arXiv subjects

V. Bobrovs

Publications and source records attributed to V. Bobrovs.

4 recordsLinked to original sources

arXiv2026

Biocompatible Vaterite Carriers Enable Multimodal Quantum Sensing with Nanodiamonds

Mobile nanodiamond quantum sensors in liquids are affected by Brownian rotation, variable photon collection, and perturbations from optical trapping. Here we assemble 40-nm nitrogen-vacancy nanodiamonds on porous, birefringent vaterite microspherulites, creating mobile sensors with a polarization-addressable body frame and a chemically active carbonate interface. Under 976-nm trapping, the sensors retain spin resonance and longitudinal relaxation, with less than 7% variation in contrast and an approximately 1-MHz resonance shift at 0.8 W. Zeeman-split resonances resolve magnetic fields from 0 to 0.8 mT, with a response metric of 78--144 $\mu$T Hz$^{-1/2}$. In cell-culture medium, a 10.7-$\mu$M proton-equivalent dose shortens $T_1$ from $23.4 \pm 2.3$ to $9.0 \pm 1.2$ $\mu$s, yielding concentration and pH sensitivities of $6.46$ $\mu$M Hz$^{-1/2}$ and $6.54$ mpH Hz$^{-1/2}$, respectively. A 500-fold larger proton dose in ethanol produces a weaker response. A grand-canonical charge-regulation model links proton chemical potential to interfacial switching, establishing a route to multimodal quantum sensing in complex liquids.

quant-ph↗

arXiv2025

Hybrid Superscattering Driven by Toroidal Dipole

The dynamic toroidal dipole is a unique radiation source beyond standard multipoles. Since its first demonstration 15 years ago, it has attracted growing theoretical and experimental interest. Research mainly aims to enhance its weak electromagnetic coupling to free space. Here we report on a surprising finding that the toroidal dipole can, in fact, be engaged in the enhancement of electromagnetic scattering per se driving the so-called superscattering the regime of anomalously strong light scattering where the total cross-section of the effect exceeds the fundamental single-channel limit. We introduce a new paradigm of hybrid superscattering enabled by the toroidal dipole, which we implement with a dielectric scatterer of a simple geometry, and demonstrate for the first time that two complementary mechanisms of superscattering the Friedrich-Wintgen mechanism and resonance overlap can act synergistically to yield the substantially enhanced effect. Using coupled-dipole theory, full-wave numerical modeling and coupled-mode theory, we identify and quantify the dominant multipolar contributions and show that the normalized scattering cross-section exceeds the dipole limit due to a toroidal dipole-magnetic quadrupole interplay. These findings are supported by experimental measurements in the GHz frequency range using a dimer of ceramic cubes, which confirm both the spectral and spatial features of toroidal superscattering. Our results open a new powerful route to engineering strong light-matter interaction via peculiar toroidal modes (never observed before) with potential applications in toroidal superscattering metamaterials and metasurfaces, photonic devices, and sensors.

physics.optics↗

arXiv2025

Tailor-Made Metasurface Camouflage

Reducing electromagnetic scattering from an object has always been a task, inspiring efforts across disciplines such as materials science and electromagnetic theory. The pursuit of electromagnetic cloaking significantly advanced the field of metamaterials, yet achieving broadband, conformal cloaking for complex, non-trivial objects remains an unresolved challenge. Here, we introduce the concept of 'tailor-made metasurfaces' - machine-designed aperiodic structures optimized to suppress scattering from arbitrary objects by accounting for their layout, including resonant or large-scale features. Specifically, we demonstrated a wideband ~20% fractional bandwidth scattering suppression of more than 20-30 dB for various generic test objects, including randomly distributed wire meshes, spheres, and polygons. The demonstrated evolutionary optimization marks a leap forward in electromagnetic design, enabling the development of high-performance structures to meet complex technological demands.

physics.optics↗

arXiv2024

Flexible Asymmetrically Transparent Conductive Electrode based on Photonic Nanojet Arrays

Flexible transparent electrodes, encompassing the combination of optical transparency and electrical conductivity, empower numerous optoelectronic applications. While the main efforts nowadays concentrate on developing wire meshes and conductive oxides, those technologies are still in a quest to find a balance between price, performance, and versatility. Here we propose a new platform, encompassing the advantages of nanophotonic design and roll-to-roll large-scale lithography fabrication tools, granting an ultimate balance between optical, electrical, and mechanical properties. The design is based on an array of silica microspheres deposited on a patterned thin aluminum film attached to a flexible polymer matrix. Microspheres are designed to squeeze 80% light through nanoscale apertures with the aid of the photonic nanojet effect given the light impinges the structure from the top. The photonic structure blocks the transmission for the backpropagation direction thus granting the device with the high 5-fold level of asymmetry. The patterned layer demonstrates a remarkable 2.8 {\Omega}/sq sheet resistance comparable to that of a continuous metal layer. The high conductivity is shown to be maintained after a repeatable application of strain on the flexible electrode. The technical specifications of the demonstrated transparent electrode establish it as a viable option for integrating into advanced optoelectronic devices such as solar cells, touchscreens, and organic light-emitting diodes to name a few. Its notable capacity to optimize light transmittance while ensuring consistent electrical performance, alongside its mechanical flexibility, makes the demonstrated device an essential component for applications, where such attributes are critically required.

physics.optics↗