circularly polarized Gaussian beam, the particles are confined to a stable orbit and exhibit circular motion driven by the spin (circular-polarization) degree of freedom of the beam, with angular velocity dependent on the laser power. These results reveal higher-order Mie resonances as an intrinsic mechanism behind complex optical forces. This establishes Mie-resonant nanophotonics as a flexible platform for inducing and controlling complex motion in optical tweezers for nanoparticle manipulation as well as sensing of local environments.

physics.optics↗

arXiv2024

Switchable optical trapping of Mie-resonant phase-change nanoparticles

Optical tweezers revolutionized the manipulation of nanoscale objects. Typically, tunable manipulations of optical tweezers rely on adjusting either the trapping laser beams or the optical environment surrounding the nanoparticles. We present a novel approach to achieve tunable and switchable trapping using nanoparticles made of a phase-change material (vanadium dioxide or VO$_2$). By varying the intensity of the trapping beam, we induce transitions of the VO$_2$ between monoclinic and rutile phases. Depending on the nanoparticles' sizes, they exhibit one of three behaviours: small nanoparticles (in our settings, radius $<0.12$ wavelength $λ$) remain always attracted by the laser beam in both material phases, large nanoparticles ($>0.22 λ$) remain always repelled. However, within the size range of $0.12$-$0.22 λ$, the phase transition of the VO$_2$ switches optical forces between attractive and repulsive, thereby pulling/pushing them towards/away from the beam centre. The effect is reversible, allowing the same particle to be attracted and repelled repeatedly. The phenomenon is governed by Mie resonances supported by the nanoparticle and their alterations during the phase transition of the VO$_2$. This work provides an alternative solution for dynamic optical tweezers and paves a way to new possibilities, including optical sorting, light-driven optomechanics and single-molecule biophysics.

physics.optics↗

arXiv2023

The Acoustophotoelectric Effect: Efficient Phonon-Photon-Electron Coupling in Zero-Voltage-Biased 2D SnS$_2$ for Broadband Photodetection

Two-dimensional (2D) layered metal dichalcogenides constitute a promising class of materials for photodetector applications due to their excellent optoelectronic properties. The most common photodetectors, which work on the principle of photoconductive or photovoltaic effects, however, require either the application of external voltage biases or built-in electric fields, which makes it challenging to simultaneously achieve high responsivities across broadband wavelength excitation - especially beyond the material's nominal band gap - while producing low dark currents. In this work, we report the discovery of an intricate phonon-photon-electron coupling - which we term the acoustophotoelectric effect - in SnS$_2$ that facilitates efficient photodetection through the application of 100-MHz-order propagating surface acoustic waves (SAWs). This effect not only reduces the band gap of SnS$_2$, but also provides the requisite momentum for indirect band gap transition of the photoexcited charge carriers, to enable broadband photodetection beyond the visible light range, whilst maintaining pA-order dark currents - remarkably without the need for any external voltage bias. More specifically, we show in the infrared excitation range that it is possible to achieve up to eight orders of magnitude improvement in the material's photoresponsivity compared to that previously reported for SnS$_2$-based photodetectors, in addition to exhibiting superior performance compared to most other 2D materials reported to date for photodetection.

physics.app-ph↗

arXiv2021

Helicity-selective Raman scattering from in-plane anisotropic α-MoO$_3$

Hyperbolic crystals like α-MoO$_3$ can support large wavevectors and photon density as compared to the commonly used dielectric crystals, which makes them a highly desirable platform for compact photonic devices. The extreme anisotropy of the dielectric constant in these crystals is intricately linked with the anisotropic character of the phonons, which along with photon confinement leads to the rich physics of phonon polaritons. However, the chiral nature of phonons in these hyperbolic crystals have not been studied in detail. In this study, we report our observations of helicity selective Raman scattering from flakes of α-MoO$_3$. Both helicity-preserving and helicity-reversing Raman scattering are observed. We observe that helical selectivity is largely governed by the underlying crystal symmetry. This study shed light on the chiral character of the high symmetry phonons in these hyperbolic crystals. It paves the way for exploiting proposed schemes of coupling chiral phonon modes into propagating surface plasmon polaritons and for compact photonic circuits based on helical polarized light.

physics.optics↗

arXiv2015

In situ characterisation of nanoscale electromechanical properties of quasi-two-dimensional MoS2 and MoO3

Precise manipulation of electronic band structures of two-dimensional (2D) transition metal dichalcogenides and oxides (TMD&Os) via localised strain engineering is an exciting avenue for exploiting their unique characteristics for electronics, optoelectronics, and nanoelectromechanical systems (NEMS) applications. This work experimentally demonstrates that mechanically-induced electrical transitions can be engineered in quasi-2D molybdenum disulphide (MoS2) and molybdenum trioxide (MoO3) using an in situ electrical nanoindentation technique. It is shown that localised strains on such quasi-2D layers can induce carrier transport alterations, thereby changing their electrical conduction behaviour. Such strain effects offer a potential tool for precisely manipulating the electronic transport properties of 2D TMD&Os, and understanding the interactions of the atomic electronic states in such layered materials.

cond-mat.mtrl-sci↗